There is increasing evidence suggesting that estrogens augment skeletal muscle regeneration processes after injury. To study the contribution of estrogen receptors α and β (ERα and ERβ) during muscle regeneration, skeletal muscles of ovariectomized (OVX) rats, as well as ERa‐ and ERβ‐knockout (αErko and βErko) mice, were injured with a myotoxin (notexin). OVX rats were simultaneously treated with the ER‐selective ligands genistein, ERα agonist 16α‐LE2 (alpha), ERβ agonist 8β‐VE2 (beta), or 17β‐estradiol (E ₂ ). OVX rats showed significantly elevated serum creatine kinase (CK) activity after muscle injury compared to intact sham‐treated animals. Treatment with ER ligands significantly reduced CK activity. TNF‐α, IL‐10, and MCP‐1 expression served to characterize immune responses. Treatment with all ER ligands, but particularly E ₂ and beta, reduced TNF‐α, but elevated MCP‐1 and IL‐10 expression. PCNA and MyoD expression served to define satellite cell activation and proliferation and were found to be up‐regulated by beta and E ₂ . To further study muscle regeneration responses, expression of the embryonic myosin heavy chain (MHC) was analyzed. Beta and E ₂ but not alpha increased embryonic MHC expression compared to OVX. The absence of ERβ in βErko mice negatively affected CK activity levels and expression of satellite cell and muscle regeneration markers (MHC embryonic, MyoD, Pax7) compared with aErko and wild‐type mice. In a classic Hershberger assay using male rats, beta stimulated muscle growth, accompanied by a strong induction of IGF‐1 expression. Our data provide evidence that ERβ signaling is involved in the regulation of skeletal muscle growth and regeneration by stimulating anabolic pathways, activating satellite cells and modulating immune responses.—Velders, M., Schleipen, B., Fritzemeier, K. H., Zierau, O., Diel, P. Selective estrogen receptor‐β activation stimulates skeletal muscle growth and regeneration. FASEB J. 26, 1909‐1920 (2012). www.fasebj.org

Androgens are modulators of skeletal muscle adaptation and regeneration processes. The control of satellite cell activity is a key mechanism during this process. In this study, we analyzed the ability of dihydrotestosterone (DHT) and anabolic steroids to induce and modulate the differentiation of C2C12 myoblastoma cells toward myotubes. C2C12 cells were dose-dependently treated with DHT and anabolic steroids. The time-dependent effects on differentiation were measured and correlated with the expression of genes involved in the regulation of satellite cell activity. The distribution of C2C12 cells within the cell cycle was measured by flow cytometry and differentiation by creatine kinase (CK) activity. Gene expression was analyzed using quantitative real-time PCR and confocal microscopy. The treatment with DHT and anabolic steroids resulted in a stimulation of C2C12 cell proliferation and CK activity. The antiandrogen flutamide was able to antagonize this effect. The expression of the androgen receptor, SOX8, SOX9, Delta, Notch, myostatin, and paired box gene7 (Pax7) was modulated by androgens. The treatment with DHT and anabolic steroids resulted in a strong stimulation of myostatin expression not only in undifferentiated cells but also in myotubes. The stimulation could be antagonized by flutamide. The expression of Pax7 was detectable in C2C12 cells early after treatment with DHT. Our results demonstrate that the key mechanisms of satellite cell differentiation are modulated by androgens. Androgens stimulate the proliferation of C2C12 cells, accelerate the process of differentiation, and increase the expression of myostatin in undifferentiated and differentiated cells. Our findings may have implications not only for the treatment of muscular diseases but also for the improvement of doping analytical methods.