探討雌激素受體在熱效力下對骨骼肌肉細胞分化及葡萄糖攝取的影響

Abstract

糖尿病是新陳代謝症候群的一種，其中九成以上的患者屬於胰島素抗性之第二型糖尿病。目前醫界對於第二型糖尿病的治療對策主要是給予胰島素或搭配胰島素增敏劑，但患者的血糖控制仍有待改善。由過去的研究發現糖尿病患者其肌肉組織中慢肌的比例較正常人下降，而慢肌是屬於對胰島素較敏感且葡萄糖攝取能力較好的肌肉；此外，骨骼肌中雌激素受體α有助於骨骼肌葡萄糖攝取。根據前人實驗，發現於39℃培養小鼠骨骼肌細胞株C2C12可促使慢肌表現增加，因此本論文利用2%馬血清促使小鼠骨骼肌細胞株C2C12分化後將其分別置於37℃、39℃、32℃等不同培養溫度培養6天，觀察不同溫度對肌肉細胞分化、雌激素受體α表現及葡萄糖攝取量的影響。實驗結果顯示，當無胰島素刺激時，在39℃組慢肌、雌激素受體α表現及葡萄糖攝取量均較37℃組顯著增加；32℃組慢肌表現及葡萄糖攝取量均較37℃培養組顯著下降。為確認雌激素受體α表現是否影響慢肌生成，利用雌激素受體α拮抗劑MPP抑制雌激素受體α作用，發現39℃MPP刺激組葡萄糖攝取量及慢肌表現均較無MPP刺激組顯著下降，32℃MPP刺激組葡萄糖攝取較無MPP刺激組顯著下降，但慢肌表現不受影響，顯示肌肉細胞中雌激素受體α表現多寡是影響39℃肌肉細胞慢肌生成及增加葡萄糖攝取量的重要因子。將未分化的肌原細胞放入不同溫度培養1天，39℃組雌激素受體α表現較37℃組顯著增加，而32℃則否，證實肌肉細胞中雌激素受體α表現與39℃組細胞分化有關。利用給予ERα、ERβ拮抗劑比較兩者對肌肉分化及葡萄糖攝取的影響，確認ERα為慢肌分化與葡萄糖攝取的主要影響因子。給予胰島素刺激，39℃組葡萄糖攝取量及Akt活化均較37℃、32℃組顯著增加。綜合前述實驗結果顯示C2C12肌肉細胞在39℃培養下，因ＥＲα表現增加促進慢肌生成，進而提高肌肉葡萄糖攝取量，本論文希望研究結果對血糖控制有所助益。

The diabetes prevalence rate is greater in men than women. The slow muscle is decreased and the fast muscle is increased in the diabetic patients. It has bene found that hyperthermia used as physical therapy for muscle injury increased slow muscle expression. We proposed that heat stress and estrogen receptors may play a role in the muscle cell differentiation and glucose uptake. The mice skeletal C2C12 myoblast were seeded in 10% FBS growth medium at 37oC incubator. When the myoblast reached to 95% confluency, the medium was changed to 2% horse serum differentiation medium. After 2-4 days differentiation, the cells were cultured at 32oC or 39oC for 2-4 days or 3hr/day for 4 days. We found that the cell exposed to 39oC significantly increased ER and slow muscle MyHCI expression and glucose uptake but no changed in ER, PGC-1, fast muscle MyHCII and GLUT4 compared to the cell exposed to 37oC. In addition, the 39oC heat stress enhanced insulin-stimulating pAkt/Akt signaling and glucose uptake. In contrast, the cell exposed to 32oC significantly decreased slow muscle MyHCI expression and glucose uptake and inhibited insulin-stimulating pAKT/AKT signaling and glucose uptake compared to the cell exposed to 37oC. Supplementation of ER antagonist significantly decreased ER, slow muscle MyHCI and fast muscle MyHCII expression and glucose uptake and inhibited insulin-stimulating glucose uptake. In contract, ER antagonist had no effect on slow muscle MyHCI and fast muscle MyHCII expression and insulin-stimulating glucose uptake. We concluded that 39oC heat stress increase ER expression to increase slow muscle expression during muscle differentiation and enhance insulin signaling for glucose uptake.