OSTEOCLAST MARKERS ACCUMULATE ON CELLS DEVELOPING FROM HUMAN PERIPHERAL-BLOOD MONONUCLEAR PRECURSORS

Recent studies show that human osteoclasts develop in vitro from hemat opoietic cells; however, special cultures conditions and/or cytokine m obilized peripheral blood are apparently required. Here, we report tha t cells expressing osteoclast markers differentiate from precursors pr esent in nonmobilized peripheral blood mononuclear cells (PBMC), witho ut the addition of stromal cells, growth factors, cytokines or steroid s; and characterize their phenotype. Three days after establishing hig h-density PBMC cultures (1.5 X 10(6) cells/cm(2)), in serum-containing medium, small adherent colonies of tartrate resistant acid phosphatas e positive (TRAP+) cells emerge, amidst massive monocyte cell death. T hese adherent cells have an eccentrically placed, round nucleus, and e xpress low levels of TRAP and sodium fluoride-resistant- alpha-naphthy l-acetate-esterase (NaF-R-NSE). Over the next week, this cell populati on accumulates phenotypic markers of osteoclasts (vitronectin receptor [VR], calcitonin receptor, TRAP, cathepsin K protein, and mRNA) with increased nuclearity, covering the entire surface by 15 days. When cul tured on bone, VR+, TRAP+ cells of low multinuclearity appear and cove r up to 50% of the surface. Resorption lacunae can be observed by day 22. Although these pits are not nearly as numerous as the cells of pre osteoclast phenotype, they do represent the activity of a subset of os teoclast-like cells that has achieved osteoclastic maturity under thes e culture conditions. Transcripts for osteoprotegerin ligand (OPGL), a n osteoclast differentiation factor (also known as RANKL and TRANCE) a re expressed, likely by adherent cells. Thus, an adherent population o f cells, with preosteoclast/osteoclast phenotypic properties, arises s electively under simple culture conditions from normal PBMC. Further c haracterization of these cells should identify factors involved in the growth, terminal differentiation and activation of osteoclasts. I. Ce ll. Biochem. 72:67-80, 1999. (C) 1999 Wiley-Liss, Inc.