Role of Sterols & Insulin in Cardiac Autonomic Response

相当多的证据支持副交感神经刺激在保护心脏免受心律失常发生中的作用。糖尿病的主要并发症是自主神经病变的发展，其与心脏对自主刺激的反应受损有关。糖尿病患者猝死的发生率增加，高胆固醇血症和其他心脏危险因素加剧了猝死，这可能是由于至少在 部分原因是副交感神经反应受损时心律失常的可能性增加。本申请的长期目标是确定固醇、降脂、胰岛素信号传导和心脏对副交感神经刺激的反应之间的新关系。在一个细胞培养模型，其中胚胎鸡心房细胞培养在培养基中补充脂蛋白耗尽血清（LPDS），我们以前已经 证明脂蛋白消耗导致对副交感神经刺激的负性变时性反应的显著增强和M2毒蕈碱受体、异源三聚体G蛋白的α亚基Ga（i2）和向内整流K通道蛋白GIRK 1的表达增加，其介导心脏对副交感神经刺激的反应。基于表明所有3个基因的表达可能通过固醇调节元件结合蛋白SREBP（调节胆固醇、脂肪酸和葡萄糖代谢的转录因子）与其上游启动子中的推定固醇调节元件的结合来调节的初步数据，我们将测试4个主要假设：1.）M2、Galpha（i2）和GIRK 1/GIRK 4在鸡胚中的表达 心房细胞在转录水平上受SREBP协调调节; 2.）脂蛋白耗竭通过对SREBP的双重作用刺激M2、Ga（i2）和GIRK 1/GIRK 4表达以及心脏的副交感神经反应：SREBP水平的增加和SREBP的Ras依赖性磷酸化; 3.）胰岛素通过对SREBP的水平和磷酸化的类似双重作用刺激M2、Galpha（i2）和GIRK 1/GIRK 4表达以及鸡心房细胞的副交感神经反应; 4.）SREBP表达调节小鼠心脏的副交感神经反应性和这些心脏心房肌细胞中IKAch的毒蕈碱刺激。这些研究将支持降脂、胰岛素功能和心脏副交感神经反应之间存在新的关系，这可能对心律失常的发生和治疗具有重要意义。

Considerable evidence supports a role for parasympathetic stimulation in protection of the heart from the genesis of iarrhythmias. A major complication of diabetes mellitus is the development of an autonomic neuropathy which is associated with an impaired response of the heart to autonomic stimulation. The increased incidence of sudden death in diabetic patients, which is exacerbated by hypercholesterolemia and other cardiac risk factors, may be due at least in part to the increased likelihood of arrhythmia in the presence of an impaired parasympathetic response. The long-term goal of this application is to determine a new relationship between sterols, lipid lowering, insulin signaling and the response of the heart to parasympathetic stimulation. In a cell culture model for lipid lowering, in which embryonic chick atrial cells are cultured in medium supplement with lipoprotein depleted serum (LPDS), we have previously demonstrated that lipoprotein depletion results in a marked enhancement of the negative chronotropic response to parasympathetic stimulation and an increased expression of the M2 muscarinic receptor, the alpha-subunit of the heterotrimeric G-protein, Galpha(i2); and the inward rectifying K channel protein, GIRK1, which mediate the response of the heart to parasympathetic stimulation. Based on preliminary data which suggest that the expression of all 3 of these genes might be regulated by the binding of a sterol regulatory element binding protein, SREBP, a transcription factor which regulates cholesterol, fatty acid and glucose metabolism, to a putative sterol regulatory element in their upstream promoters, we will test 4 major hypotheses: 1.) that the expression of M2, Galpha(i2) and GIRK1/GIRK4 in embryonic chick atrial cells is coordinately regulated by SREBP at the level of transcription; 2.) that lipoprotein depletion stimulates M2, Galpha(i2) and GIRK1/GIRK4 expression and the parasympathetic response of the heart by a dual effect on SREBP: an increase in the level of SREBP and a Ras dependent phosphorylation of SREBP and; 3.) that insulin stimulates M2, Galpha(i2) and GIRK1/GIRK4 expression and the parasympathetic response of chick atrial cells via a similar dual effect on the level and phosphorylation of SREBP and; 4.) that SREBP expression regulates parasympathetic responsiveness of the mouse heart and muscarinic stimulation of IKAch in atrial myocytes from these hearts. These studies would support the existence of a new relationship between lipid lowering, insulin function and the parasympathetic response of the heart which could have important implications for the genesis and treatment of cardiac arrhythmias.