Adenosine, Via A _2B Receptors, Inhibits Human (P-SMC) Progenitor Smooth Muscle Cell Growth

Abstract

c-Kit+ progenitor smooth muscle cells (P-SMCs) can develop into SMCs that contribute to injury-induced neointimal thickening. Here, we investigated whether adenosine reduces P-SMC migration and proliferation and whether this contributes to adenosine's inhibitory actions on neointima formation. In human P-SMCs, 2-chloroadenosine (stable adenosine analogue) and BAY60-6583 (A2B agonist) inhibited P-SMC proliferation and migration. Likewise, increasing endogenous adenosine by blocking adenosine metabolism with erythro-9-(2-hydroxy-3-nonyl) adenine (inhibits adenosine deaminase) and 5-iodotubercidin (inhibits adenosine kinase) attenuated P-SMC proliferation and migration. Neither N6-cyclopentyladenosine (A1 agonist), CGS21680 (A2A agonist), nor N6-(3-iodobenzyl)-adenosine-5'-Nmethyluronamide (A3 agonist) affected P-SMC proliferation or migration. 2-Chloroadenosine increased cyclic AMP, reduced Akt phosphorylation (activates cyclin D expression), and reduced levels of cyclin D1 (promotes cell-cycle progression). Moreover, 2-chloroadenosine inhibited expression of Skp2 (promotes proteolysis of p27Kip1) and upregulated levels of p27Kip1 (negative cell-cycle regulator). A2B receptor knockdown prevented the effects of 2-chloroadenosine on cyclic AMP production and P-SMC proliferation and migration. Likewise, inhibition of adenylyl cyclase and protein kinase A rescued P-SMCs from the inhibitory effects of 2-chloroadenosine. The inhibitory effects of adenosine were similar in male and female P-SMCs. In vivo, peri-arterial (rat carotid artery) 2-chloroadenosine (20 mol/L for 7 days) reduced neointimal hyperplasia by 64.5% (P<0.05; intima/media ratio: control, 1.4±0.02; treated, 0.53±0.012) and reduced neointimal c-Kit+ cells. Adenosine inhibits P-SMC migration and proliferation via the A2B receptor/cyclic AMP/protein kinase A axis, which reduces cyclin D1 expression and activity via inhibiting Akt phosphorylation and Skp2 expression and upregulating p27kip1 levels. Adenosine attenuates neointima formation in part by inhibiting infiltration and proliferation of c-Kit+ P-SMCs.

Therapeutic Perspectives of Adenosine Deaminase Inhibition in Cardiovascular Diseases

“…Extracellular purines play a significant role in cardiovascular system homeostasis. Adenosine that is abundantly produced on the surface of endothelial and vascular smooth muscle cells by ecto-nucleotidases, dampens via P1 receptors endothelial activation, immune cell adhesion, smooth muscle cell proliferation and foam cell formation that all together initiate and drive atherosclerotic process in the vessel wall [ 4 , 107 , 108 , 109 , 110 ]. Under stress conditions related to atherosclerosis, such as hypoxia, depressed cellular energy state lead to acute increase and release of adenosine from the cell [ 111 ].…”

Dipyridamole and vascular healing following stent implantation

“…Briefly, ADOR-A2B signaling leads to activation of adenylyl cyclase leading to augmentation of cAMP and PKA; PKA subsequently inhibits proliferation by blocking several pathways (ERK1/2, Akt and Skp2) that converge at Cyclin D with the collective result being diminished G1 cyclin expression and reduced cell cycle progression as a result (11). This mechanism is also maintained in circulating progenitor SMCs, another documented source of NI proliferation (5,12). The role of adenosine and circulating progenitors is also supported by rescue of the observed effects by wild type bone marrow transplant in ADOR-A2B knockout mice (10).…”

“…Adenosine signals primarily via 4 receptors with preclinical work suggesting a potential role for adenosine receptor (ADOR)-A2B in the regulation of the vascular effects observed, particularly NI proliferation (10). Indeed, in vitro and in vivo arterial injury models supports adenosine mitigating NI formation via ADOR-A2B-mediated inhibition of SMC proliferation (11)(12)(13). Despite this promising preclinical work, ADO has yet to establish itself as a viable therapeutic approach for ISR, owing in part to its innate limitations, particularly its short half-life (7)(8)(9)14).…”

Adenosine and the Cardiovascular System: The Good and the Bad

“…Vascular muscle cell proliferation is an important component of vascular remodeling which is regulated partly through A 2B receptors [148] and it was shown that activation of A 2B R protects against vascular injury [149].…”