G-protein-coupled estrogen receptor-1 facilitates chondrocyte proliferation in pubertal epiphyseal growth plate via PTHrP/Ihh regulation.

Aims: Oestrogen drives long-bone development through various oestrogen receptors. G-protein-coupled oestrogen receptor-1 (GPER-1), a membrane oestrogen receptor, mediates longitudinal bone growth during early puberty; however, the underlying mechanisms remain unclear. Therefore, this study elucidated the mechanisms underlying GPER-1-mediated bone growth.

Methods: A GPER-1 agonist (G1), GPER-1 antagonist (G15), and chondrocyte-specific GPER-1 knockout experiment (Col2a1-Cre; GPER-1^f/f, CKO) were used to investigate the role of GPER-1 in growth plate chondrocytes from C57BL/6 mice (total number = 48). We investigated the effects of GPER-1 activation or inhibition on the tibial growth plate and bone growth, including changes in proliferation and hypertrophy, and the expression of parathyroid hormone-related peptide (PTHrP), Indian hedgehog (Ihh), and their ratio (PTHrP/Ihh).

Results: G1 treatment-induced GPER-1 activation increased tibial growth plate thickness, proliferative zone thickness, and chondrocyte proliferation in mice. The hypertrophic zone thickness and type X collagen-stained area decreased in four-week-old G1-treated mice compared with the control group. GPER-1 activation increased the PTHrP/Ihh ratio in the growth plates of four- and eight-week-old mice. In contrast, blocking or deleting GPER-1 decreased the proliferative zones of the growth plate, proliferative chondrocytes, and PTHrP/Ihh. Additionally, the hyperopic zones of the growth plates increased with GPER-1 deficiency. In vitro micromass-3D cultured chondrocyte studies confirmed that G1 treatment increased proliferation, decreased hypertrophy, and increased PTHrP/Ihh protein levels.

Conclusion: This study demonstrates that GPER-1 maintains proliferation but suppresses chondrocyte hypertrophy in growth plates by upregulating PTHrP/Ihh during early puberty in male and female mice. Our findings suggest that GPER-1 may serve as a potential target for therapeutic modulation of linear bone growth during puberty.