Ethanol inhibits brain-derived neurotrophic factor-mediated intracellular signaling and activator protein-1 activation in cerebellar granule neurons

Developmental exposure to ethanol causes profound damage to the cerebellum, ranging from aberration in neuronal differentiation to cell loss. As a major neurotrophic factor, brain-derived neurotrophic factor (BDNF) and its receptor TrkB are expressed in the developing, as well as adult, cerebellum. Many neurotrophic effects of BDNF are mediated by gene transcription. We hypothesized that ethanol interfered with BDNF signaling and disrupted BDNF-regulated transcriptional activity. Using a transgenic mouse model expressing an activator protein-1 (AP-1) luciferase reporter construct, we demonstrated that BDNF stimulated AP-1 transactivation in cultured cerebellar granule neurons. This observation was validated by the study using a human neuronal cell line expressing inducible TrkB (TB8 neuroblastoma cells). BDNF induced AP-1 transactivation, as well as increased the binding activity of AP-1 protein complex to a DNA sequence containing AP-1 sites in TB8 cells. BDNF-mediated AP-1 activation was mediated by PI3K/Akt and JNK pathways; BDNF activated Akt and JNKs, and blocking these pathways significantly inhibited BDNF-stimulated AP-1 transactivation. More importantly, ethanol inhibited BDNF-mediated activation of PI3K/Akt and JNKs, and blocked BDNF-stimulated AP-1 activation. Since ethanol did not affect either the expression or autophosphorylation of TrkB, it could be concluded that the site of ethanol action was downstream of TrkB. The present study establishes that this AP-1 reporter transgenic mouse model is valuable for assessing AP-1 activity in the CNS neurons. Our results provide an insight into molecular mechanism(s) of ethanol action. (C) 2004 IBRO. Published by Elsevier Ltd. All rights reserved.