Impact of hepatic HSP72 on insulin signaling

Abstract

Heat shock protein 72 (HSP72) is a major inducible molecule in the heat shock response that enhances intracellular stress tolerance. Decreased expression of HSP72 is observed in type 2 diabetes, which may contribute to the development of insulin resistance and chronic inflammation. We used HSP72 knockout (HSP72-KO) mice to investigate the impact of HSP72 on glucose metabolism and endoplasmic reticulum (ER) stress, particularly in the liver. Under a high-fat diet (HFD) condition, HSP72-KO mice showed glucose intolerance, insulin resistance, impaired insulin secretion, and enhanced hepatic gluconeogenic activity. Furthermore, activity of the c-Jun NH2-terminal kinase (JNK) was increased and insulin signaling suppressed in the liver. Liver-specific expression of HSP72 by lentivirus (lenti) in HFD-fed HSP72-KO mice ameliorated insulin resistance and hepatic gluconeogenic activity. Furthermore, increased adipocyte size and hepatic steatosis induced by the HFD were suppressed in HSP72-KO lenti-HSP72 mice. Increased JNK activity and ER stress upon HFD were suppressed in the liver as well as the white adipose tissue of HSP72-KO lenti-HSP72 mice. Thus, HSP72 KO caused a deterioration in glucose metabolism, hepatic gluconeogenic activity, and β-cell function. Moreover, liver-specific recovery of HSP72 restored glucose homeostasis. Therefore, hepatic HSP72 may play a critical role in the pathogenesis of type 2 diabetes.