AKT signaling in hepatocytes rapidly increases glucose phosphorylation and contribution to glycogen without affecting metabolite pool sizes or glycogen breakdown

Abstract

Background and aimsHepatic insulin action is essential for whole body glucose homeostasis. Insulins inhibition of glycogen breakdown, suppression of gluconeogenesis, and activation of glycogen synthesis are critical for postprandial glucose disposal. AKT, a serine-threonine kinase and well-established insulin signaling target, regulates hepatic glucose metabolism through transcriptional and posttranslational mechanisms. However, current knowledge about AKTs regulation of hepatic glucose metabolism largely stems from genetic loss of function models, precluding observation of rapid, transcription-independent effects. MethodsStable isotope tracing using [U-13C]-glucose was coupled with pharmacological inhibition of AKT using MK-2206 in primary rat hepatocytes. Bulk metabolomics was performed on AKT knockout livers and primary rat hepatocytes treated with MK-2206. Radiolabeled glucose was used to quantify short-term changes to glycogen synthesis. ResultsMK-2206 treatment decreased glucose contribution to glucose 6-phosphate and uridine diphosphate glucose within minutes without significantly affecting total metabolite pool sizes or changes to glucokinase protein levels. This was accompanied by a decrease in glucose contribution to glycogen, independent of changes to glycogen breakdown or glycogen synthase phosphorylation. ConclusionsTogether, these results demonstrate that AKT acutely regulates glucose contribution to glycogen and its upstream precursors, suggesting a transcription-independent, glucokinase-centered mechanism for glycogen synthesis through the direct pathway.