OLETF(Otsuka Long Evans Tokushima Fatty) 쥐에서 식이제한이 간의 당대사에 미치는 영향

Abstract

Background: An increase in gluconeogenesis in the liver is largely responsible for the enhanced hepatic glucose production and fasting hyperglycemia in individuals with diabetes mellitus. PPARγ-coactivator 1(PGC-1) and AMPK(AMP-activated protein kinase) regulate the expression of several enzymes on the glucose metabolism in liver. Dietary restriction is known to be effective in the therapy of diabetes mellitus for stabilizing glucose homeostasis and improving diabetic control, in part by enhancing sensitivity to insulin and improving pancreatic β-cell dysfunction. While much is known about the effects of starvation on the glucose metabolism in liver, relatively little is known about the effects of dietary restriction without malnutrition. This study was performed to evaluate the response to dietary restriction on the glucose metabolism, especially expression of glycolytic enzymes and transcriptional factors such as PGC-1 and AMPK in liver of diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Methods: OLETF rats(male, 24 weeks) for diabetic model and Long-Evans Tokushima Otsuka (LETO) rats(male, 24 weeks) for control group were used in this study. At 20 weeks, all of OLETF rats underwent an oral glucose tolerance test after an overnight fast. From the 24 weeks, all of these rats were received an allotment of food equal to 70 % of the food intake measures in last weeks. This study was performed for 3 weeks and each glycolytic enzymes such as glucose kinase, pyruvate kinase, phosphofructokinase and transcriptional factors as PPARs and PGC-1, AMPK mRNA expression were measured at 1, 2, and 3 weeks after the beginning of 30% dietary restriction. Body weight and blood glucose levels were investigated at each week by spectrophotometric assay, and levels of mRNA expression were determined by real-time PCR Results: The liver PGC-1 mRNA levels were increased to 19% in non-diabetic LETO rats after 3 weeks of dietary restriction, but significant change was not observed in diabetic OLETF rats. The liver PGC-1 mRNA levels was not different statistically between two groups before dietary restriction, but there was a significant difference in mRNA level between two groups after 3 weeks of dietary restriction. The liver PPARγ mRNA expressions were not changed in non-diabetic LETO rats but increased to 23% in diabetic OLETF rats by dietary restriction. The levels of PPARγ mRNA in LETO rats were significantly increased than OLETF rats before dietary restriction, but there were no significant differences between two groups after 3 weeks of dietary restriction because progressively increased mRNA levels in OLETF rats. There were no difference on the PPARα and PPARβ mRNA expressions between OLETF and LETO rats. AMPK mRNA expression were significantly increased after 3 weeks of dietary restriction in LETO and OLETF rats except β1 subtype of LETO rats. Actually, mRNA levels of AMPK were slightly higher in LETO rats than in OLETF rats after dietary restriction. The expression of glycolytic enzymes such as glucokinase, pyruvate kinase, and phosphofructokinase were varied during dietary restriction. The mRNA expression of glucokinase and pyruvate kinase were progressively increased by dietary restriction, but levels of phosphofructokinase was not changed significantly during dietary restriction in both groups. Conclusion: The liver PGC-1 expression response to dietary restriction are altered in OLETF rats compared to LETO rats. The levels of PGC-1 mRNA was progressively increased in LETO rats after dietary restriction but there were no change in OLETF rats after dietary restriction. In opposition, PPARγ mRNA expressions were not changed in LETO rats but increased in OLETF rats by dietary restriction. The mRNA levels of AMPK and other glycolytic enzymes were not different between two groups. These findings suggested that PGC-1 expression was altered in diabetic OLETF rat in liver and this PCG-1 expression may some roles on the aberrant glucose metabolism in diabetes mellitus.