Extracellular 3',5'-cAMP-adenosine pathway inhibits glomerular mesangial cell growth

Abnormal growth of glomerular mesangial cells (GMCs) contributes to the pathophysiology of many types of nephropathy. Because adenosine is an autocrine/paracrine factor that potentially could regulate GMC proliferation and because the extracellular 3',5'-cAMP-adenosine pathway (i.e., the conversion of extracellular 3',5'-cAMP to 5'-AMP and adenosine on the cell surface) could generate adenosine in the biophase of GMC receptors, we investigated the role of the 3',5'-cAMP-adenosine pathway in modulating growth [cell proliferation, DNA synthesis ([(3)H]thymidine incorporation), collagen synthesis ([(3)H]proline incorporation), and mitogen-activated protein kinase activity] of GMCs. The addition of exogenous 3',5'-cAMP to human GMCs increased extracellular levels of 5'-AMP, adenosine, and inosine, and 3-isobutyl-1-methylxanthine (phosphodiesterase inhibitor), 1,3-dipropyl-8-p-sulfophenylxanthine (ecto-phosphodiesterase inhibitor), and alpha,beta-methylene-adenosine-5'-diphosphate (ecto-5'-nucleotidase inhibitor) attenuated the increases in adenosine and inosine. Forskolin augmented extracellular 3',5'-cAMP and adenosine concentrations, and 2',5'-dideoxyadenosine (adenylyl cyclase inhibitor) blocked these increases. Exogenous 3',5'-cAMP and forskolin inhibited all indices of cell growth, and antagonism of A(2) [(E)-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-methylxanthine, KF17837] or A(1)/A(2) (1,3-dipropyl-8-p-sulfophenylxanthine, DPSPX), but not A(1) (8-cyclopentyl-1,3-dipropylxanthine), or A(3){N-(2-methoxyphenyl)-N'-[2-(3-pyridinyl)-4-quinazolinyl]-urea, VUF5574}, adenosine receptors blocked the growth-inhibitory actions of exogenous 3',5'-cAMP, but not the effects of 8-bromo-3',5'-cAMP (stable 3',5'-cAMP analog). Erythro-9-(2-hydroxy-3-nonyl)adenine (adenosine deaminase inhibitor) plus 5-iodotubercidin (adenosine kinase inhibitor) enhanced the growth inhibition by exogenous 3',5'-cAMP and forskolin, and A(2) receptor antagonism blocked this effect. In rat GMCs, down-regulation of A(2B) receptors with antisense, but not sense or scrambled, oligonucleotides abrogated the inhibitory effects of 3',5'-cAMP and forskolin on cell growth. The extracellular 3',5'-cAMP-adenosine pathway exists in GMCs and attenuates cell growth via A(2B) receptors. Pharmacological augmentation of this pathway could abate pathological glomerular remodeling.