A2B adenosine receptors stimulate IL-6 production in primary murine microglia through p38 MAPK kinase pathway

The hallmark of neuroinflammation is the activation of microglia, the immunocompetent cells of the CNS, releasing a number of proinflammatory mediators implicated in the pathogenesis of neuronal diseases. Adenosine is an ubiquitous autacoid regulating several microglia functions through four receptor subtypes named A(1), A(2A), A(2B) and A(3) (ARs), that represent good targets to suppress inflammation occurring in CNS. Here we investigated the potential role of ARs in the modulation of IL-6 secretion and cell proliferation in primary microglial cells. The A(2B)AR agonist 2-[[6-Amino-3,5-dicyano444-(cyclopropylmethoxy)pheny11-2-pyridinyllthiol-acetamide (BAY60-6583) stimulated IL-6 increase under normoxia and hypoxia, in a dose- and time-dependent way. In cells incubated with the blockers of phospholipase C (PLC), protein kinase C epsilon (PKC-epsilon) and PKC delta (PKC-delta) the IL-6 increase due to A2BAR activation was strongly reduced, whilst it was not affected by the inhibitor of adenylyl cyclase (AC). Investigation of cellular signalling involved in the A(2B)AR effect revealed that only the inhibitor of p38 mitogen activated protein kinase (MAPK) was able to block the agonist's effect on IL-6 secretion, whilst inhibitors of pERK1/2, JNK1/2 MAPKs and Akt were not. Stimulation of p38 by BAY60-6583 was A(2B)AR-dependent, through a pathway affecting PLC, PKC-epsilon and PKC-delta but not AC, in both normoxia and hypoxia. Finally, BAY60-6583 increased microglial cell proliferation involving A(2B)AR, PLC, PKC-epsilon, PKC-delta and p38 signalling. In conclusion, A(2B)ARs activation increased IL-6 secretion and cell proliferation in murine primary microglial cells, through PLC, PKC-epsilon, PKC-delta and p38 pathways, thus suggesting their involvement in microglial activation and neuroinflammation. (C) 2016 Elsevier Ltd. All rights reserved.