Mesenchymal Stem Cell Derived Exosomes as a Mediator of Neuroinflammation and Neuronal Damage Following Cortical Injury

Exosomes are extracellular vesicles that mediate cell‐to‐cell communication and have promising therapeutic effects for cortical injury caused by stroke or trauma. Accordingly, we tested exosomes derived from mesenchymal stem cells as a therapy to enhance recovery in our nonhuman primate model of cortical injury. Aged female monkeys were trained on fine motor hand tasks and randomly assigned to exosome (n=5) or a vehicle control (PBS) (n=5) groups. A lesion was then made in the hand representation of the primary motor cortex (M1). At 24 hours and 14 days post‐injury, monkeys were each given 4×10 11 exosomes/kg or vehicle. At 15 days post‐injury, post‐operative testing on motor tasks resumed for 12 weeks. Treated monkeys all demonstrated a greater degree of functional recovery than vehicle controls. To assess mechanisms underlying exosome‐mediated enhancement of recovery, serum, cerebrospinal fluid (CSF), and terminal brain tissue were analyzed for markers of neuronal damage and neuroinflammation. To assess neuronal damage, we quantified Myelin Basic Protein (MBP) in CSF using ELISA, which showed a sharp increase 24‐hours after injury across all monkeys, followed by a decline in both groups. However, the decline in [MBP] was more rapid in exosome treated monkeys compared to vehicle, suggesting that exosomes had an immediate effect to reduce this marker of cortical injury. In addition, ELISA analysis of serum showed decreased RANTES (p=0.04) and Eotaxin (p=0.03) in exosome‐treated monkeys, suggesting an exosome‐mediated reduction of inflammation across the recovery period. To assess whether exosomes affected cellular markers of inflammation in the brain, we characterized microglial protein expression and morphology using immunohistochemistry and confocal microscopy. Optical density quantification of microglial markers Iba1, P2RY12, and the MHCII antigen‐presenting marker, LN3, showed that exosome‐treated animals had significantly lower expression (p=0.019) and smaller LN3+ puncta sizes (p=0.028). Sholl analysis of microglial morphology showed greater ramification length (p=0.019), number of intersections (p=0.02), and 3D convex‐hull volume of coverage (p=0.016) in exosome treated monkeys. Quantification of microglial cell density by morphology and LN3 expression further showed that exosome‐treatment reduced the number of hypertrophic “inflammatory” LN3+ microglia (p<0.05) and increased ramified microglia (LN3− and LN3+) (p<0.05). These results demonstrate that exosome treatment significantly reduces injury related damage and biomarkers of peripheral and brain inflammation, providing compelling data for the translational value of exosomes as a treatment for human stroke patients. Support or Funding Information Supported by NIH grant R21NS102991‐02 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .