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 pathological hypertrophy and heart failure. However, much of our current knowledge about RBFox1 focuses on nuclear RBFox1 with a major impact on global alternative splicing changes in the diseased heart. Yet, RBFox1 gene also generates a cytosolic isoform through alternative splicing (RBFox1c), but the specific function of RBFox1c in heart has not been characterized.
RBFox1c expression is significantly repressed in the mouse failing heart and hypertrophic cardiomyocytes. We performed RNA-seq combined with GO and IPA analysis to determine the impact of RBFox1c expression in culture. Among the genes suppressed specifically by RBFox1c but not the nucleus RBFox1 are groups of pro-inflammatory genes. Both Motif enrichment analysis and de novo motif discovery identified significant enrichment of RBFox1 binding motif in the 3’UTRs of the RBFox1c regulated genes. Using CLIP analysis followed by RT-PCR, we observed RBFox1c, but not nuclear RBFox1 specifically interacted with targeted inflammatory gene 3’UTR. In the cardiac specific RBFox1 knockout mice, enhanced cardiac fibrosis was observed following TAC, associated with elevated expression of RBFox1c dependent inflammatory genes. In contrast, cardiac specific expression of RBFox1c significantly reduced cardiac fibrosis and inflammatory gene expression following TAC, associated with improved ejection fraction and reduced hypertrophic marker gene expression. Further, we tested the effect of RBFox1c expression on cardiac fibrosis response using NRVM conditioned media. We showed the conditioned media from the hypertrophic cardiomyocytes potently induce fibroblast proliferation. However, RBFox1c expression can suppress phenylephrine and isoproterenol induced fibroblasts proliferation.
RBFox1 regulates cardiac transcriptome reprogramming at two post-transcriptional steps. The RBFox1 nuclei isoform regulates global RNA splicing reprogramming in heart, while the RBFox1c regulates inflammatory gene expression and fibrotic remodeling potentially through potential interaction with their 3’UTR and targeted RNA degradation.