Insulin signaling regulates longevity through protein phosphorylation in Caenorhabditis elegans

Abstract

Insulin/IGF-1 Signaling (IIS) is known to constrain longevity by inhibiting the transcription factor FOXO. How phosphorylation mediated by IIS kinases regulates lifespan beyond FOXO remains unclear. Here, we profile IIS-dependent phosphorylation changes in a large-scale quantitative phosphoproteomic analysis of wild-type and three IIS mutant Caenorhabditis elegans strains. We quantify more than 15,000 phosphosites and find that 476 of these are differentially phosphorylated in the long-lived daf-2/insulin receptor mutant. We develop a machine learning-based method to prioritize 25 potential lifespan-related phosphosites. We perform validations to show that AKT-1 pT492 inhibits DAF-16/FOXO and compensates the loss of daf-2 function, that EIF-2α pS49 potently inhibits protein synthesis and daf-2 longevity, and that reduced phosphorylation of multiple germline proteins apparently transmits reduced DAF-2 signaling to the soma. In addition, an analysis of kinases with enriched substrates detects that casein kinase 2 (CK2) subunits negatively regulate lifespan. Our study reveals detailed functional insights into longevity.

ATF-4 and hydrogen sulfide signalling mediate longevity from inhibition of translation or mTORC1

“…Although inhibition of mTORC1 has received widespread enthusiasm as an anti-ageing strategy, mTORC1 maintains fundamental processes that include protein synthesis, mRNA splicing, and metabolic pathways 2,3,[48][49][50] , suggesting that not all effects of mTORC1 suppression are necessarily beneficial. Similarly, although conditions that suppress ISR signalling can promote longevity through effects on selective translation 15 , ISR signalling through eIF2 contributes to lifespan extension from reduced insulin/IGF-1 signalling 24 , and our results demonstrate that the downstream ISR effector ATF-4 is a potent pro-longevity factor. Furthermore, while pharmacological ISR inhibition preserves cognitive functions during ageing by maintaining protein synthesis 14,16 , our findings suggest that ISR suppression could reduce levels of H2S, which has been shown to prevent neurodegeneration 51,52 .…”

“…We next investigated whether translation inhibition might increase lifespan independently of this canonical ISR signalling, using a well-characterized eIF2 mutant (eif2(qd338)) in which the serine at which inhibitory phosphorylation occurs during the ISR (S49 in C. elegans; S51 in mammals) is mutated to phenylalanine, so that eIF2 phosphorylation and ISR induction are blocked 23 . A mutation that prevents phosphorylation of this serine partially suppresses lifespan extension from reduced insulin/IGF-1 signalling, suggesting that ISR signalling is important for longevity in this context 24 . Importantly, the eif2(qd338) mutation did not interfere with the atf-4dependent increase in lifespan that was seen with ifg-1 knockdown (Fig.…”

Degrading intestinal DAF-2 nearly doubles Caenorhabditis elegans lifespan without affecting development or reproduction

“…IIS is a master regulator of glucose metabolism and lipid metabolism across the animal kingdom (Chatterjee and Perrimon, 2021;Zhang and Liu, 2014). In C. elegans, IIS also positively regulates protein synthesis (Li et al, 2021;Stout et al, 2013). The transcriptional changes shared by whole-body and intestinespecific DAF-2 degradation include up-regulation of peroxisome and fatty acid degradation, and down-regulation of RNA and protein metabolism.…”

“…Notably, RNA-seq analysis underscored down-regulation of genes functioning in protein and RNA metabolism as common features shared by daf-2(e1370), whole-body, and intestinespecific DAF-2 AID (Figure 6A and 6B). Previous studies have shown that decreasing protein synthesis extends lifespan (Depuydt et al, 2013;Lan et al, 2019;Pan et al, 2007;Syntichaki et al, 2007;Tiku et al, 2017) and accounts for ~40% of the lifespan extension by daf-2(e1370) (Li et al, 2021). In comparison, little is known about how down-regulation of RNA metabolism contributes to daf-2 longevity.…”

“…The intestine displayed a higher degree of similarity with the hypodermis than with the neurons, but down-regulation of structural constituents of ribosome and translation is a shared transcriptional response among all three tissues (Figure 7B). Therefore, decreased protein synthesis, an important mechanism for IIS longevity (Li et al, 2021), is propagated from the intestine to other tissues. Decreased protein synthesis is also a molecular signature of longevity by Dietary Restriction (DR) (Kapahi, 2010;Lan et al, 2019;Stout et al, 2013).…”