Abstract 173: Expanded Role for Thrombin/PAR1 Signaling in Cardiac Fibroblast Activation

Abstract

Cardiac fibrosis is a feature of numerous types of heart disease that lead to disability and death and is characterized by the transformation of cardiac fibroblasts (CFs) to myofibroblasts (myofibs) that synthesize and release large amounts of collagen-rich extracellular matrix (ECM), thereby resulting in reduced cardiac function and eventually heart failure. CFs are the most abundant cell type in the heart and regulate the production of ECM as a normal part of wound repair but disease can result if CFs become overactive, at least in part by increased transformation to myofibs. Cardiac fibrosis can occur spontaneously in advanced age, after acute injury (e.g., myocardial infarction) and in disease states (e.g., diabetes mellitus and heart failure). We sought to identify novel therapeutic targets for cardiac fibrosis by using an unbiased approach (RT-PCR array) to define the most abundantly expressed G protein-coupled receptors (GPCRs) predicted to regulate the CF/myofib transformation. Certain GPCRs, e.g. angiotensin and endothelin receptors, can promote cardiac fibrosis but few others are known to do this. We hypothesized that previously unrecognized GPCRs play an important role in regulating the function of CFs. Using the RT-PCR GPCR array, we found that the protease-activated receptor 1 (PAR1) is the most abundant GPCR in adult rat CFs (rCFs). Thrombin activation of PAR1 in rCFs elevates (with distinct kinetics) the expression of a variety of pro-fibrotic markers, induces morphological changes to the myofib phenotype and stimulates synthesis of collagen, the primary ECM component without affecting cell proliferation. The thrombin-induced initiation of a proliferation-independent pro-fibrotic response in adult rCFs contrasts with effects of thrombin in neonatal rCFs, suggesting a differential wound repair response in the adult versus the still-developing heart. By defining the level of expression of GPCRs in rCFs and revealing an expanded role for PAR1 in the wound repair response of the heart, the data provide a proof-of-principle that our approach can identify novel functional and disease-relevant GPCRs in CFs-- and likely in other cardiovascular cells as well.