Differential regulation of GDNF, neurturin, and their receptors in primarycultures of rat glial cells

Glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) bind to GFR alpha -1 and GFR alpha -2 receptors, respectively, and their neurot rophic activity is mediated by the tyrosine kinase receptor, Ret. All these molecules were found to be expressed in primary cultures of rat glial cell s, which were largely composed of astrocytes and maintained in serum-free m edium. Although GDNF, NTN and Ret mRNA levels were at the limit of detectio n, RNase protection assays revealed relatively high amounts of GFR alpha -1 and GFR alpha transcripts. To characterize signals controlling their expre ssion, glial cells were exposed to serum or treated with hormones acting th rough nuclear receptors and by activators of the cAMP or protein kinase C ( PKC)-dependent pathways. Retinoic acid or 1,25-dihydroxyvitamin D3 appeared ineffective. In contrast, the 5-fold increase in GFR alpha -2 mRNA after 2 4 hr of treatment with 10(-10) M of tri-iodothyronine, suggests a physiolog ical role of thyroid hormone in the regulation of this receptor in vivo. Th e serum induced a 7-fold increase in GFR alpha -1 mRNA levels. These change s may be mediated by the cAMP or PKC pathways because both forskolin and TP A up-regulated the GFR alpha -1 gene. Interestingly, only TPA led to a coor dinated increase in the levels of GDNF, GFR alpha -1 and GFR alpha -2 mRNAs . On the other hand, NTN transcripts remained constant, irrespective of the culture conditions. Taken together, these results indicate that GDNF famil y ligands and their receptors are regulated in glial cells by common or ind ependent transductional pathways, which could modulate their specific expre ssion during brain development or in the case of trauma. (C) 2001 Wiley-Lis s, Inc.