| 摘要: | 肥胖與糖尿病、高血壓、癌症和心血管疾病的風險有關，其特徵在於增加脂肪細胞的有絲分裂與脂肪的形成。然而，脂肪細胞的有絲分裂和脂肪形成是可以通過內分泌、遺傳、生長因子和營養來調節。本論文的總體目標主旨是在了解內皮素 (ET) 訊息途徑在控制前脂肪細胞有絲分裂作用與綠茶表沒食子兒茶素沒食子酸酯 (EGCG；主要兒茶素)、胰島素 (INS) 和類胰島素生長因子 (IGFs) 之間的關聯。這項研究的結果 (第一章) 表明第一型內皮素是透過ETAR、PKC、STAT3、AMPK、c-JUN、ERK、鞘氨醇激?和鞘磷脂?途徑刺激3T3-L1前脂肪細胞的生長。我們發現第三型內皮素 (第二章) 透過ETAR、AMPK、JNK/c-JUN途徑，而不是ERK與PKC途徑去刺激3T3-L1前脂肪細胞生長。這結果顯示，第一型內皮素與第三型內皮素會透過不同的訊息途徑去刺激前脂肪細胞的增生。第一型內皮素 (第三章) 可能透過ETAR、ETBR、PKC、STAT3和AMPK途徑去影響人類白色前脂肪細胞的生長。結果顯示EGCG (第四章) 透過ERK、c-Jun和SATA3途徑去抑制第一型內皮素所誘導的前脂肪細胞的生長。有趣的是我們也發現沒食子酸 (gallic acid) 與兒茶素 (catechin) 抑制第一型內皮素誘導的前脂肪細胞的生長，而表兒茶素 (epicatechin) 或表沒食子兒茶素 (epigallocatechin) 或表兒茶素沒食子酸酯 (epicatechin gallate) 則沒有這樣的作用，研究結果證明綠茶中的兒茶素具有特異性的調節作用。內皮素、胰島素或類胰島素生長因子對前脂肪細胞生長的交互作用中 (第五章)，結果表明第一型內皮素和胰島素會透過ERK途徑的協同作用來增強前脂肪細胞生長，而不是透過p38或JNK途徑。我們觀察到第二型內皮素或第三型內皮素與胰島素刺激前脂肪細胞生長具有相似的協同作用。此外，第一型內皮素、第二型內皮素、第三型內皮素都會增強類胰島素生長因子所影響的3T3-L1前脂肪細胞的生長。本文的研究結果清楚地描述各種內皮素荷爾蒙調控白色前脂肪細胞生長會透過不同的訊號途徑，並可能提供內皮素、EGCG、胰島素和類胰島素生長因子介導前脂肪細胞生長相互作用的機制，進而導致脂肪細胞活性的變化和調節脂肪細胞相關的肥胖症和其他生物醫學疾病。;Obesity is associated with the risks of diabetes, hypertension, cancer, and cardiovascular diseases and is characterized with increased mitogenesis and adipogenesis of fat cells. In turn, adipocyte mitogenesis and adipogenesis can be regulated by endocrine, genetic, growth factors, and nutritional cues. The overall objective of the dissertation was designed to understand the endothelin (ET) signaling pathways in controlling preadipocyte mitogenesis in relation to green tea epigallocatechin gallate (EGCG; the major catechin), insulin (INS), and insulin-like growth factors (IGFs). The results of this study (Chapter One) indicated that ET-1 stimulated 3T3-L1 preadipocyte growth via the ETAR, PKC, STAT3, AMPK, c-JUN, ERK, sphingosine kinase, and sphingomyelinase pathways. ET-3 (Chapter Two) was found to stimulate 3T3-L1 preadipocyte growth via the ETAR, AMPK, JNK/c-JUN, but not ERK or PKC, pathways. This suggests that ET-3 exhibits somewhat different signals from ET-1 to stimulate preadipocyte proliferation. ET-1 (Chapter Three) was found to stimulate human primary preadipocyte growth possibly via the ETAR, ETBR, PKC, STAT3, and AMPK pathways. Interestingly, neither ET-2 nor ET-3 altered the growth of human white preadipocyte. EGCG (Chapter Four) was found to suppress ET-1-induced growth of 3T3-L1 preadipocytes though the ERK, c-JUN, and STAT3 pathways. Interestingly, gallic acid, catechin, but not epicatechin, or epigallocatechin, or epicatechin gallate, were also found to inhibit ET-1-induced growth of preadipocytes, suggesting the catechin-specific effect of green tea. The interactive effect of ET with INS or IGF on preadipocyte growth (Chapter Five) indicated that ET-1 and insulin had a synergistic effect on preadipocyte growth via the ERK but not p38 or JNK pathway. A similar synergistic effect of either ET-2 or ET-3 with INS to stimulate preadipocyte growth was observed. In addition, ET-1, ET-2, or ET-3 generally enhanced IGF-stimulated growth of 3T3-L1 preadipocytes. The results of this dissertation delineate distinct signal pathways of various ET hormones in controlling white preadipocyte growth and may provide a mechanism by which ETs interact with EGCG, INS, and IGF to mediate preadipocyte growth and thereby leading to changes in fat cell activity and coordinating fat cell-related obesity and other biomedical diseases. |
