Understanding the role of DNA methylation dynamics at Bdnf during fear conditioning

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Project Summary/Abstract   Post-Traumatic Stress Disorder (PTSD) is driven, in part, by aberrant fear consolidation in the brain. Signaling by neurotrophic factors and chromatin dynamics are crucial for this memory consolidation. Signaling between brain-derived neurotrophic factor (Bdnf) and its primary receptor, tyrosine-receptor kinase B (TrkB), plays an important role in the consolidation of fear in the amygdala. Indeed, it has been shown that both amygdala specific knockout of Bdnf and blockage of Bdnf-TrkB signaling interfere with consolidation. Thus both presynaptic transcription as well as post-synaptic signaling is crucial for its function. Furthermore, studies have demonstrated an associated between DNA methylation (5-mC) levels, and differential transcription of Bdnf, suggesting that epigenetic modifications are driving transcriptional regulatory processes at the Bdnf gene during fear memory consolidation. We aim to profile the DNA hydroxymethylation (5-hmC) levels at Bdnf and employ a Cas9-Tet1 construct to investigate the causal relationship between site-directed epigenetic modulation and fear consolidation. Neural tissues possess very high levels of 5-hmC, as compared to other tissues. Canonically, 5-mC has been considered to be a relatively stable epigenetic mark, delineating tissue-specific promoter activation. However, two important pieces of evidence have demonstrated the importance of 5-mC regulation for fear consolidation: dynamic DNA methylation is necessary for fear consolidation, and manipulation of the Tet1 enzyme, one enzyme responsible for the conversion of 5-mC to 5-hmC, interfered with contextual fear memory. We hypothesize that 5-hmC will dynamically regulate Bdnf during fear consolidation, and that these 5-hmC alterations will be necessary for the consolidation of fear memory. In aim 1 we will use genome-wide and locus-specific approaches to profile 5-hmC and 5-mC at Bdnf during fear conditioning. In aim 2 we will perform proof-of-concept Cas9-Tet1 epigenomic engineering experiments in vitro and in behaving mice, and we will elucidate the relationship between dynamic 5-hmC at candidate loci within Bdnf and fear consolidation.