Sex-Specific Reversal of Stress-Induced Depressogenic Behaviors by Inhibition of HMGB1, TLR4, and NF-κB Signaling.

Acute stress and inflammatory mediators are linked to stress-related mental disorders, yet sex-specific differences in the molecular pathways connecting them remain poorly understood. Male and female C57BL/6 mice underwent predator stress while restrained. Apathy/anhedonia and behavioral despair were assessed using the splash test (ST) and tail suspension test (TST). Neuroinflammatory signaling was assessed by immunohistochemistry through measurements of HMGB1 release and NF-κB nuclear translocation in the anterior cingulate cortex (ACC) and the nucleus accumbens (NAc). To further assess the roles of HMGB1, NF-κB and TLR4 in acute stress-induced behavioral changes in both sexes, mice were administered the respective inhibitors prior to stress, and changes in depression-like behaviors were subsequently assessed. Finally, microglial numbers and cleaved caspase-1 levels were evaluated by immunohistochemistry, and microglial ramifications were assessed by Sholl analysis. Acute stress induced increased immobility in the TST and decreased grooming in the ST in both sexes. Although stress triggered comparable increases in HMGB1 release and NF-κB translocation in both sexes, pharmacological inhibition of HMGB1, TLR4, and NF-κB exerted antidepressant effects exclusively in males. In females, none of the inhibitors was effective in reversing acute stress-induced immobility in TST and decreased grooming in ST. Although the numbers of microglia recruited by acute stress were similar in both sexes, they were more ramified in females regardless of stress exposure. Cleaved caspase-1 levels were elevated only in males after stress exposure, without any alteration in females. These findings underscore sex-specific differences in acute stress-induced alterations in the brain. The results suggest that downstream signaling pathways may differ by sex or that females possess protective mechanisms that constrain the behavioral consequences of neuroinflammation. This study highlights the necessity of considering sex as a critical biological variable in developing interventions for stress-related disorders.