β2-adrenergic stimulation induces interleukin-6 by increasing Arid5a, a stabilizer of mRNA, through cAMP/PKA/CREB pathway in cardiac fibroblasts.

BACKGROUND AND PURPOSE

In cardiovascular diseases, cardiac fibroblasts (CFs) participate in the myocardial inflammation by producing pro-inflammatory cytokines, worsening the prognosis. β2-adrenergic receptor (AR) and β3AR are expressed in CFs, and β-adrenergic stimulation promotes CFs to produce pro-inflammatory cytokines. However, the mechanism of the expression of pro-inflammatory cytokines in response to β-adrenergic stimulation remains to be fully elucidated.

EXPERIMENTAL APPROACH

CFs were isolated from adult wild-type or AT-rich interactive domain-containing protein 5A (Arid5a) knockout mice. The expression of mRNA was measured by real-time RT-PCR. Interleukin (IL)-6 protein was measured by ELISA. The activity of nuclear factor-κB (NF-κB) and cyclic AMP (cAMP) response element binding protein (CREB) was assessed by ELISA-like assay or Western blotting.

KEY RESULTS

The β-adrenergic stimulation remarkably induced IL-6 mRNA and protein through β2AR in CFs. The activation of adenylate cyclase and the enhancement of intracellular cAMP resulted in the upregulation of IL-6 mRNA expression. The induction of IL-6 transcript by β2AR signaling was independent of NF-κB. Concomitant with IL-6, the expression of Arid5a, an IL-6 mRNA stabilizing factor, was enhanced by β2-adrenergic stimulation and by cAMP increase. Importantly, β2AR signaling-mediated IL-6 induction was suppressed in Arid5a knockout CFs. Finally, β2AR stimulation phosphorylated CREB via PKA pathway, and the activation of CREB was essential for the induction of Arid5a and IL-6 mRNA.

CONCLUSION AND IMPLICATIONS

β2-adrenergic stimulation post-transcriptionally upregulates the expression of IL-6 by the induction of Arid5a through cAMP/PKA/CREB pathway in adult CFs. β2AR/Arid5a/IL-6 axis could be a therapeutic target against cardiac inflammation.