Abstract 263: Cytosolic RBFox1 in Cardiac Pathological Remodeling

Background: RBFox1 is known to be an RNA splicing regulator with enriched expression in cardiac muscle. Loss of RBFox1 expression is a molecular hallmark associated with heart failure in mouse and human. Genetic manipulation of RBFox1 reveals a major function of RBFox1 in the pathogenesis of cardiac hypertrophy, fibrosis and dysfunction under pathological stresses. However, much of our current knowledge about RBFox1 focuses on the nuclear RBFox1 with a major impact on global alternative splicing changes. Yet, RBFox1 gene also generates a cytosolic isoform-RBFox1c through alternative splicing, and the specific function of RBFox1c has not been characterized. Goal and Methods: This study investigated the functional impact and the underlying mechanism of the RBFox1c in cardiac pathological remodeling and targeted gene regulation. Results: RBFox1c expression is significantly repressed in stressed cardiomyocytes in vivo and in vitro. RNA-Seq combined with IPA analyses from cardiomyocytes revealed RBFox1c but not the nucleus RBFox1 specifically suppressed pro-inflammatory genes. In the cardiac specific RBFox1 knockout mice, enhanced cardiac fibrosis is observed following I/R injury associated with elevated expression of pro-inflammatory genes. In contrast, cardiac specific expression of RBFox1c reduced cardiac fibrosis and inflammatory gene expression following pressure-overload and myocardial infarct injury associated with improved ejection fraction. Motif enrichment analysis identified significant enrichment of the RBFox1 binding motif in the 3’UTR of the RBFox1c regulated genes. We performed CLIP analysis followed by RT-PCR and observed RBFox1c interacted with inflammatory gene 3’UTR. Lastly, we explored the interactome of RBFox1c and found RBFox1c specifically interacted with a component of RNA decay machinery-Upf1. Indeed, while expression of RBFox1c repressed inflammatory gene expression, inactivation of Upf1 abolished this effect in cardiomyocytes. Conclusion: RBFox1 regulates cardiac transcriptome reprogramming at two post-transcriptional steps. The RBFox1 nuclei isoform regulates RNA splicing reprogramming, and the RBFox1c represses proinflammatory genes via recruitment of Upf1 mediated RNA degradation.