Role of G Protein-coupled Estrogen Receptor-1 and Matrix Metalloproteinases 2 and 9 in the Effects of Estradiol-17beta on Proliferation, Protein Synthesis and Protein Degradation in Bovine Satellite Cell Cultures

Abstract Text: In feedlot steers, Estrogen (E2) and combined E2 and trenbolone acetate (TBA) (a testosterone analog) implants enhance rate and efficiency of muscle growth; and, consequently, these compounds are widely used as growth promoters. Although the positive effects of E2 are well established, the mechanism(s) involved is not well understood. Combined E2/TBA implants result in significantly increased muscle satellite cell number in feedlot steers. Additionally, E2 treatment stimulates proliferation of cultured bovine satellite cells (BSC). The ability of E2 to stimulate satellite cell proliferation is significant because satellite cells provide nuclei needed to support postnatal muscle fiber hypertrophy and are crucial in determining the rate and extent of muscle growth. To identify the mechanism(s) involved in E2-stimulated muscle growth, we have focused on identifying the receptors involved in the effects of E2 on BSC proliferation, protein synthesis and protein degradation. Our previous studies have shown that silencing expression of estrogen receptor 1 (ESR1) or epidermal growth factor receptor (EGFR) suppresses E2-stimulated BSC proliferation. Studies in nonmuscle cells have shown that binding of E2 to G protein-coupled estrogen receptor (GPER)-1 results in activation of matrix metalloproteinases  2 and 9 (MMP2/9) resulting in proteolytic release of heparin binding epidermal growth factor-like growth factor (hbEGF) from the cell surface. Released hbEGF binds to and activates EGFR resulting in increased proliferation. To determine if GPER-1 and MMP2/9 are involved in the ability of E2 or IGF-1 to affect BSC, we have utilized specific inhibitors to inhibit the activity of GPER-1 and MMP2/9 and assessed the impact of this inhibition on the effects of E2 on proliferation, protein synthesis and protein degradation rates in BSC cultures. Treatment of BSC cultures with G36, a GPER-1 specific inhibitor, or with an inhibitor of MMP2/9 activity completely suppressed E2-stimulated proliferation and protein synthesis (p < 0.05) but had no effect on the ability of E2 to suppress protein degradation. Our results show that both GPER-1 and MMP2/9 are necessary for E2-stimulated proliferation and protein synthesis in BSC cultures.

Keywords: bovine, satellite cell, muscle, Estradiol-17beta