Microglial vesicles improve post-stroke recovery by preventing immune cell senescence and favoring oligodendrogenesis

Contrastingmyelin damage through the generation ofnewmye- linating oligodendrocytes represents a promising approach to promote functional recoveryafter stroke.Here, we askedwhether activation of microglia and monocyte-derived macrophages af- fects the regenerative process sustained byG protein-coupled re- ceptor 17 (GPR17)-expressing oligodendrocyte precursor cells (OPCs), a subpopulation of OPCs specifically reacting to ischemic injury. GPR17-iCreERT2:CAG-eGFP reporter mice were employed to trace the fate of GPR17-expressing OPCs, labeled by the green fluorescent protein (GFP), after permanent middle cerebral artery occlusion. By microglia/macrophages pharmacological depletion studies, we show that innate immune cells favor GFP+ OPC reaction and limit myelin damage early af- ter injury, whereas they lose their pro-resolving capacity and ac- quire a dystrophic “senescent-like” phenotype at later stages. Intracerebral infusion of regenerative microglia-derived extra- cellular vesicles (EVs) restores protectivemicroglia/macrophages functions, limiting their senescence during the post-stroke phase, and enhances thematurationofGFP+OPCs at lesionborders, re- sulting in ameliorated neurological functionality. In vitro exper- iments showthatEV-carried transmembrane tumor necrosis fac- tor (tmTNF) mediates the pro-differentiating effects on OPCs, with future implications for regenerative therapies.