Beyond Myoblasts: DUX4 Drives Fibrosis and Myogenic Reprogramming in Mesenchymal Stem Cells

We developed a cellular model of mesenchymal stem cells (MSCs) with inducible DUX4 expression (MSC-DUX4) to investigate the potential role of MSCs in facioscapulohumeral muscular dystrophy (FSHD). DUX4 expression was successfully induced, with MSC-DUX4 maintaining the characteristic surface marker profile of MSCs. Unlike myoblasts, which rapidly undergo apoptosis upon DUX4 induction, MSC-DUX4 remained viable although they exhibited increased reactive oxygen species (ROS) accumulation. Transcriptomic analysis revealed broad changes, including strong upregulation of several myogenic genes, suggesting that DUX4 confers a partial myogenic program to MSCs. Indeed, Dox-induced MSC-DUX4 formed myotube-like structures expressing myogenic markers (myogenin, Troponin T, MF20), though fusion efficiency was markedly reduced compared to myoblasts, indicating limited and likely defective myogenic differentiation capacity. In parallel, adipogenic and osteogenic potentials were strongly impaired, as demonstrated by reduced lipid and calcium deposition, altered expression of FABP4 and leptin. Moreover, DUX4-expressing MSCs displayed pro-fibrotic features, including enhanced collagen III/IV and fibronectin, suggesting impaired extracellular matrix turnover. Together, these findings indicate that DUX4 induces a unique phenotype in MSCs, characterized by impaired differentiation, oxidative stress, partial myogenic reprogramming, and pro-fibrotic activity, contributing to muscle pathology in FSHD.