Abstract

BACKGROUND
Glucolipotoxicity plays an important role in the progression of type 2 diabetes mellitus via inducing insulin secretory dysfunction. Expression of insulin gene in pancreatic beta cell might be regulated by AMP-activated protein kinase (AMPK), which is recognized as a key molecule of energy metabolism. We studied the effects of AMPK on glucolipotoxicity-induced beta-cell dysfunction by suppression of PPAR-gamma-coactivator-1 (PGC-1) in vitro and in vivo. Method: Glucolipotoxicity was induced by 33.3 mM glucose and 0.6 mM (palmitate and oleate) for 3 days in isolated rat islets. Messenger RNA (mRNA) expressions of beta-cell specific gene like insulin, BETA2/NeuroD and PGC-1 induced by glucolipotoxic condition and their changes with 5-aminoimidazole-4-carboxy-amide-1-D-ribofuranoside (AICAR) treatment were investigated using RT-PCR. We also examined glucose stimulated insulin secretion in same conditions. Furthermore, SD rats were submitted to a 90% partial pancreatectomy (Px) and randomized into two groups; Ad-GFP-infected Px rats (n = 3) and Ad-siPGC- 1-infected Px rats (n = 3). Then, the Px rats were infected with Ad-GFP or Ad-siPGC-1 (1 x 10(9) pfu) via celiac artery. After 12 days of viral infection, we measured body weight and performed the intraperitoneal glucose tolerance test (IP-GTT). RESULTS: Glucolipotoxicity resulted in blunting of glucose-stimulated insulin secretion, which was recovered by the AICAR treatment in vitro. Suppression in their expressions of insulin and BETA2/NeuroD gene by glucolipotoxic condition were improved with AICAR treatment. However, PGC-1alpha expression was gradually increased by glucolipotoxicity, and suppressed by AICAR treatment. Overexpression of PGC-1 using an adenoviral vector in freshly isolated rat islets suppressed insulin gene expression. We also confirmed the function of PGC-1 using an Ad-siPGC-1 in vivo. Direct infection of Ad-siPGC-1 in 90% pancreatectomized rats significantly improved glucose tolerance and increased body weight. CONCLUSION: AMPK could protect against glucolipotoxicity induced beta-cell dysfunction and the suppression of PGC-1 gene expression might involved in the insulin regulatory mechanism by AMPK.

• Keywords: AICAR (5-aminoimidazole-4-carboxy-amide-1-D-ribofuranoside);AMP-activated protein Kinase (AMPK);Pancreatectomy;PPAR-gamma-coactivator-1 (PGC-1);