Na+ channel mRNA splicing in heart failure

描述（由申请人提供）：尽管有广泛的研究和新的治疗方法，人类收缩期心力衰竭（HF）仍然是影响数百万美国人的重大临床问题，HF相关心律失常仍然是高发病率和高死亡率的一个原因。最近，三种SCN5a心脏Na+通道mRNA选择性剪接变异在人HF组织中被发现上调。这些剪接变异是由SCN5a末端外显子（即外显子28）的隐剪接序列剪接引起的，编码的心脏Na+通道在结构域IV的孔形成段之前被截断。变异水平达到SCN5a mRNA总量的50%以上。正如预期的那样，这些变体并没有形成功能性通道。此外，变异的存在导致全长SCN5a mRNA丰度降低，但没有改变总SCN5a mRNA。该应用旨在建立HF中异常剪接发生的机制，以及截断Na+通道变体的存在如何导致全长通道mRNA的显性负调控。初步数据表明，缺氧和血管紧张素II （AngII）可以通过诱导mRNA剪接因子CROP/hLuc7A及其辅助因子RBM25的表达来指示SCN5a的病理剪接调节，这些剪接因子通过与SCN5a异常剪接发生的外显子28中的一个或多个RBM25结合序列CGGGC(A)相互作用来改变SCN5a剪接调节。此外，数据显示，截断的Na+通道在内质网（ER）中积累并启动未折叠蛋白反应（UPR）途径，导致Na+通道翻译减少，全长SCN5a转录物的半衰期缩短。假设。基于以上，我们假设hLuc7A/RBM25复合体导致了Na+通道mRNA的异常剪接，而UPR导致了异常剪接转录物对Na+通道的主要负面影响。具体的目标。具体目的1：确定hLuc7A/RBM25剪接调控通路是否参与SCN5a mRNA变异体表达增加的机制。具体目标2：确定未折叠蛋白反应（UPR）中的三种主要途径在多大程度上导致功能性Na+通道的减少。具体目的3：证明hLuc7A/RBM25调控、未折叠蛋白反应（UPR）激活、Na+通道mRNA变异和Na+通道测量在人类心力衰竭样本中的关系。

DESCRIPTION (provided by applicant): Despite the extensive research and novel treatments, human systolic heart failure (HF) remains a substantial clinical problem affecting millions of Americans and HF associated arrhythmia still remains a cause of the high morbidity and mortality. Recently, three SCN5a cardiac Na+ channel mRNA alternative splicing variants were found to be upregulated in human HF tissue. These splicing variants resulted from splicing at cryptic splice sequences in the terminal exon of SCN5a (i.e., exon 28) and encoded cardiac Na+ channels truncated before the pore forming segment of domain IV. Variant levels reached greater that >50% of the total SCN5a mRNA. As expected, these variants did not form functional channels. Moreover, the presence of the variants caused reduced abundance of the full-length SCN5a mRNA without alteration of total SCN5a mRNA. This application proposes to establish the mechanism whereby the abnormal splicing occurs in HF and how the presence of truncated Na+ channel variants causes a dominant negative downregulation of the full-length channel mRNA. Preliminary data suggest hypoxia and angiotensin II (AngII) can signal pathological SCN5a splicing regulation by inducing expression of the mRNA splicing factor, CROP/hLuc7A, and its co-factor RBM25, which alter SCN5a splicing regulation by interacting with one or more RBM25 binding sequences CGGGC(A) in SCN5a exon 28, the exon where abnormal splicing of SCN5a occurs. Furthermore, data show that truncated Na+ channels accumulate in endoplasmic reticulum (ER) and initiate the unfolded protein response (UPR) pathway, causing reduced Na+ channel translation and a shortened half-life of the full-length SCN5a transcript. Hypothesis. Based on the above, we hypothesized that the hLuc7A/RBM25 complex contributes to abnormal Na+ channel mRNA splicing and that the UPR contributes to the dominant negative effect the abnormally spliced transcripts have on the Na+ channel. Specific Objectives. Specific aim 1: To establish whether the hLuc7A/RBM25 splicing regulation pathway is involved in the mechanism to increase SCN5a mRNA variant expression. Specific aim 2: To determine to what extent the three major pathways in the unfolded protein response (UPR) are responsible for the reduction in functional Na+ channels. Specific aim 3: To demonstrate the relationship of hLuc7A/RBM25 regulation, the unfolded protein response (UPR) activation, Na+ channel mRNA variants, and Na+ channel measures in human heart failure samples.