Anti-β1-adrenergic receptor autoantibodies are potent stimulators of the ERK1/2 pathway in cardiac cells

Objective: Antibodies specific for the beta 1-adrenergic receptor (beta 1AR) are highly prevalent in patients with idiopathic dilated cardiomyopathy (DCM) and known to contribute to the pathogenesis of heart failure, though the precise molecular mechanisms involved are largely unknown. Methods: We have explored the effects of beta(1)AR autoantibodies obtained from DCM patients on extracellular signal-regulated kinase (ERK) activation in murine cardiomyocytes. Results: We find that human beta(1)AR autoantibodies potently stimulate ERK1/2 in cardiac cells by using signalling pathways different from those triggered by the classic beta-agonist isoproterenol, also leading to a different pattern of activated ERK subcellular localization. The extent of ERK stimulation by endogenous cardiac beta(1)AR is markedly enhanced in the presence of both beta(1)AR-autoantibodies and isoproterenol. Interestingly, beta(1)AR-autoantibody-mediated ERK activation is not blocked by some beta AR antagonists used in the treatment of heart failure. Conclusions: Our results suggest that these antibodies elicit a distinct beta(1)AR active conformation that would lead to the engagement of signaling effectors different from those recruited by classic beta-agonists, a finding that could lead to better understanding of DCM pathogenesis and aid in designing diagnostic and therapeutic strategies. (C) 2007 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.