The origin of osteoclasts: evidence, clinical implications and investigative challenges of an extra-skeletal source

Tritrichomonas foetus Cell Division Involves DNA Endoreplication and Multiple Fissions

Tritrichomonas foetus and Trichomonas vaginalis are extracellular flagellated parasites that inhabit animals and humans, respectively. Cell division is a crucial process in most living organisms that leads to the formation of 2 daughter cells from a single mother cell. It has been assumed that T. vaginalis and T. foetus modes of reproduction are exclusively by binary fission. However, here, we showed that multinuclearity is a phenomenon regularly observed in different T. foetus and T. vaginalis strains in standard culture conditions. Additionally, we revealed that nutritional depletion or nutritional deprivation led to different dormant phenotypes. Although multinucleated T. foetus are mostly observed during nutritional depletion, numerous cells with 1 larger nucleus have been observed under nutritional deprivation conditions. In both cases, when the standard culture media conditions are restored, the cytoplasm of these multinucleated cells separates, and numerous parasites are generated in a short period of time by the fission multiple. We also revealed that DNA endoreplication occurs both in large and multiple nuclei of parasites under nutritional deprivation and depletion conditions, suggesting an important function in stress nutritional situations. These results provide valuable data about the cell division process of these extracellular parasites. IMPORTANCE Nowadays, it's known that T. foetus and T. vaginalis generate daughter cells by binary fission. Here, we report that both parasites are also capable of dividing by multiple fission under stress conditions. We also demonstrated, for the first time, that T. foetus can increase its DNA content per parasite without concluding the cytokinesis process (endoreplication) under stress conditions, which represents an efficient strategy for subsequent fast multiplication when the context becomes favorable. Additionally, we revealed the existence of novel dormant forms of resistance (multinucleated or mononucleated polyploid parasites), different than the previously described pseudocysts, that are formed under stress conditions. Thus, it is necessary to evaluate the role of these structures in the parasites' transmission in the future.

How Many Is Enough? - Challenges of Multinucleated Cell Division in Malaria Parasites

Regulating the number of progeny generated by replicative cell cycles is critical for any organism to best adapt to its environment. Classically, the decision whether to divide further is made after cell division is completed by cytokinesis and can be triggered by intrinsic or extrinsic factors. Contrarily, cell cycles of some species, such as the malaria-causing parasites, go through multinucleated cell stages. Hence, their number of progeny is determined prior to the completion of cell division. This should fundamentally affect how the process is regulated and raises questions about advantages and challenges of multinucleation in eukaryotes. Throughout their life cycle Plasmodium spp. parasites undergo four phases of extensive proliferation, which differ over three orders of magnitude in the amount of daughter cells that are produced by a single progenitor. Even during the asexual blood stage proliferation parasites can produce very variable numbers of progeny within one replicative cycle. Here, we review the few factors that have been shown to affect those numbers. We further provide a comparative quantification of merozoite numbers in several P. knowlesi and P. falciparum parasite strains, and we discuss the general processes that may regulate progeny number in the context of host-parasite interactions. Finally, we provide a perspective of the critical knowledge gaps hindering our understanding of the molecular mechanisms underlying this exciting and atypical mode of parasite multiplication.

Simvastatin inhibits the adipogenesis of bone marrow‑derived mesenchymal stem cells through the downregulation of chemerin/CMKLR1 signaling

Simvastatin is effective in the treatment of osteoporosis, partly through the inhibition of the adipogenesis of bone-marrow derived mesenchymal stem cells (BMSCs). The present study focused on the mechanisms responsible for the inhibitory effects of simvastatin on adipogenesis and examined the effects of simvastatin on the expression of peroxisome proliferator-activated receptor γ (PPARγ), chemerin, chemokine-like receptor 1 (CMKLR1), G protein-coupled receptor 1 (GPR1) and the adipocyte marker gene, adiponectin. BMSCs were isolated from 4-week-old female Sprague-Dawley (SD) rats, and adipogenesis was measured by the absorbance values at 490 nm of Oil Red O dye. The expression of each gene was evaluated by western blot analysis or reverse transcription-quantitative PCR (RT-qPCR). The expression of chemerin increased during adipogenesis, while CMKLR1 exhibited a trend towards a decreased expression. On days 7 and 14, the simvastatin-treated cells exhibited a down-regulated expression of chemerin, whereas the upregulated expression of its receptor, CMKLR1 was observed. The results also revealed that CMKLR1 is required for adipogenesis and the simvastatin-mediated inhibitory effect on adipogenesis. Simvastatin regulated adipogenesis by negatively modulating chemerin-CMKLR1 signaling. Importantly, simvastatin stimulation inhibited the upregulation of PPARγ and PPARγ-mediated chemerin expression to prevent adipogenesis. Treatment with the PPARγ agonist, rosiglitazone, partially reversed the negative regulatory effects of simvastatin. On the whole, the findings of the present study demonstrate that simvastatin inhibits the adipogenesis of BMSCs through the downregulation of PPARγ and subsequently prevents the PPARγ-mediated induction of chemerin/CMKLR1 signaling.

Manipulation of osteoclastogenesis: Bioactive multiphasic silica/collagen composites and their effects of surface and degradation products

The intent of the present study was to demonstrate that multiphasic silica/collagen xerogels are able to manipulate cellular processes. These xerogels were prepared by a sol-gel approach allowing the incorporation of mineral phases. The resulting nanocomposites are designed as biomaterial for bone regeneration. Human osteoclasts derived from peripheral blood mononuclear cells were cultured both indirectly and directly, either in presence of different xerogel types or on their surface, to investigate the factor with the main influence on osteoclastogenesis. To this end, the incorporation of a third phase to silica/collagen xerogels was used to affect osteoclastogenesis. In cell culture, ambient ion conditions controlled by both the degradation products of the xerogel and the bioactivity-dependent ion release and reprecipitation were shown to have the main effect on osteoclast specific enzyme tartrate-resistant acid phosphatase (TRAP) 5b. Late stage of osteoclastogenesis characterized by resorption was strongly dependent on the xerogels composition. Surface chemistry of the xerogels was displayed to play an important role in osteoclast resorption. Biphasic silica/collagen xerogels and triphasic xerogels with calcium carbonate offered widespread resorbed areas, whereas hydroxyapatite containing xerogels showed distinctly reduced resorption. The incorporation of strontium carbonate and phosphate, respectively, as third phase changed TRAP 5b activity dose-dependently and inhibited resorption within 21 days. Quantitative evaluation on osteoclast differentiation was carried out using biochemical methods (TRAP 5b, cathepsin K) and was supported by confocal laser scanning microscopy and scanning electron microscopy (SEM). Qualitative estimation of resorption was carried out by SEM.

Molecular and cellular basis of bone resorption

Osteoclast research has an exciting history and a challenging future. More than 3 decades ago, it became evident that bone-resorbing osteoclasts are of hematopoietic origin and are ultimately linked to the "basic multicellular unit," where they team up with the other cell types, including bone-forming osteoblasts. Since 2 decades, we have learned about the signaling pathways controlling genes relevant for osteoclastogenesis and bone resorption. It took another decade until the hypothesized "osteoclast differentiation" factor was discovered and was translated into an approved pharmacologic strategy. Here, the focus is on another molecular target, cathepsin K, a cysteine protease being released by the osteoclast into the resorption compartment. Genetic deletion and pharmacological blocking of cathepsin K reduces bone resorption but with ongoing bone formation. This observation not only holds great promise to become a new pharmacologic strategy, but it also provides new insights into the coordinated work of cells in the "basic multicellular unit" and thus, bridges the history and future of osteoclast research. This article is a short primer on osteoclast biology for readers of the special issue on odanacatib, a cathepsin K inhibitor.

An insight into the regulatory mechanisms of cells involved in resorption of dental hard tissues

Dental resorptions constitute a challenge to dentistry due to the complexity of cellular and molecular biology. The various cells involved in resorption, collectively orchestrate the interplay between various cytokines, hormones, enzymes, and hard tissues influencing the progression of resorption. The concern and curiosity on this subject are not new. This paper attempts to review the various regulatory mechanisms of cells involved in resorption of mineralized dental tissues.

Osteoclast activity and subtypes as a function of physiology and pathology--implications for future treatments of osteoporosis

Osteoclasts have traditionally been associated exclusively with catabolic functions that are a prerequisite for bone resorption. However, emerging data suggest that osteoclasts also carry out functions that are important for optimal bone formation and bone quality. Moreover, recent findings indicate that osteoclasts have different subtypes depending on their location, genotype, and possibly in response to drug intervention. The aim of the current review is to describe the subtypes of osteoclasts in four different settings: 1) physiological, in relation to turnover of different bone types; 2) pathological, as exemplified by monogenomic disorders; 3) pathological, as identified by different disorders; and 4) in drug-induced situations. The profiles of these subtypes strongly suggest that these osteoclasts belong to a heterogeneous cell population, namely, a diverse macrophage-associated cell type with bone catabolic and anabolic functions that are dependent on both local and systemic parameters. Further insight into these osteoclast subtypes may be important for understanding cell-cell communication in the bone microenvironment, treatment effects, and ultimately bone quality.

The regulation of osteoclastic development and function

Cells of the osteoblastic lineage exert a dominant influence on osteoclastic bone resorption. They form a communicating network of osteocytes, surface osteocytes and osteoblasts that seems well placed to monitor the structure and performance of bone and to judge where bone formation or resorption is appropriate. Osteoblasts produce prostaglandins (PGs) which strongly inhibit osteoclastic resorption. None of the agents that stimulate resorption in intact bone, such as parathyroid hormone (PTH), interleukin 1 (IL-1), 1,25-(OH)2 vitamin D3 (1,25-(OH)2D3) or tumour necrosis factors, affects isolated osteoclasts, but all induce osteoblastic cells to produce osteoclastic resorption stimulatory activity (ORSA) that acts directly on osteoclasts. Osteoblasts seem to initiate resorption as well as stimulating or inhibiting it. Contact with bone mineral appears to be necessary: osteoclasts resorb mineralized but not unmineralized bone. All bone surfaces are lined by unmineralized organic material. Osteoblastic cells secrete neutral proteases, including collagenase, in response to hormonal stimulators of bone resorption. Incubation of osteoblasts, in the presence of PTH, on such surfaces or preincubation of the bone with collagenase predisposes bone to osteoclastic resorption. Agents that stimulate resorption in organ cultures seem to share these osteoblast-mediated mechanisms for induction and stimulation of resorption but 1,25-(OH)2D3 stimulates it through an additional mechanism. We have found that osteoclasts can be induced from haemopoietic tissue (including haemopoietic spleen cells) in the presence of 1,25-(OH)2D3--PTH and IL-1 have no effect in this system. Because osteoclasts lack receptors for 1,25-(OH)2D3 these results suggest either that osteoclast precursors lose 1,25-(OH)2D3 receptors during differentiation, or that a 1,25-(OH)2D3-responsive accessory cell in bone marrow induces osteoclastic differentiation in the presence of 1,25-(OH)2D3.

Effects of local and whole body irradiation on appearance of osteoclasts during wound healing of tooth extraction sockets in rats

We examined effects of local and whole body irradiation before tooth extraction on appearance and differentiation of osteoclasts in the alveolar bone of rat maxillary first molars. Wistar rats weighting 100 g were divided into three groups: non-irradiation group, local irradiation group, and whole body irradiation group. In the local irradiation group, a field made with lead blocks was placed over the maxillary left first molar tooth. In the whole body irradiation group, the animals were irradiated in cages. Both groups were irradiated at 8 Gy. The number of osteoclasts around the interradicular alveolar bone showed chronological changes common to non-irradiated and irradiated animals. Several osteoclasts appeared one day after tooth extraction, and the maximal peak was observed 3 days after extraction. Local irradiation had no difference from non-irradiated controls. In animals receiving whole body irradiation, tooth extraction one day after irradiation caused smaller number of osteoclasts than that 7 day after irradiation during the experimental period. Whole body-irradiated rats had small osteoclasts with only a few nuclei and narrow resorption lacunae, indicating deficiency of radioresistant osteoclast precursor cells. Injection of intact bone marrow cells to whole body-irradiated animals immediately after tooth extraction recovered to some content the number of osteoclasts. These findings suggest that bone resorption in the wound healing of alveolar socket requires radioresistant, postmitotic osteoclast precursor cells from hematopoietic organs, but not from local sources around the alveolar socket, at the initial phase of wound healing.

Bovine deciduous dentine is more susceptible to osteoclastic resorption than permanent dentine: results of quantitative analyses

Many clinical reports suggest that deciduous teeth exhibit a greater susceptibility to resorption than permanent ones. To examine the difference between deciduous and permanent dentine in their susceptibility to osteoclastic resorption, osteoclast-like cells (OCLs) were cultured on deciduous and permanent dentine slices. The number, area, depth, and volume of resorption pits were then measured, using image-analyzing systems. We measured the level of degraded collagen (cross-linked N-telopeptide of type I collagen; NTx) in culture medium using an enzyme-linked immunosorbent assay (ELISA). The levels of cathepsin K, matrix metallo proteinase (MMP)-9, and MMP-13 mRNAs in the cells attached to dentine were also analyzed by real-time reverse transcription polymerase chain reaction (RT-PCR). Deciduous dentine slices exhibited a significant (twofold) increase in resorbed area compared with the permanent slices. Three-dimensional analysis revealed that the volume of pits in deciduous dentine differed significantly (fourfold) compared to that in the permanent dentine. The depth of pits also followed the same trend. However, there was no significant difference in the number of pits or osteoclasts on the dentine slices. The NTx level in deciduous media was significantly more than that in permanent media. The mRNA levels also followed the same trend. These results suggest that deciduous dentine is more susceptible to resorption than permanent dentine and signals from the substrate play an important role in physiological resorption.

Regulation of the differentiation and function of osteoclasts

The osteoclast is the cell that resorbs bone. It has been known for many years that its formation and function are regulated by cells of the osteoblastic lineage. Recently the molecular basis for this regulation was identified; osteoblastic cells induce osteoclastic differentiation and resorptive activity through expression of tumour necrosis factor (TNF) activation-induced cytokine (TRANCE) (also known as RANKL, ODF, OPGL, and TNFSF11), a novel membrane-inserted member of the TNF superfamily. Osteoclastic regulation is assisted through secretion of an inhibitor, osteoprotegerin (OPG) (OCIF, TNFRSF11B), a soluble (decoy) receptor for TRANCE. Osteoclast formation and survival also depend on and are substantially enhanced by transforming growth factor-beta (TGF-beta), which is abundant in bone matrix. Surprisingly, not only TRANCE but also TNF-alpha can induce osteoclast formation in vitro from bone marrow-derived mononuclear phagocytes, especially in the presence of TGF-beta. Whether or not TNF-alpha does the same in vivo, its ability to generate osteoclasts in vitro has significant implications regarding the nature of osteoclasts and their relationship to other mononuclear phagocytes, and a possible wider role for TRANCE in macrophage pathobiology. A hypothesis is presented in which the osteoclast is a mononuclear phagocyte directed towards a debriding function by TGF-beta, activated for this function by TRANCE, and induced to become specifically osteoclastic by the characteristics of the substrate or signals from bone cells that betoken such characteristics.

Bone and bone healing

Bone is composed of cells and organic matrix (30%), and minerals (70%). A vascular network consisting of nutrient, metaphyseal, and periosteal vessels richly supplies adult bone. Fracture healing consists of three interrelated phases: inflammatory, repair, and remodeling, and culminates in the ability of bone to return to original tissue structure. Many growth factors and regulatory proteins have been implicated in bone repair. Of these, transforming growth factor-B appears to be the major regulator of bone metabolism. This regulates differentiation and proliferation of mesenchymal cells into chondroblasts, osteoblasts, and osteoclasts.

Osteoclast activation and recruitment after application of orthodontic force

In this study, whole body radioactive cobalt 60 (Co60) irradiation was used in an orthodontic tooth movement model to investigate osteoclast activation and recruitment in adult rats. Seventy-five rats were divided into three groups and were irradiated with Co60 ranging from 10 to 26 Gray. An orthodontic appliance was fitted to each rat 12 days after initiation of irradiation. Identical appliances were fitted on an additional 25 unirradiated rats. Groups of rats were sacrificed 1 week before and on the day of appliance placement as well as 1, 2, 3, 4, or 5 weeks after appliance placement. Histologic sections from decalcified maxillary processes were prepared and osteoclasts were counted. Results showed that regardless of irradiation dosage, osteoclast number did not decrease during the first 3 weeks of orthodontic treatment; animals receiving lower (ie, 10 Gray) total irradiation actually showed a transient increase in the osteoclast number. In addition, regardless of dose in the irradiated rats, the total time osteoclasts were present in the periodontal membrane after orthodontic activation was reduced from 4 to 3 weeks. These findings lead us to hypothesize that osteoclasts involved in appliance-induced remodeling are initially from precursors in the periodontal membrane. During prolonged periods of orthodontic force application, replacement osteoclasts originate from bone marrow precursors. Although an orthodontic bone resorption cycle lasts 4 weeks, the life span of individual osteoclasts is limited to 9 to 10 days. The clinical significance of this finding remains to be elucidated.

Involvement of hydrogen peroxide in the differentiation of clonal HD-11EM cells into osteoclast-like cells

The present study uses the osteoclast precursor clonal line, HD-11EM, to study the potential of hydrogen peroxide (H2O2) in mediating the differentiation of HD-11EM into osteoclast-like cells. HD-11EM cells are a newly established clonal cell line that, in response to 1alpha,25-(OH)2D3, differentiate into osteoclast-like cells that are multinucleated (more than three nuclei), express tartrate-resistant acid phosphatase (TRAP), and excavate resorption pits when cultured on dentin slices in the presence of osteoblasts (Hsia et al., 1995, J. Bone Miner. Res., 10(Suppl 1):S424; Hsia, and Hauschka, 1997, unpublished data). Here we demonstrate that HD-11EM express the reduced nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase specific cytochrome b558 subunits, and that stimulation of HD-11EM with 1 or 10 nM 1alpha,25-(OH)2D3 increases the extracellular release of H2O2 within 5-10 min. Ours is the first report that stimulation of a cell with 1alpha,25-(OH)2D3 enhances the activation of NADPH-oxidase and increases the basal release of superoxide and the formation of its dismutation product, H2O2. To determine the possible involvement of H2O2 in the differentiation of HD-11EM, these cells were exposed to glucose/glucose oxidase. This enzyme system was used to deliver a pure and continuous source of H2O2 in nanomole amounts consistent with quantities produced by HD-11EM in response to 1alpha,25-(OH)2D3. Both 1alpha,25-(OH)2D3 and the exogenously generated H2O2 stimulated a dose- and time-dependent increase in TRAP activity/cell and the number of multinucleated cells 24-48 hr after treatment. Northern analysis confirmed an increase in expression of TRAP mRNA in response to either 1alpha,25-(OH)2D3 or H2O2. Decreases in cell proliferation and v-myc mRNA were also observed in response to these agents. Taken together, our findings indicate that production of H2O2 by HD-11EM is an important local factor involved in differentiation of HD-11EM into osteoclast-like cells, and suggest that H2O2 may play a role in native osteoclast differentiation.

Cathepsin K mRNA detection is restricted to osteoclasts during fetal mouse development

We recently identified a novel cysteine protease, cathepsin K, by random sequencing of an osteoclast cDNA library, and in situ hybridization studies in adult human tissues demonstrated high and specific expression in osteoclasts. To determine whether the expression of cathepsin K mRNA during mouse embryogenesis was more widespread, cryostat sections of early (day 11-13) and late (day 15-17) mouse fetuses were analyzed by in situ hybridization. Serial cross-sections were collected through each fetus, and co-reacted for tartrate-resistant acid phosphatase (TRAP) and nonspecific esterase (NSE), selective markers for the osteoclast, and precursor cells derived from the macrophage/monocyte lineage, respectively. In the 11-13 day fetuses, cathepsin K mRNA was not expressed in any extraskeletal tissue; at this stage of embryogenesis, no osteoclasts are present. However, in the 15-17 day fetuses, a distinctive, developmental stage-dependent pattern of cathepsin K expression was observed in osteoclasts and preosteoclasts at sites of cartilage and bone modeling. Cathepsin K positive osteoclasts differentiated within a peripheral zone of the osteogenic stacked cell layer of the cartilage rudiments (prior to ossification), migrated and/or resorbed the bone collar, and invaded the cartilage core. Furthermore, following the invasive penetration of vasculature into the degenerating cartilage core, the calcified cartilage was resorbed by cathepsin K positive mononuclear osteoclast precursors (NSE+ve, negligible TRAP); cells positive for both enzymes were identified indicative of osteoclast differentiation. The deposition of bone by osteoblasts onto the cartilage remnants is followed by mononucleated and multinucleated osteoclastic resorption; these osteoclasts demonstrated intense cathepsin K expression. Similar expression patterns were observed at sites of intramembranous ossification. No expression was observed in chondrocytes, osteoblasts, marrow, or in any other nonskeletal tissue at these time points. These data indicated that cathepsin K expression during embryogenesis occurred only following the onset of osteoclast differentiation.

Chick osteocyte-derived protein inhibits osteoclastic bone resorption

In order to investigate the role of osteocytes in bone resorption, we examined the homogenate and conditioned medium from purified chick calvarial osteocytes in a pit-formation assay using unfractionated bone cells from mice. The osteocyte homogenate markedly inhibited pit formation, whereas the conditioned medium of osteocytes had no effect. This inhibitory activity was not the result of cytotoxicity of the homogenate. A novel bone-resorption-inhibitory protein was purified from collagenase-digested chick calvarial fragments enriched in osteocytes. The inhibitory protein, of molecular mass 18.5 kDa, showed significant dose-dependent inhibition of pit formation by unfractionated bone cells from mice and rabbits, and by human giant tumour cells. This protein also inhibited the bone-resorbing activity of purified osteoclasts in the pit-formation assay in the absence of other effector cells. Microinjection of the protein into osteoclasts caused disruption of the podosomes in the cells. The N-terminal 25-amino-acid sequence of the protein showed 68% identity to a part of Rho-GTP-dissociation inhibitor. Thus chick calvarial osteocytes may be involved in the regulation of bone resorption by osteoclasts.

Catecholamines modulate growth and differentiation of human preosteoclastic cells

Using a clonal cell line of human osteoclast precursors (FLG 29.1 cells), that after treatment with 12-O-tetradecanoyl phorbol 13-acetate (TPA) show many functional characteristics of osteoclasts, we demonstrated that catecholamines act as inducers of osteoclast maturation in vitro and as stimulators of osteoclast activity via the binding to beta 2 adrenergic receptors. Scatchard analysis of 125I-labelled iodocyanopindolol to untreated (undifferentiated) or TPA-treated (differentiated) FLG 29.1 cells revealed the presence of a single high-affinity site with a Kd value around 24 pM and 8 pM respectively and with superimposable binding capacity (1.18 fmol/mg protein). Catecholamines increased in a dose-dependent fashion the intracellular cyclic AMP (cAMP) accumulation in both undifferentiated and TPA-treated FLG 29.1 cells. Pretreatment of untreated and TPA-treated FLG 29.1 cells with propranolol inhibited the catecholamine effect on cAMP accumulation, while pretreatment with clonidine had no effect. Catecholamines also reduced cell proliferation, increased tartrate-resistant acid phosphatase (TRAcP) activity, interleukin 6 (IL-6) production, multi-nuclearity and response to salmon calcitonin (sCT) in undifferentiated FLG 29.1 cells. In differentiated FLG 29.1 cells only IL-6 release was induced by catecholamine treatment. These findings support a potential role for catecholamines in modulating osteoclast differentiation and mature osteoclast activity.

Human osteoclast-like cells in primary culture

We describe a method for the isolation and culture of osteoclast-like cells from cancellous bone chips of iliac crests from patients undergoing reconstructive maxillofacial surgery. Under aseptic conditions, bone chips were cut into small pieces, incubated briefly with collagenase, and the isolated bone cells were separated from the bone chips by filtration using a nylon mesh. Bone cells were then cultured on a variety of surfaces for up to 10 days. Cell motility and fusion, together with the development of tartrate-resistant acid phosphatase activity, were seen in many cells soon after culture. The large osteoclast-like cells adhered to human cortical bone slices and produced resorption pits. These morphological and functional characteristics suggest that the cells we isolated and cultured were human osteoclasts and their precursors. Thus this method may provide a reliable means of obtaining human osteoclasts from normal tissue for short-term studies of their metabolism or from various skeletal diseases to study pathological aberrations and mechanisms.

Ontogenesis of chondro/osteoclasts and their precursors in the mandibular condyle of the mouse

Tartrate-resistant acid phosphatase (TRAP) histochemistry has been used to follow chondro/osteoclasts and their precursors during ontogenesis of the mandibular condyle of the mouse (from day 16 of gestation until day 15 of neonatal life). TRAP+ mono-, bi-, and multinuclear cells were counted separately in the perichondrium, along the resorption front and in the subchondral spongiosa. Index of cellular density was calculated by dividing the absolute numbers of cells by the length of resorption front or the area of spongiosa, respectively. The study revealed that TRAP+ cells are present in the perichondrium of the mandibular condylar cartilage from the first day of its existence as an organ, namely day 17 of gestation. These cells are more numerous in the posterior part of the condyle, and reach their maximal number on the third day of neonatal life. Along the resorption front, mono-, bi-, and multinucleated TRAP+ cells were counted. Their total number and their respective indexes of cellular density changed variably during the observation period: (a) the number of mononuclear cells increased gradually and, by the end of the observation period, was 13 times greater than it was at the beginning; (b) the number of binuclear cells increased threefold; and (c) the number of multinuclear cells stayed constant, except for a small peak around the time of birth. The changes in the spongiosa showed an opposite trend. In the spongiosa, the index of cellular density of the mononuclear TRAP+ cells increased slightly during ontogenesis. The number of binuclear cells increased twofold, while the number of multinuclear cells increased 17-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional and structural interactions between osteoblastic and preosteoclastic cells in vitro

Osteoblasts are involved in the bone resorption process by regulating osteoclast maturation and activity. In order to elucidate the mechanisms underlying osteoblast/preosteoclast cell interactions, we developed an in vitro model of co-cultured human clonal cell lines of osteoclast precursors (FLG 29.1) and osteoblastic cells (Saos-2), and evaluated the migratory, adhesive, cytochemical, morphological, and biochemical properties of the co-cultured cells. In Boyden chemotactic chambers, FLG 29.1 cells exhibited a marked migratory response toward the Saos-2 cells. Moreover, they preferentially adhered to the osteoblastic monolayer. Direct co-culture of the two cell types induced: (1) positive staining for tartrate-resistant acid phosphatase in FLG 29.1 cells; (2) a decrease of the alkaline phosphatase activity expressed by Saos-2 cells; (3) the appearance of typical ultrastructural features of mature osteoclasts in FLG 29.1 cells; (4) the release into the culture medium of granulocyte-macrophage colony stimulating factor. The addition of parathyroid hormone to the co-culture further potentiated the differentiation of the preosteoclasts, the cells tending to fuse into large multinucleated elements. These in vitro interactions between osteoblasts and osteoclast precursors offer a new model for studying the mechanisms that control osteoclastogenesis in bone tissue.

Generation of multinucleated osteoclast-like cells from canine bone marrow: effects of canine distemper virus

Recent evidence has implicated canine distemper virus (CDV) as a possible aetiologic agent in Paget's disease of bone and the canine bone disorder, metaphyseal osteopathy. We have therefore examined the effects of CDV on the formation of multinucleated osteoclast-like cells in cultures of canine bone marrow mononuclear cells. Marrow cells from a distemper-infected dog and from five uninfected dogs were cultured in the presence of 1 alpha, 25-(OH)2 vitamin D3 and the number of tartrate resistant acid phosphatase positive multinucleated cells (MNCs) was determined. The presence of calcitonin (CT) receptors was confirmed by autoradiography with 125I-labeled human CT. Cultures from the distemper-infected dog contained a higher level of MNCs than those from the normal dogs. The in vitro addition of CDV to the cultures from all the dogs produced a dose-dependent increase in the number of MNCs, and an increase in size of these cells in the cultures from the infected dog. Cells infected with CDV were hyperresponsive to 1 alpha,25-(OH)2 vitamin D3. The presence of the virus in the relevant samples was confirmed using molecular techniques. In situ hybridization studies also revealed a significant increase in the level of infection following in vitro addition of the virus to the culture from the distemper-infected dog, suggesting that further infection had taken place. Resorption pits were formed on bone slices, although the number of pits was not significantly altered by viral infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of doxycycline on surgically induced osteoclast recruitment in the rat

The influence of systemic doxycycline on the number of surgically induced osteoclasts was studied in young albino rats. Forty Wistar rats, aged 50 d at the start of the experiments, were randomly assigned to two groups. The experimental group (20 animals) received 0.5 mg/ml doxycycline added to the drinking water. Mucoperiosteal flaps were raised on the palatal aspect of left maxillary molars in all animals. Two rats from each group were killed daily during a post-operative period of 10 d, and specimens were prepared for light microscopy. Cellular counts in serial sections of crestal bone indicated a delay of initial surface colonization of 2 d. Statistical analysis revealed a smaller number of osteoclasts in doxycycline-treated animals as compared to control rats. In conclusion, systemic doxycycline suppresses recruitment of osteoclasts following surgery.

In vitro structural and functional relationships between preosteoclastic and bone endothelial cells: a juxtacrine model for migration and adhesion of osteoclast precursors

The role of vascularization in the process of bone resorption has not been clarified. The interactions between vascular endothelium and osteoclast progenitors were analyzed using clonal cell lines of bone-derived endothelial and preosteoclastic cells. Insulin-like growth factor I is a major chemotactic stimulator of preosteoclastic cell migration mediated by bone endothelial cells. Osteoclast precursors rapidly adhered to bone endothelial monolayers. This phenomenon appeared to be cell-specific and mediated through the binding of vitronectin and fibronectin receptors to fibronectin. In addition, direct contact with bone endothelial cells induced osteoclast progenitors to differentiate into more mature elements, with the tendency to cluster together to form large multinucleated cells. These findings demonstrated specific in vitro interactions between bone endothelial cells and osteoclast progenitors, offering a new model for understanding the molecular mechanisms which direct the processes of osteoclast recruitment and ontogeny.

Biosynthesis of bone sialoprotein by a human osteoclast-like cell line (FLG 29.1)

Biosynthesis of bone sialoprotein (BSP) by a human osteoclastic cell line (FLG 29.1) during its differentiation induced by phorbol 12-myristate 13-acetate (TPA) was studied using metabolic radiolabeling experiments. The FLG 29.1 cells were metabolically radiolabeled with [3H]glucosamine and [35S]sulfate, and the labeled glycoproteins were analyzed by anion exchange chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoprecipitation experiments. One of the major glycoproteins synthesized by the TPA-treated FLG 29.1 cells was sulfated, had an identical electrophoretic mobility to purified BSP, and could be immunoprecipitated with a specific antibody against human BSP (LF 6). Thus, this glycoprotein was tentatively identified as the BSP. Furthermore, mRNA for BSP was also detected in TPA-treated FLG 29.1 cells by RNA-polymerase chain reaction. Most BSP synthesized by FLG 29.1 cells remained cell-associated, and this is in contrast with those synthesized by osteoblasts, where the protein is rapidly released into the extracellular matrix. Immunocytochemistry using an anti-BSP antibody showed a prominent paranuclear (suggestive of Golgi apparatus) localization of BSP in the TPA-treated FLG 29.1 cells after permeabilization, while untreated cells were not significantly immunostained. Localization of BSP at the plasma membrane was also demonstrated in the TPA-treated FLG 29.1 cells by the fluorescence-activated cell sorting analysis. Since TPA has been demonstrated to induce expression of various osteoclastic characteristics in FLG 29.1 cells, induction of BSP expression by TPA suggests that the protein may play a role during the differentiation process of osteoclasts or in functions of differentiated osteoclasts.

Calcitonin receptor isoforms in mouse and rat osteoclasts

Calcitonin receptors (CTRs) from several species have recently been cloned and shown to belong to the 7 transmembrane domain class of receptor. We have identified two CTR isoforms in the rat, termed C1a and C1b, identical except for a 37-amino-acid insert in the putative second extracellular domain of C1b. To examine the CTR isoforms expressed in rat and mouse osteoclasts and the time course of their appearance in culture, bone marrow cells were cultured from C57/Bl6J mice and osteoclasts were isolated from newborn rat long bones. CTR-bearing cells were detected by autoradiography of 125I-salmon CT binding, and cultures were stained for tartrate-resistant acid phosphatase (TRAP). RNA was extracted from parallel cultures, and CTR mRNA was detected by Northern blot analysis, using a rat digoxigenin-labeled riboprobe. Characterization of mRNA for the CTR isoforms was by reverse transcription-polymerase chain reaction (RT-PCR) using primer sets and oligonucleotide probes specific for the two rat receptor isoforms. In mouse marrow cultures, TRAP positive mononucleated cells were present by day 2 of culture at which time CTR positive cells were few. Multinucleated cells with both these markers were seen only from day 4 and later. By Northern analysis of total RNA, a band of approximately 4 kb could be detected in day 4 and later cultures. RT-PCR showed that mouse homologs of both C1a and C1b mRNA species were expressed early in cultures of mouse osteoclasts, although at each time C1a appeared to predominate.(ABSTRACT TRUNCATED AT 250 WORDS)

Recognition of cryptic sites in human and mouse laminins by rat osteoclasts is mediated by beta 3 and beta 1 integrins

Laminins may be encountered by osteoclasts and their precursors in basement membranes when they migrate from periosteal vasculature during skeletal development and in pathological situations. We have examined the recognition by osteoclasts of intact laminins and their proteolytic derivatives, and analysed the mechanism of adhesion. Rat osteoclasts fail to bind intact mouse Engelbreth-Holm-Swarm (EHS) laminin (3% adhesion relative to adhesion to foetal calf serum proteins) and bind only weakly to native human placental laminin (13%) or human merosin (9%). Pepsin treatment of native mouse EHS and human laminins increased osteoclast adhesion. Rat osteoclasts adhered to mouse EHS laminin-derived P1 fragment (70%), but failed to bind the E8 fragment, which contains adhesion sites recognised by some integrins. Binding to human and mouse P1 laminins was abolished by treatment with RGD-containing peptides and required divalent cations, but not by YIGSR peptide. Combinations of monoclonal antibodies to rat beta 3 and alpha v integrins reduced binding to P1 fragment by 91% and to human laminin by 72%, demonstrating that the major integrin involved in rat osteoclast adhesion to proteolysed laminin is alpha v beta 3. Antiserum to beta 1 integrin inhibited adhesion to human laminin by 40%, but to P1 fragment by only 8%; this suggests that beta 1 integrins(s) contribute to osteoclast adhesion to human laminin but probably not to P1 fragment. The involvement of alpha v beta 3 integrin was confirmed using a recombinant human alpha v beta 3 solid phase binding assay, alpha v beta 3 bound to mouse P1 fragment and proteolytically digested human laminin, but not intact laminins.(ABSTRACT TRUNCATED AT 250 WORDS)

Role for autocrine TGF-beta 1 in regulating differentiation of a human leukemic cell line toward osteoclast-like cells

Increasing evidence suggests that transforming growth factor-beta (TGF-beta) is involved in bone formation during remodeling. Using a recently cloned human leukemic cell line (FLG 29.1 cells) we demonstrate that these cells synthesize and secrete TGF-beta 1 and that exogenous or autocrine TGF-beta 1 can induce the same features of osteoclastic-like cells, exerting its effects through the binding to TGF-beta specific receptors. Scatchard analysis of 125I-labeled TGF-beta 1 to FLG 29.1 cells revealed the presence of a single high affinity binding site with a Kd value of approximately 25 pM and a binding capacity of approximately 900 sites/cell. Affinity labeling experiments showed that FLG 29.1 cells express type I and type II TGF-beta receptors. Stimulation of FLG 29.1 cells with low TGF-beta 1 doses reduced cell proliferation and increased cell adhesion and tartrate resistant acid phosphatase (TRAcP) activity. Pretreatment of FLG 29.1 cells with TGF-beta 1 caused a significant and dose-dependent response to calcitonin. Northern blot of total mRNA and analysis of the conditioned media (CM) showed that TGF-beta 1 was synthesized by FLG 29.1 cells. TPA treatment, which induces partial differentiation of these cells, markedly increased TGF-beta 1 mRNA expression and growth factor release. The majority of TGF-beta 1 secreted by TPA-treated cells was in its latent form. However, anti-TGF-beta antibodies inhibited TGF-beta 1 and TPA-induced growth inhibition, calcitonin responsiveness, and TRAcP activity, suggesting that the TPA effect is mediated in part by autocrine TGF-beta 1 and indicating that the cells can activate and respond to the TGF-beta that they secrete. These findings support a potential autocrine role for TGF-beta 1 in osteoclast differentiation.

Cellular biology of bone resorption

Past knowledge and the recent developments on the formation, activation and mode of action of osteoclasts, with particular reference to the regulation of each individual step, have been reviewed. The following conclusions of consensus have emerged. 1. The resorption of bone is the result of successive steps that can be regulated individually. 2. Osteoclast progenitors are formed in bone marrow. This is followed by their vascular dissemination and the generation of resting preosteoclasts and osteoclasts in bone. 3. The exact pathways of differentiation of the osteoclast progenators to mature osteoclasts are debatable, but there is clear evidence that stromal cells support osteoclast generation. 4. Osteoclasts are activated following contact with mineralized bone. This appears to be controlled by osteoblasts that expose mineral to osteoclasts and/or release a factor that activates these cells. 5. Activated osteoclasts dissolve the bone mineral and digest the organic matter of bone by the action of agents secreted in the segregated microcompartments underlying their ruffled borders. The mineral is solubilized by protons generated from CO2 by carbonic anhydrase and secreted by an ATP-driven vacuolar H(+)-K(+)-ATPase located at the ruffled border. The organic matrix of the bone is removed by acid proteinases, particularly cysteine-proteinases that are secreted together with other lysosomal enzymes in the acid environment of the resorption zone. 6. Osteoclastic bone resorption is directly regulated by a polypeptide hormone, calcitonin (CT), and locally, by ionized calcium (Ca2+) generated as a result of osteoclastic bone resorption. 7. There is new evidence that osteoclast activity may also be influenced by the endothelial cells via generation of products including PG, NO and endothelin.

Growth hormone involvement in the regulation of tartrate-resistant acid phosphatase-positive cells that are active in cartilage and bone resorption

Young male Sprague-Dawley rats (5-7 weeks old, 80-120 g) were hypophysectomized (HX) and maintained on thyroxin and dexamethasone replacement therapies. Ten days after surgery, some HX rats received a single injection of human growth hormone (hGH), and others five daily injections of hGH. Tartrate-resistant acid phosphatase (TRAP) histochemistry was employed in order to evaluate the number of cells of resorptive potential in the metaphyseal bone of the proximal tibiae of HX rats and was compared with normal rats and HX rats that further received hGH replacement therapy. In normal rats, two populations of TRAP-positive cells were identified: multinuclear cells, which showed histological characteristics of osteoclasts, and small mononuclear cells, the number of which was overwhelming when compared with the number of TRAP-positive multinuclear cells. Both populations were reduced in the HX rat, but more so the mononuclear cells, which were assumed to represent the precursor pool of mature osteoclasts and chondroclasts (P < 0.005). Five daily injections of hGH to HX rats brought about a significant increase in the number of TRAP-positive multinuclear cells, the number of nuclei of these cells, and the number of mononuclear TRAP-positive cells, throughout the metaphyseal bone (P < 0.05). A single injection of hGH increased only the number of TRAP-positive multinuclear cells in the trabecula/bone marrow interface (P < 0.05), indicating a very rapid fusion of precursor cells into mature osteoclasts in that particular location.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of vitronectin receptor-mediated osteoclast adhesion by Arg-Gly-Asp peptide analogs: a structure-function analysis

This study details the investigation of induction of retractile shape change in the osteoclast through inhibition of adhesion between osteoclasts and matrix with (1) peptide analogs bearing an Arg-Gly-Asp (RGD) sequence, (2) antibodies to the integrin alpha V beta 3 vitronectin receptor, and (3) the RGD-containing snake venom peptide echistatin. Osteoclast retraction on dentin has been demonstrated for GRGDSP peptide, in contrast to the inactivity of the analog containing the conservative RGE sequence modification. An osteoclast adhesion assay employing rat or chick bone cells and serum-coated glass coverslips as substrate was developed for routine evaluation of inhibition of adhesion. Antibodies F4 and F11 to the beta 3 chain of rat vitronectin receptor were effective at submicromolar concentrations in rat osteoclasts (IC50 0.29 and 0.05 microM, respectively), whereas MAb 23C6 to human/chick vitronectin receptor was somewhat less effective against chick osteoclasts (IC50 1.6 microM). A rank order of RGD analog activity (mean IC50, microM) in the serum-coated glass adhesion assay was derived for the linear peptides GRGDSP (201 microM), GRGDTP (180 microM), Ac-RGDS-NH2 (84 microM), Ac-RGDV-NH2 (68 microM), RGDV (43 microM), GRGDS (38 microM), and RGDS (26 microM). The two most potent short peptides were the cyclic analog SK&F 106760 Ac-S,S-cyclo-(Cys-(N alpha Me)Arg-Gly-Asp-Pen)-NH2 (IC50 7.0 microM), and the Telios peptide H-Gly-S,S-cyclo-(Pen-Gly-Arg-Gly-Asp-Ser-Pro-Cys)-Ala-OH (IC50 6.6 microM). The snake venom peptide echistatin was the most potent substance evaluated in the serum-coated glass assay (IC50 0.78 nM) employing either rat or chick osteoclasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Peripheral inflammatory root resorption. A review of the literature with case reports

External resorptions associated with inflammation in marginal tissues are many times misdiagnosed and confused with caries and internal resorptions. A lack of uniformity in nomenclature has added to the confusion. This paper reviews the literature and presents cases to illustrate a rational approach to diagnosis and treatment. A new name is suggested to better reflect the features of this type of root resorption: peripheral inflammatory root resorption.

Phorbol ester induced osteoclast-like differentiation of a novel human leukemic cell line (FLG 29.1)

Studies on human osteoclast formation have been hampered by lack of a defined isolated progenitor cell population. We describe here the establishment of a human leukemic cell line (designated FLG 29.1) from bone marrow of a patient with acute monoblastic leukemia. The cultured cells are predominantly undifferentiated leukemic blasts, but addition of 12-o-tetradecanoylphorbol 13-acetate (TPA; 0.1 microM) induces irreversible differentiation into adherent, non-dividing, multinucleated cells. TPA-treated cells bear surface antigens typical of fetal osteoclasts, degrade 45Ca-labeled devitalized bone particles, display tartrate-resistant acid phosphatase in both mononuclear and multinuclear cells and receptors for calcitonin. Calcitonin increases intracellular cAMP accumulation in TPA-treated cells. TPA-treated cells show some ultrastructural features of osteoclasts as evidenced by transmission EM. These results indicate that FLG 29.1 cells may represent an osteoclast committed cell population, which upon induction with TPA acquire some morphological, phenotypical, and functional features of differentiated osteoclasts.

Production and characterization of new monoclonal antibodies to human osteoclasts

Two monoclonal antibodies raised against human osteoclastoma were found to show antiosteoclastic activity on frozen sections of tumor. Immunoreactivity was localized on the membrane surface. These antibodies exhibited no activity against tissue macrophages and human visceral tissue except kidney, where they stained tubules but not glomeruli. In addition, no activity was observed against rabbit or rat osteoclasts, suggesting that they might react with unique epitopes on human osteoclasts.

Multiple idiopathic root resorption. A case report and discussion of pathogenesis

A rare case of multiple idiopathic root resorption (MIRR) involving 5 adjacent anterior and posterior teeth is presented and the pathogenesis discussed. The proposition is made that MIRR results from microbiologically-induced osteoclast activity facilitated by prior osteoblast activation.

Extracellular matrix receptor and platelet antigens on osteoclasts and foreign body giant cells

Osteoclasts (OCs) and other cells of the mononuclear phagocyte system possess receptors for adhesive proteins present in the extracellular matrix. The antigenic phenotype of OCs and foreign body giant cells (FBGCs) was investigated for the presence of several integrin molecules and other largely platelet-associated antigens involved in cell adhesion reactions. Both OCs and FBGCs expressed the alpha-chains of the vitronectin receptor (CD51) and of the VLA-2 (CDw49b) and VLA-4 (CDw49d) molecules as well as their respective beta-chains, gpIIIa (CD61) and CD29. OCs and FBGCs also expressed CD9 and CD55 (DAF-Decay Accelerating Factor) and strongly reacted with antibodies directed against fibrinogen, fibronectin and vitronectin; the latter are ligands for several of the above matrix protein receptors. The data suggest that cell-cell and cell-matrix interactions involving adhesive proteins may be important in OC and FBGC function.

Skeletal development and formation of osteoclast-like cells from in situ progenitors in fetal mouse metatarsals cultured in chemically defined medium

An in vitro model system is described, using metatarsal explants from 15-day mouse embryos (E15) cultured in serumless chemically defined medium, to study fetal skeletal development with particular emphasis on de novo osteoclast formation. The normal pattern of growth and differentiation observed in vitro, assessed by ultrastructure and morphometry, demonstrate a permissive local environment which replicates physiologic temporal and spatial relationships which exist in vivo. The population of committed osteoclast progenitors present in E15 metatarsals form osteoclasts and precursors which have cytochemical and ultrastructural features, as well as kinetics of formation, that are similar to that which occurs in vivo. The responsiveness of osteoclast formation to the effects of added 1,25(OH)2D3 illustrates that controlled manipulation enables one to exploit the system for investigating the role of cytokines, growth factors and osteotropic hormones in skeletal development and osteoclast ontogeny.

Osteoclasts: structure and function

Osteoclasts are multinucleated giant cells showing specialized membrane structures, clear zones and ruffled borders, which are responsible for the process of bone resorption. These cells arrive at the resorption site via the bloodstream as mononuclear cells, derived from haemopoietic precursors in the spleen or bone marrow, which fuse prior to resorption. The osteoclast may share an early progenitor cell, the granulocyte macrophage colony-forming unit (GM-CFU) with monocytes, macrophages and granulocytes, implying that osteoclasts share the pluripotent haemopoietic stem cell with all other haemopoietic cells. In the past, elucidation of the structure of these cells relied upon traditional ultrastructural techniques. Transmission electron microscopic studies revealed details of the unique ultrastructure of these cells and, in combination with stereological techniques, showed the response of cells to various hormonal stimuli. Scanning electron microscopy not only demonstrated the surface appearance of osteoclasts, and their predilection for spreading on various substratum components, but has also been used as an adjunct in resorption assays in which areas of resorption lacunae are measured as indicators of cell activity. Recent advances in fields such as immunocytochemistry and freeze fracture techniques have contributed towards a more detailed delineation of antigenic profile, cytoskeletal structure and localization of enzymatic pathways. The osteoclast is subject to extensive regulatory mechanisms and it has been established that the osteoblast plays a major rôle in mediating the effects of osteotropic hormones and local mediators on these cells. Hence, research aimed at elucidating the coupling mechanisms between these two cells may result in new therapies for bone disease.

Repair of intra-membranous bone fractures and defects in rats. Immunolocalization of bone and cartilage proteins and proteoglycans

Osseous healing of experimental fractures and defects in membranous bone was studied in an animal model and the appearance and localization of selected bone and cartilage proteins and proteoglycans determined by polyclonal antibodies. The bone lesions were made in the parietal bone of young rats and subsequently studied on days 3, 5, 8, 15, 30, and 100 after surgery. The bone matrix proteins investigated (62 kDa, bone sialoprotein I and II, and osteopontin) appeared early, adjacent to the periosteal surfaces (pericranium and dura mater) and the marginal bone. The staining reactions were maximal at days 8 or 15 after trauma. Similar patterns were discerned for some cartilage macromolecules studied (58 kDa, 59 kDa, and chondrocalcin), although others showed no labelling whatsoever (148 kDa, and 400 kDa proteins). The proteoglycans PG-S1, PG-S2, and PG-LA were not identified. No callus or cartilage formation were associated with the bone healing process, and the differences between the regenerative pattern of the fractures and defects were limited. The findings emphasize the importance of rigid fixation in craniomaxillofacial surgery.

Immunophenotypic differences between osteoclasts and macrophage polykaryons: immunohistological distinction and implications for osteoclast ontogeny and function

The antigenic phenotype of human fetal osteoclasts was compared with that of human tissue macrophages and macrophage polykaryons in foreign body lesions using a large number of monoclonal antibodies directed against myeloid (granulocyte/mononuclear phagocyte) antigens. Osteoclasts expressed a restricted range of macrophage-associated antigens including CD13, CD15A, CD44, CD45, CD54, (ICAM-1), CD71 (transferrin receptor), and CD68. These antigens were also present on macrophages and macrophage polykaryons both of which also strongly expressed CD11a,b,c, CD18, (LFA family), CD14, CD31, CD36, CD37, CD39 and CD43 antigens. There was also weak and occasional expression of CD16 (FcRIII), CD25 (interleukin 2 receptor), CD32 (FcRII), CD35 (C3b receptor) and HLA-DR by macrophage polykaryons. The presence of some macrophage associated antigens on osteoclasts is consistent with their originating from cells of the mononuclear phagocyte system. The numerous differences in antigenic phenotype between osteoclasts and macrophage polykaryons, however, suggest that their pathways of development and differentiation are not identical. The differences discerned in antigenic phenotype should also permit distinction between these polykaryons (and possibly their mononuclear precursors) in normal and diseased tissues.

Review of calcium hydroxide

Calcium hydroxide is a material which has been used for a variety of purposes since its introduction into dentistry in the early part of the twentieth century. In its pure form, the substance has a high pH, and its dental use relates chiefly to its ability to stimulate mineralization, and also to its antibacterial properties. A range of products has been formulated with different therapeutic actions, the effects of which are partially dependent upon the tissue to which they are applied. The material is reviewed under the following general headings: biochemical actions; dental formulation; uses.

The osteoclast, which derives from a haemopoietic stem cell, is not depleted in aplastic anaemia

The osteoclast derives from the haemopoietic stem cell but its relationship with the other progeny of the haemopoietic system is unknown. Osteoclast numbers were assessed in patients with aplastic anaemia and were found not to be depleted compared with a control population. This suggests that the osteoclast may develop along a separate lineage which is independent of the colony forming unit granulocyte, erythroid cell, monocyte, and megakaryocyte (CFU GEMM).

Defective osteoclast differentiation and function in the osteopetrotic (os) rabbit

We tested the ability of normal osteoclast progenitors found in neonatal liver and bone marrow to develop into functional osteoclasts when co-cultured with metatarsals from newborn osteopetrotic rabbits; the latter inherit an osteoclast incompetence resistant to cure by bone marrow transplantation. This system, developed by Burger and colleagues, has been shown to produce normal, functional osteoclasts when used with normal metatarsals. Our study tested the competence of the mutant skeletal microenvironment for differentiation of normal osteoclasts. Mutant and normal metatarsals were cultured alone or with normal liver, spleen, or bone marrow for up to 14 days. All normal cultures possessed a marrow cavity and contained numerous osteoclasts with cytochemical characteristics (tartrate-resistant acid phosphatase) of active cells. Mutant metatarsals co-cultured with normal spleen, liver, or bone marrow failed to develop a marrow cavity (evidence in itself of reduced bone resorption) and had osteoclasts reduced in both numbers and cytochemically detectable activity. Similar metatarsal cultures of an osteopetrotic rat mutation (incisors--absent) curable by bone-marrow transplantation exhibited marrow cavity development in mutant metatarsals co-cultured with normal spleen. These data suggest that the skeletal environment of osteopetrotic rabbits contains an inhibitor or lacks a promoter of osteoclast differentiation and function.

Histochemistry and biochemistry of tartrate-resistant acid phosphatase (TRAP) and tartrate-resistant acid adenosine triphosphatase (TrATPase) in bone, bone marrow and spleen: implications for osteoclast ontogeny

In order to evaluate the usefulness of a recently described acid ATPase as a marker for osteoclast differentiation, we have performed histochemical and biochemical analyses of the distribution of tartrate-resistant acid phosphatase (TRAP) and tartrate-resistant acid ATPase (TrATPase) in bone, bone marrow and spleen. Histochemical studies of bone demonstrated that multinucleated osteoclasts stained for both TRAP and TrATPase. However, staining for TRAP covered the entire cytoplasm, whereas TrATPase staining was localized primarily to cytoplasmic areas next to bone and on adjacent mineralized surfaces. Occasionally TrATPase-positive mononuclear cells were observed on excavations in the bone surface. In the spleen, mononuclear TRAP-positive cells were located in the marginal zone between the white and red pulp, whereas no staining for TrATPase was observed. Comparison of the biochemically measured TRAP and TrATPase activities showed that bone had the highest specific activity for both enzymes followed by the bone marrow and spleen. However, enzyme activity in the spleen compared to bone was about 4-fold higher for TRAP compared to TrATPase. Additional evidence for a restricted expression of TrATPase to bone relative to spleen was obtained by in vitro translation studies. These data indicate that TrATPase is a more selective marker than TRAP in histochemical and biochemical studies of osteoclast differentiation and furthermore suggest that development of TrATPase is a late acquisition in osteoclast ontogeny.

Osteoclasts and a small population of peripheral blood cells share common surface antigens

Several methods have been tried to identify mononuclear osteoclast precursors. We used a panel of 13 osteoclast-recognizing monoclonal antibodies (mabs) for the identification of osteoclast precursor cells from the bone, bone marrow, and peripheral blood of egg laying hens. Almost all mabs stained some mononuclear cells in the bone. Seven mabs recognized few mononuclear cells in the bone marrow and five mabs gave the positive immunofluorescence reaction in the white blood cell fraction. Possible immediate osteoclast precursor cells differing from osteoclasts in their densities were identified in the bone. Three mabs (K38, K52, and K70) stained the same amount of mononuclear cells (2.6-3.4%) enriched in Percoll density centrifugation. Of the monoclonal antibodies that recognized few cells in blood, K41 stained only osteoclasts. K47 and K52 also recognized some mononuclear cells in the bone marrow. Other monoclonal antibodies K51 and K70 were more unspecific, since they stained cells derived from other tissues. Blood cells detected with these different monoclonal antibodies were negative for tartrate-resistant acid phosphatase (TRAP). On the basis of our results, we suggest that there is in the blood a specific TRAP-negative cell population, which is a good candidate for osteoclast precursor.