Abstract 240: Predictive and Experimental Modeling of Bag3-associated Cardiomyocyte Dysfunction

• Published in: Circulation research 2018-08, Vol.123 (Suppl_1)
• Main Authors: McDermott-Roe, Christopher, Lv, Wenjian, Shehu, Amarda, Benjamin, Ivor, Geurts, Aron, Musunuru, Kiran
• Format: Article
• Language: English
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/res.123.suppl_1.240

Abstract only High throughput sequencing continues to uncover novel potentially pathogenic variants in cases of familial cardiomyopathy. Clinical interpretation of such variants is challenging, and hence definitive assignment of causality frequently remains unestablished. A case in point is provided by BAG3, a critical regulator of protein quality control in cardiomyocytes, which has been recurrently linked to dilated cardiomyopathy (DCM). Using theoretical and experimental approaches, we assessed the impact of a functionally-uncharacterized DCM-associated variant in BAG3 (c.1430G>A; p.Arg477His). Molecular dynamics simulations of wildtype and mutant forms of BAG3 suggested the residue substitution perturbs a crucial interaction between BAG3 and HSC70 by altering electrostatic field distribution, conformational rigidity and side-chain orientation. Acute and stable expression of the mutant BAG3 protein led to reduced HSC70 engagement and protein aggregation in HEK293 and HL1 cells. Using the CRISPR-Cas9 system, we then introduced the variant into a healthy induced pluripotent stem cell line line and upon differentiation into cardiomyocytes, observed protein aggregation and a sensitivity to pro-apoptotic stressors. In conclusion, disease-in-a-dish modeling was used to study the molecular and cellular consequences of a potentially pathogenic BAG3 variant. We define what we believe is the primary molecular lesion and propose ectopic protein quality control and potentiated stress sensitivity as possible pathogenic drivers and potential therapeutic entry points.