Signaling pathways and survival effects of BDNF and NT-3 on cultured cerebellar granule cells.

We investigated the signaling pathways exerted by brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in relation to their survival-promoting effects on dissociated cultures of cerebellar granule cells prepared from postnatal 9-day-old rats. Granule neuron survival in culture was supported by BDNF, but not significantly by either nerve growth factor (NGF) or NT-3. BDNF and NT-3 resulted in not only the respective autophosphorylation of the Trk receptors, TrkB or TrkC, but also tyrosine phosphorylation of SHC, a protein involved in controlling p21ras activity, and phosphatidylinositol-3' (PI-3') kinase. NGF does not result in TrkA phosphorylation. In parallel, c-fos was induced within 30 min, in response to BDNF and NT-3. NT-3 induced the phosphorylation of these proteins to a lesser extent than BDNF. BDNF also induced the tyrosine phosphorylation of phospholipase C gamma (PLC gamma), but the NT-3-induced one was not detected. We postulate that no survival promotion by NT-3 is due to lesser level of trkC expression and of the NT-3-induced signaling in the cultured cerebellar granule neurons. Wortmannin, a specific inhibitor of PI-3' inhibited the BDNF effect on neuronal survival. PI-3' kinase-dependent pathways might be involved in the promotion of cerebellar granule cell survival by BDNF.