General Control Nonderepressible 2 (GCN2) Kinase Regulates Body Composition and Antioxidant Defenses during Dietary Methionine Restriction.

Abstract

Dietary methionine restriction (MR) produces physiological responses associated with resistance to metabolic disease and increased lifespan, but the sensing mechanism remains to be established. As a part of the integrated stress response pathway (ISR), the eukaryotic initiation factor 2 (eIF2) kinase GCN2 is a sensor of amino acid insufficiency by diet, drug or genetics. We hypothesized that phosphorylation of eIF2 (eIF2~P) by GCN2 mediates the metabolic phenotype by dietary MR. C57Bl/6J wildtype mice (WT) or mice deleted for Gcn2 (KO) were fed an obesity‐promoting diet (60% kcal fat) sufficient in methionine (0.86% kcal met, CON) for 1 week. Mice then remained on CON or were switched to an obesity‐promoting diet restricted in methionine (0.12% kcal met, MR) for an additional 5 weeks (n=6–8 per group). Results were evaluated by 2 factor ANOVA and Tukey post hoc with a significance level set at p<0.05. MR reduced body weight in WT and KO mice similarly (↓22%) even though MR mice consumed more energy (↑13%) than CON mice. WTMR mice also lost a significant amount of body fat (↓15%) as compared to WTCON but surprisingly, KOMR mice lost an insignificant amount of body fat as compared to KOCON (↓4%). Consistent with this difference in body composition, subcutaneous fat weights were decreased ~60% in WTMR as compared to WTCON but unchanged in KOMR as compared to KOCON. In the liver, activation of the ISR was indicated in both WTMR and KOMR via eIF2~P. MR also induced ISR genes Atf5, Atf3, Asns, Fgf21 and a profile of antioxidant genes including Ho1 and Nqo1 regardless of GCN2 status. On the other hand, MR reduced expression of fatty acid synthesis genes Fasn and Scd1 to a greater extent in the liver of WT versus KO mice. Furthermore, expression of the hepatic antioxidant defense gene Sod2 was increased in WTMR but not KOMR. These results indicate that GCN2 contributes to but is not a primary sensor of MR because activation of the ISR in the liver and reduction of body weight occurred largely independent of GCN2. However, certain physiological outcomes such as body composition and mitochondrial oxidative defenses in the liver were influenced by GCN2 status. Our study provides new insights into the GCN2 dependent and independent mechanisms by which MR alters metabolism and cellular defenses.Support or Funding InformationNIH HD070487, USDA NIFA NC1184, INSPIRE at Rutgers, Rutgers University