Biomedical subjects

David M Findlay

Publications and source records attributed to David M Findlay.

22 records · Page 2Linked to original sources

PubMed2004

The nitrogen-containing bisphosphonate, zoledronic acid, influences RANKL expression in human osteoblast-like cells by activating TNF-alpha converting enzyme (TACE).

UNLABELLED: Bisphosphonates are used to prevent osteoclast-mediated bone loss. Zoledronic acid inhibits osteoclast maturation indirectly by increasing OPG protein secretion and decreasing transmembrane RANKL expression in human osteoblasts. The decreased transmembrane RANKL expression seems to be related to the upregulation of the RANKL sheddase, TACE. INTRODUCTION: Bisphosphonates (BPs) exhibit high affinity for hydroxyapatite mineral in bone and are used extensively to treat malignancy-associated bone disease and postmenopausal bone loss by inhibiting osteoclast (OC)-mediated bone resorption. MATERIALS AND METHODS: We examined the effect of the most potent nitrogen-containing BP available, zoledronic acid (ZOL), on the expression of RANKL and osteoprotegerin (OPG), critical factors in the regulation of OC formation and activation, in primary osteoblast (OB)-like cells derived from human bone, using flow cytometry, ELISA, semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), in situ immunofluorescence staining, and Western blotting. RESULTS: Our studies show that ZOL, while not significantly affecting RANKL or OPG gene expression, markedly increased OPG protein secretion and reduced transmembrane RANKL protein expression in OB-like cells. The reduction in transmembrane RANKL expression was preceded by a marked increase in the expression of the metalloprotease-disintegrin, TNF-alpha converting enzyme (TACE). In addition, the decreased transmembrane expression of RANKL could be partially reversed by a TACE inhibitor, TAPI-2. CONCLUSIONS: Our studies indicate that ZOL, in addition to its direct effects on mature OCs, may inhibit the recruitment and differentiation of OCs by cleavage of transmembrane RANKL in OB-like cells by upregulating the sheddase, TACE.

ADAM Proteins↗

PubMed2003

Receptor activator of nuclear factor-kappaB ligand expression by human myeloma cells mediates osteoclast formation in vitro and correlates with bone destruction in vivo.

Multiple myeloma (MM) is an incurable B-cell malignancy able to mediate massive destruction of the axial skeleton. The aim of this study was to examine the involvement of the tumor necrosis factor-ligand family member, receptor activator of nuclear factor-kappaB ligand (RANKL), and its naturally occurring antagonist, osteoprotegerin (OPG), in MM biology. Using flow cytometry and two independent anti-RANKL antibodies, we demonstrate RANKL expression in CD38(+++)CD45(+) and CD38(+++)CD45(-) myeloma plasma cell (MPC) subpopulations derived from patients with osteolytic MM. In addition, highly purified subpopulations of MPC express mRNA for both transmembrane and soluble RANKL isoforms but lack expression of OPG mRNA and protein. We also show that RANKL expressed by MPC is functional as in vitro coculture of CD38(+++)CD45(+) and CD38(+++)CD45(-) MPC subpopulations with peripheral blood mononuclear cells resulted in the formation of multinucleate, tartrate-resistant acid phosphatase-positive osteoclasts-like cells capable of forming typical resorption pits. Furthermore, high expression of membrane-associated RANKL by CD38(+++) MPC correlated with the presence of multiple radiological bone lesions in individuals with MM. Together, our data strongly suggest that RANKL expression by MPC confers on them the ability to participate directly in the formation of osteoclast in vivo and extends our knowledge of the involvement of RANKL and OPG in the osteolysis characteristic of this disease.

Carrier Proteins↗

PubMed2003

RANKL expression is related to the differentiation state of human osteoblasts.

Human osteoblast phenotypes that support osteoclast differentiation and bone formation are not well characterized. Osteoblast differentiation markers were examined in relation to RANKL expression. RANKL expression was induced preferentially in immature cells. These results support an important link between diverse osteoblast functions. Cells of the osteoblast lineage support two apparently distinct functions: bone formation and promotion of osteoclast formation. The aim of this study was to examine the relationship between these phenotypes in human osteoblasts (NHBC), in terms of the pre-osteoblast marker, STRO-1, and the mature osteoblast marker, alkaline phosphatase (AP), and the expression of genes involved in osteoclast formation, RANKL and OPG. The osteotropic stimuli, 1alpha,25(OH)2vitamin D3 (vitD3) and dexamethasone, were found to have profound proliferative and phenotypic effects on NHBCs. VitD3 inhibited NHBC proliferation and increased the percentage of cells expressing STRO-1 over an extended culture period, implying that vitD3 promotes and maintains an immature osteogenic phenotype. Concomitantly, RANKL mRNA expression was upregulated and maintained in NHBC in response to vitD3. Dexamethasone progressively promoted the proliferation of AP-expressing cells, resulting in the overall maturation of the cultures. Dexamethasone had little effect on RANKL mRNA expression and downregulated OPG mRNA expression in a donor-dependent manner. Regression analysis showed that RANKL mRNA expression was associated negatively with the percentage of cells expressing AP (p < 0.01) in vitD3- and dexamethasone-treated NHBCs. In contrast, RANKL mRNA expression was associated positively with the percentage of STRO-1+ cells (p < 0.01). In NHBCs sorted by FACS based on STRO-1 expression (STRO-1bright and STRO-1dim populations), it was found that vitD3 upregulated the expression of RANKL mRNA preferentially in STRO-1bright cells. The results suggest that immature osteoblasts respond to osteotropic factors in a potentially pro-osteoclastogenic manner. Additionally, the dual roles of osteoblasts, in supporting osteoclastogenesis or forming bone, may be performed by the same lineage of cells at different stages of their maturation.

Carrier Proteins↗

PubMed2002

Chemotherapeutic agents sensitize osteogenic sarcoma cells, but not normal human bone cells, to Apo2L/TRAIL-induced apoptosis.

Apo2L/TRAIL is a member of the tumor necrosis factor (TNF) family of cytokines that induces death of cancer cells but not normal cells. Its potent apoptotic activity is mediated through its cell surface death domain-containing receptors, DR4 and DR5. Apo2L/TRAIL interacts also with 3 "decoy" receptors that do not induce apoptosis, DcR1, DcR2, which lack functional death domains, and osteoprotegerin (OPG). The aim of our study was to investigate the cytotoxic activity of Apo2L/TRAIL on established osteogenic sarcoma cell lines (BTK-143, HOS, MG-63, SJSA-1, G-292 and SAOS2) and in primary cultures of normal human bone (NHB) cells. When used alone, Apo2L/TRAIL at 100 ng/ml for 24 hr induced greater than 80% cell death in only 1 (BTK-143) of the 6 osteogenic sarcoma cell lines. In contrast, Apo2L/TRAIL-resistant cells were susceptible to Apo2L/TRAIL-mediated apoptosis in the presence of the anticancer drugs, Doxorubicin (DOX), Cisplatin (CDDP) and Etoposide (ETP) but not Methotrexate (MTX) or Cyclophosphamide (CPM). Importantly, neither Apo2L/TRAIL alone nor in combination with any of these drugs affected primary normal human bone cells under equivalent conditions. Apo2L/TRAIL-induced apoptosis, and its augmentation by chemotherapy in the resistant cell lines was mediated through caspase-8 and caspase-3 activation. Furthermore, Apo2L/TRAIL-induced apoptosis and its augmentation by chemotherapy was effectively inhibited by caspase-8 zIETD-fmk and caspase-3 zDEVD-fmk protease inhibitors and by the pan-caspase inhibitor zVAD-fmk. The pattern of basal Apo2L/TRAIL receptor mRNA expression, or expression of the intracellular caspase inhibitor FLICE-inhibitory protein, FLIP, could not be readily correlated with resistance or sensitivity to Apo2L/TRAIL-induced apoptosis. However, the augmentation of Apo2L/TRAIL effects by chemotherapy was associated with drug-induced up-regulation of death receptors DR4 and DR5 mRNA and protein. No obvious correlation was seen between the expression of OPG mRNA or protein and susceptibility of cells to Apo2L/TRAIL-induced apoptosis. Stable over-expression of a dominant negative form of the Fas-associated death domain protein (FADD) in the Apo2L/TRAIL-sensitive BTK-143 cells completely inhibited Apo2L/TRAIL-induced cell death. Our results indicate that chemotherapy and Apo2L/TRAIL act synergistically to kill cancer cells but not normal bone-derived osteoblast-like cells, which has implications for future therapy of osteosarcoma.

Apoptosis Regulatory Proteins↗