Hyperthermia With Mild Electrical Stimulation Protects Pancreatic b-Cells From Cell Stresses and Apoptosis

Induction of heat shock protein (HSP) 72 improves metabolic profiles in diabetic model mice. However, its effect on pancreatic b-cells is not known. The current study investigated whether HSP72 induction can reduce b-cell stress signaling and apoptosis and preserve b-cell mass. MIN6 cells and db/db mice were shamtreated or treated with heat shock (HS) and mild electrical stimulation (MES) (HS+MES) to induce HSP72. Several cellular markers, metabolic parameters, and b-cell mass were evaluated. HS+MES treatment or HSP72 overexpression increased HSP72 protein levels and decreased tumor necrosis factor (TNF)-a–induced Jun NH2terminal kinase (JNK) phosphorylation, endoplasmic reticulum (ER) stress, and proapoptotic signal in MIN6 cells. In db/db mice, HS+MES treatment for 12 weeks significantly improved insulin sensitivity and glucose homeostasis. Upon glucose challenge, a significant increase in insulin secretion was observed in vivo. Compared with sham treatment, levels of HSP72, insulin, pancreatic duodenal homeobox-1, GLUT2, and insulin receptor substrate-2 were upregulated in the pancreatic islets of HS+MEStreated mice, whereas JNK phosphorylation, nuclear translocation of forkhead box class O-1, and nuclear factor-kB p65 were reduced. Apoptotic signals, ER stress, and oxidative stress markers were attenuated. Thus, HSP72 induction by HS+MES treatment protects b-cells from apoptosis by attenuating JNK activation and cell stresses. HS+MES combination therapy may preserve pancreatic b-cell volume to ameliorate glucose homeostasis in diabetes.