Sex-dependent neuronal loss and apoptosis-associated signaling in the anterior cingulate and anterior insular cortices in a late-stage MIA mouse model of osteoarthritis.

Osteoarthritis (OA) is a leading cause of disability worldwide, with chronic pain representing its most debilitating symptom and frequently accompanied by affective and cognitive comorbidities. Increasing evidence implicates maladaptive supraspinal plasticity within cortical regions involved in pain affect, including the anterior cingulate cortex (ACC) and anterior insular cortex (AIC), however, the relationship between these behavioral impairments and neuronal alterations, as well as potential sex-specific vulnerability, remains poorly documented. Using a monosodium iodoacetate (MIA) model of knee OA in adult male and female mice, we examined the temporal progression of sensory, affective, and cognitive alterations at early (day 7) and advanced (day 28) stages of disease. Pain sensitivity, locomotor and gait changes, anxiety- and depression-like behaviors, and working-memory performance were assessed using established behavioral paradigms, followed by analyses of apoptosis-associated neuronal signaling in the ACC and AIC. MIA induced robust mechanical and thermal hypersensitivity and gait impairment in both sexes, while early emotional and cognitive alterations were not observed. In contrast, advanced OA was associated with pronounced anxiety- and depression-like behaviors and impaired working memory. Notably, analysis at day 28 post-MIA revealed a significant increase in apoptotic signaling and neuronal loss in both cortical regions, with females exhibiting greater vulnerability, particularly within the AIC, paralleling their more severe affective phenotypes. Together, these findings indicate that chronic OA pain is associated with progressive, sex-dependent neuronal loss within key cortical pain-affective circuits and highlight supraspinal remodeling as a potential substrate underlying the emotional and cognitive burden of OA pain.