In Duchenne muscular dystrophy (DMD), the defining hallmark of disease is loss of dystrophin, a structural protein that stabilizes the sarcolemma. Dystrophic muscle also exhibits severe immune infiltration distinct from, yet synergistic with, a lack of dystrophin. The resulting cycles of immune-mediated degeneration and regeneration ultimately end in fibrosis and permanent myofiber loss. Unfortunately, pathways leading to this immune response seen in DMD progression are not fully understood, posing a considerable obstacle to development of therapeutics.
Exosomes are small extracellular vesicles that contain lipids, proteins, and/or nucleic acids, and have recently been established as a key mediator of intercellular communication. Increasingly, exosomes have been implicated in diseases featuring chronic inflammation, such as asthma, arthritis, and Alzheimer’s. In preliminary studies on dystrophic myotubes and macrophages in vitro, we found inflammation induces packaging of inflammatory and dystrophin-targeting miRNAs into exosomes. Additionally, in vivo, we observed elevated levels of serum exosomes in mdx vs. WT mice. However, research on exosomes in DMD currently lacks information on the functional benefits of exosome inhibition in live models.
Here, we performed daily dosing of 2–8-week-old mdx mice with GW4869, an established exosome inhibitor, and ketoconazole, an FDA-approved drug recently found to inhibit exosome biogenesis in vitro. We find treatment of mdx mice with either GW4869 or ketoconazole improves motor function, including increases in hindlimb grip strength and increased hang time in wire hang and box hang assays. Additionally, spleen size, an indicator of systemic inflammation, was significantly reduced in treated groups. These findings suggest that exosome inhibition may curtail the inflammatory cycle that results in functional losses in dystrophic muscle, making the exosome biosynthesis pathway a promising novel drug target for DMD. Future experiments will use resistive pulse sensing to quantify reduction of circulating serum exosomes, and qPCR to determine exosomal miRNA content for each treatment group.