ALTERED CARDIAC MYOCYTE SIGNALING IN DIABETIC MYOCARDIUM AND FUNCTIONAL SEQUELAE

描述（由申请人提供）：糖尿病与心肌病相关，在没有高血压或冠状动脉疾病的情况下发生，其特征是心室肥厚，心室舒张度降低，充盈率峰值降低。糖尿病性心肌病的发展可能是由于心肌细胞中脂质的不正常积累。胰岛素的作用依赖于细胞内信号通路的激活，该通路刺激丝氨酸/苏氨酸激酶Akt2，导致葡萄糖摄取、葡萄糖氧化和糖原合成增加。胰岛素刺激的Akt2激活也可能导致脂质代谢的改变。本项目的主要假设是糖尿病性心肌病是由于Akt2信号通路刺激减少导致细胞内磷脂酶活性改变和脂质代谢异常而发生的。心脏细胞内表达多种pla2，包括cPLA2和iPLA2。糖尿病心肌的特点是cPLA2和iPLA的表达和活性增加，它们可以从膜磷脂中释放游离脂肪酸，包括花生四烯酸和溶血磷脂。初步数据表明，Akt2调节心脏糖代谢和细胞内磷脂酶A2 （PLA2）活性。本项目将在缺乏Akt2激酶的小鼠中研究Akt2在糖尿病性心肌病发病机制中的具体作用。此外，我们将利用cPLA2 -/- Akt2 -/-和iPLA2 -/- Akt2 -/-双敲除小鼠，研究Akt2与细胞内磷脂酶cPLA2和iPLA2在糖尿病心肌病发病机制中的生化生物学关系。本项目的实验结果将有助于确定参与心肌细胞功能、代谢和缺血损伤反应调节的特定信号机制。公共卫生相关性：糖尿病是一种与高血糖相关的常见疾病，在美国导致了大量的痛苦和死亡。众所周知，糖尿病患者会患上一种叫做糖尿病性心肌病的心脏问题，这种疾病会导致心力衰竭。血糖水平是由胰岛素调节的，胰岛素从胰腺中释放出来，作用于全身的许多组织，导致葡萄糖进入细胞，流出血液。当胰岛素进入不同的组织并与细胞结合时，它会激活细胞内一系列被称为信号蛋白的酶，从而提高细胞从血液中吸收葡萄糖的能力。细胞内传递胰岛素信号的一种关键蛋白质叫做Akt2。在青少年和成人发病型糖尿病中，Akt2在心脏细胞中都没有被正确激活。在本研究中，我们研究了Akt2缺陷是否与糖尿病患者的心脏异常有关。分析Akt2在糖尿病性心肌病中的作用可能会导致新的治疗方法，可能有助于降低与糖尿病相关的高死亡率。

DESCRIPTION (provided by applicant): Diabetes mellitus is associated with a cardiomyopathy that occurs in the absence of hypertension or coronary artery disease and that is characterized by ventricular hypertrophy, decreased ventricular diastolic relaxation, and a reduced peak filling rate. Diabetic cardiomyopathy may develop because of the dysfunctional accumulation of lipids in cardiac myocytes. Insulin action is dependent on the activation of an intracellular signaling pathway that stimulates the serine/threonine kinase Akt2, leading to increased glucose uptake, glucose oxidation and glycogen synthesis. Insulin- stimulated Akt2 activation also may result in altered lipid metabolism. The primary hypothesis of this project is that diabetic cardiomyopathy develops as a result of reduced stimulation of the Akt2 signaling pathway that leads to alterations in intracellular phospholipase activity and abnormal lipid metabolism. Several intracellular PLA2s are expressed in heart, including cPLA2 and iPLA2 . Diabetic myocardium is characterized by an increase in the expression and activity of cPLA2 and iPLA , which liberate free fatty acids, including arachidonic acid, and lysophospholipids from membrane phospholipids. Preliminary data suggests that Akt2 regulates cardiac glucose metabolism and intracellular phospholipase A2 (PLA2) activity. In this project, the specific role of Akt2 in the pathogenesis of diabetic cardiomyopathy will be investigated in mice lacking this kinase. In addition, the biochemical and biological relationship between Akt2 and the intracellular phospholipases cPLA2 and iPLA2 in the pathogenesis of diabetic cardiomyopathy will be investigated by use of cPLA2 -/- akt2-/- and iPLA2 -/- akt2-/- double knockout mice. Experimental results from this project will help to define specific signaling mechanisms involved in the regulation of cardiac myocyte function, metabolism and response to ischemic injury. PUBLIC HEALTH RELEVANCE: Diabetes mellitus, a common disease that is associated with high blood sugar, leads to a tremendous amount of suffering and death in the United States. Patients with diabetes are known to develop a heart problem called diabetic cardiomyopathy that can lead to heart failure. Blood sugar levels are regulated by the action of the hormone insulin that is released from the pancreas and that acts in many tissues throughout the body, causing glucose to go into cells and out of the bloodstream. When insulin travels to different tissues and binds to cells, it activates a cascade of enzymes inside of cells, called signaling proteins, leading to the increased ability of cells to take up glucose from the bloodstream. A critical protein inside of cells that relays the insulin signal is called Akt2. In both juvenile and adult onset forms of diabetes, Akt2 is not activated properly in heart cells. In this proposal, we investigate whether defective Akt2 action is responsible for the heart abnormalities that develop in diabetes. The analysis of the role of Akt2 in diabetic cardiomyopathy may lead to new therapies that may help to reduce the high mortality rate associated with diabetes.