| 1. |
- Aufschnaiter, Andreas, et al.
(författare)
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Taking out the garbage : cathepsin D and calcineurin in neurodegeneration
- 2017
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Ingår i: Neural Regeneration Research. - : Medknow. - 1673-5374 .- 1876-7958. ; 12:11, s. 1776-1779
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Forskningsöversikt (refereegranskat)abstract
- Cellular homeostasis requires a tightly controlled balance between protein synthesis, folding and degradation. Especially long-lived, post-mitotic cells such as neurons depend on an efficient proteostasis system to maintain cellular health over decades. Thus, a functional decline of processes contributing to protein degradation such as autophagy and general lysosomal proteolytic capacity is connected to several age-associated neurodegenerative disorders, including Parkinson's, Alzheimer's and Huntington's diseases. These so called proteinopathies are characterized by the accumulation and misfolding of distinct proteins, subsequently driving cellular demise. We recently linked efficient lysosomal protein breakdown via the protease cathepsin D to the Ca2+/calmodulin-dependent phosphatase calcineurin. In a yeast model for Parkinson's disease, functional calcineurin was required for proper trafficking of cathepsin D to the lysosome and for recycling of its endosomal sorting receptor to allow further rounds of shuttling. Here, we discuss these findings in relation to present knowledge about the involvement of cathepsin D in proteinopathies in general and a possible connection between this protease, calcineurin signalling and endosomal sorting in particular. As dysregulation of Ca2+ homeostasis as well as lysosomal impairment is connected to a plethora of neurodegenerative disorders, this novel interplay might very well impact pathologies beyond Parkinson's disease.
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| 2. |
- Aufschnaiter, Andreas, et al.
(författare)
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The Coordinated Action of Calcineurin and Cathepsin D Protects Against alpha-Synuclein Toxicity
- 2017
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Ingår i: Frontiers in Molecular Neuroscience. - : Frontiers Media SA. - 1662-5099. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- The degeneration of dopaminergic neurons during Parkinson's disease (PD) is intimately linked to malfunction of alpha-synuclein (alpha Syn), the main component of the proteinaceous intracellular inclusions characteristic for this pathology. The cytotoxicity of alpha Syn has been attributed to disturbances in several biological processes conserved from yeast to humans, including Ca2+ homeostasis, general lysosomal function and autophagy. However, the precise sequence of events that eventually results in cell death remains unclear. Here, we establish a connection between the major lysosomal protease cathepsin D (CatD) and the Ca2+/calmodulin-dependent phosphatase calcineurin. In a yeast model for PD, high levels of human alpha Syn triggered cytosolic acidification and reduced vacuolar hydrolytic capacity, finally leading to cell death. This could be counteracted by overexpression of yeast CatD (Pep4), which re-installed pH homeostasis and vacuolar proteolytic function, decreased alpha Syn oligomers and aggregates, and provided cytoprotection. Interestingly, these beneficial effects of Pep4 were independent of autophagy. Instead, they required functional calcineurin signaling, since deletion of calcineurin strongly reduced both the proteolytic activity of endogenous Pep4 and the cytoprotective capacity of overexpressed Pep4. Calcineurin contributed to proper endosomal targeting of Pep4 to the vacuole and the recycling of the Pep4 sorting receptor Pep1 from prevacuolar compartments back to the trans-Golgi network. Altogether, we demonstrate that stimulation of this novel calcineurin-Pep4 axis reduces alpha Syn cytotoxicity.
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| 3. |
- Berndtsson, Jens, et al.
(författare)
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Respiratory supercomplexes enhance electron transport by decreasing cytochrome c diffusion distance
- 2020
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Ingår i: Embo Reports. - : EMBO. - 1469-221X .- 1469-3178. ; 21
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Tidskriftsartikel (refereegranskat)abstract
- Respiratory chains are crucial for cellular energy conversion and consist of multi-subunit complexes that can assemble into supercomplexes. These structures have been intensively characterized in various organisms, but their physiological roles remain unclear. Here, we elucidate their function by leveraging a high-resolution structural model of yeast respiratory supercomplexes that allowed us to inhibit supercomplex formation by mutation of key residues in the interaction interface. Analyses of a mutant defective in supercomplex formation, which still contains fully functional individual complexes, show that the lack of supercomplex assembly delays the diffusion of cytochromec between the separated complexes, thus reducing electron transfer efficiency. Consequently, competitive cellular fitness is severely reduced in the absence of supercomplex formation and can be restored by overexpression of cytochromec. In sum, our results establish how respiratory supercomplexes increase the efficiency of cellular energy conversion, thereby providing an evolutionary advantage for aerobic organisms.
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| 4. |
- Kohler, Andreas, 1988-, et al.
(författare)
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Apitoxin and its components against cancer, neurodegeneration and rheumatoid arthritis : limitations and possibilities
- 2020
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Ingår i: Toxins. - : MDPI. - 2072-6651. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- Natural products represent important sources for the discovery and design of novel drugs. Bee venom and its isolated components have been intensively studied with respect to their potential to counteract or ameliorate diverse human diseases. Despite extensive research and significant advances in recent years, multifactorial diseases such as cancer, rheumatoid arthritis and neurodegenerative diseases remain major healthcare issues at present. Although pure bee venom, apitoxin, is mostly described to mediate anti-inflammatory, anti-arthritic and neuroprotective effects, its primary component melittin may represent an anticancer therapeutic. In this review, we approach the possibilities and limitations of apitoxin and its components in the treatment of these multifactorial diseases. We further discuss the observed unspecific cytotoxicity of melittin that strongly restricts its therapeutic use and review interesting possibilities of a beneficial use by selectively targeting melittin to cancer cells.
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| 5. |
- Kohler, Andreas, Dr. rer. nat. 1988-, et al.
(författare)
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Early fate decision for mitochondrially encoded proteins by a molecular triage
- 2023
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Ingår i: Molecular Cell. - : Cell Press. - 1097-2765 .- 1097-4164. ; 83:19
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Tidskriftsartikel (refereegranskat)abstract
- Folding of newly synthesized proteins poses challenges for a functional proteome. Dedicated protein quality control (PQC) systems either promote the folding of nascent polypeptides at ribosomes or, if this fails, ensure their degradation. Although well studied for cytosolic protein biogenesis, it is not understood how these processes work for mitochondrially encoded proteins, key subunits of the oxidative phosphorylation (OXPHOS) system. Here, we identify dedicated hubs in proximity to mitoribosomal tunnel exits coordinating mitochondrial protein biogenesis and quality control. Conserved prohibitin (PHB)/m-AAA protease supercomplexes and the availability of assembly chaperones determine the fate of newly synthesized proteins by molecular triaging. The localization of these competing activities in the vicinity of the mitoribosomal tunnel exit allows for a prompt decision on whether newly synthesized proteins are fed into OXPHOS assembly or are degraded.
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| 6. |
- Kohler, Andreas, Dr. rer. nat. 1988-, et al.
(författare)
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Mitochondrial lipids in neurodegeneration
- 2016
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Ingår i: Cell and Tissue Research. - : Springer. - 0302-766X .- 1432-0878. ; 367:1, s. 125-140
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Mitochondrial dysfunction is a common feature of many neurodegenerative diseases, including proteinopathies such as Alzheimer’s or Parkinson’s disease, which are characterized by the deposition of aggregated proteins in the form of insoluble fibrils or plaques. The distinct molecular processes that eventually result in mitochondrial dysfunction during neurodegeneration are well studied but still not fully understood. However, defects in mitochondrial fission and fusion, mitophagy, oxidative phosphorylation and mitochondrial bioenergetics have been linked to cellular demise. These processes are influenced by the lipid environment within mitochondrial membranes as, besides membrane structure and curvature, recruitment and activity of different proteins also largely depend on the respective lipid composition. Hence, the interaction of neurotoxic proteins with certain lipids and the modification of lipid composition in different cell compartments, in particular mitochondria, decisively impact cell death associated with neurodegeneration. Here, we discuss the relevance of mitochondrial lipids in the pathological alterations that result in neuronal demise, focussing on proteinopathies.
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| 7. |
- Kohler, Andreas, Dr. rer. nat. 1988-, et al.
(författare)
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The enzymatic core of the Parkinson’s disease-associated protein LRRK2 impairs mitochondrial biogenesis in aging yeast
- 2018
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Ingår i: Frontiers in Molecular Neuroscience. - : Frontiers Media S.A.. - 1662-5099. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Mitochondrial dysfunction is a prominent trait of cellular decline during aging and intimately linked to neuronal degeneration during Parkinson’s disease (PD). Various proteins associated with PD have been shown to differentially impact mitochondrial dynamics, quality control and function, including the leucine-rich repeat kinase 2 (LRRK2). Here, we demonstrate that high levels of the enzymatic core of human LRRK2, harboring GTPase as well as kinase activity, decreases mitochondrial mass via an impairment of mitochondrial biogenesis in aging yeast. We link mitochondrial depletion to a global downregulation of mitochondria-related gene transcripts and show that this catalytic core of LRRK2 localizes to mitochondria and selectively compromises respiratory chain complex IV formation. With progressing cellular age, this culminates in dissipation of mitochondrial transmembrane potential, decreased respiratory capacity, ATP depletion and generation of reactive oxygen species. Ultimately, the collapse of the mitochondrial network results in cell death. A point mutation in LRRK2 that increases the intrinsic GTPase activity diminishes mitochondrial impairment and consequently provides cytoprotection. In sum, we report that a downregulation of mitochondrial biogenesis rather than excessive degradation of mitochondria underlies the reduction of mitochondrial abundance induced by the enzymatic core of LRRK2 in aging yeast cells. Thus, our data provide a novel perspective for deciphering the causative mechanisms of LRRK2-associated PD pathology.
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| 8. |
- Kohler, Andreas, 1988-, et al.
(författare)
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The mitochondrial network in Parkinson's disease
- 2020
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Ingår i: Genetics, neurology, behavior, and diet in parkinson's disease. - : Academic Press. - 9780128159507 ; , s. 123-138
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Bokkapitel (refereegranskat)abstract
- Neuronal dysfunction during sporadic and familial forms of Parkinson’s disease is intimately connected to mitochondrial dysfunction. Diverse genetic and environmental factors contributing to Parkinson’s disease development and progression have been shown to interfere with and to compromise mitochondrial bioenergetics, dynamics and trafficking. Mitochondria are highly dynamic organelles, constantly changing shape and abundance via coordinated fission and fusion events to adapt to cellular needs. Moreover, direct contact between mitochondria and other organelles allows interconnected signaling, and exchange of metabolites and ions. Several proteins associated with familial Parkinson’s disease modulate the equilibrium between fission and fusion, govern distinct mitochondrial degradation pathways and impact the formation of tethering complexes that facilitate interorganellar contact. Here, we discuss molecular mechanisms of mitochondrial dysfunction in Parkinson’s disease, focusing on mitochondrial dynamics and contact sites.
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| 9. |
- Kohler, Verena, 1992-, et al.
(författare)
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Closing the gap : membrane contact sites in the regulation of autophagy
- 2020
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Ingår i: Cells. - : MDPI. - 2073-4409. ; 9:5, s. 1184-1184
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Forskningsöversikt (refereegranskat)abstract
- In all eukaryotic cells, intracellular organization and spatial separation of incompatible biochemical processes is established by individual cellular subcompartments in form of membrane-bound organelles. Virtually all of these organelles are physically connected via membrane contact sites (MCS), allowing interorganellar communication and a functional integration of cellular processes. These MCS coordinate the exchange of diverse metabolites and serve as hubs for lipid synthesis and trafficking. While this of course indirectly impacts on a plethora of biological functions, including autophagy, accumulating evidence shows that MCS can also directly regulate autophagic processes. Here, we focus on the nexus between interorganellar contacts and autophagy in yeast and mammalian cells, highlighting similarities and differences. We discuss MCS connecting the ER to mitochondria or the plasma membrane, crucial for early steps of both selective and non-selective autophagy, the yeast-specific nuclear–vacuolar tethering system and its role in microautophagy, the emerging function of distinct autophagy-related proteins in organellar tethering as well as novel MCS transiently emanating from the growing phagophore and mature autophagosome.
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| 10. |
- Kohler, Verena, 1992-, et al.
(författare)
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Conjugative type IV secretion in Gram-positive pathogens : TraG, a lytic transglycosylase and endopeptidase, interacts with translocation channel protein TraM
- 2017
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Ingår i: Plasmid. - : Elsevier BV. - 0147-619X .- 1095-9890. ; 91, s. 9-18
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Tidskriftsartikel (refereegranskat)abstract
- Conjugative transfer plays a major role in the transmission of antibiotic resistance in bacteria. pIP501 is a Grampositive conjugative model plasmid with the broadest transfer host-range known so far and is frequently found in Enterococcus faecalis and Enterococcus faecium clinical isolates. The pIP501 type IV secretion system is encoded by 15 transfer genes. In this work, we focus on the VirB1-like protein TraG, a modular peptidoglycan metabolizing enzyme, and the VirB8-homolog TraM, a potential member of the translocation channel. By providing full-length traG in trans, but not with a truncated variant, we achieved full recovery of wild type transfer efficiency in the traG-knockout mutant E. faecalis pIP501AtraG. With peptidoglycan digestion experiments and tandem mass spectrometry we could assign lytic transglycosylase and endopeptidase activity to TraG, with the CHAP domain alone displaying endopeptidase activity. We identified a novel interaction between TraG and TraM in a bacterial 2-hybrid assay. In addition we found that both proteins localize in focal spots at the E. faecalis cell membrane using immunostaining and fluorescence microscopy. Extracellular protease digestion to evaluate protein cell surface exposure revealed that correct membrane localization of TraM requires the transmembrane helix of TraG. Thus, we suggest an essential role for TraG in the assembly of the pIP501 type IV secretion system.
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