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Caloric restriction (CR) without malnutrition is one of the most consistent strategies for increasing mean and maximal lifespan and delaying the onset of age-associated diseases. Stress resistance is a common trait of many long-lived mutants and life-extending interventions, including CR. Indeed, better protection against heat shock and other genotoxic insults have helped explain the pro-survival properties of CR. In this study, both in vitro and in vivo responses to heat shock were investigated using two different models of CR. Murine B16F10 melanoma cells treated with serum from CR-fed rats showed lower proliferation, increased tolerance to heat shock and enhanced HSP-70 expression, compared to serum from ad libitum-fed animals. Similar effects were observed in B16F10 cells implanted subcutaneously in male C57BL/6 mice subjected to CR. Microarray analysis identified a number of genes and pathways whose expression profile were similar in both models. These results suggest that the use of an in vitro model could be a good alternative to study the mechanisms by which CR exerts its anti-tumorigenic effects.

The levels of microRNAs (miRNAs) are altered under different conditions such as cancer, senescence, and aging. Here, we have identified differentially expressed miRNAs in skeletal muscle from young and old rhesus monkeys using RNA sequencing. In old muscle, several miRNAs were upregulated, including miR-451, miR-144, miR-18a and miR-15a, while a few miRNAs were downregulated, including miR-181a and miR-181b. A number of novel miRNAs were also identified, particularly in old muscle. We also examined the impact of caloric restriction (CR) on miRNA abundance by reverse transcription (RT) followed by real-time, quantitative (q)PCR analysis and found that CR rescued the levels of miR-181b and chr1:205580546, and also dampened the age-induced increase in miR-451 and miR-144 levels. Our results reveal that there are changes in expression of known and novel miRNAs with skeletal muscle aging and that CR may reverse some of these changes to a younger phenotype.

The cumulative effects of cellular senescence and cell loss over time in various tissues and organs are considered major contributing factors to the ageing process. In various organisms, caloric restriction (CR) slows ageing and increases lifespan, at least in part, by activating nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases of the sirtuin family. Here, we use an in vitro model of CR to study the effects of this dietary regime on replicative senescence, cellular lifespan and modulation of the SIRT1 signaling pathway in normal human diploid fibroblasts. We found that serum from calorie-restricted animals was able to delay senescence and significantly increase replicative lifespan in these cells, when compared to serum from ad libitum fed animals. These effects correlated with CR-mediated increases in SIRT1 and decreases in p53 expression levels. In addition, we show that manipulation of SIRT1 levels by either over-expression or siRNA-mediated knockdown resulted in delayed and accelerated cellular senescence, respectively. Our results demonstrate that CR can delay senescence and increase replicative lifespan of normal human diploid fibroblasts in vitro and suggest that SIRT1 plays an important role in these processes. (185 words).

Stem cells undergo a shift in metabolic substrate utilization during specification and/or differentiation, a process that has been termed metabolic reprogramming. Here, we report that during the transition from quiescence to proliferation, skeletal muscle stem cells experience a metabolic switch from fatty acid oxidation to glycolysis. This reprogramming of cellular metabolism decreases intracellular NAD+ levels and the activity of the histone deacetylase SIRT1, leading to elevated H4K16 acetylation and activation of muscle gene transcription. Selective genetic ablation of the SIRT1 deacetylase domain in skeletal muscle results in increased H4K16 acetylation and deregulated activation of the myogenic program in SCs. Moreover, mice with muscle-specific inactivation of the SIRT1 deacetylase domain display reduced myofiber size, impaired muscle regeneration, and derepression of muscle developmental genes. Overall, these findings reveal how metabolic cues can be mechanistically translated into epigenetic modifications that regulate skeletal muscle stem cell biology.

A decrease in the activity of the Indy gene (I'm not dead yet) in flies extends life span without a decline in fertility, physical activity, flight velocity or metabolic rate. Naturally occurring variants in Indy, worldwide, modify Indy expression and increase reproduction and longevity, indicating that alterations in Indy expression in the wild imparts significant improvement in fitness and longevity. The Indy gene codes for a high-affinity dicarboxylate/citrate plasma membrane transporter that is found most abundantly at the plasma membrane of adult fat body, oenocytes and midgut cells, the primary sites of intermediary metabolism in the fly. Decreases in Indy affect metabolism similarly to calorie restriction (CR). CR down-regulates Indy in normal flies, and Indy long-lived flies share phenotypes with long-lived CR flies that include decreased insulin-like signaling, lipid storage, and weight, as well as resistance to starvation and increased spontaneous physical activity.Knock-out of a mammalian homolog of Indy (mINDY; SLC13A5) in the mouse protects mice from age-related or high-fat-feeding-related insulin resistance and adiposity, and promotes phenotypes similar to those seen in CR. mINDY-deleted mice show increased hepatic mitochondrial biogenesis, lipid oxidation, and energy expenditure, as well as decreased hepatic de novo lipogenesis, activation of hepatic AMPK, induction of PGC-1alpha, inhibition of ACC-2, and reduction of SREBP-1c. mINDY-deleted mice have reduced body weight, and preserve normal insulin signaling during aging or on high-fat diets, indicating that some of the positive effects of Indy in flies can be extended to mammals. Indy's effect on mammalian energy metabolism suggests that Indy is a potential target for treatment of obesity and type 2 diabetes, and that understanding of its regulation could lead to discovery of new agents for extending healthy life span and provide valuable insight into the genetic mechanisms of normal aging.