Abstract 13837: Adrenergic Receptors β2 and β3 Transduce Differential Signals in Cardiac Fibroblasts

Abstract

Background: Cardiac fibroblasts (CFs) are the most prevalent cell types in heart and play important roles in cardiac remodeling. While the roles of β-adrenergic receptor (βAR) signaling in cardiomyocytes (CMs) are well characterized, those in CFs remain to be elusive due to lack of convenient method to assess those signaling. There are three subtypes of, βAR β1, β2, β3 and β2AR is reported to be expressed in CFs by which enhances cell proliferation and production of inflammatory cytokines. Clinical efficacy of non-selective β blocker carvedilol for heart failure (HF) surpasses that of β1 selective blocker metoprolol, suggesting critical roles of β2 and β3AR in the pathogenesis of HF. Objective: To elucidate the signaling downstream βARs in CFs in heart. Methods and Results: Caveolae is an important microdomain for signal transduction, such as βAR, present in CMs or CFs. To elucidate βAR signaling of caveolae in CFs, we generated a fusion protein composed of phospholamban (PLN) and caveolin3 (Cav3) representing PKA activation as phosphorylation at S16 of PLN and CaMKII as that at T17 in caveolae. Thus, activation of PKA or CaMKII is detectable by anti-phospho-S16 or T17 antibody, respectively. In neonatal rat CFs (NRCFs) infected PLN-Cav3 adenovirus, stimulation by isoproterenol (ISO) led to enhanced phosphorylation of both S16 and T17, suggesting PKA and CaMKII activation in caveolae of CFs. RT-PCR analyses showed β2AR and β3AR were present in NRCFs. Stimulation with β2AR selective agonists activated both PKA and CaMKII, while β3AR elicited solely PKA activation, analyzed by using β3AR selective agonist/antagonist. In addition, in order to examine the significance of βAR stimulation for heart failure, we administered ISO continuously for two weeks in β2ARKO mice. As a result, fibrosis was suppressed in β2ARKO mice compared with wild-type mice (0.35% vs 2.37%, p<0.05) suggesting critical roles of β2AR in development of cardiac fibrosis caused by βAR stimulation in mice. Conclusions: Both β2 and β3AR are expressed in NRCFs and transduce distinct signaling and β2AR selective stimulation elicit development of cardiac fibrosis via activation of CaMKII signaling. Thus, selective βAR regulation could be potential novel anti-fibrotic therapeutics in HF.