Epigenetic mechanisms underlying stress-enhanced fear learning in males and females

About This Grant

Project Summary/Abstract Fear is important for survival, but excess fear can be problematic when it interferes with daily functioning. One disorder marked by such exaggerated fear responses is post-traumatic stress disorder (PTSD) in which exposure to a traumatic event predisposes an individual to show excessive subsequent fear responding. Notably, women are nearly twice as likely as men to develop PTSD, suggesting there may be sex-specific mechanisms that gate sensitivity to acute stress. Recent work from our lab has identified the repressive histone deacetylase 3 (HDAC3) as a key mechanism that modulates the persistent effects of stress. Specifically, we found that acute stress reduces HDAC3 in the amygdala and locally blocking HDAC3 during weak stress transforms this event into one that drives persistent fear sensitization in male mice. Surprisingly, in female mice, the same mild stress drove persistent and robust fear sensitization that was not further enhanced by HDAC3 inhibition, suggesting that the threshold for inactivating HDAC3 is much lower in females. This proposal aims to systematically investigate the role of HDAC3 and histone acetylation more broadly in regulating stress-enhanced fear learning in male and female mice. Specifically, we hypothesize that acute stress establishes an epigenetic molecular memory in the amygdala primarily via histone acetylation, opening the local chromatin at key fear memory genes to enable their excessive transcription in response to subsequent mild fear conditioning. We further hypothesize that females require less intense stress to establish these changes. To fully test this hypothesis, we propose three aims. In Aim 1, we will determine the role of HDAC3 in establishing stress-enhanced fear learning in males and females. We will bidirectionally manipulate HDAC3 in the amygdala during varying amounts of acute stress and test whether that alters subsequent fear learning in male and female mice. In Aim 2, we will determine the mechanisms through which acute stress persistently enhances subsequent fear memory in both sexes. Using RNA- and ChIP-seq, we will test whether intense acute stress establishes an epigenetic molecular memory that enables excessive or aberrant expression of key fear memory genes in response to subsequent fear conditioning. Then we will use HSV-CRISPRi to causally test whether top candidate genes are required for this sensitization. Finally, in Aim 3, we will determine how HDAC3 modulates susceptibility in a sex-specific manner. Using 2-shock stress that establishes persistent sensitization only in female mice, we will determine which genes might support sex-specific sensitization. We will also determine which of these genes might promote sensitization in male mice when HDAC3 is blocked. Finally, we will bidirectionally manipulate these genes with our established HSV-CRISPRi and HSV-CRISPRa systems and directly test whether HDAC3 functions through these genes to promote stress-enhanced fear learning. Together, our findings will identify sex-specific mechanisms through which acute stress persistently changes the brain’s response to subsequent fear.