Abstract Body: Cardiac hypertrophy is associated with an increased risk of mortality, largely due to growth of myocytes in response to pathological stimulation. Post-transcriptional regulation plays an important role in maintaining cell homeostasis during pathological remodeling, such as modification, alternative splicing, and degradation. While most of current literature explores the role of transcriptional regulation during cardiac hypertrophic response, the role of targeted mRNA degradation remains unknown.
Using a BRIC-Seq (5’bromo-uridine immunoprecipitation-chase deep-sequencing) in normal and hypertrophic cardiomyocytes we found a global shift in RNA stability. In addition, GO analysis have identified that the mRNA with altered half-life is involved in cardiac hypertrophy, inflammation and metabolic processes without any impact on classic nonsense mediated decay (NMD) targets, suggesting a previously uncharacterized cardiac hypertrophic stress induced transcriptome remodeling at the level of mRNA degradation. Among the known factors involved in mRNA degradation, we found only Upf1 (Up-frameshift protein 1), but not other Upf family members, is significantly induced in hypertrophic cardiomyocytes and failing mouse hearts, suggesting the changes in RNA stability during hypertrophy may be an Upf1-dependent but NMD-independent mechanism.
Using cultured cardiomyocytes, we have identified that loss of Upf1 expression led to cardiac hypertrophy while restoring expression of Upf1 protected phenylephrine induced cardiac hypertrophy based on marker gene expression. In vivo, we further demonstrated loss of Upf1 exacerbates myocardial infarction induced cardiac pathogenesis using AAV9 mediated Upf1 inactivation, suggesting that Upf1 mediated mRNA stability regulation plays an important role in cardiac pathological remodeling. Mechanistically, we have validated that Upf1 interacts directly with RBFox1, a cardiac enriched RNA binding protein, using targeted co-IP analysis and proximity ligation assay, and this interaction is disrupted upon hypertrophy stimulation. Lastly, we found that RBFox1 could provide target specificity in this novel Upf1 dependent, yet NMD independent RNA decay during cardiac hypertrophy.
In summary, we have identified a global shift of mRNA stability in stressed myocytes regulated by Upf1-RBFox1 complex, targeted manipulation of the stress regulated mRNA stability could potentially provide new therapeutic targets for cardiac disease.