Septal HDAC1 facilitates long-lasting extinction of social fear in male mice

Social anxiety disorder (SAD) is primarily caused by traumatic social events and is characterized by intense fear and avoidance of socially enriched contexts. Formation of such intense social aversion requires learning of the association between trauma and originally neutral social stimuli. Acetylation of histones in response to learning is critical for long-term memory formation. Class I histone deacetylases (HDACs) have emerged as powerful negative regulators of long-term memory formation. However, the lack of clarity in isoform and spatial specificity in HDAC function exists. Utilizing the social fear conditioning (SFC) as well as cued fear conditioning (CFC) paradigms, we aimed to functionally characterize the role of class I HDACs, especially HDAC1, in the regulation of aversive memories in social versus non-social contexts. Using cFos expression as a marker of cellular activity, we revealed that the lateral septum (LS) was specifically activated post-acquisition in socially fear conditioned (SFC+) mice. We further measured an increase in activity-inducing HDAC1 phosphorylation at serine residues within the septum of SFC+ mice during extinction of social fear. Pharmacological inhibition of HDAC1 within the LS facilitated, while viral overexpression of septal HDAC1 impaired extinction of social fear. Finally, we found that the abovementioned facilitation of extinction memory by HDAC1 inhibition was long-lasting and persists even after 30 days of extinction. Our results show that LS-HDAC1 is a key regulator of long-lasting social fear extinction, which points towards HDAC1 as a potential therapeutic target for SAD.