LAUSR

BACKGROUND We reported 3 novel non-synonymous single-nucleotide variants of Bcl2-associated athanogene 3 (BAG3) in African Americans with heart failure (HF) which are associated with 2-fold increase in cardiac events (HF hospitalization, heart transplant or death). METHODS We expressed BAG3 variants (P63A, P380S and A479V) via adenovirus-mediated gene transfer in adult left ventricular myocytes isolated from either wild-type (WT) or cardiac-specific BAG3 haplo-insufficient (cBAG3+/-) mice: the latter to simulate the clinical situation in which BAG3 variants are only found on one allele. RESULTS Compared to WT myocytes, cBAG3+/- myocytes expressed ∼50% of endogenous BAG3 levels and exhibited decreased [Ca2+]i and contraction amplitudes after isoproterenol due to reduced L-type Ca2+ current. BAG3 repletion with WT BAG3 but not P380S, A479V or P63A/P380S variants restored contraction amplitudes in cBAG3+/- myocytes to those measured in WT myocytes, suggesting excitation-contraction (EC) abnormalities partly account for HF in patients harboring these mutants. Since P63A is near the WW domain (residues 21-55) and A479V is in the BAG domain (residues 420-499), we expressed BAG3 deletion mutants (Δ1-61 and Δ421-575) in WT myocytes and demonstrated that the BAG but not the WW domain was involved in enhancement of EC by isoproterenol. CONCLUSION The BAG3 variants contribute to heart failure in African American patients partly by reducing myocyte excitation-contraction under stress, and that both the BAG and PXXP domains are involved in mediating β-adrenergic responsiveness in myocytes.