BMSC-EVs improve post-stroke cognition by promoting regionally distinct synaptic repair via Sema3G-Nrp2/PlexinA4...

Cognitive impairment is a common sequela of ischemic stroke, primarily driven by disrupted synaptic structural plasticity in the hippocampus. Although bone marrow mesenchymal stem cell-derived extracellular vesicles (BMSC-EVs) are known to promote synaptic plasticity, their heterogeneous effects across hippocampal subregions and associated regulatory mechanisms remain unclear. In this study, BMSC-EVs were intravenously administered 24 h post-reperfusion in a rat model of transient middle cerebral artery occlusion (tMCAO), with additional injections on days 3, 5, and 7. Behavioral assessments (mNSS, Morris Water Maze, Y-maze) showed significant improvements in neurological and cognitive functions (P < 0.05). Histological observation and analyses revealed differential synaptic remodeling. The dentate gyrus (DG) exhibited the most pronounced response, including a significant increase in spine density beyond sham levels (P < 0.01), a shift towards mature spine morphologies, and enhanced axonal integrity as indicated by NF200 expression (P < 0.001). The CA3 region showed improved neuronal survival (P < 0.05), dendritic complexity, and elevated expression of Syn and PSD-95 (P < 0.01 and P < 0.001, respectively). In contrast, the CA1 region displayed limited structural recovery, despite moderate yet significant increases in Syn and PSD-95 expression (P < 0.001). Mechanistically, BMSC-EVs restored ischemia-induced downregulation of Semaphorin 3G (Sema3G), Neuropilin-2 (Nrp2), and PlexinA4 (P < 0.05 to P < 0.001), suggesting a correlation between BMSC-EVs treatment and activation of the Sema3G-Nrp2/PlexinA4 signaling pathway, which may facilitate neurovascular interactions crucial for synaptic remodeling. In conclusion, this study demonstrates that BMSC-EVs enhance hippocampal synaptic plasticity in a region-distinct manner, with the DG and CA3 regions showing the most robust response. These effects are associated with synaptic protein regulation and the Sema3G-Nrp2/PlexinA4 axis.