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Decreased insulin-mTOR signaling enables exceptional longevity in the nematode C. elegans by activating geroprotective transcription factors, including DAF-16, SKN-1 and HSF-1. Few studies have examined whether and how increased insulin-mTOR may actively drive organismic aging. Here we show that an agonist insulin INS-7 is drastically over-produced and causes shortened lifespan in lpd-3 mutants, a C. elegans model of human Alkuraya-Kučinskas syndrome. Lipidomic profiling reveals marked increase in the abundance of hexaceramide species in lpd-3 mutants, consistent with up-regulation of the genes encoding biosynthetic enzymes for hexaceramides, including HYL-1 ( H omolog of Y east L ongevity). Reducing HYL-1 activity decreases INS-7 levels and rescues the shortened lifespan of lpd-3 mutants through InsR/DAF-2 and mTOR/LET-363. We propose that increased insulin signaling exhibits late-life antagonistic pleiotropy and shortens lifespans through sphingolipid-hexaceramide and mTOR regulatory pathways.

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.

Additional file 1: Fig. S1. C. elegans TMEM-132 is a member of the evolutionarily conserved TMEM132 protein family. Fig. S2. C. elegans TMEM-132 maintains morphologically complex PVD, ADE but not AWC neurons. Fig. S3 Efficacy of RNAi in neurons by feeding from bacteria. Fig. S4. Enrichment of mammalian TMEM132D expression in the brain and claustral neurons. Fig. S5. TMEM132D regulates F-actin abundance.

Additional file 2: Table S1. List of genes encoding putative TMEM132D interactors identified from yeast-two-hybrid screens.

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER) protein that can be secreted and protects dopamine neurons and cardiomyocytes from ER stress and apoptosis. The mechanism of action of extracellular MANF has long been elusive. From a genetic screen for mutants with abnormal ER stress response, we identified the gene Y54G2A.23 as the evolutionarily conserved C. elegans MANF orthologue. We find that MANF binds to the lipid sulfatide, also known as 3-O-sulfogalactosylceramide present in serum and outer-cell membrane leaflets, directly in isolated forms and in reconstituted lipid micelles. Sulfatide binding promotes cellular MANF uptake and cytoprotection from hypoxia-induced cell death. Heightened ER stress responses of MANF-null C. elegans mutants and mammalian cells are alleviated by human MANF in a sulfatide-dependent manner. Our results demonstrate conserved roles of MANF in sulfatide binding and ER stress response, supporting sulfatide as a long-sought lipid mediator of MANF's cytoprotection.

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER) protein that can be secreted and protects dopamine neurons and cardiomyocytes from ER stress and apoptosis. The mechanism of action of extracellular MANF has long been elusive. From a genetic screen for mutants with abnormal ER stress response, we identified the gene Y54G2A.23 as the evolutionarily conserved C. elegans MANF orthologue. We find that MANF binds to the lipid sulfatide, also known as 3-O-sulfogalactosylceramide present in serum and outer-cell membrane leaflets, directly in isolated forms and in reconstituted lipid micelles. Sulfatide binding promotes cellular MANF uptake and cytoprotection from hypoxia-induced cell death. Heightened ER stress responses of MANF-null C. elegans mutants and mammalian cells are alleviated by human MANF in a sulfatide-dependent manner. Our results demonstrate conserved roles of MANF in sulfatide binding and ER stress response, supporting sulfatide as a long-sought lipid mediator of MANF’s cytoprotection., MANF is a secreted ER stress-inducible protein that protects neurons, pancreatic β cells and cardiomyocytes from cell death under oxidative stress, hypoxic or ischemic conditions. Here the authors show that MANF confers cytoprotection through direct binding to sulfatide followed by cellular uptake in both C. elegans and mammalian cells.