Subacute calorie restriction and rapamycin discordantly alter mouse liver proteome homeostasis and reverse aging effects

Abstract

Calorie restriction (CR) and rapamycin (RP) extend lifespan and improve health across model organisms. Both treatments inhibit mammalian target of rapamycin (mTOR) signaling, a conserved longevity pathway and a key regulator of protein homeostasis, yet their effects on proteome homeostasis are relatively unknown. To comprehensively study the effects of aging, CR, and RP on protein homeostasis, we performed the first simultaneous measurement of mRNA translation, protein turnover, and abundance in livers of young (3 month) and old (25 month) mice subjected to 10-week RP or 40% CR. Protein abundance and turnover were measured in vivo using 2H3–leucine heavy isotope labeling followed by LC-MS/MS, and translation was assessed by polysome profiling. We observed 35–60% increased protein half-lives after CR and 15% increased half-lives after RP compared to age-matched controls. Surprisingly, the effects of RP and CR on protein turnover and abundance differed greatly between canonical pathways, with opposite effects in mitochondrial (mt) dysfunction and eIF2 signaling pathways. CR most closely recapitulated the young phenotype in the top pathways. Polysome profiles indicated that CR reduced polysome loading while RP increased polysome loading in young and old mice, suggesting distinct mechanisms of reduced protein synthesis. CR and RP both attenuated protein oxidative damage. Our findings collectively suggest that CR and RP extend lifespan in part through the reduction of protein synthetic burden and damage and a concomitant increase in protein quality. However, these results challenge the notion that RP is a faithful CR mimetic and highlight mechanistic differences between the two interventions.

Reduced in vivo hepatic proteome replacement rates but not cell proliferation rates predict maximum lifespan extension in mice

“…(2015) recently published an elegant study that is highly complementary to the results presented here and provides mechanistic insights into improved proteostasis in two of the three models evaluated here. Using heavy‐leucine labeling, this group found that 10 weeks of 40% CR in 25‐month‐old mice and 10 weeks of 14 ppm Rapa treatment in 3‐month‐old mice reduced hepatic protein RRs by 30% and 13%, respectively.…”

“…These results are consistent with a recent study employing short‐term (10 weeks) 40% CR in older mice (25‐month‐old). Using heavy‐leucine labeling, these authors observed a ~33% reduction in hepatic protein RRs in CR compared to AL mice (Karunadharma et al ., 2015). …”

“…3C and Table 1). These findings are consistent with a recent study using a similar experimental design (10 weeks of 14 ppm Rapa treatment in 3‐month‐old mice) that reported a ~13% reduction in hepatic protein RRs in Rapa‐treated compared to control mice (Karunadharma et al ., 2015). …”

Diverse interventions that extend mouse lifespan suppress shared age-associated epigenetic changes at critical gene regulatory regions

“…Notwithstanding the more efficient suppression of age-associated epigenetic changes by CR, the epigenetic effects of CR and rapamycin were not identical and this might further underlie some of the differences between them that have been noted in previous studies, for example in endocrine and metabolic phenotypes and gene expression profiles [55, 62]. Of note, rapamycin in particular appears to induce additional changes unrelated to age-associated changes.…”

Impaired autophagy activity is linked to elevated ER-stress and inflammation in aging adipose tissue

“…Emerging evidence suggests that caloric restriction augment autophagy activity in many organs including skeletal muscle [36], liver [37], kidney [38], heart [39], and brain [40] in rodents. In this study, we provide further evidence that caloric restriction promotes autophagy function of adipose tissue SVFs (Fig.…”