UCLA

Progressive fibrosis of muscles in Duchenne muscular dystrophy impairs muscle function and contributes to premature death of patients. The use of many potentially-therapeutic molecules is limited by an inability to target their delivery specifically to sites of active muscle pathology. In this dissertation research, we tested the hypothesis that inflammatory cells can function as vectors to deliver therapeutic molecules to sites of active pathology in dystrophic muscle. We designed a transgene in which expression of leukemia inhibitory factor (LIF) is driven by the promoter for CD11b, a surface marker highly expressed by mature macrophages. Expression of the transgene (CD11b/LIF) in the mdx mouse model of Duchenne muscular dystrophy increased LIF protein content at inflammatory muscle lesions without off-target expression. Transplantation of transgenic bone marrow cells to non-transgenic, mdx mice showed that a single intervention can provide long-term benefits to dystrophic muscles. The primary benefit of the transgene was reduced fibrosis. Transgenic LIF inhibited fibrogenesis by reducing transforming growth factor-β expression and reducing the numbers of fibro/adipogenic progenitor cells in mdx muscles. CD11b/LIF expression also biased macrophages away from a CD163+/CD206+, pro-fibrotic phenotype and reduced their intramuscular numbers. Reduced chemotactic response of CD11b/LIF+ macrophages to C-C motif chemokine ligand-2 contributed to the reduced macrophage numbers. The dispersion of cytolytic, CD68+ macrophages was impaired in transgenic muscles early in the pathology. Localized accumulation of CD68+ macrophages increased the numbers of injured fibers. At later stages of the pathology, the transgene did not affect macrophage distribution but did reduce muscle damage. Collectively, our observations show that targeted expression of the CD11b/LIF transgene improves dystrophic muscle health. More importantly, we have shown that genetically-modified macrophages can be used as vectors for the delivery of therapeutic molecules to diseased tissues with a significant inflammatory component.