Adenosine A2A Receptor Stimulation Increases Angiogenesis by Down-Regulating Production of the Antiangiogenic Matrix Protein Thrombospondin 1
Abstract
Abstract Topical adenosine A 2A receptor agonists promote wound healing by, among other effects, increasing microvessel formation. Results of representational display analysis of human umbilical vein endothelial cells suggested that A 2A receptor occupancy modulates expression of the antiangiogenic matrix protein thrombospondin 1 (TSP1). We therefore determined whether A 2A receptor occupation stimulates angiogenesis by modulating TSP1 secretion. Human microvascular endothelial cells (HMVEC) were treated with medium alone, 2- p -2-carboxyethyl phenethyl-amino-5′- N -ethylcarboxamido-adenosine (CGS-21680), or 2-2-(4-chlorophenyl)ethoxyadenosine (MRE0094), selective A 2A receptor agonists. TSP1 protein secretion was down-regulated after treatment with the A 2A agonists CGS-21680 or MRE0094 in a dose-dependent manner (EC 50 = 6.65 nM and 0.23 μM respectively). The selective A 2A receptor antagonist 4-{2-7-amino-2-(2-furyl)1,2,4triazolo-2,3- a 1,3,5triazin-5-ylaminoethyl}phenol (ZM241385) but not the A1 and A 2B receptor antagonists diphenylcyclopentylxanthine, enprofylline, and N -(4-acetylphenyl)-2-4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1 H -purin-8-yl)phenoxyacetamide (MRS1706) completely abrogated the A 2A receptor agonist-mediated effect on TSP1. Vascular tube formation by HMVEC was increased by adenosine A 2A receptor agonists in a dose-dependent fashion (EC 50 = 0.1 μM for both), and this effect was reversed by the A 2A antagonist. Moreover, in the presence of antibodies to TSP1 and CD36, the receptor for TSP1, the adenosine A 2A receptor agonists stimulated no increase in vascular tube formation. These results indicate that the angiogenic effects of adenosine A 2A receptor activation are, at least in part, caused by the suppression of TSP1 secretion.