Functional effects of enhancing or silencing adenosine A2b receptors in cardiac fibroblasts

Cardiac fibroblasts (CF) express adenosine (ADO) receptors, and pharmacological evidence suggests the possible involvement of the A(2) (A(2a) and A(2b)) receptor (A(2a)R and A(2b)R) subtypes in inhibiting cell functions involved in fibrosis. The main objective of this study was to define the contributions of A(2a) and/or A(2b) receptors in modulating ADO-induced decreases in CF functions. For this purpose, CF were either treated pharmacologically or had the A(2a)R or A(2b)R levels modified through the use of recombinant adenovirus or siRNA. The assessment of mRNA expression in adult rat CF yielded evidence for A(1)R, A(2b)R, A(2a)R, and A(3)R. Endogenously or exogenously enhanced ADO significantly inhibits CF proliferation, collagen, and protein synthesis. A(2)R and A(2a)R agonists, although capable of inhibiting CF protein and collagen synthesis, were unable to define the contributions derived from A(2a)R or A(2b)R. Overexpression of A(2b)R in CF yielded significant decreases in basal levels of collagen and protein synthesis and correlated with increases in cAMP levels. However, at higher doses of ADO receptor agonists, significant increases in protein and collagen synthesis were observed. CF with underexpression of A(2b)R yielded increases in protein and collagen synthesis. In contrast, A(2a)R underexpression did not modify ADO-induced decreases in CF protein or collagen synthesis. In conclusion, results derived from the molecular manipulation of receptor levels indicate that A(2b)R are critically involved in ADO-mediated inhibition of CF functions.