Human osteoclasts and osteoclast-like cells synthesize and release high basal and inflammatory stimulated levels of the potent chemokine interleukin-8

The forgotten key players in rheumatoid arthritis: IL-8 and IL-17 - Unmet needs and therapeutic perspectives

Despite the relevant advances in our understanding of the pathogenetic mechanisms regulating inflammation in rheumatoid arthritis (RA) and the development of effective therapeutics, to date, there is still a proportion of patients with RA who do not respond to treatment and end up progressing toward the development of joint damage, extra-articular complications, and disability. This is mainly due to the inter-individual heterogeneity of the molecular and cellular taxonomy of the synovial membrane, which represents the target tissue of RA inflammation. Tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) are crucial key players in RA pathogenesis fueling the inflammatory cascade, as supported by experimental evidence derived from in vivo animal models and the effectiveness of biologic-Disease Modifying Anti-Rheumatic Drugs (b-DMARDs) in patients with RA. However, additional inflammatory soluble mediators such as IL-8 and IL-17 exert their pathogenetic actions promoting the detrimental activation of immune and stromal cells in RA synovial membrane, tendons, and extra-articular sites, as well as blood vessels and lungs, causing extra-articular complications, which might be excluded by the action of anti-TNFα and anti-IL6R targeted therapies. In this narrative review, we will discuss the role of IL-8 and IL-17 in promoting inflammation in multiple biological compartments (i.e., synovial membrane, blood vessels, and lung, respectively) in animal models of arthritis and patients with RA and how their selective targeting could improve the management of treatment resistance in patients.

Effect of teriparatide on drug treatment of tuberculous spondylitis: an experimental study

Tuberculous spondylitis often develops catastrophic bone destruction with uncontrolled inflammation. Because anti-tuberculous drugs do not have a role in bone formation, a combination drug therapy with a bone anabolic agent could help in fracture prevention and promote bone reconstruction. This study aimed to investigate the influence of teriparatide on the effect of anti-tuberculous drugs in tuberculous spondylitis treatment. We used the virulent Mycobacterium tuberculosis (Mtb) H37Rv strain. First, we investigated the interaction between teriparatide and anti-tuberculosis drugs (isoniazid and rifampin) by measuring the minimal inhibitory concentration (MIC) against H37Rv. Second, we evaluated the therapeutic effect of anti-tuberculosis drugs and teriparatide on our previously developed in vitro tuberculous spondylitis model of an Mtb-infected MG-63 osteoblastic cell line using acid-fast bacilli staining and colony-forming unit counts. Selected chemokines (interleukin [IL]-8, interferon γ-induced protein 10 kDa [IP-10], monocyte chemoattractant protein [MCP]-1, and regulated upon activation, normal T cell expressed and presumably secreted [RANTES]) and osteoblast proliferation (alkaline phosphatase [ALP] and alizarin red S [ARS] staining) were measured. Teriparatide did not affect the MIC of isoniazid and rifampin. In the Mtb-infected MG-63 spondylitis model, isoniazid and rifampin treatment significantly reduced Mtb growth, and cotreatment with teriparatide did not change the anti-tuberculosis effect of isoniazid (INH) and rifampin (RFP). IP-10 and RANTES levels were significantly increased by Mtb infection, whereas teriparatide did not affect all chemokine levels as inflammatory markers. ALP and ARS staining indicated that teriparatide promoted osteoblastic function even with Mtb infection. Cotreatment with teriparatide and the anti-tuberculosis drugs activated bone formation (ALP-positive area increased by 705%, P = 0.0031). Teriparatide was effective against Mtb-infected MG63 cells without the anti-tuberculosis drugs (ARS-positive area increased by 326%, P = 0.0037). Teriparatide had no effect on the efficacy of anti-tuberculosis drugs and no adverse effect on the activity of Mtb infection in osteoblasts. Furthermore, regulation of representative osteoblastic inflammatory chemokines was not changed by teriparatide treatment. In the in vitro Mtb-infected MG-63 cell model of tuberculous spondylitis, cotreatment with the anti-tuberculosis drugs and teriparatide increased osteoblastic function.

Local and Systemic Cytokine, Chemokine, and FGF Profile in Bacterial Chondronecrosis with Osteomyelitis (BCO)-Affected Broilers

Complex disease states, like bacterial chondronecrosis with osteomyelitis (BCO), not only result in physiological symptoms, such as lameness, but also a complex systemic reaction involving immune and growth factor responses. For the modern broiler (meat-type) chickens, BCO is an animal welfare, production, and economic concern involving bacterial infection, inflammation, and bone attrition with a poorly defined etiology. It is, therefore, critical to define the key inflammatory and bone-related factors involved in BCO. In this study, the local bone and systemic blood profile of inflammatory modulators, cytokines, and chemokines was elucidated along with inflammasome and key FGF genes. BCO-affected bone showed increased expression of cytokines IL-1β, while BCO-affected blood expressed upregulated TNFα and IL-12. The chemokine profile revealed increased IL-8 expression in both BCO-affected bone and blood in addition to inflammasome NLRC5 being upregulated in circulation. The key FGF receptor, FGFR1, was significantly downregulated in BCO-affected bone. The exposure of two different bone cell types, hFOB and chicken primary chondrocytes, to plasma from BCO-affected birds, as well as recombinant TNFα, resulted in significantly decreased cell viability. These results demonstrate an expression of proinflammatory and bone-resorptive factors and their potential contribution to BCO etiology through their impact on bone cell viability. This unique profile could be used for improved non-invasive detection of BCO and provides potential targets for treatments.

The role of renin angiotensin system in the pathophysiology of rheumatoid arthritis

BACKGROUND

In rheumatoid arthritis (RA) and osteoarthritis (OA), chronic inflammatory processes lead to progresive joint destruction. The renin-angiotensin system (RAS) is involved in the pathogenesis of RA and OA. The aim of this mini-review article is to summarize evidence on the role of RAS in RA and OA.

METHODS

A non-systematic search in Pubmed included terms as "rheumatoid arthritis", "renin angiotensin system", "osteopenia", "RANKL", "DKK-1", "MMP", "inflammation", "angiogenesis", "local renin-angiotensin system", "angiotensin converting enzyme", "AT2 receptor", "Ang-(1-7)", "VEGF", "angiotensine receptor blocker", "angiotensin converting enzyme inhibitors", "renin inhibitors".

RESULTS

Both RAS axes, the classical one, formed by angiotensin converting enzyme (ACE), angiotensin (Ang) II and AT1 receptor (AT1R) and the counter-regulatory one, composed by ACE2, Ang-(1-7) and the Mas receptor, modulate inflammation and tissue damage. Ang II activates pro-inflammatory mediators and oxidative stress. Conversely, Ang-(1-7) exerts anti-inflammatory actions, decreasing cytokine release, leukocyte attraction, density of vessels, tissue damage and fibrosis. Angiogenesis facilitates inflammatory cells invasion, while osteopenia causes joint dysfunction. Up-regulated osteoclastogenisis and down-regulated osteoblastogeneses were associaed with the activation of the classical RAS axis. Three different pathways, RANKL, DKK-1 and MMPs are enhanced by classical RAS activation. The treatment of RA included methotrexate and corticosteroids, which can cause side effects. Studies with angiotensin receptor blockers (ARBs), angiotensin converting enzyme inhibitors (ACEi) and renin inhibitors have been conducted in experimental and clinical RA with promising results.

CONCLUSION

The classical RAS activation is an important mechanism in RA pathogenesis and the benefit of ARB and ACEi administration should be further investigated.

Impact of humanised isolation and culture conditions on stemness and osteogenic potential of bone marrow derived mesenchymal stromal cells

Therapeutic potential of human bone marrow stromal/stem cells (hBMSC) must be developed using well defined xenogenic-free conditions. hBMSC were isolated from healthy donors (n = 3) using different isolation and expansion methods. Donor I was isolated and expanded by either bone marrow directly seeded and cells expanded in 10% AB human serum (AB) +5 ng/ml fibroblast growth factor-2 (FGF2) [Direct(AB + FGF_low)] or Ammonium-Chloride-Potassium Lysing Buffer was used before the cells were expanded in 10% AB +5 ng/ml FGF-2 [ACK(AB + FGF_low)] or Lymphoprep density gradient medium was used before the cells were expanded in 10% AB +5 ng/ml FGF2 [Lympho(AB + FGF_low)] or bone marrow directly seeded and cells expanded in 10% pooled platelet lysate plasma (PL) + heparin (2 I/U/mL) [Direct(PL)]. Groups for donors II and III were: Direct(AB + FGF_low) or 10% AB +10 ng/ml FGF2 [Direct(AB + FGF_high)] or Direct(PL). HBMSCs were assessed for viability, multi-potency, osteogenic, inflammatory response and replicative senescence in vitro after 1 and 3 weeks. Pre-selected culture conditions, Direct(AB + FGF_high) or Direct(PL), were seeded on biphasic calcium phosphate granules and subcutaneously implanted in NOD/SCID mice. After 1 and 11 weeks, explants were analysed for inflammatory and osteogenic response at gene level and histologically. To identify implanted human cells, in situ hybridisation was performed. hBMSC from all conditions showed in vitro multi-lineage potency. hBMSCs expanded in PL expressed stemness markers in vitro at significantly higher levels. Generally, cells expanded in AB + FGF2 conditions expressed higher osteogenic markers after 1 week both in vitro and in vivo. After 11 weeks in vivo, Direct(AB + FGF_high) formed mature ectopic bone, compared to immature mineralised tissues formed by Direct(PL) implants. Mouse responses showed a significant upregulation of IL-1α and IL-1β expression in Direct(PL). After 1 week, human cells were observed in both groups and after 11 weeks in Direct(AB + FGF_high) only. To conclude, results showed a significant effect of the isolation methods and demonstrated a relatively consistent pattern of efficacy from all donors. A tendency of hBMSC expanded in PL to retain a more stem-like phenotype elucidates their delayed differentiation and different inflammatory expressions.

Chemokines in Physiological and Pathological Bone Remodeling

The bone matrix is constantly remodeled by bone-resorbing osteoclasts and bone-forming osteoblasts. These two cell types are fundamentally different in terms of progenitor cells, mode of action and regulation by specific molecules, acting either systemically or locally. Importantly, there is increasing evidence for an impact of cell types or molecules of the adaptive and innate immune system on bone remodeling. Understanding these influences is the major goal of a novel research area termed osteoimmunology, which is of key relevance in the context of inflammation-induced bone loss, skeletal metastases, and diseases of impaired bone remodeling, such as osteoporosis. This review article aims at summarizing the current knowledge on one particular aspect of osteoimmunology, namely the impact of chemokines on skeletal cells in order to regulate bone remodeling under physiological and pathological conditions. Chemokines have key roles in the adaptive immune system by controlling migration, localization, and function of immune cells during inflammation. The vast majority of chemokines are divided into two subgroups based on the pattern of cysteine residues. More specifically, there are 27 known C-C-chemokines, binding to 10 different C-C receptors, and 17 known C-X-C-chemokines binding to seven different C-X-C receptors. Three additional chemokines do not fall into this category, and only one of them, i.e., CX3CL1, has been shown to influence bone remodeling cell types. There is a large amount of published studies demonstrating specific effects of certain chemokines on differentiation and function of osteoclasts and/or osteoblasts. Chemokine signaling by skeletal cells or by other cells of the bone marrow niche regulates bone formation and resorption through autocrine and paracrine mechanisms. In vivo evidence from mouse deficiency models strongly supports the role of certain chemokine signaling pathways in bone remodeling. We will summarize these data in the present review with a special focus on the most established subsets of chemokines. In combination with the other review articles of this issue, the knowledge presented here confirms that there is a physiologically relevant crosstalk between the innate immune system and bone remodeling cell types, whose molecular understanding is of high clinical relevance.

Efficacy of copolymer scaffolds delivering human demineralised dentine matrix for bone regeneration

Poly(L-lactide-co-ε-caprolactone) scaffolds were functionalised by 10 or 20 µg/mL of human demineralised dentine matrix. Release kinetics up to 21 days and their osteogenic potential on human bone marrow stromal cells after 7 and 21 days were studied. A total of 390 proteins were identified by mass spectrometry. Bone regeneration proteins showed initial burst of release. Human bone marrow stromal cells were cultured on scaffolds physisorbed with 20 µg/mL and cultured in basal medium (DDM group) or physisorbed and cultured in osteogenic medium or cultured on non-functionalised scaffolds in osteogenic medium. The human bone marrow stromal cells proliferated less in demineralised dentine matrix group and activated ERK/1/2 after both time points. Cells on DDM group showed highest expression of IL-6 and IL-8 at 7 days and expressed higher collagen type 1 alpha 2, SPP1 and bone morphogenetic protein-2 until 21 days. Extracellular protein revealed higher collagen type 1 and bone morphogenetic protein-2 at 21 days in demineralised dentine matrix group. Cells on DDM group showed signs of mineralisation. The functionalised scaffolds were able to stimulate osteogenic differentiation of human bone marrow stromal cells.

Mechanisms leading from systemic autoimmunity to joint-specific disease in rheumatoid arthritis

A key unanswered question in the pathophysiology of rheumatoid arthritis (RA) is how systemic autoimmunity progresses to joint-specific inflammation. In patients with seropositive RA (that is, characterized by the presence of autoantibodies) evidence is accumulating that immunity against post-translationally modified (such as citrullinated) autoantigens might be triggered in mucosal organs, such as the lung, long before the first signs of inflammation are seen in the joints. However, the mechanism by which systemic autoimmunity specifically homes to the joint and bone compartment, thereby triggering inflammation, remains elusive. This Review summarizes potential pathways involved in this joint-homing mechanism, focusing particularly on osteoclasts as the primary targets of anti-citrullinated protein antibodies (ACPAs) in the bone and joint compartment. Osteoclasts are dependent on citrullinating enzymes for their normal differentiation and are unique in displaying citrullinated antigens on their cell surface in a non-inflamed state. The binding of ACPAs to osteoclasts releases the chemokine IL-8, leading to bone erosion and pain. This process initiates a chain of events that could lead to attraction and activation of neutrophils, resulting in a complex series of proinflammatory processes in the synovium, eventually leading to RA.

The immunopathogenesis of seropositive rheumatoid arthritis: from triggering to targeting

Patients with rheumatoid arthritis can be divided into two major subsets characterized by the presence versus absence of antibodies to citrullinated protein antigens (ACPAs) and of rheumatoid factor (RF). The antibody-positive subset of disease, also known as seropositive rheumatoid arthritis, constitutes approximately two-thirds of all cases of rheumatoid arthritis and generally has a more severe disease course. ACPAs and RF are often present in the blood long before any signs of joint inflammation, which suggests that the triggering of autoimmunity may occur at sites other than the joints (for example, in the lung). This Review summarizes recent progress in our understanding of this gradual disease development in seropositive patients. We also emphasize the implications of this new understanding for the development of preventive and therapeutic strategies. Similar temporal and spatial separation of immune triggering and clinical manifestations, with novel opportunities for early intervention, may also occur in other immune-mediated diseases.

Temporomandibular Joint Cytokine Profiles in the Horse

It has been suggested that dental abnormalities lead to temporomandibular joint inflammation and pain that may be mitigated by regular dental care. There is considerable literature on the pathophysiology of equine joint disease including studies on cytokine profiles in diseased appendicular joints. This study examined the effects of age and dental malocclusions summarized as a dental pathology score on equine temporomandibular joint cytokine (IL-1, IL-6, IL-8, TNF α and TGF-β1, -β2, -β3) concentrations. TGF-β3 was not detected in any joint sample. IL-1, IL-6 and TNF α were not influenced by age. Foals had significantly lower concentrations of IL-8 and TGF-β1, and higher levels of TGF-β2 compared with older horses. Age did not effect cytokine concentration in older horses although there was a trend towards increasing IL-8 with age. The dental pathology score increased with age in mature horses, however there was no effect of dental pathology score on cytokine concentration. There was no effect of incisor eruption, and presence or number of periodontal lesions on temporomandibular joint cytokine concentration. Our findings indicate that age but not dental pathology affected temporomandibular joint proinflammatory cytokine concentration in this population of horses.

Effect of Vitamin D on Peripheral Blood Mononuclear Cells from Patients with Psoriasis Vulgaris and Psoriatic Arthritis

Background

Psoriasis, a chronic skin disease with or without joint inflammation, has increased circulating proinflammatory cytokine levels. Vitamin D is involved in calcium homeostasis, bone formation, osteoclastogenesis and osteoclast activity, as well as regulation of immune response. We aimed to study osteoclast differentiation and cytokine secretion of peripheral blood mononuclear cells (PBMCs) from patients with psoriasis vulgaris and psoriatic arthritis, in response to 1,25(OH)₂D₃.

Methods

Serum levels of bone turnover markers were measured by ELISA in patients with psoriasis vulgaris and psoriatic arthritis, and healthy controls. PBMCs were isolated and cultured with or without RANKL/M-CSF and 1,25(OH)₂D₃. Osteoclast differentiation and cytokine secretion were assessed.

Results

Psoriatic arthritis patients had lower osteocalcin, as well as higher C-telopeptide of type I collagen and cathepsin K serum levels compared with psoriasis vulgaris patients and controls. RANKL/M-CSF-stimulated PBMCs from psoriatic arthritis patients produced higher proinflammatory cytokine levels and had a differential secretion profile in response to 1,25(OH)₂D₃, compared with psoriasis vulgaris and control PBMCs.

Conclusions

Our data confirmed altered bone turnover in psoriatic arthritis patients, and demonstrated increased osteoclastogenic potential and proinflammatory cytokine secretion capacity of these PBMCs compared with psoriasis vulgaris and controls. 1,25(OH)₂D₃ abrogated these effects.

Identification of a novel chemokine-dependent molecular mechanism underlying rheumatoid arthritis-associated autoantibody-mediated bone loss

Objectives

Rheumatoid arthritis (RA)-specific anti-citrullinated protein/peptide antibodies (ACPAs) appear before disease onset and are associated with bone destruction. We aimed to dissect the role of ACPAs in osteoclast (OC) activation and to identify key cellular mediators in this process.

Methods

Polyclonal ACPA were isolated from the synovial fluid (SF) and peripheral blood of patients with RA. Monoclonal ACPAs were isolated from single SF B-cells of patients with RA. OCs were developed from blood cell precursors with or without ACPAs. We analysed expression of citrullinated targets and peptidylarginine deiminases (PAD) enzymes by immunohistochemistry and cell supernatants by cytometric bead array. The effect of an anti-interleukin (IL)-8 neutralising antibody and a pan-PAD inhibitor was tested in the OC cultures. Monoclonal ACPAs were injected into mice and bone structure was analysed by micro-CT before and after CXCR1/2 blocking with reparixin.

Results

Protein citrullination by PADs is essential for OC differentiation. Polyclonal ACPAs enhance OC differentiation through a PAD-dependent IL-8-mediated autocrine loop that is completely abolished by IL-8 neutralisation. Some, but not all, human monoclonal ACPAs derived from single SF B-cells of patients with RA and exhibiting distinct epitope specificities promote OC differentiation in cell cultures. Transfer of the monoclonal ACPAs into mice induced bone loss that was completely reversed by the IL-8 antagonist reparixin.

Conclusions

We provide novel insights into the key role of citrullination and PAD enzymes during OC differentiation and ACPA-induced OC activation. Our findings suggest that IL8-dependent OC activation may constitute an early event in the initiation of the joint specific inflammation in ACPA-positive RA.

[Biological agents and fracture risk]

In patients with chronic inflammatory diseases, including rheumatic ones, the risk of fractures exceeds that in the population. Chronic inflammation is one of the most discussed and most important pathogenic factors of reduced bone mineral density (BMD), its worse quality and increased fracture risk. The chronic inflammatory process contributes to the imbalance of bone remodeling toward bone resorption. The use of biological agents in patients with rheumatic and other autoimmune diseases effectively suppresses systemic inflammation and increases BMD. However, the effect of the biological agents in lessening the risk of fractures remains unproven.

The dynamics of adult haematopoiesis in the bone and bone marrow environment

This review explores the dynamic relationship between bone and bone marrow in the genesis and regulation of adult haematopoiesis and will provide an overview of the haematopoietic hierarchical system. This will include the haematopoietic stem cell (HSC) and its niches, as well as discuss emerging evidence of the reciprocal interplay between bone and bone marrow, and support of the pleiotropic role played by bone cells in the regulation of HSC proliferation, differentiation and function. In addition, this review will present demineralized bone matrix as a unique acellular matrix platform that permits the generation of ectopic de novo bone and bone marrow and provides a means of investigating the temporal sequence of bone and bone marrow regeneration. It is anticipated that the utilization of this matrix-based approach will help researchers in gaining deeper insights into the major events leading to adult haematopoiesis in the bone marrow. Furthermore, this model may potentially offer new avenues to manipulate the HSC niche and hence influence the functional output of the haematopoietic system.

M-CSF priming of osteoclast precursors can cause osteoclastogenesis-insensitivity, which can be prevented and overcome on bone

Osteoclasts and macrophages share progenitors that must receive decisive lineage signals driving them into their respective differentiation routes. Macrophage colony stimulation factor M-CSF is a common factor; bone is likely the stimulus for osteoclast differentiation. To elucidate the effect of both, shared mouse bone marrow precursor myeloid blast was pre-cultured with M-CSF on plastic and on bone. M-CSF priming prior to stimulation with M-CSF and osteoclast differentiation factor RANKL resulted in a complete loss of osteoclastogenic potential without bone. Such M-CSF primed cells expressed the receptor RANK, but lacked the crucial osteoclastogenic transcription factor NFATc1. This coincided with a steeply decreased expression of osteoclast genes TRACP and DC-STAMP, but an increased expression of the macrophage markers F4/80 and CD11b. Compellingly, M-CSF priming on bone accelerated the osteoclastogenic potential: M-CSF primed cells that had received only one day M-CSF and RANKL and were grown on bone already expressed an array of genes that are associated with osteoclast differentiation and these cells differentiated into osteoclasts within 2 days. Osteoclastogenesis-insensitive precursors grown in the absence of bone regained their osteoclastogenic potential when transferred to bone. This implies that adhesion to bone dictates the fate of osteoclast precursors. Common macrophage-osteoclast precursors may become insensitive to differentiate into osteoclasts and regain osteoclastogenesis when bound to bone or when in the vicinity of bone.

Autocrine signaling is a key regulatory element during osteoclastogenesis

Osteoclasts are responsible for bone destruction in degenerative, inflammatory and metastatic bone disorders. Although osteoclastogenesis has been well-characterized in mouse models, many questions remain regarding the regulation of osteoclast formation in human diseases. We examined the regulation of human precursors induced to differentiate and fuse into multinucleated osteoclasts by receptor activator of nuclear factor kappa-B ligand (RANKL). High-content single cell microscopy enabled the time-resolved quantification of both the population of monocytic precursors and the emerging osteoclasts. We observed that prior to induction of osteoclast fusion, RANKL stimulated precursor proliferation, acting in part through an autocrine mediator. Cytokines secreted during osteoclastogenesis were resolved using multiplexed quantification combined with a Partial Least Squares Regression model to identify the relative importance of specific cytokines for the osteoclastogenesis outcome. Interleukin 8 (IL-8) was identified as one of RANKL-induced cytokines and validated for its role in osteoclast formation using inhibitors of the IL-8 cognate receptors CXCR1 and CXCR2 or an IL-8 blocking antibody. These insights demonstrate that autocrine signaling induced by RANKL represents a key regulatory component of human osteoclastogenesis.

Cytokines in osteoblast-conditioned medium promote the migration of breast cancer cells

Bone is one of the most common metastatic sites for breast cancer. In this study, we observed a promoting effect of osteoblast-conditioned medium (OCM) on the migration of MCF-7, a noninvasive cell line of breast cancer cells. Cytokine antibody array was used to compare the cytokines of OCM with the conditioned medium of non-differentiated osteoblast cells, which consequently revealed factors related to migration, such as IL8, IL6, CSF2 (G-CSF), CSF3 (GM-CSF), and TNFRSF11B (osteoprotegerin). The expression of genes related to migration was also estimated with a PCR array, which showed that 9 genes were upregulated and 26 genes downregulated. Moreover, activated p38, ERK, and AKT pathways were found in the OCM treatment group. This finding indicated the migration ability of breast cancer cells, which move toward the bone depending on the presence of specific cytokines in its surrounding microenvironment.

The transcription factor DLX3 regulates the osteogenic differentiation of human dental follicle precursor cells

The transcription factor DLX3 plays a decisive role in bone development of vertebrates. In neural-crest derived stem cells from the dental follicle (DFCs), DLX3 is differentially expressed during osteogenic differentiation, while other osteogenic transcription factors such as DLX5 or RUNX2 are not highly induced. DLX3 has therefore a decisive role in the differentiation of DFCs, but its actual biological effects and regulation are unknown. This study investigated the DLX3-regulated processes in DFCs. After DLX3 overexpression, DFCs acquired a spindle-like cell shape with reorganized actin filaments. Here, marker genes for cell morphology, proliferation, apoptosis, and osteogenic differentiation were significantly regulated as shown in a microarray analysis. Further experiments showed that DFCs viability is directly influenced by the expression of DLX3, for example, the amount of apoptotic cells was increased after DLX3 silencing. This transcription factor stimulates the osteogenic differentiation of DFCs and regulates the BMP/SMAD1-pathway. Interestingly, BMP2 did highly induce DLX3 and reverse the inhibitory effect of DLX3 silencing in osteogenic differentiation. However, after DLX3 overexpression in DFCs, a BMP2 supplementation did not improve the expression of DLX3 and the osteogenic differentiation. In conclusion, DLX3 influences cell viability and regulates osteogenic differentiation of DFCs via a BMP2-dependent pathway and a feedback control.

Secretion of IL-6 and IL-8 from lysophosphatidic acid-stimulated oral squamous cell carcinoma promotes osteoclastogenesis and bone resorption

Lysophosphatidic acid (LPA) is a bioactive lipid with a growth factor-like activity on a large range of cell types. Several pieces of evidence raise the possibility that LPA may play an important role in bone metastasis. Bone is a frequent metastatic site for oral cancer. However, the role of LPA in the progression of oral cancer metastasis to the bone is poorly understood. Here, we provide evidence for the role of LPA in the progression of oral cancer bone metastases and its regulatory mechanism. LPA induced the secretion of IL-6 and IL-8 in oral squamous cell carcinoma (OSCC). LPA-stimulated secretion of IL-6 and IL-8 is partly dependent on the LPA and EGF receptor (EGFR) pathways. ERK1/2 and Akt-mediated NF-κB and AP-1 were responsible for the LPA-induced IL-6 and IL-8 secretion. Moreover, conditioned medium (CM) derived from the LPA-stimulated OSCC supported osteoclast formation in bone marrow-derived macrophages (BMMs). Neutralization against both human IL-6 and IL-8 suppressed osteoclast formation induced by CM derived from the LPA-stimulated OSCC. Direct treatment with recombinant IL-6 (rIL-6) and/or soluble IL-6 receptor (sIL-6R), or IL-8 (rIL-8) reproduced the effect of the CM derived from the LPA-stimulated OSCC on osteoclast formation. In addition, CM derived from the LPA-stimulated OSCC induced receptor activator of nuclear factor (NF)-κB ligand (RANKL) expression in human osteoblasts and direct treatment with rIL-6 and/or sIL-6R or rIL-8 mimicked the effect of the CM derived from the LPA-stimulated OSCC for RANKL expression. Taken together, LPA may be a potent inducer of osteolytic factor IL-6 and IL-8 in OSCC. LPA-induced IL-6 and IL-8 exerted propound effects on RANKL expression in osteoblast and thereby promoted osteoclast formation from osteoclast precursors.

Osteoimmunology at the nexus of arthritis, osteoporosis, cancer, and infection

Over the past decade and a half, the biomedical community has uncovered a previously unappreciated reciprocal relationship between cells of the immune and skeletal systems. Work in this field, which has been termed "osteoimmunology," has resulted in the development of clinical therapeutics for seemingly disparate diseases linked by the common themes of inflammation and bone remodeling. Here, the important concepts and discoveries in osteoimmunology are discussed in the context of the diseases bridging these two organ systems, including arthritis, osteoporosis, cancer, and infection, and the targeted treatments used by clinicians to combat them.

Predictors of osteoclast activity in patients with sickle cell disease

BACKGROUND

Bone changes are common in sickle cell disease, but the pathogenesis is not fully understood. Tartrate-resistant acid phosphatase (TRACP) type 5b is produced by bone-resorbing osteoclasts. In other forms of hemolytic anemia, increased iron stores are associated with osteoporosis. We hypothesized that transfusional iron overload would be associated with increased osteoclast activity in patients with sickle cell disease.

DESIGN AND METHODS

We examined tartrate-resistant acid phosphatase 5b concentrations in patients with sickle cell disease and normal controls of similar age and sex distribution at steady state. Serum tartrate-resistant acid phosphatase 5b concentration was measured using an immunocapture enzyme assay and plasma concentrations of other cytokines were assayed using the Bio-Plex suspension array system. Tricuspid regurgitation velocity, an indirect measure of systolic pulmonary artery pressure, was determined by echocardiography.

RESULTS

Tartrate-resistant acid phosphatase 5b concentrations were higher in 58 adults with sickle cell disease than in 22 controls (medians of 4.4 versus 2.4 U/L, respectively; P=0.0001). Among the patients with sickle cell disease, tartrate-resistant acid phosphatase 5b independently correlated with blood urea nitrogen (standardized beta=0.40, P=0.003), interleukin-8 (standardized beta=0.30, P=0.020), and chemokine C-C motif ligand 5 (standardized beta=-0.28, P=0.031) concentrations, but not with serum ferritin concentration. Frequent blood transfusions (>10 units in life time) were not associated with higher tartrate-resistant acid phosphatase 5b levels in multivariate analysis. There were strong correlations among tartrate-resistant acid phosphatase 5b, alkaline phosphatase and tricuspid regurgitation velocity (r>0.35, P<0.001).

CONCLUSIONS

Patients with sickle cell disease have increased osteoclast activity as reflected by serum tartrate-resistant acid phosphatase 5b concentrations. Our results may support a potential role of inflammation rather than increased iron stores in stimulating osteoclast activity in sickle cell disease. The positive relationships among tartrate-resistant acid phosphatase 5b, alkaline phosphatase and tricuspid regurgitation velocity raise the possibility of a common pathway in the pulmonary and bone complications of sickle cell disease.

Effect of zoledronate on oral wound healing in rats

PURPOSE

Osteonecrosis of the jaw (ONJ) is a growing concern in patients who receive bisphosphonates that target osteoclasts. As osteoclasts play multifunctional roles in the bone marrow, their suppression likely affects bone homeostasis and alters wound healing of the jaw. The objective was to delineate the impact of osteoclast suppression in the bone marrow and wound healing of the jaw.

EXPERIMENTAL DESIGN

Zoledronate was administered to senile rats for 14 weeks. A portion of the gingiva was removed to denude the palatal bone. Gene expression in the bone marrow was assessed and histologic sections were analyzed to determine the wound healing status.

RESULTS

Angiogenesis-related genes, CD31 and VEGF-A, were not altered by zoledronate. VEGF-C, which plays a role in lymphangiogenesis, was suppressed. There was a decrease in gene expression of Tcirg1 and MMP-13. Bone denudation caused extensive osteocyte death indicative of bone necrosis. In zoledronate-treated rats, the necrotic bone was retained in the wound while, in controls, osteoclastic resorption of the necrotic bone was prominent. Even though large necrotic bone areas existed in zoledronate-treated rats, overlaying soft tissue healed clinically. Immunohistochemical staining showed rich vascularity in the overlaying soft tissue.

CONCLUSIONS

Zoledronate therapy impacts bone marrow by suppressing genes associated with lymphangiogenesis and tissue remodeling, such as VEGF-C and MMP-13. Zoledronate was associated with impaired osseous wound healing but had no effect on angiogenic markers in the bone marrow or soft tissue wound healing. Zoledronate selectively blunts healing in bone but does not affect soft tissue healing in the oral cavity.

RANKL inhibition by osteoprotegerin prevents bone loss without affecting local or systemic inflammation parameters in two rat arthritis models: comparison with anti-TNFalpha or anti-IL-1 therapies

INTRODUCTION

Rat adjuvant-induced arthritis (AIA) and collagen-induced arthritis (CIA) feature bone loss and systemic increases in TNFalpha, IL-1beta, and receptor activator of NF-kappaB ligand (RANKL). Anti-IL-1 or anti-TNFalpha therapies consistently reduce inflammation in these models, but systemic bone loss often persists. RANKL inhibition consistently prevents bone loss in both models without reducing joint inflammation. Effects of these therapies on systemic markers of bone turnover and inflammation have not been directly compared.

METHODS

Lewis rats with established AIA or CIA were treated for 10 days (from day 4 post onset) with either PBS (Veh), TNFalpha inhibitor (pegsunercept), IL-1 inhibitor (anakinra), or RANKL inhibitor (osteoprotegerin (OPG)-Fc). Local inflammation was evaluated by monitoring hind paw swelling. Bone mineral density (BMD) of paws and lumbar vertebrae was assessed by dual X-ray absorptiometry. Markers and mediators of bone resorption (RANKL, tartrate-resistant acid phosphatase 5b (TRACP 5B)) and inflammation (prostaglandin E2 (PGE2), acute-phase protein alpha-1-acid glycoprotein (alpha1AGP), multiple cytokines) were measured in serum (day 14 post onset).

RESULTS

Arthritis progression significantly increased paw swelling and ankle and vertebral BMD loss. Anti-TNFalpha reduced paw swelling in both models, and reduced ankle BMD loss in AIA rats. Anti-IL-1 decreased paw swelling in CIA rats, and reduced ankle BMD loss in both models. Anti-TNFalpha and anti-IL-1 failed to prevent vertebral BMD loss in either model. OPG-Fc reduced BMD loss in ankles and vertebrae in both models, but had no effect on paw swelling. Serum RANKL was elevated in AIA-Veh and CIA-Veh rats. While antiTNFalpha and anti-IL-1 partially normalized serum RANKL without any changes in serum TRACP 5B, OPG-Fc treatment reduced serum TRACP 5B by over 90% in both CIA and AIA rats. CIA-Veh and AIA-Veh rats had increased serum alpha1AGP, IL-1beta, IL-8 and chemokine (C-C motif) ligand 2 (CCL2), and AIA-Veh rats also had significantly greater serum PGE2, TNFalpha and IL-17. Anti-TNFalpha reduced systemic alpha1AGP, CCL2 and PGE2 in AIA rats, while anti-IL-1 decreased systemic alpha1AGP, IL-8 and PGE2. In contrast, RANKL inhibition by OPG-Fc did not lessen systemic cytokine levels in either model.

CONCLUSIONS

Anti-TNFalpha or anti-IL-1 therapy inhibited parameters of local and systemic inflammation, and partially reduced local but not systemic bone loss in AIA and CIA rats. RANKL inhibition prevented local and systemic bone loss without significantly inhibiting local or systemic inflammatory parameters.

The chemokine Cxcl1 is a novel target gene of parathyroid hormone (PTH)/PTH-related protein in committed osteoblasts

The PTH receptor (PTHR1) is expressed on osteoblasts and responds to PTH or PTHrP in an endocrine or autocrine/paracrine manner, respectively. A microarray study carried out on PTHR1-positive osteoblasts (Kusa 4b10 cells) identified the cysteine-X-cysteine (CXC) family chemokine ligand 1 (Cxcl1) as a novel immediate PTH/PTHrP-responsive gene. Cxcl1 is a potent neutrophil chemoattractant with recognized roles in angiogenesis and inflammation, but a role in bone biology has not been described. Cxcl1 mRNA levels were up-regulated 1 h after either PTH or PTHrP treatment of differentiated Kusa 4b10 osteoblasts (15-fold) and mouse calvarial osteoblasts (160-fold) and in rat metaphyseal bone (5-fold) 1 h after a single sc injection of PTH. Furthermore, PTH treatment stimulated a 10-fold increase in secreted Cxcl1 protein by both Kusa 4b10 cells and calvarial osteoblasts. Immunohistochemistry and PCR demonstrated that CXCR2, the receptor for Cxcl1, is highly expressed in osteoclast precursors (hemopoietic cells) but is predominantly undetectable in the osteoblast lineage, suggesting that osteoblast-derived Cxcl1 may act as a chemoattractant for osteoclast precursors. Confirming this hypothesis, recombinant Cxcl1 dose-dependently stimulated migration of osteoclast precursors in cell culture studies, as did conditioned media from Kusa 4b10 cells treated with PTH. These data indicate that local action through the PTHR1 could stimulate cells of the osteoblast lineage to release a chemokine capable of attracting osteoclast precursors to the bone environment.

Acidic pH stimulates the production of the angiogenic CXC chemokine, CXCL8 (interleukin-8), in human adult mesenchymal stem cells via the extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, and NF-kappaB pathways

Blood vessel injury results in limited oxygen tension and diffusion leading to hypoxia, increased anaerobic metabolism, and elevated production of acidic metabolites that cannot be easily removed due to the reduced blood flow. Therefore, an acidic extracellular pH occurs in the local microenvironment of disrupted bone. The potential role of acidic pH and glu-leu-arg (ELR(+)) CXC chemokines in early events in bone repair was studied in human mesenchymal stem cells (hMSCs) treated with medium of decreasing pH (7.4, 7.0, 6.7, and 6.4). The cells showed a reciprocal increase in CXCL8 (interleukin-8, IL-8) mRNA levels as extracellular pH decreased. At pH 6.4, CXCL8 mRNA was induced >60x in comparison to levels at pH 7.4. hMSCs treated with osteogenic medium (OGM) also showed an increase in CXCL8 mRNA with decreasing pH; although, at a lower level than that seen in cells grown in non-OGM. CXCL8 protein was secreted into the medium at all pHs with maximal induction at pH 6.7. Inhibition of the G-protein-coupled receptor alpha, G(alphai), suppressed CXCL8 levels in response to acidic pH; whereas phospholipase C inhibition had no effect on CXCL8. The use of specific mitogen-activated protein kinase (MAPK) signal transduction inhibitors indicated that the pH-dependent increase in CXCL8 mRNA is due to activation of ERK and p38 pathways. The JNK pathway was not involved. NF-kappaB inhibition resulted in a decrease in CXCL8 levels in hMSCs grown in non-OGM. However, OGM-differentiated hMSCs showed an increase in CXCL8 levels when treated with the NF-kappaB inhibitor PDTC, a pyrrolidine derivative of dithiocarbamate.

Angiogenic CXC chemokine expression during differentiation of human mesenchymal stem cells towards the osteoblastic lineage

The potential role of ELR(+) CXC chemokines in early events in bone repair was studied using human mesenchymal stem cells (hMSCs). Inflammation, which occurs in the initial phase of tissue healing in general, is critical to bone repair. Release of cytokines from infiltrating immune cells and injured bone can lead to recruitment of MSCs to the region of repair. CXC chemokines bearing the Glu-Leu-Arg (ELR) motif are also released by inflammatory cells and serve as angiogenic factors stimulating chemotaxis and proliferation of endothelial cells. hMSCs, induced to differentiate with osteogenic medium (OGM) containing ascorbate, beta-glycerophosphate (beta-GP), and dexamethasone (DEX), showed an increase in mRNA and protein secretion of the ELR(+) CXC chemokines CXCL8 and CXCL1. CXCL8 mRNA half-life studies reveal an increase in mRNA stability upon OGM stimulation. Increased expression and secretion is a result of DEX in OGM and is dose-dependent. Inhibition of the glucocorticoid receptor with mifepristone only partially inhibits DEX-stimulated CXCL8 expression indicating both glucocorticoid receptor dependent and independent pathways. Treatment with signal transduction inhibitors demonstrate that this expression is due to activation of the ERK and p38 mitogen-activated protein kinase (MAPK) pathways and is mediated through the G(alphai)-coupled receptors. Angiogenesis assays demonstrate that OGM-stimulated conditioned media containing secreted CXCL8 and CXCL1 can induce angiogenesis of human microvascular endothelial cells in an in vitro Matrigel assay.

Osteoimmunology: interactions of the bone and immune system

Bone and the immune system are both complex tissues that respectively regulate the skeleton and the body's response to invading pathogens. It has now become clear that these organ systems often interact in their function. This is particularly true for the development of immune cells in the bone marrow and for the function of bone cells in health and disease. Because these two disciplines developed independently, investigators in each don't always fully appreciate the significance that the other system has on the function of the tissue they are studying. This review is meant to provide a broad overview of the many ways that bone and immune cells interact so that a better understanding of the role that each plays in the development and function of the other can develop. It is hoped that an appreciation of the interactions of these two organ systems will lead to better therapeutics for diseases that affect either or both.

The bone microenvironment in metastasis; what is special about bone?

The skeleton is a common destination for many cancer metastases including breast and prostate cancer. There are many characteristics of bone that make it an ideal environment for cancer cell migration and colonization. Metaphyseal bone, found at the ends of long bone, in ribs, and in vertebrae, is comprised of trabecular bone interspersed with marrow and rich vasculature. The specialized microvasculature is adapted for the easy passage of cells in and out of the bone marrow. Moreover, the metasphyseal regions of bone are constantly undergoing remodeling, a process that releases growth factors from the matrix. Bone turnover also involves the production of numerous cytokines and chemokines that provide a means of communication between osteoblasts and osteoclasts, but co-incidentally can also attract and support metastatic cells. Once in the marrow, cancer cells can interact directly and indirectly with osteoblasts and osteclasts, as well as hematopoietic and stromal cells. Cancer cells secrete factors that affect the network of cells in the bone microenvironment as well as interact with other cytokines. Additionally, transient cells of the immune system may join the local mileau to ultimately support cancer cell growth. However, most metastasized cells that enter the bone marrow are transient; a few may remain in a dormant state for many years. Advances in understanding the bone cell-tumor cell interactions are key to controlling, if not preventing metastasis to bone.

HIV1 protease inhibitors selectively induce inflammatory chemokine expression in primary human osteoblasts

HIV-infected patients are at increased risk of decreased bone mineral density. Several studies have implicated antiretroviral therapy as a contributor to the decreased bone mineral density seen in treated HIV-1 patients. Whilst the exact molecular mechanisms underlying decreased bone density remain to be elucidated, inflammation has been postulated to be an important pathogenomic mechanism. In this study, we have explored primary human osteoblast gene expression in response to protease inhibitors (PIs), by oligonucleotide microarray analysis. A list of dysregulated genes, correlated with the inflammatory response, increased significantly after NFV and RTV exposure. Analysis of gene and protein expression determined a selectively increase of the pro-inflammatory cytokines monocyte chemoattractant protein (MCP)-1 and interleukin-8 (IL-8) following exposure to a pharmacological concentration of NFV and RTV. These data suggested that generation of local inflammatory cascades may contribute to the development of decreased bone mineral density in highly active antiretroviral therapy (HAART)-treated HIV patients.

Osteoclasts degrade endosteal components and promote mobilization of hematopoietic progenitor cells

Here we investigated the potential role of bone-resorbing osteoclasts in homeostasis and stress-induced mobilization of hematopoietic progenitors. Different stress situations induced activity of osteoclasts (OCLs) along the stem cell-rich endosteum region of bone, secretion of proteolytic enzymes and mobilization of progenitors. Specific stimulation of OCLs with RANKL recruited mainly immature progenitors to the circulation in a CXCR4- and MMP-9-dependent manner; however, RANKL did not induce mobilization in young female PTPepsilon-knockout mice with defective OCL bone adhesion and resorption. Inhibition of OCLs with calcitonin reduced progenitor egress in homeostasis, G-CSF mobilization and stress situations. RANKL-stimulated bone-resorbing OCLs also reduced the stem cell niche components SDF-1, stem cell factor (SCF) and osteopontin along the endosteum, which was associated with progenitor mobilization. Finally, the major bone-resorbing proteinase, cathepsin K, also cleaved SDF-1 and SCF. Our findings indicate involvement of OCLs in selective progenitor recruitment as part of homeostasis and host defense, linking bone remodeling with regulation of hematopoiesis.

Chemokine gene activation in human bone marrow-derived osteoblasts following exposure to particulate wear debris

Particulate wear debris induces the expression of pro-inflammatory cytokine and chemokine genes in various cell types of the periprosthetic region. We have previously reported that titanium particles stimulate the selective induction of interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) chemokines in human osteoblast-like osteosarcoma cells. In this study, we characterize the human bone marrow-derived osteoblast chemokine response to titanium particles. We demonstrate that titanium particles result in enhanced IL-8 and MCP-1 protein secretion as well as differential chemokine gene activation. Osteoblast chemokine expression was regulated at the level of gene transcription, with a time-dependent induction of NF-kappaB activation. Inhibition studies with N-acetyl-L-cysteine (Nac) and MG-132 suggest that titanium particle activation of NF-kappaB activity and IL-8 chemokine expression involves oxidant signaling and IkappaBalpha-proteasomal degradation. Activation of the NF-kappaB transcription factor, as well as the IL-8 gene, are redox-regulated. We also demonstrate that while cytochalasin D, a potent inhibitor of phagocytosis, suppressed the titanium particle effect on IL-8 protein release in human bone marrow-derived osteoblasts, the inhibitor had no effect on IL-8 expression in MG-63 osteoblast-like cells. Collectively, these results provide insight into the potential mechanisms responsible for the particulate activation of osteoblast chemokine expression and suggest an important role for the osteoblast in the pathogenesis of periprosthetic osteolysis.

Parathyroid hormone-related protein (PTHrP) as a causative factor of cancer-associated wasting: possible involvement of PTHrP in the repression of locomotor activity in rats bearing human tumor xenografts

Nude rats bearing the LC-6-JCK human lung cancer xenograft displayed cancer-associated wasting syndrome in addition to humoral hypercalcemia of malignancy. In these rats, not only PTHrP but also several other human proinflammatory cytokines, such as IL-6, leukemia-inducing factor, IL-8, IL-5 and IL-11, were secreted to the bloodstream. Proinflammatory cytokines induce acute-phase reactions, as evidenced by a decrease of serum albumin and an increase in alpha1-acid glycoprotein. Tumor resection abolished the production of proinflammatory cytokines and improved acute-phase reactions, whereas anti-PTHrP antibody affected neither proinflammatory cytokine production nor acute-phase reactions. Nevertheless, tumor resection and administration of anti-PTHrP antibody similarly and markedly attenuated not only hypercalcemia but also loss of fat, muscle and body weight. Body weight gain by anti-PTHrP antibody was associated with increased food consumption; increased body weight from anti-PTHrP antibody was observed when animals were freely fed but not when they were given the same feeding as those that received only vehicle. Furthermore, nude rats bearing LC-6-JCK showed reduced locomotor activity, less eating and drinking and low blood phosphorus; and anti-PTHrP antibody restored them. Although alendronate, a bisphosphonate drug, decreased blood calcium, it affected neither locomotor activity nor serum phosphorus level. These results indicate that PTHrP represses physical activity and energy metabolism independently of hypercalcemia and proinflammatory cytokine actions and that deregulation of such physiologic activities and functions by PTHrP is at least in part involved in PTHrP-induced wasting syndrome.

KC chemokine expression by TGF-beta in C3H10T1/2 cells induced towards osteoblasts

The effects of TGF-beta on expression of the platelet-derived growth factor-induced KC protein were explored in mouse mesenchymal C3H10T1/2 and pre-osteoblastic MC3T3-E1 cells to identify a potential role for TGF-beta in expression of angiogenic cytokines during osteogenic differentiation. KC is a member of the CXC chemokine family with homology to human IL-8, a potent neutrophilic chemotactic cytokine. TGF-beta treatment results in increased KC mRNA and protein secretion in C3H10T1/2 induced towards the osteoblastic lineage with all-trans-retinoic acid. This is due to up-regulated transcription rather than enhanced mRNA stability. No induction of KC expression was seen in untreated C3H10T1/2 or MC3T3-E1 upon TGF-beta stimulation. Use of the translational inhibitor cycloheximide results in mRNA "superinduction" suggesting other factors are involved that normally function to down-regulate KC expression. TGF-beta-stimulated conditioned media were a potent chemostimulant for human microvascular endothelial cells (HMEC-1). This activity could be inhibited by pre-incubation with anti-KC neutralizing antibodies.

Estrogen deficiency accelerates murine autoimmune arthritis associated with receptor activator of nuclear factor-kappa B ligand-mediated osteoclastogenesis

The aims of this study were to evaluate the in vivo effects of estrogen deficiency in MRL/lpr mice as a model for rheumatoid arthritis and to analyze the possible relationship between immune dysregulation and receptor activator of nuclear factor-kappaB ligand (RANKL)-mediated osteoclastogenesis. Experimental studies were performed in ovariectomized (Ovx)-MRL/lpr, Ovx-MRL+/+, sham-operated-MRL/lpr, and sham-operated-MRL+/+ mice. Severe autoimmune arthritis developed in younger Ovx-MRL/lpr mice until 24 wk of age, whereas these lesions were entirely recovered by pharmacological levels of estrogen administration. A significant elevation in serum rheumatoid factor, anti-double-stranded DNA, and anti-type II collagen was found in Ovx-MRL/lpr mice and recovered in mice that underwent estrogen administration. A high proportion of CD4(+) T cells bearing RANKL was found, and an enhanced expression of RANKL mRNA and an impaired osteoprotegerin mRNA was detected in the synovium. An increase in both osteoclast formation and bone resorption pits was found. These results indicate that estrogen deficiency may play a crucial role in acceleration of autoimmune arthritis associated with RANKL-mediated osteoclastogenesis in a murine model for rheumatoid arthritis.

Mono-iodoacetate-induced histologic changes in subchondral bone and articular cartilage of rat femorotibial joints: an animal model of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by joint pain and a progressive loss of articular cartilage. Studies to elucidate the pathophysiology of OA have been hampered by the lack of a rapid, reproducible animal model that mimics both the histopathology and symptoms associated with the disease. Injection of mono-iodoacetate (MIA), an inhibitor of glycolysis, into the femorotibial joint of rodents promotes loss of articular cartilage similar to that noted in human OA. Here, we describe the histopathology in the subchondral bone and cartilage of rat (Wistar) knee joints treated with a single intra articular injection of MIA (1 mg) and sacrificed at 1, 3, 5, 7, 14, 28, and 56 days postinjection. Histologically, the early time points (days 1-7) were characterized by areas of chondrocyte degeneration/necrosis sometimes involving the entire thickness of the articular cartilage in the tibial plateaus and femoral condyles. Changes to the subchondral bone, as evidenced by increased numbers of osteoclasts and osteoblasts, were noted at by day 7. By 28 days, there was focal fragmentation and collapse of bony trabeculae with fibrosis and increased osteoclastic activity. By 56 days there were large areas of bone remodeling evidenced by osteoclastic bone resorption and newly formed trabeculae with loss of marrow hematopoietic cells. Subchondral cysts and subchondral sclerosis were present in some rats. In conclusion, intra-articular injection of MIA induces loss of articular cartilage with progression of subchondral bone lesions that mimic those of OA. This model offers a rapid and minimally invasive method to reproduce OA-like lesions in a rodent species.

Breast cancer metastasis to bone: it is not all about PTHrP

Breast cancer shows a predilection for metastasis to bone. Interestingly, approximately 80% of patients with breast cancer also have bone metastases develop at some point during the course of their disease. Osteolytic breast cancer induces bonedestruction via the stimulation of osteoclasts. Breast cancer cells produce many known stimulators of bone resorption with significant research effort focused on the role of parathyroid hormone-related protein (PTHrP). However, a recent prospective clinical trial has questioned the primary role of PTHrP in this process. The overexpression of interleukin-8 (IL-8) in metastatic breast cancer cells prompted additional investigation of the role of IL-8 in osteolysis. Recombinant IL-8 induces the expression of RANKL mRNA and protein in osteoblastic cells and stimulates formation of bone resorbing osteoclasts, even in the absence of RANKL. The ability of IL-8 to directly stimulate osteoclastogenesis via RANKL dependent and independent mechanisms suggests it may play an important role in the process of osteoclast formation and function. Therefore, we propose that cytokines such as IL-8 are involved in the early stages of breast cancer metastasis and initiate the process of osteoclastic bone resorption. In this modified model of breast cancer metastasis to bone, PTHrP expression is induced later to stimulate the vicious cycle of bone destruction.

Urinalysis for interleukin-8 in the non-invasive diagnosis of acute and chronic inflammatory diseases

BACKGROUND AND AIMS

Given its role in mediating inflammation, the use of urinary interleukin-8 (IL-8) was assessed in the non-invasive diagnosis of acute and chronic inflammatory diseases.

METHODS

IL-8 was measured by an enzyme linked immunosorbent assay in random urine samples (1 ml each) carrying code numbers and taken from 208 patients: 177 adults and 31 children presenting with a range of active or inactive inflammatory conditions.

RESULTS

In the appropriate controls and in patients with inactive inflammation, the median urinary IL-8 levels ranged from 7-12 pg/ml, compared with 104 pg/ml in active ulcerative colitis (p = 0.002), 54 in active Crohn's disease (p = 0.025), 93 in active rheumatoid arthritis (p = 0.001), 107 in acute cholecystitis (p<0.0001), 127 in acute appendicitis (p = 0.0001), and 548 pg/ml in urinary tract infection (p<0.0001). Children with non-viral inflammation/infection also had higher IL-8 values (median, 199 pg/ml; p = 0.0001) than those with viral infection (median, 7 pg/ml) or non-specific conditions (median, 10 pg/ml). In the study group as a whole urinary IL-8 values correlated positively with peripheral blood white cell count (r = 0.32; p < 0.001), erythrocyte sedimentation rate (r = 0.41; p<0.001), and C-reactive protein (r = 0.33; p<0.001).

CONCLUSION

Taking the appropriate clinical situation into account, urinary IL-8 measurement helps in the non-invasive assessment of active inflammation in at least a number of common acute and chronic conditions.

Stem cell mobilization

Successful blood and marrow transplant (BMT), both autologous and allogeneic, requires the infusion of a sufficient number of hematopoietic progenitor/stem cells (HPCs) capable of homing to the marrow cavity and regenerating a full array of hematopoietic cell lineages in a timely fashion. At present, the most commonly used surrogate marker for HPCs is the cell surface marker CD34, identified in the clinical laboratory by flow cytometry. Clinical studies have shown that infusion of at least 2 x 10(6) CD34(+) cells/kg recipient body weight results in reliable engraftment as measured by recovery of adequate neutrophil and platelet counts approximately 14 days after transplant. Recruitment of HPCs from the marrow into the blood is termed mobilization, or, more commonly, stem cell mobilization. In Section I, Dr. Tsvee Lapidot and colleagues review the wide range of factors influencing stem cell mobilization. Our current understanding focuses on chemokines, proteolytic enzymes, adhesion molecules, cytokines and stromal cell-stem cell interactions. On the basis of this understanding, new approaches to mobilization have been designed and are now starting to undergo clinical testing. In Section II, Dr. Michele Cottler-Fox describes factors predicting the ability to mobilize the older patient with myeloma. In addition, clinical approaches to improving collection by individualizing the timing of apheresis and adjusting the volume of blood processed to achieve a desired product are discussed. Key to this process is the daily enumeration of blood CD34(+) cells. Newer methods of enumerating and mobilizing autologous blood HPCs are discussed. In Section III, Dr. John DiPersio and colleagues provide data on clinical results of mobilizing allogeneic donors with G-CSF, GM-CSF and the combination of both as relates to the number and type of cells collected by apheresis. Newer methods of stem cell mobilization as well as the relationship of graft composition on immune reconstitution and GVHD are discussed.

Modulation of growth factor/cytokine synthesis and signaling by 1alpha,25-dihydroxyvitamin D(3): implications in cell growth and differentiation

Distinct from its classic functions in the regulation of calcium and phosphorus metabolism as a systemic hormone, 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] is involved in the local control and regulation of cellular growth and differentiation in various tissues, including epidermis (keratinocytes) and bone (osteoblasts and osteoclasts). In this review, the impact of 1alpha,25(OH)(2)D(3) on growth factor/cytokine synthesis and signaling is discussed, particularly as it pertains to bone cells and keratinocytes. 1alpha,25(OH)(2)D(3) not only regulates growth factor/cytokine synthesis but may also alter growth factor signaling. Recently discovered examples for such interactions are the interactions between the vitamin D receptor and the mothers against decapentaplegic-related proteins that function downstream of TGFbeta receptors. Inhibitory effects of 1alpha,25(OH)(2)D(3) on keratinocytes through TGFbeta activation and IL-1alpha, IL-6, and IL-8 suppression may provide a rationale for its beneficial effects in the treatment of hyperproliferative skin disorders, whereas stimulatory effects through the epidermal growth factor-related family members and platelet-derived growth factor may be operative in its beneficial effects in skin atrophy and wound healing. Modulation of cytokines and growth factors by 1alpha,25(OH)(2)D(3) during bone remodeling plays an important role in the coupling of osteoblastic bone formation with osteoclastic resorption to maintain bone mass.

Differential regulation of chemokine secretion in tuberculous and staphylococcal osteomyelitis

Bone infection or osteomyelitis is characterized by uncontrolled inflammation and destructive bone loss although little is known about immunopathogenesis of infection. We investigated control of chemokine secretion from osteoblasts infected with either Mycobacterium tuberculosis, which normally elicits a granulomatous host response, or Staphylococcus aureus, which drives a host response dominated by neutrophil influx. We show that M. tuberculosis infection of cultured and primary osteoblasts induces extensive secretion of the chemokines interleukin (IL)-8, inducible protein (IP) 10, RANTES, and monocyte chemoattractant protein (MCP) 1 within 72 h (1630 +/- 280 pg/ml per 4 x 10(5) cells, 74,130 +/- 8480 pg/ml per 4 x 10(5) cells, 18,330 +/- 3040 pg/ml per 4 x 10(5) cells, and 138,670 +/- 13,340 pg/ml per 4 x 10(5) cells, respectively, for MG-63 osteoblasts). S. aureus infection also results in secretion of these chemokines but secretion is delayed and of lesser magnitude (210 +/- 10 pg/ml per 4 x 10(5) cells, 11,570 +/- 1240 pg/ml per 4 x 10(5) cells, 930 +/- 34 pg/ml per 4 x 10(5) cells, and 13,770 +/- 720 pg/ml per 4 x 10(5) cells for IL-8, IP-10, RANTES, and MCP-1, respectively). The minimal up-regulation of secretion of the neutrophil attractant IL-8 in staphylococcal infection is both striking and unexpected. In both infections, chemokine secretion was dependent on the presence of live organisms. Differences in kinetics and magnitude of chemokine secretion are associated with distinct patterns of mRNA expression, as assessed by ribonuclease protection assay (RPA) and reverse-transcription polymerase chain reaction (RT-PCR). In addition, nuclear localization of the transcription factor activator protein (AP) 1 in M. tuberculosis-infected osteoblasts also is distinct as compared with S. aureus-infected cells. In summary, this study shows that osteoblasts have an important pathogen-specific role in control of chemokine gene expression and secretion during the human immune response to osteomyelitis.

Nitric oxide as the mediator of the antiosteoporotic actions of estrogen, statins, and essential fatty acids

Estrogen, statins, and essential fatty acids and their metabolites can prevent osteoporosis. However, it is not certain how these three structurally different agents can have the same beneficial action. It is suggested that all three, in addition to their other modes of action in the prevention of osteoporosis, have the ability to augment constitutional (or endothelial) nitric oxide generation, which is known to be beneficial in osteoporosis. If so, it will be interesting to study whether nitric oxide donors and/or nitric oxide precursors can be given together with estrogen, statins, or essential fatty acids to potentiate their benefit in osteoporosis.

Receptor activator of NF-kappa B and osteoprotegerin expression by human microvascular endothelial cells, regulation by inflammatory cytokines, and role in human osteoclastogenesis

The receptor activator of NF-kappaB (RANKL) is the essential signal required for full osteoclast (OC) development, activation, and survival. RANKL is highly expressed in areas of trabecular bone remodeling and inflammatory bone loss, is increased on marrow stromal cells or osteoblasts by osteotropic hormones or cytokines, and is neutralized by osteoprotegerin (OPG), a soluble decoy receptor also crucial for preventing arterial calcification. Vascular endothelial cells (VEC) are critically involved in bone development and remodeling and influence OC recruitment, formation, and activity. Although OCs develop and function in close association with bone VEC and sinusoids, signals mediating their interactions are not well known. Here, we show for the first time that human microvascular endothelial cells (HMVEC) express transcripts for both RANKL and OPG; inflammatory cytokines tumor necrosis factor-alpha and interleukin-1alpha elevate RANKL and OPG expression 5-40-fold in HMVEC (with an early OPG peak that declines as RANKL rises), and RANKL protein increases on the surface of tumor necrosis factor-alpha-activated HMVEC. Cytokine-activated HMVEC promoted the formation, fusion, and bone resorption of OCs formed in co-cultures with circulating human monocytic precursors via a RANKL-mediated mechanism fully antagonized by exogenous OPG. Furthermore, paraffin sections of human osteoporotic fractured bone exhibited increased RANKL immunostaining in vivo on VEC located near resorbing OCs in regions undergoing active bone turnover. Therefore, cytokine-activated VEC may contribute to inflammatory-mediated bone loss via regulated production of RANKL and OPG. VEC-derived OPG may also serve as an autocrine signal to inhibit blood vessel calcification.

Kaposi sarcoma is a therapeutic target for vitamin D3receptor agonist

Kaposi sarcoma (KS) is responsive to a number of different steroid hormones, such as glucocorticoids and retinoids. An active metabolite of vitamin D, 1α,25 dihydroxyvitamin D3, was used to study the effect of this steroid hormone in KS. Steroid hormones exert their effect through their cognate nuclear receptors, which for vitamin D metabolites is the vitamin D receptor (VDR). It was first shown that KS cell lines and primary tumor tissue express high levels of VDR, whereas endothelial cells had minimal expression and fibroblasts had no expression. Second, KS cell growth was inhibited by VDR agonist 1α,25 dihydroxyvitamin D3 with a 50% inhibitory concentration of 5 × 10 −8 mol/L, whereas endothelial cells and fibroblast cells showed no response. Studies on the mechanism of KS tumor growth inhibition by 1α,25 dihydroxyvitamin D3 showed that production of autocrine growth factors interleukin (IL)-6 and IL-8 was reduced in a dose-dependent manner, whereas no effect was observed on vascular endothelial growth factor and basic fibroblast growth factor. Transcription initiated at the IL-6 promoter was repressed by VDR agonist. The DNA sequences required to mediate this repression were localized to nucleotides −225/−110 in the 5′-flanking region. The antitumor activity of VDR agonists was also confirmed in KS tumor xenograft and after topical application in patients with KS. 1α,25 Dihydroxyvitamin D3 and its analogs may thus be candidates for clinical development in KS.