Abstract 15137: β2-adrenergic Signaling Promotes IL-6 Production From Cardiac Fibroblasts Through CREB/Arid5a Pathway and Induces Cardiac Hypertrophy via Paracrine System

Abstract

Background: β-adrenergic receptor (βAR) is involved in cardiac inflammation and hypertrophy. It has been revealed that βAR stimulation induces cardiac hypertrophy not only directly but also indirectly, for example, via cardiac fibroblasts (CFs). Interestingly, βAR signaling promotes the production of interleukin (IL)-6 from CFs. However, it has not been clarified the relationship between IL-6 released from CFs and cardiac hypertrophy after βAR stimulation. Objective: To elucidate the mechanisms by which βAR signaling promotes the production of IL-6 in CFs and the effects of CFs-secreted IL-6 on cardiac hypertrophy. Methods: CFs were isolated from adult mice. The expression of mRNA was measured by quantitative RT-PCR and the secretion of IL-6 into the medium was quantified by ELISA. Cardiac hypertrophy was assessed by echocardiography, cross-sectional area or cell surface area of cardiomyocytes. Results: RT-PCR revealed that β2AR and β3AR, but not β1AR, were mainly expressed in CFs. Salbutamol (SAL), a selective β2AR agonist, increased IL-6 mRNA by 20-fold, whereas CL-316243, a selective β3AR agonist, did only negligibly. Moreover, SAL, not CL-31243, upregulated the mRNA expression of AT-rich interaction domain 5A (Arid5a), an IL-6 mRNA stabilizing factor, by 4 times. CFs from Arid5a -null mice exhibited reduced expression of IL-6 mRNA and protein, compared with wild-type (WT) CFs, with or without SAL. SAL phosphorylated CREB, suggesting that SAL activated CREB pathway. The compound 666-15, a CREB inhibitor, suppressed SAL-induced IL-6 and Arid5a upregulation. Importantly, WT and IL-6 -null mice were continuously treated with isoproterenol (ISO), a non-selective βAR agonist, for 2 weeks. Cardiac dilatation and cardiomyocyte enlargement were induced by chronic ISO treatment in WT mice, but to lesser extent in IL-6 -null mice. Finally, conditioned media from WT CFs treated with ISO enlarged cultured neonatal rat cardiomyocytes by 10%, while not those from IL-6 -null CFs. Conclusion: β2AR signaling induced IL-6 via CREB/Arid5a axis in CFs. Moreover, CFs-secreted IL-6 contributed to the enlargement of cardiomyocytes through paracrine signaling. β2AR signaling in CFs could be a therapeutic target against cardiac hypertrophy.