P.1.022 Epigenetic modifications in transgenic mouse with human polymorphism (Val66Met) of BDNF gene

Abstract

Epigenetic mechanisms involve self-perpetuating changes in chromatin structure and function that have been shown to regulate neuronal differentiation, neurodegeneration, circadian rhythms, seizure, memory, drug addiction, and stress response. Chromatin contains regions highly condensed (heterochromatin), and regions less condensed (euchromatin). The different regions reflect distinct functional states: euchromatin is activately transcribed, while heterochromatin is usually transcriptionally inactive. Post-translational modifications of histone tail residues, such as acetylation or methylation, can remodel the structure of chromatin activating or repressing gene expression. Several lines of evidence suggest an important role for BDNF in the pathogenesis of anxiety and mood disorder. Moreover, a human polymorphism in the BDNF gene (Val66Met) that causes a Met/Val substitution in codon 66 of proBDNF has been associated with major susceptibility to cognitive deficits, neuropsychiatric and neurodegenerative diseases, eating and metabolic disorders. The BDNF Val66Met transgenic mouse is the only existing animal model that recapitulates the phenotypic hallmarks of the human polymorphism. Indeed, both human and mice BDNFMet allele carriers show reduced hippocampal volume and cognitive deficit [1,2]. Moreover the human and the mouse BDNF Val66Met-carrier show alterations in the extinction of fear conditioning, a type of learning involved in phobias and post-traumatic stress disorder. The aim of this work was to study the impact of the BDNF Val66Met polymorphism on the epigenetic mechanisms that regulate expression of genes involved in synaptic plasticity, such as the trascriptional factors CREB and c-Fos, the neurotrophic factor BDNF and the NMDA receptor subunits. To analyse epigenetic modifications at the gene promoters, we employed the chromatin immunoprecipitation (ChIP) technique followed by amplification of immunoprecipitated DNA fragments by quantitative q-PCR (qChIP) and specific primers. Chromatin was immunoprecipitated with specific antibodies that recognize post-translational modifications in the H3 histone protein [anti-acetyl histone H3 (Lys9,14), marker of active gene expression and anti-trimethyl histone H3 (Lys27), marker of silenced genes].