Osteoclasts

Osteoclasts are large multinucleated cells of the monocyte/macrophage lineage that resorb bone by secreting protons and lysosomal enzymes such as cathepsin K onto the bone surface. Together with bone-forming osteoblasts, they maintain skeletal homeostasis through continuous remodeling. Excessive osteoclast activity drives bone loss in osteoporosis and inflammatory bone disease.