Abstract
The protein L-isoaspartyl-O-methyltransferase functions to initiate the repair of isomerized aspartyl and asparaginyl residues that spontaneously accumulate with age in a variety of organisms. Caenorhabditis elegans nematodes lacking the pcm-1 gene encoding this enzyme display a normal lifespan and phenotype under standard laboratory growth conditions. However, significant defects in development, egg laying, dauer survival, and autophagy have been observed in pcm-1 mutant nematodes when deprived of food and when exposed to oxidative stress. Interestingly, overexpression of this repair enzyme in both Drosophila and C. elegans extends adult lifespan under thermal stress. In this work, we show the involvement of the insulin/insulin-like growth factor-1 signaling (IIS) pathway in PCM-1-dependent lifespan extension in C. elegans. We demonstrate that reducing the levels of the DAF-16 downstream transcriptional effector of the IIS pathway by RNA interference reduces the lifespan extension resulting from PCM-1 overexpression. Using quantitative real-time PCR analysis, we show the up-regulation of DAF-16-dependent stress response genes in the PCM-1 overexpressor animals compared to wild-type and pcm-1 mutant nematodes under mild thermal stress conditions. Additionally, similar to other long-lived C. elegans mutants in the IIS pathway, including daf-2 and age-1 mutants, PCM-1 overexpressor adult animals display increased resistance to severe thermal stress, whereas pcm-1 mutant animals survive less long under these conditions. Although we observe a higher accumulation of damaged proteins in pcm-1 mutant nematodes, the basal level of isoaspartyl residues detected in wild-type animals was not reduced by PCM-1 overexpression. Our results support a signaling role for the protein L-isoaspartyl methyltransferase in lifespan extension that involves the IIS pathway, but that may be independent of its function in overall protein repair.
Highlights
A master regulator of aging in the nematode Caenorhabditis elegans is the insulin/insulin-like growth factor-1 signaling (IIS) pathway
PCM-1 overexpression extends lifespan in a DAF-16-dependent manner It has previously been shown that PCM-1 overexpression extends the lifespan of adult nematodes under mild thermal stress [17]
Nematodes expressing a PCM-1 protein with a mutated AdoMet-binding site in a pcm-1 null background (PL54 strain) had a lifespan that was similar to wild-type (N2) animals under the same conditions indicating that the lifespan extension of the overexpressor (PL51) strain was dependent on the methyltransferase activity of PCM-1 [17]
Summary
A master regulator of aging in the nematode Caenorhabditis elegans is the insulin/insulin-like growth factor-1 signaling (IIS) pathway. Activation of the DAF-2 insulin-like receptor in C. elegans triggers the successive phosphorylation and activation of several kinases including AGE-1 (Class 1A phosphatidylinositol-3-kinase) and AKT (protein kinase B); the activated AKT kinase can subsequently phosphorylate the FoxO transcription factor DAF-16, excluding it from the nucleus and thereby rendering it inactive [2,3]. When this kinase cascade of phosphorylation events is deactivated, the DAF-16 transcription factor enters the nucleus, leading to the enhanced expression of genes involved in longevity, dauer formation, and stress resistance [2,3]. The long-lived phenotype for the daf-2 pathway mutants is abolished upon additional mutation of the DAF-16 transcription factor [5,7,8]
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