CHARACTERIZATION OF THE SIGNALING PATHWAYS INVOLVED IN ATP AND BASIC FIBROBLAST GROWTH FACTOR-INDUCED ASTROGLIOSIS

1 A brief challenge of rat astrocytes with either alpha,beta-methylene ATP (alpha,beta-meATP) or basic fibroblast growth factor (bFGF) result ed, three days later, in morphological differentiation of cells, as sh own by marked elongation of astrocytic processes, The P2 receptor anta gonist suramin prevented alpha,beta-meATP- but not bFGF-induced astroc ytic elongation. Similar effects on astrocytic elongation were also ob served with ATP and other P2 receptor agonists (beta,gamma meATP, ADP beta S, 2meSATP and, to a lesser extent, UTP). 2 Pertussis toxin compl etely abolished alpha,beta meATP- but not bFGF-induced effects. No eff ects were exerted by cr,beta-meATP on cyclic AMP production: similarly , neomycin had no effects on elongation of processes induced by the pu rine analogue, suggesting that adenylyl cyclase and phospholipase C ar e 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-ind uced astrocytic elongation. 3 Challenge of cultures with alpha,beta-me ATP rapidly and concentration-dependently increased [H-3]-arachidonic acid (AA) release from cells, suggesting that activation of phospholip ase A(2) (PLA(2)) may be involved in the long-term functional effects evokeded by purine analogues. Consistently exogenously added AA marked ly elongated astrocytic processes. Moreover, various PLA(2) inhibitors (e.g. mepacrine and dexamethasone) prevented both the early alpha,bet a-meATP-induced [H-3]-AA release and/or the associated long-term morph ological changes, without affecting the astrocytic elongation induced by bFGF. Finally, the protein kinase C (PKC) inhibitor H7 fully abolis hed alpha,beta-meATP- but not bFGF-induced effects. 4 Both alpha,beta- meATP and bFGF rapidly and transiently induced the nuclear accumulatio n of Fos and Jun. Both c-fos and c-jun induction by the purine analogu e 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 differe ntiation of astrocytes occurs via independent transductional pathways. For the purine analogue, signalling involves a G(i)/G(o) protein-coup led P2Y-receptor which may be linked to activation of PLA(2) (involvem ent of an arachidonate-sensitive PKC is speculated); for bFGF, a tyros ine kinase receptor is involved. Both pathways merge on some common in tracellular target, as suggested by induction of primary response gene s, 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 react ive astrogliosis, which has intriguing implications in nervous system diseases characterized by degenerative events.