糖尿病性心肌病是糖尿病重要的併發症之一。在心臟相關病發症中，最終會導致左心室肥大以及心臟收縮舒張功能的異常，甚至心衰竭。目前已知高葡萄糖會造成細胞產生大量活性氧化物(ROS, Reactive oxygen species )造成氧化壓力。在實驗中，首先觀察到第一型糖尿病大鼠心輸出能力變弱，並且也發現抑制型旋轉蛋白表現量以及其轉錄因子GATA-4 ser105磷酸化程度顯著提高，若先以胰島素或Phlorizin矯正降低血糖後，則可回復抑制型旋轉蛋白的表現量，因此也指出高血糖確實影響抑制型旋轉蛋白表現量，並且GATA-4可能參與在此過程中，但目前仍沒有相關研究指出高葡萄糖造成GATA-4磷酸化的機制。過去研究指出，透過MEK/ERK可以直接磷酸化GATA-4，加強GATA-4轉錄活性，並且細胞核中GSK-3β則是負調控的作用促使GATA-4出核。因此利用高葡萄糖培養基(30 mmol/L)處理H9c2心肌細胞模擬高血糖的生理環境。實驗結果顯示高葡萄糖培養基會造成H9c2心肌細胞產生大量ROS，抑制型旋轉蛋白表現量顯著提高以及GATA-4 ser105磷酸化程度也明顯上升。若前處理活性氧化物清除劑Tiron(100 nmol/L)以及ERK阻斷劑PD98059(20 μmol/L) 則可以抑制高葡萄糖培養基所造成的改變。另外也發現隨著高葡萄糖處理的時間，GATA-4在細胞核內分佈以及不活化態的GSK-3β ser9磷酸化也是隨之增加，若前處理活性氧化物清除劑以及ERK阻斷劑可以降低GATA-4細胞核分佈數量以及GSK-3β ser9磷酸化程度。若以GATA4 RNAi將細胞內GATA4 mRNA沉默化後，細胞內抑制型心肌旋轉蛋白表現量並不會受到高葡萄糖影響。利用Phenylephrine(PE)刺激H9c2細胞探討抑制型肌旋轉蛋白表現量改變對於心肌收縮能力的影響。實驗結果中，與控制組相比，高葡萄糖培養基處理H9c2心肌細胞加入PE (1 μmol/L)後細胞收縮能力明顯，而GATA-4 RNAi高葡萄糖組H9c2心肌細胞在加入PE後，其細胞收縮能力則不受到高葡萄糖之影響。綜合以上結果，高葡萄糖確實會透過增加GATA-4轉錄能力造成抑制型心肌旋轉蛋白高表現，最終導致細胞收縮能力降低，在動物模式上，亦可觀察到心輸出量減少。

Diabetic cardiomyopathy as diabetes-specific complication refers to a disease process which eventually leads to left ventricular hypertrophy and diastolic and systolic dysfunction. Recent reports have shown that hyperglycemia induces reactive oxygen species (ROS) in cardiomyocytes, which contributes to diabetic cardiomyopathy. In this study, we observed the lower cardiac output in STZ-induced diabetic rats. The expression of cardiac troponin I (cTnI) and level of GATA-4 phosphorylation was increased. This changes could be reversed by insulin or phlorizin pretreatment. We also demonstrated that the condition of hyperglycemia was failed to increased the expression of cTnI, when GATA-4 is absent. Activation of ERK is known as its ability to phosphorylate serine105 of GATA4, and this had been reported to increase the DNA binding activity of this transcription factor. On the other hand, GSK-3β could directly interact with GATA-4 and cause GATA4 exported from nuclear. In current study, ROS production, higher level of cTnI expression and GATA-4 phosphorylation were observed in high glucose (HG)-treated H9c2 cells. GATA-4 nuclear translocalization and GSK-3β ser9 phosphorylation level were elevated in HG treated H9c2 cells. These changes could be reversed in the presence of tiron (ROS scavengers) , PD98059 (MEK/ERK inhibitors), and GATA-4 RNAi. Results of cell contractility assay also indicate that HG decreased contractility of H9c2 cells. Further more, contractilities was not affected by HG in H9c2 cells after GATA-4 knockdown. Taken together, we have demonstrated that hyperglycemia cause systolic dysfunction and elevatd expression of cTnI in cardiomyocytes through GATA-4 phosphorylation.

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