| 摘要: | 根據先前研究指出，綠茶表沒食子兒茶素沒食子酸酯 (Epigallocatechin gallate, EGCG) 和 microRNA (miR) 藉由抑制脂肪細胞分裂及脂肪分化過程，進而抑制脂肪細胞生長及脂肪生成，但鮮少研究探討EGCG 藉由調控miR影響脂肪細胞生長。雖然先前實驗結果發現EGCG可能藉由調控miR-let-7a及HMGA2表現影響3T3-L1白色前脂肪細胞生長，但需更進一步實驗驗證，而且目前也無研究指出EGCG是否藉由調控miR路徑影響米色前脂肪細胞生長，故本論文探討EGCG是否影響D12及X9米色前脂肪細胞的生長，以及證實EGCG是否藉由調控miR-let-7a/HMGA2路徑調控3T3-L1白色及D12及X9米色前脂肪細胞的生長。結果發現EGCG會抑制D12及X9米脂細胞的生長，且也會時間性及劑量依賴性地上調miR-let-7a及減少HMGA2基因表現。此外，大量表達miR-let-7a後，3T3-L1、D12及X9細胞生長明顯受到抑制，且HMGA2基因表現顯著性下降。而抑制miR-let-7a表現後，阻擋了EGCG對3T3-L1、D12及X9細胞生長之抑制作用，以及上調miR-let-7a及減少HMGA2基因表現之作用。接著根據雙冷光酵素報導基因檢測實驗結果得知，miR-let-7a可直接作用於HMGA2 3’UTR，但無法作用於mutant HMGA2 3’UTR site，由此可知HMGA2為miR-let-7a之標靶基因。進一步的發現，大量表達HMGA2後，D12及3T3-L1細胞數目明顯增加，且阻擋EGCG對D12及3T3-L1細胞生長及HMGA2基因表現之抑制作用。總之，EGCG 藉由調控miR-let-7a/HMGA2的路徑，進而影響D12及X9米色以及3T3-L1白色前脂肪細胞的生長。本篇研究成果可能有助於解釋 EGCG 介導脂肪細胞活性和脂肪細胞相關疾病的miR 信號傳導機制。;Green tea epigallocatechin gallate (EGCG) and microRNA (miR) have been reported to inhibit the growth and fat synthesis of fat cell by suppressing mitogenic and adipogenic processes, respectively. Few studies have reported how EGCG affects fat cell growth by regulating miR molecules. Although previous report had shown that EGCG might affect 3T3-L1 white preadipocyte growth by regulating miR-let-7a and HMGA2 expressions, the contention remains to be demonstrated in further studies. No reports were found whether EGCG affects beige preadipocyte growth through the miR pathway. Thus, this study investigated whether EGCG affects beige preadipocyte growth, and demonstrated whether the miR-let-7a/HMGA2 pathways transduce EGCG signals to regulate growths of white and beige preadipocytes. Using D12 and X9 cells, we found that EGCG inhibited beige preadipocyte growth and that EGCG time- and dose-dependently upregulated miR-let-7a mRNA levels and downregulated HMGA2 gene expression. In addition, overexpression of miR-let-7a significantly inhibited growths of D12, X9, and 3T3-L1 cells, and decreased HMGA2 gene expression. Whereas, the miR-let-7a inhibitor antagonized the inhibitory effects of EGCG on cell number and cell viability of all three cell lines. Moreover, miR-let-7a inhibitor reversed the EGCG-increased level of miR-let-7a mRNA and the EGCG-decreased level of HMGA2 gene expression. Further dual-luciferase report assay indicated that miR-let-7a could directly bind to the HMGA2 3′-UTR site but not mutant HMGA2 3′-UTR site, suggesting that HMGA2 is the miR-let-7a target. Also, overexpression of HMGA2 induced increases in both cell number and cell viability and antagonized EGCG-suppressed growth and HMGA2 expression in D12 beige and 3T3-L1 white preadipocytes. We concluded that EGCG inhibits growths of D12 and X9 beige and 3T3-L1 white preadipocytes through modulations of the miR-let-7a and HMGA2 pathways. Results of this study may help explain the miR signaling mechanism through which EGCG mediates fat cell activity and fat cell-associated disease. |
