O Kudo

Interleukin-6 and interleukin-11 support human osteoclast formation by a RANKL-independent mechanism.

Interleukin-6 (IL-6) and interleukin-11 (IL-11) are known to influence osteoclast formation and bone resorption. In order to determine whether IL-6 and IL-11 could independently support human osteoclast formation, these factors were added to cultures of human peripheral blood mononuclear cells of the monocyte (CD14(+)) fraction in the presence of macrophage colony-stimulating factor (M-CSF). Under these conditions, IL-6 and IL-11 induced the formation of multinucleated cells which were positive for TRAP, VNR, and calcitonin receptor and capable of lacunar resorption. Osteoclastogenesis induced by IL-6 and IL-11 was inhibited by the addition of an anti-gp130 antibody but not by osteoprotegerin. These results indicate that IL-6 and IL-11, which are thought to play a role in several osteolytic bone disorders, are directly capable of inducing osteoclast formation by a RANKL-independent mechanism.

Proinflammatory cytokine (TNFalpha/IL-1alpha) induction of human osteoclast formation.

TNFα and IL‐1α are potent stimulators of bone resorption in vivo and in vitro. Recently, it has been demonstrated that these two cytokines directly induce osteoclastogenesis in mouse marrow cultures. This study determined whether TNFα (± IL‐1α) is also capable of inducing human osteoclastogenesis. The CD14+ monocyte fraction of human peripheral mononuclear cells was cultured with TNFα ± IL‐1α in the presence of M‐CSF. TNFα induced the formation of multinucleated cells (MNCs) which were positive for TRAP, VNR and cathepsin K and showed evidence of resorption pit formation. IL‐1α stimulated TNFα‐induced lacunar resorption two‐ to four‐fold. Osteoprotegerin, the decoy receptor for RANKL, did not inhibit this process. Anti‐human IL‐1α neutralizing antibodies significantly inhibited resorption without inhibiting the formation of TRAP+/VNR+ MNCs. These results suggest that, in the presence of M‐CSF, TNFα is sufficient for inducing human osteoclast differentiation from circulating precursors by a process which is distinct from the RANK/RANKL signalling pathway. Copyright

Two distinct cellular mechanisms of osteoclast formation and bone resorption in periprosthetic osteolysis.

Purpose: TNFα and IL‐1α are proinflammatory cytokines that are abundant in periprosthetic tissues. These cytokines stimulate bone resorption and have recently been shown to directly induce osteoclast formation in mouse marrow cultures. We examined whether TNFα and IL‐1α can directly induce osteoclast formation from human arthroplasty‐derived (CD14+) macrophages by a mechanism independent of RANKL‐induced osteoclastogenesis.

Isolation of Human Osteoclasts Formed In Vitro: Hormonal Effects on the Bone-Resorbing Activity of Human Osteoclasts

Osteoclasts are multinucleated cells that carry out bone resorption. Analysis of the direct effect of hormones on the bone-resorbing activity of human osteoclasts has been limited by difficulties in isolating these cells from the human skeleton. In this study, human osteoclasts formed from cultures of peripheral blood mononuclear precursors (PBMCs) on a Type-I collagen gel were isolated by collagenase treatment for investigating their resorptive activity. PBMCs were cultured in the presence of M-CSF, soluble RANKL, dexamethasone, and 1,25(OH)2D3. The isolated multinucleated cells expressed the osteoclast markers, TRAP, VNR, cathepsin K, calcitonin receptors and were capable of extensive lacunar resorption. Calcitonin inhibited the motility and resorptive activity of osteoclasts. RANKL significantly stimulated osteoclast resorption, but 1,25(OH)2D3, PTH, and OPG did not. These findings indicate that calcitonin and RANKL act directly on human osteoclasts to inhibit and stimulate osteoclast bone-resorbing activity, respectively, and that PTH, 1,25(OH)2D3, and OPG are more likely to influence osteoclast activity indirectly. This technique of human osteoclast isolation should permit the effects of cellular and hormonal/humoral factors on the bone-resorbing activity of mature human osteoclasts to be assessed independently of any effect such factors have on osteoclast formation. It should also make it possible to examine directly the resorptive activity and other characteristics of osteoclasts in specific bone disorders such as Pagets disease.

Menatetrenone (Vitamin K2) Acts Directly on Circulating Human Osteoclast Precursors

It is still not certain what the direct effect of menatetrenone is on osteoclast precursors. In the present study, we investigated whether menatetrenone has a direct effect on circulating osteoclast precursors to influence osteoclast differentiation. Monocytes isolated from human peripheral blood were cultured with receptor-activated NF-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). Menatetrenone or vitamin K1 was then added to the cultures. Geranylgeraniol or phytol (the respective side chain) was also added to the cultures instead of menatetrenone or vitamin K1, respectively. After 7 and 14 days incubation, cultures were evaluated for cytochemical and functional evidence of osteoclast formation. The number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNCs) and the percentage area of lacunar resorption induced by RANKL and M-CSF were decreased when menatetrenone or geranylgeraniol was added to the cultures. Dose-dependent inhibition of osteoclast formation and lacunar resorption was seen when the cultures were treated with menatetrenone or geranylgeraniol. In contrast, vitamin K1 or phytol did not affect the number of TRAP-positive MNCs nor the percentage area of lacunar resorption. These results indicate that menatetrenone not only influences osteoclast formation via bone stromal cells but also acts directly on circulating osteoclast precursors to influence osteoclast differentiation. These findings also suggest that geranylgeraniol, the side chain of menatetrenone, plays an important role in this inhibitory effect.

Osteoclast differentiation factor induces synovial macrophage-osteoclast differentiation in rheumatoid arthritis.

Abstract The aim of this study was to clarify the role of osteoclast differentiation factor (ODF) and osteoprotegerin (OPG) in synovial macrophage–osteoclast differentiation. Synovial macrophages were cultured in the presence of macrophage-colony-stimulating factor (M-CSF) and/or ODF. OPG was added to cocultures of synovial macrophages and UMR106. The cultures on glass coverslips were stained with osteoclast-associated markers, tartrate-resistant acid phosphatase (TRAP), and vitronectin receptor (VNR), as well as macrophage-associated markers CD11b and CD14. Functional evidence of osteoclast formation was determined by a resorption pit assay. To investigate whether rheumatoid arthritis (RA) synovial cells expressed messenger RNA (mRNA) for ODF, OPG, and the receptor activator of NF-κB (RANK), we performed a polymerase chain reaction (PCR) analysis. The addition of M-CSF or ODF alone induced TRAP-positive multinucleated cell formation. Resorption pits were rarely detected with M-CSF alone. ODF was capable of inducing bone resorption and enhancing osteoclastogenesis, as well as bone resorption in the presence of M-CSF. In the coculture system, both osteoclast formation and bone resorption were inhibited by OPG in a dose-dependent manner. In all experiments, synovial cells, including macrophages and fibroblasts, expressed the mRNA for RANK, ODF, and OPG. Our findings suggest that ODF plays a role in regulating RA synovial macrophage–osteoclast differentiation, and that synovial cells might have the ability to produce ODF. OPG might be further developed as a new strategy for treating bone destruction in RA joints.