Sex-dependent effects of injury and mesenchymal stromal cell-derived extracellular vesicle treatment on layer 3 pyramidal neuron properties of perilesional pre-motor cortex in rhesus monkeys
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Abstract
Cortical injury, such as stroke, commonly involves regions of the cortex affecting motor function. While functional recovery within these regions is associated with neuroplasticity and reorganization of neural circuits, complete recovery is uncommon and sexually dimorphic. Therefore, the use of ameliorative treatments to restore function is of high interest, however understanding of the underlying mechanisms and efficacy of treatment on neuron function and the surrounding cortical milieu across sex is sparse. Bone marrow mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have been shown to systemically enhance motor function recovery after injury to the primary motor cortex in aged female rhesus monkeys by dampening injury-related electrophysiologic and morphologic changes in perilesional PMv layer 3 pyramidal neurons. However, it has not yet been determined whether males and females may differentially benefit from EV treatment after cortical injury. In this study, we investigated how EV treatment in both male and female monkeys may impact recovery at behavioral and cellular levels. Aging rhesus macaques (Macaca mulatta) underwent pre-operative testing to measure grasp function before undergoing surgery to create a unilateral lesion within the dominant hand representation area of the primary motor cortex. After EV administration 24 hours and 14 days post-surgery, grasp function was reassessed for 12 weeks. Then, using in vitro whole-cell patch-clamp recording and intracellular fillings in acute slices from ventral premotor cortex (PMv), we demonstrate that MSC-EVs improve functional recovery, but underlying changes in pyramidal neuronal properties differed across sex. While EV-treated male and female rhesus macaques successfully regained baseline levels of hand motor function in fewer days compared to vehicles, treated females exhibited decreased hyperexcitability in neuronal firing properties compared to vehicles, while EV-treated males displayed lower tau and faster single AP properties, but no change in firing frequency. Morphologically, EV treated females exhibited greater overall spine density in both apical and basal dendrites compared to vehicle females after EV-treatment. While no difference in overall spine density was found between EV-treated and vehicle males, EV-treated males displayed lower density of mushroom spines compared to vehicles. EV-treated males displayed lower total spine densities compared to EV-treated females, specifically in mushroom and stubby spines, however, both EV-treated males and females exhibited greater density of stubby spines compared to vehicles. Overall, we demonstrate that EV treatment enhances functional recovery but differentially affects post-cortical injury outcomes within perilesional layer 3 pyramidal neurons between males and females.
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2025