It has long been understood that many of the same manipulations that increase longevity in Caenorhabditis elegans also increase resistance to various acute stressors, and vice-versa; moreover these findings hold in more complex organisms as well. Nevertheless, the mechanistic relationship between these phenotypes remains unclear, and in many cases the overlap between stress resistance and longevity is inexact. Here we review the known connections between stress resistance and longevity, discuss instances in which these connections are absent, and summarize the theoretical explanations that have been posited for these phenomena. deletions in Caenorhabditis elegans alter the localization of intracellular reactive oxygen species and show molecular compensation. J Gerontol A Biol Sci Med Sci. 2009; 64:530-539. 30. McCord JM, Fridovich I. Superoxide dismutase. an enzymic function for erythrocuprein (hemocuprein). J Biol Chem. 1969; 244:6049-6055. 31. Walker TK, Tosic J. The ;catalase test', with special reference to acetobacter species. Biochem J. 1943; 37:10-12. 32. Mills GC. The purification and properties of glutathione peroxidase of erythrocytes. J Biol Chem. 1959; 234:502-506. 33. Brenot A, King KY, Janowiak B, Griffith O, Caparon MG. Contribution of glutathione peroxidase to the virulence of streptococcus pyogenes. Infect Immun. 2004; 72:408-413. 34. Larsen PL. Aging and resistance to oxidative damage in. A redox-sensitive peroxiredoxin that is important for longevity has tissue-and stress-specific roles in stress resistance.

Rapamycin, an inhibitor of mechanistic target of rapamycin complex 1 (mTORC1), extends the lifespans of yeast, flies, and mice. Calorie restriction, which increases lifespan and insulin sensitivity, is proposed to function by inhibition of mTORC1, yet paradoxically, chronic administration of rapamycin substantially impairs glucose tolerance and insulin action. We demonstrate that rapamycin disrupted a second mTOR complex, mTORC2, in vivo and that mTORC2 was required for the insulin-mediated suppression of hepatic gluconeogenesis. Further, decreased mTORC1 signaling was sufficient to extend lifespan independently from changes in glucose homeostasis, as female mice heterozygous for both mTOR and mLST8 exhibited decreased mTORC1 activity and extended lifespan, but had normal glucose tolerance and insulin sensitivity. Thus, mTORC2 disruption is an important mediator of the effects of rapamycin in vivo.

A major cause of cell death caused by genotoxic stress is thought to be due to the depletion of NAD(+) from the nucleus and the cytoplasm. Here we show that NAD(+) levels in mitochondria remain at physiological levels following genotoxic stress and can maintain cell viability even when nuclear and cytoplasmic pools of NAD(+) are depleted. Rodents fasted for 48 hr show increased levels of the NAD(+) biosynthetic enzyme Nampt and a concomitant increase in mitochondrial NAD(+). Increased Nampt provides protection against cell death and requires an intact mitochondrial NAD(+) salvage pathway as well as the mitochondrial NAD(+)-dependent deacetylases SIRT3 and SIRT4. We discuss the relevance of these findings to understanding how nutrition modulates physiology and to the evolution of apoptosis.

Little is known about how pro-obesity diets regulate tissue stem and progenitor cell function. Here we find that high fat diet (HFD)-induced obesity augments the numbers and function of Lgr5+ intestinal stem-cells (ISCs) of the mammalian intestine. Mechanistically, HFD induces a robust peroxisome proliferator-activated receptor delta (PPAR-d) signature in intestinal stem and (non-ISC) progenitor cells, and pharmacologic activation of PPAR-d recapitulates the effects of a HFD on these cells. Like a HFD, ex vivo treatment of intestinal organoid cultures with fatty acid constituents of the HFD enhances the self-renewal potential of these organoid bodies in a PPAR-d dependent manner. Interestingly, HFD- and agonist-activated PPAR-d signaling endow organoid-initiating capacity to progenitors, and enforced PPAR-d signaling permits these progenitors to form in vivo tumors upon loss of the tumor suppressor Apc. These findings highlight how diet-modulated PPAR-d activation alters not only the function of intestinal stem and progenitor cells, but also their capacity to initiate tumors.

SUMMARY How adult tissue stem and niche cells respond to the nutritional state of an organism is not well understood. Here, we find that Paneth cells, a key constituent of the mammalian intestinal stem cell (ISC) niche, augment stem cell function in response to calorie restriction (CR). CR acts by reducing mTOR complex 1 (mTORC1) signaling in Paneth cells, and the ISC-enhancing effects of CR can be mimicked by rapamycin. Calorie intake regulates mTORC1 in Paneth cells, but not ISCs, and forced mTORC1 activation in Paneth cells during CR abolishes their effects on ISCs. Finally, increased expression in Paneth cells of bone stromal antigen 1 (Bst-1), an ectoenzyme that produces the paracrine factor cyclic ADP ribose (cADPR), mediates the effects of CR and rapamycin on ISC function. Our findings establish that mTORC1 non-cell autonomously regulates stem cell self-renewal, and highlight a significant role of the mammalian intestinal niche in coupling stem cell function to organismal physiology.

Summary The TOR kinase, which is present in the functionally distinct complexes TORC1 and TORC2, is essential for growth but associated with disease and aging. Elucidation of how TOR modulates lifespan will identify mechanisms of fundamental importance in aging, and TOR functions. Here we show that when TORC1 is inhibited genetically in C. elegans, SKN-1/Nrf and DAF-16/FoxO activate protective genes, and increase stress resistance and longevity. SKN-1 also upregulates TORC1 pathway gene expression in a feedback loop. Rapamycin triggers a similar protective response in C. elegans and mice but increases worm lifespan dependent upon SKN-1 and not DAF-16, apparently by interfering with TORC2 along with TORC1. TORC1, TORC2, and insulin/IGF-1-like signaling regulate SKN-1 activity through different mechanisms. We conclude that modulation of SKN-1/Nrf and DAF-16/FoxO may be generally important in the effects of TOR signaling in vivo, and that these transcription factors mediate an opposing relationship between growth signals and longevity.

A molecule that treats multiple age-related diseases would have a major impact on global health and economics. The SIRT1 deacetylase has drawn attention in this regard as a target for drug design. Yet controversy exists around the mechanism of sirtuin-activating compounds (STACs). We found that specific hydrophobic motifs found in SIRT1 substrates such as PGC-1α and FOXO3a facilitate SIRT1 activation by STACs. A single amino acid in SIRT1, Glu230, located in a structured N-terminal domain, was critical for activation by all previously reported STAC scaffolds and a new class of chemically distinct activators. In primary cells reconstituted with activation-defective SIRT1, the metabolic effects of STACs were blocked. Thus, SIRT1 can be directly activated through an allosteric mechanism common to chemically diverse STACs.

Protein restricted, high carbohydrate diets improve metabolic health in rodents, yet the precise dietary components that are responsible for these effects have not been identified. Further, the applicability of these studies to humans is unclear. Here, we demonstrate in a randomized controlled trial that a moderately protein restricted (PR) diet also improves markers of metabolic health in humans. Intriguingly, we find that feeding mice a diet specifically reduced in branched chain amino acids (BCAAs) is sufficient to improve glucose tolerance and body composition equivalently to a PR diet, via metabolically distinct pathways. Our results highlight a critical role for dietary quality at the level of amino acids in the maintenance of metabolic health, and suggest that diets specifically reduced in BCAAs, or pharmacological interventions in this pathway, may offer a translatable way to achieve many of the metabolic benefits of a PR diet.