| 摘要: | 肥胖症目前也是全世界（包括台灣）常見疾病之一，與癌症、糖尿病、高血壓及心臟血 管疾病之間息息相關，其主要特徵是脂肪細胞數目和細胞內油滴的增加，這是因為該細胞進 行增生與分化的結果，而這兩種生理過程會受到營養因素與微核醣核酸(microRNA，簡稱miR) 所調控。例如本實驗室發現綠茶表沒食子酸酯型兒茶素酸酯(epigallocatechin gallate;簡稱 EGCG；佔不發酵茶中最大量的兒茶素)，第一、藉由ERK 和Cdk2 蛋白激酶會抑制前脂肪 細胞的增生，第二、藉由EGCG 接受器(即所謂67-kDa 層粘連蛋白接受器，英文簡稱為67LR) 會抑制胰島素與類胰島素生長因子對前脂肪細胞增生與對脂肪細胞攝取葡萄糖能力的誘導作 用，第三、EGCG 會減少脂肪分化因子（例如C/EBP 和PPAR）的蛋白質表達，使得前脂 肪細胞分化成脂肪細胞的過程受到抑制。在活體動物試驗上，我們也發現EGCG 會減輕老鼠體 重、體脂、白脂組織重量、血酯與瘦脂激素含量。最近，我們的初步數據顯示: EGCG 會調節 3T3-L1 前脂肪細胞與脂肪細胞內miR 基因的表現，在前脂肪細胞，EGCG 會增加22 種miR 基 因表現和減少28 種miR 基因表現，例如它會正調節miR-363-5p 與-2136 基因表現，也會負 調節miR-494 與-7052 基因表現， 並會正調節第三型活化性轉錄因子(Activating transcription factor-3; 是miR-494 的標的基因) 和第三型鞘磷脂磷酸二酯酶 (Sphingomyelin phosphodiesterase-3;是miR-2136 的標的基因)。在已分化白脂細胞，EGCG 在20 μM 會增加細胞內20 種miR 基因表現以及減少5 種miR 基因表現。由於我們實驗室曾發 現EGCG 會藉由ERK、AMPK、glutathione、EGCG receptor 等分子路徑而調節脂肪細胞的功能， 故本專題的假設是EGCG 可能也會經由ERK、AMPK、glutathione、EGCG receptor 等訊息分子 路徑，使得脂肪細胞內miR 基因表現受到調節，因而調節該細胞的生長或其他功能。 【為了檢驗上面的假設以及全盤性瞭解綠茶EGCG 對肥胖症和脂肪細胞功能的影響，本三年專 題計畫研究主旨是探討EGCG 對脂肪細胞內miR-494 與-7052 基因表現的影響之訊息傳遞路 徑，子目的一和二將探討MAPK 訊息傳遞路徑與AMPK 訊息傳遞路徑分別對EGCG 所調節脂肪細 胞內miR-494 與-7052 基因表現的影響，子目的三和四將探討Glutathione 訊息傳遞路徑與 EGCG 接受器訊息傳遞路徑分別對EGCG 所調節脂肪細胞內miR-494 與-7052 基因表現的影響， 子目的五與六是分別探討EGCG 在正常小鼠和高脂食物誘導型肥胖小鼠身上對脂肪組織內 miR-494 與-7052 基因表現與血液中兩者含量的影響。】 預期的影響性:首度闡明綠茶EGCG 對脂肪細胞內miR-494 與-7052 基因表現的影響之訊 息傳遞路徑；首度指出EGCG 在正常小鼠與肥胖鼠身上會調節其脂肪組織與血液中miR-494 與-7052 含量的功能；由於茶葉和茶飲在台灣是非常重要的農產與飲料，而且與減肥之間關 係密切，透過本基礎研究而了解茶成分的新作用，可做為改良與增加茶的高附加價值之參考； 本研究成果的新發現，可提供學術專業知識與專利智慧財產之價值，以做為未來應用綠茶以 及與EGCG 相關的健康飲料、健康食品或營養物品於肥胖症以及其他相關生醫疾病的預防與 治療上之重要參考。 ;Obesity is a common disease in the world’s population, including Taiwan, and associates with risks of cancer, diabetes, hypertension, and cardiovascular disease. It is characterized by increased number of fat cells and their lipids due to mitogenesis and differentiation. In turn, the two processes can be regulated by nutritional factors and microRNA (miR) molecules. In particular, green tea epigallocatechin gallate (EGCG), the most abundant catechin in unfermented tea, was found in our lab to 1) suppress preadipocyte mitogenesis through the ERK and Cdk2 pathways, 2) suppress insulin- and IGF-induced increases in both preadipocyte mitogenesis and adipocyte glucose uptake through the EGCG receptor (so-called 67-kDa laminin receptor (67LR)) or AMP-activated protein kinase (AMPK) pathways, and 3) modulate adipocyte differentiation through suppressions of C/EBP and PPARγ. In vivo, EGCG reduced body weight, body and tissue fats, and blood levels of lipids and leptin in rats. Our recent preliminary data showed that EGCG regulated miR expression in 3T3-L1 preadipocytes and adipocytes. In 3T3-L1 white preadipocytes, EGCG at 20 μM for 24 h upregulated 22 miR expressions and downregulated 28 miR expressions. In particular, EGCG stimulated miR-363-5p and -2136 expressions and reduced miR-494 and -7052 expressions. Also, EGCG stimulated the expressions of activating transcription factor-3 (a miR-494 target gene) and sphingomyelin phosphodiesterase-3(a miR-2136 target gene). In differentiated 3T3-L1 white adipocytes, EGCG at 20 μM for 24 h upregulated 20 miR expressions and downregulated 5 miR expressions, respectively. EGCG was found by our lab to regulate fat cell functions through the ERK, AMPK, glutathione, and EGCG receptor pathways; thus, the hypothesis arises that any of the signaling molecules may mediate EGCG’s actions on miR-494 and -7052 genes in fat cells and thereby coordinating fat cell growth and other functions. To test the hypothesis and to fully understand the impacts of green tea EGCG on obesity and fat cell functions, the overall objective of this 3-year study is to investigate the signal pathways involved in EGCG modulations of miR-494 and -7052 gene expressions in fat cells. Aims I and II are to study the MAPK signaling pathway and AMPK signaling pathway involved in EGCG modulations of miR-494 and -7052 expressions, respectively. Aims III and IV are to study the GSH signaling pathway and the EGCG receptor signaling pathway involved in EGCG modulations of miR-494 and -7052 expressions, respectively. Aim V and VI are to study the in vivo effects of EGCG on adipose tissue and circulating miR-494 and -7052 levels in normal and high-fat diet-induced obesity mice, respectively. We anticipate being the first lab to elucidate a signaling mechanism that underlies novel actions of green EGCG on miR-494 and -7052 expressions in fat cells, as well as understanding how EGCG acts on circulating and adipose tissue miR molecules in normal and obese mice. As tea production and tea drink are important in Taiwan and associate with weight loss, our new discoveries may provide the fundamental basis for improving and creating the high value added tea product. Understanding what signaling elements transduce EGCG signals in fat cell miR expression may provide the intellectual merits for academic and patent development plans, as well as may be possibly utilized in the prevention and treatment of obesity using green tea- and EGCG-based beverages, health food, and nutrients. |
