Alternative Protein Isoforms in Ventricular Remodeling

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PROJECT SUMMARY Cardiac hypertrophy and failure involve a rewiring of gene expression through alternative splicing, but it remains unclear which splicing changes are relevant to disease development, and how splice variants affect protein function. Although many alternative transcript isoforms have been discovered, not all are translated into proteins and instead may be degraded via non-sense mediated decay or co-translational protein quality control. Proteomics methods that can identify and quantitate splice variant proteins empirically and on a large scale provide essential tools to study how alternative splicing regulates cardiac gene expression. We and others showed that tissue-specific splice variant proteins may be identified using a combined RNA sequencing and mass spectrometry approach. Accordingly, our goal here is to examine the mechanisms by which alternative splicing regulates the genetic program in hypertrophic and failing hearts, by identifying the proteins and pathways that are coordinately regulated by splicing, the resulting complement of protein isoform species (`proteoforms') in the heart, and the consequences of proteoform sequences on protein structure and function. Specifically, we plan to: (1) apply a quantitative RNA-guided proteomics framework to identify key isoform switches at the transcript and the protein level, with emphasis on the changes in splice factors and RNA-binding proteins in mouse models of systolic and diastolic dysfunction; (2) combine RNA-guided proteomics and proteome-wide biophysics approaches, we will interrogate the impact of splice variants on protein structure and thermal stability, and discover significant isoforms through alternative splicing, intrinsically disordered, and regulatory post-translational modification modules. We anticipate the successful completion of these aims will generate new conceptual insights into how alternative splicing regulatory networks reprogram the cardiac proteome in pathological remodeling and heart failure, and more generally, contribute to methods and concepts to elucidate the regulation and function of alternative splicing in the heart.