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.
The cause of sudden death in heart failure is unknown. This application will explore one potential cause, abnormal sodium channel processing, establishing the mechanism and possible elucidating prevention strategies. Moreover, if white cells show similar abnormalities, this work may lead to a blood test to predict sudden death risk in heart failure.
|Yang, Kai-Chien; Kyle, John W; Makielski, Jonathan C et al. (2015) Mechanisms of sudden cardiac death: oxidants and metabolism. Circ Res 116:1937-55|
|Liu, Man; Dudley Jr, Samuel C (2015) Role for the Unfolded Protein Response in Heart Disease and Cardiac Arrhythmias. Int J Mol Sci 17:|
|Negi, Smita I; Greener, Ian; Anand, Aashish et al. (2015) A Circulating Biomarker Risk-Prediction Model Correlates with CHADS-2 Risk Score in Chronic Atrial Fibrillation. IJC Metab Endocr 6:24-26|
|Jeong, Euy-Myoung; Dudley Jr, Samuel C (2015) Diastolic dysfunction. Circ J 79:470-7|
|Liu, Man; Yang, Kai-Chien; Dudley Jr, Samuel C (2014) Cardiac sodium channel mutations: why so many phenotypes? Nat Rev Cardiol 11:607-15|
|Gao, Ge; Brahmanandam, Vikram; Raicu, Mihai et al. (2014) Enhanced risk profiling of implanted defibrillator shocks with circulating SCN5A mRNA splicing variants: a pilot trial. J Am Coll Cardiol 63:2261-9|
|Liu, Man; Dudley Jr, Samuel C (2014) Targeting the unfolded protein response in heart diseases. Expert Opin Ther Targets 18:719-23|
|Yang, Kai-Chien; Rutledge, Cody A; Mao, Mao et al. (2014) Caveolin-1 modulates cardiac gap junction homeostasis and arrhythmogenecity by regulating cSrc tyrosine kinase. Circ Arrhythm Electrophysiol 7:701-10|
|Jeong, Euy-Myoung; Dudley Jr, Samuel C (2014) New diagnostic and therapeutic possibilities for diastolic heart failure. R I Med J (2013) 97:35-7|
|Rutledge, Cody A; Ng, Fu Siong; Sulkin, Matthew S et al. (2014) c-Src kinase inhibition reduces arrhythmia inducibility and connexin43 dysregulation after myocardial infarction. J Am Coll Cardiol 63:928-34|
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