| Summary: | 碩士 === 國立陽明大學 === 生理學研究所 === 98 === Endothelin-1 (ET-1), a vasoconstrictor peptide mainly synthesized and secreted by endothelial cells, is suggested to be an important role of development in obesity-associated with disorder. Some evidence showed that ET-1 may regulate lipid metabolism in adipocytes. Previous studies suggested that ET-1 induces lipolysis via endothelin type A receptor (ETAR) and extracellular signal-regulated kinase (ERK) activation in rat adipocytes and 3T3-L1 adipocytes. In addition, hormone sensitive lipase (HSL) was considered to be the rate-limiting enzyme in lipolysis. However, the regulation mechanism of ET-1-induced lipolysis is still unknown. In this present study, we used 3T3-L1 adipocytes as a cell model and the effect of lipolysis was determined by measuring glycerol release. The phosphorylation of ERK and HSL was detected by Western blot and immunoprecipitation. The ETAR antagonist BQ610, ERK inhibitor PD98059, guanylyl cyclase (GC) inhibitor LY83583 and inositol 1,4,5-trisphosphate (IP3) receptor blocker 2-APB were used to clarify the involvement of ETAR, ERK, GC/cyclic guanosine monophosphate (cGMP) and IP3/calcium in ET-1-induced lipolysis. Our results showed that the effect of ET-1 on lipolysis caused a significant increase in both time- and dose-dependent manners. Furthermore, BQ610, PD98059, LY83583 and 2-APB decreased ET-1-induced HSL phosphorylation. To explore the role of ERK in ET-1-stimulated GC/cGMP pathway or IP3/calcium pathway, pretreatment with 2-APB, but not LY83583, attenuated ET-1-induced ERK phosphorylation. In conclusion, ET-1 induced lipolysis in 3T3-L1 adipocytes via ETAR, ERK and partially mediated by GC/cGMP and IP3/calcium, and subsequently induced phosphorylation of HSL. Furthermore, ERK phosphorylation by ET-1-medated IP3/calcium pathway was involved in the process of ET-1-induced lipolysis.
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