Abstract 240: Asb2-dependent Proteolysis of the Cytoskeleton Directs Cardiac Development and Disease

Abstract

Congenital heart diseases (CHDs) account for 25% of birth defects and are major risk factors for adult cardiovascular problems. Partial disease penetrance is seen even in autosomal dominant disorders and genotype/phenotype correlations remain a clinical challenge; thus, the need to understand different regulators of cardiac formation. The Ubiquitin-Proteasome System (UPS) is important in controlling protein turnover during organ development but its role in the mammalian heart remains ambiguous. We have identified a specificity subunit of ubiquitin-mediated proteolysis (Asb2) as being specific for the cardiac myogenic lineage. Asb2 was previously shown to regulate hematopoietic and skeletal muscle cell differentiation through targeting filamin proteins (FlnA, B and C), actin-binding proteins important for cytoskeleton stabilization. In our present study, we show that Asb2 is markedly enriched in myocardial progenitor cells and cardiomyocytes. To investigate the role of Asb2 and UPS dependent proteolysis in heart development, we generated two cardiac-specific murine knockouts (KOs): Nkx Cre .Asb2 -/- and Mef2c Cre .Asb2 -/- (deleting Asb2 in early cardiomyocyte progenitors and anterior heart field progenitors, respectively). Both KOs are embryonic lethal with pericardial edema. We used tissue clarifying and confocal microscopy to define the morphological defects of the Asb2 null heart. Moreover, we found that FlnA is overexpressed in the hearts of these mice and its deletion therein partially rescues their lethality. In addition, using transcriptomic analysis on Asb2-null e9.5 hearts, we identified novel potential Asb2 targets in the heart. Finally, to understand the role of Asb2 in the differentiation and function of human cardiomyocytes, we used CRISPR/Cas9 genome editing technique to generate Asb2-null human induced pluripotent stem cells. Collectively, our study provides a novel mechanistic understanding of the role of the UPS proteasome in cardiac development, myocardial function, and disease pathogenesis. Given recent interests in both the UPS and the cytoskeleton as therapeutic targets, our study provides an innovative platform for the development of pharmacotherapy for cardiac disease.