Long bone osteoclasts display an augmented osteoclast phenotype compared to calvarial osteoclasts.
Osteoclasts are multinucleated cells specialized in degrading bone and characterized by high expression of the enzymes tartrate-resistant acid phosphatase (TRAP) and cathepsin K (CtsK). Recent studies show that osteoclasts exhibit phenotypic differences depending on their anatomical site of action. Using immunohistochemistry, RT-qPCR, FPLC chromatography and immunoblotting, we compared TRAP expression in calvaria and long bone. TRAP protein and enzyme activity levels were higher in long bones compared to calvaria. In addition, proteolytic processing of TRAP was more extensive in long bones than calvaria which correlated with higher cysteine proteinase activity and protein expression of CtsK. These two types of bones also exhibited a differential expression of monomeric TRAP and CtsK isoforms. Analysis of CtsK(-/-) mice revealed that CtsK is involved in proteolytic processing of TRAP in calvaria. Moreover, long bone osteoclasts exhibited higher expression of not only TRAP and CtsK but also of the membrane markers CD68 and CD163. The results suggest that long bone osteoclasts display an augmented osteoclastic phenotype with stronger expression of both membranous and secreted osteoclast proteins.
Department of Laboratory Medicine, Division of Pathology, Karolinska Institutet, F46 Karolinska University Hospital, Huddinge SE-141 86, Sweden. Serhan.Zenger@ki.se
Serhan
S
Zenger
Barbro
B
Ek-Rylander
Göran
G
Andersson
D000135:Acid Phosphatase / Q000096:biosynthesis*; D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis; D015214:Antigens, Differentiation, Myelomonocytic / Q000096:biosynthesis; D001842:Bone and Bones / Q000166:cytology*; D057056:Cysteine Proteases / Q000096:biosynthesis*; D007527:Isoenzymes / Q000096:biosynthesis*; D051379:Mice; D008817:Mice, Mutant Strains; D010010:Osteoclasts / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000096:biosynthesis; D012886:Skull / Q000166:cytology*; D000071681:Tartrate-Resistant Acid Phosphatase; D000098902:CD163 Antigen; D000097382:CD68 Molecule
D000135:Acid Phosphatase; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D057056:Cysteine Proteases; D007527:Isoenzymes; D011956:Receptors, Cell Surface; D000071681:Tartrate-Resistant Acid Phosphatase; D000098902:CD163 Antigen; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C000605511:Acp5 protein, mouse