Mechanisms of Preconditioning Against Surgical Stress by Short-Term Dietary Protein Restriction

Dietary restriction (DR) or reduced food intake without malnutrition encompasses a variety of dietary interventions including reduction of calories or specific macronutrients such as amino acids or total protein. Even though DR is known to result in various beneficial health effects, including extended longevity and increased stress resistance, the underlying nutritional and genetic requirements remain incompletely understood. Previous studies in lower organisms, as well as in mammals, point to the importance of the restriction of dietary protein intake in DR benefits. Previously our lab has shown that short-term restriction of intake of individual essential amino acids protects against hepatic ischemia reperfusion injury (IRI) via activation of the amino acid deprivation sensing protein, general control non-derepressible 2 (GCN2). Interestingly, GCN2 was no longer required for the protective effects of total dietary protein restriction (PR) against hepatic IRI. We thus investigated the potential role of a distinct amino acid sensing pathway involving the mechanistic target of rapamycin complex 1 (mTORC1) kinase, which is normally repressed upon PR. To test the hypothesis that reduced mTORC1 signaling is required for benefits of PR against hepatic IRI, we used a mouse model with liver specific deletion of the mTORC1 repressor gene tuberous sclerosis complex 1 (TSC1), leading to constitutive hepatic mTORC1 activation (LTsc1KO). Although one week of PR was able to reduce circulating growth factors and amino acid levels and activate hepatic GCN2 signaling in both LTsc1KO and WT mice, LTsc1KO mice failed to gain the preconditioning benefits of PR against hepatic IRI. To understand the molecular mechanism underlying the genetic requirement for the TSC complex in PR benefits, we focused on the observation that PR improved hepatic insulin sensitivity in WT but not LTsc1KO mice. Additional data from liver specific insulin receptor knockout (LIrKO) mice and in WT mice using pharmacological PI3K inhibition by wortmannin indicated a partial requirement for post-reperfusion insulin/Akt signaling in PR-mediated protection from hepatic IRI. In addition to defects in insulin signaling important for PR action, LTsc1KOs also failed to upregulate hepatic production of another potent protective molecule, hydrogen sulfide (H2S), which was increased in WT mice upon PR and required for PR-mediated protection from hepatic IRI. Finally, we investigated the mechanisms of regulation of hepatic H2S production. Using an in vitro model of increased H2S production upon serum deprivation, we identified growth hormone (GH) as a negative regulator of H2S production through JAK/STAT signaling, and increased autophagy as the likely source of free cysteine, the substrate for cystathionine gamma lyase (CGL)-mediated H2S production. The mechanistic details of how in vivo PR translates into increased H2S production, and the potential role of mTORC1, GH signaling and autophagy in this process remain to be fully elucidated.Biological Sciences in Public Healt

The TSC Complex Is Required for the Benefits of Dietary Protein Restriction on Stress Resistance In Vivo

Protein restriction (PR) is important for the benefits of dietary restriction on longevity and stress resistance, but relevant nutrient sensors and downstream effectors in mammals remain poorly defined. We used PR-mediated protection from hepatic ischemia reperfusion injury to probe genetic requirements for the evolutionarily conserved nutrient sensors GCN2 and mTORC1 in stress resistance. One week of PR reduced free amino acids and circulating growth factors, activating GCN2 and mTORC1 repressor tuberous sclerosis complex (TSC). However, although GCN2 was dispensable for PR-induced protection, hepatic TSC1 was required. PR improved hepatic insulin sensitivity in a TSC1-dependent manner prior to ischemia, facilitating increased prosurvival signaling and reduced apoptosis after reperfusion. These benefits were partially abrogated by pharmacological PI3K inhibition or genetic deletion of the insulin receptor in hepatocytes. In conclusion, improved insulin sensitivity upon short-term PR required TSC1, facilitated increased prosurvival signaling after injury, and contributed partially to PR-mediated resistance to clinically relevant ischemia reperfusion injury

Dietary restriction protects against experimental cerebral malaria via leptin modulation and T cell mTORC1 suppression

Host nutrition can affect the outcome of parasitic diseases through metabolic effects on host immunity and/or the parasite. Here we show that modulation of mouse immunometabolism through brief restriction of food intake (dietary restriction, DR) prevents neuropathology in experimental cerebral malaria (ECM). While no effects are detected on parasite growth, DR reduces parasite accumulation in peripheral tissues including brain, and increases clearance in the spleen. Leptin, a host-derived adipokine linking appetite, energy balance and immune function, is required for ECM pathology and its levels are reduced upon DR. Recombinant leptin abrogates DR benefits, while pharmacological or genetic inhibition of leptin signaling protects against ECM. DR reduces mTORC1 activity in T cells, and this effect is abrogated upon leptin administration. Furthermore, mTORC1 inhibition with rapamycin prevents ECM pathology. Our results suggest that leptin and mTORC1 provide a novel mechanistic link between nutrition, immunometabolism and ECM pathology, with potential therapeutic implications for cerebral malaria

Hypothalamic-pituitary axis regulates hydrogen sulfide production

Decreased growth hormone (GH) and thyroid hormone (TH) signaling are associated with longevity and metabolic fitness. The mechanisms underlying these benefits are poorly understood, but may overlap with those of dietary restriction (DR), which imparts similar benefits. Recently we discovered that hydrogen sulfide (H2S) is increased upon DR and plays an essential role in mediating DR benefits across evolutionary boundaries. Here we found increased hepatic H2S production in long-lived mouse strains of reduced GH and/or TH action, and in a cell-autonomous manner upon serum withdrawal in vitro. Negative regulation of hepatic H2S production by GH and TH was additive and occurred via distinct mechanisms, namely direct transcriptional repression of the H2S-producing enzyme cystathionine g-lyase (CGL) by TH, and substrate-level control of H2S production by GH. Mice lacking CGL failed to downregulate systemic T4 metabolism and circulating IGF-1, revealing an essential role for H2S in the regulation of key longevity-associated hormones.117Nsciescopu