Pharmacological inhibition of Htr2b ameliorates bone destruction in glucocorticoid-induced osteonecrosis of the femoral head by suppressing Ca2+/ERK ‑ dependent osteoclast hyperactivation.

Glucocorticoid-induced osteonecrosis of the femoral head (GIONFH) is a progressive and disabling disease caused by the prolonged use of glucocorticoids. Accumulating evidence has established an association between hyperactivated osteoclasts and pathological bone erosion in GIONFH. Expression of 5-hydroxytryptamine receptor 2b (Htr2b), a canonical serotonin receptor, is upregulated during osteoclast maturation. Nevertheless, the underlying mechanisms governing this phenomenon, especially in relation to GIONFH, remain unexplored. In this study, the expression of Htr2b in osteoclast precursor cells (OPCs) treated with dexamethasone (DEX) was assessed using RNA sequencing. Functional validation was subsequently performed through siRNA-mediated knockdown and RS-127445-mediated pharmacological inhibition of Htr2b. Based on the developmental physiological features of the murine femoral head, we developed an innovative GIONFH model using six-month-old C57BL/6J mice and subjected them to an RS-127445 therapeutic intervention. RNA sequencing revealed significant upregulation of Htr2b expression in DEX-stimulated hyperactive osteoclasts. In vitro results demonstrated that Htr2b inhibition impeded osteoclast hyperactivation under DEX stimulation by suppressing nuclear factor of activated T cells 1 (Nfatc1) expression and nuclear translocation. At the mechanistic level, Htr2b inhibition interfered with calcium oscillation and ERK1/2 phosphorylation, thereby ceasing osteoclastogenesis. In vivo, integrated micro-CT and histomorphometry analyses revealed that RS-127445 (10 mg/kg) rescued methylprednisolone (MPS)-induced bone destruction and vascular damage in the femoral head by inhibiting osteoclast activity and promoting vascular formation. Our findings highlight the positive role of Htr2b in osteoclastogenesis exposed to glucocorticoids, suggesting that Htr2b is a novel therapeutic target for early pathological changes of GIONFH.