How an organism dies is a fundamental yet poorly understood question in biology. An organism can die of many causes, including stress-induced phenoptosis, also defined as organismic death that is regulated by its genome-encoded programs. The mechanism of stress-induced phenoptosis is still largely unknown. Here, we show that transient but severe freezing-thaw stress (FTS) in Caenorhabditis elegans induces rapid and robust phenoptosis that is regulated by G-protein coupled receptor (GPCR) signaling. RNAi screens identify the GPCR-encoding fshr-1 in mediating transcriptional responses to FTS. FSHR-1 increases ligand interaction upon FTS and activates a cyclic AMP-PKA cascade leading to a genetic program to promote organismic death under severe stress. FSHR-1/GPCR signaling up-regulates the bZIP-type transcription factor ZIP-10, linking FTS to expression of genes involved in lipid remodeling, proteostasis, and aging. A mathematical model suggests how genes may promote organismic death under severe stress conditions, potentially benefiting growth of the clonal population with individuals less stressed and more reproductively privileged. Our studies reveal the roles of FSHR-1/GPCR-mediated signaling in stress-induced gene expression and phenoptosis in C. elegans, providing empirical new insights into mechanisms of stress-induced phenoptosis with evolutionary implications.

The adult brain consumes glucose for energy needs and stores glucose as glycogen mainly in astrocytes. Schulz et al. (2020. J. Cell Biol.https://doi.org/10.1083/jcb.201807127) identify the stress-regulated metabolic enzyme GDPGP1 that promotes neuronal survival likely through glycogen reserves in mouse and C. elegans neurons.

TMEM39A encodes an evolutionarily conserved transmembrane protein and carries single-nucleotide polymorphisms associated with increased risk of major human autoimmune diseases, including multiple sclerosis. The exact cellular function of TMEM39A remains not well understood. Here, we report that TMEM-39, the sole Caenorhabditis elegans (C. elegans) ortholog of TMEM39A, regulates lysosome distribution and accumulation. Elimination of tmem-39 leads to lysosome tubularization and reduced lysosome mobility, as well as accumulation of the lysosome-associated membrane protein LMP-1. In mammalian cells, loss of TMEM39A leads to redistribution of lysosomes from the perinuclear region to cell periphery. Mechanistically, TMEM39A interacts with the dynein intermediate light chain DYNC1I2 to maintain proper lysosome distribution. Deficiency of tmem-39 or the DYNC1I2 homolog in C. elegans impairs mTOR signaling and activates the downstream TFEB-like transcription factor HLH-30. We propose evolutionarily conserved roles of TMEM39 family proteins in regulating lysosome distribution and lysosome-associated signaling, dysfunction of which in humans may underlie aspects of autoimmune diseases.

Oxygen deprivation followed by reoxygenation causes pathological responses in many disorders, including ischemic stroke, heart attacks, and reperfusion injury. Key aspects of ischemia-reperfusion can be modeled by a Caenorhabditis elegans behavior, the O2-ON response, which is suppressed by hypoxic preconditioning or inactivation of the O2-sensing HIF (hypoxia-inducible factor) hydroxylase EGL-9. From a genetic screen, we found that the cytochrome P450 oxygenase CYP-13A12 acts in response to the EGL-9-HIF-1 pathway to facilitate the O2-ON response. CYP-13A12 promotes oxidation of polyunsaturated fatty acids into eicosanoids, signaling molecules that can strongly affect inflammatory pain and ischemia-reperfusion injury responses in mammals. We propose that roles of the EGL-9-HIF-1 pathway and cytochrome P450 in controlling responses to reoxygenation after anoxia are evolutionarily conserved.

Many organisms in nature have evolved mechanisms to tolerate severe hypoxia or ischemia, including the hibernation-capable Arctic ground squirrel (AGS). Although hypoxic or ischemia tolerance in AGS involves physiological adaptations, little is known about the critical cellular mechanisms underlying intrinsic AGS cell resilience to metabolic stress. Through cell survival-based cDNA expression screens in neural progenitor cells, we identify a genetic variant of AGS Atp5g1 that confers cell resilience to metabolic stress. Atp5g1 encodes a subunit of the mitochondrial ATP synthase. Ectopic expression in mouse cells and CRISPR/Cas9 base editing of endogenous AGS loci revealed causal roles of one AGS-specific amino acid substitution in mediating cytoprotection by AGS ATP5G1. AGS ATP5G1 promotes metabolic stress resilience by modulating mitochondrial morphological change and metabolic functions. Our results identify a naturally occurring variant of ATP5G1 from a mammalian hibernator that critically contributes to intrinsic cytoprotection against metabolic stress.

Animals utilize conserved mechanisms to regulate oxidative stress. The C. elegans SKN-1 protein is homologous to the vertebrate Nrf (NF-E2-related factor) family of cap 'n' collar (CnC) transcription factors and functions as a core regulator of xenobiotic and oxidative stress responses. The WD40 repeat-containing protein WDR-23 is a key negative regulator of SKN-1 activity. We previously found that the oxidative stress induced by excess iodide can be relieved by loss of function in the BLI-3/TSP-15/DOXA-1 dual oxidase complex. To further understand the molecular mechanism of this process, we screened for new mutants that can survive in excess iodide and identified gain-of-function mutations in skn-1 and loss-of-function mutations in wdr-23 The SKN-1C isoform functions in the hypodermis to affect animal's response to excess iodide, while the SKN-1A isoform appears to play a minor role. wdr-23(lf) can interact with bli-3 mutations in a manner different from skn-1(gf) Transcriptome studies suggest that excess iodide causes developmental arrest largely independent of changes in gene expression, and wdr-23(lf) could affect the expression of a subset of genes by a mechanism different from SKN-1 activation. We propose that WDR-23 and SKN-1 coordinate with the BLI-3/TSP-15/DOXA-1 dual oxidase complex in response to iodide-triggered oxidative stress.

Dysregulation of collagen production and secretion contributes to aging and tissue fibrosis of major organs. How procollagen proteins in the endoplasmic reticulum (ER) route as specialized cargos for secretion remains to be fully elucidated. Here, we report that TMEM39, an ER-localized transmembrane protein, regulates production and secretory cargo trafficking of procollagen. We identify the C. elegans ortholog TMEM-39 from an unbiased RNAi screen and show that deficiency of tmem-39 leads to striking defects in cuticle collagen production and constitutively high ER stress response. RNAi knockdown of the tmem-39 ortholog in Drosophila causes similar defects in collagen secretion from fat body cells. The cytosolic domain of human TMEM39A binds to Sec23A, a vesicle coat protein that drives collagen secretion and vesicular trafficking. TMEM-39 regulation of collagen secretion is independent of ER stress response and autophagy. We propose that the roles of TMEM-39 in collagen secretion and ER homeostasis are likely evolutionarily conserved.

How multicellular organisms respond to and are impacted by severe hypothermic stress is largely unknown. From C. elegans screens for mutants abnormally responding to cold-warming stimuli, we identify a molecular genetic pathway comprising ISY-1, a conserved uncharacterized protein, and ZIP-10, a bZIP-type transcription factor. ISY-1 gatekeeps the ZIP-10 transcriptional program by regulating the microRNA mir-60. Downstream of ISY-1 and mir-60, zip-10 levels rapidly and specifically increase upon transient cold-warming exposure. Prolonged zip-10 up-regulation induces several protease-encoding genes and promotes stress-induced organismic death, or phenoptosis, of C. elegans. zip-10 deficiency confers enhanced resistance to prolonged cold-warming stress, more prominently in adults than larvae. We conclude that the ZIP-10 genetic program mediates cold-warming response and may have evolved to promote wild-population kin selection under resource-limiting and thermal stress conditions.

Cells adapt to temperature shifts by adjusting levels of lipid desaturation and membrane fluidity. This fundamental process occurs in nearly all forms of life, but its mechanism in eukaryotes is unknown. We discovered that the evolutionarily conserved Caenorhabditis elegans gene acdh-11 (acyl-CoA dehydrogenase [ACDH]) facilitates heat adaptation by regulating the lipid desaturase FAT-7. Human ACDH deficiency causes the most common inherited disorders of fatty acid oxidation, with syndromes that are exacerbated by hyperthermia. Heat upregulates acdh-11 expression to decrease fat-7 expression. We solved the high-resolution crystal structure of ACDH-11 and established the molecular basis of its selective and high-affinity binding to C11/C12-chain fatty acids. ACDH-11 sequesters C11/C12-chain fatty acids and prevents these fatty acids from activating nuclear hormone receptors and driving fat-7 expression. Thus, the ACDH-11 pathway drives heat adaptation by linking temperature shifts to regulation of lipid desaturase levels and membrane fluidity via an unprecedented mode of fatty acid signaling.

Collagen is the most abundant protein in animals. Its dysregulation contributes to aging and many human disorders, including pathological tissue fibrosis in major organs. How premature collagen proteins in the endoplasmic reticulum (ER) assemble and route for secretion remains molecularly undefined. From an RNA interference screen, we identified an uncharacterized Caenorhabditis elegans gene tmem-131, deficiency of which impairs collagen production and activates ER stress response. We find that amino termini of human TMEM131 contain bacterial PapD chaperone-like domains, which recruit premature collagen monomers for proper assembly and secretion. Carboxy termini of TMEM131 interact with TRAPPC8, a component of the TRAPP tethering complex, to drive collagen cargo trafficking from ER to the Golgi. We provide evidence that previously undescribed roles of TMEM131 in collagen recruitment and secretion are evolutionarily conserved in C. elegans, Drosophila, and humans.