Biased activation of β 2 -AR/Gi/GRK2 signal pathway attenuated β 1 -AR sustained activation induced by β 1 -adrenergic receptor autoantibody

Heart failure is the terminal stage of many cardiac diseases, in which β 1 -adrenoceptor (β 1 -AR) autoantibody (β 1 -AA) has a causative role. By continuously activating β 1 -AR, β 1 -AA can induce cytotoxicity, leading to cardiomyocyte apoptosis and heart dysfunction. However, the mechanism underlying the persistent activation of β 1 -AR by β 1 -AA is not fully understood. Receptor endocytosis has a critical role in terminating signals over time. β 2 -adrenoceptor (β 2 -AR) is involved in the regulation of β 1 -AR signaling. This research aimed to clarify the mechanism of the β 1 -AA-induced sustained activation of β 1 -AR and explore the role of the β 2 -AR/Gi-signaling pathway in this process. The beating frequency of neonatal rat cardiomyocytes, cyclic adenosine monophosphate content, and intracellular Ca 2+ levels were examined to detect the activation of β 1 -AA. Total internal reflection fluorescence microscopy was used to detect the endocytosis of β 1 -AR. ICI118551 was used to assess β 2 -AR/Gi function in β 1 -AR sustained activation induced by β 1 -AA in vitro and in vivo. Monoclonal β 1 -AA derived from a mouse hybridoma could continuously activate β 1 -AR. β 1 -AA-restricted β 1 -AR endocytosis, which was reversed by overexpressing the endocytosis scaffold protein β-arrestin1/2, resulting in the cessation of β 1 -AR signaling. β 2 -AR could promote β 1 -AR endocytosis, as demonstrated by overexpressing/interfering with β 2 -AR in HL-1 cells, whereas β 1 -AA inhibited the binding of β 2 -AR to β 1 -AR, as determined by surface plasmon resonance. ICI118551 biasedly activated the β 2 -AR/Gi/G protein-coupled receptor kinase 2 (GRK2) pathway, leading to the arrest of limited endocytosis and continuous activation of β 1 -AR by β 1 -AA in vitro. In vivo, ICI118551 treatment attenuated myocardial fiber rupture and left ventricular dysfunction in β 1 -AA-positive mice. This study showed that β 1 -AA continuously activated β 1 -AR by inhibiting receptor endocytosis. Biased activation of the β 2 -AR/Gi/GRK2 signaling pathway could promote β 1 -AR endocytosis restricted by β 1 -AA, terminate signal transduction, and alleviate heart damage.