Quantitative 3D assessment of muscle dystrophy through X-ray phase-contrast tomography

Duchenne muscular dystrophy (DMD) is characterized by progressive skeletal muscle degeneration and weakness. DMD is the most common muscular dystrophy; commonly diagnosed in childhood, it has a deadly outcome, typically for respiratory or cardiac failure. In spite of a longer disease course, obtained in recent years thanks to palliative pharmacological treatments, DMD remains one of the foremost public health challenges. The intricate interaction between dysfunctional skeletal muscle fibers and the resident different cell types, including inflammatory and fibroadipogenic progenitors, directly contributes to the progression of the disease, affecting its severity. In this study, we used the remarkable precision of X-ray phase-contrast tomography (XPCT) to conduct an unprecedented three-dimensional (3D) examination of skeletal muscle architecture, comparing healthy and dystrophic mdx mice. The morphological features observed in XPCT images were compared to conventional histological sections, corroborated by morphometric evaluation of bidimensional parameters. Through XPCT, we followed the spatial disposition of degenerating or distorted dystrophic myofibers along a length of approximately 1.3 mm. In addition, the exploitation of micro-XPCT, unveiled significant quantitative differences between healthy and mdx muscles in numerous 3D parameters, such as myofiber length, variability in myofiber caliber, myofiber volume, and the volume of interstitial tissues and cells. We propose XPCT as a novel imaging tool for the ex vivo characterization of the fine architecture of dystrophic muscles: this approach is particularly relevant to highlight the outcomes of a treatment in pre-clinical models and provides the structural bases underlying the functional features of the diseased skeletal muscle.