Chronic β2-adrenergic receptor stimulation increases proliferation of human cardiac fibroblasts via an autocrine mechanism

Objective: The aim of this Study was to determine whether chronic beta-adrenergic receptor (beta-AR) stimulation induces proliferation of human cardiac fibroblasts and to investigate the mechanism(s) involved. Methods and results: In vitro cultures of human cardiac fibroblasts were established from biopsies of right atrial appendage. RT-PCR analysis and pharmacological studies demonstrated that these cells express predominantly the P,-AR Subtype Coupled to activation of adenylyl cyclase and p44/42 initogen-activated protein kinase (MAPK). Proliferation was determined by cell Counting over a 6-day period in medium containing 2.5% fetal calf serum (Control) or supplemented with the non-selective beta-AR agonist isoproterenol (ISO). ISO induced a concentration-dependent increase in cardiac fibroblast proliferation, which was maximal at 1 mumol/l. This increased proliferation was inhibited by the beta(2)-AR-selective antagonist ICI-118.551, but not the beta(1)-AR-selcctive antagonist atenolol. Direct activation of adenylyl cyclasc alone (0.1 - 10 mumol/l forskolin) stimulated cyclic AMP production and MAPK activation, but did not induce cell proliferation. Since catecholamines are not considered to be 'classical' growth factors. we subsequently investigated whether beta-AR stimulation results in secretion of growth factors that are able to stimulate proliferation in an autocrine manner. Conditioned medium obtained from cardiac fibroblasts treated with ISO for 48 h increased proliferation of parallel cultures of fibroblasts in the presence of the beta-AR antagonist alprenolol. Heat-treatment of this conditioned medium fully prevented the increase in cell proliferation, indicating that the autocrine factor(s) are heat-sensitive proteins. Conclusions: Chronic beta(2)-AR stimulation increases proliferation of human cardiac fibroblasts via a mechanism involving increased secretion of heat-sensitive growth factors. (C) 2003 European Society of Cardiology. Published by Elsevier Science B.V. All rights reserved.