Early intermittent low-dose sclerostin antibody treatment promotes surface bone formation and reduces bone loss, but also decreases osteocyte apoptosis and mechanotransduction in ovariectomized rats: a pilot study

Abstract

Neutralizing sclerostin antibodies (Scl-Ab) mitigate bone loss and promote bone formation to address fracture risk in postmenopausal osteoporosis. Clinically, this treatment is administered monthly for women at high risk of fragility fractures, who are often years into menopause. Preclinical studies have demonstrated that dampening of bone formation occurs with continuous dosing at supraphysiological doses. Osteoporotic bone loss occurs rapidly during early menopause, followed by longer-term changes in bone mineralization and osteocyte activity. Whether earlier administration of lower-exposure Scl-Ab can mitigate bone loss and osteocyte-driven secondary mineralisation is unknown. The objective of this study was to evaluate the effects of early intermittent low-dose Scl-Abon: (1) osteoclastogenesis and bone resorption, (2) perilacunar remodelling, (3) secondary mineralization, and (4) osteocyte mechanosensitivity. Female retired breeder Wistar rats underwent bilateral ovariectomy and received monthly low-dose Scl-Ab injections (2 mg/kg/month) from 3 to 14 weeks post-OVX, while a control group remained untreated. Early intermittent low-dose Scl-Ab treatment increased bone formation and reduced osteoclastogenesis and catabolic gene expression ((Sost, Ctsk, Mmp9) compared to untreated rats. Treatment also decreased the percentage of empty lacunae and the number of MMP14+ osteocytes, accompanied by lower perilacunar mineral density and smaller lacunar size, indicating improved osteocyte survival and reduced perilacunar remodelling. Conversely, expression of osteocyte-mediated mineralization genes (DMP1, PHEX, OPN, ALP) and mechanotransduction-related genes (Vcl, integrins 5, V, {beta}1, CX43, Axin2, IFT88, Adcy6, Pkd1, Cav1) were reduced. Together, these findings suggest that early intermittent low-dose Scl-Ab therapy promotes surface bone formation while attenuating osteocyte-mediated secondary mineralization after initial bone loss. Mini AbstractEarly intermittent low-dose sclerostin antibody treatment reduced osteoclastogenesis, bone resorption, and perilacunar remodelling, while promoting bone formation, decreasing osteocyte apoptosis, and downregulating genes associated with secondary mineralization and mechanosensitivity in ovariectomized rats. These findings suggest early intervention with Scl-Ab enhances bone formation and limits osteocyte apoptosis and subsequent secondary mineralization.