UCLA

During cardiac development and pathological remodeling, there is a transcriptome maturation and remodeling event well established at transcription level. However, with high-throughput sequencing technology, we are able to obtain a more comprehensive understanding of the real transcriptome complexity at single base resolution. In order to understand the cardiac transcriptome complexity and dynamics during normal and disease conditions, we performed deep RNA- Sequencing on pressured overload induced mouse failing hearts and compared with sham operated control hearts. From this study, we have identified a significant number of genes undergo alternative splicing during heart disease. We have also provided evidence there is a large number of previously un-annotated novel splicing variants, lncRNA and novel transcript clusters, some of these could have potential impact on cardiac disease.

From the sequencing analysis, we chose to carry out detailed characterization of a novel cardiac specific splicing variant in PKCalpha;. Both biochemistry and cell

studies suggested this novel splicing variant has significant higher auto- phosphorylation level at baseline but has different activation profile responding to hypertrophic stimuli. This is potentially due to this novel PKCalpha; splicing variant has unique interacting partner and downstream target. We further demonstrated that, the alternative splicing of this novel PKCalpha; variant is, at least partially regulated by RBFox1.

RNA splicing contributes significantly to total transcriptome complexity but its functional role and regulation in cardiac development and diseases remain poorly understood. Based on total transcriptome analysis, we identified a significant number of alternative RNA splicing events in mouse failing hearts that resembled the pattern in fetal hearts. A muscle specific isoform of an RNA splicing regulator RBFox1 (A2BP1) is induced during cardiac development. Inactivation of zRBFox1 gene in zebrafish led to lethal phenotype associated with impaired cardiac function. RBFox1 regulates alternative splicing of transcription factor MEF2s, producing splicing variants with distinct transcriptional activities and different impact on cardiac development. RBFox1 expression is diminished in mouse and human failing hearts. Restoring RBFox1 expression significantly attenuates hypertrophy and heart failure induced by pressure-overload in mice. Therefore, RBFox1-MEF2 represents a previously uncharacterized regulatory circuit in cardiac transcriptional network with important impact on both cardiac development and diseases.