Abstract
Glucokinase (GCK) is the principal hexokinase (HK) in the liver, operating as a glucose sensor to regulate glucose metabolism and lipid homeostasis. Recently, we proposed HK domain-containing 1 (HKDC1) to be a fifth HK with expression in the liver. Here, we reveal HKDC1 to have low glucose-phosphorylating ability and demonstrate its association with the mitochondria in hepatocytes. As we have shown previously that genetic deletion of HKDC1 leads to altered hepatic triglyceride levels, we also explored the influence of overexpression of HKDC1 in hepatocytes on cellular metabolism, observing reduced glycolytic capacity and maximal mitochondrial respiration with concurrent reductions in glucose oxidation and mitochondrial membrane potential. Furthermore, we found that acute in vivo overexpression of HKDC1 in the liver induced substantial changes in mitochondrial dynamics. Altogether, these findings suggest that overexpression of HKDC1 causes mitochondrial dysfunction in hepatocytes. However, its overexpression was not enough to alter energy storage in the liver but led to mild improvement in glucose tolerance. We next investigated the conditions necessary to induce HKDC1 expression, observing HKDC1 expression to be elevated in human patients whose livers were at more advanced stages of nonalcoholic fatty liver disease (NAFLD) and similarly, found high liver expression in mice on diets causing high levels of liver inflammation and fibrosis. Overall, our data suggest that HKDC1 expression in hepatocytes results in defective mitochondrial function and altered hepatocellular metabolism and speculate that its expression in the liver may play a role in the development of NAFLD.