Pro-apoptotic effects of anti-β₁-adrenergic receptor antibodies in cultured rat cardiomyocytes: Actions on endoplasmic reticulum and the prosurvival PI3K-Akt pathway

An anti-beta(1)-adrenergic receptor antibody against the second extracellular receptor loop (beta(1)-EC(II)) has been shown to cause myocyte apoptosis and dilated cardiomyopathy in animals. We report in this review that the anti-beta(1)-EC(II) antibody increases intracellular Ca(++) transients and exerts a direct apoptotic effect in cultured neonatal rat cardiomyocytes. Both Fab and Fc fragments are required for the full expression of the apoptotic effects of the anti-beta(1)-EC(II) antibody. Our studies further suggest that the anti-beta(1)-EC(II)-antibody acts primarily on the cardiac beta(1)-adrenergic receptor and its post-receptor activation of Ca(++)/Calmodulin dependent protein kinase II (CaMKII) and p-38 mitogen-activated protein kinase (MAPK), leading to endoplasmic reticulum stress as evidenced by the increased expressions of GRP78 and CHOP, as well as the increased processing of the initiator procaspase-12. Also, observed with the apoptotic effect of anti-beta(1)-EC(II) antibody is reduced activity of the phosphatidylinositol (PI) 3-kinase/Akt/STAT3 signaling pathway. Our results suggest that agents that block the activation of p38-MAPK/endoplasmic reticulum stress or reverse the suppression of the prosurvival PI3K/Akt/STAT3 pathway may be explored as potential novel therapeutic modalities in the treatment of dilated cardiomyopathy.