Diabetes & Metabolism Journal

Original Articles

AICAR Reversed the Glucolipotoxicity Induced beta-cell Dysfunction through Suppression of PPAR-gamma-coactivator-1 (PGC-1) Overexpression.: Hyuk Sang Kwon, Ji Won Kim, Heon Seok Park, Seung Hyun Ko, Bong Yun Cha, Ho Young Son, Kun Ho Yoon; Korean Diabetes J. 2007;31(4):310-318. Published online July 1, 2007; DOI: https://doi.org/10.4093/jkda.2007.31.4.310

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Abstract PDF: 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.

Hypothalamic AMPK Activity in Diabetic Rats.: Churl Namkoong, Min Seon Kim, Woo Je Lee, Pil Geum Jang, Seong Min Han, Eun Hee Koh, Joong Yeol Park, Ki Up Lee; Korean Diabetes J. 2004;28(6):468-477. Published online December 1, 2004

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Abstract PDF: BACKGROUND
AMP-activated protein kinase (AMPK) acts as a cellular energy sensor that is activated during states of low energy charge and it regulates the various metabolic pathways to reestablish the normal cellular energy balance. It has recently been demonstrated that AMPK activity is altered by the state of energy metabolism in the hypothalamic neurons and this mediates the feeding response. METHODS: Diabetes was induced by an intra-peritoneal injection of streptozotocin (STZ) in Sprague-Dawley rats. The diabetic rats were maintained for 3 weeks with or without insulin treatment. 3 weeks later, we collected hypothalamus and we then assayed the phosphorylation of AMPK and the activity of acetyl CoA carboxylase (ACC) and isoform-specfic AMPK. To determine the effect of hypothalamic AMPK inhibition on diabetic hyperphagia, we administered an AMPK inhibitor, compound C, into the third ventricle in the STZ-induced diabetic rats. RESULTS: Phosphorylation of AMPK, which is a marker of AMPK activation, increased in the hypothalamus of the STZ-induced diabetic rats (DR). Moreover, 2-AMPK activity, but not 1-AMPK activity, increased by 2-fold in hypothalamus of the DRs. Phosphorylation of hypothalamic acetyl CoA carboxylase (ACC), a key downstream enzyme of AMPK, also increased in the DRs and this caused a reduction in ACC activity. Insulin treatment completely reversed the diabetesinduced changes in the hypothalamic AMPK and ACC, suggesting that insulin deficiency was associated with the changes in hypothalamic AMPK and ACC. Inhibition of AMPK by an intracerebroventricular administration of AMPK inhibitor, compound C, attenuated the development of diabetic hyperphagia and reduced the blood glucose levels in DRs. CONCLUSION: We have demonstrated that hypothalamic AMPK activity increased in the DRs, and inhibition of hypothalamic AMPK activity attenuated the development of diabetic hyperphagia. These data indicate that the enhanced hypothalamic AMPK activity may contribute to the development of diabetic hyperphagia

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