Involvement of cAMP-PKA pathway in adenosine A1 and A2A receptor-mediated regulation of acetaldehyde-induced activation of HSCs

The present study was undertaken to investigate the mechanism by which adenosine receptors (ARs)-mediated the cAMP/PKA/CREB signal pathway regulates the activation of acetaldehyde-induced hepatic stellate cells (HSCs). Primary HSCs were isolated from SD rats, cultured in vitro, and activated with different concentrations of acetaldehyde at different time points. Quantitative real-time PCR and Western blotting were used to quantify both protein and mRNA levels of the four AR (A(1)R, A(2A)R, A(2B)R, and A(3)R) in rat HSCs. Selective inhibitors of PDEs and the Gi/o protein pathway, general AR agonists, and AR subtype specific agents were used to study the AR signaling. The level of cAMP was measured by radio-immunoassay, and the expression of alpha-SMA, collagen type I and III, PICA and p-CREB were also detected by Western blotting. Acetaldehyde could significantly promote HSC proliferation, with a maximum stimulatory effect observed at 48 h after exposure to 200 mu M acetaldehyde. All four AR subtypes could be present in rat HSCs, and the mRNA and protein expression levels for A(2A)R and AiR in much greater abundance than those for A(2B)R and A(3)R. The expression of A(2A)R and A(1)R was significantly increased in acetaldehyde-induced HSCs as compared with that of control group, whereas the expression of A(2B)R and A(3)R remained unaffected by the addition of acetaldehyde. Curiously, there is coupling of A(2A)R to the Gs-AC signaling, as well as coupling of AiR to the Gi/o-AC signaling pathway in acetaldehyde-induced HSCs. Both the A(2A)R and AiR antagonists could suppress the activation of HSC, although they have opposing effects on cAMP signal transduction. These results suggested that a combination of cAMP/PKA/CREB signals via A(2A)R and A(1)R likely mediate the activation of acetaldehyde-induced HSCs, and AiR coupled to the Gi/o-AC signaling pathway may be masked by the more predominant A(2A)R that coupled to the Gs-AC signaling pathway. (C) 2015 Elsevier B.V. and Societe Francaise de Biochimie et Biologie Moleculaire (SFBBM). All rights reserved.