Modulation of tartrate-resistant acid phosphatase expression by calcitriol in CSF-induced macrophage colonies

The osteoclast is thought to be a hemopoietically derived cell, but questions exist about which hemopoietic growth factors are responsible for proliferation of osteoclast precursors. Experiments were thus performed to see if recombinant human colony-stimulating factors (CSFs) influenced the expression of tartrate-resistant acid phosphatase (TRAP), an osteoclast marker enzyme, by monkey bone marrow colonies in vitro. In addition, the effect of 1,25-dihydroxyvitamin D3 (calcitriol) on CSF-induced colony growth and TRAP expression was also determined. Bone marrow was obtained from a single Macaca nemestrina monkey, kept frozen in liquid nitrogen, and aliquots of frozen cells were thawed and placed at 10(5) cells per plate in a standard cell colony-forming unit (CFU-C) assay. The recombinant human CSFs (granulocyte-macrophage CSF, GM-CSF; macrophage CSF, M-CSF; interleukin 3, IL-3; and granulocyte CSF, G-CSF) were added to the cultures at 50 U/ml, and calcitriol was titrated for each CSF from 0.1 to 100 nM. Day-14 colonies were stained to demonstrate TRAP-positive cells in individual colonies. GM-CSF caused an increase (193%, p less than 0.0004) in total colony numbers that was only partially inhibited by calcitriol. IL-3 and M-CSF had less effect, and G-CSF had no effect. GM-CSF also caused a large increase in TRAP-positive macrophage (M) colonies (326%, p less than 0.0001) and changed the relative proportion of TRAP-positive M colonies from 39% to 62% of all M colonies. M-CSF caused less increase in numbers of TRAP-positive M colonies and had no effect on the proportion of TRAP-positive colonies. When GM-CSF was present, calcitriol caused a maximum number of TRAP-positive colonies to appear at 1 nM, and it caused a drastic decrease in TRAP-positive colonies at higher doses. Calcitriol at 10 nM caused TRAP-negative colonies to increase in number and proportion when GM-CSF was present, but in the presence of M-CSF, the same dose of calcitriol caused a decline in numbers of TRAP-negative colonies. These results suggest that GM-CSF may be important in the replication of TRAP-positive mononuclear cells that resemble osteoclast precursors and that myeloid cell development may be weighted toward TRAP-positive or TRAP-negative progeny depending on whether GM-CSF or M-CSF predominates. They further suggest that calcitriol concentration may be critical in this process.