| 摘要: | 根據文獻研究，綠茶的多種兒茶素，尤其是表沒食子兒茶素沒食子酸酯(EGCG) 可減輕體重並調節脂肪細胞的活性。雖然EGCG被發現調控白色脂肪細胞、米色脂肪細胞和棕色脂肪細胞的生長及分化，但是EGCG及其結構相關的兒茶素，如表兒茶素（EC）、表沒食子兒茶素（EGC）和表兒茶素沒食子酸酯（ECG），對米色脂肪細胞成脂分化的確切機制仍尚未釐清。因此，本論文的目的是研究兒茶素對 D12 米色脂肪細胞分化的影響。結果表明茶中的兒茶素對米色脂肪細胞分化具有差異性作用，如總三酸甘油酯累積的變化所示，一般來說，EGCG 比Catechin、EC、ECG 和 EGC 更有效地減少三酸甘油酯的累積以及細胞數。此外，EGCG抑制D12 米色細胞中成脂分化指標基因的表達，包括 C/EBPα、Cidea 、PGC-1α、PPAR γ 、TBX1和 UCP-1，且呈現劑量依賴性。由於白色脂肪細胞的分化可以通過 microRNA ( miR )-let-7a和 miR-143進行調節，因此本論文也探討D12米色脂肪細胞分化期間處理EGCG時，miR-let-7a和 miR-143的表達變化。結果顯示miR-let-7a和miR-143在米色脂肪細胞分化期間第8天時顯著增加其表現量，EGCG顯著抑制miR-let-7a表達並增加miR-143表現量，且EGCG的影響呈現劑量依賴性。此外，在EGCG誘導下顯著增加HMGA2 （miR-let-7a的標的基因）及其蛋白質含量，但是對DLK1（miR-143的標的基因）的表達沒有顯著影響。為了探討EGCG對三種脂肪細胞分化期間的影響，使用了3T3-L1白色脂肪細胞和HIB1B棕色脂肪細胞進行比較，我們發現白色脂肪細胞分化期間的EGCG處理組，Cidea、PGC-1α和UCP1的mRNA表現量增加，而C/EBPα 和PPARγ的 mRNA表現量下降。有趣的是，EGCG抑制棕色脂肪細胞分化期間所有分化指標基因mRNA表達，C/EBPα 、CIDEA、PGC-1α、PPARγ 和UCP1的 mRNA表現量都下降。綜上所述，EGCG對成脂分化過程的影響呈現脂肪細胞類型非依賴性以及兒茶素依賴性。由於肥胖與脂肪細胞的活性有關，而米色脂肪細胞和棕色脂肪細胞的活性與癌症患者的惡病質有關，本論文的結果提供兒茶素用於肥胖症及癌症惡病質的可能性。;Green tea catechins, particularly epigallocatechin gallate (EGCG), have been reported to reduce body weight and regulate fat cell activity. Although EGCG was found to mediate the growth and differentiation of white, beige, and brown fat cells, the exact mechanisms of the actions of EGCG and other structurally-related tea catechins, such as epicatechin (EC), epigallocatechin (EGC), and epicatechin gallate (ECG), on beige adipogenic differentiation are still not clear. Thus, the objective of the present thesis was designed to investigate the effect of tea catechin on the differentiation of D12 beige fat cells. The results indicated catechin-specific effect of tea on beige cell differentiation, as indicated by changes in the total triglyceride accumulation. Generally, EGCG was more effective than catechin, EC, ECG, and EGC to reduce the accumulation of triglyceride, as well as reducing the number of cells. In addition, EGCG dose-dependently suppressed the expression of adipogenic differentiation marker genes in D12 beige cells, including C/EBPα, Cidea, PGC-1α, PPARγ, TBX1, and UCP-1. Since the differentiation of white fat cells can be regulated by microRNA (miR)-let-7a and miR-143, changes in their expression during adipogenic differentiation of D12 cells induced by EGCG were accessed. The results showed that miR-let-7a and miR-143 significantly increased their expression levels during the 8-day period of beige fat cell differentiation and that EGCG significantly inhibited miR-let-7a mRNA expression and increased miR-143 mRNA levels in a dose-dependent way. Also, EGCG induced significant increases in the HMGA2 (a target of miR-let-7a) mRNA and protein levels and had no significant effect on DLK1 (a target of miR-143) mRNA expression. Using 3T3-L1 white and HIB1B brown fat cells for comparison with the effect of EGCG on the differentiation among three fat cell types, we found that EGCG induced increases in levels of Cidea, PGC-1α and UCP1 mRNAs and decreases in levels of C/EBPα and PPARγ mRNAs during the differentiation of white fat cells. Interestingly, EGCG inhibited the mRNA expression of all C/EBPα, Cidea, PGC-1α, PPARγ, and UCP1 mRNAs during brown fat cell differentiation. In conclusions, the effect of EGCG on the process of adipogenic differentiation appears fat cell type-independent and catechin-dependent. As obesity is associated with fat cell activity and as the activities of beige and brown fat cells are associated with cachexia of cancer patients, the results of the present thesis may provide the evidence by which tea catechin exert its effects on obesity and cancer cachexia. |
