Chronic beta2-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.


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 beta(2)-AR subtype coupled to activation of adenylyl cyclase and p44/42 mitogen-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 micromol/l. This increased proliferation was inhibited by the beta(2)-AR-selective antagonist ICI-118,551, but not the beta(1)-AR-selective antagonist atenolol. Direct activation of adenylyl cyclase alone (0.1-10 micromol/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(2)-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.
Turner
Neil A
NA
Integrated Molecular Cardiology Group, Institute for Cardiovascular Research, Worsley Building, University of Leeds, UK. cvsnat@leeds.ac.uk
Porter
Karen E
KE
Smith
William H T
WH
White
Hazel L
HL
Ball
Stephen G
SG
Balmforth
Anthony J
AJ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D019898:Autocrine Communication / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000166:cytology* / Q000187:drug effects; D006325:Heart Atria / Q000166:cytology / Q000378:metabolism; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism; D011412:Propanolamines / Q000494:pharmacology; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D018343:Receptors, Adrenergic, beta-2; C026777:ICI 118551; D000242:Cyclic AMP; D020928:Mitogen-Activated Protein Kinases; D007545:Isoproterenol