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At least 73 records · Page 4Linked to original sources
PubMed2000

Vasoactive intestinal peptide regulates osteoclast activity via specific binding sites on both osteoclasts and osteoblasts.

Clinical and experimental observations, together with immunohistochemical findings, suggest that neuro-osteogenic interactions may occur in the skeleton. In this study, we have examined the effect of vasoactive intestinal peptide (VIP), one of the neuropeptides present in bone, on the activity of the bone-resorbing osteoclast. Effects on bone resorption were assessed by counting the number of pits formed by rat osteoclasts incubated on devitalized slices of bovine cortical bone. Under conditions with an initially sparse density of stromal cells/osteoblasts, VIP caused a rapid cytoplasmic contraction and decreased motility of osteoclasts. This was coupled with a decrease in the number of resorption lacunae and a decrease in the total area resorbed by the osteoclasts in 48-h cultures. Time-course experiments revealed that the inhibitory effects on contraction and motility were transient and that the cells gradually regained their activity, such that, when culture time was prolonged to 120 h, a stimulatory effect by VIP on bone resorption was observed. When osteoclasts were incubated on bone slices, in the presence of an initially large number of stromal cells/osteoblasts, VIP treatment increased the number of resorption pits and total bone area resorbed in 48-h cultures. Using atomic force microscopy, we provide direct evidence that both osteoclasts and stromal cells/osteoblasts bind VIP. Also, VIP was shown to cause a rapid rise of intracellular calcium in osteoclasts and in a proportion (20%) of stromal cells/osteoblasts. Taken together, these data suggest that differentiated osteoclasts are equipped with receptors for VIP that are linked to a transient inhibition of osteoclast activity and, in addition, that stromal cells/osteoblasts have VIP receptors coupled to a delayed stimulation of osteoclastic resorption.

Animals↗
PubMed2001

Generation of human osteoclasts in stromal cell-free and stromal cell-rich cultures: differences in osteoclast CD11c/CD18 integrin expression.

Osteoclasts form in the presence of macrophage colony-stimulating factor (M-CSF) and receptor activator of Nfkappab ligand (RANKL), a membrane-bound differentiation factor that is now available as a soluble recombinant molecule. Acquisition of the osteoclast phenotype [the alphavbeta3 subunit of the vitronectin receptor (VNR)-, calcitonin receptor (CTR)- and F-actin ring-positive cells] is associated with loss of monocyte/macrophage-associated integrins, specifically CD11b, CD11c and CD18. We hypothesized that differences in the osteoclast integrin adhesion molecule profile may exist in osteoclasts generated in stromal cell-rich and in stromal-free conditions. Unlike osteoclasts generated in vivo, F-actin ring-positive (resorbing) osteoclasts formed in soluble RANKL in vitro, in the absence of stromal cells, and co-expressed CD11c and CD18. However, when osteoclasts were generated from peripheral blood mononuclear cells (PBMNCs) in co-cultures with the murine bone marrow stromal cell line 218 (which does not produce membrane-bound RANKL) in the presence of soluble RANKL, CD11c and CD18 were not expressed by osteoclasts. These findings indicate that the persistent expression of CD11c and CD18 is not accounted for by RANKL being presented in a soluble form and that membrane-bound RANKL is not required for the normal integrin expression in resorbing osteoclasts. This study demonstrates that potentially misleading information may arise by using data obtained from osteoclasts generated in the absence of stromal cells as they do not completely reflect the situation in vivo.

Actins↗
PubMed2000

Mechanism of stimulation of osteoclastic bone resorption through Gas6/Tyro 3, a receptor tyrosine kinase signaling, in mouse osteoclasts.

The signaling through receptor tyrosine kinases expressed on mature osteoclasts has recently been suggested to be involved in osteoclastic bone resorption. This study investigated the mechanism and the possible physiological relevance of Gas6/Tyro 3, a receptor tyrosine kinase signaling pathway in osteoclasts in stimulating osteoclastic bone resorption using several mouse culture systems. Gas6, expressed ubiquitously in bone cells, did not affect the differentiation or the survival of osteoclasts, but stimulated osteoclast function to form resorbed pits on a dentine slice. The expression of its receptor, Tyro 3, was seen only in mature osteoclasts among bone cells. Gas6 up-regulated the phosphorylation of cellular proteins including p42/p44 mitogen-activated protein kinase (MAPK), but not p38 or c-Jun N-terminal kinase MAPK, and increased the kinase activity of immunoprecipitated Tyro 3 in isolated osteoclasts. The ability of Gas6 to stimulate pit formation resorbed by osteoclasts was abrogated by PD98059, a specific inhibitor of p42/p44 MAPK. In addition, the Gas6 mRNA level in bone marrow was up-regulated by ovariectomy and was reduced by estrogen replacement. These results strongly suggest that Gas6 acts directly on mature osteoclasts through activation of Tyro 3 and p42/p44 MAPK, possibly contributing to the bone loss by estrogen deficiency.

Animals↗
PubMed1998

Cadherin-6 mediates the heterotypic interactions between the hemopoietic osteoclast cell lineage and stromal cells in a murine model of osteoclast differentiation.

Osteoclasts are multinucleated cells of hemopoietic origin that are responsible for bone resorption during physiological bone remodeling and in a variety of bone diseases. Osteoclast development requires direct heterotypic cell-cell interactions of the hemopoietic osteoclast precursors with the neighboring osteoblast/stromal cells. However, the molecular mechanisms underlying these heterotypic interactions are poorly understood. We isolated cadherin-6 isoform, denoted cadherin-6/2 from a cDNA library of human osteoclast-like cells. The isolated cadherin-6/2 is 3,423 bp in size consisting of an open reading frame of 2,115 bp, which encodes 705 amino acids. This isoform lacks 85 amino acids between positions 333 and 418 and contains 9 different amino acids in the extracellular domain compared with the previously described cadherin-6. The human osteoclast-like cells also expressed another isoform denoted cadherin-6/1 together with the cadherin-6. Introduction of cadherin-6/2 into L-cells that showed no cell-cell contact caused evident morphological changes accompanied with tight cell-cell association, indicating the cadherin-6/2 we isolated here is functional. Moreover, expression of dominant-negative or antisense cadherin-6/2 construct in bone marrow-derived mouse stromal ST2 cells, which express only cadherin-6/2, markedly impaired their ability to support osteoclast formation in a mouse coculture model of osteoclastogenesis. Our results suggest that cadherin-6 may be a contributory molecule to the heterotypic interactions between the hemopoietic osteoclast cell lineage and osteoblast/bone marrow stromal cells required for the osteoclast differentiation. Since both osteoclasts and osteoblasts/bone marrow stromal cells are the primary cells controlling physiological bone remodeling, expression of cadherin-6 isoforms in these two cell types of different origin suggests a critical role of these molecules in the relationship of osteoclast precursors and cells of osteoblastic lineage within the bone microenvironment.

Amino Acid Sequence↗
PubMed1994

Carboxyl-terminal parathyroid hormone fragments stimulate osteoclast-like cell formation and osteoclastic activity.

The controversy still exists about the biological activity of carboxyl (C)-terminal PTH fragments. The present study was performed to examine the effect of C-terminal PTH fragments on osteoclast-like cell formation and bone-resorbing activity. In contrast to human (h) PTH-(1-34) or hPTH-(1-84), any C-terminal fragments examined [hPTH-(35-84), hPTH-(53-84), and hPTH-(69-84)] did not affect cellular cAMP production and intracellular calcium in osteoblastic UMR-106 cells. Although hPTH-(1-84) caused an increase in cAMP production and intracellular calcium less effectively than hPTH-(1-34) in UMR-106 cells, the former caused a stimulation of osteoclast-like cell formation in osteoblast-containing mouse bone cell cultures more effectively than the latter. All of the C-terminal fragments significantly stimulated osteoclast-like cell formation, and their effectiveness seemed to depend on the amino acid length of the fragments. The conditioned medium from UMR-106 cells pretreated with C-terminal PTH as well as amino-terminal PTH significantly stimulated osteoclast-like cell formation from mouse hemopoietic blast cells supported by granulocyte-macrophage colony-stimulating factor. Moreover, all of the C-terminal fragments stimulated osteoclast-like cell formation from hemopoietic blast cells even in the absence of osteoblasts, and their effectiveness seemed to depend on the length of fragments. As for bone-resorbing activity by mature osteoclasts, all of the C-terminal fragments stimulated bone resorption in osteoblast-containing mouse bone cell cultures, whereas these fragments did not affect the bone-resorbing activity of isolated rabbit osteoclasts. The present study first indicates that C-terminal PTH fragments stimulate osteoclast-like cell formation as well as bone-resorbing activity by mature osteoclasts in the presence of osteoblasts and accelerate osteoclast-like cell formation from hemopoietic blast cells in the absence of osteoblasts.

Animals↗
PubMed1998

A combination of osteoclast differentiation factor and macrophage-colony stimulating factor is sufficient for both human and mouse osteoclast formation in vitro.

Both human and murine osteoclasts can be derived in vitro from hematopoietic cells or monocytes that are co-cultured with osteoblasts or marrow-derived stromal cells. The osteoclastogenic stimulus provided by murine osteoblasts and marrow-derived stromal cells is now known to be mediated by osteoclast differentiation factor (ODF), a membrane-bound tumor necrosis factor-related ligand. This study demonstrates that mouse spleen cells and monocytes form osteoclasts when cultured in the presence of macrophage-colony stimulating factor (M-CSF) and a soluble form of murine ODF (sODF). Numerous multinucleated osteoclasts expressing tartrate resistant acid phosphatase (TRAP) and calcitonin receptor (CTR) formed within 7 days of culture and engaged in extensive lacunar bone resorption. Osteoclast number and bone resorption area was dependent on sODF concentration. Long-term cultured human monocytes also formed bone resorbing osteoclasts in response to co-stimulation by sODF and M-CSF, although this required more than 11 days in culture. This human osteoclast differentiation was strongly inhibited by granulocyte-macrophage colony stimulating factor. This study further characterises murine osteoclast differentiation caused by sODF and M-CSF co-stimulation in vitro, and shows that the same co-stimulation causes human osteoclast differentiation to occur. We propose that this methodology can be employed to investigate the direct effects of cytokines and other factors on human osteoclast differentiation.

Acid Phosphatase↗
PubMed1997

Dexamethasone stimulates osteoclast-like cell formation by directly acting on hemopoietic blast cells and enhances osteoclast-like cell formation stimulated by parathyroid hormone and prostaglandin E2.

Although an excess of glucocorticoid induces secondary osteoporosis, the mechanism still remains unclear, particularly in regard to glucocorticoid-stimulated bone resorption. We examined the effects of dexamethasone (Dex) on osteoclast-like cell formation and bone-resorbing activity by employing mouse bone and spleen cell cultures and further investigated whether Dex would modulate osteoclast-like cell formation stimulated by several bone-resorbing factors. Dex stimulated osteoclast-like cell formation in stromal cell-containing mouse bone cell cultures in a concentration-dependent manner. Also, Dex significantly stimulated osteoclast-like cell formation from hemopoietic blast cells in spleen cell cultures derived from 5-fluorouracil-pretreated mice. In contrast, Dex (10(-8) M) did not affect the bone-resorbing activity of mature osteoclasts. Pretreatment with 10(-8) M Dex significantly enhanced osteoclast-like cell formation in unfractionated mouse bone cell cultures stimulated by 10(-8) M human (h) parathyroid hormone (PTH) (1-34), 10(-8) M hPTH-related protein (1-34) and 10(-6) M prostaglandin E2, but not by 10(-8) M 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Moreover, pretreatment with 10(-8) M Dex significantly enhanced osteoclast-like cell formation stimulated by both forskolin and dbcAMP. In contrast, pretreatment with 10(-8) M Dex significantly inhibited osteoclast-like cell formation in mouse spleen cell cultures stimulated by both 10(-8) M hPTH(1-34) and 10(-8) M 1,25(OH)2D3. These findings suggest that Dex stimulates osteoclast-like cell formation, at least in part by directly acting on hemopoietic blast cells. They further suggest that Dex enhances osteoclast-like cell formation stimulated by PTH and prostaglandin E2 through an indirect pathway via cells other than hemopoietic blast cells.

Animals↗
PubMed1986

Human osteoclast-specific antigens are expressed by osteoclasts in a wide range of non-human species.

A series of monoclonal antibodies have been developed which react specifically with human osteoclasts in human fetal bone and a range of neoplastic and non-neoplastic bone lesions. We have examined whether such antibodies retain reactivity and specificity with osteoclasts isolated from the bone of newborn non-human mammals and embryonic chickens. Of seven osteoclast-specific monoclonal antibodies, three retain their reactivity with rabbit and two with guinea-pig; none react with mouse or rat osteoclasts; two antibodies detect avian osteoclasts. The extensive retention of some osteoclast antigens during phylogeny suggests that they might represent functionally important molecules in the regulation of osteoclast activity. Moreover, the existence of antibodies capable of defining multi- and mononuclear osteoclasts, from species where osteoclast function is well characterized, suggests possible experimental routes towards the isolation, and hence study of purified populations of osteoclasts and their precursors.

Animals↗
PubMed2004

Osteoclastic bone resorption through receptor tyrosine kinase and extracellular signal-regulated kinase signaling in mature osteoclasts.

It has recently been suggested that signaling through receptor tyrosine kinases (RTKs) expressed on mature osteoclasts is involved in osteoclastic bone resorption. This study investigated the role and mechanism of two major RTKs expressed on mature osteoclasts, fibroblast growth factor receptor type 1 (FGFR1) and Tyro 3. Among the FGF receptors (FGFR1-4), only FGFR1 was detected on isolated mouse osteoclasts, while all FGFRs were identified on mouse osteoblasts. Tyro 3 was seen only in mature osteoclasts among bone cells. FGF-2 moderately stimulated pit formation by isolated rabbit osteoclasts at low concentrations (>==10(-12) M), whereas at high concentrations (>==10(-9) M) it strongly stimulated pit formation by unfractionated bone cells. Gas6, the ligand of Tyro 3, was expressed ubiquitously in bone cells and stimulated osteoclast function to form resorbed pits on a dentine slice. Both FGF-2 and Gas6 upregulated the phosphorylation of cellular proteins, including extracellular signal-regulated kinase (ERK), and increased the kinase activity of immunoprecipitated FGFR1 and Tyro 3, respectively, in mouse osteoclasts. The stimulation of these cytokines on mouse and rabbit osteoclast functions was abrogated by PD98059, a specific inhibitor of ERK. These results strongly suggest that these cytokines act directly on mature osteoclasts through the activation of RTKs and ERK, causing the stimulation of bone resorption.

Journal Article↗
PubMed1999

Fra-1 potentiates osteoclastic differentiation in osteoclast-macrophage precursor cell lines.

c-Fos, a component of the dimeric transcription factor AP-1, is necessary for osteoclast formation. To determine whether c-Fos can substitute for any or all of the stimuli needed for osteoclast induction, we infected osteoclast precursors with retroviral vectors expressing c-Fos or the Fos-related protein, Fra-1. The infected cells were incubated with or without osteoclast-inductive stimuli. Osteoclast formation from retroviral-infected precursors remained completely dependent on osteoclast-inductive stromal cells. Unexpectedly, infection of bipotential osteoclast-macrophage precursor cell lines with retroviruses expressing Fra-1 but not c-Fos caused a 10-100-fold increase in the number of precursors that developed calcitonin receptors associated with an increase in bone resorption. These observations suggest that, in the precursor cell lines, Fra-1 is a limiting factor for full responsiveness to the osteoclast-inductive environment. Fra-1 is therefore likely to play a role in osteoclast differentiation which is distinct from that of c-Fos.

Autoradiography↗
PubMed2006

An osteoclastic protein-tyrosine phosphatase is a potential positive regulator of the c-Src protein-tyrosine kinase activity: a mediator of osteoclast activity.

This study tested the hypothesis that an osteoclastic protein-tyrosine phosphatase, PTP-oc, enhances osteoclast activity through c-Src activation. The effects of several resorption activators and inhibitors on PTP-oc expression, resorption activity, and c-Src activation were determined in rabbit osteoclasts. PTP-oc expression was assayed with immunoblots and semi-quantitative RT-PCR. Osteoclastic activity was determined by the resorption pit assay; and c-Src activation was monitored by P-tyr527 (PY527) dephosphorylation, and in vitro kinase assay. Treatment of osteoclasts with PTH, PGE2, 1,25(OH)2D3, IL-1, but not RANKL or IL-6, significantly stimulated resorption activity, increased PTP-oc mRNA and protein levels, and reduced c-Src PY527 level with corresponding activation of c-Src protein-tyrosine kinase activity. The PTP-oc antisense phosphorothioated oligo treatment blocked the basal and IL-1alpha-mediated, but not RANKL-mediated, resorption activity of isolated osteoclasts. The antisense oligo treatment also significantly reduced the average depth of resorption pits created by rabbit osteoclasts under basal conditions. Calcitonin and alendondrate, significantly reduced resorption activity and PTP-oc expression, and increased c-Src PY527 with corresponding reduction in its PTK activity. The cellular PTP-oc protein level correlated with the resorption activity. Among the various signaling proteins co-immunoprecipitated with PTP-oc, the resorption effectors caused corresponding changes in the tyrosyl phosphorylation level of only c-Src. The GST-PTP-oc fusion protein dephosphorylated PY-527-containing c-Src peptide in time- and dose-dependent manner in vitro. In summary, (1) PTP-oc is regulated in part at transcriptional level, (2) upregulation of PTP-oc in osteoclasts led to c-Src activation, and (3) PY527 of c-Src may be a cellular substrate of PTP-oc. These findings are consistent with the hypothesis that PTP-oc is a positive regulator of c-Src in osteoclasts.

Animals↗
PubMed1996

Vitamin K2 inhibits osteoclastic bone resorption by inducing osteoclast apoptosis.

In contrast to vitamin K1(VK1), vitamin K2(VK2) inhibited osteoclastic bone resorption by unfractionated bone cells and isolated osteoclasts. To investigate the mechanism of inhibition of osteoclastic bone resorption by VK2, we examined the effect of this vitamin on osteoclast apoptosis using a DNA-binding fluorescent dye, Hoechst 33258. In unfractionated bone cells and isolated osteoclasts on dentin slices, we first demonstrated that VK2 induced osteoclast apoptosis, but VK1 did not. Moreover, cycloheximide inhibited VK2-induced osteoclast apoptosis. These results suggest the possibility that VK2 inhibits osteoclastic bone resorption by targeting osteoclasts to undergo apoptosis, which leads to cell death.

Animals↗
PubMed2006

Calvarial osteoclasts express a higher level of tartrate-resistant acid phosphatase than long bone osteoclasts and activation does not depend on cathepsin K or L activity.

Bone resorption by osteoclasts depends on the activity of various proteolytic enzymes, in particular those belonging to the group of cysteine proteinases. Next to these enzymes, tartrate-resistant acid phosphatase (TRAP) is considered to participate in this process. TRAP is synthesized as an inactive proenzyme, and in vitro studies have shown its activation by cysteine proteinases. In the present study, the possible involvement of the latter enzyme class in the in vivo modulation of TRAP was investigated using mice deficient for cathepsin K and/or L and in bones that express a high (long bone) or low (calvaria) level of cysteine proteinase activity. The results demonstrated, in mice lacking cathepsin K but not in those deficient for cathepsin L, significantly higher levels of TRAP activity in long bone. This higher activity was due to a higher number of osteoclasts. Next, we found considerable differences in TRAP activity between calvarial and long bones. Calvarial bones contained a 25-fold higher level of activity than long bones. This difference was seen in all mice, irrespective of genotype. Osteoclasts isolated from the two types of bone revealed that calvarial osteoclasts expressed higher enzyme activity as well as a higher level of mRNA for the enzyme. Analysis of TRAP-deficient mice revealed higher levels of nondigested bone matrix components in and around calvarial osteoclasts than in long bone osteoclasts. Finally, inhibition of cysteine proteinase activity by specific inhibitors resulted in increased TRAP activity. Our data suggest that neither cathepsin K nor L is essential in activating TRAP. The findings also point to functional differences between osteoclasts from different bone sites in terms of participation of TRAP in degradation of bone matrix. We propose that the higher level of TRAP activity in calvarial osteoclasts compared to that in long bone cells may partially compensate for the lower cysteine proteinase activity found in calvarial osteoclasts and TRAP may contribute to the degradation of noncollagenous proteins during the digestion of this type of bone.

Acid Phosphatase↗
PubMed2004

Inhibition of osteoclast formation by 3-methylcholanthrene, a ligand for arylhydrocarbon receptor: suppression of osteoclast differentiation factor in osteogenic cells.

We investigated the effects of 3-methylcholanthrene (3MC), a ligand for arylhydrocarbon receptor (AhR), on osteoclastogenesis. Osteoclast-like cells, in cocultures with mouse spleen cells and clonal osteogenic stromal ST2 cells, are formed from spleen cells by a combination of the receptor activator of nuclear factor-kappaB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) produced by ST2 cells in response to 1alpha,25(OH)(2) Vitamin D(3). 3MC dose-dependently inhibited the formation of mono- and multinuclear osteoclast-like cells. However, 3MC did not inhibit the formation of osteoclast-like cells from mouse spleen cells which was supported by the exogenous soluble RANKL and M-CSF. 3MC did not affect the formation of an actin ring and pits on slices of dentine by osteoclast-like cells, both of which are typical indices of osteoclast activity. These results suggest that 3MC affects osteoclast-supporting cells such as ST2 cells but not osteoclast precursor cells and mature osteoclastic cells. When we measured the expression levels of RANKL mRNA in ST2 cells, 3MC dose-dependently decreased the level of this mRNA. However, 3MC did not affect levels of mRNAs for osteoprotegerin (OPG), M-CSF, and the receptor of 1alpha,25(OH)(2) Vitamin D(3) in ST2 cells. Furthermore, soluble RANKL was able to counteract the inhibitory effect of 3MC on the formation of osteoclast-like cells. Our findings indicate that 3MC inhibits osteoclastogenesis via the inhibition of RANKL expression in osteoblastic cells.

Animals↗
PubMed2000

Direct stimulation of osteoclastic bone resorption by bone morphogenetic protein (BMP)-2 and expression of BMP receptors in mature osteoclasts.

Bone morphogenetic proteins (BMPs) play an important role in various kinds of pattern formation and organogenesis during vertebrate development. In the skeleton, BMPs induce the differentiation of cells of chondrocytic and osteoblastic cell lineage and enhance their function. However, the action of BMPs on osteoclastic bone resorption, a process essential for pathophysiological bone development and regeneration, is still controversial. In this study, we examine the direct effect of BMPs on osteoclastic bone-resorbing activity in a culture of highly purified rabbit mature osteoclasts. BMP-2 caused a dose- and time-dependent increase in bone resorption pits excavated by the isolated osteoclasts. BMP-4 also stimulated osteoclastic bone resorption. The increase in osteoclastic bone resorption induced by BMP-2 was abolished by the simultaneous addition of follistatin, a BMP/activin binding protein that negates their biological activity. Just as it increased bone resorption, BMP-2 also elevated the messenger RNA expressions of cathepsin K and carbonic anhydrase II, which are key enzymes for the degradation of organic and inorganic bone matrices, respectively. Type IA and II BMP receptors (BMPRs), and their downstream signal transduction molecules, Smad1 and Smad5, were expressed in isolated osteoclasts as well as in osteoblastic cells, whereas type IB BMPR was undetectable. BMPs directly stimulate mature osteoclast function probably mediated by BMPR-IA and BMPR-II and their downstream molecules expressed in osteoclasts. The results presented here expand our understanding of the multifunctional roles of BMPs in bone development.

Animals↗
PubMed2001

Intercellular calcium signaling occurs between human osteoblasts and osteoclasts and requires activation of osteoclast P2X7 receptors.

Signaling between osteoblasts and osteoclasts is important in bone homeostasis. We previously showed that human osteoblasts propagate intercellular calcium signals via two mechanisms: autocrine activation of P2Y receptors, and gap junctional communication. In the current work we identified mechanically induced intercellular calcium signaling between osteoblasts and osteoclasts and among osteoclasts. Intercellular calcium responses in osteoclasts required P2 receptor activation but not gap junctional communication. Pharmacological studies and reverse transcriptase-PCR amplification demonstrated that human osteoclasts expressed functional P2Y1 receptors, but, unexpectedly, desensitization of P2Y1 did not block calcium signaling to osteoclasts. We also found that osteoclasts expressed functional P2X7 receptors and showed that pharmacological inhibition of these receptors blocked calcium signaling to osteoclasts. Thus these studies show that calcium signaling between osteoblasts and osteoclasts occurs via activation of P2 receptors, but that different families of P2 receptors are required for calcium signaling in these two cell types. Intercellular calcium signaling among bone cells is therefore amenable to pharmacological manipulation that will specifically affect only bone-forming or bone-resorbing cells. P2 receptors may be important drug targets for the modulation of bone turnover.

Adult↗
PubMed2004

An osteoclastic protein-tyrosine phosphatase may play a role in differentiation and activity of human monocytic U-937 cell-derived, osteoclast-like cells.

This study investigated if an osteoclastic protein-tyrosine phosphatase (PTP), PTP-oc, plays a role in the functional activity and differentiation of osteoclastic cells by determining the effects of overexpression of wild-type (WT)- or phosphatase-deficient (PD)-PTP-oc on bone resorption activity and differentiation of human promyelomonocytic U-937 cells, which could be induced to differentiate into "osteoclast-like" cells by phorbol ester/1,25(OH)(2)D(3) treatment. U-937 cells overexpressing WT- or PD-PTP-oc were produced with a transposon-based vector. The size and depth of resorption pits created by WT-PTP-oc-overexpressing osteoclast-like cells were greater, while those by PD-PTP-oc-overexpressing osteoclast-like cells were less, than those created by control osteoclast-like cells. Overexpression of WT-PTP-oc also enhanced, while overexpression of PD-PTP-oc suppressed, their differentiation into osteoclast-like cells. Overexpression of WT-PTP-oc increased apoptosis and proliferation of U-937 cells, and overexpression of PD-PTP-oc reduced cell proliferation. Cells overexpressing WT-PTP-oc has also led to greater c-Src and NF-kappabeta activation, whereas cells overexpressing PD-PTP-oc resulted in less c-Src and NF-kappabeta activation. c-Src activation and NF-kappabeta activation each correlated with resorption activity and differentiation into osteoclast-like cells. In summary, these results show that 1) PTP-oc regulates both the activity and the differentiation of osteoclast-like cells derived from U-937 cells; 2) PTP-oc enzymatic activity is important to these processes; 3) high PTP-oc enzymatic activity caused an increase in U-937 cell apoptosis and proliferation, leading to no significant changes in the number of viable cells; and 4) some of the PTP-oc actions are mediated in part by the c-Src and/or NF-kappabeta pathways.

Apoptosis↗
PubMed2001

Interferon-gamma down-regulates gene expression of cathepsin K in osteoclasts and inhibits osteoclast formation.

The cytokine, IFN-gamma, has been shown in vitro to inhibit bone resorption, but the mechanisms responsible for this inhibition have not been clearly defined. Cathepsin K is a major protease responsible for bone resorption. IFN-gamma may inhibit bone resorption through down-regulation of osteoclast genes, including cathepsin K. To test the hypothesis, we investigated the effect of IFN-gamma on cathepsin K expression in the MOCP-5 and wild-type mouse bone marrow co-culture systems by Northern blot as well as osteoclast formation at different stages of differentiation. The results show that IFN-gamma down-regulates mRNA levels of cathepsin K in a time- and dose-dependent manner. Consequently, cathepsin K protein production is also reduced by IFN-gamma. Moreover, our results indicate that IFN-gamma inhibits osteoclast formation only early in osteoclast differentiation. IL-6 and TNFalpha did not significantly affect cathepsin K gene expression in osteoclasts. However, IL-1alpha stimulated gene expression. In conclusion, our data suggest that the actions of IFN-gamma on osteoclastic bone resorption may be mediated by its effects on both osteoclast formation at an early stage and osteoclast gene expression in mature osteoclasts.

Animals↗