An osteoclast (from the Greek words for "bone" and "broken") is a type of bone cell that removes bone tissue by removing the bone's mineralized matrix. This process is known as bone resorption. Osteoclasts and osteoblasts are instrumental in controlling the amount of bone tissue. Osteoblasts form bone; osteoclasts resorb bone. Osteoclasts are formed by the fusion of cells of the monocyte-macrophage cell line. Osteoclasts are characterized by high expression of tartrate resistant acid phosphatase (TRAP) and cathepsin K.

acid ATPase

• constitutes a unique form in the family of tartrate-resistant acid phosphatases and may thus have the potential as a marker for osteoclast ontogeny and function. PMID: 2533053

Calcitonin (CT) receptor (CTR)

• a specific marker of the differentiated osteoclast that is regulated by calcitonin. PMID: 7664679
• a marker of osteoclast heterogeneity in osteopetrotic rodents. PMID: 2845732

Carboxyterminal Telopeptide of Type 1 Collagen (1CTP)

• a marker of osteoclastic bone resorption. PMID: 9223389

Cathepsin K

• a member of the papain superfamily of cysteine proteases and plays a pivotal role in osteoclast-mediated bone resorption. PMID: 12910475, PMID: 11277265
• a novel cysteine protease previously reported to be restricted in its expression to osteoclasts. PMID: 9393764
• predominantly expressed in osteoclasts and is closely related to cathepsins L. PMID: 8874809

CKBB (creatine kinase BB)

• predominantly found in brain and is not normally detected in the blood. PMID: 8889843
• Creatine kinase-BB in mammalian osteopetrosis is related to osteoclastic number and size, where it probably reflects the differentiation and maturation of inactive bone resorbing cells. PMID: 10943208

DAMP (acidotrophic amine 3-(2,4-dinitroanillino)-3'-amino-N-methyldipropylamine)

• A low pH marker for visualization of acidic compartments in cultured osteoclasts. PMID: 10639743

ED1

• The antibody ED1 stains monocytes, macrophages and osteoclast in the bone marrow and in the newly formed fracture callus. PMID: 15626449
• the combined use of TRAP and ED1 can be used to identify OC and their precursors in vivo. PMID: 12052261
• characterizes rat osteoclasts, monocytes, and macrophages. PMID: 7730591

Kat1-antigen (Kat1-Ag)

• a reliable immunological marker for identifying osteoclast precursors of rats: detection of subpopulations among precursors and initiation of osteoclastogenesis. PMID: 11326749

P1CP (procollagen carboxyterminal propeptide)

• an indicator of osteoblastic bone formation. PMID: 9223389

RANK

• a cell surface marker of human osteoclast precursors in peripheral blood, bone marrow, and giant cell tumors of bone. PMID: 16939392

Tartrate-resistant acid ATPase

• a cytochemical marker for osteoclasts. PMID: 2461980

TRAP (tartrate-resistant acid phosphatase)

• an important cytochemical marker of osteoclasts. PMID: 9102061
• a marker of osteoclast function. PMID: 6809291
• TRAcP activity alone is not a reliable marker for osteoclasts in bone marrow cultures. PMID: 2064844

Vacuolar-Type Proton Pump (E11)

• osteoclast differentiation marker. PMID: 1701138

Vitronectin Receptor (VR, VNR)

• fully differentiated osteoclast marker. PMID: 11448014, PMID: 1701138
• Rat osteoclast precursors in vivo express a vitronectin receptor and a chloride-bicarbonate exchanger. PMID: 9862219

Other Osteoclast Markers

• calcitonin receptor binding is a morphological and functional marker of osteoclasts that can be used in assessing the pathophysiology of disorders of bone remodeling. PMID: 2845732
• histochemical demonstration of TR-AP versus TS-AP on GMA-embedded bone sections by means of a pre-incubation method can be used as an identification marker of (pre)osteoclasts. PMID: 3745910
• Osteoclasts derive from hematopoietic stem cells according to marker, giant lysosomes of beige mice. PMID: 6112089
• Giant lysosomes, a cytoplasmic marker in osteoclasts of beige mice. PMID: 7391859
• Alkaline phosphatase expression during monocyte differentiation. Overlapping markers as a link between monocytic cells, dendritic cells, osteoclasts and osteoblasts. PMID: 10879691