Activation of phosphoenolpyruvate carboxykinase increases intracellular glucose levels in podocytes under hyperglycemic conditions

Gluconeogenesis (GNG) is a process of glucose synthesis from non-carbohydrate precursors, which is enhanced in diabetic kidneys, contributing to elevations of blood glucose. Podocytes mainly utilize glucose to maintain glomerular filtration barrier integrity. However, their gluconeogenic potential has not yet been elucidated and the magnitude of this process has not been assessed under high glucose (HG) conditions. The present study demonstrated that podocytes express a set of key gluconeogenic enzymes at the mRNA and protein levels, including cytosolic and mitochondrial isoforms of phosphoenolpyruvate carboxykinase (PCK). High glucose-exposed podocytes exhibited an increase in PCK activity, which was linked to a decrease in intracellular levels of oxaloacetate (a PCK substrate), an increase in intracellular glucose levels and an increase in glucose efflux to the extracellular environment. Moreover, PCK inactivation in hyperglycemic podocytes increased the intracellular content of lactate, a preferred substrate for GNG, and decreased glycogen levels, suggesting the direction of glucose to glycogen synthesis under HG conditions. Additionally, the PCK inhibitor abolished the negative effect of HG on the activity of hexokinase and pyruvate kinase in podocytes, suggesting that inhibiting PCK may enhance the glycolytic pathway in hyperglycemia. Overall, an increase in PCK activity in response to HG concentrations may enhance GNG in podocytes, contributing to cell glucose overload. The present results broaden our understanding of metabolic changes that underlie HG-induced podocyte dysfunction and spotlight potential therapeutic targets for the treatment of diabetic kidney disease.