Tartrate-resistant acid phosphatase in mononuclear and multinuclear cells during the bone resorption of tooth eruption

Tartrate-resistant acid phosphatase (TRAP) has been used as a cytochemical marker for the cell mediators of bone resorption, osteoclasts and their mononuclear precursors. We have applied a cytochemical method for TRAP to study the dependence of the osteoclast-mediated bone resorption of tooth eruption on the dental follicle, a connective tissue investment of the developing tooth, by analyzing the TRAP activity of mononuclear cells in the dental follicle before and during pre-molar eruption in dogs. The percentage of TRAP-positive monocyte cells increases until mid-eruption, slightly preceding a previously demonstrated rise in numbers of osteoclasts on adjacent bone surfaces. These data suggest an ontogenetic relationship between follicular mononuclear cells and osteoclasts on adjacent alveolar bone surfaces during tooth eruption. However, because TRAP occurs in other tissues and is not an exclusive indicator of pre-osteoclasts, proof of their relationship will have to await application of more definitive techniques.     

Osteoimmunology: cytokines and the skeletal system

It has become clear that complex interactions underlie the relationship between the skeletal and immune systems. This is particularly true for the development of immune cells in the bone marrow as well as the functions of bone cells in skeletal homeostasis and pathologies. Because these two disciplines developed independently, investigators with an interest in either often do not fully appreciate the influence of the other system on the functions of the tissue that they are studying. With these issues in mind, this review will focus on several key areas that are mediated by crosstalk between the bone and immune systems. A more complete appreciation of the interactions between immune and bone cells should lead to better therapeutic strategies for diseases that affect either or both systems.     

Immunolocalization of vascular endothelial growth factor on intramuscular ectopic osteoinduction by bone morphogenetic protein-2

When recombinant human bone morphogenetic protein-2 (rhBMP-2) is implanted in soft tissues, bony tissue is induced during the course of endochondral ossification. The relationship between endochondral ossification and vascularization is important in bone formation, and vascular endothelial growth factor (VEGF) is considered to play an important role in this process. In this study, the immunohistological localization of VEGF was investigated in rhBMP-2-induced ectopic endochondral ossification in the calf muscle of rats. In addition, the characteristics of anti-VEGF antibody-reactive cells were histologically investigated using electron microscopy to examine the cause of endochondral ossification induced by recombinant human bone morphogenetic protein-2. The role of VEGF in rhBMP-2-induced osteoinduction and vascular induction was studied by observing the relationship between the localizations of anti-VEGF antibody-reactive cells and vascularization. During the process of rhBMP-2-induced ectopic endochondral ossification, fibroblast-like cells, which were located at the margin of the implant and reactive to BMP-2 at 5 days, were positive for VEGF immunostaining. Hypertrophic chondrocytes appeared 9 days and osteoblasts appeared 14 to 21 days after implantation, and all these cells were reactive with anti-VEGF antibody. Bony trabeculae subsequently appeared in the muscle, and new blood vessels were formed alongside the trabeculae. When VEGF was added to rhBMP, more new blood vessels and bone were formed in the induced bone. These findings suggested that rhBMP-2 induced the differentiation of undifferentiated mesenchymal cells to chondrocytes and osteoblasts, and these differentiated cells expressed VEGF, creating an advantageous environment for vascularization in bony tissue.     

Nervous activity in a stem cell niche

In this issue of Cell, report a new regulatory axis for the mobilization of hematopoietic stem cells that links these cells to the nervous system and bone in an unanticipated way. The new findings suggest that the nervous system, which has the inherent ability to integrate information from throughout the organism, may govern the local relationship between stem cells and their niches.     

Comparative Proteome Analysis of hAT-MSCs Isolated from Chronic Renal Failure Patients with Differences in Their Bone Turnover Status

The relationship between the stem cells and the bone turnover in uremic bone disease due to chronic renal failure (CRF) is not described. The aim of this study was to investigate the effect of bone turnover status on stem cell properties. To search for the presence of such link and shed some light on stem-cell relevant mechanisms of bone turnover, we carried out a study with mesenchymal stem cells. Tissue biopsies were taken from the abdominal subcutaneous adipose tissue of a CRF patient with secondary hyperparathyroidism with the high turnover bone disease. This patient underwent parathyroidectomy operation (PTX) and another sample was taken from this patient after PTX. A CRF patient with adynamic bone disease with low turnover and a healthy control were also included. Mesenchymal stem cells isolated from the subjects were analyzed using proteomic and molecular approaches. Except ALP activity, the bone turnover status did not affect common stem cell properties. However, detailed proteome analysis revealed the presence of regulated protein spots. A total of 32 protein spots were identified following 2D gel electrophoresis and MALDI-TOF/TOF analyzes. The identified proteins were classified into seven distinct groups and their potential relationship to bone turnover were discussed. Distinct protein expression patterns emerged in relation to the bone turnover status indicate a possible link between the stem cells and bone turnover in uremic bone disease due to CRF.     

LepR+ cells dispute hegemony with Gli1+ cells in bone marrow fibrosis

Bone marrow fibrosis is a reactive process, and a central pathological feature of primary myelofibrosis. Revealing the origin of fibroblastic cells in the bone marrow is crucial, as these cells are considered an ideal, and essential target for anti-fibrotic therapy. In 2 recent studies, Decker et al. (2017) and Schneider et al. (2017), by using state-of-the-art techniques including in vivo lineage-tracing, provide evidence that leptin receptor (LepR)-expressing and Gli1-expressing cells are responsible for fibrotic tissue deposition in the bone marrow. However, what is the relationship between these 2 bone marrow cell populations, and what are their relative contributions to bone marrow fibrosis remain unclear. From a drug development perspective, these works bring new cellular targets for bone marrow fibrosis.     

Kinetics of osteoprogenitor proliferation and osteoblast differentiation in vitro.

Fetal rat calvaria cells plated at very low density generate discrete colonies, some of which are bone colonies (nodules) from individual osteoprogenitors that divide and differentiate. We have analyzed the relationship between cell proliferation and acquisition of tissue-specific differentiation markers in bone colonies followed individually from the original single cell to the fully mineralized state. The size distribution of fully formed nodules is unimodal, suggesting that the coupling between proliferation and differentiation of osteoprogenitor cells is governed by a stochastic element, but distributed around an optimum, corresponding to the peak colony size/division potential. Kinetic analysis of colony growth showed that osteoprogenitors undergo 9-10 population doublings before the appearance of the first morphologically differentiated osteoblasts in the developing colony. Double immunolabeling showed that these proliferating cells express a gradient of bone markers, from proliferative alkaline phosphatase-negative cells at the periphery of colonies, to postmitotic, osteocalcin-producing osteoblasts at the centers. An inverse relationship exists between cell division and expression of osteocalcin, the latter being restricted to late-stage, BrdU-negative osteoblasts, while the expression of all other markers is acquired before the cessation of proliferation, but not concomitantly. Bone sialoprotein expression is biphasic, detectable in some of the early, alkaline phosphatase-negative cells, and again later in both late preosteoblast (BrdU-positive) and osteoblast (BrdU-negative, osteocalcin-positive) cells. In late-stage, heavily mineralized nodules, staining for osteocalcin and bone sialoprotein is not detectable in the oldest/most mature cells. Our observations support the view that the bone nodule "tissue-like" structure, originating from a single osteoprogenitor and finally encompassing mineralized matrix production, recapitulates successive stages of the osteoblast differentiation pathway, in a proliferation/maturation sequence. Understanding the complexity of the proliferation/differentiation kinetics that occurs within bone nodules will aid in the qualitative and/or quantitative interpretation of tissue-specific marker expression during osteoblastic differentiation.     

Bioactive fatty acids: role in bone biology and bone cell function

Bone is a unique tissue providing support, movement, and mineral balance for the body. Bone growth is achieved in the young by a process called modeling, and maintained during adulthood by a process termed remodeling. Three types of cells are responsible for the formation of cartilage and bone; the chondrocyte, osteoblast, and osteoclast. These cells are under the influence of a plethora of regulatory molecules, which govern their action to provide an individual optimal bone mass. Interruption of this homeostatic machinery, especially in the elderly, often results in a loss of bone mass (osteoporosis) or cartilage damage (rheumatoid arthritis). Many pharmacological agents have been made available in an effort to prevent or alleviate these pathologies, however, one vector often overlooked is the diet. This review focuses on the relationship between dietary polyunsaturated fatty acids and bone biology, both in vivo and in vitro.     

The relationship between bone marrow adipose tissue and bone metabolism in postmenopausal osteoporosis

Postmenopausal osteoporosis (PMOP) is a prevalent skeletal disorder associated with menopause-related estrogen withdrawal. PMOP is characterized by low bone mass, deterioration of the skeletal microarchitecture, and subsequent increased susceptibility to fragility fractures, thus contributing to disability and mortality. Accumulating evidence indicates that abnormal expansion of marrow adipose tissue (MAT) plays a crucial role in the onset and progression of PMOP, in part because both bone marrow adipocytes and osteoblasts share a common ancestor lineage. The cohabitation of MAT adipocytes, mesenchymal stromal cells, hematopoietic cells, osteoblasts and osteoclasts in the bone marrow creates a microenvironment that permits adipocytes to act directly on other cell types in the marrow. Furthermore, MAT, which is recognized as an endocrine organ, regulates bone remodeling through the secretion of adipokines and cytokines. Although an enhanced MAT volume is linked to low bone mass and fractures in PMOP, the detailed interactions between MAT and bone metabolism remain largely unknown. In this review, we examine the possible mechanisms of MAT expansion under estrogen withdrawal and further summarize emerging findings regarding the pathological roles of MAT in bone remodeling. We also discuss the current therapies targeting MAT in osteoporosis. A comprehensive understanding of the relationship between MAT expansion and bone metabolism in estrogen deficiency conditions will provide new insights into potential therapeutic targets for PMOP.     

DAP12 Overexpression Induces Osteopenia and Impaired Early Hematopoiesis

ITAM-bearing transmembrane signaling adaptors such as DAP12 and FcRγ are important players in bone homeostasis, but their precise role and functions are still unknown. It has been shown that osteoclast differentiation results from the integration of the RANK and of the DAP12 and FcRγ signaling pathways. DAP12-deficient mice suffer from a mild osteopetrosis and culture of their bone marrow cells in the presence of M-CSF and RANKL, fails to give rise to multinucleated osteoclasts. Here, we report that mice overexpressing human DAP12 have an osteopenic bone phenotype due to an increased number of osteoclasts on the surface of trabecular and cortical bone. This enhanced number of osteoclasts is associated with an increased number of proliferating myeloid progenitors in Tg-hDAP12 mice. It is concomitant with an arrest of B cell development at the Pre-Pro B/Pre B stage in the bone marrow of Tg-hDAP12 mice and important decrease of follicular and marginal B cells in the spleen of these animals. Our data show that the overexpression of DAP12 results in both increased osteoclastogenesis and impaired hematopoiesis underlining the relationship between bone homeostasis and hematopoiesis.     

Effects of 1,25-dihydroxyvitamin D3 on bone resorption and 45Ca2+ efflux in bone cells

1,25-dihydroxyvitamin D3[1,25(OH)2D3] effects on bone resorption in organ culture and on 45Ca2+ efflux rates in bone cells were measured in presence of a calcium channel inhibitor, diltiazem. Though, diltiazem reduced the 45Ca release from mice calvaria it did not act at the same Ca compartment as 1,25(OH)2D3 to alter Ca2+ flux parameters. It therefore seems difficult to hypothesize a simple relationship between bone resorption and Ca2+ movements in bone cells.     

Effect of human endothelial cells on human bone marrow stromal cell phenotype: role of VEGF?

Angiogenesis is a tightly regulated process involved in growth, repair, and bone remodeling. Several studies have shown that there is a reciprocal regulation and functional relationship between endothelial cells and osteoblast-like cells during osteogenesis, where systemic hormones and paracrine growth factors play an active role. Angiogenesis is induced by a variety of growth factors; among them vascular endothelial growth factor (VEGF) may be an important mediator for the angiogenic process involved in bone physiology. We studied the VEGF effect on osteoblast progenitor cells (Human Bone Marrow Stromal Cells: HBMSE) cultured alone or associated with endothelial cells (Human Umbilical Vein Endothelial Cells: HUVEC) in different co-culture models (co-culture with or without direct contact, conditioned medium), to determine the influence of VEGF on these cells and on their relationship. In agreement with other studies, we show that HBMSC express and synthesize VEGF, HUVEC conditioned medium has a proliferative effect on them, and early osteoblastic marker (Alkaline phosphatase activity) levels increase when these cells are co-cultured with HUVEC only in direct contact. However, unlike previous studies, we did not find that VEGF increased these processes. These results suggest that the intercommunication between endothelial cells and osteoblastic-like cells requires not only diffusible factors, but also involving cell membrane proteins.     

CFU-F from dog marrow: a colony assay and its significance

A colony assay method is described for studying dog fibroblast colony development in marrow cells derived from resected ribs. The assay showed an increased number of fibroblast colony forming units (CFU-F) in cell suspensions prepared from resected ribs compared to cell suspensions prepared from bone marrow aspirates or from peripheral blood. A linear relationship between the number of cells plated and the number of fibroblastoid colonies was demonstrated in each case. The proportion of phagocytic cells was lower in cultures prepared from resected ribs than in those prepared from bone marrow aspirates. Staining for acid phosphatase and with sudan black showed differences between phagocytic cells and non-phagocytic fibroblasts. When left in plastic dishes for 2 hrs, 81% +/- 10% of the CFU-F adhered to the plastic dishes. Velocity sedimentation separation showed a modal sedimentation rate of 6.49 mm/h.     

Calcium homeostasis: solving the solubility problem

This report summarizes the evidence that the control of the concentration of free calcium ions in body fluids is centered at mineralized bone surfaces. This process involves an increase in the solubility of bone mineral produced by the non-collagenous proteins existing in the bone extracellular fluid (ECF) and on the adjacent surfaces of bone. The result is a basic equilibrium level produced in the absence of parathyroid hormone (PTH), which is well above the solubility of bone mineral. The effect of PTH is to increase the solubility of bone mineral still further, but the mechanism by which the hormone acts is unknown. The lining cells of the bone contain receptors for PTH and can be observed to respond to this hormone, but the relationship between this response and the increased solubility of bone remains to be discovered. Further research in this field is strongly urged.     

电磁辐射对大鼠内皮祖细胞和肾脏组织学的影响

目的:研究电磁辐射对体外培养骨髓来源的内皮祖细胞(EPCs)增殖、迁移、黏附能力的影响,并探讨其与肾脏疾病的可能关系。方法:密度梯度离心法获取大鼠骨髓单个核细胞(MNCs),接种至纤维连接素包被的培养板上,培养6d后进行免疫细胞化学和免疫荧光鉴定EPCs。采用MTT比色法、Transwell小室和黏附能力测定实验,观察平均功率密度为65mW/cm2,时间20min的电磁辐射对EPCs的增殖、迁移、黏附能力的影响;同等剂量全身照射大鼠,光镜和透射电镜观察大鼠肾脏组织学和超微结构的变化。结果:从大鼠骨髓能成功分离培养获得EPCs。EPCs的增殖、迁移、黏附能力较对照组显著下降;大鼠接受全身照射后各时相点无明显组织学改变,但超微结构显示在照射后3h后开始出现肾小球毛细血管袢足突肿胀,12h后出现部分足突融合。结论:电磁辐射导致EPCs生物功能显著减弱,肾小球超微结构改变,电磁辐射可能与起肾脏疾病的发生有关。     

Polyamines affect histamine synthesis during early stages of IL‐3‐induced bone marrow cell differentiation

Mast cells synthesize and store histamine, a key immunomodulatory mediator. Polyamines are essential for every living cell. Previously, we detected an antagonistic relationship between the metabolisms of these amines in established mast cell and basophilic cell lines. Here, we used the IL‐3‐driven mouse bone marrow‐derived mast cell (BMMC) culture system to further investigate this antagonism in a mast cell model of deeper physiological significance. Polyamines and histamine levels followed opposite profiles along the bone marrow cell cultures leading to BMMCs. α‐Difluoromethylornithine (DFMO)‐induced polyamine depletion resulted in an upregulation of histidine decarboxylase (HDC, the histamine‐synthesizing enzyme) expression and activity, accompanied by increased histamine levels, specifically during early stages of these cell cultures, where an active histamine synthesis process occurs. In contrast, DFMO did not induce any effect in either HDC activity or histamine levels of differentiated BMMCs or C57.1 mast cells, that exhibit a nearly inactive histamine synthesis rate. Sequence‐specific DNA methylation analysis revealed that the DFMO‐induced HDC mRNA upregulation observed in early bone marrow cell cultures is not attributable to a demethylation of the gene promoter caused by the pharmacological polyamine depletion. Taken together, the results support an inverse relationship between histamine and polyamine metabolisms during the bone marrow cell cultures leading to BMMCs and, moreover, suggest that the regulation of the histamine synthesis occurring during the early stages of these cultures depends on the concentrations of polyamines. J. Cell. Biochem. 108: 261–271, 2009. © 2009 Wiley‐Liss, Inc.     

Inhibition of erythroid cell growth in irradiated mice by allogeneic lymphoid cells: Specificity of the response

Allogeneic lymphocytes can inhibit proliferation of erythroid cells in the spleens of irradiated mice grafted with syngeneic bone marrow cells. Since there is a linear relationship between the number of injected lymphocytes and erythroid activity, the method is frequently used as a graft-vs-host assay. In this investigation we show that the reduction of erythroid activity is due to both a reaction of the lymphocytes against the tissues of the host and against the grafted bone marrow cells. Thus, reduced erythropoietic activity does not necessarily indicate that the bone marrow targets possess antigens against which the lymphocytes are reactive.     

Origin and differentiation of natural killer cells. I. Characteristics of a transplantable NK cell precursor

To study the origin and differentiation of natural killer (NK) cells, we developed an assay for the transplantable precursor of NK(YAC-1) cells present in the bone marrow. Mice were depleted of endogenous NK(YAC-1) cells by injection of anti-asialo GM1 antibody, followed by lethal whole body irradiation. Normal syngeneic bone marrow cells were transplanted into such pretreated mice. Regeneration of NK(YAC-1) activity in the recipient mice was monitored by two different assays: the ability of spleen cells to lyse YAC-1 cells in vitro and the ability to clear i.v. injected, 125IUdR-labeled YAC-1 cells from the lungs. With both assays, a dose-response relationship between the number of bone marrow cells injected and the degree of NK(YAC-1) activity generated could be demonstrated. However, the lung clearance assay appeared superior because the NK regeneration could be detected earlier and with lower numbers of injected marrow cells. With this assay, several characteristics of the NK precursors and their differentiation could be defined. 1) The generation of mature, lytic NK cells from their transplantable precursor requires an intact "marrow microenvironment" in the recipient mice, because differentiation failed to occur in mice rendered osteopetrotic by estradiol treatment. 2) The NK(YAC-1) precursors lack the surface antigens (NK-2.1, asialo GM1, Qa-5, Thy-1) that are characteristically seen on mature NK cells. 3) The NK-precursors could be eliminated from the bone marrow with anti-Qa-2 or anti-H-2 antisera + complement, indicating that these two antigens are expressed on the precursors. The relationship between NK(YAC-1) precursors and multipotent myeloid stem cells (CFU-S) was investigated by utilizing W/Wv and Sl/Sld mutant mice. Bone marrow cells of W/Wv anemic mice, although markedly deficient in CFU-S, have a normal frequency of NK(YAC-1) precursors. Sl/Sld mice that lack a suitable microenvironment for the development of CFU-S allowed normal differentiation of NK(YAC-1) precursors when transplanted with normal bone marrow cells. Together, these data suggest that multipotent myeloid progenitor cells, as defined by the CFU-S assay, and the NK(YAC-1) precursors are not closely related.     

Bone and the immune system

There are several lines of evidence which provide support for an important relationship between immune cells and bone. Clinical studies of immunodeficiency syndromes have shown that abnormalities in bone shape are evident on x-rays, and peculiarities in the structure of the growth plate have been identified by histopathology. Studies of bone histology, and quantitation of cellular abnormalities, are scarce. Abnormalities in bone turnover, have, however, been identified in the nude mouse model. Many lines of evidence derived from in vitro bone studies have shown that lymphokines and monokines can influence bone formation and bone resorption. Some clinical studies of postmenopausal osteoporosis have indicated the possible presence of immune cell changes in this condition. Although several hypotheses have been formed regarding the exact mechanisms of the effect of immune cytokine on bone, this is clearly a very large area of study and there is a need for additional carefully controlled experiments with special emphasis on bone cells and bone matrix, especially in the human. As knowledge progresses regarding immunology and hematology, a clearer understanding of the lineages of the osteoblast and osteoclast will emerge and we will better understand how specialized bone cells interact with and react to their immune cell neighbors in the bone marrow and to immune system signals. These findings will have especially important implications for the local bone loss seen in rheumatoid arthritis, periodontal disease, and chronic osteomyelitis.