| 1. |
- Alikhani, Nyosha, et al.
(författare)
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Decreased proteolytic activity of the mitochondrial amyloid-β degrading enzyme, PreP peptidasome, in Alzheimer's disease brain mitochondria
- 2011
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Ingår i: Journal of Alzheimer's Disease. - 1387-2877 .- 1875-8908. ; 27:1, s. 75-87
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Tidskriftsartikel (refereegranskat)abstract
- Accumulation of amyloid-β peptide (Aβ), the neurotoxic peptide implicated in the pathogenesis of Alzheimer's disease (AD), has been shown in brain mitochondria of AD patients and of AD transgenic mouse models. The presence of Aβ in mitochondria leads to free radical generation and neuronal stress. Recently, we identified the presequence protease, PreP, localized in the mitochondrial matrix in mammalian mitochondria as the novel mitochondrial Aβ-degrading enzyme. In the present study, we examined PreP activity in the mitochondrial matrix of the human brain's temporal lobe, an area of the brain highly susceptible to Aβ accumulation and reactive oxygen species (ROS) production. We found significantly lower hPreP activity in AD brains compared with non-AD age-matched controls. By contrast, in the cerebellum, a brain region typically spared from Aβ accumulation, there was no significant difference in hPreP activity when comparing AD samples to non-AD controls. We also found significantly reduced PreP activity in the mitochondrial matrix of AD transgenic mouse brains (Tg mAβPP and Tg mAβPP/ABAD) when compared to non-transgenic aged-matched mice. Furthermore, mitochondrial fractions isolated from AD brains and Tg mAβPP mice had higher levels of 4-hydroxynonenal, an oxidative product, as compared with those from non-AD and nonTg mice. Accordingly, activity of cytochrome c oxidase was significantly reduced in the AD mitochondria. These findings suggest that decreased PreP proteolytic activity, possibly due to enhanced ROS production, contributes to Aβ accumulation in mitochondria leading to the mitochondrial toxicity and neuronal death that is exacerbated in AD. Clearance of mitochondrial Aβ by PreP may thus be of importance in the pathology of AD.
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| 2. |
- Hedskog, Louise, et al.
(författare)
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Biochemical studies of poly t variants in the alzheimer's disease associated tomm40 gene
- 2012
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Ingår i: Journal of Alzheimer's Disease. - 1387-2877 .- 1875-8908. ; 31:3, s. 527-536
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Tidskriftsartikel (refereegranskat)abstract
- The apolipoprotein E (APOE) gene remains the most strongly established risk factor for late onset Alzheimer's disease (LOAD). Recently the gene, TOMM40, which is in linkage disequilibrium with APOE, was identified to be associated with LOAD in genome-wide association studies. One of the identified polymorphisms in TOMM40 is rs10524523, which is located in intron 6 and composed of thymidine repeats varying between 14 to 36 base-pairs in length. Reported results are contradictory in regard to the very long poly-T variant that has been associated with both increased and decreased risk of LOAD. Our study aimed to elucidate the functional implication of rs10524523 in an in vitro model of human fibroblast cells obtained from cognitively healthy APOE epsilon 3/epsilon 4 carriers harboring very long or short poly-T variants coupled to their APOE epsilon 3 allele. We have studied (i) expression levels of TOM40 protein and mRNA, (ii) TOM40 mRNA splicing, and (iii) mitochondrial function and morphology; and we have found no significant differences in regards to very long or short poly-T variant.
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| 3. |
- Hedskog, Louise, et al.
(författare)
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Modulation of the endoplasmic reticulum-mitochondria interface in Alzheimer's disease and related models
- 2013
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:19, s. 7916-7921
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Tidskriftsartikel (refereegranskat)abstract
- It is well-established that subcompartments of endoplasmic reticulum (ER) are in physical contact with the mitochondria. These lipid raft-like regions of ER are referred to as mitochondria-associated ER membranes (MAMs), and they play an important role in, for example, lipid synthesis, calcium homeostasis, and apoptotic signaling. Perturbation of MAM function has previously been suggested in Alzheimer's disease (AD) as shown in fibroblasts from AD patients and a neuroblastoma cell line containing familial presenilin-2 AD mutation. The effect of AD pathogenesis on the ER-mitochondria interplay in the brain has so far remained unknown. Here, we studied ER-mitochondria contacts in human AD brain and related AD mouse and neuronal cell models. We found uniform distribution of MAM in neurons. Phosphofurin acidic cluster sorting protein-2 and sigma 1 receptor, two MAM-associated proteins, were shown to be essential for neuronal survival, because siRNA knockdown resulted in degeneration. Up-regulated MAM-associated proteins were found in the AD brain and amyloid precursor protein (APP)(Swe/Lon) mouse model, in which up-regulation was observed before the appearance of plaques. By studying an ER-mitochondria bridging complex, inositol-1,4,5-triphosphate receptor-voltage-dependent anion channel, we revealed that nanomolar concentrations of amyloid beta-peptide increased inositol-1,4,5-triphosphate receptor and voltage-dependent anion channel protein expression and elevated the number of ER-mitochondria contact points and mitochondrial calcium concentrations. Our data suggest an important role of ER-mitochondria contacts and cross-talk in AD pathology.
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| 4. |
- Moreira Pinho, Catarina, 1986-
(författare)
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Mitochondria in Alzheimer's Disease : The Presequence Protease and Mitochondria-Associated ER Membranes
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alzheimer’s disease (AD) is one of the most prevalent age-related neurodegenerative disorders and the accumulation of the amyloid-β peptide (Aβ) in the temporal lobe has been implicated in the pathology of AD. Synaptic transmission in neuronal cells is a highly energy dependent process, which relies on the presence and proper function of mitochondria. A growing number of studies have analyzed the roles of mitochondria in AD. Interestingly, Aβ accumulation in mitochondria was detected in AD patient brains and in AD mouse models, which was associated with the formation of reactive oxygen species (ROS) and neuronal death. In mitochondria, the only protease capable of clearing Aβ is the Presequence Protease, PreP.The aim of this thesis was to study the involvement of mitochondria and hPreP in AD. We investigated how the mitochondria-associated endoplasmic reticulum (ER) membranes (MAM), which are involved in the regulation of Ca2+ signaling, phospholipids synthesis and apoptosis, are affected in AD. We observed MAM at synapses and found that these structures are essential for neuronal and astrocytic survival. We detected altered MAM protein levels in AD patient brains and in AD mouse models in early stages of the disease and found that MAM can be functionally modulated by Aβ. We analyzed human PreP (hPreP) activity in brain extracts from AD patients and different factors that can affect hPreP function. Interestingly, we detected low hPreP activity in AD patient brains and in AD mouse models, which were associated with increased ROS levels and lower cytochrome c oxidase activity. This suggested that protein oxidation could contribute to impaired activity. Furthermore, we investigated a potential correlation between 18 single nucleotide polymorphisms (SNPs) in the PITRM1 gene, encoding hPreP, and the risk for developing AD. Even though we could not find any genetic correlation in the Swedish population examined, biochemical analysis of four non-synonymous hPreP-SNPs, selected on the basis of their location in hPreP structure, showed lower hPreP activity. Furthermore, we demonstrated in vivo and in vitro that the hPreP presequence is processed at amino acid 28 by mitochondrial processing peptidase (MPP) and that inefficient processing does not affect the enzymatic activity of hPreP but it decreases the stability of the protein.Together, these results indicate that MAM dysfunctions, inefficient Aβ clearance in mitochondria by hPreP, hPreP mutations or inefficient processing, may contribute to the development of AD.
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| 5. |
- Mossmann, Dirk, et al.
(författare)
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Amyloid-beta Peptide Induces Mitochondrial Dysfunction by Inhibition of Preprotein Maturation
- 2014
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Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131 .- 1932-7420. ; 20:4, s. 662-669
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Tidskriftsartikel (refereegranskat)abstract
- Most mitochondrial proteins possess N-terminal presequences that are required for targeting and import into the organelle. Upon import, presequences are cleaved off by matrix processing peptidases and subsequently degraded by the peptidasome Cym1/PreP, which also degrades Amyloid-beta peptides (A beta). Here we find that impaired turnover of presequence peptides results in feedback inhibition of presequence processing enzymes. Moreover, A beta inhibits degradation of presequence peptides by PreP, resulting in accumulation of mitochondrial preproteins and processing intermediates. Dysfunctional preprotein maturation leads to rapid protein degradation and an imbalanced organellar proteome. Our findings reveal a general mechanism by which A beta peptide can induce the multiple diverse mitochondrial dysfunctions accompanying Alzheimer's disease.
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| 6. |
- Pinho, Catarina Moreira, et al.
(författare)
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Genetic and biochemical studies of SNPs of the mitochondrial A beta-degrading protease, hPreP
- 2010
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Ingår i: Neuroscience Letters. - : Elsevier BV. - 0304-3940 .- 1872-7972. ; 469:2, s. 204-208
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Tidskriftsartikel (refereegranskat)abstract
- Several studies suggest mitochondrial dysfunction as a possible mechanism underlying the development of Alzheimer disease (AD). There is data showing that amyloid-beta (A beta) peptide is present in AD brain mitochondria. The human presequence protease (hPreP) was recently shown to be the major mitochondrial A beta-degrading enzyme. We investigated if there is an increased susceptibility to AD, which can be attributed to genetic variation in the hPreP gene PITRM1 and if the proteolytic efficiency of recombinant hPreP variants is affected. When a total of 673 AD cases and 649 controls were genotyped for 18 single nucleotide polymorphisms (SNPs), no genetic association between any of the SNPs and the risk for AD was found. In contrast, functional analysis of four non-synonymous SNPs in hPreP revealed a decreased activity compared to wild type hPreP. Using A beta, the presequence of ATP synthase F-1 beta subunit and a fluorescent peptide as substrates, the lowest activity was observed for the hPreP(A525D) variant, corresponding to rs1224893, which displayed only 20-30% of wild type activity. Furthermore, the activity of all variants was restored by the addition of Mg2+, suggesting an important role for this metal during proteolysis. In conclusion, our data suggest that genetic variation in the hPreP gene PITRM1 may potentially contribute to mitochondrial dysfunctions.
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| 7. |
- Pinho, Catarina Moreira, et al.
(författare)
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Mitochondrial import and degradation of amyloid-beta peptide
- 2014
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 1837:7, s. 1069-1074
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Forskningsöversikt (refereegranskat)abstract
- Mitochondrial dysfunctions associated with amyloid-beta peptide (A beta) accumulation in mitochondria have been observed in Alzheimer's disease (AD) patients' brains and in AD mice models. A beta is produced by sequential action of beta- and gamma-secretases cleaving the amyloid precursor protein (APP). The gamma-secretase complex was found in mitochondria-associated endoplasmic reticulum membranes (MAM) suggesting that this could be a potential site of A beta production, from which A beta is further transported into the mitochondria. In vitro, A beta was shown to be imported into the mitochondria through the translocase of the outer membrane (TOM) complex. The mitochondrial presequence protease (Prep) is responsible for A beta degradation reducing toxic effects of A beta on mitochondrial functions. The proteolytic activity of PreP is, however, lower in AD brain temporal lobe mitochondria and in AD transgenic mice models, possibly due to an increased reactive oxygen species (ROS) production. Here, we review the intracellular mechanisms of A beta production, its mitochondrial import and the intra-mitochondrial degradation. We also discuss the implications of a reduced efficiency of mitochondrial A beta clearance for AD. Understanding the underlying mechanisms may provide new insights into mitochondria related pathogenesis of AD and development of drug therapy against AD. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.
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| 8. |
- Teixeira, Pedro Filipe, et al.
(författare)
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In vitro oxidative inactivation of human presequence protease (hPreP)
- 2012
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Ingår i: Free Radical Biology & Medicine. - : Elsevier BV. - 0891-5849 .- 1873-4596. ; 53:11, s. 2188-2195
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Tidskriftsartikel (refereegranskat)abstract
- The mitochondrial peptidasome called presequence protease (Prep) is responsible for the degradation of presequences and other unstructured peptides including the amyloid-beta, peptide, whose accumulation may have deleterious effects on mitochondrial function. Recent studies showed that PreP activity is reduced in Alzheimer disease (AD) patients and AD mouse models compared to controls, which correlated with an enhanced reactive oxygen species production in mitochondria. In this study, we have investigated the effects of a biologically relevant oxidant, hydrogen peroxide (H2O2), on the activity of recombinant human PreP (hPreP). H2O2 inhibited hPreP activity in a concentration-dependent manner, resulting in oxidation of amino acid residues (detected by carbonylation) and lowered protein stability. Substitution of the evolutionarily conserved methionine 206 for leucine resulted in increased sensitivity of hPreP to oxidation, indicating a possible protective role of M2O6 as internal antioxidant. The activity of hPreP oxidized at low concentrations of H2O2 could be restored by methionine sulfoxide reductase A (MsrA), an enzyme that localizes to the mitochondrial matrix, suggesting that hPreP constitutes a substrate for MsrA. In summary, our in vitro results suggest a possible redox control of hPreP in the mitochondrial matrix and support the protective role of the conserved methionine 206 residue as an internal antioxidant.
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