Pro-Fibrotic Role of the A2B Adenosine Receptor in Human Cardiac Fibroblasts

Abstract

Background and Aims: Adenosine is a signaling nucleoside and the interstitial levels of this nucleoside are elevated in certain pathophysiological conditions. Results of our previous studies suggest that adenosine play an important role in pulmonary fibrosis. The goal of the current study is to determine the potential role of adenosine and its receptor subtypes in cardiac fibrosis using the primary human cardiac fibroblasts (HCF) as a model system. Methods: Expression of adenosine receptors (AdoR), a-smooth muscle actin and a-1 pro-collagen was determined using real-time RT-PCR. The concentrations of IL-6, soluble ST-2 and PAPPA in the cell supernatants were measured using ELISA. The concentration of soluble collagen was determined using Sircol collagen assay. Results: Among the four subtypes of AdoRs, the A2B AdoR was expressed at the highest level in HCF. NECA, a stable analog of adenosine, significantly increased the release of IL-6 in a concentration-dependent manner, with a maximal increase of 2.4 6 0.1 fold over the basal level. In addition, NECA (10mM) increased the expression of a-smooth muscle actin and a-1 pro-collagen, and the production of collagen (1.8 6 0.1 fold induction, from 3.4 6 0.2 to 6.0 6 0.4 mg/ml, p!0.05) from HCF. Furthermore, NECA increased the release of two novel biomarkers of cardiovascular diseases (CVD), soluble ST-2 (1.7 6 0.1 fold induction, from 1.5 6 0.1 to 2.6 6 0.1 ng/ml, p!0.05) and PAPPA (4.46 0.6 fold induction, from 1.46 0.5 to 6.26 0.8 ng/ml, p!0.05). The effects of NECA on release of IL-6, collagen, ST-2, and PAPPA and expression of a-smooth muscle actin and a-1 pro-collagen were completely abolished by a selective A2B AdoR antagonist, GS-6201. Conclusions: This study indicates that the A2B AdoR is the predominant subtype of AdoRs expressed in primary human HCF. Activation of this receptor increases the release of IL-6, production of collagen, expression of fibrotic markers and release of biomarkers of CVD. These findings suggest that A2B AdoR might mediate the fibrotic response in heart diseases.