Musculoskeletal magnetic resonance imaging in the DE50-MD dog model of Duchenne muscular dystrophy

Abstract

The DE50-MD canine model of Duchenne muscular dystrophy (DMD) has a dystrophin gene splice site mutation causing deletion of exon 50, an out-of-frame transcript and absence of dystrophin expression in striated muscles. We hypothesized that the musculoskeletal phenotype of DE50-MD dogs could be detected using Magnetic Resonance Imaging (MRI), that it would progress with age and that it would reflect those in other canine models and DMD patients. 15 DE50-MD and 10 age-matched littermate wild type (WT) male dogs underwent MRI every 3 months from 3 to 18 months of age. Normalized muscle volumes, global muscle T2 and ratio of post- to pre-gadolinium T1-weighted SI were evaluated in 7 pelvic limb and 4 lumbar muscles bilaterally. DE50-MD dogs, compared to WT, had smaller volumes in all muscles, except the cranial sartorius; global muscle T2 was significantly higher in DE50-MD dogs compared to WT. Muscle volumes plateaued and global muscle T2 decreased with age. Normalized muscle volumes and global muscle T2 revealed significant differences between groups longitudinally and should be useful to determine efficacy of therapeutics in this model with suitable power and low sample sizes. Musculoskeletal changes reflect those of DMD patients and other dog models.

Keywords: DE50-MD; DMD; Imaging biomarkers; MRI; Musculoskeletal.

Fig 1

(A) Pelvic limb muscles of 12-month-old wildtype (WT) dog on T1-weighted sequence: cranial sartorius (red), rectus femoris (orange), vastus lateralis (dark blue), biceps femoris (green), semitendinosus (yellow), gracilis (light blue), adductor (pink); (B) Lumbar muscles of 12-month-old wildtype dog on T1-weighted sequence: longissimus lumborum (red), multifidus lumborum (mid-blue), iliocostalis lumborum (purple), iliopsoas (dark orange).

Fig. 2

(A) Mid femoral pelvic limb transverse slice T1-weighted MRI images and (B) lumbar spine transverse slice T1-weighted MRI images in a wildtype (WT) and a DE50-MD dogs at multiple time-points; biceps femoris muscles (white outline) were more angular and there was increased fat surrounding lumbar muscles (arrows) in DE50-MD dogs.

Fig 3

(A) Mid femoral pelvic limb transverse slice T2-weighted MRI and (B) lumbar spine transverse slice T2-weighted MRI images in a wildtype (WT) dog and DE50-MD dog at multiple time-points; arrowheads highlight areas in pelvic limb and lumbar muscles of DE50-MD dogs that are more heterogeneous when compared to the opposite side as well as when compared to WT dogs.

Fig 4

Principal component 1 in wildtype (WT) and DE50-MD dogs from 3-months to 18-months of age (p<0.001); points are staggered and not all dogs were included at every time point.

Fig 5

(A) Mid femoral pelvic limb transverse slice T1-weighted MRI images in 12-month-old wildtype (WT) and DE50-MD dogs, outlining pelvic limb muscles; Mean muscle volume normalised to femur length of (i) cranial sartorius muscle (p=0.47), (ii) rectus femoris muscle, (iii) biceps femoris muscle, (iv) semitendinosus muscle, (v) gracilis muscle and (vi) adductor muscle in DE50-MD dogs (n=12) and WT dogs (n=10) every 3 months, from 3 to 18-months of age (**p<0.01, ***p<0.001); points are staggered and not all dogs were included at every time point. (B) Mid L5 transverse slice T1-weighted MRI images in 12-month-old wildtype (WT) and DE50-MD dogs outlining lumbar muscles; Mean muscle volume normalised to femur length of (i) longissimus lumborum muscle, (ii) multifidus lumborum muscle, (iii) iliocostalis muscle and (iv) iliopsoas muscle in DE50-MD dogs (n=12) and WT dogs (n=10) every 3 months, from 3 to 18-months of age (***p<0.001); points are staggered and not all dogs were included at every time point.

Fig 5

(A) Mid femoral pelvic limb transverse slice T1-weighted MRI images in 12-month-old wildtype (WT) and DE50-MD dogs, outlining pelvic limb muscles; Mean muscle volume normalised to femur length of (i) cranial sartorius muscle (p=0.47), (ii) rectus femoris muscle, (iii) biceps femoris muscle, (iv) semitendinosus muscle, (v) gracilis muscle and (vi) adductor muscle in DE50-MD dogs (n=12) and WT dogs (n=10) every 3 months, from 3 to 18-months of age (**p<0.01, ***p<0.001); points are staggered and not all dogs were included at every time point. (B) Mid L5 transverse slice T1-weighted MRI images in 12-month-old wildtype (WT) and DE50-MD dogs outlining lumbar muscles; Mean muscle volume normalised to femur length of (i) longissimus lumborum muscle, (ii) multifidus lumborum muscle, (iii) iliocostalis muscle and (iv) iliopsoas muscle in DE50-MD dogs (n=12) and WT dogs (n=10) every 3 months, from 3 to 18-months of age (***p<0.001); points are staggered and not all dogs were included at every time point.

Fig 6

Mid femoral pelvic limb transverse slice multi-slice echo T2-weighted sequence (global muscle T2 map) MRI images in 12-month-old wildtype (WT) and DE50-MD dogs outlining pelvic limb muscles; mean global muscle T2 signal intensity of (i) cranial sartorius muscle, (ii) rectus femoris muscle, (iii) biceps femoris muscle, (iv) semitendinosus muscle, (v) gracilis muscle, (vi) adductor muscle and (vii) vastus lateralis muscle in DE50-MD dogs (n=12) and WT dogs (n=10) every 3 months, from 3 to 18-months of age (*p<0.05, **p<0.01, ***p<0.001); points are staggered at each time point and not all dogs were included at every time point.

Fig 7

Mid L5 transverse slice T1-weighted MRI images in 12-month-old wildtype (WT) and DE50-MD dogs outlining lumbar muscles; Mean muscle volume normalised to L5 length ratio of the (i) longissimus lumborum muscle, (ii) multifidus lumborum muscle, (iii) iliocostalis lumborum muscle and (iv) iliopsoas muscle in DE50-MD dogs (n=12) and WT dogs (n=10) every 3 months, from 3 to 18-months of age (***p<0.001); points are staggered and not all dogs were included at every time point.

Fig 8

Mid femoral pelvic limb transverse slice T1-weighted MRI images in 12-month-old wildtype (WT) and DE50-MD dogs, outlining the cranial sartorius (red); i) Cranial sartorius muscle circularity in DE50-MD dogs (n=11) and WT dogs (n=10) every 3 months, from 3 to 18-months of age (**p<0.01, ***p<0.001); points are staggered and not all dogs were included at every time point.