P2 receptor‐mediated stimulation of the PI3‐K/Akt‐pathway in vivo

Abstract ATP acts as a growth factor as well as a toxic agent by stimulating P2 receptors. The P2 receptor‐activated signaling cascades mediating cellular growth and cell survival after injury are only incompletely understood. Therefore, the aim of the present study was to identify the role of the phosphoinositide 3 kinase (PI3‐K/Akt) and the mitogen‐activated protein kinase/extracellular signal regulated protein kinase (MAPK/ERK) pathways in P2Y receptor‐mediated astrogliosis after traumatic injury and after microinfusion of ADPβS (P2Y 1,12,13 receptor agonist) into the rat nucleus accumbens (NAc). Mechanical damage and even more the concomitant treatment with ADPβS, enhanced P2Y 1 receptor‐expression in the NAc, which could be reduced by pretreatment with the P2X/Y receptor antagonist PPADS. Quantitative Western blot analysis indicated a significant increase in phosphorylated (p)Akt and pERK1/2 2 h after ADPβS‐microinjection. Pretreatment with PPADS or wortmannin abolished the up‐regulation of pAkt by injury alone or ADPβS‐treatment. The ADPβS‐enhanced expression of the early apoptosis marker active caspase 3 was reduced by PPADS and PD98059, but not by wortmannin. Multiple immunofluorescence labeling indicated a time‐dependent expression of pAkt and pMAPK on astrocytes and neurons and additionally the colocalization of pAkt, pMAPK, and active caspase 3 with the P2Y 1 receptor especially at astrocytes. In conclusion, the data show for the first time the involvement of PI3‐K/Akt‐pathway in processes of injury‐induced astroglial proliferation and anti‐apoptosis via activation of P2Y 1 receptors in vivo , suggesting specific roles of P2 receptors in glial cell pathophysiology in neurodegenerative diseases. © 2008 Wiley‐Liss, Inc.