綠茶表沒食子酸酯型唲茶素酸酯抑制第一型内皮素作用於脂肪細胞上攝入葡萄糖的訊息機制

本研究探討綠茶唲茶素中表沒食子酸酯型唲茶素酸酯(簡寫為EGCG)調控第一型內皮素(簡寫為ET-1 )在短時間(0.5小時)、中長時間(2小時)、長時間(6小時)刺激脂肪細胞攝入葡萄糖的訊息機制。利用3T3-L1脂肪細胞，實驗中發現，在ET-1處理0.5小時和2小時的環境下，預先處理PI3K的抑制劑LY294002及wortmannin時，EGCG無法抑制由ET-1所誘導的葡萄糖攝取作用，然而在前處理ERK/MAPK的抑制劑PD98059及U0126的組別中則無此效應，因此推測EGCG會使ET-1在短時間處理時所減弱葡萄糖攝取的作用與PI3K/AKT此訊息路徑相關。另一方面也發現，當脂肪細胞在已有JAK2的抑制劑AG490(50 µM )的環境下，ET-1處理0.5小時、2小時的組別中會發現葡萄糖攝取有增加的趨勢，因此可推論EGCG的作用會與JAK2/STAT-3訊息相關。在脂肪細胞裡鑑定到一個EGCG接受子[已知為67-kDa laminin接受子 (67LR)]。在本研究中，預先處理67 LR 抗體時無論是在處理0.5、2、6小時ET-1的環境下，皆呈現EGCG無法抑制ET-1促進葡萄糖攝取的現象，因此推論EGCG會透過67LR來抑制由ET-1所誘導的葡萄糖攝取。另外本實驗中發現在ET-1處理0.5小時的環境下，預先處理抗氧化劑NAC時脂肪細胞本身及由ET-1所誘導的葡萄糖攝取的能力皆有增加的趨勢，因而推測NAC在短時間影響脂肪細胞本身及ET-1所促進的葡萄糖攝取作用與ROS的生成相關。而在預先處理AMPK抑制劑compound C的組別中，無論是在處理0.5、2、6小時ET-1的環境下，皆呈現EGCG無法抑制ET-1促進葡萄糖攝取的現象，因此推論EGCG會透過AMPK來抑制由ET-1所誘導的葡萄糖攝取現象。而當ET-1處理2小時和6小時，EGCG會藉由AMPK的路徑去減弱ET-1所促使的GLUT-1蛋白表現，進而減少葡萄糖攝取的作用。

關鍵字

綠茶表沒食子酸酯型唲茶素酸酯；第一型内皮素；葡萄糖攝取；葡萄糖運送蛋白；訊息機制

並列摘要

This study investigated the possible mechanism involved in EGCG modulation of ET-1-stimulated glucose uptake in 3T3-L1 adipocytes. We found that pretreatment with the PI3K inhibitors, such as LY294002 and wortmannin, inhibited EGCG-induced decreases on the acutely ET-1 stimulated glucose uptake in adipocytes. However, none of the ERK/MAPK inhibitors, such as PD98059 and U0126, significantly blocked the anti-ET-1 effects of EGCG on adipocyte glucose uptake. These data suggest that PI3K activation is necessary for the effects of EGCG on the acutely ET-1-stimulated glucose uptake in adipocytes. Interestingly, we observed that pretreatment with the JAK2/STAT3 inhibitors, such as AG490(50 µM ), increased the basal glucose uptake and the ET-1-dependent glucose uptake, suggesting the JAK2/STAT3-dependent effect of EGCG. The EGCG receptor [also known as the 67-kDa laminin receptor (67LR)] was identified in fat cells. Pretreatment of adipocytes with 67LR antibody, but not normal rabbit immunoglobulin, prevented the effects of EGCG on ET-1-induced glucose uptake in adipocytes. These data suggest that EGCG exerts its anti-ET-1 actions on adipocyte glucose uptake via the 67LR. However, NAC(an antioxidant) acutely increased the basal glucose uptake and ET-1 stimulated glucose uptake, indicating that NAC possibly affected glucose uptake by suppressing not only the ET-1-dependent ROS production but also the ET-1-independent ROS production. Pretreatment with the AMPK inhibitor, such as compound C, blocked the anti-ET-1 effects of EGCG on adipocyte glucose uptake, and prevented the effects of EGCG on the chronically ET-1-stimulated GLUT-1 protein expression. This suggests that EGCG inhibits the chronically ET-1 action on adipocyte glucose uptake through the activation of AMPK pathway that results in alterations of GLUT-1 protein expression. Results of this study may help understand the mechanism of how green tea EGCG modulates hormone-mediated obesity.

並列關鍵字

EGCG ； ET-1 ； glucose uptake ； glucose transporter ； signaling mechanism

參考文獻

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綠茶表沒食子酸酯型唲茶素酸酯抑制第一型内皮素作用於脂肪細胞上攝入葡萄糖的訊息機制

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