Transgenic mice expressing tunable levels of DUX4 develop characteristic facioscapulohumeral muscular dystrophy-like pathophysiology ranging in severity

Takako I. Jones; Guo-Liang Chew; Pamela Barraza-Flores; Spencer Schreier; Monique Ramirez; Ryan D. Wuebbles; Dean J. Burkin; Robert K. Bradley; Peter L. Jones

We similarly assayed the moderate and severe bi-transgenic mouse models for ex vivo muscle function, both of which showed significant differences in treadmill fitness compared with the ACTA1-MCM controls and the mild model mice upon TMX injection ( Figure 4D and E) . For the moderate model analysis, female mice were run on the treadmill until exhaustion, as above, prior to TMX injection, and then run twice per week until sacrificed and assayed at MD14, the peak of DUX4-FL protein expression ( Figure 2D and I) and impaired treadmill running ( Figure 4D ) for the moderate model. The isolated EDL muscles from the moderate model mice were significantly weaker and stiffer compared with the ACTA1-MCM controls ( Figure 5 and S4); however, these muscles only showed small, but significant, decreases in specific force measurements and stiffness when compared with the mild bi-transgenic mice. The DUX4dependent impairment of muscle function was much more striking in the severe bi-transgenic model mice. Male and female mice were run on the treadmill until exhaustion, as before, prior to TMX injection and again at SD2, SD5, and SD7 (female) or SD8 (male), then sacrificed at The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. It . https://doi.org/10.1101/471094 doi: bioRxiv preprint decreases in all specific force measurements, and muscles were significantly stiffer after eccentric stretches when compared with ACTA1-MCM controls and the bi-transgenic mild model mice. In addition, the severe model mice were virtually non-responsive to low frequency stimuli (<30Hz) and were severely impaired across the force frequency assay range ( Figure 5C and S5F). When compared with the moderate model mice, muscles from the severe model were again significantly weaker. Overall, we conclude that murine skeletal muscles can tolerate a very low level of DUX4-FL expression without significant impairment of function; however, increases in DUX4-FL expression eventually lead to muscle weakness and loss of function in a dose-dependent manner.