Project description:To adapt mitochondrial function to the ever-changing intra- and extra-cellular environment, multiple mitochondrial stress response (MSR) pathways, including the mitochondrial unfolded protein response (UPRmt), have evolved. However, how the mitochondrial stress signal is sensed and relayed to UPRmt transcription factors, such as ATFS-1 in Caenorhabditis elegans, remains largely unknown. Here, we show that a panel of vacuolar H+-ATPase (v-ATPase) subunits and the target of rapamycin complex 1 (TORC1) activity are essential for the cytosolic relay of mitochondrial stress to ATFS-1, and for the induction of the UPRmt. Mechanistically, mitochondrial stress stimulates v-ATPase/Rheb-dependent TORC1 activation, subsequently promoting ATFS-1 translation. Increased translation of ATFS-1 upon mitochondrial stress furthermore relies on a set of ribosomal components, but is independent of GCN-2/PEK-1 signaling. Finally, the v-ATPase and ribosomal subunits are required for mitochondrial surveillance and mitochondrial stress-induced longevity. These results reveal a v-ATPase-TORC1-ATFS-1 signaling pathway that links mitochondrial stress to the UPRmt through intimate crosstalks between multiple organelles.
Project description:The mitochondrial unfolded protein response (UPR mt ) is regulated by the bZIP protein ATFS-1 which promotes mitochondrial protein homeostasis (proteostasis) and mitochondrial biogenesis in Caenorhabditis elegans . Upon mitochondrial perturbation, the ATFS-1-dependent transcriptional program promotes gene expression, leading to mitochondrial recovery. Conversely, atfs-1 -deletion worms harbor dysfunctional mitochondria, are developmentally impaired, and short-lived. However, atfs-1 -deletion worms develop to adults suggesting the presence of other signaling pathways that promote mitochondrial function and biogenesis in the absence of atfs-1 . We hypothesized that additional transcription factors regulate, or promote, mitochondrial function in the absence of atfs-1 . Here, we screened for transcription factors that could reduce the decline in mitochondrial function in the atfs-1 mutants when inhibited. Here, we demonstrate that inhibition of the nuclear hormone receptor NHR-180 re-establishes a functional mitochondrial network in atfs-1(null) worms, increases mtDNA content, and improves the developmental rate of wildtype worms. NHR-180 increases transcription of genes required for cytosolic protein synthesis in response to mitochondrial perturbation. Inhibition of the S6 kinase homolog, rsks-1 , in atfs-1(null) worms leads to a recovery of the mitochondrial network and mtDNA content consistent with nhr-180 regulating expression of protein synthesis components. Consistent with the observations in C. elegans , S6 kinase inhibition also increased mitochondrial biogenesis in mammalian atf5 -knockout cells that harbor severely impaired mitochondria. Intriguingly, nhr-180 or S6 kinase inhibition also rescues mitochondrial dysfunction caused by mutations in multiple genes required for oxidative phosphorylation. Combined, these studies suggest that increased protein synthesis contributes to the mitochondrial dysfunction caused by perturbations in OXPHOS gene expression and suggest a relatively straightforward approach to reducing the impact of mitochondrial dysfunction.
Project description:ATFS-1 has been shown to regulate transcription of mitochondrial chaperone genes such as mtHsp70/hsp-6 and hsp-60 in response to mitocondrial stress. To identify the entire ATFS-1-mediated response, we compared the transcript profiles from wild-type and atfs-1(tm4525) worms raised in the absence and presence of mitochondrial stress. We used microarrays to identify genes regulated by ATFS-1 during mitochondrial stress RNA samples were prepared from wild-type(wt) and atfs-1(tm4525)(mutant) worms fed either control(RNAi) or spg-7(RNAi). Worms were synchronized by bleaching, raised in liquid culture and harvested at the L4 stage. Control is denoted as C and spg-7 treatment is denoted T. Each experiment was performed in triplicate indicated as 1,2 and 3.
Project description:We previously reported that the RNA endonculease HOE-1 (RNaseZ/ELAC2) is necessary and sufficient for activation of the mitochondrial unfolded protein response (UPRmt) in C. elegans (PMID: 35451962). To comprehensively assess the broader cellular consequences of increased nuclear activity of HOE-1, we conducted RNA sequencing on day 2 adult wildtype animals vs animals in which endogenous HOE-1 is elevated in the nucleus via perturbation of its nuclear export signal (hoe-1(ΔNES)). Additionally, wildtype and hoe-1(ΔNES) animals were grown on both control and atfs-1 RNAi (ATFS-1 is the central transcription factor for UPRmt) to determine gene expression that is atfs-1 dependent. This analysis revealed that differential gene expression in hoe-1(ΔNES) animals exhibits a strong mitochondrial signature. Notably, gene ontology (GO) analysis of significantly upregulated genes showed a significant overrepresentation of mitochondrial associated genes. Moreover, knockdown of atfs-1 strongly compromised the differentially expressed gene profile. Together these data suggest that increased nuclear activity of HOE-1 preferential impacts expression of mitochondrial genes.
Project description:ATFS-1 has been shown to regulate transcription of mitochondrial chaperone genes such as mtHsp70/hsp-6 and hsp-60 in response to mitocondrial stress. To identify the entire ATFS-1-mediated response, we compared the transcript profiles from wild-type and atfs-1(tm4525) worms raised in the absence and presence of mitochondrial stress. We used microarrays to identify genes regulated by ATFS-1 during mitochondrial stress
Project description:We previously identified a number of genes which were differentially expressed during mitochondrial stress in an ATFS-1-dependent manner using an atfs-1 loss-of-function mutant allele . To complement the findings from our previous microarray, we compared the transcript profiles from wild-type and atfs-1(et18) gain-of-function worms (which have constitutively active ATFS-1) in the absence of mitochondrial stress. We used microarrays to identify genes regulated by ATFS-1 using a gain-of-function allele of atfs-1.
Project description:To better understand genome coordination and OXPHOS recovery during mitochondrial dysfunction, we examined ATFS-1, a transcription factor that regulates mitochondria-to nuclear communication during the mitochondrial UPR, via ChIP-sequencing. Wildtype worms treated spg-7(RNAi) are analyzed in the presence and absence of ATFS-1 antibody to identify ATFS-1 targets. Individual samples were analyzed. Wildtype worms treated spg-7(RNAi) in the absence of antibody is used as a control.
Project description:ATFS-1 has been shown to regulate transcription of mitochondrial chaperone genes such as mtHsp70/hsp-6 and hsp-60 in response to mitocondrial stress. To identify the entire ATFS-1-mediated response, we compared the transcript profiles from wild-type and atfs-1(tm4525) worms raised in the absence and presence of mitochondrial stress. We used microarrays to identify genes regulated by ZIP-3