Estrogens improve differentiation of facioscapulohumeral muscular dystrophy myoblasts by antagonizing DUX4 activity.

Abstract Facioscapulohumeral muscular dystrophy (FSHD) is characterized by extreme variability in symptoms with females being less severely affected than males and presenting a higher proportion of asymptomatic carriers. Gender factors involved in the disease have not been completely defined. Using myoblasts derived from FSHD patients, both primary and immortalized cell cultures, we investigated the effect of estrogens on muscle differentiation features. Our results demonstrate that estrogens improve the differentiation of isolated FSHD myoblasts without affecting cell proliferation or survival. Particularly, fusion index and positivity to the differentiation marker myosin heavy chain are significantly reduced in FSHD myoblasts grown in estrogen-deprived medium compared to CTR whereas estrogen supplementation recover this reduction. This effect is mediated by estrogen receptor beta (ER?) which antagonizes the function of the homeobox protein DUX4. Estrogen decreases DUX4 residency on the promoter of its targets whose transcription is accordingly reduced. Interestingly, during myoblast differentiation the levels and activity of DUX4 increase progressively associated with its enhanced recruitment in the nucleus; ER? interferes with this recruitment by re-localizing DUX4 in the cytoplasm. This work identifies estrogens as a potential factor underlying FSHD gender difference with protective function against this disease.