| 摘要: | 肥胖症乃指男性的體脂肪超過百分之二十五；女性的體脂肪超過百分之三十，以及體重（Kg）除以身高的平方（m2）超過三十。近年來，肥胖症是全世界（包括台灣）常見的疾病，與其他高危險群的疾病相關，例如癌症、糖尿病、高血壓、心臟血管疾病及高膽固醇等等，導致於各國因微胖和肥胖症必須付出更多的經濟成本，以及在罹患率、罹病率和死亡率逐漸攀升。然而肥胖症的啟始與特徵是脂肪細胞的數目和該細胞內油滴的增加，主要是因為該細胞進行增生與分化的過程，而這些過程是受到遺傳、內分泌、代謝、環境及營養等種種因素所調節。因此，瞭解某特定營養因子調節脂肪細胞的生長、分化與自然凋亡的作用機制和訊息傳導途徑，將有助於預防肥胖症的起動與惡化，使得人類可預防那些因肥胖所引起的疾病。綠茶唲茶素是一種多酚類黃酮，俗稱維生素P。尤其是表沒食子酸酯型唲茶素酸酯（英文名epigallocatechin gallate；簡稱EGCG），在活體的試驗，它具有降低癌症、關節炎、神經退化、過敏、膽固醇與糖尿病等風險。根據我們之前的報告，發現EGCG 也有減輕正常鼠（瘦體激素的接受器正常）與肥胖鼠（瘦體激素的接受器異常）的體重，以及減少體脂肪與脂肪組織的重量，顯示EGCG 的減重與降酯功能與瘦體激素接受器的完整性無關。為了支持EGCG 的減肥作用，我們在體外的脂肪細胞做試驗，今年分別在不同的國際期刊上發表指出，第一、EGCG 透過蛋白質激.ERK 和Cdk2 的途徑，抑制前脂肪細胞的增生；第二、EGCG 減少脂肪分化因子（例如C/EBPα和PPARγ）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；第三、EGCG 降低Cdk2 的活性和提高caspase-3 的活性，使得前脂肪細胞自然凋亡。此外，EGCG 會直接減少抗胰島素激素（resistin）的基因表達，並且抑制胰島素、第一型與第二型類胰島素生長因子刺激MEK1 激.的活性，以及該荷爾蒙與生長因子接受器的活性。以上的研究成果，顯示EGCG 的作用，可直接或間接性調節荷爾蒙與生長因子對於脂肪細胞的生長、分化與自然凋亡的過程。既然EGCG 那麼的重要，關於EGCG 的接受器是否存在脂肪細胞，以及該受器是否調節脂肪細胞的生長、分化與自然凋亡的訊息傳導途徑，迄今仍然付之闕如。根據之前的報導，EGCG 接受器就是67-kDa laminin receptor (簡稱67LR)，最早發現於癌細胞株，後來也被發現在其它正常的細胞，例如肌肉與神經細胞，不過在脂肪細胞尚未獲得證實，然而脂肪細胞內部卻具有多種型式的laminin 蛋白質和其它類型的LR（例如integrin）。以上種種的研究跡象，造成EGCG 對脂肪細胞的調控方面之瞭解，非常有限與混淆不清。因此，透過67LR 的訊息傳導途徑，將有助於釐清EGCG 調節脂肪細胞的生長、分化與自然凋亡的作用機轉。我們實驗室最近已有初步的結果，首度證實67LR 存在前脂肪細胞、分化中與已分化的脂肪細胞內，並且觀察到在67LR 抗體的前處理之下，可以防止EGCG 減少前脂肪細胞的數目。所以在此提出三年的專題研究計畫，主旨是要進一步瞭解EGCG 如何透過EGCG 接受器67LR 的訊息傳導途徑，調節脂肪細胞的生長、分化與自然凋亡等過程。第一年、將瞭解EGCG 如何透過67LR 的訊息傳導途徑，調節脂肪細胞的生長；第二年、將瞭解EGCG 如何透過67LR 的訊息傳導途徑，調節脂肪細胞的分化；第三年將瞭解EGCG 如何透過67LR 的訊息傳導途徑，調節前脂肪細胞與脂肪細胞的自然凋亡。因此，本研究將對綠茶EGCG 調節脂肪細胞的生長、分化與自然凋亡，深入瞭解其作用的基本機制，並創新認知過去EGCG 對脂肪細胞的作用。由於EGCG 具有減重、降酯、抑制脂肪細胞的生長與分化、及誘導脂肪細胞的自然凋亡。所以在這三年的專題計畫，將有助於EGCG 對脂肪細胞的作用機制之瞭解，也一定使得該綠茶唲茶素，以及含有EGCG 成份的相類似傳統草藥，應用予肥胖症以及其它肥胖症相關疾病的預防與治療。未來在國內外的學術地位和應用價值上，也必定會取得世界導航的角色。 Obesity refers to a body fat above 25% for men and above 30% for women and the body mass index of above 30 Kg/m2. It is common in the world』s population, including Taiwan, and is a disease associated with risks of cancer, diabetes, hypertension, cardiovascular disease, and high cholesterol levels. Maybe of this reason, estimates of the economic costs, prevalence, morbidity, and mortality associated with more-modest degrees of being overweight and obese are rising. Development of obesity is characterized by increased number of fat cells and their lipids due to the processes of so-called mitogenesis and differentiation, which are regulated by genetic, endocrine, metabolic, environmental, and nutritional factors. Accordingly, an understanding of the mechanism through which a particular nutrient affects the mitogenesis and death of preadipocytes and their differentiation to adipocytes would help prevent the initiation and progression of obesity and its associated diseases in humans. Green tea catechins (GTCs) are polyphenolic flavonoids once called vitamin P. GTCs, especially (-)-epigallocatechin gallate (EGCG), have been found to lower the incidence of cancers, arthritis, neurodegenerate diseases, allergy, cholesterol, and diabetes in vivo. Also, our previous report showed that EGCG reduced body weight and body and tissue fats in lean and obese male Zucker rats, suggesting the effect of EGCG was independent of an intact leptin receptor. In supporting the antiobese effect of EGCG, our in vitro data have reported that the antimitogenic effect of EGCG on preadipocytes depends on the ERK and Cdk2 pathways, that EGCG modulates the differentiation of preadipocytes to adipocytes via decreasing expression of adipogenic differentiation factors, such as C/EBPβ and PPARγ, and that the apoptotic effect of EGCG on preadipocytes depends on the Cdk2 and caspase-3 pathways. In addition, EGCG directly reduces resistin gene expression, and indirectly inhibits insulin-, IGF-I-, IGF-II-stimulated MEK1 activity and their respective receptor activity, suggesting that the effect of EGCG on fat cells was direct or mediated by modulating hormone- or growth factor-mediated cell growth, differentiation, and apoptosis. Despite the importance of EGCG, relatively little is know about the presence of the EGCG receptor in fat cells and its receptor signaling in regulating the mitogenesis, differentiation, and apoptosis of fat cells. The fact that the EGCG receptor, the so-called 67-kDa laminin receptor (67LR), was discovered in cancer cells and found in normal cells (i.e., muscle and nerve cells), but was not identified in fat cells, and the fact that fat cells have different isoforms of laminins have also caused much controversy. Thus, a thorough examination of the signaling of 67LR through which EGCG executes its modulation of fat cell activities should help clarify these obervations. We have the preliminary data to indicate that 67LR is present in proliferative and differentiating preadipocytes and adipocytes, and that pretreatment with 67LR antibody prevents EGCG-induced decreases in the cell number of fat cells. The overall objective of our 3-year project is to understand the EGCG-induced signal transduction in the control of growth, differentiation, and apoptosis of fat cells through the pathway of the EGCG receptor 67LR. In first year, we will understand the signal transduction of the 67LR in the modulation of fat cell growth by green tea EGCG. In the second year, we will understand the signaling mechanism of the 67LR in the modulation of preadipocyte differentiation to adipocytes by EGCG. In the third year, we will understand the signaling mechanism of the 67LR in the apoptotic induction of both preadipocytes and adipocytes by EGCG. Thus, this study will provide us with the fundamental basis and important new insight into the mechanism of action of EGCG in the regulation of mitogenesis, differentiation, and apoptosis of fat cells. As EGCG functions to reduce body weight, inhibit fat cell adipogenesis, and induce preadipocyte and adipocyte apoptosis, the mechanistic results of this 3-year study would help explain the mechanism by which EGCG modulates obesity, as well as may possibly be utilized in the treatment and prevention of obesity and obesity-related diseases using green tea or other EGCG-based folk medicines. 研究期間：9608 ~ 9707 |
