Interleukin 4 enhances osteoblast macrophage colony-stimulating factor, but not interleukin 6, production

An Exploration of the Role of Osteoclast Lineage Cells in Bone Tissue Engineering

Bone defects because of age, trauma, and surgery, which are exacerbated by medication side effects and common diseases such as osteoporosis, diabetes, and rheumatoid arthritis, are a problem of epidemic scale. The present clinical standard for treating these defects includes autografts and allografts. Although both treatments can promote robust regenerative outcomes, they fail to strike a desirable balance of availability, side effect profile, consistent regenerative efficacy, and affordability. This difficulty has contributed to the rise of bone tissue engineering (BTE) as a potential avenue through which enhanced bone regeneration could be delivered. BTE is founded upon a paradigm of using biomaterials, bioactive factors, osteoblast lineage cells (ObLCs), and vascularization to cue deficient bone tissue into a state of regeneration. Despite promising preclinical results, BTE has had modest success in being translated into the clinical setting. One barrier has been the simplicity of its paradigm relative to the complexity of biological bone. Therefore, this paradigm must be critically examined and expanded to better account for this complexity. One potential avenue for this is a more detailed consideration of osteoclast lineage cells (OcLCs). Although these cells ostensibly oppose ObLCs and bone regeneration through their resorptive functions, a myriad of investigations have shed light on their potential to influence bone equilibrium in more complex ways through their interactions with both ObLCs and bone matrix. Most BTE research has not systematically evaluated their influence. Yet contrary to expectations associated with the paradigm, a selection of BTE investigations has demonstrated that this influence can enhance bone regeneration in certain contexts. In addition, much work has elucidated the role of many controllable scaffold parameters in both inhibiting and stimulating the activity of OcLCs in parallel to bone regeneration. Therefore, this review aims to detail and explore the implications of OcLCs in BTE and how they can be leveraged to improve upon the existing BTE paradigm.

Association of Specific Genetic Polymorphisms with Atraumatic Osteonecrosis of the Femoral Head: A Narrative Review

INTRODUCTION

Atraumatic ONFH is one of the leading cause of hip morbidity in the working-age group. It is a multi-factorial disease whose root cause can be attributed to single-nucleotide polymorphism. Identifying such polymorphisms could pave the way for new modalities of treatment for ONFH.

METHODOLOGY

Two databases were electronically searched for relevant articles. The articles were screened through titles, abstract and full texts to include the relevant studies. A secondary search was done through the reference list of selected articles.

RESULTS

A total of 52 studies were included among the 181 hits. All 181 were case-control studies. Summary of these studies identifies multiple SNPs which can cause ONFH. There were 117 SNPs in all 181 studies, of which 92 were associated with the causation of ONFH and 25 were protective against ONFH.

CONCLUSION

SNPs play an essential role in causing atraumatic ONFH. Identification of SNP that contribute to causing ONFH may help reduce the disease burden by early identification, diagnosis and treatment, including targeted gene therapy.

Osteoblast-Osteoclast Communication and Bone Homeostasis

Bone remodeling is tightly regulated by a cross-talk between bone-forming osteoblasts and bone-resorbing osteoclasts. Osteoblasts and osteoclasts communicate with each other to regulate cellular behavior, survival and differentiation through direct cell-to-cell contact or through secretory proteins. A direct interaction between osteoblasts and osteoclasts allows bidirectional transduction of activation signals through EFNB2-EPHB4, FASL-FAS or SEMA3A-NRP1, regulating differentiation and survival of osteoblasts or osteoclasts. Alternatively, osteoblasts produce a range of different secretory molecules, including M-CSF, RANKL/OPG, WNT5A, and WNT16, that promote or suppress osteoclast differentiation and development. Osteoclasts also influence osteoblast formation and differentiation through secretion of soluble factors, including S1P, SEMA4D, CTHRC1 and C3. Here we review the current knowledge regarding membrane bound- and soluble factors governing cross-talk between osteoblasts and osteoclasts.

Osteoblast-osteoclast interactions

Bone homeostasis depends on the resorption of bones by osteoclasts and formation of bones by the osteoblasts. Imbalance of this tightly coupled process can cause diseases such as osteoporosis. Thus, the mechanisms that regulate communication between osteoclasts and osteoblasts are critical to bone cell biology. It has been shown that osteoblasts and osteoclasts can communicate with each other through direct cell-cell contact, cytokines, and extracellular matrix interaction. Osteoblasts can affect osteoclast formation, differentiation, or apoptosis through several pathways, such as OPG/RANKL/RANK, RANKL/LGR4/RANK, Ephrin2/ephB4, and Fas/FasL pathways. Conversely, osteoclasts also influence formation of bones by osteoblasts via the d2 isoform of the vacuolar (H+) ATPase (v-ATPase) V0 domain (Atp6v0d2), complement component 3a, semaphorin 4D or microRNAs. In addition, cytokines released from the resorbed bone matrix, such as TGF-β and IGF-1, also affect the activity of osteoblasts. Drugs could be developed by enhancing or restricting some of these interactions. Several reviews have been performed on the osteoblast-osteoclast communication. However, few reviews have shown the research advances in the recent years. In this review, we summarized the current knowledge on osteoblast-osteoclast communication.

Ginsenoside Rg1 improves bone marrow haematopoietic activity via extramedullary haematopoiesis of the spleen

Cyclophosphamide (CY) is a chemotherapeutic agent used for cancer and immunological diseases. It induces cytotoxicity of bone marrow and causes myelosuppression and extramedullary haematopoiesis (EMH) in treated patients. EMH is characterized with the emergence of multipotent haematopoietic progenitors most likely in the spleen and liver. Previous studies indicated that a Chinese medicine, ginsenoside Rg1, confers a significant effect to elevate the number of lineage (Lin⁻) Sca-1⁺ c-Kit⁺ haematopoietic stem and progenitor cells (HSPCs) and restore the function of bone marrow in CY-treated myelosuppressed mice. However, whether the amelioration of bone marrow by Rg1 accompanies an alleviation of EMH in the spleen was still unknown. In our study, the cellularity and weight of the spleen were significantly reduced after Rg1 treatment in CY-treated mice. Moreover, the number of c-Kit⁺ HSPCs was significantly decreased but not as a result of apoptosis, indicating that Rg1 alleviated EMH of the spleen induced by CY. Unexpectedly, the proliferation activity of c-Kit⁺ HSPCs was only up-regulated in the spleen, but not in the bone marrow, after Rg1 treatment in CY-treated mice. We also found that a fraction of c-Kit⁺/CD45⁺ HSPCs was simultaneously increased in the circulation after Rg1 treatment. Interestingly, the effects of Rg1 on the elevation of HSPCs in bone marrow and in the peripheral blood were suppressed in CY-treated splenectomized mice. These results demonstrated that Rg1 improves myelosuppression induced by CY through its action on the proliferation of HSPCs in EMH of the spleen and migration of HSPCs from the spleen to the bone marrow.

Review of cellular mechanisms of tumor osteolysis

The cellular and biochemical mechanisms that direct the destruction of bone at sites of tumor osteolysis are unknown. To better understand the mechanisms through which tumors direct bone resorption, research has focused on developing in vivo and in vitro experimental models that are useful for studying this process. In vivo experimental systems have been developed that permit study of tumor osteolysis from human and murine tumors, and that permit the study of tumors that arise from (sarcoma) or can metastasize (breast cancer) to bone. Recent research has focused on three questions: (1) Are osteoclasts or tumor cells responsible for bone resorption during tumor osteolysis? (2) What are the cellular mechanisms that are responsible for bone resorption during tumor osteolysis, and (3) what are the tumor cell products that regulate the cellular mechanisms that are responsible for tumor osteolysis? It has been determined that osteoclasts are responsible for bone resorption at sites of tumor osteolysis by enhancing the binding of osteoclast to bone, by inducing osteoclastic bone resorption, and by stimulating osteoclast formation. Attempts to identify tumor cell products that regulate these cellular mechanisms are in progress, and findings suggest that production of macrophage colony stimulating factor may be required for tumor osteolysis to occur with some tumors.

Human osteoblast-like cells and osteosarcoma cell lines synthesize macrophage inhibitory protein 1alpha in response to interleukin 1beta and tumour necrosis factor alpha stimulation in vitro

Recent investigations have demonstrated that macrophage inhibitory protein 1alpha (MIP-1alpha) plays a critical role in haematopoiesis. In part, MIP-1alpha limits the differentiation of early haematopoietic cells, thereby ensuring that sufficient quantities of blood precursors are available to meet haematopoietic demands. MIP-1alpha is produced by cells of the marrow microenvironment (marrow stromal cells) in response to a variety of stimuli, including interleukin 1beta (IL-1beta) and tumour necrosis factor alpha (TNF-alpha). Our recent investigations demonstrated that normal human osteoblast-like cells (HOBs) maintain the early phenotype of haematopoietic precursors, like other members of the bone marrow stroma. Although the precise molecular mechanisms for these observations have not been determined, the production of MIP-1alpha remains one such possibility. In the present study, we investigated whether cells of the osteoblast lineage under basal, IL-1beta and/or TNF-alpha stimulation produce MIP-1alpha. We observed that IL-1beta and TNF-alpha stimulated HOBs and human osteosarcoma cells to rapidly express MIP-1alpha mRNA and to secrete large quantities of the protein. MIP-1alpha mRNA and protein was not, however, detected under basal conditions. Perhaps more importantly, enriched human CD34+ bone marrow cells in co-culture may be capable of stimulating the expression of MIP-1alpha mRNA by HOBs in vitro. These findings suggest that human osteoblast-like cells may produce MIP-1alpha in vivo to support haematopoiesis at sites where osteoblasts and haematopoietic cells are closely associated.

Bone marrow cells produce soluble factors that inhibit osteoclast activity

Cytokines that stimulate bone resorption are produced by cells found in bone marrow. However, marrow cells produce multiple factors, some of which may be inhibitors of osteoclast differentiation or activity. Thus, it is not possible to predict a priori whether the mixture of factors produced by marrow cells will have a net stimulatory or inhibitory effect on bone resorption. In this study, we showed that the net effect of whole marrow is to inhibit osteoclast activity induced by parathyroid hormone. Fractionation of the marrow revealed that the inhibitory activity was in the marrow fluid. However, conditioned media obtained from marrow cell cultures also inhibited osteoclast activity. Thus, it is likely that the inhibitory factors are produced in vivo by cells residing in the marrow. These inhibitory factors may represent a physiological regulatory process that plays an important role in maintaining the balance between bone resorption and formation. Because we have previously shown that interleukin-6 is one of the cytokines that parathyroid hormone induces in osteoblastic cells to stimulate osteoclast activity, one potential mechanism by which the marrow-derived inhibitory factors might act is by preventing this production of interleukin-6. However, we found that the marrow cell-conditioned media do not inhibit the production or activity of interleukin-6. Thus, the inhibitory factors appear to block osteoclast activity through a mechanism that does not involve interleukin-6. Taken together, these results demonstrate the importance of factors that inhibit bone resorption and emphasize that the presence of cytokines that stimulate bone resorption in conditions such as osteoporosis and orthopaedic implant loosening should be interpreted with caution unless evidence exists demonstrating their functional importance.

Endothelin stimulates osteoblastic production of IL-6 but not macrophage colony-stimulating factor

Endothelins (ET) are vasoactive polypeptide hormones that stimulate osteoblastic signal transduction events. Using MC3T3-E1 and primary osteoblasts, we studied ET effects on interleukin-6 (IL-6) and macrophage colony-stimulating factor (M-CSF) production. Enzyme-linked immunosorbent assay analysis showed a dose-dependent 3- to 3.5-fold increase in IL-6 with 100 nM ET-1 stimulation within 4 (primary osteoblasts) to 8 (MC3T3-E1) h. ET-3 was less effective at enhancing IL-6 production, with a maximal twofold increase after 100 nM ET-3 after 4 h. No significant increase in M-CSF production was noted with ET-1 or ET-3 in either cell type. Reverse-transcriptase polymerase chain reaction analysis demonstrated both ET(A) and ET(B) receptors on primary osteoblasts and only ET(A) receptors on MC3T3-E1. ET-1-stimulated IL-6 production was blocked by the inhibitor BQ-123, implicating ET(A) receptor involvement. Increased IL-6 protein was coupled with elevated IL-6 mRNA levels and a twofold increase in IL-6 message half-life.

Augmented Production of Interleukin-6 by Normal Human Osteoblasts in Response to CD34+ Hematopoietic Bone Marrow Cells In Vitro

Based on anatomic and developmental findings characterizing hematopoietic cells in close approximation with endosteal cells, we have begun an analysis of osteoblast/hematopoietic cell interactions. We explore here the functional interdependence between these two cell types from the standpoint of de novo cytokine secretion. We determined that, over a 96-hour period, CD34+ bone marrow cells had no significant effect on osteoblast secretion of granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, or transforming growth factor-β1 , but in some experiments minor increases in leukemia inhibitory factor levels were observed. However, when CD34+ bone marrow cells were cocultured in direct contact with osteoblasts, a 222% ± 55% (range, 153% to 288%) augmentation in interleukin-6 (IL-6) synthesis was observed. The accumulation of IL-6 protein was most rapid during the initial 24-hour period, accounting for nearly 55% of the total IL-6 produced by osteoblasts in the absence of blood cells and 77% of the total in the presence of the CD34+ cells. Cell-to-cell contact does not appear to be required for this activity, as determined by coculturing the two cell types separated by porous micromembranes. The identity of the soluble activity produced by the CD34+ cells remains unknown, but is not likely due to IL-1β or tumor necrosis factor-α, as determined with neutralizing antibodies. To our knowledge, these data represent the first demonstration that early hematopoietic cells induce the production of molecules required for the function of normal bone marrow microenvironments, in this case through the induction of hematopoietic cytokine (IL-6) secretion by osteoblasts.

PCR phenotyping of cytokines, growth factors and their receptors and bone matrix proteins in human osteoblast-like cell lines

The expression of a total of 58 cytokines, growth factors, and their corresponding receptors and bone matrix proteins was assessed using reverse transcription-linked polymerase chain reaction (RT-PCR) analysis to determine the similarity in the expression profile between clonal osteosarcoma-derived human osteoblast-like cell lines and primary human osteoblast-like cell cultures derived from human trabecular bone explants. The spectrum of cytokines, growth factors, and bone-related proteins expressed by three human osteosarcoma-derived cell lines, TE-85, MG-63, SaOS-2, and primary human osteoblast-like cells was found to be highly comparable and for the first time the expression of EGF, ECGF, FGF beta, oncostatin M, TNF beta, and SCF by human osteoblast-like cells was detected. Also the expression of several receptor types including IL-4R, IL-7R, IFN alpha/beta R, and SCFR was detected that has not been previously described for human osteoblast-like cells. For the factors examined, no qualitative variations in the expression profile were observed in the six primary human osteoblast-like cell cultures used in this study. Of the 58 factors examined, only 13 showed some degree of nonuniformity of expression between all of the three cell lines and primary cell cultures. These differences were seen especially in the expression of cytokine receptor mRNA and to a lesser extent with some cytokines. Differences in receptor expression would suggest that the possible spectrum of response to exogenously added factors, or even autocrine/ paracrine networks would be determined by the repertoire of receptors expressed by each cell type. Whether the differences are related to the status of cell maturation within the osteoblast development lineage or to their abberant regulation of expression cannot be concluded at this stage. However, this PCR-phenotyping approach rapidly provides a resource of information, which can be subsequently used for further in depth studies to facilitate the analysis of the molecular mechanisms, whereby the target gene of interest is modulated in a model cell line. In addition, this study indicates that at least based on the transcript expression profile of the factors analyzed, human osteosarcoma-derived osteoblast-like cells are useful as models for their nontransformed counterparts.

Interleukin-4 inhibits prostaglandin G/H synthase-2 and cytosolic phospholipase A2 induction in neonatal mouse parietal bone cultures

We have shown previously that prostaglandin (PG) production in 7-day-old neonatal mouse calvarial cultures is regulated largely by changes in prostaglandin G/H synthase-2 (PGHS-2) expression and to a lesser extent by changes in arachidonic acid (AA) release. In this study, we examined the effects of interleukin-4 (IL-4), and its interactions with other cytokines and with parathyroid hormone (PTH), on mRNA levels of PGHS-2, PGHS-1, and cytosolic phospholipase A2 (cPLA2) and on medium protaglandin E2 (PGE2) levels in calvarial cultures. IL-1 and tumor necrosis factor-alpha (TNF-alpha), both at 1-100 ng/ml, and PTH at 0.1-10 nM increased PGHS-2 and cPLA2 mRNA and medium PGE2 levels dose-dependently after 4 h of treatment. IL-6 and IL-11 at 1-100 ng/ml did not affect mRNA or PGE2 levels. IL-4 at 1-100 ng/ml decreased PGHS-2 and cPLA2 mRNA and PGE2 levels in control as well as IL-1, TNF-alpha, and PTH-stimulated cultures. The inhibition of PGHS-2 and cPLA2 mRNA expression by IL-4 (10 ng/ml) was present at 1 h, reached a maximum at 4 h, and persisted for 24 h. The effects were maintained in the presence of cycloheximide. IL-4 also decreased PGHS-2 protein levels in control and IL-1-stimulated cultures. PGHS-1 mRNA levels were not stimulated by any of the factors studied nor inhibited by IL-4. IL-4 partially inhibited control and PTH-stimulated 45Ca release from prelabeled mouse calvariae at 4 days. However, neither the inhibition of resorption by IL-4 nor the stimulation by IL-1 and PTH were altered by indomethacin (1 microM). We conclude that (1) IL-1, TNF-alpha, and PTH, but not IL-6 nor IL-11, can increase the expression of PGHS-2, cPLA2, and PGE2 production in cultured mouse calvariae; (2) IL-4 inhibits PGE2 production in both control and stimulated calvarial cultures by inhibiting PGHS-2 and cPLA2; and (3) IL-4 has an inhibitory effect on bone resorption which is independent of PG production.

Local concentrations of macrophage colony-stimulating factor mediate osteoclastic differentiation

Macrophage colony-stimulating factor (M-CSF) is essential for differentiation of osteoclasts and macrophages from a common bone marrow precursor. Using ST-2 stromal cell/murine bone marrow coculture, we studied the effects of increasing amounts of M-CSF on differentiation of macrophages and osteoclasts. Addition of exogenous M-CSF caused a dose-dependent 98% decrease in tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells, accompanied by a 2.5-fold increase in nonspecific esterase-staining macrophages. Similar decrease in osteoclastic functional activity, including 125I-labeled calcitonin binding and calcitonin-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) production, were observed. Addition of exogenous M-CSF beyond 6 days in coculture had a decreasing ability to inhibit osteoclast formation, suggesting that M-CSF exerts its effects early in osteoclast differentiation, during the proposed proliferative phase of osteoclast formation. Similarly, early addition of neutralizing anti-M-CSF inhibited osteoclast formation, with diminishing effects beyond day 9. These results suggest that local high concentrations of M-CSF may influence the early determination of terminal differentiation into either macrophages or osteoclasts.