Inorganic phosphate modulates responsiveness to 24,25(OH)2D 3 in chondrogenic ATDC5 cells

Tracy A. Denison, Christopher F. Koch, Irving M. Shapiro, Zvi Schwartz, Barbara D. Boyan

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


Chondrogenic ATDC5 cells were used as a model of in vitro endochondral maturation to study the role of inorganic phosphate (Pi) in the regulation of growth plate chondrocytes by vitamin D3 metabolites. ATDC5 cells that were cultured for 10 days post-confluence in differentiation media and then treated for 24 h with Pi produced a type II collagen matrix based on immunohistochemistry and expressed mRNAs for several chondrocytic markers, including aggrecan, collagen types II and X, cartilage oligomeric matrix protein, and SOX9. Pi also caused a decrease in [35S]-sulfate incorporation and stimulated apoptosis, as evidenced by increased DNA fragmentation and caspase-3 activity. In addition, treatment with Pi induced sensitivity to 24,25-dihydroxyvitamin D3 and this effect was both dose-dependent and was blocked by phosphonoformic acid (PFA), a specific inhibitor of sodium dependent type III Pi transporters. Treatment with 24R,25(OH)2D 3 reduced cell number and increased alkaline phosphatase specific activity in a dose-dependent manner. Moreover, 24R,25(OH)2D 3 reversed the Pi-induced decrease in incorporation of [ 3H]-thymidine and [35S]-sulfate incorporation, as well as the Pi-induced increase in apoptosis. These results suggest that Pi acts as an early chondrogenic differentiation factor, inducing response to 24R,25(OH)2D3; treatment of committed chondrocytes with Pi induces apoptosis, but 24R,25(OH)2D3 mitigates these effects, indicating a possible inhibitory feedback loop.

Original languageEnglish (US)
Pages (from-to)155-162
Number of pages8
JournalJournal of Cellular Biochemistry
Issue number1
StatePublished - May 1 2009


  • 24,25-dihydroxy vitamin D3
  • ATDC5 cells
  • Chondrogenesis
  • Phosphate

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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