PKA-mediated BMAL1 phosphorylation promotes β(1)-adrenoceptor autoantibody-induced cardiomyocyte death.

As a core circadian transcription factor, BMAL1 orchestrates cardiovascular homeostasis. However, whether β(1)-adrenoceptor autoantibody (β(1)-AA) promotes abnormal BMAL1 expression and accelerates cardiomyocyte death remains unclear. This study reveals the role and mechanism of BMAL1 phosphorylation in cardiomyocyte death induced by β(1)-AA. We demonstrated that β(1)-AA disrupted the rhythmic expression of BMAL1 in myocardial tissue and H9c2 cells, specifically upregulating BMAL1 at CT8. Bmal1 knockdown did not reverse the β(1)-AA-induced reduction in cell viability. Furthermore, β(1)-AA increased BMAL1 phosphorylation at Ser42, leading to its cytoplasmic accumulation. The dephosphorylation-mimic BMAL1 mutant (S42A) significantly alleviated the upregulation of cytoplasmic BMAL1, the downregulation of Per2 and Nr1d1 mRNA levels, and the reduction in cell viability induced by β(1)-AA. Additionally, BMAL1 phosphorylation was reversed by inhibiting PKA activity. These findings indicate that β(1)-AA promotes BMAL1 phosphorylation at Ser42 via PKA activation, resulting in cytoplasmic accumulation of BMAL1, suppression of Per2 and Nr1d1 transcription, and ultimately cardiomyocyte death.