Estrogenic hormones counteract FSHD features in a muose model of muscle regeneration

The wide range of clinical symptoms in FSHD patients suggests the presence of modifying factors, still partially explored. Our group demonstrated that estrogens improve in vitro muscle differentiation of myoblasts from FSHD patients. Estrogens, through estrogen receptor beta (ER?), displace DUX4 from its target promoters and antagonize its transcriptional pathogenetic activity during myoblast differentiation. In this work, we confirm these data in vivo by analyzing the effect of estrogen on the regenerative potential of human muscle-precursor cells (PVCs) derived from healthy individuals and engineered to express DUX4 (DUX4-PVCs) or derived from FSHD patients. DUX4-PVCs were implanted into injured hindlimb muscle of NOD-scid-gamma (NSG) mice treated with 17?-estradiol (E2), 3?-diol (a specific ligand of ER? present in males), or EtOH (vehicle). Animals were monitored by a functional treadmill test and at the molecular levels by immunohistochemistry, gene, and protein expression. Our data demonstrate that human PVCs participate in mouse muscle regeneration and form functional heterokaryon muscle fibers that increase run ability recovery. The expression of DUX4 impairs this function and determines the increased formation of fibrotic tissue. Of relevance, both E2 and 3?-diol rescue this impairment, enhancing muscle formation and reducing the fibrotic response. Accordingly, both mouse hormone treatments rescue functional running ability reduced by DUX4 expression. Overall, these results suggest that estrogen hormones improve DUX4-PVCs regeneration ability and support the hypothesis of their beneficial activity in humans. In addition, our data substantiate the usefulness of the implantation/regeneration system here developed as an FSHD experimental model