Relaxin modulates cardiac fibroblast proliferation, differentiation, and collagen production and reverses cardiac fibrosis in vivo

Abstract

Cardiac fibrosis is a key component of heart disease and involves the proliferation and differentiation of matrix-producing fibroblasts. The effects of an antifibrotic peptide hormone, relaxin, in inhibiting this process were investigated. We used rat atrial and ventricular fibroblasts, which respond to pr-fibrotic stimuli and express the relaxin receptor (LGR7), in addition to two in vivo models of cardiac fibrosis. Cardiac fibroblasts, when plated at low density or stimulated with TGF-β or angiotensin II (Ang II), accelerated fibroblast differentiation into myofibroblasts, as demonstrated by significantly increased α-smooth muscle actin expression, collagen synthesis, and collagen deposition (by up to 95% with TGF-β and 40% with Ang II; all P < 0.05). Fibroblast proliferation was significantly increased by 10 -8 M and 10-7 M Ang II (63-75%; P < 0.01) or 0.1-1 μg/ml IGF-I (27-40%; P < 0.05). Relaxin alone had no marked effect on these parameters, but it significantly inhibited Ang II- and IGF-I-mediated fibroblast proliferation (by 15-50%) and Ang II- and TGF-β-mediateci fibroblast differentiation, as detected by decreased expression of α-smooth muscle actin (by 65-88%) and collagen (by 60-80%). Relaxin also increased matrix metalloproteinase-2 expression in the presence of TGF-β (P < 0.01) and Ang II (P < 0.05). Furthermore, relaxin decreased collagen overexpression when administered to two models of established fibrotic cardiomyopathy, one due to relaxin deficiency (by 40%; P < 0.05) and the other to cardiac-restricted overexpression of β2-adrenergic receptors (by 58%; P < 0.01). These coherent findings indicate that relaxin regulates fibroblast proliferation, differentiation, and collagen deposition and may have therapeutic potential in diseased states characterized by cardiac fibrosis.