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Logo of annrheumdAnnals of the Rheumatic DiseasesCurrent TOCInstructions for authors
 
Ann Rheum Dis. Jan 2004; 63(1): 67–70.
PMCID: PMC1754733

Metabolic activation stimulates acid secretion and expression of matrix degrading proteases in human osteoblasts

Abstract

Background: Both cellular and matrix components of healthy bone are permanently renewed in a balanced homoeostasis. Osteoclastic bone resorption involves the expression of vacuolar-type ATPase proton pumps (vATPase) on the outer cell membrane and the secretion of matrix degrading proteases. Osteoblasts modulate the deposition of bone mineral components and secrete extracellular matrix proteins.

Objectives: To investigate the ability of osteoblasts and osteosarcoma to secrete acid and express matrix degrading proteases upon metabolic activation. To examine also the potential contribution of vATPases to proton secretion expressed on osteoblasts.

Methods: Osteoblasts were isolated from trabecular bone and characterised by reverse transcriptase-polymerase chain reaction and immunohistochemistry. Proton secretion was analysed by a cytosensor microphysiometer.

Results: Osteoblasts not only express matrix degrading proteases upon stimulation with tumour necrosis factor or with phorbol ester but they also secrete protons upon activation. Proton secretion by osteoblasts is associated partially with proton pump ATPases.

Conclusion: These data suggest that, in addition to monocyte derived osteoclasts, cytokine activated mesenchymal osteoblasts and osteosarcoma cells may contribute to the acidic milieu required for bone degradation.

Figure 1
Activation of proton secretion (rmax/req in per cent) in osteoblasts upon stimulation by PMA or TNF. (A) Osteoblasts were preincubated for about 20 minutes in running medium to reach metabolic quiescence characterised by a low spontaneous acidification ...
Figure 2
Blocking proton secretion by osteoblasts upon addition of Bafilomycin A1 or Amiloride. Osteoblast-like cells were incubated in medium containing 1 mM and 2 mM Bafilomycin A 1 or 500 mM and 10000 mM Amiloride. Pericellular acidification was recorded by ...

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