P.343 - Xenografts of human myogenic cells into mice form pure human muscle: a new model for FSHD

Abstract

Facioscapulohumeral Muscular Dystrophy (FSHD) is one of the most common muscular dystrophies in man, with a prevalence of 1 in ~8,000 individuals worldwide. Studies of the pathogenic mechanisms underlying human myopathies and muscular dystrophies often require animal models, but a model that recapitulates the signature pathophysiology of FSHD is not yet available. Our laboratory has developed a novel mouse model for FSHD. We optimized methods to xenograft immortalized human muscle precursor cells (hMPCs) to promote the formation of mature human myofibers following implantation into the hindlimbs of NOD-Rag1nullIL2rγnull immune-deficient mice. Specifically, intermittent neuromuscular electrical stimulation (iNMES) increases the number and size of the engrafted human myofibers, and decreases the distances between the largest fibers and their neighbours. Some grafts are comprised of only human myofibers, >1000 in all, with no murine fibers remaining. The human myofibers are innervated, their contractile apparatus is fully differentiated, and they are comprised of human myonuclei, with minimal contamination by murine myonuclei. We used these methods to generate mature human muscle tissue from immortalized FSHD and control hMPCs. FSHD but not control xenografts express DUX4 and several downstream gene products, such as ZSCAN4 and TRIM43. Furthermore, the FSHD grafts but not controls have D4Z4 repeats that are hypomethylated. Our results are consistent with the properties of biopsies of FSHD and healthy muscles. Thus, our methods provide a novel tool for studying FSHD-derived human muscle under controlled conditions within the mouse hindlimb and for testing new therapeutic agents in vivo.