Intermittent Hypoxia Disrupts Glucose Homeostasis in Liver Cells in an Insulin-Dependent and Independent Manner

Abstract

Background/Aims: Obstructive sleep apnea is associated with diabetes and insulin resistance, but the underlying mechanisms remain unclear. The purpose of the current study was to determine the molecular effects of intermittent hypoxia (IH) on hepatic insulin signaling and glucose homeostasis, and whether c-Jun NH2-terminal-kinase (JNK) contributed to metabolic responses to IH in liver cells. Methods: The human HepG2 cells and rat FAO cells were exposed to 10, 30, 120, 240 or 360 cycles of IH (1% O2 for 60 s followed by 21% O2 for 60s, 7.5 cycles per hour) or normoxia as a control. In a subgroup, we exposed cells to 360 cycles of IH with the JNK inhibitor SP600125. After IH exposure, cell glycogen content and glucose output were measured using colorimetric assay kits. Canonical insulin signaling and gluconeogenic genes were measured by western blot and quantitative polymerase chain reaction. Results: IH decreased insulin-stimulated protein kinase B (AKT)/glycogen synthase kinase-3β (GSK-3β) phosphorylation in a time-dependent manner, while inhibiting forkhead box protein O1 (FOXO1) expression and phosphoenolpyruvate carboxykinase (PEPCK) transcription independent of insulin signaling. JNK inhibitor SP600125 partially restored AKT/ GSK-3β phosphorylation and glycogen synthesis, but did not affect other IH-induced glucose metabolic changes. Conclusion: IH in vitro impaired insulin signal transduction in liver cells as assessed by inhibited AKT/GSK-3β phosphorylation via JNK activation. IH inhibited FOXO1 and gluconeogenesis in an insulin-independent manner.

Keywords

• Intermittent hypoxia
• Liver cells
• Glucose homeostasis
• Forkhead box protein O1
• C-Jun NH2-terminal-kinase