Tailored multipotent mesenchymal stromal cell harvested exosomes carrying elevated miR-17-92 cluster enhance neurovascular remodeling & improve functional recovery after stroke in rats

Introduction: MSC generated exosomes mediate therapeutic benefits of MSCs for stroke, which are at least in-part attributed to their miRNA contents. In vitro, the miR-17-92 cluster promotes oligodendrogenesis, neurogenesis and axonal outgrowth, and tailored MSC exosomes enriched with the miR-17-92 cluster promote axonal outgrowth of primary cortical neurons. We therefore investigated whether the miR-17-92 cluster enriched exosomes (Exo-miR-17-92+) harvested from MSCs enhance neurological recovery compared to control MSC derived exosomes (Exo-Con).Methods: Rats (n=8/group) subjected to 2 hours of transient MCAO were intravenously administered ExomiR-17-92+, Exo-Con, or liposomes, and were sacrificed 28 days post MCAO. Foot-fault test, and a modified neurologic severity score (mNSS) were carried out at 1, 3, 7, 14, 21 and 28 days after MCAO by an investigator blinded to the treatments. Histochemistry, immunohistochemistry and Golgi-Cox staining were used to assess dendritic, axonal, synaptic and myelin remodeling. Expression of PTEN and activation of its downstream proteins, Akt, mTOR and GSK-3β in the peri-infarct region were measured by means of Western blots. Results: Compared with the liposome treatment, both exosome treatment groups exhibited significant improvement of functional recovery (P\u3c0.05, respectively), but Ex-miR-17-92+ treatment had more robust effects on improvement of neurological function (P\u3c0.05), and enhancements of oligodendrogenesis, neurogenesis and neurite remodeling/neuronal dendrite plasticity in the ischemic boundary zone (IBZ) than the Ex-Con treatment (P\u3c0.05, respectively). Moreover, Ex-miR-17-92+ treatment substantially inhibited PTEN, a validated miR-17-92 cluster target gene, and subsequently increased the phosphorylation of PTEN downstream proteins, Akt, mTOR, and decreased the activity of GSK-3β by phosphorylating GSK-3β in neurons compared to Ex-Con treatment (P\u3c0.05, respectively). Conclusions: Our data suggest that treatment of stroke with tailored exosomes enriched with the miR-17- 92 cluster increases neural plasticity and functional recovery after stroke, possibly via targeting PTEN to activate the PI3K/Akt/mTOR/GSK-3β signaling pathway