The effect of modulating the dystrophic skeletal muscle environment on satellite cell engraftment

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

Response of plasma microRNAs to nusinersen treatment in patients with SMA.

peer reviewedOBJECTIVE: Spinal muscular atrophy (SMA) is a common genetic cause of infant mortality. Nusinersen treatment ameliorates the clinical outcome of SMA, however, some patients respond well, while others have limited response. We investigated microRNAs in blood samples from SMA patients and their response to nusinersen treatment evaluating the potential of circulating microRNAs as biomarkers for SMA. METHODS: In a discovery cohort study, microRNA next-generation sequencing was performed in blood samples from SMA patients (SMA type 2, n = 10; SMA type 3, n = 10) and controls (n = 7). The dysregulated microRNAs were further analysed in the therapeutic response cohort comprised of SMA type 1 patients (n = 22) who had received nusinersen treatment, at three time points along the treatment course (baseline, 2 and 6 months of treatment). The levels of the studied microRNAs were correlated to the SMA clinical outcome measures. RESULTS: In the discovery cohort, 69 microRNAs were dysregulated between SMA patients and controls. In the therapeutic response cohort, the baseline plasma levels of miR-107, miR-142-5p, miR-335-5p, miR-423-3p, miR-660-5p, miR-378a-3p and miR-23a-3p were associated with the 2 and 6 months response to nusinersen treatment. Furthermore, the levels of miR-107, miR-142-5p, miR-335-5p, miR-423-3p, miR-660-5p and miR-378-3p at 2 months of treatment were associated with the response after 6 months of nusinersen treatment. INTERPRETATION: Blood microRNAs could be used as biomarkers to indicate SMA patients' response to nusinersen and to monitor the efficacy of the therapeutic intervention. In addition, some of these microRNAs provide insight into processes involved in SMA that could be exploited as novel therapeutic targets