Mechanisms of Long-term Cardiac Ion Channel Regulation

描述（由申请人提供）：心肌细胞钙离子失调导致心脏发育缺陷和心脏老化疾病。本研究的长期目标是提供一种分子机制，解释心脏l型钙通道（LTCC）如何感知和转导稳态调节心肌细胞的信号。心肌细胞在向细胞核传递钙信号方面存在一个难题。在每个心脏周期中，细胞质钙振幅变化10倍，然而钙的改变在某种程度上被不同地解码为长期的转录信号。在此资助期内，我们将测试Ca通道活性和心脏l型Ca通道本身是否编码Ca信号以进行长期调节。在过去的资助期内，我们发现RGK长期抑制ICa，L （LTCC电流），并且这种RGK对ICa，L的抑制导致CaV1.2 mRNA的代偿上调。这表明ICa，L阻断可能是细胞核中转录事件的信号。在新的研究中，我们证实并扩展了这一概念，表明ltcc -药理学阻断，而不是内部Ca一般是扰乱心脏发育的原因。同样，在成熟心脏中，长期阻断LTCC也会引起LTCC和ICa、L的代偿性上调。我们的驱动假设是，信号不是简单地由钙决定的，而是由活跃的钙通道决定的。LTCC的移动片段定位于细胞核或t小管的发现，加上最近关于该肽是转录因子的报道，推动了令人兴奋的新假设，即LTCC的这一片段调节LTCC的表达。我们将从三个方面来研究这方面的长期渠道监管：1。我们将评估LTCC结构域的核易位，并确定LTCC活性与亚细胞定位之间的相互作用；2. 我们将确定LTCC自动调节自身转录的能力；和3。我们将确定LTCC阻断后SL Ca处理蛋白的代偿性变化。这项工作可能提供了LTCC功能和下游信号事件之间缺失的分子联系。公共卫生相关性：这些研究表明，广泛用于阻断LTCC的临床相关药物可能会通过矛盾地增加LTCC功能而无意中加剧心功能障碍。这一建议将有助于理解一种新的机制，即控制心脏电活动的离子通道也可能控制对维持心脏结构和功能至关重要的长期信号通路。

DESCRIPTION (provided by applicant): Ca dysregulation in cardiac myocytes contributes to heart development defects and diseases of the aging heart. The long-term objective of this proposal is to provide a molecular mechanism that explains how cardiac L-type Ca channels (LTCC) sense and transduce signals that homeostatically regulate cardiac myocytes. Cardiac myocytes present a conundrum with respect to Ca signaling to the nucleus. Cytosolic Ca amplitude varies >10-fold during each cardiac cycle, yet alterations of Ca somehow are differentially decoded for longer-term transcriptional signaling. In this funding period we will test whether Ca channel activity and the cardiac L-type Ca channel itself encodes Ca signaling for long-term regulation. In the past funding period we discovered that RGK chronically inhibited ICa,L (LTCC current), and this RGK inhibition of ICa,L resulted in a compensatory up-regulation of CaV1.2 mRNA. This suggests that ICa,L block may signal transcriptional events in the nucleus. In new studies we confirmed and extended this notion by showing that LTCC-pharmacological- block, but not internal Ca in general is responsible for perturbing heart development. Along the same lines, in mature heart, long-term blockade of LTCC also causes a compensatory up-regulation of LTCC and ICa,L. Our driving hypothesis is that signaling is not simply determined by Ca, but by active Ca channels. The discovery that mobile segment of LTCC is localized to the nucleus or t-tubules coupled with the recent report that this peptide is a transcription factor drives the exciting new hypothesis that this segment of the LTCC, regulates LTCC expression. We will study this aspect of long-term channel regulation in three aims: 1. We will assess nuclear translocation of a domain of the LTCC, and determine the interaction between LTCC activity and sub- cellular localization; 2. We will determine the ability of LTCC to auto-regulate itself transcriptionally; and 3. We will determine the compensatory changes of SL Ca handling proteins in response to LTCC blockade. This work may provide a missing molecular link between LTCC function and downstream signaling events. PUBLIC HEALTH RELEVANCE: These studies show that widely used clinically-relevant drugs that are used to block LTCC may inadvertently exacerbate heart dysfunction by paradoxically increasing LTCC function. This proposal will lead to understanding of a new mechanism whereby ion channels that control cardiac electrical activity also may control long-term signaling pathways that are critical for maintenance of cardiac structure and function.