Characterization of osteoclasts from patients harboring a G215R mutation in ClC-7 causing autosomal dominant osteopetrosis type II

Am J Pathol. 2004 May;164(5):1537-45. doi: 10.1016/S0002-9440(10)63712-1.


Autosomal dominant osteopetrosis II (ADOII) is a relatively benign disorder caused by a missense mutation in the ClCN7 gene. In this study, we characterize the osteoclasts from patients with ADOII, caused by a G215R mutation, and investigate the effect on osteoclast function in vitro. Osteoclasts from ADOII patients and healthy age- and sex-matched controls, were used to evaluate osteoclastogenesis, cell fusion, acidification, and resorptive activity. ADOII osteoclasts in vivo have increased number and size. However, in vitro we observed no significant changes in the osteoclast formation rate, the morphology, and the expression of markers, such as cathepsin K and tartrate-resistant acid phosphatase. When mature ADOII osteoclasts were investigated on mineralized bone, they degraded the bone material, however only to 10 to 20% of the level in controls. We show by acridine orange, that the reduced chloride transport leads to reduced acidification. We show that the residual activity is sensitive to inhibitors of cathepsins and chloride channels, confirming that resorption is reduced but present. In conclusion, this is the first functional in vitro study of human ADOII osteoclasts. We show normal osteoclastogenesis in ADOII osteoclasts. However, the residual activity of the ClC-7 channel in ADOII osteoclasts does not allow sufficient acidification and thereby resorption.

MeSH terms

  • Acid Phosphatase / biosynthesis
  • Acridine Orange / pharmacology
  • Age Factors
  • Biological Transport
  • Bone Resorption
  • Calcium Phosphates / pharmacology
  • Cathepsin K
  • Cathepsins / biosynthesis
  • Cell Differentiation
  • Cell Fusion
  • Chloride Channels / genetics*
  • Chloride Channels / physiology
  • Chlorides / metabolism
  • Enzyme Inhibitors / pharmacology
  • Humans
  • Immunoblotting
  • Immunohistochemistry
  • Isoenzymes / biosynthesis
  • Lipopolysaccharide Receptors / biosynthesis
  • Macrolides / pharmacology
  • Monocytes / metabolism
  • Mutation*
  • Osteoclasts / metabolism*
  • Osteopetrosis / diagnosis
  • Osteopetrosis / genetics*
  • Sex Factors
  • Tartrate-Resistant Acid Phosphatase
  • Time Factors


  • CLCN7 protein, human
  • Calcium Phosphates
  • Chloride Channels
  • Chlorides
  • Enzyme Inhibitors
  • Isoenzymes
  • Lipopolysaccharide Receptors
  • Macrolides
  • bafilomycin A1
  • calcium phosphate
  • Acid Phosphatase
  • Tartrate-Resistant Acid Phosphatase
  • Cathepsins
  • CTSK protein, human
  • Cathepsin K
  • Acridine Orange