β₃-adrenergic receptor activation induces TGFβ1 expression in cardiomyocytes via the PKG/JNK/c-Jun pathway

In heart failure, the expression of cardiac β₃-adrenergic receptors (β₃-ARs) increases. However, the precise role of β₃-AR signaling within cardiomyocytes remains unclear. Transforming growth factor β1 (TGFβ1) is a crucial cytokine mediating the cardiac remodeling that plays a causal role in the progression of heart failure. Here, we set out to determine the effect of β₃-AR activation on TGFβ1 expression in rat cardiomyocytes and examine the underlying mechanism. The selective β₃-AR agonist BRL37344 induced an increase in TGFβ1 expression and the phosphorylation of c-Jun N-terminal kinase (JNK) and c-Jun in β₃-AR-overexpressing cardiomyocytes. Those effects of BRL37344 were suppressed by a β₃-AR antagonist. Moreover, the inhibition of JNK and c-Jun activity by a JNK inhibitor and c-Jun siRNA blocked the increase in TGFβ1 expression upon β₃-AR activation. A protein kinase G (PKG) inhibitor also attenuated β₃-AR-agonist-induced TGFβ1 expression and the phosphorylation of JNK and c-Jun. In conclusion, the β₃-AR activation in cardiomyocytes increases the expression of TGFβ1 via the PKG/JNK/c-Jun pathway. These results help us further understand the role of β₃-AR signaling in heart failure.