Abstract Body: Autoimmune responses targeting β1-adrenergic receptor (β1AR) leading to the production of autoantibodies (AAbs) are implicated in the pathogenesis of dilated cardiomyopathy (DCM). However, our recent studies indicate that β1AR AAbs of the IgG3 subclass (IgG3(+) β1AR AAbs) are associated with beneficial outcomes in patients which facilitate a uniquely biased β1AR signaling in response to β-blockers, distinguishing them from other subclasses. Understanding the mechanistic basis of this signaling pathway is critical for developing effective therapeutic strategies. Our findings reveal that phosphorylation of β1AR is significantly increased in response to IgG3(−) AAbs but remains unchanged with IgG3(+) AAbs. To further dissect the signaling pathway mediated by AAbs, HEK-β1AR cells were treated with human sera containing either IgG3(+) or IgG3(−) β1AR AAbs, followed by immunoprecipitation of β1AR and crosslinking mass spectrometry (XL-MS) analysis. This approach identified Insulin Receptor Substrate 4 (IRS-4) as a key differentially recruited signaling molecule. Further immunoprecipitation and western blot analysis demonstrated that IgG3(−) AAbs stabilize the β1AR-IRS-4 interaction, leading to increased IRS-4 phosphorylation. This, in turn, activates the PI3K-AKT signaling pathway, promoting GLUT-4 translocation to the plasma membrane and enhancing glucose uptake contrary to the IgG3(+) AAbs. Additionally, IRS-4 knockdown experiments established that IRS-4 is essential for AAb-mediated PI3K-AKT activation and GLUT-4 translocation. These findings suggest that β1AR autoantibodies influence not only cardiovascular function but also metabolic pathways, potentially playing a role in glucose homeostasis and insulin sensitivity. This study underscores the need for further research into β1AR AAb-targeted therapies for metabolic disorders associated with cardiovascular disease.

Keywords: Autoantibody, β1-adrenergic receptor (β1AR), IgG3, insulin receptor substrate 4 (IRS-4), PI3K-AKT signaling, glucose uptake