G. Mbalaviele et al., Human mesenchymal stem cells promote human osteoclast differentiation fromCD34(+) bone marrow hematopoietic progenitors, ENDOCRINOL, 140(8), 1999, pp. 3736-3743
Interactions between osteoclast progenitors and stromal cells derived from
mesenchymal stem cells (MSCs) within the bone marrow are important for oste
oclast differentiation. In vitro models of osteoclastogenesis are well esta
blished in animal species; however, such assays do not necessarily reflect
human osteoclastogenesis. We sought to establish a reproducible coculture m
odel of human osteoclastogenesis using highly purified human marrow-derived
MSCs (hMSCs) and CD34(+) hematopoietic stem cells (HSCs). After 3 weeks, c
oculture of hMSCs and HSCs resulted in an increase in hematopoietic cell nu
mber with formation of multinucleated osteoclast-like cells Ocls). Cocultur
e of hMSCs with HSCs, transduced with a retroviral vector that expresses en
hanced green fluorescent protein, produced enhanced green fluorescent prote
in(+) Ocls, further demonstrating that Ocls arise from HSCs. These Ocls exp
ress calcitonin and vitronectin receptors and tartrate-resistant acid phosp
hatase and possess the ability to resorb bone. Ocl formation in this assay
is cell contact dependent and is independent of added exogenous factors. Co
nditioned medium from the coculture contained high levels of interleukin (I
L)-6, IL-11, leukemia inhibitory factor (LIF), and macrophage-colony stimul
ating factor. IL-6 and LIF were present at low levels in cultures of hMSCs
but undetectable in cultures of HSCs alone. These data suggest that cocultu
re with HSCs induce hMSCs to secrete cytokines involved in Ocl formation. A
ddition of neutralizing anti-IL6, IL-11, LIF, or macrophage-colony stimulat
ing factor antibodies to the coculture inhibited Ocl formation. hMSCs seem
to support Ocl formation as undifferentiated progenitor cells, because trea
tment of hMSCs with dexamethasone, ascorbic acid, and beta-glycerophosphate
(to induce osteogenic differentiation) actually inhibited osteoclastogenes
is in this coculture model. In conclusion, we have developed a simple and r
eproducible assay using culture-expanded hMSCs and purified HSCs with which
to study the mechanisms of human osteoclastogenesis.