Doreste Gonzalez, Bruno; (2018) The effect of modulating the dystrophic skeletal muscle environment on satellite cell engraftment. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Satellite cells derived from normal donor mice contribute to muscle regeneration and restore dystrophin expression when transplanted into dystrophin-deficient mice (mdxnu/nu). However, unless the local host muscle environment has been modulated with high doses of gamma-radiation to incapacitate host satellite cells, but maintaining a functional niche, donor satellite cell engraftment is negligible. This work aimed to determine the cells and pathway(s) within host muscle which are responsible for mediating the radiation-induced effect. I first investigated whether this effect was mediated by apoptotic cells, by quantifying the percentage of TUNEL positive cells in muscles at basal levels and at different time points after irradiation. There was a correlation between the percentage of TUNEL positive cells and the time for optimal engraftment in mdxnu/nu host muscles. This suggests that apoptotic cells within host muscle might be mediators of the radiation-induced promotion of donor satellite cell engraftment. Then I performed a series of co-transplantation experiments to determine whether different cell preparations within the pre-irradiated mdxnu/nu muscle would enhance donor satellite cell transplantation. Three cell preparations (satellite cells, monocytic cell suspension, and single myofibres) were isolated from pre-irradiated mdxnu/nu donors and grafted with donor 3F-nLacZ-2E satellite cells into mdxnu/nu hosts. None of these preparations significantly enhanced donor satellite cell engraftment in non-irradiated hosts. Finally, I performed RNA sequencing on differentially treated muscles to investigate possible signalling pathways involved in enhancing satellite cell engraftment in pre-irradiated muscles. This revealed a phenotype consistent with type I and type II interferon responses after irradiation, leading to the secretion of the IL-6 family of cytokines. Further investigation confirmed an upregulation of LIF in pre-irradiated muscle. Overall, my findings suggest that irradiation of host muscle alters the inflammatory phenotype and elicits the secretion of the IL-6 family of cytokines, which are powerful regulators of satellite cell proliferation and differentiation.

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