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NFkappaB activation is required for the neuroprotective effects of pigment epithelium-derived factor (PEDF) on cerebellar granule neurons.

Pigment epithelium-derived factor (PEDF) protects immature cerebellar granule cells (1-3 days in vitro) against induced apoptosis and mature cells (5+ days in vitro) against glutamate toxicity, but its precise mechanism is still unknown. Because the transcription factor NFkappaB blocks cell death, including neuronal apoptosis, we have investigated the ability of PEDF to exert its effects via NFkappaB activation. PEDF induced an increased phosphorylation of IkappaBalpha, decreased levels of IkappaB proteins, and translocation of p65 (RelA) to the nucleus followed by a time-dependent increase of NFkappaB-DNA binding activity in both immature and mature neurons. The protective effects of PEDF against both induced apoptosis and glutamate toxicity were blocked by the addition of either the IkappaB kinase inhibitor BAY 11-7082, which inhibits the phosphorylation of IkappaB, or N-acetyl-Leu-Leu-norleucinal, which blocks proteosome degradation of IkappaB, demonstrating that NFkappaB is required for the neuroprotective effects of PEDF. Reverse transcription-polymerase chain reaction analysis revealed that up-regulation of the anti-apoptotic genes for Bcl-2, Bcl-x, and manganese superoxide dismutase was observed in PEDF-treated immature but not mature neurons. Up-regulation of nerve growth factor, brain-derived neurotrophic factor, and glial cell-derived neurotrophic factor mRNA was long-lasting in mature neurons. These results suggest that PEDF promotes neuronal survival through activation of NFkappaB, which in turn induces expression of anti-apoptotic and/or neurotrophic factor genes.