osteoklaastien

Osteoklaasten is a term used in histology to denote bone-resorbing cells, most often equated with osteoclasts. The term appears in several languages as an alternative or historical variant of osteoclast.

Osteoklaasten are large multinucleated cells that originate from the monocyte-macrophage lineage. They adhere to the bone surface, form a sealed resorption lacuna, and resorb bone by acidification and enzymatic digestion. The resorptive apparatus includes proton pumps, chloride channels, and proteolytic enzymes such as cathepsin K. Their activity is essential for bone remodeling, a process balanced by osteoblast-driven bone formation.

Differentiation and activity are regulated by the RANKL–RANK–OPG axis. Osteoblasts and stromal cells express RANKL, promoting osteoclast formation; osteoprotegerin (OPG) inhibits this signaling. Hormones and cytokines, notably parathyroid hormone, vitamin D, and calcitonin, modulate osteoklaasten activity and overall bone turnover.

Clinical relevance includes diseases arising from imbalanced activity. Excessive osteoklaasten activity contributes to osteoporosis and osteolytic lesions in cancers; insufficient activity leads to conditions such as osteopetrosis. Therapeutic approaches target resorption, with bisphosphonates and monoclonal antibodies that inhibit RANKL (for example denosumab) used to reduce osteoclast-mediated bone loss.

In research and diagnosis, osteoklaasten can be identified by histochemical staining for tartrate-resistant acid phosphatase (TRAP) and by biomarkers of bone turnover in serum or urine. Imaging and bone biopsy provide complementary assessments of resorption activity.