Diabetes & Metabolism Journal

Original Articles

Transcriptional Regulation of Insulin and CXCL10 Gene by Peroxisome Proliferator Activated Receptor gamma Coactivator-1alpha.: Won Gu Jang, In Kyu Lee, Eun Jung Kim, Seong Yeol Ryu, Bo Wan Kim, Jung Guk Kim; Korean Diabetes J. 2007;31(4):326-335. Published online July 1, 2007; DOI: https://doi.org/10.4093/jkda.2007.31.4.326

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Abstract PDF: BACKGROUND
Peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha), which act as a coactivator of nuclear receptors and several other transcription factors. This study was performed to evaluate the expressional regulation of insulin and inflammatory response genes by PGC-1alpha. METHODS: Transient transfection assays were performed to measure the promoter activity of the insulin and CXCL10 gene. The insulin gene expression levels in INS-1 cells were determined by Northern blot analysis. Differentially expressed genes by PGC-1alpha overexpression in HASMCs were confirmed using DNA microarray, real-time PCR and Northen blot analysis. RESULTS: Insulin promoter activity and mRNA levels were suppressed by GR and Ad-PGC-1alpha. Northern blot analysis of the INS-1 cells revealed that infection with Ad-PGC-1alpha markedly reduced the amount of insulin mRNA and treatment of Dex enhanced this effect in an additive manner. The PGC-1alpha-specific siRNA decreased insulin expression that was induced by Dex in the GR-expressing INS-1 cells was nearly restored by this siRNA treatment. We found that when vascular smooth muscle cells (VSMCs) overexpressed PGC-1alpha, immune or inflammatory response genes were highly expressed. For example, promoter activity and mRNA level of CXCL10 gene were increased by PGC-1alpha. CONCLUSION: PGC-1alpha overexpression inhibited insulin promoter activity in INS-1 cells and enhanced expressions of inflammatory response genes (CXCL10, CXCL11, TNFLSF10) in VSMCs.

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.

Effects of Caloric Restriction on the Expression of PGC-1 and PPARs mRNA in Liver of Otsuka Long-Evans Tokushima Fatty Rats.: Sang Yong Kim, Jin Hwa Kim, Hak Yeon Bae, Byoung Rai Lee; Korean Diabetes J. 2006;30(3):161-169. Published online May 1, 2006; DOI: https://doi.org/10.4093/jkda.2006.30.3.161

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Abstract PDF: BACKGROUND
Gluconeogenesis is strongly stimulated during fasting and is aberrantly activated in diabetes mellitus. PPARgamma-coactivator 1 (PGC-1) and Peroxisome proliferator -activated receptors (PPARs) costimulate the expression of key enzymes of gluconeogenetic pathway. This study was performed to evaluate the response to dietary caloric restriction (CR) on the PPARs and PGC-1 expression in liver of diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. METHODS: Diabetic OLETF rats (male, 24 weeks) and Long-Evans Tokushima Otsuka (LETO) rats (male, 24 weeks) were used in this study. Liver PPARs and PGC-1 mRNA, and blood glucose levels were investigated at 1, 2, and 3 weeks after the beginning of 30% CR. PPARs and PGC-1 mRNA were determined by RT-PCR and blood glucose levels were measured by spectrophotometric assay. RESULTS: The liver PGC-1 mRNA expressions were increased to 19% in non-diabetic LETO rats but significant change was not observed in diabetic OLETF rats by 30% CR. The liver PPARgamma mRNA expressions were not changed in non-diabetic LETO rats but increased to 23% in diabetic OLETF rats by 30% CR. The difference of PPARalpha and PPARbeta mRNA expressions in liver of OLETF and LETO rats were not observed. CONCLUSION: The liver PPARgamma and PGC-1 expression response to CR are altered in OLETF rats compared to in LETO rats. These findings suggested that PPARgamma and PGC-1 expression control system altered in diabetic OLETF rat liver and altered PPARgamma and PCG-1 expression may some roles on the aberrantly activated gluconeogenesis in diabetes mellitus.

Protective Effect of PGC-1 on Lipid Overload-induced Apoptosis in Vascular Endothelial Cell.: Eun Hee Koh, Youn Mi Kim, Ha Jung Kim, Woo Je Lee, Jong Chul Won, Min Seon Kim, Ki Up Lee, Joong Yeol Park; Korean Diabetes J. 2006;30(3):151-160. Published online May 1, 2006; DOI: https://doi.org/10.4093/jkda.2006.30.3.151

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Abstract PDF: BACKGROUND
Fatty acids contribute to endothelial cell dysfunction and apoptosis by inducing accumulation of long chain fatty acyl CoA (LCAC), which increases oxidative stress in vascular endothelial cells. Forced expression of PGC-1 was shown to induce mitochondrial biogenesis and to control expression of mitochondrial enzymes involved in fatty acid oxidation. This study was undertaken to test the hypothesis that PGC-1 overexpression could prevent endothelial cell apoptosis by enhancing fatty acid oxidation and relieving oxidative stress in vascular endothelium. METHODS: Adenoviruses containing human PGC-1 (Ad-PGC-1) and beta-galactosidase (Ad-beta-gal) were transfected to confluent human aortic endothelial cells (HAECs). To investigate the effect of adenoviral PGC-1 gene transfer on apoptosis, combined treatment of linoleic acid (LA), an unsaturated fatty acid, was performed. RESULTS: PGC-1 overexpression inhibited the increase in ROS production and apoptosis of HAECs induced by LA. Also, PGC-1 led to a significant increase in fatty acid oxidation and decrease in triglyceride content in HAECs. LA caused the decrease of adenine nucleotide translocase (ANT) activity and transient mitochondrial hyperpolarization, which was followed by depolarization. PGC-1 overexpression prevented these processes. CONCLUSION: In summary, PGC-1 overexpression inhibited mitochondrial dysfunction and apoptosis by facilitating fatty acid oxidation and protecting against the damage from oxidative stress in HAECs. The data collectively suggest that the regulation of intracellular PGC-1 expression might play a critical role in preventing atherosclerosis.

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