Epigenetic modification of hippocampal Bdnf DNA in adult rats in an animal model of post-traumatic stress disorder

Abstract

Epigenetic alterations of the brain-derived neurotrophic factor (Bdnf) gene have been linked with memory, stress, and neuropsychiatric disorders. Here we examined whether there was a link between an established rat model of post-traumatic stress disorder (PTSD) and Bdnf DNA methylation. Adult male Sprague-Dawley rats were given psychosocial stress composed of two acute cat exposures in conjunction with 31 days of daily social instability. These manipulations have been shown previously to produce physiological and behavioral sequelae in rats that are comparable to symptoms observed in traumatized people with PTSD. We then assessed Bdnf DNA methylation patterns (at exon IV) and gene expression. We have found here that the psychosocial stress regimen significantly increased Bdnf DNA methylation in the dorsal hippocampus, with the most robust hypermethylation detected in the dorsal CA1 subregion. Conversely, the psychosocial stress regimen significantly decreased methylation in the ventral hippocampus (CA3). No changes in Bdnf DNA methylation were detected in the medial prefrontal cortex or basolateral amygdala. In addition, there were decreased levels of Bdnf mRNA in both the dorsal and ventral CA1. These results provide evidence that traumatic stress occurring in adulthood can induce CNS gene methylation, and specifically, support the hypothesis that epigenetic marking of the Bdnf gene may underlie hippocampal dysfunction in response to traumatic stress. Furthermore, this work provides support for the speculative notion that altered hippocampal Bdnf DNA methylation is a cellular mechanism underlying the persistent cognitive deficits which are prominent features of the pathophysiology of PTSD.

Figure 1

Schematic of target Bdnf exon IV amplicon and its 12 CG dinucleotides relative to the transcription initiation site (bent arrow).

Figure 2

Levels of methylated Bdnfexon IV DNA in dorsal dentate (A), CA3 (B), and CA1 (C) in control (no stress) and stress-exposed rats. *** p< 0.001 vs. no stress controls. DG n=7–8/group, CA3 n=8/group, CA1 n=6/group. Data are mean ± SEM.

Figure 3

Levels of methylated Bdnfexon IV DNA in ventral dentate (A), CA3 (B), and CA1 (C) in control (no stress) and stress-exposed rats. *** p< 0.001 vs. no stress controls. DG n=8/group, CA3 n=7–8/group, CA1 n=8/group. Data are mean ± SEM.

Figure 4

Exon IV mRNA levels in PTSD-like rats. Dorsal CA1, ** p< 0.01 vs. no stress controls, n=8/group. Ventral CA1, * p< 0.05 vs. no stress controls, n=8/group. Data are mean ± SEM.

Figure 5

Levels of methylated Bdnfexon IV DNA in medial prefrontal cortex (A), and basolateral amygdala (B) in control (no stress) and stress-exposed rats. Medial prefrontal cortex n=9–10/group, basolateral amygdala n=10/group. Data are mean ± SEM.