Regulation And Mechanism Of ATGL Expression In Lipolysis Mediated By Leptin

Triglycerides in the body fat tissue play an important role in the maintenance of energy balance. The hydrolysis of triglycerides is a series of orderly controled process under different lipases involved. The recent studies discovered that ATGL has the definite ability to hydrolys triglycerides, and plays the most basic role in triglycerides lipolysis. ATGL is closely related to glucose tolerance, insulin sensitivity and the concentration of free fatty acids. So the regulation of ATGL expression is very much concerned. Studies confirm that nutrition, hormones and cytokines can control the expression of ATGL. Leptin, as a fat cell cytokine, can increase the fat decomposition. Many phenomenas suggests that ATGL plays an important role in leptin promoting triglycerides hydrolysis. But until recently now, the regulation and its mechanism of ATGL in lepin promoting fat hydrolysis have not be yet directly and systematicly studied.Therefore, in this study we used the pig , with the most similarity to human in physiology and biochemistry, as a model animal, using RT-PCR, cell culture, glycerol and FFA determination, semi-quantitative RT-PCR, western blot, and other methods, cloned the total length of pig ATGL CDS, studied the ATGL expression and its mechanism in leptin promoting lipid hydrolysis. The results achieved were as follows:1 Successfully cloned the pig ATGL gene complete CDS which length is 1446 bp, and get the GenBank accession number which is EU373817. Homologous alignment analysis showed that the pig ATGL gene has 87% and 82%homology to that of human and mouse respectively. The high level of nucleotide identity suggests that porcine ATGL gene has a similar function and expression regulation with human and mouse. The cloned pig ATGL complete CDS has provided a solid foundation for research regulation of ATGL expession in leptin promoting the lipid hydrolysis.2 Defined the promotion of leptin in a concentration-dependent manner on pig fat cells lipolysis. Compared with the control group, 5,20 and 50 ng/mL of leptin all could significantly promote the release of glycerol (P <0.01) and in a concentration-dependent manner with 50 ng/mL leptin getting the largest glycerol release; while compared with the control group, 5,20 and 50 ng/mL of leptin could reduce the release of FFA, but the difference was not significant (P> 0.05).3 Investigated the effects of leptin on the ATGL mRNA and protein expression in vitro and in vivo. Studies in pig fat cells in vitro showed that 5,20 and 50 ng/mL of leptin promoted ATGL mRNA expression, and reduced the ATGL protein expression in a concentration-dependent manner respectively. Also, the studies on the subcutaneous tissue showed that ATGL mRNA and protein expression were closely related to serum leptin levels, with high levels of leptin could promote ATGL mRNA expression, but at the same time reduce the ATGL protein expression.4 Studied the preliminary mechanism of leptin on ATGL expression, found that JAK-STAT signaling pathway, MAPK signaling pathway and PPARγall play an important role in leptin on ATGL expression. AG490 and SB205380, the specific inhibitors respectively for JAK-STAT signaling pathway and MAPK signaling pathway, decreased ATGL mRNA expression by 35.02% and 23.26% respectively; while they both increased ATGL protein expression Significantly (P <0.01).