Biomedical subjects

Yu Sin Lau

Publications and source records attributed to Yu Sin Lau.

3 recordsLinked to original sources

PubMed2006

Hepatocyte growth factor can substitute for M-CSF to support osteoclastogenesis.

Osteopetrotic mice lacking functional macrophage-colony stimulating factor (M-CSF) recover with ageing, suggesting that alternative osteoclastogenesis pathways exist. Hepatocyte growth factor (HGF) and M-CSF signal through tyrosine kinase receptors and phosphorylate common transducers and effectors such as Src, Grb2, and PI3-Kinase. HGF is known to play a role in osteoclast formation, and in this study we have determined whether HGF could replace M-CSF to support human osteoclastogenesis. We found that the HGF receptor, c-Met, is expressed by the CD14(+) monocyte fraction of human peripheral blood mononuclear cells (PBMC). HGF was able to support monocyte-osteoclast differentiation in the presence of receptor activator for nuclear factor kappaB ligand as evidenced by the formation of numerous multinucleated tartrate-resistant acid phosphatase and vitronectin receptor positive cells which formed F-actin rings and were capable of lacunar resorption. The addition of a neutralising antibody to M-CSF did not inhibit osteoclast differentiation. HGF is a well-established survival factor and viability assays and live/dead staining showed that it promoted the survival and proliferation of monocytes and osteoclasts in a manner similar to M-CSF. Our findings indicate that HGF can substitute for M-CSF to support human osteoclast formation.

Adult↗

PubMed2006

Staphylococcus aureus capsular material promotes osteoclast formation.

Osteomyelitis, which is most frequently due to infection by Staphylococcus aureus, commonly causes bone destruction. S. aureus is known to secrete a number of surface-associated proteins that are potent stimulators of bone resorption. The precise cellular and humoral mechanisms that mediate this stimulatory effect are uncertain. In this study, we have determined whether osteoclast formation and resorption is directly promoted by surface-associated proteins. Surface-associated material (SAM) obtained from a 24-hour culture of S. aureus was added to cultures of mouse and human monocytes. Human monocyte cultures were incubated in the presence and absence of a soluble receptor activator of nuclear factor kappa B ligand (RANKL) and macrophage colony stimulating factor (M-CSF). In cultures where M-CSF, RANKL, and SAM were added together, osteoclast formation did not exceed that seen in cultures with M-CSF and RANKL. In keeping with this finding, SAM did not increase osteoclast formation and resorption when mouse monocytes were cocultured with RANKL-expressing osteoblasts. In the absence of RANKL, however, SAM was capable of inducing osteoclast formation in cultures of human monocytes. This finding was evidenced by the generation of vitronectin receptor and tartrate-resistant acid phosphatasepositive multinucleated cells that were capable of lacunar resorption. Inhibitors of RANKL-dependent (RANK:Fc, OPG) and RANKL-independent (anti-TNF-alpha, gp130, IL-8, TGF-beta) osteoclast formation did not inhibit SAM-induced osteoclast formation. SAM did not stimulate mature osteoclast resorption activity. These findings indicate that RANKL, which is present in the circulation as a soluble factor, does not play a role in osteoclast formation in the presence of S. aureus SAM and that S. aureus SAM contains a soluble factor that promotes osteoclast formation by a RANKL-independent mechanism.

Animals↗

PubMed2005

Phenotypic and molecular studies of giant-cell tumors of bone and soft tissue.

Giant-cell tumor of bone (GCTB) and giant-cell tumor of soft tissue (GCTST) are tumors that contain a prominent osteoclastlike giant-cell component. The precise relationship between these morphologically similar tumors is unclear, and the cellular mechanism whereby giant cells accumulate within these and other locally aggressive tumors is uncertain. In this study, we have examined the cytochemical, functional, and molecular phenotype of the mononuclear and multinucleated components of GCTB and GCTST. Giant cells in GCTB and GCTST exhibited an osteoclast phenotype expressing tartrate-resistant acid phosphatase and vitronectin receptor and being capable of lacunar resorption. The mononuclear stromal cells derived from GCTB and GCTST exhibited an osteoblast phenotype, expressing alkaline phosphatase, and the receptor activator for nuclear factor kappaB ligand (RANKL), a factor that is essential for osteoclast formation. These cells also expressed osteoprotegerin (OPG), an inhibitor of osteoclastogenesis, and TRAIL, a receptor that binds OPG. Lacunar resorption by giant cells isolated from GCTB and GCTST was inhibited by OPG, zoledronate, and calcitonin. These findings indicate that the mononuclear and giant-cell components of GCTB and GCTST have similar phenotypic features and that the accumulation of osteoclasts in these giant-cell-rich tumors occurs by a RANKL-dependent process. RANKL expression by osteoblastlike mononuclear stromal cells in these tumors stimulates osteoclast formation and resorption; this would account for the osteolysis associated with these giant-cell-rich tumors. Inhibitors of osteoclast formation and activity are likely to be effective in controlling the osteolysis associated with GCTB and possibly other giant-cell-rich lesions.

Apoptosis Regulatory Proteins↗