Exosomal miR-29 mediates the therapeutic effects of placenta derived mesenchymal stromal cells in Duchenne muscular dystrophy

Background: Duchenne muscular dystrophy (DMD) is a degenerative lethal, X-linked disease of skeletal and cardiac muscles caused by mutations in the dystrophin gene. Cell therapy using different cell types, including mesenchymal stem cells (MSCs), has been considered as a potential approach for the treatment of DMD. The safety and therapeutic impact of these cells have been demonstrated in preclinical and clinical studies and their functions are attributed to paracrine effects that are mediated by secreted cytokines and extracellular vesicles. Methods: Here, we studied the therapeutic effects of MSCs derived from bone marrow, adipose tissue, umbilical cord and placenta on the differentiation of human myoblasts from healthy controls and Duchenne patients and on mdx mice using novel quantitative miRNA reporters, ImageStreamX and confocal microscopy for exosome delivery and in vivo imaging techniques. Results: Treatment of myoblasts with the different MSCs or exosomes secreted by these cells demonstrated that placenta derived MSCs (PLMSCs) and their exosomes (PL-exosomes) exerted a preferential differentiation effects on mouse and human myoblasts compared to cells/exosomes derived from bone marrow and adipose tissues. Similarly, PLMSCs and PL-exosomes decreased the expression of fibrogenic genes in DMD patient myoblasts and increased the expression of utrophin in these cells. The PL-MSC effects were mediated by the transfer of exosomal miR-29 to the myoblasts. Intramuscular transplantation of MSCs or exosomes in mdx mice resulted in decreased creatine kinase level, decreased inflammatory cytokine expression and increased utrophin expression. In addition, the PL-MSCs and PL-exosomes significantly decreased the level of fibrosis in the diaphragm and cardiac muscles and the expression of TGF-beta. Imaging analyses using MSCs or exosomes labeled with fluorescent dyes demonstrated localization and engraftment of the cells and exosomes in the muscle tissues up to 4 weeks post-treatment. Summary/Conclusion: These results demonstrate that PL-MSCs and their secreted exosomes have important clinical applications in cell therapy of DMD partly via the delivery of exosomal miR-29 and targeting of multiples pathways including tissue fibrosis, inflammation and utrophin expression