Lipid biosynthesis coordinates a Mitochondrial to Cytosolic Stress Response
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ABSTRACT: Defects in mitochondrial metabolism have been increasingly linked with age-onset protein misfolding diseases such as Alzheimerâs, Parkinsonâs, and Huntingtonâs. In response to protein folding stress, compartment-specific unfolded protein responses (UPRs) within the endoplasmic reticulum, mitochondria, and cytosol work in parallel to ensure cellular protein homeostasis. While perturbation of individual compartments can make other compartments more susceptible to protein stress, the cellular conditions that trigger cross-communication between the individual UPRs remain poorly understood. We have uncovered a conserved, robust mechanism linking mitochondrial protein homeostasis and the cytosolic folding environment through changes in lipid homeostasis. Metabolic restructuring caused by mitochondrial stress or small molecule activators trigger changes in gene expression coordinated uniquely by both the mitochondrial and cytosolic UPRs, protecting the cell from disease-associated proteins. Our data suggest an intricate and unique system of communication between UPRs in response to metabolic changes that could unveil new targets for diseases of protein misfolding. Because the induction of the MCSR due to hsp-6 RNAi required both hsf-1 and dve-1, key transcription factors required for the HSR and UPRmt, respectively, we asked which gene sets are coordinately regulated by both factors. We performed microarray analyses to determine which genes have their expression altered by hsp-6 RNAi and whether these genes are regulated either by hsf-1, dve-1 or both
Project description:Defects in mitochondrial metabolism have been increasingly linked with age-onset protein misfolding diseases such as Alzheimer’s, Parkinson’s, and Huntington’s. In response to protein folding stress, compartment-specific unfolded protein responses (UPRs) within the endoplasmic reticulum, mitochondria, and cytosol work in parallel to ensure cellular protein homeostasis. While perturbation of individual compartments can make other compartments more susceptible to protein stress, the cellular conditions that trigger cross-communication between the individual UPRs remain poorly understood. We have uncovered a conserved, robust mechanism linking mitochondrial protein homeostasis and the cytosolic folding environment through changes in lipid homeostasis. Metabolic restructuring caused by mitochondrial stress or small molecule activators trigger changes in gene expression coordinated uniquely by both the mitochondrial and cytosolic UPRs, protecting the cell from disease-associated proteins. Our data suggest an intricate and unique system of communication between UPRs in response to metabolic changes that could unveil new targets for diseases of protein misfolding.
Project description:To cope with a challenging and unpredictable environment, living systems have evolved several organelle-specific stress responses, e.g. the cytosolic heat shock response (HSR), the endoplasmic reticulum unfolded protein response (UPRER) and the mitochondrial unfolded protein response (UPRmt). UPRmt monitors mitochondrial function and homeostasis in general. However, the mechanism of UPRmt remains largely unexplored. Here we identified that histone deacetylase HDA-1 is associated with homeobox domain-containing protein DVE-1 in UPRmt activation in Caenorhabditis elegans. Knocking down ATP synthase subunit atp-2 generates mitochondrial stress and induces UPRmt. After analyzing the mRNA profiles of worms on L4440 RNAi, hda-1 RNAi or dve-1 RNAi and untreated or treated with atp-2 RNAi, we found that 283 hda-1_dependent genes and 218 dve-1_dependent genes were upregulated in response to atp-2 RNAi.
Project description:The special AT-rich sequence-binding (SATB) protein DVE-1 is widely recognized for its pivotal involvement in orchestrating the retrograde mitochondrial unfolded protein response (mitoUPR) in C. elegans. In our study of downstream factors contributing to lifespan extension in sensory ciliary mutants, we find that DVE-1 is crucial for this longevity effect independent of its canonical mitoUPR function. Additionally, DVE-1 also influences lifespan under conditions of dietary restriction and germline loss, again distinct from its role in mitoUPR. Mechanistically, while mitochondrial stress typically prompts nuclear accumulation of DVE-1 to initiate the transcriptional mitoUPR program, these long-lived mutants reduce DVE-1 nuclear accumulation, likely by enhancing its cytosolic translocation. This observation suggests a cytosolic role for DVE-1 in lifespan extension. Overall, our study implies that, in contrast to the more narrowly defined role of the mitoUPR-related transcription factor ATFS-1, DVE-1 may possess broader functions than previously recognized in modulating longevity and defending against stress.
Project description:The mitochondrial matrix is unique in that it must integrate folding and assembly of proteins derived from nuclear and mitochondrial genomes. In C. elegans, the mitochondrial unfolded protein response (UPRmt) senses matrix protein misfolding and induces a program of nuclear gene expression, including mitochondrial chaperonins, to promote mitochondrial proteostasis. While misfolded mitochondrial matrix-localized ornithine trans-carbamylase (OTC) induces chaperonin expression, our understanding of mammalian UPRmt is rudimentary, reflecting a lack of acute triggers for UPRmt activation. This limitation has prevented analysis of the cellular responses to matrix protein misfolding and the effects of UPRmt on mitochondrial translation to control protein folding loads. Here, we combine pharmacological inhibitors of matrix-localized HSP90/TRAP1 or LON protease, which promote chaperonin expression, with global transcriptional and proteomic analysis to reveal an extensive and acute response of human cells to UPRmt. This response involved widespread induction of nuclear genes, including matrix-localized proteins involved in folding, pre-RNA processing and translation. Functional studies revealed rapid but reversible translation inhibition in mitochondria occurring concurrently with defects in pre-RNA processing due to transcriptional repression and LON-dependent turnover of the mitochondrial pre-RNA processing nuclease MRPP3. This study reveals that acute mitochondrial protein folding stress activates both increased chaperone availability within the matrix and reduced matrix-localized protein synthesis through translational inhibition, and provides a framework for further dissection of mammalian UPRmt. triplicate experiment of 3 conditions (untreated, GTPP treatment, CDDO treatment)
Project description:The mitochondrial matrix is unique in that it must integrate folding and assembly of proteins derived from nuclear and mitochondrial genomes. In C. elegans, the mitochondrial unfolded protein response (UPRmt) senses matrix protein misfolding and induces a program of nuclear gene expression, including mitochondrial chaperonins, to promote mitochondrial proteostasis. While misfolded mitochondrial matrix-localized ornithine trans-carbamylase (OTC) induces chaperonin expression, our understanding of mammalian UPRmt is rudimentary, reflecting a lack of acute triggers for UPRmt activation. This limitation has prevented analysis of the cellular responses to matrix protein misfolding and the effects of UPRmt on mitochondrial translation to control protein folding loads. Here, we combine pharmacological inhibitors of matrix-localized HSP90/TRAP1 or LON protease, which promote chaperonin expression, with global transcriptional and proteomic analysis to reveal an extensive and acute response of human cells to UPRmt. This response involved widespread induction of nuclear genes, including matrix-localized proteins involved in folding, pre-RNA processing and translation. Functional studies revealed rapid but reversible translation inhibition in mitochondria occurring concurrently with defects in pre-RNA processing due to transcriptional repression and LON-dependent turnover of the mitochondrial pre-RNA processing nuclease MRPP3. This study reveals that acute mitochondrial protein folding stress activates both increased chaperone availability within the matrix and reduced matrix-localized protein synthesis through translational inhibition, and provides a framework for further dissection of mammalian UPRmt. triplicate experiment of 2 conditions (untreated, GTPP treatment)
Project description:Impaired protein homeostasis promotes age-associated tissue dysregulation, presenting a need for therapeutic approaches that can restore proteome integrity. The heat shock factor HSF-1 is the master transcriptional regulator of proteostasis and regulates the expression of heat shock proteins (HSPs), which facilitate proper protein folding, localisation, and degradation. Increased HSF-1 activity can suppress proteotoxicity and enhance longevity across species. Studies into the mechanisms behind these beneficial effects have mostly focused on HSPs; however, the precise mechanisms by which increased HSF-1 activity extends lifespan are not known. To address this, we conducted an RNAi screen for genes that promote longevity, in C. elegans over expressing HSF-1 (hsf-1 OE). We found that ubiquilin-1 (ubql-1), a multifaceted shuttle protein that functions in protein degradation pathways is necessary for full lifespan extension in hsf-1OE worms. Surprisingly, we find that lack of ubql-1 does not impact proteostasis capacity, but does alter mitochondrial dynamics, in hsf-1 OE worms. These effects are independent of mitophagy or the mitochondrial unfolded protein response (mitoUPR) suggesting enhanced turnover of mitochondrial outer membrane proteins may be important for increased longevity via the HSF-1-ubiquilin-1 axis. Additionally, we reveal a role for ubql-1, a protein quality control regulator in regulating lipid homeostasis in hsf-1 OE animals. Lack of ubql-1 in hsf-1 OE animals supresses the expression of a key mitochondrial β-oxidation and lipid mobilization gene regulated by NHR-49 - acyl-CoA synthetase-2, ACS-2 amongst other genes. We propose that ubql-1 is required for mito-fusion and metabolic modulations that promote longevity in hsf-1 OE by interacting with NHR-49.
Project description:The mitochondrial matrix is unique in that it must integrate folding and assembly of proteins derived from nuclear and mitochondrial genomes. In C. elegans, the mitochondrial unfolded protein response (UPRmt) senses matrix protein misfolding and induces a program of nuclear gene expression, including mitochondrial chaperonins, to promote mitochondrial proteostasis. While misfolded mitochondrial matrix-localized ornithine trans-carbamylase (OTC) induces chaperonin expression, our understanding of mammalian UPRmt is rudimentary, reflecting a lack of acute triggers for UPRmt activation. This limitation has prevented analysis of the cellular responses to matrix protein misfolding and the effects of UPRmt on mitochondrial translation to control protein folding loads. Here, we combine pharmacological inhibitors of matrix-localized HSP90/TRAP1 or LON protease, which promote chaperonin expression, with global transcriptional and proteomic analysis to reveal an extensive and acute response of human cells to UPRmt. This response involved widespread induction of nuclear genes, including matrix-localized proteins involved in folding, pre-RNA processing and translation. Functional studies revealed rapid but reversible translation inhibition in mitochondria occurring concurrently with defects in pre-RNA processing due to transcriptional repression and LON-dependent turnover of the mitochondrial pre-RNA processing nuclease MRPP3. This study reveals that acute mitochondrial protein folding stress activates both increased chaperone availability within the matrix and reduced matrix-localized protein synthesis through translational inhibition, and provides a framework for further dissection of mammalian UPRmt.
Project description:The mitochondrial matrix is unique in that it must integrate folding and assembly of proteins derived from nuclear and mitochondrial genomes. In C. elegans, the mitochondrial unfolded protein response (UPRmt) senses matrix protein misfolding and induces a program of nuclear gene expression, including mitochondrial chaperonins, to promote mitochondrial proteostasis. While misfolded mitochondrial matrix-localized ornithine trans-carbamylase (OTC) induces chaperonin expression, our understanding of mammalian UPRmt is rudimentary, reflecting a lack of acute triggers for UPRmt activation. This limitation has prevented analysis of the cellular responses to matrix protein misfolding and the effects of UPRmt on mitochondrial translation to control protein folding loads. Here, we combine pharmacological inhibitors of matrix-localized HSP90/TRAP1 or LON protease, which promote chaperonin expression, with global transcriptional and proteomic analysis to reveal an extensive and acute response of human cells to UPRmt. This response involved widespread induction of nuclear genes, including matrix-localized proteins involved in folding, pre-RNA processing and translation. Functional studies revealed rapid but reversible translation inhibition in mitochondria occurring concurrently with defects in pre-RNA processing due to transcriptional repression and LON-dependent turnover of the mitochondrial pre-RNA processing nuclease MRPP3. This study reveals that acute mitochondrial protein folding stress activates both increased chaperone availability within the matrix and reduced matrix-localized protein synthesis through translational inhibition, and provides a framework for further dissection of mammalian UPRmt.
Project description:Mitochondria are important organelles, but their function is often challenged by toxic products of metabolism as well as by pathogen attack. The mitochondrial unfolded protein response (UPRmt) monitors mitochondrial function in general: it is responsible for buffering the mitochondrial protein folding environment, and controlling mitochondria-nuclear balance of the electron transport chain (ETC) components. Besides, UPRmt plays essential roles in aging and lifespan. Here we found that knocking down histone deacetylase hda-1 robustly attenuated UPRmt and lifespan extension. We identified HDA-1 as a required factor for UPRmt activation and HDA-1 is associated with the homeobox domain-containing protein DVE-1.So, we performed ChIP-seq of worms to find DNA regions on which HDA-1 and DVE-1 bound, and if their binding depend on each other.
Project description:Mitochondrial DNA-depleted human skin fibroblasts (HSF rho0) with suppressed oxidative phosphorylation were characterized by significant changes in the expression of 2100 nuclear genes, encoding numerous protein classes, in NF-kappaB and STAT3 signaling pathways and by decreased activity of the mitochondrial death pathway, compared to the parent rho+ HSF. In contrast, the extrinsic TRAIL/TRAIL-Receptor-mediated death pathway remained highly active, and exogenous TRAIL induced higher levels of apoptosis in rho0 cells compared to rho+ HSF. Global gene expression analysis using microarray and quantitative RT-PCR demonstrated that expression levels of many growth factors and their adaptor proteins (FGF13, HGF, IGFBP4, IGFBP6, IGFL2), cytokines (IL6, IL17B, IL18, IL19, IL28B) and cytokine receptors (IL1R1, IL21R, IL31RA) were substantially decreased after mitochondrial depletion. Some of these genes were targets of NF-kappaB and STAT3, and their protein products could regulate the STAT3 signaling pathway. Alpha-irradiation induced expression of several NF-kappaB/STAT3 target genes, including IL1A, IL1B, IL6, PTGS2/COX2 and MMP12, in rho+ HSF, but this response was substantially decreased in rho0 HSF. Suppression of the IKK-NF-kappaB pathway by the small molecular inhibitor BMS-345541 and of the JAK2-STAT3 pathway by AG490 dramatically increased TRAIL-induced apoptosis in the control and irradiated rho+ HSF. Inhibitory antibodies against IL6, the main activator of JAK2-STAT3 pathway, added into the cell media, also increased TRAIL-induced apoptosis in rho+ HSF. However, NF-kappaB activation was partially lost in mitochondrial DNA-depleted HSF resulting in downregulation of the basal or radiation-induced expression of numerous NF-kappaB targets, further suppressing IL6-JAK2-STAT3, that in concert with NF-kappaB, regulated protection against TRAIL-induced apoptosis. There are 12 total samples, 3 biological replicates each of HSF rho+ and rho0 cells that were not irradiated (control=C) or irradiated (alpha=A). Cells were harvested at 4 hours after treatment.