GCN2 regulates the CCAAT enhancer binding protein beta and hepatic gluconeogenesis

Mice deficient for general control nondepressible-2 (Gcn2) either globally or specifically in the liver display reduced capacity to maintain glucose homeostasis during fasting, suggesting the hypothesis that GCN2 may regulate gluconeogenesis (GNG), which normally plays a key role maintaining peripheral glucose homeostasis. Gcn2-deficient mice exhibit normal insulin sensitivity and plasma insulin but show reduced GNG when administered pyruvate, a gluconeogenic substrate. The basal expression of phosphoenolpyruvate carboxykinase, a rate-limiting enzyme in GNG, is abnormally elevated in Gcn2 knockout (KO) mice in the fed state but fails to be further induced during fasting. The level of tricarboxylic acid cycle intermediates, including malate and oxaloacetate, and the NADH-to-NAD(+) ratio are perturbed in the liver of Gcn2 KO mice either in the fed or fasted state, which may directly impinge upon GNG. Additionally, the expression of the CCAAT enhancer-binding protein-β (C/EBPβ) in the liver fails to be induced in Gcn2 KO mice after 24 h fasting, and the liver-specific Cebpβ KO mice show reduced fasting GNG similar to that seen in Gcn2-deficient mice. Our study demonstrates that GCN2 is important in maintaining GNG in the liver, which is likely to be mediated through regulation of C/EBPβ.