Characterization of the signalling pathways involved in ATP and basic fibroblast growth factor-induced astrogliosis

1 A brief challenge of rat astrocytes with either alpha,beta-methyleneATP (alpha,beta-meATP) or basic fibroblast growth factor (bFGF) resulted, three days later, in morphological differentiation of cells, as shown by marked elongation of astrocytic processes, The P2 receptor antagonist suramin prevented alpha,beta-meATP- but not bFGF-induced astrocytic elongation. Similar effects on astrocytic elongation were also observed with ATP and other P2 receptor agonists (beta,gamma meATP, ADP beta S, 2meSATP and, to a lesser extent, UTP). 2 Pertussis toxin completely abolished alpha,beta meATP- but not bFGF-induced effects. No effects were exerted by cr,beta-meATP on cyclic AMP production: similarly, neomycin had no effects on elongation of processes induced by the purine analogue, suggesting that adenylyl cyclase and phospholipase C are probably not involved in alpha,beta-meATP-induced effects (see also the accompanying paper by Centemeri et ai., 1997). The tyrosine-kinase inhibitor genistein greatly reduced bFGF-but not alpha,beta-meATP-induced astrocytic elongation. 3 Challenge of cultures with alpha,beta-meATP rapidly and concentration-dependently increased [H-3]-arachidonic acid (AA) release from cells, suggesting that activation of phospholipase A(2) (PLA(2)) may be involved in the long-term functional effects evokeded by purine analogues. Consistently exogenously added AA markedly elongated astrocytic processes. Moreover, various PLA(2) inhibitors (e.g. mepacrine and dexamethasone) prevented both the early alpha,beta-meATP-induced [H-3]-AA release and/or the associated long-term morphological changes, without affecting the astrocytic elongation induced by bFGF. Finally, the protein kinase C (PKC) inhibitor H7 fully abolished alpha,beta-meATP- but not bFGF-induced effects. 4 Both alpha,beta-meATP and bFGF rapidly and transiently induced the nuclear accumulation of Fos and Jun. Both c-fos and c-jun induction by the purine analogue could be fully prevented by pretreatment with suramin. In contrast, the effects of bFGF were unaffected by this P2 receptor antagonist. 5 It was concluded that alpha,beta-meATP- and bFGF-morphological differentiation of astrocytes occurs via independent transductional pathways. For the purine analogue, signalling involves a G(i)/G(o) protein-coupled P2Y-receptor which may be linked to activation of PLA(2) (involvement of an arachidonate-sensitive PKC is speculated); for bFGF, a tyrosine kinase receptor is involved. Both pathways merge on some common intracellular target, as suggested by induction of primary response genes, which in turn may regulate late response genes mediating long-term phenotypic changes of astroglial cells. 6 These findings implicate P2 receptors as novel targets for the pharmacological regulation of reactive astrogliosis, which has intriguing implications in nervous system diseases characterized by degenerative events.