c-Fms and the αvβ3 integrin collaborate during osteoclast differentiation
Roberta Faccio, … , F. Patrick Ross, Steven L. Teitelbaum
Roberta Faccio, … , F. Patrick Ross, Steven L. Teitelbaum
Published March 1, 2003
Citation Information: J Clin Invest. 2003;111(5):749-758. https://doi.org/10.1172/JCI16924.
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c-Fms and the αvβ3 integrin collaborate during osteoclast differentiation

Abstract

β3 integrin–null osteoclasts are dysfunctional, but their numbers are increased in vivo. In vitro, however, the number of β3–/– osteoclasts is reduced because of arrested differentiation. This paradox suggests cytokine regulation of β3–/– osteoclastogenesis differs in vitro and in vivo. In vitro, additional MCSF, but not receptor activator of NF-κB ligand (RANKL), completely rescues β3–/– osteoclastogenesis. Similarly, activation of extracellular signal-regulated kinases (ERKs) and expression of c-Fos, both essential for osteoclastogenesis, are attenuated in β3–/– preosteoclasts, but completely restored by additional MCSF. In fact, circulating and bone marrow cell membrane-bound MCSFs are enhanced in β3–/– mice, correlating with the increase in the osteoclast number. To identify components of the MCSF receptor that is critical for osteoclastogenesis in β3–/– cells, we retrovirally transduced authentic osteoclast precursors with chimeric c-Fms constructs containing various cytoplasmic domain mutations. Normalization of osteoclastogenesis and ERK activation, in β3–/– cells, uniquely requires c-Fms tyrosine 697. Finally, like high-dose MCSF, overexpression of c-Fos normalizes the number of β3–/– osteoclasts in vitro, but not their ability to resorb dentin. Thus, while c-Fms and αvβ3 collaborate in the osteoclastogenic process via shared activation of the ERK/c-Fos signaling pathway, the integrin is essential for matrix degradation.

Authors

Roberta Faccio, Sunao Takeshita, Alberta Zallone, F. Patrick Ross, Steven L. Teitelbaum

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Figure 10

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c-Fos overexpression by β3–/– cells rescues osteoclastogenesis but not m...
c-Fos overexpression by β3–/– cells rescues osteoclastogenesis but not matrix resorption. β3+/+ BMMs and β3–/– BMMs retrovirally transduced with pBabe vector (MOCK) or pBabe/c-Fos were selected in puromycin for 5 days, and resistant cells were used in the indicated experiments. (a) An equal number of BMMs were plated in 96-well plates and cultured in the presence of RANKL and low-dose MCSF. After 7 days, cells were stained for TRAP activity. While osteoclastogenesis remained arrested in MOCK-transduced β3–/– cells, those overexpressing c-Fos generated OCs indistinguishable from WT. (b) Equal amounts of protein were loaded in each lane, and c-Fos content was assessed by immunoblot. β3–/– OCs retrovirally transduced with pBabe/c-Fos vector expressed the same level of c-Fos protein as did β3+/+ cells (arrow). (c) β3+/+, MOCK β3–/–, and c-Fos β3–/– pre-OCs were plated on dentin slices with RANKL and low-dose MCSF. MOCK β3–/– cells were also cultured with RANKL and high-dose MCSF. After four days, dentin slices were stained for TRAP activity (+ Cells), or the cells were removed to visualize resorptive pits (– Cells). β3+/+ cells differentiated into OCs with a characteristic resorptive phenotype and excavated many large, well-demarcated lacunae. MOCK-transduced β3–/– cells formed few OCs in the presence of low-dose MCSF and generated poorly defined, small pits. High-dose MCSF and c-Fos overexpression yielded numerous multinucleated TRAP-expressing OCs that exhibited a nonresorbing phenotype and also generated poorly defined, small pits. Indicated are the mean numbers of pits ± SEM from three different fields per variable. ×10.