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的发生中的作用。糖尿病的一个主要并发症是自主神经病变的发展，这与心脏对自主神经刺激的反应受损有关。糖尿病患者猝死的发生率增加，并因高胆固醇血症和其他心脏危险因素而加剧，可能至少是由于 部分原因是副交感神经反应受损时发生心律失常的可能性增加。这项应用的长期目标是确定类固醇、降脂、胰岛素信号和心脏对副交感刺激的反应之间的新关系。在一个用于降脂的细胞培养模型中，胚胎鸡心房细胞在添加脂蛋白耗竭血清(LPDs)的培养液中培养，我们以前曾 研究表明，脂蛋白耗竭导致对副交感神经刺激的负性变时性反应显著增强，M2毒碱受体、异三聚体G蛋白的阿尔法亚单位Galpha(I2)和介导心脏对副交感神经刺激反应的内向整流性K通道蛋白GIRK1的表达增加。根据初步数据显示，所有这些基因的表达可能受到固醇调节元件结合蛋白SREBP的调控，SREBP是一种调节胆固醇、脂肪酸和葡萄糖代谢的转录因子，与其上游启动子中的一个可能的固醇调节元件结合，我们将检验4个主要假设：1.M2、Galpha(I2)和GIRK1/GIRK4在雏鸡胚胎中的表达 结论：1.心房细胞受SREBP在转录水平上的协同调控；脂蛋白耗竭通过对SREBP的双重作用刺激M2、Galpha(I2)和GIRK1/GIRK4的表达和心脏的副交感反应：SREBP水平增加和SREBP和RAS依赖的磷酸化。胰岛素通过对SREBP水平和磷酸化的类似双重作用，刺激鸡心房细胞M2、Galpha(I2)和GIRK1/GIRK4的表达和副交感反应。SREBP的表达调节小鼠心脏的副交感反应和这些心脏的心房肌细胞对IKAch的毒鼠碱刺激。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一种新的关系，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.