GPR65 Functions as a Key Factor of Bone Aging and a Novel Therapeutic Target for Osteoporosis.

Osteoporosis (OP) is a metabolic bone disease, characterized by loss of bone mass and destruction of bone microstructure, which has a high incidence of disability. Identification of the key factors of pathogenesis is essential for diagnosis and therapy. In this study, we have identified the proton-sensing receptor GPR65, which is specifically expressed in osteoclasts and is significantly down-expressed in osteoclast differentiation, aging, ovariectomy (OVX)-, and tail suspension (TS)-induced osteoporotic bone tissue. In vivo experiments confirmed that knockout of GPR65 exacerbates bone loss and OP induced by TS, OVX, and aging. In vitro experiments demonstrated that silencing GPR65 or application of either endogenous or exogenous antagonist of GPR65 promotes osteoclast differentiation, whereas overexpression of GPR65 or application of either endogenous or exogenous agonist inhibits osteoclast differentiation, and knockout of Gpr65 mitigates this effect. Mechanistic studies revealed that GPR65 inhibits osteoclast differentiation by binding to Gαq, activating GSK3β, and suppressing its phosphorylation, thereby inhibiting the nuclear translocation of NFATc1 that mediates osteoclast differentiation. Furthermore, application of GPR65 agonist alleviated OVX-induced OP in vivo, indicating GPR65 as a novel therapeutic target for bone aging and OP.