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

To determine if increases in DUX4-FL protein and target gene expression levels in skeletal muscles correlate with altered muscle function and strength, we performed treadmill exhaustion assays and ex vivo muscle physiology studies. Adult ACTA1-MCM control and bitransgenic mice showed size differences between males, with bi-transgenic males being significantly smaller than controls (~26g and ~23g, respectively; Figure S3B and D), while females for both genotypes showed no significant size differences prior to TMX injection (~22g and ~21g, respectively; Figure S3A and C). Therefore, male and female mice were analyzed separately to assess potential sex differences in presentation of the phenotypes. The treadmill analysis protocol consisted of running the mice on a slightly inclined treadmill, slowly increasing the speed until the mice could not run any longer, and measuring the time to fatigue, with a maximum assay time of 20 min. We found these particular conditions (see Methods) provided highly consistent results and a readily assayable window for these three mouse models. Both male and female ACTA1-MCM control mice, injected with the appropriate TMX dose for the group being assayed, showed steady levels of near maximum treadmill running fitness (~20 min) over the course of the assays (Figure 4 , blue lines). Similarly, treadmill fitness for male and . CC-BY-NC 4.0 International license is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the author/funder.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 female bi-transgenic mice was not significantly different from the ACTA1-MCM controls ( Figure 4 , green lines). However, male and female mice injected with TMX to produce either a moderate level of pathology (1X 5mg/kg TMX) or a severe level of pathology (2X 10mg/kg TMX) were significantly less fit compared with controls ( Figure 4 , red lines). Interestingly, both the moderate and severe models showed sex-specific treadmill fitness profiles in which the female mice ( Figure 4A , C) were more severely affected than the male mice ( Figure 4B , D).