OCSTAMP (osteoclast stimulatory transmembrane protein) is a cell surface receptor that functions as a critical mediator of osteoclast multinucleation and bone resorption. As one of the identified "master fusogens" alongside DC-STAMP, OCSTAMP promotes cell-cell fusion between osteoclast precursors of monocyte/macrophage lineage, enabling formation of multinucleated osteoclasts 1. This fusion process is essential for osteoclast maturation and functional competence, allowing cytoskeletal reorganization including actin ring and ruffled border formation necessary for bone resorption 1. OCSTAMP expression is epigenetically regulated during osteoclastogenesis through histone modifications and is coordinately induced with other fusion mediators like DC-STAMP and ATP6V0D2 2. MicroRNA-6924-5p directly targets OCSTAMP's 3'UTR to inhibit osteoclastogenesis, providing a regulatory mechanism for controlling osteoclast formation 3. Beyond bone metabolism, OCSTAMP has recently emerged as a pathogenic factor in silicosis; elevated OCSTAMP expression accelerates lung fibrosis by promoting ferroptosis of alveolar epithelial cells, and OCSTAMP inhibition via siRNA mitigates disease progression 4. Pharmacological targeting of OCSTAMP-mediated osteoclast fusion shows therapeutic promise for treating pathological bone loss including osteoporosis and cancer-induced osteolysis 56.