Osteoclastic Potential of Human CFU-GM: Biphasic Effect of GM-CSF

Abstract

Human osteoclasts can be efficiently generated in vitro from cord blood mononuclear cells and derived CFU-GM colonies. However, CFU-M colonies are poorly osteoclastogenic. Short-term (2-48 h) treatment with GM-CSF stimulates osteoclast formation by proliferating precursors, whereas longer exposure favors dendritic cell formation.Introduction: Osteoclasts (OC) differentiate from cells of the myelomonocytic lineage under the influence of macrophage-colony stimulating factor (M-CSF) and RANKL. However, cells of this lineage can also differentiate to macrophages and dendritic cells (DC) depending on the cytokine environment. The aims of this study were to develop an efficient human osteoclastogenesis model and to investigate the roles of granulocyte macrophage-colony stimulating factor (GM-CSF) and M-CSF in human OC differentiation. Materials and Methods: A human osteoclastogenesis model, using as precursors colony forming unit-granulocyte macrophage (CFU-GM) colonies generated from umbilical cord mononuclear cells cultured in methylcellulose with GM-CSF, interleukin (IL)-3 and stem cell factor (SCF), has been developed. CFU-GM, colony forming unitmacrophage (CFU-M), or mixed colonies were cultured on dentine with soluble RANKL (sRANKL) and human M-CSF with and without GM-CSF. Major endpoints were OC number, dentine resorption, and CD1a ϩ DC clusters. Results: Osteoclast generation from CFU-GM and mixed colonies treated with M-CSF and sRANKL for 7-14 days was highly efficient, but CFU-M colonies were poorly osteoclastogenic under these conditions. Pretreatment of precursors with M-CSF for 7 or 14 days maintained the precursor pool, but OCs were smaller and resorption was reduced. The effect of GM-CSF treatment was biphasic, depending on the timing and duration of exposure. Short-term treatment (2-48 h) at the beginning of the culture stimulated cell proliferation and enhanced OC formation up to 100%, independent of sRANKL. Longer-term GM-CSF treatment in the presence of sRANKL, however, inhibited OC generation with the formation of extensive CD1a ϩ DC clusters, accompanied by downregulation of c-Fos mRNA. Delaying the addition of GM-CSF resulted in progressively less inhibition of osteoclastogenesis. Conclusions: Human CFU-GM, but not CFU-M, progenitors have high osteoclastogenic potential. GM-CSF plays an important role in osteoclastogenesis and has a biphasic effect: Short-term treatment potentiates OC differentiation by proliferating precursors, but persistent exposure favors DC formation.

Nmp4/CIZ Suppresses the Parathyroid Hormone Anabolic Window by Restricting Mesenchymal Stem Cell and Osteoprogenitor Frequency

“…Although CFU-C cells were elevated in the Nmp4-KO mice, this only approached significance, and there was no difference in the levels of CFU-M cells between the genotypes. The precise lineage of the osteoclast and its relationship to other hematopoietic cells is controversial; however, there are a number of studies supporting the hypothesis that the osteoclast lineage branches to terminal differentiation via the CFU-GM cells before further passage toward the monocyte/macrophage lineage [39,40]. No differences between WT and Nmp4-KO mice in CD8 + T cells were detected in the PBL (average -SD, number of mice/ experimental group 11-14; statistical differences were determined using a 2-way ANOVA).…”

IL-23 Inhibits Osteoclastogenesis Indirectly through Lymphocytes and Is Required for the Maintenance of Bone Mass in Mice

“…GM-CSF powerfully inhibits osteoclast formation, but only in progenitors exposed to both GM-CSF with RANKL (16). When GM-CSF treatment is withdrawn before RANKL exposure, no inhibition occurs (41); indeed, osteoclast progenitors expand (42). IL-23 elicits T cell IL-17 and IL-6 production, both stimulators of osteoblast RANKL expression (43).…”

What We Learn from Bone Complications in Congenital Diseases? Thalassemia, an Example

“…Hodge et al, describe Osteoclasts as multinucleated cells which differentiate from early myelomonocytic progenitors rather than more differentiated monocyte/macrophage progenitors (Hodge et al, 2004). Roodman describes their function as they reabsorb bone by secreting proteases which dissolve the matrix and produce acid that releases bone mineral into the extracellular space under the ruffled border of the plasma membrane of osteoclasts (Roodman, 2004).…”