Reductions in protein degradation in the retrosplenial cortex regulate contextual fear memory formation in a sex-independent manner.

The retrosplenial cortex (RSC), which serves as a hub to connect the hippocampus and amygdala with other cortical regions, has been shown to play a role in the formation of contextual fear memories. However, the molecular mechanisms by which the RSC forms memories and whether sex differences exist within these mechanisms remain largely unknown. Increases in ubiquitin-proteasome-mediated protein degradation have been shown to be sex-dependently involved in the formation of contextual fear memories in multiple brain regions, including the hippocampus and amygdala. To date, whether increases in protein degradation are needed in the RSC for memory formation in either sex has yet to be examined. Here, we found that proteasome function in the RSC decreases after contextual fear conditioning in both male and female rats. Consistent with this, increasing proteasome activity in the RSC via CRISPR-dCas9-mediated upregulation of Psmd14 impaired contextual fear memory in a mixed sex cohort. Interestingly, proteomic analysis of degradation-specific lysine-48 (K48) polyubiquitination in the RSC of fear-conditioned rats showed largely distinct protein degradation targets and impacted pathways across the sexes. This suggests that despite the shared need for reductions in protein degradation, males and females are using this mechanism in different ways to form the same memory. Together, these data demonstrate that reductions in protein degradation in the RSC are critical for contextual fear memory formation in both males and females and indicate that the molecular changes in the RSC during memory formation may be distinct from those of other more commonly studied brain regions.