Hepatic IDH2 regulates glycolysis and gluconeogenesis

Abstract

Background and aims: The liver plays a central role in controlling glucose and lipid metabolism. IDH2, a mitochondrial protein, controls TCA cycle flux. However, its role in regulating metabolism in obesity is still unclear. This study intends to investigate the impact of hepatic IDH2 expression on overnutrition-regulated glucose and lipid metabolism.

Methods: Hepatic IDH2 was knocked-out in mice by the approach of CRISPR-Cas9. Mice were subjected to starvation and refeeding for hepatic glucose and lipid studies in vivo. Primary hepatocytes and mouse normal liver cell line, AML12 cells were used for experiments in vitro.

Results: This study found that IDH2 protein levels were elevated in the livers of obese people and mice with high-fat diet consumption or hepatic steatosis. Liver IDH2-deletion mice (IDH2^LKO) were resistant to high-fat diet-induced body weight gain, with lower serum glucose and TG levels, increased insulin sensitivity, and higher FGF21 secretion, despite the higher TG content in the liver. Consistently, overexpression of IDH2 in hepatocytes promoted gluconeogenesis and enhanced glycogenesis. By performing mass spectrometry and proteomics analyses, we further demonstrated that IDH2-deficiency in hepatocytes accelerated ATP production by increasing forward TCA cycle flux, thus promoting glycolysis pathway and decreasing glycogen synthesis at refeeding state, and inhibiting hepatic gluconeogenesis, increasing β-oxidation during starvation. Moreover, experiments in vivo demonstrated that IDH2-knockout might not exacerbate hepatic inflammatory responses in the NASH model.

Conclusions: Elevated hepatic IDH2 under over-nutrition state contributes to elevated gluconeogenesis and glycogen synthesis. Inhibition of IDH2 in the liver could be a potential therapeutic target for obesity and diabetes.

Keywords: Gluconeogenesis; Glycolysis; IDH2; Over-nutrition; TCA cycle.