SEX-DEPENDENT NPAS4 EXPRESSION IN THE MEDIAL PREFRONTAL CORTEX PREDICTS RESILIENCE TO STRESS

Stressful experiences increase the risk of major depressive disorder. Adaptive responses to stress depend on experience-dependent neural plasticity that supports behavioral flexibility, resulting in individual trajectories of vulnerability or resilience. Biological sex is a key determinant of stress responses, yet preclinical research has largely focused on males. We therefore aimed to identify sex-specific circuit-level mechanisms supporting adaptive stress responses. The learned helplessness (LH) model was used in C57BL/6 mice to assess individual responses to unpredictable and inescapable footshocks. Animals were categorized as helpless or resilient based on their escape behaviors. Control mice underwent identical contextual procedures without shocks. Transcriptional profiles were analyzed using bulk and single-nucleus RNA-sequencing from the infralimbic and prelimbic cortices and the anterior cingulate cortex. Following LH exposure, 14.68% of males (16/109) and 28.57% of females (30/105) were classified as resilient. Across sexes and brain regions, Neuronal PAS domain protein 4 (Npas4) emerged as the most robustly upregulated gene. Beyond Npas4, females showed 111 differentially expressed genes in the infralimbic and prelimbic cortices, while the anterior cingulate cortex showed 5 genes in males and 12 in females (FDR < 0.05). Network analysis further identified Npas4 as a central hub of co-expression gene modules associated with stress resilience. Single-nucleus RNA-sequencing mapped Npas4 expression primarily in glutamatergic and GABAergic neurons. By applying the same stress paradigm in males and females, our findings identify Npas4 as a consistent marker of resilience, more prominent in females, highlighting its relevance for understanding sex-specific stress adaptation in depression-related neurobiology.