Breed Specific Pattern Of Hepatic Gluconeogenesis And Glucocorticoid Action In The Pig

Previous study demonstrated significant difference in the basal plasma cortisol levels between Erhualian(EHL) and Pietrain(PIE) pigs.In order to unravel the glucocorticoid action in porcine hepatic gluconeogenesis,the two breeds of pigs were employed to investigate breed specific pattern of biochemical indices related to hepatic gluconeogenesis and hepatic gluconeogenesis enzymes expression,in association with the hepatic glucocorticoid receptor(GR) and 11β-hydroxysteroid dehydrogenase type 1(11β-HSD1) expression.Furthermore,the methylation status of 5′-UTR in hepatic GR gene was determined to clarify the possible mechanism underlying the breed-specific transcriptional regulation of hepatic GR expression.1 Differences of blood and liver biochemical indices between two breedsLiver glycogen content in EHL pigs was significantly lower compared with PIE pigs (P＜0.01),but no difference was detected on the liver glucose content.EHL pigs exhibited significantly lower plasma lactate acid concentration,but higher liver lactate acid content, compared to PIE pigs.These results indicate that EHL pigs may have higher capacity of lactate acid metabolism in the liver.2 Differences of hepatic gluconeogenesis key enzymes expression between two breedsHepatic mRNA expression of gluconeogenesis key enzymes was determined with relative quantitative REAL-TIME RT-PCR.EHL pigs exhibited significantly higher expression of Pyruvate carboxylase(PC) mRNA(P＜0.01) than PIE pigs.No difference was observed in Cytosol phosphoenolpyruvate carboxykinase(PEPCK-C) mRNA,whereas Mitochondria phosphoenolpyruvate carboxykinase(PEPCK-M) mRNA was higher in EHL pigs(P＜0.05).Fructose-1,6-bisphosphatase(FBPase) mRNA was higher in EHL pigs compared with PIE pigs.There is no difference in Glucose-6-phosphatase(G-6-P) mRNA between two breeds of pigs.The results indicated that EHL pigs may have higher hepatic gluconeogenesis capacity than PIE pigs owing to higher expression of PC and FBPase mRNA in the liver.Lactate acid is one of the important precursors for hepatic gluconeogenesis,these results suggest that the higher expression of relative genes may contribute to the higher capacity of lactate acid metabolism in EHL pigs.3 Difference of liver cortisol content between two breedsIn order to clarify whether higher plasma cortisol level may lead to higher liver cortisol content in EHL pigs,hepatic cortisol content was measured with RIA after extraction by dichloromethane.No difference was observed between two breeds of pigs. The results suggest that the up regulation of hepatic GR expression,rather than higher liver cortisol,results in the higher expression of hepatic gluconeogenesis enzymes in EHL pigs.4 Differences of GR and 11β-HSD1 expression between two breedsLiver GR and 11β-HSD1 mRNA were determined with relative quantitative REAL-TIME RT-PCR.EHL pigs demonstrated higher(P＜0.05) liver expression of GR and 11β-HSD1 mRNA,indicating higher glucocorticoid action in the liver.The higher expression of the GR mRNA may contribute to the higher expression of hepatic gluconeogenesis enzymes.5 Difference of the methylation of GR 5′UTR between two breedsThe methylation of 5′-UTR of GR gene was determined with Bisulfate sequencing PCR method.No difference was detected between the two breeds of pigs.It indicates that the breed difference in hepatic GR expression is not caused by the difference in methylation status of the detected segment of 5′-UTR of GR gene.