Adenosine receptor activation induces vascular endothelial growth factor in human retinal endothelial cells

Adenosine, released in increased amounts by hypoxic tissues, is thought to be an angiogenic factor that links altered cellular metabolism caused by ox ygen deprivation to compensatory angiogenesis. Adenosine interacts with 4 s ubtypes of G protein-coupled receptors, termed A(1), A(2A), A(2B), and A(3) . We investigated whether adenosine causes proliferation of human retinal e ndothelial cells (HRECs) and synthesis of vascular endothelial growth facto r (VEGF) and, if so, which adenosine receptor subtype mediates these effect s. The nonselective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosi ne (NECA), in a concentration-dependent manner, increased both VEGF mRNA an d protein expression by HRECs, as well as proliferation. This proliferative effect of NECA was inhibited by the addition of anti-human VEGF antibody. NECA also increased insulin-like growth factor-I and basic fibroblast growt h factor mRNA expression in a time-dependent manner and cAMP accumulation i n these cells. In contrast, neither the A(1) agonist N-6-cyclopentyladenosi ne nor the A(2A) agonist 2-p-(2-carboxyethyl) phenethylamino-NECA caused an y of the above effects of NECA, The effects of NECA were not significantly attenuated by either the A(2A) antagonist SCH58261 or the A(1) antagonist 8 -cyclopentyl-1,3-dipropylxanthine. However, the nonselective adenosine rece ptor antagonist xanthine amine congener completely inhibited the effects of NECA, Addition of antisense oligonucleotide complementary to A(2B) adenosi ne receptor mRNA inhibited VEGF protein production by HRECs after NECA stim ulation. Thus, the A(2B) adenosine receptor subtype appears to mediate the actions of adenosine to increase growth factor production, cAMP content, an d cell proliferation of HRECs. Adenosine activates the A(2B) adenosine rece ptor in HRECs, which may lead to neovascularization by a mechanism involvin g increased angiogenic growth factor expression.