Alterations in connexin 43 during diabetic cardiomyopathy: Competition of tyrosine nitration versus phosphorylation 在糖尿病心肌病中间隙连接蛋白43的变化：酪氨酸硝化作用与磷酸化作用的竞争

Background Cardiac conduction abnormalities are observed early in the progression of type 1 diabetes (T1D), but the mechanism(s) involved are undefined. Connexin 43, a critical component of ventricular gap junctions, depends on tyrosine phosphorylation status to modulate channel conductance; changes in connexin 43 content, distribution, and/or phosphorylation status may be involved in cardiac rhythm disturbances. We tested the hypothesis that cardiac content and/or distribution of connexin 43 is altered in a rat model of T1D cardiomyopathy, investigating a mechanistic role for tyrosine. Methods Electrocardiographic analyses were conducted during the progression of diabetic cardiomyopathy in rats dosed with streptozotocin (STZ; 65 mg/kg) 3, 7, and 35 days after the induction of diabetes. Following functional analyses, we conducted immunohistochemical and immunoprecipitation studies to assess alterations in connexin 43. Results There was significant evidence of ventricular conduction abnormalities (QRS complex, Q‐T interval) as early as 7 days after STZ, persisting throughout the study. Connexin 43 levels were increased 7 days after STZ and remained elevated throughout the study. Connexin 40 content was unchanged relative to controls throughout the study. Changes in connexin 43 distribution were also observed: connexin 43 staining was dispersed from myocyte short axis junctions. Connexin 43 tyrosine phosphorylation declined during the progression of diabetes, with concurrent increases in tyrosine nitration. Conclusions The data suggest that changes in connexin 43 content and distribution occur during experimental diabetes and likely contribute to alterations in cardiac function, and that oxidative modification of tyrosine‐mediated signaling may play a mechanistic role. 摘要 背景：在1型糖尿病的早期进展中就能够观察到心脏传导的异常，但是有关的机制却尚未明确。间隙连接蛋白43，一个心室间隙连接的关键组分，依靠酪氨酸磷酸化状态才能调节通道电导；间隙连接蛋白43的含量、分布和/或磷酸化状态的变化都可能与心律失常相关。我们对以下假设进行了检验，亦即在1型糖尿病心肌病大鼠模型中间隙连接蛋白43在心脏的含量和/或分布出现了变化，并调查了酪氨酸在发病机制中的作用。 方法：使用一剂链脲霉素（STZ，65 mg/kg）诱导大鼠糖尿病后的3、7以及35天时在糖尿病心肌病的进展过程中进行心电图分析。接着进行功能分析，我们进行了免疫组化以及免疫沉淀研究以评估间隙连接蛋白43的变化。 结果：早在使用STZ后的第7天就发现了心室传导异常的重要证据（QRS波群，Q‐T间期），并且在整个研究期间都存在。使用STZ 7天后间隙连接蛋白43水平就有所升高，并且在整个研究期间维持升高。在整个研究期内间隙连接蛋白40的含量与对照组相比都没有变化。还观察到了间隙连接蛋白43的分布出现了变化：间隙连接蛋白43的染色从心肌短轴连接处扩散开了。在糖尿病进展期间，间隙连接蛋白43的酪氨酸磷酸化减少了，同时酪氨酸的硝化作用增加了。 结论：这些数据提示实验性糖尿病大鼠的间隙连接蛋白43的含量与分布都出现了变化，而且可能导致心脏功能变化，酪氨酸氧化修饰介导的信号通路可能在发病机制中具有重要的作用。