Jiajian Shi

Fasting-induced metabolic remodeling is a fundamental process maintaining systemic homeostasis, with profound implications for metabolic disease interventions. During fasting, liver establishes a regulatory network centered on gluconeogenesis that integrates major fuels to keep physiological energy homeostasis. Here, we report that GAPDH, a key enzyme in both glycolysis and gluconeogenesis, senses fasting stress in the liver. Compared to wildtype controls, hepatocyte Gapdh deficiency (Gap^Alb) mice show comparable blood glucose, decreased amino acid levels and aggravated lipid accumulation in the liver after overnight fasting. Mechanistically, Gapdh depletion decreases serine levels, and serine supplementation inhibits PA-DAG (phosphatidic acid-diacylglycerols) axis by downregulating Lipin1 (a phosphohydrolase in DAG synthesis) upon overnight fasting. Furthermore, knockdown of Lipin1 rescued the effects observed in fasted Gap^Alb mice. Similarly, Gap^Alb mice showed enhanced hepatic lipid accumulation under ketogenic diets, and serine supplementation abolished these effects. Together, we find hepatic GAPDH as a central hub in glucose-amino acid-fat metabolism during nutritional limitation.