UC Irvine

Mesenchymal Stem Cell-derived Exosomes Promote Neurologic Recovery in Experimental Autoimmune Encephalomyelitis model of Multiple Sclerosis

By

Milad Riazifar

Doctor of Philosophy in Pharmacological Sciences

University of California, 2017

Professor Weian Zhao, Chair

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) in which autoreactive T cells attack CNS, resulting in demyelination, neuronal injury and death, which account for the neurological disability. Preclinical studies revealed immunomodulatory and immunosuppressive properties of mesenchymal stem cell (MSC) to treat MS. However, Lung entrapment, maldifferentiation, phenotype change and potentially tumor formation are current challenges for stem cell therapy. The much smaller size of MSC-derived exosomes (Exo), allow reduced lung entrapment, achieve superior biocompatibility, are more stable and expose fewer risks, which together makes them an attractive alternative.

Here, using experimental autoimmune encephalomyelitis (EAE) as a MS mouse model (n=30), we show that systemic injection of MSC-Exo (150 μg) result in sustained recovery and improved motor function (p<0.01). This recovery is associated reduced in neuroinflammation and increased remyelination (p<0.05). Biodistribution experiments show that Exo were mostly found in liver and spleen in healthy and EAE mice, but also in spinal cords of EAE, but not healthy animals. This suggests the involvement Exo in the spinal cord lesion repair. Using Foxp3-eGFP Treg reporter C57BL/6 mice (n=20) we showed that number of CD4+/CD25+/Foxp3+ regulatory T cells (Tregs) increase within the spinal cords of Exo treated animals compared to control (43.3% vs. 26.3%; p<0.05). Systemic injection of MSC-Exo results in clinical recovery in these mice as well (p<0.05). Additionally, co-culture of MSC-Exo (20 μg) with activated T cells result in reduced T cell proliferation and increased Treg numbers in vitro compared to control (14.9 ± 3.5 vs. 5.2 ± 1.2; p<0.05), proposing the capability of Exo to induce Tregs. Eliminating RNA by UV light reduced the function of the exosomes in Treg induction (p<0.05), and deep RNA sequencing revealed that the MSC-Exo are highly enriched in mRNAs with anti-inflammatory properties (i.e. indoleamine 2, 3-dioxygenase, Thymosin β). Similarly, proteomics identified numerous proteins with anti-inflammatory and neuroprotective properties in the Exo fractions (i.e. Glypican-1, Galectin-1, HSP70). In summary, this study describes the potential of MSC-Exo as therapeutics in autoimmune neurodegenerative diseases