NFAT-induced Regional Variations in Kv4 Channel Expression in Heart

描述（由申请人提供）：电压门控K+ (Kv)电流在左心室壁上有差异分布。左心室心外膜细胞（EPI）的Kv4电流大于心内膜细胞（ENDO）。这种Kv4通道功能的不均匀分布对正常心肌复极至关重要。我们最近报道，通过激活Ca2+敏感磷酸酶钙调磷酸酶和转录因子NFATc3， [Ca2+]i的变化被转导为Kv4表达的变化。这导致我们发现，通过左心室游离壁的[Ca2+]i/钙调神经磷酸酶/NFATc3信号传导差异是Kv4表达跨壁变化的基础。然而，[Ca2+]j、钙调神经磷酸酶和NFATc3信号传导的区域差异机制尚不清楚。本应用程序中提出的工作采用了我们小组开发的一系列新技术和方法来解决这些重要问题。我们的初步数据表明，所提出的实验不仅是可行的，而且将为心脏中千伏通道调节提供新的基础信息。提出的工作涉及三个具体假设。首先，我们将验证[Ca2+]j的区域差异是脑室内钙调磷酸酶活性异质性的基础。其次，我们将验证局部和全局[Ca2+]i信号调节心室肌细胞中NFAT易位和基因表达的假设。然后，我们将使用这些数据来确定ENDO和EPI细胞之间[Ca2+]j信号的变化如何导致NFAT活性的区域差异。最后，我们将验证钙调神经磷酸酶/NFATc3信号传导对于维持心室Kv电流异质性至关重要的假设。综上所述，这项工作将首次提供心脏钙信号、兴奋性和收缩性的综合观点，并显著增强我们对健康和疾病中调节Kv通道功能的基本机制的理解。

DESCRIPTION (provided by applicant): Voltage-gated K+ (Kv) currents are differentially distributed across the left ventricular wall. Kv4 currents are larger in left ventricular epicardial (EPI) cells than in endocardial (ENDO) cells. This non-uniform distribution of Kv4 channel function is essential for normal myocardial repolarization. We recently reported that variations in [Ca2+]i are transduced into changes in Kv4 expression through the activation of the Ca2+-sensitive phosphatase calcineurin and the transcription factor NFATc3. This led to our discovery that differential [Ca2+]i/calcineurin/NFATc3 signaling across the left ventricular free wall underlies transmural variations in Kv4 expression. However, the mechanisms underlying regional differences in [Ca2+]j, calcineurin, and NFATc3 signaling are poorly understood. The work proposed in this application employs a series of novel techniques and approaches developed by our group to address these important issues. Our preliminary data suggest that the proposed experiments are not only feasible but will provide new fundamental information regarding Kv channel regulation in the heart. The proposed work addresses three specific hypotheses. First, we will test the hypothesis that regional variations in [Ca2+]j underlie heterogeneous calcineurin activity in the ventricle. Second, we will test the hypothesis that local and global [Ca2+]i signals modulate NFAT translocation and gene expression in ventricular myocytes. We will then use these data to determine how variations in [Ca2+]j signals between ENDO and EPI cells lead to regional differences in NFAT activity. Finally, we will test the hypothesis that calcineurin/NFATc3 signaling is essential for maintaining Kv current heterogeneity in the ventricle. Taken together, this work will provide the first integrated view of calcium signaling, excitability, and contractility in the heart and significantly enhance our understanding of the basic mechanisms, which regulate Kv channel function in health and disease.