Natural History of a Mouse Model Overexpressing the Dp71 Dystrophin Isoform

Figure 1. Dp71 overexpression and skeletal muscle function in del52;WT mice. (A) Western blotting with an antibody targeting the dystrophin C-terminal domain was done using total protein extracts from the tibialis anterior (TA) and the heart (12 μg each) of 6-month-old wild-type and del52;WT mice. Desmin was detected as a loading control. Quantification of Dp427 and Dp71 protein is on the right, with levels expressed relative to the average intensity of the corresponding wild-type samples for each tissue. Error bars: SEM, n = 5/group, * p < 0.05, unpaired two-tailed t-test. (B) Forelimb and total limb grip strength across age for wild-type, mdx, and del52;WT mice. Values are normalized to body weight. (C) Average fall times on the rotarod test across age. Dots represent individual mice. For (B,C), error bars: SEM, n = 5–19 (wild-type), 7–14 (mdx), 8–11 (del52;WT), * p < 0.05, ** p < 0.01, *** p < 0.001, one-way ANOVA with Tukey’s test.

Figure 2. Cardiac function in del52;WT mice. (A) Electrocardiography results across age for wild-type, mdx, and del52;WT mice. (B) Ejection fraction and fractional shortening across age, as obtained through echocardiography. For (A,B), error bars: SEM, n = 8–12 (wild-type and del52;WT), 5–8 (mdx), * p < 0.05, ** p < 0.01, *** p < 0.001, one-way ANOVA with Tukey’s test. (C) Representative M-mode (parasternal long axis) echocardiography images of the left ventricle in the three groups of mice across age. (D) Representative pressure/volume loops at baseline and with occlusion for wild-type and del52;WT mice at 6 months are shown on the left. Quantification of selected parameters from the loops is shown on the right. Dots represent individual mice. Error bars: SEM, n = 3 (wild-type), 7 (del52;WT), * p < 0.05, ** p < 0.01, unpaired two-tailed t-test.

Figure 3. Histological analysis of skeletal and cardiac muscle in del52;WT mice. (A) Representative hematoxylin/eosin-stained images of tibialis anterior muscles in wild-type and del52;WT mice at 6 and 12 months. Scale bar: 100 μm. (B) Representative immunofluorescence images of collagen type I (green) and nuclei (blue) in the cardiac muscle of wild-type and del52;WT mice at 12 months. Scale bar: 100 μm. (C) Quantification of collagen type I area in cardiac muscle immunofluorescence images. Dots represent individual mice. Error bars: SEM, n = 3/group. (D) Quantification of the minimal Feret’s diameter of individual cardiomyocytes in cardiac muscle immunofluorescence images. Box: P25-P75, central line: median, whiskers: range. n = 3/group (average 1535 and 1951 fibers counted per replicate for wild-type and del52;WT, respectively), *** p < 0.001, unpaired two-tailed t-test. (E) Data in (D), but as a frequency distribution.