1. |
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2. |
- Appelqvist, Hanna, et al.
(författare)
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Sensitivity to Lysosome-Dependent Cell Death is Directly Regulated by Lysosomal Cholesterol Content
- 2012
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 7:11
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Tidskriftsartikel (refereegranskat)abstract
- Alterations in lipid homeostasis are implicated in several neurodegenerative diseases, although the mechanisms responsible are poorly understood. We evaluated the impact of cholesterol accumulation, induced by U18666A, quinacrine or mutations in the cholesterol transporting Niemann-Pick disease type C1 (NPC1) protein, on lysosomal stability and sensitivity to lysosome-mediated cell death. We found that neurons with lysosomal cholesterol accumulation were protected from oxidative stress-induced apoptosis. In addition, human fibroblasts with cholesterol-loaded lysosomes showed higher lysosomal membrane stability than controls. Previous studies have shown that cholesterol accumulation is accompanied by the storage of lipids such as sphingomyelin, glycosphingolipids and sphingosine and an up regulation of lysosomal associated membrane protein-2 (LAMP-2), which may also influence lysosomal stability. However, in this study the use of myriocin and LAMP deficient fibroblasts excluded these factors as responsible for the rescuing effect and instead suggested that primarily lysosomal cholesterol content determined the cellular sensitivity to toxic insults. Further strengthening this concept, depletion of cholesterol using methyl-β-cyclodextrin or 25-hydroxycholesterol decreased the stability of lysosomes and cells became more prone to undergo apoptosis. In conclusion, cholesterol content regulated lysosomal membrane permeabilization and thereby influenced cell death sensitivity. Our data suggests that lysosomal cholesterol modulation might be used as a therapeutic strategy for conditions associated with accelerated or repressed apoptosis.
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3. |
- Eriksson, Ida, et al.
(författare)
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The histone deacetylase inhibitor trichostatin A reduces lysosomal pH and enhances cisplatin-induced apoptosis
- 2013
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Ingår i: Experimental Cell Research. - : Elsevier. - 0014-4827 .- 1090-2422. ; 319:1, s. 12-20
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Tidskriftsartikel (refereegranskat)abstract
- High activity of histone deacetylases (HDACs) has been documented in several types of cancer and may be associated with survival advantage. In a head and neck squamous cell carcinoma cell line, cisplatin-induced apoptosis was augmented by pretreatment with the HDAC inhibitor trichostatin Apoptosis was accompanied by lysosomal membrane permeabilization (LMP), as shown by immunoblotting of the lysosomal marker protease cathepsin B in extracted cytosol and by immunofluorescence. Moreover, LAMP-2 (lysosomal associated membrane protein-2) was translocated from lysosomal membranes and found in a digitonin extractable fraction together with cytosolic proteins and pretreatment with trichostatin A potentiated the release. Overall, protein level of LAMP-2 was decreased during cell death and, interestingly, inhibition of cysteine cathepsins, by the pan-cysteine cathepsin inhibitor zFA-FMK, prevented loss of LAMP-2. The importance of LAMP-2 for lysosomal membrane stability, was confirmed by showing that LAMP-2 knockout MEFs (mouse embryonic fibroblasts) were more sensitive to cisplatin as compared to the corresponding wildtype cells. Trichostatin A reduced lysosomal pH from 4.46 to 4.25 and cell death was prevented when lysosomal pH was increased by NH4Cl, or when inhibiting the activity of lysosomal proteases. We conclude that trichostatin A enhances cisplatin induced cell death by decreasing lysosomal pH, which augments cathepsin activity resulting in reduced LAMP-2 level, and might promote LMP.
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4. |
- Johansson, Ann-Charlotte, et al.
(författare)
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Cathepsin D mediates cytochrome c release and caspase activation in human fibroblast apoptosis induced by staurosporine
- 2003
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Ingår i: Cell Death and Differentiation. - : Springer Science and Business Media LLC. - 1350-9047 .- 1476-5403. ; 10:11, s. 1253-1259
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Tidskriftsartikel (refereegranskat)abstract
- There is increasing evidence that proteases other than caspases, for example, the lysosomal cathepsins B, D and L, are involved in apoptotic cell death. In the present study, we present data that suggest a role for cathepsin D in staurosporine-induced apoptosis in human foreskin fibroblasts. Cathepsin D and cytochrome c were detected partially released to the cytosol after exposure to 0.1 µM staurosporine for 1 h. After 4 h, activation of caspase-9 and -3 was initiated and later caspase-8 activation and a decrease in full-length Bid were detected. Pretreatment of cells with the cathepsin D inhibitor, pepstatin A, prevented cytochrome c release and caspase activation, and delayed cell death. These results imply that cytosolic cathepsin D is a key mediator in staurosporine-induced apoptosis. Analysis of the relative sequence of apoptotic events indicates that, in this cell type, cathepsin D acts upstream of cytochrome c release and caspase activation.
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5. |
- Johansson, Ann-Charlotte, 1976-
(författare)
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Lysosomal Membrane Permeabilization : A Cellular Suicide Strategy
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the last decade, a tremendous gain in knowledge concerning the molecular events of apoptosis signaling and execution has been achieved.The aim of this thesis was to clarify the role of lysosomal membrane permeabilization and lysosomal proteases, cathepsins, in signaling for apoptosis. We identified cathepsin D as an important factor in staurosporine-induced human fibroblast cell death. After release to the cytosol, cathepsin D promoted mitochondrial release of cytochrome c by proteolytic activation of Bid. Cathepsin D-mediated cleavage of Bid generated two fragments with the apparent molecular mass of 15 and 19 kDa. By sequence analysis, three cathepsin D-specific cleavage sites, Phe24, Trp48, and Phe183, were identified. Moreover, we investigated the mechanism by which cathepsins escape the lysosomal compartment, and found that Bax is translocated from the cytosol to lysosomes upon staurosporine treatment. In agreement with these data, recombinant Bax triggered release of cathepsins from isolated rat liver lysosomes. Conceivably, the Bcl-2 family of proteins may govern release of pro-apoptotic factors from both lysosomes and mitochondria. The importance of lysosomal cathepsins in apoptosis signaling was studied also in oral squamous cell carcinoma cells following exposure to the redox-cycling drug naphthazarin or agonistic anti-Fas antibodies. In this experimental system, cathepsins were released to the cytosol, however, inhibition of neither cathepsin D, nor cysteine cathepsin activity suppressed cell death. Interestingly, cysteine cathepsins still appeared to be involved in activation of the caspase cascade. Cathepsins are often overexpressed and secreted by cancer cells, and it has been reported that extracellular cathepsins promote tumor growth and metastasis. Here, we propose that cathepsin B secreted from cancer cells may suppress cancer cell death by shedding of the Fas death receptor.Defects in the regulation of apoptosis contribute to a wide variety of diseases, such as cancer, neurodegeneration and autoimmunity. Increased knowledge of the molecular details of apoptosis could lead to novel, more effective, treatments for these illnesses. This thesis emphasizes the importance of the lysosomal death pathway, which is a promising target for future therapeutic intervention.
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6. |
- Johansson, Ann-Charlotte, et al.
(författare)
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Regulation of apoptosis-associated lysosomal membrane permeabilization
- 2010
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Ingår i: APOPTOSIS. - : Springer Science Business Media. - 1360-8185 .- 1573-675X. ; 15:5, s. 527-540
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Tidskriftsartikel (refereegranskat)abstract
- Lysosomal membrane permeabilization (LMP) occurs in response to a large variety of cell death stimuli causing release of cathepsins from the lysosomal lumen into the cytosol where they participate in apoptosis signaling. In some settings, apoptosis induction is dependent on an early release of cathepsins, while under other circumstances LMP occurs late in the cell death process and contributes to amplification of the death signal. The mechanism underlying LMP is still incompletely understood; however, a growing body of evidence suggests that LMP may be governed by several distinct mechanisms that are likely engaged in a death stimulus- and cell-type-dependent fashion. In this review, factors contributing to permeabilization of the lysosomal membrane including reactive oxygen species, lysosomal membrane lipid composition, proteases, p53, and Bcl-2 family proteins, are described. Potential mechanisms to safeguard lysosomal integrity and confer resistance to lysosome-dependent cell death are also discussed.
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7. |
- Kågedal, Katarina, et al.
(författare)
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Lysosomal membrane permeabilization during apoptosis : Involvement of Bax?
- 2005
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Ingår i: International journal of experimental pathology (Print). - : John Wiley & Sons. - 0959-9673 .- 1365-2613. ; 86:5, s. 309-321
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Tidskriftsartikel (refereegranskat)abstract
- Bcl-2 family members have long been known to control permeabilization of the mitochondrial membrane during apoptosis, but involvement of these proteins in lysosomal membrane permeabilization (LMP) was not considered until recently. The aim of this study was to investigate the mechanism underlying the release of lysosomal proteases to the cytosol seen during apoptosis, with special emphasis on the role of Bax. In human fibroblasts, exposed to the apoptosis-inducing drug staurosporine (STS), the release of the lysosomal protease cathepsin D to the cytosol was observed by immunocytochemistry. In response to STS treatment, there was a shift in Bax immunostaining from a diffuse to a punctate pattern. Confocal microscopy showed co-localization of Bax with both lysosomes and mitochondria in dying cells. Presence of Bax at the lysosomal membrane was confirmed by immuno-electron microscopy. Furthermore, when recombinant Bax was incubated with pure lysosomal fractions, Bax inserted into the lysosomal membrane and induced the release of lysosomal enzymes. Thus, we suggest that Bax is a mediator of LMP, possibly promoting the release of lysosomal enzymes to the cytosol during apoptosis.
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8. |
- Nilsson, Cathrine, 1978-, et al.
(författare)
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Intrinsic differences in cisplatin sensitivity of head and neck cancer celllines correlates to lysosomal pH
- 2010
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Ingår i: Head and Neck. - : John Wiley & Sons. - 1043-3074 .- 1097-0347. ; 32:9, s. 1185-1194
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Tidskriftsartikel (refereegranskat)abstract
- Cisplatin is part of the treatment regime of head and neck squamous cell carcinomas (HNSCC). In order to predict the clinical outcome of the treatment, markers for evaluation of the intrinsic cisplatin sensitivity are inquired. In this study we characterize the lysosomal compartment and compare cisplatin sensitivity in five HNSCC lines and normal oral keratinocytes (NOKs). Cisplatin sensitivity differed 3-fold between the least and most sensitive cell lines, and the cisplatin LD50 correlated significantly to lysosomal pH, which varied from 4.3 in NOKs to 4.9 in the most resistant HNSCC line. Lysosomes are acidified by the V0V1-ATPase complex located in the lysosomal membrane. Interestingly, in cell lines exhibiting high lysosomal pH, we found decreased expression of the V0V1-ATPase B2 subunit, possibly explaining the defective acidification. In all cell lines, exposure to cisplatin caused activation of caspase-3. Cisplatin exposure was accompanied by lysosomal membrane permeabilization and inhibition of the llysosomal cathepsins B, D and L partly prevented cell death. No correlation between cisplatin sensitivity and expression of cathepsins B, D and L or secretion of their respective proforms into the culture medium was found in the cell lines studied. We conclude that lysosomal pH and expression of V0V1-ATPase subunits are possible future markers of intrinsic cisplatin sensitivity.
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9. |
- Roberg, Karin, et al.
(författare)
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A Pre-embedding Technique for Immunocytochemical Visualization of Cathepsin D in Cultured Cells Subjected to Oxidative Stress
- 1998
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Ingår i: Journal of Histochemistry and Cytochemistry. - : SAGE Publications. - 0022-1554 .- 1551-5044. ; 46:3, s. 411-418
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Tidskriftsartikel (refereegranskat)abstract
- We describe a pre-embedding immunocytochemical method for visualization of the lysosomal enzyme cathepsin D in cultured cells. The protein was demonstrated at both light and electron microscopic levels by neutral-pH silver enhancement of ultrasmall (0.8-nm) gold particles conjugated to the antibodies. The best morphological preservation and the highest labeling density were achieved by initial fixation for 20 min at 4C in 4% paraformaldehyde (PFA) and 0.05% glutaraldehyde (GA) in 0.15 M sodium cacodylate buffer, followed by permeabilization in sodium borohydride. Three cell types were used: human foreskin fibroblasts, histocytic lymphoma (J-774) cells, and primary rat heart myocytes. In all three, cathepsin D was demonstrated in lysosome-like structures. The rat heart myocytes were also exposed to the redox cycling substance naphthazarin (5,8-dihydroxy-1,4-naph-thoquinone) to induce oxidative stress. This was done for such a short period of time that the cells initially did not show any signs of morphological damage and retained normal plasma membrane stability, although an early and clear redistribution of cathepsin D from membrane-bound structures to the cytosol was apparent. This redistribution was followed by cell degeneration and, eventually, by cell death.
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10. |
- Roberg, Karin, et al.
(författare)
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Lysosomal release of Cathepsin D precedes relocation of Cytochrome C and loss of mitochondrial transmembrane potential during apoptosis induced by oxidative stress
- 1999
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Ingår i: Free Radical Biology & Medicine. - 0891-5849 .- 1873-4596. ; 27:11-12, s. 1228-1237
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Tidskriftsartikel (refereegranskat)abstract
- Apoptosis was induced in human foreskin fibroblasts by the redox-cycling quinone naphthazarin (5,8-dihydroxy-1,4-naphthoquinone). Most of the cells displayed ultrastructure typical of apoptosis after 8 h of exposure to naphthazarin. Apoptosis was inhibited in fibroblasts pretreated with the cathepsin D inhibitor pepstatin A. Immunofluorescence analysis of the intracellular distribution of cathepsin D revealed a distinct granular pattern in control cells, whereas cells treated with naphthazarin for 30 min exhibited more diffuse staining that corresponded to release of the enzyme from lysosomes to the cytosol. After 2 h, release of cytochrome c from mitochondria to the cytosol was indicated by immunofluorescence. The membrane-potential–sensitive probe JC-1 and flow cytometry did not detect a permanent decrease in mitochondrial transmembrane potential (ΔΨm) until after 5 h of naphthazarin treatment. Our findings show that, during naphthazarin-induced apoptosis, lysosomal destabilization (measured as release of cathepsin D) precedes release of cytochrome c, loss of ΔΨm, and morphologic alterations. Moreover, apoptosis could be inhibited by pretreatment with pepstatin A.
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11. |
- Roberg, Karin, et al.
(författare)
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Microinjection of cathepsin D induces caspase-dependent apoptosis in fibroblasts
- 2002
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Ingår i: American Journal of Pathology. - 0002-9440 .- 1525-2191. ; 161:1, s. 89-96
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Tidskriftsartikel (refereegranskat)abstract
- Recent reports have indicated that enzymes such as cathepsins D and B are translocated from lysosomal compartments to the cytosol early during apoptosis. We have previously noted that a translocation of cathepsins D and B occur before cytochrome c release and caspase activation in cardiomyocytes and human fibroblasts during oxidative stress-induced apoptosis. In the present report, we use a microinjection technique to investigate if cytosolic location of the cathepsins D and B are important for induction of apoptosis. We found that microinjection of cathepsin D into the cytosol of human fibroblasts caused apoptosis, which was detected as changes in distribution of cytochrome c, cell shrinkage, activation of caspases, chromatin condensation, and formation of pycnotic nuclei. No apoptosis was, however, induced by microinjection of cathepsin B. Moreover, apoptosis was prevented in fibroblasts pretreated with a caspase-3-like inhibitor, and also when microinjected with cathepsin D mixed with the cathepsin D inhibitor, pepstatin A. These results show that cytosolic cathepsin D can act as a proapoptotic mediator upstream of cytochrome c release and caspase activation in human fibroblasts.
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12. |
- Roberg, Karin, et al.
(författare)
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Oxidative stress causes relocation of the lysosomal enzyme cathepsin D with ensuing apoptosis in neonatal rat cardiomyocytes
- 1998
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Ingår i: American Journal of Pathology. - 0002-9440 .- 1525-2191. ; 152:5, s. 1151-1156
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Tidskriftsartikel (refereegranskat)abstract
- Exposing neonatal rat heart myocytes to the redox cycling quinone naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) for 15 to 45 minutes led to a time-dependent release of cathepsin D from many secondary lysosomes to the cytosol, as analyzed by morphometry. Cathepsin D was detected electron microscopically using a pre-embedding immunostaining technique that utilizes antibodies conjugated to ultra-small (0.8-nm) gold particles and subsequent silver enhancement. The exposure to naphthazarin also caused a decrease in both the pH and the ATP level of the cells within the same time frame. Lipid peroxidation was, however, not detected. Pretreatment of the cultures with alpha-tocopherol succinate prevented cathepsin D relocation, as shown by immunofluorescence. After exposure to naphthazarin, cells were washed, and normal culture conditions were re-established for 18 hours. Many cells then showed apoptotic morphology (ie, cellular shrinkage and chromatin condensation) as analyzed by Giemsa staining. Also, 41% of the cells stained positive with the TUNEL technique, and DNA fragmentation was detected by separation of intact and fragmented DNA. Apoptosis was significantly decreased in cultures pretreated with alpha-tocopherol succinate.
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13. |
- Stroikin, Yuri, et al.
(författare)
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Lysosome-targeted stress reveals increased stability of lipofuscin-containing lysosomes
- 2008
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Ingår i: Age (Omaha). - : Springer. - 0161-9152 .- 1574-4647. ; 30:1, s. 31-42
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Tidskriftsartikel (refereegranskat)abstract
- Cellular ageing is associated with accumulation of undegradable intralysosomal material, called lipofuscin. In order to accelerate the lipofuscin-accumulation, confluent, growth arrested human fibroblasts were cultured under hyperoxic conditions. To provide a better insight into the effects of lipofuscin on cellular functions, we compared lysosomal stability in control and lipofuscin-loaded human fibroblasts under conditions of lysosome-targeted stress induced by exposure to either the lysosomotropic detergent MSDH or the redox-cycling quinone naphthazarin. We show that lysosomal damage, assessed by acridine-orange relocation, translocation of cathepsin D to the cytosol, and alkalinization of lysosomes is more pronounced in control than in lipofuscin-loaded fibroblasts. Finding that lysosomal integrity was less affected or even preserved in case of lipofuscin-loaded cells enables us to suggest that lipofuscin exerts lysosome-stabilizing properties.
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14. |
- Sundelin, Kaarina, 1967-
(författare)
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Head and Neck Cancer : Factors Affecting Tumour Growth
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Head and neck cancer is the fifth most common cancer worldwide with an estimated annual global incidence of over 500 000 cases. These malignant tumours develop in the mucosal linings of the upper respiratory tract or in the salivary glands. The most common sites are in the oral cavity and larynx. Treatment modalities comprising surgery and chemoradiotherapy have improved significantly during the last 20 years, but not the long-term survival of patients. The aim of this thesis was to study the different factors affecting tumour growth in head and neck cancer that may have clinical implications in the future. Factors involving apoptosis, cell cycle activity, inflammation, and enzyme activity were of special interest.The results of the thesis indicate that patients with malignant salivary gland tumours having the lowest level of actively replicating cells have the best prognosis. The largest amount of replicating cells in tongue cancer specimens was found in the peripheral areas of tumour nests. Metallothionein, a protein that can hinder apoptosis, was found in excess in the same areas, whereas apoptosis activity was considerably lower. Taken together, these results indicate that the most aggressive cancer cells are found in the peripheral areas of tumours where apoptosis may be hindered.The expression of the death receptor Fas was higher in tongue cancer specimens than in normal mucosa. The expression of this receptor was studied further in two cell lines established from oral cancers. When a low dose of cisplatin was added to cell cultures, the Fas expression was enhanced in both cell lines and, furthermore, the Fas-induced apoptosis was increased in one of the cell lines. The results show that a common chemotherapeutic drug given in a low, less toxic dose may enhance receptor-mediated apoptosis of cancer cells.Malignant solid tumours are often distinguished by an increased proteolytic activity resulting in invasive growth, neo-angiogenesis, and metastases. This activity is conducted by enzymes that are secreted from tumour cells, or from normal cells in the tumour microenvironment. The regulation of enzyme secretion may be mediated by cytokines, small signalling molecules also present in cancer tissue. The results of this thesis show that two cytokines can synergistically induce enzyme secretion (matrix metalloproteinase-1 and -9) from oral cancer cells. Cytokine tumour necrosis factor-alpha and hepatocyte growth factor added alone to cell cultures strongly stimulated secretion of these enzymes. Thus, the tested cytokines, which are commonly secreted by fibroblasts and immune cells, may promote tumour growth.This thesis has contributed to an increased understanding of factors affecting tumour growth in head and neck cancer. The upcoming cancer therapies will be based on the increasing knowledge of these and other aberrant cellular mechanisms that may vary between different cancer forms.
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15. |
- Appelqvist, Hanna, et al.
(författare)
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Attenuation of the Lysosomal Death Pathway by Lysosomal Cholesterol Accumulation
- 2011
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Ingår i: American Journal of Pathology. - : American Society for Investigative Pathology (ASIP). - 0002-9440 .- 1525-2191. ; 178:2, s. 629-639
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Tidskriftsartikel (refereegranskat)abstract
- In the past decade, lysosomal membrane permeabilization (LMP) has emerged as a significant component of cell death signaling. The mechanisms by which lysosomal stability is regulated are not yet fully understood, but changes in the lysosomal membrane lipid composition have been suggested to be involved. Our aim was to investigate the importance of cholesterol in the regulation of lysosomal membrane permeability and its potential impact on apoptosis. Treatment of normal human fibroblasts with U18666A, an amphiphilic drug that inhibits cholesterol transport and causes accumulation of cholesterol in lysosomes, rescued cells from lysosome-dependent cell death induced by the lysosomotropic detergent 0-methyl-serine dodecylamide hydrochloride (MSDH), staurosporine (STS), or cisplatin. LMP was decreased by pretreating cells with U18666A, and there was a linear relationship between the cholesterol content of lysosomes and their resistance to permeabilization induced by MSDH. U18666A did not induce changes in expression or localization of 70-kDa heat shock proteins (Hsp70) or antiapoptotic Bcl-2 proteins known to protect the lysosomal membrane. Induction of autophagy also was excluded as a contributor to the protective mechanism. By using Chinese hamster ovary (CHO) cells with lysosomal cholesterol overload due to a mutation in the cholesterol transporting protein Niemann-Pick type C1 (NPC1), the relationship between lysosomal cholesterol accumulation and protection from lysosome-dependent cell death was confirmed. Cholesterol accumulation in lysosomes attenuates apoptosis by increasing lysosomal membrane stability.
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16. |
- Appelqvist, Hanna, et al.
(författare)
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Lysosomal exocytosis and caspase-8-mediated apoptosis in UVA-irradiated keratinocytes
- 2013
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Ingår i: Journal of Cell Science. - : Company of Biologists. - 0021-9533 .- 1477-9137. ; 126:24, s. 5578-5584
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet (UV) irradiation is a major environmental carcinogen involved in the development of skin cancer. To elucidate the initial signaling during UV-induced damage in human keratinocytes, we investigated lysosomal exocytosis and apoptosis induction. UVA, but not UVB, induced plasma membrane damage, which was repaired by Ca2+-dependent lysosomal exocytosis. The lysosomal exocytosis resulted in extracellular release of cathepsin D and acid sphingomyelinase (aSMase). Two hours after UVA irradiation, we detected activation of caspase-8, which was reduced by addition of anti-aSMAse. Furthermore, caspase-8 activation and apoptosis was reduced by prevention of endocytosis and by the use of cathepsin inhibitors. We conclude that lysosomal exocytosis is part of the keratinocyte response to UVA and is followed by cathepsin-dependent activation of caspase-8. The findings have implications for the understanding of UV-induced skin damage and emphasize that UVA and UVB initiate apoptosis through different signaling pathways in keratinocytes.
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17. |
- Appelqvist, Hanna, 1981-
(författare)
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Lysosomal Membrane Stability and Cathepsins in Cell Death
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lysosomes are acidic organelles that are critically involved in a number of physiological processes, including macromolecule degradation, endocytosis, autophagy, exocytosis and cholesterol homeostasis. Several pathological conditions, such as cancer, neurodegenerative disorders and lysosomal storage diseases, involve lysosomal disturbances, indicating the importance of the organelle for correct cellular function. The aim of this thesis was to investigate the role of lysosomes in cell death signaling.Previous studies have shown that permeabilization of the lysosomal membrane and release of hydrolytic enzymes such as cathepsin D to the cytosol occurs during apoptosis. We identified Bid and 14-3-3 proteins as cytosolic targets of cathepsin D in human fibroblasts. Truncated Bid, generated by cathepsin D proteolytic cleavage, stimulates Bax-mediated release of pro-apoptotic factors from the mitochondria, thereby engaging the intrinsic pathway to apoptosis.Since the presence of cathepsins in the cytosol is sufficient to induce apoptosis, the permeability of the lysosomal membrane influences the fate of the cell. In this thesis, we demonstrated that the stability of the lysosomal membrane can be manipulated by altering the lysosomal cholesterol content. Cells with high lysosomal cholesterol content were less prone to undergo apoptosis when challenged with stimuli known to induce lysosome-mediated cell death. In addition, cholesterol accumulation was associated with increased expression of lysosome-associated membrane proteins and storage of other lipids; however, these factors did not contribute to lysosomal stabilization.Lysosomal membrane permeabilization and cathepsins contribute to ultraviolet (UV) irradiation-induced apoptosis. We demonstrate plasma membrane damage induced by UVA irradiation to be rapidly repaired by lysosomal exocytosis in human keratinocytes. Despite efficient plasma membrane resealing, the cells underwent apoptosis, which was dependent on early activation of caspase-8. The activation of caspase-8 was lysosome-dependent and occurred in vesicles positive for lysosomal markers.This thesis demonstrates the importance of lysosomal stability for apoptosis regulation and that this stability can be influenced by drug intervention. Modulation of the lysosomal membrane permeability may have potential for use as a therapeutic strategy in conditions associated with accelerated or repressed apoptosis.
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18. |
- Appelqvist, Hanna, et al.
(författare)
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Lysosome-Mediated Apoptosis is Associated with Cathepsin D-Specific Processing of Bid at Phe24,Trp48, and Phe183
- 2012
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Ingår i: Annals of Clinical and Laboratory Science. - : Institute for Clinical Science. - 0091-7370 .- 1550-8080. ; 42:3, s. 231-242
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Tidskriftsartikel (refereegranskat)abstract
- Bax-mediated permeabilization of the outer mitochondrial membrane and release of apoptogenic factors into the cytosol are key events that occur during apoptosis. Likewise, apoptosis is associated with permeabilization of the lysosomal membrane and release of lysosomal cathepsins into the cytosol. This report identifies proteolytically active cathepsin D as an important component of apoptotic signaling following lysosomal membrane permeabilization in fibroblasts. Lysosome-mediated cell death is associated with degradation of Bax sequestering 14-3-3 proteins, cleavage of the Box activator Bid, and translocation of Box to mitochondria, all of which were cathepsin D-dependent. Processing of Bid could be reproduced by enforced lysosomal membrane permeabilization, using the lysosomotropic detergent O-methyl-serine dodecylamine hydrochloride (MSDH). We identified three cathepsin D-specific cleavage sites in Bid, Phe24, Trp48, and Phe183. Cathepsin D-cleaved Bid induced Bax-mediated release of cytochrome c from purified mitochondria, indicating that the fragments generated are functionally active. Moreover, apoptosis was associated with cytosolic acidification, thereby providing a more favorable environment for the cathepsin D-mediated cleavage of Bid. Our study suggests that cytosolic cathepsin D triggers Bax-mediated cytochrome c release by proteolytic activation of Bid.
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19. |
- Appelqvist, Hanna, et al.
(författare)
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The lysosome: from waste bag to potential therapeutic target
- 2013
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Ingår i: Journal of Molecular Cell Biology. - : Oxford University Press (OUP): Policy B - Oxford Open Option D. - 1674-2788 .- 1759-4685. ; 5:4, s. 214-226
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Forskningsöversikt (refereegranskat)abstract
- Lysosomes are ubiquitous membrane-bound intracellular organelles with an acidic interior. They are central for degradation and recycling of macromolecules delivered by endocytosis, phagocytosis, and autophagy. In contrast to the rather simplified view of lysosomes as waste bags, nowadays lysosomes are recognized as advanced organelles involved in many cellular processes and are considered crucial regulators of cell homeostasis. The function of lysosomes is critically dependent on soluble lysosomal hydrolases (e.g. cathepsins) as well as lysosomal membrane proteins (e.g. lysosome-associated membrane proteins). This review focuses on lysosomal involvement in digestion of intra- and extracellular material, plasma membrane repair, cholesterol homeostasis, and cell death. Regulation of lysosomal biogenesis and function via the transcription factor EB (TFEB) will also be discussed. In addition, lysosomal contribution to diseases, including lysosomal storage disorders, neurodegenerative disorders, cancer, and cardiovascular diseases, is presented.
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20. |
- Bivik, Cecilia, et al.
(författare)
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Hsp70 protects against UVB induced apoptosis by preventing release of cathepsins and cytochrome c in human melanocytes
- 2007
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Ingår i: Carcinogenesis. - : Oxford University Press (OUP). - 0143-3334 .- 1460-2180. ; 28:3, s. 537-544
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Tidskriftsartikel (refereegranskat)abstract
- Stress-induced heat shock protein 70 (Hsp70) effectively protects cells against apoptosis, although the anti-apoptotic mechanism is still undefined. Exposure of human melanocytes to heat and subsequent UVB irradiation increased the level of Hsp70 and pre-heating reduced UVB induced apoptosis. Immunofluorescence staining of Hsp70 in combination with staining of lysosomes (Lamp2) or mitochondria (Mitotracker®) in pre-heated UVB exposed cells showed co-localization of Hsp70 with both lysosomes and mitochondria in the surviving cell population. Furthermore, UVB induced apoptosis was accompanied by lysosomal and mitochondrial membrane permeabilization, detected as release of cathepsin D and cytochrome c, respectively, which were prevented by heat pre-treatment. In purified fractions of lysosomes and mitochondria, recombinant Hsp70 attached to both lysosomal and mitochondrial membranes. Moreover, in apoptotic cells Bax was translocated from a diffuse cytosolic location into punctate mitochondrial-like structures, which was inhibited by Hsp70 induction. Such inhibition of Bax translocation was abolished by transfection with Hsp70 siRNA. Furthermore, Hsp70 siRNA eliminated the apoptosis preventive effect observed after pre-heating. These findings show Hsp70 to rescue melanocytes from UVB induced apoptosis by preventing release of cathepsins from lysosomes, Bax translocation and cytochrome c release from mitochondria. Abbreviations: AIF, apoptosis-inducing factor; Hsp, heat shock protein; NAG, ß-N-acetylglucosaminidase; tBid, truncated Bid; UV, ultraviolet
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21. |
- Bivik, Cecilia, et al.
(författare)
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JNK mediates UVB-induced apoptosis upstream lysosomal membrane permeabilization and Bcl-2 family proteins
- 2008
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Ingår i: Apoptosis (London). - : Springer Science and Business Media LLC. - 1360-8185 .- 1573-675X. ; 13:9, s. 1111-1120
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Tidskriftsartikel (refereegranskat)abstract
- UVB irradiation induced phosphorylation of JNK and subsequent apoptosis in human melanocytes. Depletion of both JNK1 and JNK2 expression using siRNA transfection, protected against apoptosis, as detected by decreased nuclear fragmentation and caspase-3 activity, as well as reduced translocation of Bax to mitochondria. Moreover, release of cathepsin B and D from lysosomes to the cytosol was reduced when JNK expression was suppressed by siRNA, demonstrating a JNK dependent regulation of lysosomal membrane permeabilization. In unirradiated control melanocytes, coimmunoprecipitation showed that Bim was sequestered by Mcl-1, which had a pro-survival function. After UVB irradiation, a significant decrease in Mcl-1 protein level was found, which was prevented by addition of a proteasome inhibitor. The interaction between Bim and Mcl-1 was reduced in response to UVB irradiation and Bim was phosphorylated in a JNK dependent manner. In conclusion, these findings Suggest JNK to have an important pro-apoptotic function following UVB irradiation in human melanocytes, by acting upstream of lysosomal membrane permeabilization and Bim phosphorylation.
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22. |
- Bivik, Cecilia, 1978-
(författare)
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Regulation of UV induced apoptosis in human melanocytes
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Malignant melanoma arises from the pigment producing melanocytes in epidermis and is the most aggressive type of skin cancer. The incidence of malignant melanoma is increasing faster than any other type of cancer in white population worldwide, with a doubling rate every 10-20 years. So far, the only identified external risk factor for malignant melanoma is UV exposure. Elimination of photodamaged cells by apoptosis (programmed cell death) is essential to prevent tumor formation. Melanocytes are considered relatively resistant to apoptosis, however, the regulation of apoptosis in melanocytes is still unknown.The aim of this thesis was to investigate the apoptotic process following ultraviolet (UV) irradiation in primary cultures of human melanocytes. Focus was on regulation of mitochondrial stability by Bcl-2 family proteins and the possible participation of lysosomal proteases, cathepsins. UV irradiation activated the mitochondrial pathway of apoptosis, leading to cytochrome c release, caspase activation, and nuclear fragmentation. No change in protein expression of Bax and Bcl-2 was observed in response to UV. Instead, translocation of the Bcl-2 family proteins from cytosol to mitochondia was important in the regulation of survival and death of melanocytes. The findings further demonstrated permeabilization of the lysosomal membrane to occur early in the apoptotic process, resulting in cathepsin release into the cytosol. The cathepsins were potent pro-apoptotic mediators and triggered apoptosis upstream of Bax translocation and mitochondrial membrane permeabilization. In response to both heat and UV irradiation, there was a marked increase in expression of stress-induced heat shock protein 70 (Hsp70), which inhibited apoptosis by binding lysosomal and mitochondrial membranes and counteracting the release of cathepsins and cytochrome c. Furthermore, UV irradiation activated c-jun N-terminal kinase (JNK), which triggered apoptosis upstream of cathepsins release from the lysosomes. In addition, JNK mediated apoptosis through phosphorylation of pro-apoptotic Bim, which was released from anti-apoptotic Mcl-1, by UV induced Mcl-1 depletion.This thesis illustrates that permeabilization of mitochondria and lysosomes and release of their constituents to the cytosol participates in UV induced apoptosis signaling in human melanocytes in vitro. The process is regulated by a complex network of pro- and anti-apoptotic proteins, exerting their effects through intracellular translocation and alteration of protein expression.
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23. |
- Bivik, Cecilia, et al.
(författare)
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UVA/B induced apoptosis in human melanocytes involves translocation of cathepsins and Bcl-2 family members
- 2006
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Ingår i: Journal of Investigative Dermatology. - : Elsevier BV. - 0022-202X. ; 126:5, s. 1119-1127
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate UVA/B to induce apoptosis in human melanocytes through the mitochondrial pathway, displaying cytochrome c release, caspase-3 activation, and fragmentation of nuclei. The outcome of a death signal depends on the balance between positive and negative apoptotic regulators, such as members of the Bcl-2 protein family. Apoptotic melanocytes, containing fragmented nucleus, show translocation of the proapoptotic proteins Bax and Bid from the cytosol to punctate mitochondrial-like structures. Bcl-2, generally thought to be attached only to membranes, was in melanocytes localized in the cytosol as well. In the fraction of surviving melanocytes, that is, cells with morphologically unchanged nucleus, the antiapoptotic proteins Bcl-2 and Bcl-XL were translocated to mitochondria following UVA/B. The lysosomal proteases, cathepsin B and D, which may act as proapoptotic mediators, were released from lysosomes to the cytosol after UVA/B exposure. Proapoptotic action of the cytosolic cathepsins was confirmed by microinjection of cathepsin B, which induced nuclear fragmentation. Bax translocation and apoptosis were markedly reduced in melanocytes after pretreatment with either cysteine or aspartic cathepsin inhibitors. No initial caspase-8 activity was detected, excluding involvement of the death receptor pathway. Altogether, our results emphasize translocation of Bcl-2 family proteins to have central regulatory functions of UV-induced apoptosis in melanocytes and suggest cathepsins to be proapoptotic mediators operating upstream of Bax.
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24. |
- Bivik Eding, Cecilia, et al.
(författare)
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Melanoma Growth and Progression After Ultraviolet A Irradiation: Impact of Lysosomal Exocytosis and Cathepsin Proteases
- 2015
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Ingår i: Acta Dermato-Venereologica. - : ACTA DERMATO-VENEREOLOGICA. - 0001-5555 .- 1651-2057. ; 95:7, s. 792-797
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet (UV) irradiation is a risk factor for development of malignant melanoma. UVA-induced lysosomal exocytosis and subsequent cell growth enhancement was studied in malignant melanoma cell lines and human skin melanocytes. UVA irradiation caused plasma membrane damage that was rapidly repaired by calcium-dependent lysosomal exocytosis. Lysosomal content was released into the culture medium directly after irradiation and such conditioned media stimulated the growth of non-irradiated cell cultures. By comparing melanocytes and melanoma cells, it was found that only the melanoma cells spontaneously secreted cathepsins into the surrounding medium. Melanoma cells from a primary tumour showed pronounced invasion ability, which was prevented by addition of inhibitors of cathepsins B, D and L. Proliferation was reduced by cathepsin L inhibition in all melanoma cell lines, but did not affect melanocyte growth. In conclusion, UVA-induced release of cathepsins outside cells may be an important factor that promotes melanoma growth and progression.
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25. |
- Dabrosin, Charlotta, 1961-, et al.
(författare)
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Decreased secretion of Cathepsin D in breast cancer in vivo by tamoxifen : Mediated by the mannose-6-phosphate/IGF-II receptor?
- 2004
-
Ingår i: Breast Cancer Research and Treatment. - 0167-6806 .- 1573-7217. ; 85:3, s. 229-238
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Tidskriftsartikel (refereegranskat)abstract
- The lysosomal protease Catliepsin D (Cath D) is associated with increased invasiveness and metastasis in breast cancer. Both estrogen and tamoxifen have been reported to increase Cath D, which seems to contradict the efficacy of tamoxifen as an adjuvant for estrogen dependent breast cancer. Cath D is bioactive in the extracellular space but very little is known about hormonal regulation of secreted Cath D in vivo. In this study we used microdialysis to sample the extracellular fluid in estrogen receptor positive MCF-7 tumors in nude mice. We show that tamoxifen in combination with estradiol decreased secreted Cath D compared with estradiol treatment only in solid tumors in situ. Cell culture of MCF-7 cells revealed that estradiol and tamoxifen increased intracellular proteolytic activity of Cath D in a similar fashion whereas secretion of Cath D was increased by estradiol and inhibited by tamoxifen. Immunofluorescence showed that estradiol located Cath D to the cell surface, while tamoxifen accumulated Cath D to dense lysosomes in perinuclear regions. Moreover, tamoxifen increased the intracellular transporter of Cath D, the mannose 6-phosphate/IGF-II receptor (M6P/IGF2R). In contrast, estradiol decreased the levels of this receptor. Thus, secretion of Cath D is hormone dependent and may be mediated by altered expression of the M6P/IGF2R. Our results highlight the importance of measurements of proteins in all compartments where they are biological active and show that microdialysis is a viable technique for sampling of Cath D in vivo.
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26. |
- Dabrosin, Charlotta, 1961-, et al.
(författare)
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Variability of glutathione during the menstrual cycle - Due to estrogen effects on hepatocytes?
- 2004
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Ingår i: Free Radical Biology & Medicine. - : Elsevier BV. - 0891-5849 .- 1873-4596. ; 36:2, s. 145-151
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Tidskriftsartikel (refereegranskat)abstract
- Oxidative stress and alterations in the antioxidative defense system may be involved in carcinogenesis. We have previously shown that the levels of glutathione (GSH) in vivo in both breast tissue and subcutaneous fat were higher in the luteal phase compared with the follicular phase, suggesting an overall increase in GSH. This result was confirmed in the present study. Moreover, we exposed normal breast tissue in vivo, breast epithelial cells in vitro, and hepatocytes in culture to ovarian hormones. We found that local perfusion with estradiol, using microdialysis, in normal human breast tissue did not alter the local GSH levels in vivo. In vitro, treatment with estradiol and progesterone of normal human breast epithelial cells did not alter GSH levels. However, levels of GSH in hepatocytes were after 8 h estradiol exposure initially decreased, 76.6 ± 5% of control cells, p < .05, whereas 20 h exposure more than doubled GSH, 209 ± 26% compared with control cells, p < .01. Progesterone had no additional effect. Exposure of hepatocytes to estradiol increased the cellular content of γ-glutamylcysteine synthetase, the rate-limiting enzyme in GSH synthesis. In conclusion we suggest that estradiol affects the GSH homeostasis mainly by effects on hepatocytes, whereas local production in the breast is unaffected by estradiol.
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27. |
- Danielsson, Olof, et al.
(författare)
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Apoptosis in idiopathic inflammatory myopathies with partial invasion; a role for CD8(+)cytotoxic T cells?
- 2020
-
Ingår i: PLOS ONE. - San Francisco, CA, United States : PUBLIC LIBRARY SCIENCE. - 1932-6203. ; 15:9
-
Tidskriftsartikel (refereegranskat)abstract
- Polymyositis and inclusion body myositis are idiopathic inflammatory myopathies, with a pathology characterized by partial invasion of non-necrotic muscle fibres by CD8(+)cytotoxic T-cells, leading to fibre degeneration. Although the main effector pathway of CD8(+)T-cells is to induce apoptosis of target cells, it has remained unclear if apoptosis occurs in these diseases, and if so, if it is mediated by CD8(+)T-cells. In consecutive biopsy sections from 10 patients with partial invasion, muscle fibres and inflammatory cells were assessed by immunohistochemistry and apoptotic nuclei by the TUNEL assay. Analysis of muscle fibre morphology, staining pattern and quantification were performed on digital images, and they were compared with biopsies from 10 dermatomyositis patients and 10 controls without muscle disease. Apoptotic myonuclei were found in muscle with partial invasion, but not in the invaded fibres. Fibres with TUNEL positive nuclei were surrounded by CD8(+)T-cells, granzyme B(+)cells and macrophages, but lacked FAS receptor expression. In contrast, apoptotic myonuclei were rare in dermatomyositis and absent in controls. The findings confirm that apoptosis occurs in idiopathic inflammatory myopathies and support that it is mediated by CD8(+)cytotoxic T- cells, acting in parallel to the process of partial invasion.
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28. |
- Dilna, Aysha, et al.
(författare)
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Amyloid-beta induced membrane damage instigates tunneling nanotube-like conduits by p21-activated kinase dependent actin remodulation
- 2021
-
Ingår i: Biochimica et Biophysica Acta - Molecular Basis of Disease. - : ELSEVIER. - 0925-4439 .- 1879-260X. ; 1867:12
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Tidskriftsartikel (refereegranskat)abstract
- Alzheimers disease (AD) pathology progresses gradually via anatomically connected brain regions. Direct transfer of amyloid-beta(1-42) oligomers (oA beta) between connected neurons has been shown, however, the mechanism is not fully revealed. We observed formation of oA beta induced tunneling nanotubes (TNTs)-like nanoscaled f-actin containing membrane conduits, in differentially differentiated SH-SY5Y neuronal models. Time-lapse images showed that oA beta propagate from one cell to another via TNT-like structures. Preceding the formation of TNT-like conduits, we detected oA beta_induced plasma membrane (PM) damage and calcium-dependent repair through lysosomal-exocytosis, followed by massive endocytosis to re-establish the PM. Massive endocytosis was monitored by an influx of the membrane-staining dye TMA-DPH and PM damage was quantified by propidium iodide influx in the absence of Ca2+. The massive endocytosis eventually caused accumulation of internalized oA beta in Lamp1 positive multivesicular bodies/lysosomes via the actin cytoskeleton remodulating p21-activated kinase1 (PAK1) dependent endocytic pathway. Three-dimensional quantitative confocal imaging, structured illumination superresolution microscopy, and flowcytometry quantifications revealed that oA beta induces activation of phospho-PAK1, which modulates the formation of long stretched f-actin extensions between cells. Moreover, the formation of TNT-like conduits was inhibited by preventing PAK1-dependent internalization of oA beta using the small-molecule inhibitor IPA-3, a highly selective cell-permeable auto-regulatory inhibitor of PAK1. The present study reveals that the TNT-like conduits are probably instigated as a consequence of oA beta induced PM damage and repair process, followed by PAK1 dependent endocytosis and actin remodeling, probably to maintain cell surface expansion and/or membrane tension in equilibrium.
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29. |
- Duvetorp, Albert, 1980-
(författare)
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Different Aspects of Psoriasis : Comorbidity, Comedication and Disease Biomarkers
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Psoriasis is a common heterogeneous inflammatory disease with its predominant manifestation occurring in the skin. The impact of this disease, however, extends far beyond the skin surface. During the last decades, mounting scientific evidence of psoriasis disease impact on quality of life, stigmatization and comorbidity has led to the predominant view that psoriasis care needs a holistic approach. Epidemiological research is needed to visualize the greater picture whereas research on disease pathomechanisms can provide answers to disease evaluation challenges, facilitate development of new treatments, and provide insights into mechanistical bridges explaining comorbidity occurrence. In study I of this thesis, serum S100A8/A9 was evaluated as a possible biomarker of psoriasis skin disease activity. Dramatic reductions in S100A8 and S100A9 and S100A8/A9 heterocomplex levels were found in lesional psoriasis skin after NB-UVB treatment without any significant reduction occurring in serum. Study II was designed as a retrospective, cross-sectional population study including the adult population of the county of Jönköping. The odds of having pharmacologically treated depression among individuals with psoriasis was compared to the odds of the background population. Psoriasis was associated with an elevated depression risk. Depression was more prevalent among women (both in the background population and among individuals with psoriasis). Young age was associated with higher odds for depression among individuals with psoriasis. Study III was based on the same study population as study II. In this study the comedication burden of individuals with psoriasis was compared to the background population. Comedication assessed were prescription drugs used to treat comorbidity associated with psoriasis in previous scientific publications. Patients with psoriasis were found to have a high comedication burden. Patients receiving systemic treatment for psoriasis had a higher number of different dispensed drugs suggesting that severe disease implies a higher risk of comorbid disease. Study IV was an exploratory study assessing numerous potential biomarkers for psoriasis disease activity. Extensive Luminex analysis of skin and serum samples collected during study I was performed. No serum mediator (potential biomarker of disease activity) showed a significant change after NB-UVB (following correction for multiple testing). In skin, NB-UVB had effects on mediators of the Th17 pathway and multiple chemokines but also previously undescribed or less explored disease mediators. Study II and III suggest that comorbidity and its comedication is common among Swedish psoriasis patients in contact with the health care system. This research reinforces the perception that a holistic approach is needed when treating patients with psoriasis. Behind the failure to identify a biomarker for skin disease activity in study I and IV lurks the questions to how, if or when inflammation in the skin affects systemic inflammation and in extension comorbid disease.
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30. |
- Eriksson, Ida, et al.
(författare)
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Analysis of Lysosomal pH by Flow Cytometry Using FITC-Dextran Loaded Cells
- 2017
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Ingår i: Lysosomes. - New York, NY : Humana Press. - 9781493969326 - 9781493969340 ; , s. 179-189
-
Bokkapitel (refereegranskat)abstract
- The acidic environment of the lysosomal lumen provides an optimal milieu for the acid hydrolases and is also essential for fusion/fission of endo-lysosomal compartments and sorting of cargo. Evidence suggests that maintaining lysosomal acidity is essential to avoid disease. In this chapter, we describe a protocol for analyzing the lysosomal pH in cultured cells using the fluorescent probe fluorescein isothiocyanate (FITC)-dextran together with a dual-emission ratiometric technique suitable for flow cytometry. Fluorescence-labeled dextran is endocytosed and accumulated in the lysosomal compartment. FITC shows a pH-dependent variation in fluorescence when analyzed at maximum emission wavelength and no variation when analyzing at the isosbestic point, thereby the ratio can be used to determine the lysosomal pH. A standard curve is obtained by equilibrating intralysosomal pH with extracellular pH using the ionophore nigericin. The protocol also includes information regarding procedures to induce lysosomal alkalinization and lysosomal membrane permeabilization.
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31. |
- Eriksson, Ida, 1985-
(författare)
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Dealing with damaged lysosomes : Impact of lysosomal membrane stability in health and disease
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The lysosome is the main unit for degradation and plays important roles in various cellular processes, such as nutrient sensing, cholesterol regulation and cell death. Consequently, altered lysosomal function contributes to, or even causes, several diseases. Lysosomal membrane permeabilization (LMP) and release of lysosomal content to the cytosol can induce cell death, and is implicated in inflammation and neuronal decline in several neurodegenerative diseases. It has also emerged as a potential target in cancer therapy. Due to the detrimental effects of LMP, cells harbor several mechanisms to protect and prevent lysosomal membrane damage. The aim of this thesis was to elucidate how lysosomal membrane stability and repair mechanisms affect cell death and survival. We find that lysosomal cholesterol is upregulated in response to an increased load of reactive oxygen species in a Parkinson’s disease cell model, and that augmented cholesterol protects from LMP. However, cholesterol also induces accumulation of α-synuclein and inhibits lysosome-mediated degradation, which can destabilize the lysosomal membrane and accelerate the course of disease. Further, we demonstrate that lysosomal membrane damage is counteracted by a calcium-dependent repair mechanism to prevent LMP. Lysosomes damaged beyond repair are instead sequestered in an autophagosome and degraded by intact lysosomes in a process called lysophagy. As a result, small vesicles containing lysosomal membrane proteins are generated, which we believe are used to restore lysosomal function. We show that malignant cells are more sensitive to LMP, and that they differ in their activation of damage-response mechanisms compared to normal cells. Moreover, in malignant cells, the intracellular position of the lysosomes determines the susceptibility to lysosomal damage. Peripherally located lysosomes are less sensitive, and by relocating lysosomes to the perinuclear area in the cell, we can sensitize lysosomes to LMP induction. In summary, this thesis demonstrates the importance of damage-response mechanisms to protect from lysosomal membrane damage and maintain cellular function. It also indicates that targeting of lysosomal stability and repair is a potential therapeutic strategy in both neurodegenerative diseases and in cancer.
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32. |
- Eriksson, Ida, et al.
(författare)
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Impact of high cholesterol in a Parkinsons disease model: Prevention of lysosomal leakage versus stimulation of alpha-synuclein aggregation
- 2017
-
Ingår i: European Journal of Cell Biology. - : ELSEVIER GMBH, URBAN & FISCHER VERLAG. - 0171-9335 .- 1618-1298. ; 96:2, s. 99-109
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Tidskriftsartikel (refereegranskat)abstract
- Parkinsons disease is characterized by accumulation of intraneuronal cytoplasmic inclusions, Lewy bodies, which mainly consist of aggregated alpha-synuclein. Controversies exist as to whether high blood cholesterol is a risk factor for the development of the disease and whether statin treatment could have a protective effect. Using a model system of BE(2)-M17 neuroblastoma cells treated with the neurotoxin 1-methyl-4-phenylpyridinium (MPP+), we found that MPP+-induced cell death was accompanied by cholesterol accumulation in a lysosomal-like pattern in pre-apoptotic cells. To study the effects of lysosomal cholesterol accumulation, we increased lysosomal cholesterol through pre-treatment with U18666A and found delayed leakage of lysosomal contents into the cytosol, which reduced cell death. This suggests that increased lysosomal cholesterol is a stress response mechanism to protect lysosomal membrane integrity in response to early apoptotic stress. However, high cholesterol also stimulated the accumulation of alpha-synuclein. Treatment with the cholesterol-lowering drug lovastatin reduced MPP+-induced cell death by inhibiting the production of reactive oxygen species, but did not prevent lysosomal cholesterol increase nor affect alpha-synuclein accumulation. Our study indicates a dual role of high cholesterol in Parkinsons disease, in which it acts both as a protector against lysosomal membrane permeabilization and as a stimulator of alpha-synuclein accumulation. (C) 2017 Elsevier GmbH. All rights reserved.
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33. |
- Eriksson, Ida, et al.
(författare)
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Lysosomal Function and Intracellular Position Determine the Malignant Phenotype in Melanoma
- 2023
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Ingår i: Journal of Investigative Dermatology. - : ELSEVIER SCIENCE INC. - 0022-202X .- 1523-1747. ; 143:9, s. 1769-
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Tidskriftsartikel (refereegranskat)abstract
- Lysosomes are central in cell homeostasis and participate in macromolecular degradation, plasma membrane repair, exosome release, cell adhesion/migration, and apoptosis. In cancer, alterations in lysosomal function and spatial distribution may facilitate disease progression. In this study, we show enhanced lysosomal activity in malignant melanoma cells compared with that in normal human melanocytes. Most lysosomes show perinuclear location in melanocytes, while they are more dispersed in melanoma, with retained proteolytic activity and low pH also in the peripheral population. Rab7a expression is lower in melanoma cells than in melanocytes, and by increasing Rab7a, lysosomes are relocated to the perinuclear region in melanoma. Exposure to the lysosome-destabilizing drug L-leucyl-L-leucine methyl ester causes higher damage in the perinuclear subset of lysosomes in melanomas, whereas differences in subpopulation susceptibility cannot be found in melanocytes. Interestingly, melanoma cells recruit the endosomal sorting complex required for transport-III core protein CHMP4B, involved in lysosomal membrane repair, rather than initiate lysophagy. However, when the perinuclear lysosomal position is promoted by Rab7a overexpression or kinesore treatment, lysophagy is increased. In addition, Rab7a overexpression is accompanied by reduced migration capacity. Taken together, the study emphasizes that alterations in lysosomal properties facilitate the malignant phenotype and declares the targeting of lysosomal function as a future therapeutic approach.
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34. |
- Eriksson, Ida, et al.
(författare)
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Lysosomes in Cancer-At the Crossroad of Good and Evil
- 2024
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Ingår i: Cells. - : MDPI. - 2073-4409. ; 13:5
-
Forskningsöversikt (refereegranskat)abstract
- Although it has been known for decades that lysosomes are central for degradation and recycling in the cell, their pivotal role as nutrient sensing signaling hubs has recently become of central interest. Since lysosomes are highly dynamic and in constant change regarding content and intracellular position, fusion/fission events allow communication between organelles in the cell, as well as cell-to-cell communication via exocytosis of lysosomal content and release of extracellular vesicles. Lysosomes also mediate different forms of regulated cell death by permeabilization of the lysosomal membrane and release of their content to the cytosol. In cancer cells, lysosomal biogenesis and autophagy are increased to support the increased metabolism and allow growth even under nutrient- and oxygen-poor conditions. Tumor cells also induce exocytosis of lysosomal content to the extracellular space to promote invasion and metastasis. However, due to the enhanced lysosomal function, cancer cells are often more susceptible to lysosomal membrane permeabilization, providing an alternative strategy to induce cell death. This review summarizes the current knowledge of cancer-associated alterations in lysosomal structure and function and illustrates how lysosomal exocytosis and release of extracellular vesicles affect disease progression. We focus on functional differences depending on lysosomal localization and the regulation of intracellular transport, and lastly provide insight how new therapeutic strategies can exploit the power of the lysosome and improve cancer treatment.
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35. |
- Eriksson, Ida, et al.
(författare)
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Real-Time Monitoring of Lysosomal Membrane Permeabilization Using Acridine Orange
- 2023
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Ingår i: METHODS AND PROTOCOLS. - : MDPI. - 2409-9279. ; 6:4
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Tidskriftsartikel (refereegranskat)abstract
- Loss of lysosomal membrane integrity results in leakage of lysosomal hydrolases to the cytosol which might harm cell function and induce cell death. Destabilization of lysosomes often precede apoptotic or necrotic cell death and occur during both physiological and pathological conditions. The weak base acridine orange readily enters cells and accumulates in the acidic environment of lysosomes. Vital staining with acridine orange is a well-proven technique to observe lysosomal destabilization using fluorescence microscopy and flow cytometry. These analyses are, however, time consuming and only adapted for discrete time points, which make them unsuitable for large-scale approaches. Therefore, we have developed a time-saving, high-throughput microplate reader-based method to follow destabilization of the lysosomal membrane in real-time using acridine orange. This protocol can easily be adopted for patient samples since the number of cells per sample is low and the time for analysis is short.
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36. |
- Eriksson, Ida, et al.
(författare)
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Restoration of lysosomal function after damage is accompanied by recycling of lysosomal membrane proteins
- 2020
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Ingår i: Cell Death and Disease. - : NATURE PUBLISHING GROUP. - 2041-4889. ; 11:5
-
Tidskriftsartikel (refereegranskat)abstract
- Lysosomes are central organelles for cellular degradation and energy homeostasis. In addition, lysosomal membrane permeabilization (LMP) and subsequent release of lysosomal content to the cytosol can initiate programmed cell death. The extent of LMP and available repair mechanisms determine the cell fate after lysosomal damage. In this study, we aimed to investigate the premises for lysosomal membrane repair after LMP and found that lysosomal membrane damage initiated by l-leucyl-l-leucine methyl ester (LLOMe) caused caspase-dependent apoptosis in almost 50% of the cells, while the rest recovered. Immediately after LLOMe addition, lysosomal proteases were detected in the cytosol and the ESCRT-components ALIX and CHMP4B were recruited to the lysosomal membrane. Next, lysophagic clearance of damaged lysosomes was evident and a concentration-dependent translocation of several lysosomal membrane proteins, including LAMP2, to the cytosol was found. LAMP2 was present in small vesicles with the N-terminal protein chain facing the lumen of the vesicle. We conclude that lysophagic clearance of damaged lysosomes results in generation of lysosomal membrane protein complexes, which constitute small membrane enclosed units, possibly for recycling of lysosomal membrane proteins. These lysosomal membrane complexes enable an efficient regeneration of lysosomes to regain cell functionality.
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37. |
- Garvin, Stina, 1977-, et al.
(författare)
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Resveratrol induces apoptosis and inhibits angiogenesis in human breast cancer xenografts in vivo
- 2006
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Ingår i: Cancer Letters. - : Elsevier BV. - 0304-3835 .- 1872-7980. ; 231:1, s. 113-122
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Tidskriftsartikel (refereegranskat)abstract
- Resveratrol, a polyphenol found in grapes and wine, is considered a potential cancer chemopreventive agent. Resveratrol has been shown to induce transcription via both ERα and ERβ. We observed significantly lower tumor growth, decreased angiogenesis, and increased apoptotic index in ERα- ERβ+ MDA-MB-231 tumors in resveratrol-treated nude mice compared with controls. In vitro we found a significant increase in apoptosis in resveratrol-treated MDA-MB-231 cells in addition to significantly reduced extracellular levels of VEGF. This study supports the potential use of resveratrol as a chemotherapeutic agent in breast cancers. © 2005 Elsevier Ireland Ltd. All rights reserved.
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38. |
- Gati, Istvan, et al.
(författare)
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Culturing of diagnostic muscle biopsies as spheroid-like structures: a pilot study of morphology and viability
- 2010
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Ingår i: Neurological Research. - : Forefront Publishing Group. - 0161-6412 .- 1743-1328. ; 32:6, s. 650-655
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The aim of this study was to establish three-dimensional cultures originating from muscle biopsies and evaluate the viability and morphology. Method: Muscle biopsies from patients with suspected neuromuscular disorders were obtained and established as primary muscle tissue cultures. Tissue pieces, 1-2 mm of diameters, were placed in culture medium and subjected to sporadic stirring to prevent attachment and outgrowth as monolayer cells. Morphology and ability to attach to the surface were investigated by light microscopy. Viability was evaluated by Tc-99m-tetrofosmin uptake. After 1 month, histology was evaluated by light microscopy and immunocytochemistry. The findings of a healthy muscle and a dystrophic muscle were compared. Results: Initially, the tissue pieces were unshaped but formed spheroid-like structures during the culture period. For dystrophic muscle, attachment capacity to the surface was initially potent and decreased during the culture period, whereas control muscle showed weak attachment from the start that increased during the culture period. The uptake of Tc-99m-tetrofosmin increased in control muscle, while it decreased in dystrophic muscle, during the culture period. The histological investigation demonstrated larger destruction of myofiber, weaker satellite cell activation and reduced myofiber regeneration in the dystrophic muscle as compared to the control muscle. Conclusion: The cellular components of the muscle tissue can survive and proliferate as spheroid-like primary cultures. The cellular composition resembles the in vivo condition, which allows studies of degeneration of the original fibers, and activation and proliferation of the satellite cells. The culture system may provide better understanding of the degeneration and regeneration processes in different muscle disorders and allow investigations of pharmacological interventions.
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39. |
- Gati, Istvan, 1954-, et al.
(författare)
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Effects of inhibitors of the arachidonic acid cascade on primary muscle culture from a Duchenne muscular dystrophy patient
- 2007
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Ingår i: Prostaglandins, Leukotrienes and Essential Fatty Acids. - : Elsevier BV. - 0952-3278 .- 1532-2823. ; 77:3-4, s. 217-223
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to elucidate the mechanisms of action for potential targets of therapeutic intervention related to the arachidonic acid cascade in muscular dystrophy. Primary cultures from a Duchenne patient were used to study the expression of dystrophin-1, utrophin, desmin, neonatal myosin heavy chain (MHCn) and Bcl-2 during inhibition of phospholipase A2 (PLA2), cyclooxygenase (COX) and lipoxygenase (LOX). Hypo-osmotic treatment was applied in order to trigger Ca2+ influx and PLA2 activity. Inhibition of PLA2 and LOX with prednisolone and nordihydroguaiaretic acid (NDGA) caused a semi-quantitative increase of utrophin and Bcl-2-, and a dose-dependent, quantitative increase of desmin expression, an effect that was augmented by hypo-osmotic treatment. Our results indicate that LOX inhibitors, similarly to corticosteroids, can be beneficial in the treatment of muscular dystrophies. © 2007 Elsevier Ltd. All rights reserved.
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40. |
- Gréen,, Anna, 1973-, et al.
(författare)
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Translocation of Histone H1 Subtypes Between Chromatin and Cytoplasm During Mitosis in Normal Human Fibroblasts
- 2010
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Ingår i: Cytometry Part A. - : John Wiley & Sons. - 1552-4922 .- 1552-4930. ; 77A:5, s. 478-484
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Tidskriftsartikel (refereegranskat)abstract
- Histone H1 is an important constituent of chromatin which undergoes major structural rearrangements during mitosis. However, the role of H1, multiple H1 subtypes and H1 phosphorylation is still unclear. In normal human fibroblasts, phosphorylated H1 was found located in nuclei during prophase and in both cytoplasm and condensed chromosomes during metaphase, anaphase and telophase as detected by immunocytochemistry. Moreover, we detected remarkable differences in the distribution of the histone H1 subtypes H1.2, H1.3 and H1.5 during mitosis. H1.2 was found in chromatin during prophase, and almost solely in the cytoplasm of metaphase and early anaphase cells. In late anaphase it appeared in both chromatin and cytoplasm, and again in chromatin during telophase. H1.5 distribution pattern resembled that of H1.2, but some H1.5 remained situated in chromatin during metaphase and early anaphase. H1.3 was detected in chromatin in all cell cycle phases. We propose therefore, that H1 subtype translocation during mitosis is controlled by phosphorylation, in combination with H1 subtype inherent affinity. We conclude that H1 subtypes, or their phosphorylated variants, may be signalling molecules in mitosis or that they leave chromatin in a regulated way to give access for chromatin condensing factors or transcriptional regulators during mitosis.
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41. |
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42. |
- Kishwar, Sultana, et al.
(författare)
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Investigation of the phototoxic effect of ZnO nanorods on fibroblasts and melanoma human cells
- 2014
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Ingår i: Laser Physics Letters. - : Institute of Physics (IOP). - 1612-2011 .- 1612-202X. ; 11:11
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Tidskriftsartikel (refereegranskat)abstract
- Photo-cytotoxicity of zinc oxide (ZnO) nanowires (NWs) either bare or conjugated with photosensitizers was studied in dark and after ultraviolet light exposure, in human melanoma and foreskin fibroblast cells. ZnO NWs were grown on the capillary tip and then coated with photosensitizer. This coated tip was used as pointer for intracellular insertion of ZnO NWs and photosensitizer. ZnO NWs pointer was inserted into a specific cell and then irradiated with ultraviolet (UVA), which led to loss of mitochondrial membrane potential, as estimated by loss of the Mitotracker Red staining. Dissolved ZnO NWs showed cytotoxicity as detected by MTT viability assay and morphological evaluation. UVA-irradiation enhanced the toxicity and caused the production of reactive oxygen species (ROS) resulting in cell necrosis. ZnO NWs were photo-toxic for both normal and cancer cells, questioning their bio-safety.
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43. |
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44. |
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45. |
- Larsson (Wäster), Petra, et al.
(författare)
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Ultraviolet A and B affect human melanocytes and keratinocytes differently. A study of oxidative alterations and apoptosis
- 2005
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Ingår i: Experimental Dermatology. - : Wiley. - 0906-6705 .- 1600-0625. ; 14:2, s. 117-123
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet (UV) radiation is an etiologic agent for malignant melanoma and non-melanoma skin cancer, but the spectral range responsible for tumor induction is still to be elucidated. In this study, we compared effects of UVA and UVB irradiation on normal human melanocytes (MCs) and keratinocytes (KCs) in vitro. We demonstrate that UVA irradiation induces immediate loss of reduced glutathione (GSH) in both MCs and KCs. Exposure to UVA also causes reduced plasma membrane stability, in both cell types, as estimated by fluorescein diacetate retention and flow cytometry. Furthermore, we noted reduction in proliferation and higher apoptosis frequency 24 h after UVA irradiation. UVB irradiation of KCs caused instant reduction of reduced GSH and impaired plasma membrane stability. We also found decline in proliferation and increased apoptosis after 24 h. In MCs, on the other hand, UVB had no effect on GSH level or plasma membrane stability, although increased apoptotic cell death and reduced proliferation was detected. In summary, MCs and KCs showed similar response towards UVA, while UVB had more pronounced effects on KCs as compared to MCs. These results might have implications for the induction of malignant melanoma and non-melanoma skin cancer.
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46. |
- Larsson Wäster, Petra, et al.
(författare)
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Ultraviolet (UV) A- and UVB-induced redox alterations and activation of nuclear factor-kappaB in human melanocytes - protective effects of alpha-tocopherol
- 2006
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Ingår i: British Journal of Dermatology. - : Oxford University Press (OUP). - 0007-0963 .- 1365-2133. ; 155:2, s. 292-300
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Tidskriftsartikel (refereegranskat)abstract
- Background Despite compelling evidence that ultraviolet (UV) irradiation causes melanoma the knowledge concerning reaction pathways and signalling transduction in melanocytes is still limited. Objectives To evaluate the protective capacity of α-tocopherol and β-carotene during UVA and UVB irradiation of human melanocytes in vitro. Methods Primary cultures of normal human melanocytes were irradiated by different wavelengths within the UV spectrum (UVA 6 J cm−2, UVB 60 mJ cm−2). Redox alterations and apoptosis were studied and the protective potential of α-tocopherol and β-carotene was evaluated. Results UVA and UVB irradiation decreased the intracellular concentration of reduced glutathione and activated the transcription factor nuclear factor (NF)-κB, detected as the increased level of the p65 subunit and translocation to the nucleus. This coincided with a rise in the level of γ-glutamyl-cysteine-synthetase, the rate-limiting enzyme of the glutathione synthesis. UVA and UVB caused apoptotic cell death as detected by nuclear fragmentation and caspase activation 24 h postirradiation. Pretreatment with α-tocopherol prevented UVA- and UVB-induced glutathione loss, NF-κB translocation and diminished apoptosis, but β-carotene did not show a similar protective capacity. Further, exposure to α-tocopherol by itself reduced cell proliferation rate. Conclusions UVA and UVB irradiation affected the intracellular redox state and increased the frequency of apoptosis in human melanocytes in vitro. α-Tocopherol might be a useful substance in protecting melanocytes from UV-induced damage.
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47. |
- Lundmark, Katarzyna, et al.
(författare)
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Evaluation of tubulin ß-3 and 5 hydroxy-methyl cytosine as diagnostic and prognostic markers in malignant melanoma
- 2024
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Ingår i: Annals of Diagnostic Pathology. - : ELSEVIER SCIENCE INC. - 1092-9134 .- 1532-8198. ; 72L
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Tidskriftsartikel (refereegranskat)abstract
- Tubulin beta-3 staining pattern and staining intensity of 5-hydroxymethyl cytosine (5-hmC) are potential diagnostic and prognostic markers in melanocytic lesions that need further evaluation. Melanocytic nevi and primary cutaneous melanomas were immunohistochemically stained for tubulin-beta-3 and 5-hmC. Immunoreactivity and staining patterns were correlated with Breslow-thickness, clinical and pathological characteristics, and progression-free survival. Melanocytes showed positive tubulin beta-3 staining. However, in most nevi, tubulin beta-3 staining appeared as a gradient with intense cytoplasmic staining in cells of the superficial part of the lesion that faded to weak staining in the deep dermal part, while no gradient was found in deep penetrating nevi and melanomas. In 53 % of the melanomas, areas with loss of tubulin beta-3 staining were found. 5-hmC staining intensity was significantly higher in melanocytic nevi compared to melanomas. Breslow thickness in combination with low 5-hmC score and loss of tubulin-beta-3 staining was predictive for poor prognosis. As single markers, tubulin-beta-3 and 5-hmC can be useful to distinguish between melanocytic nevi and melanoma, but staining variability limits the use of 5-hmC. In melanomas measuring >1.5 mm, combination of low 5-hmC score and loss of tubulin-beta-3 staining may have prognostic value.
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48. |
- Lundqvist, Helen, et al.
(författare)
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Evaluation of electron spin resonance for studies of superoxide anion production by human neutrophils interacting with Staphylococcus aureus and Staphylococcus epidermidis.
- 2008
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Ingår i: Journal of Biochemical and Biophysical Methods. - : Elsevier BV. - 0165-022X .- 1872-857X. ; 70:6, s. 1059-1065
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Tidskriftsartikel (refereegranskat)abstract
- The present study evaluates electron spin resonance (ESR) and the spin trapper 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO) for analysis of superoxide radical production by human neutrophils interacting with viable Staphylococcus aureus and Staphylococcus epidermidis bacteria. To avoid auto-activation due to interaction with glass surfaces, neutrophils were preincubated in plastic tubes until the peak response was reached, and then transferred to a quartz flat cell to record the ESR spectra. The time point for peak response was identified by parallel analysis of the bacteria-neutrophil interaction using luminol amplified chemiluminescence. We found detectable ESR spectra from neutrophils interacting with as few as five bacteria of the weak activating S. epidermidis per neutrophil. Addition of the NADPH oxidase inhibitor diphenylene iodonium totally abolished spectra. Catalase, DMSO or an iron chelator had no impact on the produced spectra and ionomycin, a selective activator of intracellular NADPH oxidase, gave significant ESR spectra. Taken together, our results indicate that DEPMPO is cell permeable and detects NADPH oxidase derived superoxide anions formed in phagosomes or released by human neutrophils phagocytosing viable S. aureus and S. epidermidis. The technique may be used as a sensitive tool to evaluate superoxide anion production in human neutrophils.
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49. |
- Nilsson, Cathrine, 1978-, et al.
(författare)
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Analysis of cytosolic and lysosomal pH in apoptotic cells by flow cytometry
- 2004
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Ingår i: Methods in Cell Science. - : Springer Science and Business Media LLC. - 1381-5741 .- 1573-0603. ; 25:3-4, s. 185-194
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Tidskriftsartikel (refereegranskat)abstract
- Several reports indicate that the cytosol is acidified during apoptosis although the mechanism is not yet fully elucidated. The most acidic organelle found in the cell is the lysosome, raising the possibility that lysosomal proton release may contribute to the cytosolic acidification. We here describe methods for measurement of the cytosolic and lysosomal pH in U937 cells by a dual-emission ratiometric technique suitable for flow cytometry. Cytosolic pH was analysed in cells loaded with the fluorescent probe BCECF, while lysosomal pH was determined after endocytosis of FITC-dextran. Standard curves were obtained by incubating cells in buffers with different pH in the presence of the proton ionophore nigericin. Apoptosis was induced by exposure of cells to 10ng/ml TNF- for 4h, and apoptotic cells were identified using a fluorescent marker for active caspases. By gating of control and apoptotic cells, the cytosolic and lysosomal pH were calculated in each population. The cytosolic pH was found to decrease from 7.2 ± 0.1 to 5.8s±0.1 and the lysosomal increased from 4.3±0.4 to 5.2±0.3. These methods will be useful in future attempts to evaluate the involvement of lysosomes in the acidification of the cytosol during apoptosis.
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50. |
- Nilsson, Cathrine, 1978-, et al.
(författare)
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Cytosolic acidification and lysosomal alkalinization during TNF-α induced apoptosis in U937 cells
- 2006
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Ingår i: Apoptosis (London). - : Springer Netherlands. - 1360-8185 .- 1573-675X. ; 11:7, s. 1149-1159
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Tidskriftsartikel (refereegranskat)abstract
- Apoptosis is often associated with acidification of the cytosol and since loss of lysosomal proton gradient and release of lysosomal content are early events during apoptosis, we investigated if the lysosomal compartment could contribute to cytosolic acidification. After exposure of U937 cells to tumor necrosis factor-α, three populations; healthy, pre-apoptotic, and apoptotic cells, were identified by flow cytometry. These populations were investigated regarding intra-cellular pH and apoptosis-associated events. There was a drop in cytosolic pH from 7.2 ± 0.1 in healthy cells to 6.8 ± 0.1 in pre-apoptotic, caspase-negative cells. In apoptotic, caspase-positive cells, the pH was further decreased to 5.7 ± 0.04. The cytosolic acidification was not affected by addition of specific inhibitors towards caspases or the mitochondrial F0F1-ATPase. In parallel to the cytosolic acidification, a rise in lysosomal pH from 4.3 ± 0.3, in the healthy population, to 4.8 ± 0.3 and 5.5 ± 0.3 in the pre-apoptotic- and apoptotic populations, respectively, was detected. In addition, lysosomal membrane permeability increased as detected as release of cathepsin D from lysosomes to the cytosol in pre-apoptotic and apoptotic cells. We, thus, suggest that lysosomal proton release is the cause of the cytosolic acidification of U937 cells exposed to TNF-α.
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