Biology subjects

Behl, C.

Publications and source records attributed to Behl, C..

7 recordsLinked to original sources

bioRxiv2024

The role of the synaptic vesicle protein SV2A in regulating mitochondrial morphology and autophagy.

The synaptic vesicle glycoprotein 2A (SV2A) is a transmembrane protein of synaptic vesicles. It is involved in key functions of neurons, focused on the regulation of neurotransmitter release. Here we report three novel findings suggesting a completely new role of SV2A. First, we demonstrate that SV2A is localized at the outer mitochondrial membrane (OMM) using confocal and super-resolution microscopy. Second, Inactivation of SV2A in our cell and animal models leads to fragmented mitochondria. In addition, SV2A also affects the basal autophagic flux as well as mitophagy. Third, using proteomics analysis we demonstrate that SV2A interacts with the fission factor DRP1 and the autophagy factor ATG9A. Using AlphaFold3 we provide a first glimpse of the molecular interaction between DRP1 and SV2A. Our findings demonstrate that SV2A is not only a vesicular protein but also a mitochondrial protein in the OMM with defined functions regulating mitochondrial morphology and autophagy.

molecular biology↗

bioRxiv2023

Adaptive epigenetic regulation of neuronal metabolism by a mitochondrial redox signal

Different signaling pathways connect the mitochondrion with the transcriptional machinery in the nucleus. Redox events are thought to play a substantial role along this axis, however, many open questions about their specificity, quantitative importance and mode of action remain. Here, we have employed subtoxic doses of the complex I inhibitor MPP+ in human neuronal LUHMES cells to characterize the contribution of scavengeable redox signals to mito-nuclear communication. MPP+ evoked a broadly targeted transcriptional induction of nuclear-encoded respiratory chain complex (RCC) subunits. Nanomolar doses of phenothiazine (PHT), a mitochondrially active antioxidant, attenuated these transcriptional effects by approximately half, but did not modulate the bioenergetic markers ATP, NAD+, NADH, lactate, or glucose. Transcriptional induction by MPP+ was accompanied by a loss of nuclear 5-methyl-cytosine and an increase in histone H3K14 acetylation, both of which were entirely prevented by PHT. Inhibitor and PHT reversibility experiments suggested that these alterations were mediated by lowered DNMT3B and SIRT1 levels, respectively. Analysis of MPTP-treated mice recapitulated the PHT-reversible induction of histone acetylation and DNMT3B suppression in vivo. Moreover, PHT completely abrogated the statistical significance of the association of MPP+ with the selective induction of mitochondrially imported proteins and RCC subunits. We conclude that the mitochondrion employs a redox signal to announce impending, but not yet acute mitochondrial distress to the nucleus, in order to selectively upregulate mito-metabolic genes via chromatin reorganization. Our results have implications for the interpretation of the observed epigenetic changes in Parkinsons disease and other neurodegenerative disorders.

cell biology↗

bioRxiv2023

Co-chaperone BAG3 directly target autophagic degradation via its LC3-interacting regions

The co-chaperone BAG3 is a hub for a variety of cellular pathways via its multiple domains and its interaction with HSP70 and HSPB8. Under aging and cellular stress conditions in particular, together with molecular chaperones, BAG3 ensures the sequestration of aggregated or aggregation prone ubiquitinated proteins to the autophagic-lysosomal system via ubiquitin receptors. There are emerging indications that BAG3-mediated selective macroautophagy also copes with non-ubiquitinated cargo. Phylogenetically, BAG3 comprises several highly conserved predicted LIRs, LC3-interacting regions, which might directly target BAG3 including its cargo to ATG8 proteins and directly drive their autophagic degradation. Based on pull-down experiments, peptide arrays and proximity ligation assays, our results provide evidence of an interaction of BAG3 with ATG8 proteins. In addition, we could demonstrate that mutations within the LIRs impair co-localization with ATG8 proteins in immunofluorescence. A BAG3 variant mutated in all LIRs results in a substantial decrease of BAG3 levels within purified native autophagic vesicles compared to wild-type BAG3. These results strongly suggest LC3-mediated sequestration of BAG3. Therefore, we conclude that in addition of being a key co-chaperone to HSP70, BAG3 may also act as cargo receptor for client proteins, which would significantly extend the role of BAG3 in selective macroautophagy and protein quality control. SynopsisBAG3 ensures sequestration of aggregated ubiquitinated proteins to the autophagic-lysosomal degradation. Based on emerging indications this BAG3-mediated macroautophagy may also cope with non-ubiquitinated clients and comprises conserved predicted LC3 interacting regions, we analyzed the interaction with LC3 proteins. We evidenced an interaction of BAG3 with LC3 proteins by various measures including pull-down experiments, peptide arrays, proximity ligation assays, co-localization and native autophagic vesicles analysis. These results suggest BAG3 may additionally act as cargo receptor for client proteins. Abstract Figure O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=187 SRC="FIGDIR/small/526551v1_ufig1.gif" ALT="Figure 1"> View larger version (77K): org.highwire.dtl.DTLVardef@ac40d2org.highwire.dtl.DTLVardef@d3bf3dorg.highwire.dtl.DTLVardef@1b06a53org.highwire.dtl.DTLVardef@114a453_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2022

Substrate profiling of the metalloproteinase ovastacin - Implications for its physiological function in mammalian fertilization

The metalloproteinase ovastacin is released by the mammalian egg upon fertilization and cleaves a distinct peptide bond in zona pellucida protein 2, a component of the enveloping extracellular matrix. This limited proteolysis causes zona pellucida hardening, abolishes sperm binding and thereby regulates fertility. Accordingly, this process is tightly controlled by the plasma protein fetuin-B, an endogenous competitive inhibitor. At present, little is known about how the cleavage characteristics of ovastacin differ from closely related proteases. Physiological implications of ovastacin beyond ZP2 cleavage are still obscure. In this study, we employed N-terminal amine isotopic labeling of substrates (N-TAILS) contained in the secretome of mouse embryonic fibroblasts to elucidate the substrate specificity and the precise cleavage site specificity. Furthermore, we were able to unravel the physicochemical properties governing enzyme-substrate interactions. Eventually, we identified several potential physiological substrates with significance for mammalian fertilization. These data suggest that ovastacin might regulate sperm-oocyte interaction and fertility beyond zona pellucida hardening. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=177 HEIGHT=200 SRC="FIGDIR/small/519252v1_ufig1.gif" ALT="Figure 1"> View larger version (90K): org.highwire.dtl.DTLVardef@1b27cddorg.highwire.dtl.DTLVardef@1239a3eorg.highwire.dtl.DTLVardef@638c37org.highwire.dtl.DTLVardef@18a960f_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2021

Protein content and lipid profiling of isolated native autophagosomes

Autophagy is a central eukaryotic catabolic pathway responsible for clearance and recycling of an extensive portfolio of cargoes, which are packed in vesicles, called autophagosomes, and are delivered to lysosomes for degradation. Besides basal autophagy, which constantly degrades cellular material, the pathway is highly responsive to several stress conditions. However, the exact protein content and phospholipid composition of autophagosomes under changing autophagy conditions remain elusive so far. Here, we introduce a FACS-based approach for isolation of native unmanipulated autophagosomes and ensure the quality of the preparations. Employing quantitative proteomics and phospholipidomics, we obtained a profound cargo and lipid profile of autophagosomes purified upon basal autophagy conditions, nutrient deprivation, and proteasome inhibition. Indeed, starvation only mildly affected the content profile, while interference with proteasome activity showed stronger effects and specifically altered autophagosome cargoes. Interestingly, the phospholipid composition of autophagosomes was unaffected by the different treatments. Thus, the novel isolation method enables purification of intact autophagosomes in large quantities and allows protein content and phospholipid profiling without the requirement of exhaustive cellular fractionation or genetic manipulation.

biochemistry↗

bioRxiv2019

Enhanced autophagic-lysosomal activity and increased BAG3-mediated selective macroautophagy as adaptive response of neuronal cells to chronic oxidative stress

Oxidative stress and a disturbed cellular protein homeostasis (proteostasis) belong to the most important hallmarks of aging and of neurodegenerative disorders. The proteasomal and autophagic-lysosomal degradation pathways are key measures to maintain proteostasis. Here, we report that hippocampal cells selected for full adaptation and resistance to oxidative stress induced by hydrogen peroxide (oxidative stress-resistant cells, OxSR cells) showed a massive increase in the expression of components of the cellular autophagic-lysosomal network and a significantly higher overall autophagic activity. A comparative expression analysis revealed that distinct key regulators of autophagy are upregulated in OxSR cells. The observed adaptive autophagic response was found to be independent of the upstream autophagy regulator mTOR but is accompanied by a significant upregulation of further downstream components of the canonical autophagy network such as Beclin1, WIPI1 and the transmembrane ATG9 proteins. Interestingly, the expression of the HSP70 co-chaperone BAG3, mediator of BAG3-mediated selective macroautophagy and highly relevant for the clearance of aggregated proteins in cells was found to be increased in OxSR cells that were consequently able to effectively overcome proteotoxic stress. Overexpression of BAG3 in oxidative stress-sensitive HT22 wildtype cells partly established the vesicular phenotype and the enhanced autophagic flux seen in OxSR cells suggesting that BAG3 takes over a key part in the adaptation process. A full proteome analysis demonstrated additional changes in the expression of mitochondrial proteins, metabolic enzymes and different pathway regulators in OxSR cells as consequence of the adaptation to oxidative stress in addition to autophagy-related proteins. Taken together, this analysis revealed a wide variety of pathways and players that act as adaptive response to chronic redox stress in neuronal cells.

cell biology↗

bioRxiv2018

RAB18 impacts autophagy via lipid droplet-derived lipid transfer and is rescued by ATG9A

Autophagy is a lysosomal degradation pathway that mediates protein and organelle turnover and maintains cellular homeostasis. Autophagosomes transport cargo to lysosomes and their formation is dependent on an appropriate lipid supply. Here, we show that the knockout of the RAB GTPase RAB18 interferes with lipid droplet (LD) metabolism, resulting in an impaired fatty acid mobilization. The reduced LD-derived lipid availability influences autophagy and provokes adaptive modifications of the autophagy network, which include increased ATG2B expression and ATG12-ATG5 conjugate formation as well as enhanced ATG2B and ATG9A phosphorylation. Phosphorylation of ATG9A directs this transmembrane protein to the site of autophagosome formation and this particular modification is sufficient to rescue autophagic activity under basal conditions in the absence of RAB18. However, it is incapable of enabling an increased autophagy under inductive conditions. Thus, we illustrate the role of RAB18 in connecting LDs and autophagy, further emphasize the importance of LD-derived lipids for the degradative pathway, and characterize an ATG9A phosphorylation-dependent autophagy rescue mechanism as an adaptive response that maintains autophagy under conditions of reduced LD-derived lipid availability.

cell biology↗