Nutritional stress exacerbates hepatic steatosis induced by deletion of the histidine nucleotide-binding (Hint2) mitochondrial protein

Abstract

The histidine nucleotide-binding protein, Hint2, is a mitochondrial phosphoramidase expressed in liver, brown fat, pancreas, and muscle. The livers of Hint2 knockout ( Hint2−/−) mice accumulate triglycerides and show a pattern of mitochondrial protein lysine hyperacetylation. The extent and nature of the lysine acetylation changes and the response of Hint2−/− mice to nutritional challenges that elicit a modification of protein acetylation have not been investigated. To compare the adaptation of Hint2−/− and control ( Hint2+/+) mice with episodes of fasting and high-fat diet (HFD), we subjected animals to either feeding ad libitum or fasting for 24 h, and to either a HFD or control diet for 8 wk. Triglyceride content was higher in Hint2−/− than in Hint2+/+ livers, whereas plasma triglycerides were fourfold lower. Malonyl-CoA levels were increased twofold in Hint2−/− livers. After 24 h fasting, Hint2−/− displayed a decrease in body temperature, commensurate with a decrease in mass of brown fat and downregulation of uncoupling protein 1. HFD-treated Hint2−/− livers showed more steatosis, and plasma insulin and cholesterol were higher than in Hint+/+ mice. Several proteins identified as substrates of sirtuin 3 and 5 and active in intermediary and ketone metabolism were hyperacetylated in liver and brown fat mitochondria after both HFD and fasting regimens. Glutamate dehydrogenase activity was downregulated in fed and fasted livers, and this was attributed to an increase in acetylation and ADP-ribosylation. The absence of Hint2 deregulates the posttranslational modification of several mitochondrial proteins, which impedes the adaptation to episodes of nutritional stress.