NEURITIC OUTGROWTH ASSOCIATED WITH ASTROGLIAL PHENOTYPIC CHANGES INDUCED BY ANTISENSE GLIAL FIBRILLARY ACIDIC PROTEIN (GFAP) MESSENGER-RNA IN INJURED NEURON-ASTROCYTE COCULTURES

In the adult CNS, axons fail to regenerate after injury. Among the cel l interactions that lead to this failure are those developed with astr ocytes. In an effort to elucidate the mechanisms underlying these nega tive interactions, we have used astrocytes treated with antisense glia l fibrillary acidic protein (GFAP) mRNA to inhibit the formation of gl iofilaments, indispensable for the astroglial morphological response t o injury, and have studied their permissivity for neuritic outgrowth. In a neuron-astrocyte coculture, a mechanical lesion led to hypertroph y of astrocytes neighboring the lesion. Neuronal cell bodies and neuri tes were absent both from the area of lesion and from its surroundings . Reactive astrocytes appeared, therefore, to be a nonpermissive subst rate. Transfection that used antisense GFAP mRNA blocked astroglial mo rphological changes and was characterized by both a persistence of neu ronal cell bodies in the vicinity of the lesion site and a growth of n eurites into the same region. These morphological differences were ass ociated with a 46% decrease in the GFAP translation capacity and a 50% increase in the concentration of GAP-43 in the treated cultures. Neur ons were associated mainly with an extracellular laminin network, whic h was predominant at the lesion site in treated cocultures. In contras t, those astrocytes highly laminin-immunoreactive appeared to be a non permissive substrate for neurons. These results show that inhibition i n GFAP synthesis, leading to a reduction of astroglial hypertrophy, re lieves the blockade of neuritic outgrowth that normally is observed af ter a lesion. The mechanisms may involve changes in the secretion of e xtracellular matrix molecules by astrocytes.