Inflammatory T cells rapidly induce differentiation of human bone marrow stromal cells into mature osteoblasts

IRE1α pathway: A potential bone metabolism mediator

Osteoblasts and osteoclasts collaborate in bone metabolism, facilitating bone development, maintaining normal bone density and strength, and aiding in the repair of pathological damage. Endoplasmic reticulum stress (ERS) can disrupt the intracellular equilibrium between osteoclast and osteoblast, resulting in dysfunctional bone metabolism. The inositol-requiring enzyme-1α (IRE1α) pathway-the most conservative unfolded protein response pathway activated by ERS-is crucial in regulating cell metabolism. This involvement encompasses functions such as inflammation, autophagy, and apoptosis. Many studies have highlighted the potential roles of the IRE1α pathway in osteoblasts, chondrocytes, and osteoclasts and its implication in certain bone-related diseases. These findings suggest that it may serve as a mediator for bone metabolism. However, relevant reviews on the role of the IRE1α pathway in bone metabolism remain unavailable. Therefore, this review aims to explore recent research that elucidated the intricate roles of the IRE1α pathway in bone metabolism, specifically in osteogenesis, chondrogenesis, osteoclastogenesis, and osteo-immunology. The findings may provide novel insights into regulating bone metabolism and treating bone-related diseases.

CD4+ and CD8+ T cells reduce inflammation and promote bone healing in response to titanium implants

T cells are adaptive immune cells essential in pathogenic response, cancer, and autoimmune disorders. During the integration of biomaterials with host tissue, T cells modify the local inflammatory environment by releasing cytokines that promote inflammatory resolution following implantation. T cells are vital for the modulation of innate immune cells, recruitment and proliferation of mesenchymal stem cells (MSCs), and formation of functional tissue around the biomaterial implant. We have demonstrated that deficiency of αβ T cells promotes macrophage polarization towards a pro-inflammatory phenotype and attenuates MSC recruitment and proliferation in vitro and in vivo. The goal of this study was to understand how CD4+ and CD8+ T cells, subsets of the αβ T cell family, impact the inflammatory response to titanium (Ti) biomaterials. Deficiency of either CD4+ or CD8+ T cells increased the proportion of pro-inflammatory macrophages, lowered anti-inflammatory macrophages, and diminished MSC recruitment in vitro and in vivo. In addition, new bone formation at the implantation site was significantly reduced in T cell-deficient mice compared to T cell-competent mice. Deficiency of CD4+ T cells exacerbated these effects compared to CD8+ T cell deficiency. Our results show the importance of CD4+ and CD8+ T cells in modulating the inflammatory response and promoting new bone formation in response to modified Ti implants. STATEMENT OF SIGNIFICANCE: CD4+ and CD8+ T cells are essential in modulating the peri-implant microenvironment during the inflammatory response to biomaterial implantation. This study shows that deficiency of either CD4+ or CD8+ T cell subsets altered macrophage polarization and reduced MSC recruitment and proliferation at the implantation site.

Patients with ankylosing spondylitis present a distinct CD8 T cell subset with osteogenic and cytotoxic potential

OBJECTIVES

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease affecting mainly the axial skeleton. Peripheral involvement (arthritis, enthesitis and dactylitis) and extra-musculoskeletal manifestations, including uveitis, psoriasis and bowel inflammation, occur in a relevant proportion of patients. AS is responsible for chronic and severe back pain caused by local inflammation that can lead to osteoproliferation and ultimately spinal fusion. The association of AS with the human leucocyte antigen-B27 gene, together with elevated levels of chemokines, CCL17 and CCL22, in the sera of patients with AS, led us to study the role of CCR4+ T cells in the disease pathogenesis.

METHODS

CD8+CCR4+ T cells isolated from the blood of patients with AS (n=76) or healthy donors were analysed by multiparameter flow cytometry, and gene expression was evaluated by RNA sequencing. Patients with AS were stratified according to the therapeutic regimen and current disease score.

RESULTS

CD8+CCR4+ T cells display a distinct effector phenotype and upregulate the inflammatory chemokine receptors CCR1, CCR5, CX3CR1 and L-selectin CD62L, indicating an altered migration ability. CD8+CCR4+ T cells expressing CX3CR1 present an enhanced cytotoxic profile, expressing both perforin and granzyme B. RNA-sequencing pathway analysis revealed that CD8+CCR4+ T cells from patients with active disease significantly upregulate genes promoting osteogenesis, a core process in AS pathogenesis.

CONCLUSIONS

Our results shed light on a new molecular mechanism by which T cells may selectively migrate to inflammatory loci, promote new bone formation and contribute to the pathological ossification process observed in AS.

Contribution of αβ T cells to macrophage polarization and MSC recruitment and proliferation on titanium implants

Physiochemical cues like topography and wettability can impact the inflammatory response and tissue integration after biomaterial implantation. T cells are essential for immunomodulation of innate immune cells and play an important role in the host response to biomaterial implantation. This study aimed to understand how CD4+ and CD8+ T cell subsets, members of the αβ T cell family, polarize in response to smooth, rough, or rough-hydrophilic titanium (Ti) implants and whether their presence modulates immune cell crosstalk and mesenchymal stem cell (MSC) recruitment following biomaterial implantation. Post-implantation in mice, we found that CD4+ and CD8+ T cell subsets polarized differentially in response to modified Ti surfaces. Additionally, mice lacking αβ T cells had significantly more pro-inflammatory macrophages, fewer anti-inflammatory macrophages, and reduced MSC recruitment in response to modified Ti post-implantation than αβ T cell -competent mice. Our results demonstrate that T cell activation plays a significant role during the inflammatory response to implanted biomaterials, contributing to macrophage polarization and MSC recruitment and proliferation, and the absence of αβ T cells compromises new bone formation at the implantation site. STATEMENT OF SIGNIFICANCE: T cells are essential for immunomodulation and play an important role in the host response to biomaterial implantation. Our results demonstrate that T cells actively participate during the inflammatory response to implanted biomaterials, controlling macrophage phenotype and recruitment of MSCs to the implantation site.

Low-Dose Staphylococcal Enterotoxin C2 Mutant Maintains Bone Homeostasis via Regulating Crosstalk between Bone Formation and Host T-Cell Effector Immunity

Studies in recent years have highlighted an elaborate crosstalk between T cells and bone cells, suggesting that T cells may be alternative therapeutic targets for the maintenance of bone homeostasis. Here, it is reported that systemic administration of low-dose staphylococcal enterotoxin C2 (SEC2) 2M-118, a form of mutant superantigen, dramatically alleviates ovariectomy (OVX)-induced bone loss via modulating T cells. Specially, SEC2 2M-118 treatment increases trabecular bone mass significantly via promoting bone formation in OVX mice. These beneficial effects are largely diminished in T-cell-deficient nude mice and can be rescued by T-cell reconstruction. Neutralizing assays determine interferon gamma (IFN-γ) as the key factor that mediates the beneficial effects of SEC2 2M-118 on bone. Mechanistic studies demonstrate that IFN-γ stimulates Janus kinase/signal transducer and activator of transcription (JAK-STAT) signaling, leading to enhanced production of nitric oxide, which further activates p38 mitogen-activated protein kinase (MAPK) and Runt-related transcription factor 2 (Runx2) signaling and promotes osteogenic differentiation. IFN-γ also directly inhibits osteoclast differentiation, but this effect is counteracted by proabsorptive factors tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β) secreted from IFN-γ-stimulated macrophages. Taken together, this work provides clues for developing innovative approaches which target T cells for the prevention and treatment of osteoporosis.

The hidden secrets of soluble RANKL in bone biology

The discovery of cytokine tumor necrosis factor (TNF) in the 20th century revealed numerous secrets about organ development. In particular, the functions identified for the receptor activator of nuclear factor kappa-β (NF-κβ) ligand (also known as the RANKL/osteoprotegerin ligand (OPGL) or RANK ligand/TNFSF11) in the homeostasis of skeletal structure, function and regulation were not anticipated. Empirical evidence established the receptor-ligand interaction of RANKL with RANK in osteoclast formation. Reverse signaling of RANKL triggers NF-κβ for the degradation of β-catenin to inhibit bone formation. There is also evidence that RANKL modifies the behavior of other cells in the bone microenvironment, including osteoblasts, chondrocytes, endothelial cells and lymphocytes during normal (homeostatic) and diseased (osteoimmune) states. Two forms of RANKL, i.e., soluble and membrane-bound RANKL, are produced by bone cells. Even though soluble RANKL (sRANKL) and membrane-bound RANKL (mRANKL) both stimulate osteoclast formation in vitro, their biological roles are different. mRANKL triggers osteoclastogenesis by binding to RANK through cell-cell interaction; however, sRANKL released from osteogenic cells binds to RANK without cell-cell interaction. This review attempts to hypothesize how sRANKL functions biologically in bone and explore how this hypothesis might influence future research.

Mice lacking DKK1 in T cells exhibit high bone mass and are protected from estrogen-deficiency-induced bone loss

The Wnt inhibitor Dickkopf-1 (DKK1) is a negative regulator of bone formation and bone mass and is dysregulated in various bone diseases. How DKK1 contributes to postmenopausal osteoporosis, however, remains poorly understood. Here, we show that mice lacking DKK1 in T cells are protected from ovariectomy-induced bone loss. Ovariectomy activated CD4+ and CD8+ T cells and increased their production of DKK1. Co-culture of activated T cells with osteoblasts inhibited Wnt signaling in osteoblasts, leading to impaired differentiation. Importantly, DKK1 expression in T cells also controlled physiological bone remodeling. T-cell-deficient Dkk1 knock-out mice had a higher bone mass with an increased bone formation rate and decreased numbers of osteoclasts compared with controls, a phenotype that was rescued by adoptive transfer of wild-type T cells. Thus, these findings highlight that T cells control bone remodeling in health and disease via their expression of DKK1.

Impact of low bone mass and antiresorptive therapy on antibiotic efficacy in a rat model of orthopedic device-related infection

A significant proportion of orthopedic devices are implanted in osteoporotic patients, but it is currently unclear how estrogen deficiency and/or exposure to antiresorptive bisphosphonates (BPs) influence orthopedic device-related infection (ODRI), or response to therapy. The aim of this study is to characterize the bone changes resulting from Staphylococcus epidermidis infection in a rodent ODRI model and to determine if ovariectomy (OVX) or BP treatment influences the infection or the success of antibiotic therapy. A sterile or S. epidermidis-contaminated screw was implanted into the proximal tibia of skeletally mature female Wistar rats (n = 6-9 per group). Bone changes were monitored over 28 days using in vivo micro-computed tomography scanning. OVX was performed 12 weeks before screw implantation. The BP zoledronic acid (ZOL) was administered 4 days before screw insertion. A combination antibiotic regimen (rifampin plus cefazolin) was administered from Days 7-21. In skeletally healthy animals, S. epidermidis induced marked changes in bone, with peak osteolysis occurring at Day 9 and woven bone deposition and periosteal mineralization from Day 14 onwards. Antibiotic therapy cleared the infection in the majority of animals (2/9 infected) but did not affect bone responses. OVX did not affect the pattern of infection-induced changes in bone, nor bacterial load, but reduced antibiotic efficacy (5/9 infected). ZOL treatment did not protect from osteolysis in OVX animals, or further affect antibiotic efficacy (5/9 infected) but did significantly increase the bacterial load. This study suggests that both BPs and OVX can influence host responses to bone infections involving S. epidermidis.

Lactobacillus rhamnosus attenuates bone loss and maintains bone health by skewing Treg-Th17 cell balance in Ovx mice

Osteoporosis is a systemic-skeletal disorder characterized by enhanced fragility of bones leading to increased rates of fractures and morbidity in large number of populations. Probiotics are known to be involved in management of various-inflammatory diseases including osteoporosis. But no study till date had delineated the immunomodulatory potential of Lactobacillus rhamnosus (LR) in bone-health. In the present study, we examined the effect of probiotic-LR on bone-health in ovariectomy (Ovx) induced postmenopausal mice model. In the present study, we for the first time report that LR inhibits osteoclastogenesis and modulates differentiation of Treg-Th17 cells under in vitro conditions. We further observed that LR attenuates bone loss under in vivo conditions in Ovx mice. Both the cortical and trabecular bone-content of Ovx+LR treated group was significantly higher than Ovx-group. Remarkably, the percentage of osteoclastogenic CD4+Rorγt+Th17 cells at distinct immunological sites such as BM, spleen, LN and PP were significantly reduced, whereas the percentage of anti-osteoclastogenic CD4+Foxp3+Tregs and CD8+Foxp3+Tregs were significantly enhanced in LR-treated group thereby resulting in inhibition of bone loss. The osteoprotective role of LR was further supported by serum cytokine data with a significant reduction in osteoclastogenic cytokines (IL-6, IL-17 and TNF-α) along with enhancement in anti-osteoclastogenic cytokines (IL-4, IL-10, IFN-γ) in LR treated-group. Altogether, the present study for the first time establishes the osteoprotective role of LR on bone health, thus highlighting the immunomodulatory potential of LR in the treatment and management of various bone related diseases including osteoporosis.

Parathyroid Hormone-Related Protein (PTHrP) Accelerates Soluble RANKL Signals for Downregulation of Osteogenesis of Bone Mesenchymal Stem Cells

A recent study reported the expression of receptor activator of nuclear factor-κB (RANK) in mesenchymal stem cells (MSCs) surface that negatively regulates osteogenesis of MSCs. Empirical evidence from the previous study confirmed the role of parathyroid hormone-related protein (PTHrP) in osteoblastogenesis. However, it is necessary to understand the paracrine role of PTHrP and RANKL for osteogenesis in order to explore the hidden secrets in bone biology. Considering the above concept, paracrine cues of soluble-receptor activator of nuclear factor-κB ligand (sRANKL) and PTHrP in osteogenic differentiation of MSCs were investigated. Our results confirmed that sRANKL increased the expression of surface-RANK in MSCs at the earlier stage of osteogenesis, which was downregulated later in differentiated MSCs. In contrast, RANKL expression was low at the earlier stage of MSCs proliferation and high at the differentiation stage of MSCs, which may play a fundamental role in osteoclast formation. sRANKL downregulated osteogenesis of MSCs by decreasing progressive ankylosis (ANK) protein expression while PTHrP upregulated the osteogenic exploitive effect of sRANKL. Interestingly, when they were co-cultured with MSCs, T-lymphocytes expressed high membrane-RANKL levels that contribute to osteogenesis inhibition during MSC differentiation. Thus, our results disclose that sRANKL treatment downregulates osteogenesis of MSCs by increasing RANK expression at the earlier stage of differentiation and by inhibiting ANK. Further, we demonstrated that PTHrP accelerated the downregulating osteogenic effect of sRANKL.

Mesenchymal Progenitors Derived from Different Locations in Long Bones Display Diverse Characteristics

Mesenchymal progenitors within bone marrow have multiple differentiation potential and play an essential role in the maintenance of adult skeleton homeostasis. Mesenchymal progenitors located in bone regions other than the bone marrow also display bone-forming properties. However, owing to the differences in each distinct microenvironment, the mesenchymal characteristics of skeletal progenitor cells within different regions of long bones may show some differences. In order to clearly elucidate these differences, we performed a comparative study on mesenchymal progenitors from different regions of long bones. Here, we isolated mesenchymal progenitors from the periosteum, endosteum, and bone marrow of rat long bones. The three groups exhibited similar cellular morphologies and expressed the typical surface markers associated with mesenchymal stem cells. Interestingly, after cell proliferation assays and bidirectional differentiation analysis, periosteal mesenchymal progenitors showed a higher proliferative ability and adipogenic differentiation potential. In contrast, endosteal mesenchymal progenitors were more prone to osteogenic differentiation. Using in vitro osteoclast culture systems, conditioned media from different mesenchymal progenitor cultures were used to induce osteoclastic differentiation. Osteoclast formation was found to be significantly promoted by the secretion of RANKL and IL-6 by endosteal progenitors. Overall, our results provide strong evidence for the importance of selecting the appropriate source of skeletal progenitors for applications in future skeleton regeneration therapies.

Mesenchymal Stem Cells of Dental Origin for Inducing Tissue Regeneration in Periodontitis: A Mini-Review

Periodontitis is a chronic disease that begins with a period of inflammation of the supporting tissues of the teeth table and then progresses, destroying the tissues until loss of the teeth occurs. The restoration of the damaged dental support apparatus is an extremely complex process due to the regeneration of the cementum, the periodontal ligament, and the alveolar bone. Conventional treatment relies on synthetic materials that fill defects and replace lost dental tissue, but these approaches are not substitutes for a real regeneration of tissue. To address this, there are several approaches to tissue engineering for regenerative dentistry, among them, the use of stem cells. Mesenchymal stem cells (MSC) can be obtained from various sources of adult tissues, such as bone marrow, adipose tissue, skin, and tissues of the orofacial area. MSC of dental origin, such as those found in the bone marrow, have immunosuppressive and immunotolerant properties, multipotency, high proliferation rates, and the capacity for tissue repair. However, they are poorly used as sources of tissue for therapeutic purposes. Their accessibility makes them an attractive source of mesenchymal stem cells, so this review describes the field of dental stem cell research and proposes a potential mechanism involved in periodontal tissue regeneration induced by dental MSC.

Implant-Associated Posttraumatic Osteomyelitis: Collateral Damage by Local Host Defense?

Infections following osteosynthesis or total joint replacement, also known as “implant-associated posttraumatic osteomyelitis”, represent a major complication in orthopedic and trauma surgery. While the formation of bacterial biofilms on the implanted osteosynthesis materials is generally accepted as cause of the persistent infection, the molecular mechanisms leading to the progressive and destructive local inflammatory process and eventually to bone degradation, the osteolysis, have not been delineated. Here we provide evidence supporting the hypothesis that it is not the infection per se that causes tissue degradation and osteolysis, but rather the cytotoxic, proteolytic, and proinflammatory effector functions of cells of the host defense, particularly of the infiltrating polymorphonuclear neutrophils.

Beyond Antibodies: B Cells and the OPG/RANK-RANKL Pathway in Health, Non-HIV Disease and HIV-Induced Bone Loss

HIV infection leads to severe B cell dysfunction, which manifests as impaired humoral immune response to infection and vaccinations and is not completely reversed by otherwise effective antiretroviral therapy (ART). Despite its inability to correct HIV-induced B cell dysfunction, ART has led to significantly increased lifespans in people living with HIV/AIDS. This has in turn led to escalating prevalence of non-AIDS complications in aging HIV-infected individuals, including malignancies, cardiovascular disease, bone disease, and other end-organ damage. These complications, typically associated with aging, are a significant cause of morbidity and mortality and occur significantly earlier in HIV-infected individuals. Understanding the pathophysiology of these comorbidities and delineating clinical management strategies and potential cures is gaining in importance. Bone loss and osteoporosis, which lead to increase in fragility fracture prevalence, have in recent years emerged as important non-AIDS comorbidities in patients with chronic HIV infection. Interestingly, ART exacerbates bone loss, particularly within the first couple of years following initiation. The mechanisms underlying HIV-induced bone loss are multifactorial and complicated by the fact that HIV infection is linked to multiple risk factors for osteoporosis and fracture, but a very interesting role for B cells in HIV-induced bone loss has recently emerged. Although best known for their important antibody-producing capabilities, B cells also produce two cytokines critical for bone metabolism: the key osteoclastogenic cytokine receptor activator of NF-κB ligand (RANKL) and its physiological inhibitor osteoprotegerin (OPG). Dysregulated B cell production of OPG and RANKL was shown to be a major contributor to increased bone loss and fracture risk in animal models and HIV-infected humans. This review will summarize our current knowledge of the role of the OPG/RANK–RANKL pathway in B cells in health and disease, and the contribution of B cells to HIV-induced bone loss. Data from mouse studies indicate that RANKL and OPG may also play a role in B cell function and the implications of these findings for human B cell biology, as well as therapeutic strategies targeting the OPG/RANK–RANKL pathway, will be discussed.

Tensile strength suppresses the osteogenesis of periodontal ligament cells in inflammatory microenvironments

The present study aimed to investigate the role of orthodontic force in osteogenesis differentiation, matrix deposition and mineralization in periodontal ligament cells (PDLCs) cells in inflammatory microenvironments. The mesenchymal origin of PDLCs was confirmed by vimentin and cytokeratin staining. PDLCs were exposed to inflammatory cytokines (5 ng/ml IL‑1β and 10 ng/ml TNF‑α) and/or tensile strength (0.5 Hz, 12% elongation) for 12, 24 or 48 h. Cell proliferation and tensile strength‑induced cytokine expression were assessed by MTT assay and ELISA, respectively. Runt‑related transcription factor 2 (RUNX2) and type I collagen (COL‑I) expression were analysed by reverse transcription‑quantitative polymerase chain reaction and western blot analysis. Additionally, alkaline phosphatase activity was measured, and the mineralization profile was evaluated by alizarin red S staining. PDLCs exposed to tensile strength in inflammatory microenvironments exhibited reduced proliferation and mineralization potential. Treatment with the inflammatory cytokines IL‑1β and TNF‑α increased RUNX2 expression levels; however, decreased COL‑I expression levels, indicating that bone formation and matrix deposition involve different mechanisms in PDL tissues. Notably, RUNX2 and COL‑I expression levels were decreased in PDLCs exposed to a combination of an inflammatory environment and loading strength. The decreased osteogenic potential in an inflammatory microenvironment under tensile strength suggests that orthodontic force may amplify periodontal destruction in orthodontic patients with periodontitis.

Inflammation-induced Bone Remodeling in Periodontal Disease and the Influence of Post-menopausal Osteoporosis

During physiological conditions, the skeleton is remodeled in so-called bone multi-cellular units. Such units have been estimated to exist at 1–2 x 106 sites in the adult skeleton. The number and activities of these units are regulated by a variety of hormones and cytokines. In post-menopausal osteoporosis, lack of estrogen leads to increased numbers of bone multi-cellular units and to uncoupling of bone formation and bone resorption, resulting in too little bone laid down by osteoblasts compared with the amount of bone resorbed by osteoclasts. Inflammatory processes in the vicinity of the skeleton, e.g., marginal and apical periodontitis, will affect the remodeling of the nearby bone tissue in such a way that, in most patients, the amount of bone resorbed exceeds that being formed, resulting in net bone loss (inflammation-induced osteolysis). In some patients, however, inflammation-induced bone formation exceeds resorption, and a sclerotic lesion will develop. The cellular and molecular pathogenetic mechanisms in inflammation-induced osteolysis and sclerosis are discussed in the present review. The cytokines believed to be involved in inflammation-induced remodeling are very similar to those suggested to play crucial roles in post-menopausal osteoporosis. In patients with periodontal disease and concomitant post-menopausal osteoporosis, the possibility exists that the lack of estrogen influences the activities of bone cells and immune cells in such a way that the progression of alveolar bone loss will be enhanced. In the present paper, the evidence for and against this hypothesis is presented.

CCL20/CCR6 Signaling Regulates Bone Mass Accrual in Mice

CCL20 is a member of the macrophage inflammatory protein family and is reported to signal monogamously through the receptor CCR6. Although studies have identified the genomic locations of both Ccl20 and Ccr6 as regions important for bone quality, the role of CCL20/CCR6 signaling in regulating bone mass is unknown. By micro-computed tomography (μCT) and histomorphometric analysis, we show that global loss of Ccr6 in mice significantly decreases trabecular bone mass coincident with reduced osteoblast numbers. Notably, CCL20 and CCR6 were co-expressed in osteoblast progenitors and levels increased during osteoblast differentiation, indicating the potential of CCL20/CCR6 signaling to influence osteoblasts through both autocrine and paracrine actions. With respect to autocrine effects, CCR6 was found to act as a functional G protein-coupled receptor in osteoblasts and although its loss did not appear to affect the number or proliferation rate of osteoblast progenitors, differentiation was significantly inhibited as evidenced by delays in osteoblast marker gene expression, alkaline phosphatase activity, and mineralization. In addition, CCL20 promoted osteoblast survival concordant with activation of the PI3K-AKT pathway. Beyond these potential autocrine effects, osteoblast-derived CCL20 stimulated the recruitment of macrophages and T cells, known facilitators of osteoblast differentiation and survival. Finally, we generated mice harboring a global deletion of Ccl20 and found that Ccl20(-/-) mice exhibit a reduction in bone mass similar to that observed in Ccr6(-/-) mice, confirming that this phenomenon is regulated by CCL20 rather than alternate CCR6 ligands. Collectively, these data indicate that CCL20/CCR6 signaling may play an important role in regulating bone mass accrual, potentially by modulating osteoblast maturation, survival, and the recruitment of osteoblast-supporting cells. © 2016 American Society for Bone and Mineral Research.

Increased RANKL expression in peripheral T cells is associated with decreased bone mineral density in patients with COPD

Receptor activator of nuclear factor-κB ligand (RANKL)-expressing adaptive T cells contribute to bone damage in autoimmune arthritis, although their role in chronic obstructive pulmonary disease (COPD)-associated osteoporosis is unknown. In the present study, the functional expression of RANKL in CD4+/CD8+ T cells and Th17 cells, and the potential role of these cells in COPD-associated bone loss was investigated. A total of 36 non-smokers, 38 smokers with normal lung function and 57 patients with COPD were enrolled. Femoral and vertebral bone mineral density (BMD) was assessed by dual energy X-ray absorptiometry. RANKL expression in peripheral CD4+ and CD8+ T cells and Th17 cells was evaluated by flow cytometry. For in vitro experiments, CD4+ and CD8+ T cells from 17 non-smokers were evaluated for RANKL expression following dose-dependent culture with cigarette smoke extract (CSE) for 5 days. The frequencies of RANKL-positive CD4+ and CD8+ T cells were higher in the patients with COPD than in the non-smokers (P=0.001 and P=0.002, respectively). The proportion of CD4+ T cells positive for both RANKL and interleukin-17 (IL-17) was higher in the patients with COPD than in the non-smokers (P=0.010). However, the frequency of RANKL-expressing Th17 cells was similar among all groups (P=0.508). The frequency of RANKL+CD4+ T cells inversely correlated with BMD of the lumbar vertebrae (P=0.01, r=-0.229), and that of the femoral neck (P<0.001, r=-0.350). The results of our in vitro experiments revealed that CSE increased RANKL expression in CD4+ T cells only. The percentages of RANKL-positive CD4+ T cells and RANKL- and IL-17 double-positive CD4+ T cells were increased in the peripheral blood of patients with COPD, and the former were associated with BMD. These observations suggest that RANKL+CD4+ T cells may be mechanistically linked to diseases of the lung and bone in patients with COPD.

Evaluation of the osteogenic potential of Hancornia speciosa latex in rat calvaria and its phytochemical profile

ETHNOPHARMACOLOGICAL RELEVANCE

Hancornia speciosa Gomes, commonly known as Mangabeira, is a Brazilian native fruit tree belonging to the Apocynaceae family. In folk medicine, the latex obtained from Mangabeira's trunk has been used as an adjunct therapy for bone fractures. Few pharmacological studies on the Hancornia speciosa latex have been developed and despite its popular use for bone healing there is no data about its biological effect on bone.

AIM OF THE STUDY

The present study aimed to investigate the osteogenic potential of Hancornia speciosa latex in rat calvaria, as well as its phytochemical profile.

MATERIALS AND METHODS

A neutral gel composition containing 5% latex was topical applied to a critical size bone defect and over intact calvaria of rats. Areas of newly formed bone on the borders of the defect and of calvaria periosteum were quantified, as well as the percentage of BrdU-positive cells and total cells in the periosteum at different periods of time after latex application. The cytotoxicity of the latex aqueous phase was evaluated in rat calvarial cells in vitro by MTT assay and its phytochemical profile was investigated by ESI-MS/MS.

RESULTS

The area of newly formed bone on the borders of the calvaria defect was larger in rats that received latex at 15 and 30 days of healing. After 3 days of latex application over the intact calvaria, the periosteum area was increased and newly formed bone was observed after 5 and 11 days. There was also an increase in periosteum cell proliferation and population followed latex application on calvaria (p<0.05). The latex aqueous phase limited rat calvarial cell viability in vitro in concentrations larger than 0.6mg/mL. Chlorogenic acid and naringenin-7-O-glucoside were identified in the latex aqueous phase, along with catechin and procyanidin compounds.

CONCLUSION

There was a stimulus for periosteum cell proliferation and bone formation when Hancornia speciosa latex was topically applied on rat calvaria. In addition, chlorogenic acid and naringenin-7-O-glucoside present in Hancornia speciosa latex may contribute to its effects on bone formation.

Utilizing time-lapse micro-CT-correlated bisphosphonate binding kinetics and soft tissue-derived input functions to differentiate site-specific changes in bone metabolism in vivo

The turnover of bone is a tightly regulated process between bone formation and resorption to ensure skeletal homeostasis. This process differs between bone types, with trabecular bone often associated with higher turnover than cortical bone. Analyses of bone by micro-computed tomography (micro-CT) reveal changes in structure and mineral content, but are limited in the study of metabolic activity at a single time point, while analyses of serum markers can reveal changes in bone metabolism, but cannot delineate the origin of any aberrant findings. To obtain a site-specific assessment of bone metabolic status, bisphosphonate binding kinetics were utilized. Using a fluorescently-labeled bisphosphonate, we show that early binding kinetics monitored in vivo using fluorescent molecular tomography (FMT) can monitor changes in bone metabolism in response to bone loss, stimulated by ovariectomy (OVX), or bone gain, resulting from treatment with the anabolic bone agent parathyroid hormone (PTH), and is capable of distinguishing different, metabolically distinct skeletal sites. Using time-lapse micro-CT, longitudinal bone turnover was quantified. The spine showed a significantly greater percent resorbing volume and surface in response to OVX, while mice treated with PTH showed significantly greater resorbing volume per bone surface in the spine and significantly greater forming surfaces in the knee. Correlation studies between binding kinetics and micro-CT suggest that forming surfaces, as assessed by time-lapse micro-CT, are preferentially reflected in the rate constant values while forming and resorbing bone volumes primarily affect plateau values. Additionally, we developed a blood pool correction method which now allows for quantitative multi-compartment analyses to be conducted using FMT. These results further expand our understanding of bisphosphonate binding and the use of bisphosphonate binding kinetics as a tool to monitor site-specific changes in bone metabolism in vivo.

Repercussions of NSAIDS drugs on bone tissue: the osteoblast

Non-steroidal anti-inflammatory drugs (NSAIDs) can act by modulating the behavior of osteoblasts, including their proliferation, differentiation, adhesion, and migration, but not all NSAIDs have these effects. Our objective was to update the information on this issue in a review of the literature in order to offer guidance on the prescription of the appropriate NSAID(s) to patients requiring bone tissue repair. To review current knowledge of this issue by searching for all relevant publications since 2001 in the MEDLINE, EMBASE and Cochrane Library databases, we used the following descriptors: bone tissue, osteoblast, NSAIDs, Anti-inflammatory drugs. Published studies show that most NSAIDs have an adverse effect on osteoblast growth by cell cycle arrest and apoptosis induction. The effect on differentiation varies according to the drug, dose, and treatment time. Osteoblast adhesion is increased and migration decreased by some NSAIDs, such as indomethacin and diclofenac. The antigenic profile or phagocytic function can also be modulated by NSAIDs. In general, NSAIDs have an adverse effect on bone tissue and given the routine administration of NSAIDs to individuals requiring bone repair, in which the osteoblast has an essential role, this effect on bone should be borne in mind.

Cells of the immune system orchestrate changes in bone cell function

There is a complex interplay between the cells of the immune system and bone. Immune cells, such as T and NK cells, are able to enhance osteoclast formation via the production of RANKL. Yet there is increasing evidence to show that during the resolution of inflammation or as a consequence of increased osteoclastogenesis there is an anabolic response via the formation of more osteoblasts. Furthermore, osteoblasts themselves are involved in the control of immune cell function, thus promoting the resolution of inflammation. Hence, the concept of "coupling"-how bone formation is linked to resorption-needs to be more inclusive rather than restricting our focus to osteoblast-osteoclast interactions as in a whole organism these cells are never in isolation. This review will investigate the role of immune cells in normal bone homeostasis and in inflammatory diseases where the balance between resorption and formation is lost.

FGF2 induces RANKL gene expression as well as IL1β regulated MHC class II in human bone marrow-derived mesenchymal progenitor stromal cells

Objective

Human bone marrow mesenchymal stromal cells (hBM-MSC) are being applied in tissue regeneration and treatment of autoimmune diseases (AD). Their cellular and immunophenotype depend on isolation and culture conditions which may influence their therapeutic application and reflect their in vivo biological functions. We have further characterised the phenotype induced by fibroblast growth factor 2 (FGF2) on healthy donor hBM-MSC focusing on the osteoimmunological markers osteoprotegerin (OPG), receptor activator of nuclear factor kB (RANK), RANK ligand (RANKL) and HLA-DR and their regulation of expression by the inflammatory cytokines IL1β and IFNγ.

Methods

RANK, RANKL, OPG and HLA-DR expression in hBM-MSC expanded under specific culture conditions, were measured by RT-PCR and flow cytometry. MAPKs induction by FGF2, IL1β and IFNγ in hBM-MSC was analysed by immunoblotting and RT-PCR.

Results

In hBM-MSC, OPG expression is constitutive and FGF2 independent. RANKL expression depends on FGF2 and ERK1/2 activation. IL1β and IFNγ activate ERK1/2 but fail to induce RANKL. Only IL1β induces P38MAPK. The previously described HLA-DR induced by FGF2 through ERK1/2 on hBM-MSC, is suppressed by IL1β through inhibition of CIITA transcription. HLA-DR induced by IFNγ is not affected by IL1β in hBM-MSC, but is suppressed in articular chondrocytes and lung fibroblasts.

Conclusions

RANKL expression and IL1β regulated MHC-class II, both induced via activation of the ERK1/2 signalling pathway, are specific for progenitor hBM-MSC expanded in the presence of FGF2. HLA-DR regulated by IL1β and ERK1/2 is observed on hBM-MSC during early expansion without FGF2 suggesting previous in vivo acquisition. Stromal progenitor cells with this phenotype could have an osteoimmunological role during bone regeneration.

The dual face of parathyroid hormone and prostaglandins in the osteoimmune system

The microenvironment of bone marrow, an extraordinarily heterogeneous and dynamic system, is populated by bone and immune cells, and its functional dimension has been at the forefront of recent studies in the field of osteoimmunology. The interaction of both marrow niches supports self-renewal, differentiation, and homing of the hematopoietic stem cells and provides the essential regulatory molecules for osteoblast and osteoclast homeostasis. Impaired signaling within the niches results in a pathological tableau and enhances disease, including osteoporosis and arthritis, or the rejection of hematopoietic stem cell transplants. Discovering the anabolic players that control these mechanisms has become warranted. In this review, we focus on parathyroid hormone (PTH) and prostaglandins (PGs), potent molecular mediators, both of which carry out a multitude of functions, particularly in bone lining cells and T cells. These two regulators proved to be promising therapeutic agents when strictly clinical protocols on dose treatments were applied.

Therapeutic doses of nonsteroidal anti-inflammatory drugs inhibit osteosarcoma MG-63 osteoblast-like cells maturation, viability, and biomineralization potential

Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently used to reduce pain and inflammation. However, their effect on bone metabolisms is not well known, and results in the literature are contradictory. The present study focusses on the effect of dexketoprofen, ketorolac, metamizole, and acetylsalicylic acid, at therapeutic doses, on different biochemical and phenotypic pathways in human osteoblast-like cells. Osteoblasts (MG-63 cell line) were incubated in culture medium with 1-10 μM of dexketoprofen, ketorolac, metamizole, and acetylsalicylic acid. Flow cytometry was used to study antigenic profile and phagocytic activity. The osteoblastic differentiation was evaluated by mineralization and synthesis of collagen fibers by microscopy and alkaline phosphatase activity (ALP) by spectrophotometric assay. Short-term treatment with therapeutic doses of NSAIDs modulated differentiation, antigenic profile, and phagocyte activity of osteoblast-like cells. The treatment reduced ALP synthesis and matrix mineralization. However, nonsignificant differences were observed on collagen syntheses after treatments. The percentage of CD54 expression was increased with all treatments. CD80, CD86, and HLA-DR showed a decreased expression, which depended on NSAID and the dose applied. The treatments also decreased phagocyte activity in this cellular population. The results of this paper provide evidences that NSAIDs inhibit the osteoblast differentiation process thus reducing their ability to produce new bone mineralized extracellular matrix.

Mediators of inflammation-induced bone damage in arthritis and their control by herbal products

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation of the synovial joints leading to bone and cartilage damage. Untreated inflammatory arthritis can result in severe deformities and disability. The use of anti-inflammatory agents and biologics has been the mainstay of treatment of RA. However, the prolonged use of such agents may lead to severe adverse reactions. In addition, many of these drugs are quite expensive. These limitations have necessitated the search for newer therapeutic agents for RA. Natural plant products offer a promising resource for potential antiarthritic agents. We describe here the cellular and soluble mediators of inflammation-induced bone damage (osteoimmunology) in arthritis. We also elaborate upon various herbal products that possess antiarthritic activity, particularly mentioning the specific target molecules. As the use of natural product supplements by RA patients is increasing, this paper presents timely and useful information about the mechanism of action of promising herbal products that can inhibit the progression of inflammation and bone damage in the course of arthritis.

Monocytes induce STAT3 activation in human mesenchymal stem cells to promote osteoblast formation

A major therapeutic challenge is how to replace bone once it is lost. Bone loss is a characteristic of chronic inflammatory and degenerative diseases such as rheumatoid arthritis and osteoporosis. Cells and cytokines of the immune system are known to regulate bone turnover by controlling the differentiation and activity of osteoclasts, the bone resorbing cells. However, less is known about the regulation of osteoblasts (OB), the bone forming cells. This study aimed to investigate whether immune cells also regulate OB differentiation. Using in vitro cell cultures of human bone marrow-derived mesenchymal stem cells (MSC), it was shown that monocytes/macrophages potently induced MSC differentiation into OBs. This was evident by increased alkaline phosphatase (ALP) after 7 days and the formation of mineralised bone nodules at 21 days. This monocyte-induced osteogenic effect was mediated by cell contact with MSCs leading to the production of soluble factor(s) by the monocytes. As a consequence of these interactions we observed a rapid activation of STAT3 in the MSCs. Gene profiling of STAT3 constitutively active (STAT3C) infected MSCs using Illumina whole human genome arrays showed that Runx2 and ALP were up-regulated whilst DKK1 was down-regulated in response to STAT3 signalling. STAT3C also led to the up-regulation of the oncostatin M (OSM) and LIF receptors. In the co-cultures, OSM that was produced by monocytes activated STAT3 in MSCs, and neutralising antibodies to OSM reduced ALP by 50%. These data indicate that OSM, in conjunction with other mediators, can drive MSC differentiation into OB. This study establishes a role for monocyte/macrophages as critical regulators of osteogenic differentiation via OSM production and the induction of STAT3 signalling in MSCs. Inducing the local activation of STAT3 in bone cells may be a valuable tool to increase bone formation in osteoporosis and arthritis, and in localised bone remodelling during fracture repair.

HIV: inflammation and bone

HIV infection and antiretroviral therapy (ART) are now established independent risk factors for osteoporosis. With a spate of recent studies reporting significant elevations in fracture prevalence in HIV patients, and a rapidly aging demographic, defining the mechanisms underlying HIV/ART-induced skeletal decline has become imperative. The recent emergence of the field of "osteoimmunology" has provided a conceptual framework to explain how the immune and skeletal systems interact. Furthermore, it is becoming clear that inflammatory states leading to perturbations in the immuno-skeletal interface, a convergence of common cells and cytokine mediators that regulate both immune and skeletal systems, conspire to imbalance bone turnover and induce osteoporosis. In this review we examine the role of inflammation in the bone loss associated with diverse inflammatory conditions and new concepts into how the underlying mechanisms by which inflammation and immune dysregulation impact bone turnover may be pertinent to the mechanisms involved in HIV/ART-induced bone loss.

RANKL induces organized lymph node growth by stromal cell proliferation

RANK and its ligand RANKL play important roles in the development and regulation of the immune system. We show that mice transgenic for Rank in hair follicles display massive postnatal growth of skin-draining lymph nodes. The proportions of hematopoietic and nonhematopoietic stromal cells and their organization are maintained, with the exception of an increase in B cell follicles. The hematopoietic cells are not activated and respond to immunization by foreign Ag and adjuvant. We demonstrate that soluble RANKL is overproduced from the transgenic hair follicles and that its neutralization normalizes lymph node size, inclusive area, and numbers of B cell follicles. Reticular fibroblastic and vascular stromal cells, important for secondary lymphoid organ formation and organization, express RANK and undergo hyperproliferation, which is abrogated by RANKL neutralization. In addition, they express higher levels of CXCL13 and CCL19 chemokines, as well as MAdCAM-1 and VCAM-1 cell-adhesion molecules. These findings highlight the importance of tissue-derived cues for secondary lymphoid organ homeostasis and identify RANKL as a key molecule for controlling the plasticity of the immune system.

The stimulation of an osteogenic response by classical monocyte activation

The monocyte/macrophage system plays a central role in host defense, wound healing and immune regulation at biomaterial surfaces. Monocytes can be classically and alternatively activated, and can be stimulated differently in response to variations in biomaterial surface properties. In this study, human monocytes, cultured on polystyrene surfaces (Ps), were activated either classically, by lipopolysaccharide (LPS), or alternatively, by interleukin-4 (IL-4). Monocytes were also cultured on anodically oxidized (Ox) and machined (Ma) titanium surfaces, with and without LPS stimulation. Cells were cultured for 1 and 3 days and their conditioned media (CM) were collected. The osteogenic response of hMSCs to the monocyte CM was determined by analyzing the gene expression of key osteogenic markers. The CM from classically activated monocytes increased the hMSCs expression of runt-related transcription factor 2 (Runx2) and alkaline phosphatase (ALP). Furthermore, CM from monocytes cultured on Ox surface resulted in a modest increase of the expression of bone morphogenetic protein-2 (BMP-2). LPS stimulation of the surface-seeded monocytes overwhelmed the effect of the surface properties and resulted in significant upregulation of BMP-2 and Runx2 for all samples. The results show that human monocytes, cultured on different surfaces and/or under different activation pathways, communicate pro-osteogenic signals to hMSCs. The signals involve regulation of autologous BMP-2 in the hMSCs. The classical activation results in profound and prolonged osteogenic effect compared to the effect of the investigated surface properties.

Enhanced mesenchymal stromal cell recruitment via natural killer cells by incorporation of inflammatory signals in biomaterials

An exacerbated inflammatory response questions biomaterial biocompatibility, but on the other hand, inflammation has a central role in the regulation of tissue regeneration. Therefore, it may be argued that an 'ideal' inflammatory response is crucial to achieve efficient tissue repair/regeneration. Natural killer (NK) cells, being one of the first populations arriving at an injury site, can have an important role in regulating bone repair/regeneration, particularly through interactions with mesenchymal stem/stromal cells (MSCs). Here, we studied how biomaterials designed to incorporate inflammatory signals affected NK cell behaviour and NK cell-MSC interactions. Adsorption of the pro-inflammatory molecule fibrinogen (Fg) to chitosan films led to a 1.5-fold increase in adhesion of peripheral blood human NK cells, without an increase in cytokine secretion. Most importantly, it was found that NK cells are capable of stimulating a threefold increase in human bone marrow MSC invasion, a key event taking place in tissue repair, but did not affect the expression of the differentiation marker alkaline phosphatase (ALP). Of significant importance, this NK cell-mediated MSC recruitment was modulated by Fg adsorption. Designing novel biomaterials leading to rational modulation of the inflammatory response is proposed as an alternative to current bone regeneration strategies.

Stimulation of B7-H3 (CD276) directs the differentiation of human marrow stromal cells to osteoblasts

Previous studies showed that B7-H3 (CD276), a cytokine involved in the activation of T lymphocytes, regulates murine bone formation. However, the role of B7-H3 in bone formation is barely understood. Herewith, we report, that stimulation of B7-H3 promotes the differentiation of human marrow stromal cells (hMSCs) to osteoblasts. With 4H7, a new monoclonal antibody against human B7-H3, we have identified B7-H3 is located on the surface of human marrow stromal cells. Evermore, we have found that increase of B7-H3 levels are correlated with the differentiation course of hMSCs. Stimulation of B7-H3 with 4H7 antibody considerably increases the numbers of osteoblasts generated from the hMSCs in the presence of inducing medium containing dexamethasone, sodium β-glycerophosphate and l-ascorbic acid. 4H7 treatments significantly increase osteoblast markers including alkaline phosphatase (ALP), and osteocalcin (OC) after day 7 and day 14 of the inducing hMSCs differentiation. The numbers of mineralized nodules of osteoblasts have been remarkly increased after 21 days of induced differentiation of hMSCs. However, stimulation effects of 4H7 antibody on membrane B7-H3 has been eliminated by addition of B7-H3Fc fusion protein. These results indicate 4H7 antibody specifically stimulates the membrane B7-H3 and directs the differentiation of hMSCs. Furthermore, our study also shows that stimulation of B7-H3 increases the expression of osteoprotein (OPG), and decreases the expression of its cognate ligand, the receptor activator of nuclear factor kappaB ligand (RANKL).

Effects of Indomethacin, Nimesulide, and Diclofenac on Human MG-63 Osteosarcoma Cell Line

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most widely prescribed drugs worldwide and serve as treatment of some degenerative inflammatory joint diseases. The aim of the present study was to investigate the influence of different concentrations of three NSAIDs on cell proliferation, differentiation, antigenic profile, and cell cycle in the human MG-63 osteosarcoma cell line, incubated for 24 hr. All NSAIDs had an inhibiting effect on osteoblastic proliferation. Treatments for 24 hr had small but significant effects on the antigenic profile. No treatment altered osteocalcin synthesis. Indomethacin and nimesulide treatments arrested the cell cycle at G0/G1. These results suggest that indomethacin, nimesulide, and diclofenac appear to have no effects on osteocalcin synthesis and a slight effect on the antigenic profile. They may delay bone regeneration due to their inhibiting effect on osteoblast growth. Therefore, these drugs should only be used in situations that do not require rapid bone healing.

Arterial calcifications

Arterial calcifications as found with various imaging techniques, like plain X-ray, computed tomography or ultrasound are associated with increased cardiovascular risk. The prevalence of arterial calcification increases with age and is stimulated by several common cardiovascular risk factors. In this review, the clinical importance of arterial calcification and the currently known proteins involved are discussed. Arterial calcification is the result of a complex interplay between stimulating (bone morphogenetic protein type 2 [BMP-2], RANKL) and inhibitory (matrix Gla protein, BMP-7, osteoprotegerin, fetuin-A, osteopontin) proteins. Vascular calcification is especially prevalent and related to adverse outcome in patients with renal insufficiency and diabetes mellitus. We address the special circumstances and mechanisms in these patient groups. Treatment and prevention of arterial calcification is possible by the use of specific drugs. However, it remains to be proven that reduction of vascular calcification in itself leads to a reduced cardiovascular risk.

Rodent models in bone-related research: the relevance of calvarial defects in the assessment of bone regeneration strategies

In vivo research with animal models has been a preferred experimental system in bone-related biomedical research since, by approximation, it allows relevant data gathering regarding physiological and pathological conditions that could be of use to establish more effective clinical interventions. Animal models, and more specifically rodent models, have been extensively used and have contributed greatly to the development and establishment of a wide range of translational approaches aiming to regenerate the bone tissue. In this regard, the calvarial defect model has found great application in basic and applied research, nonetheless the controversial rationalization for the use of critical size defects - defects that are unable to report spontaneous healing - or subcritical size defects in the proposed applications. Accordingly, this work aims to review the advantages and limitations of the use of rodent models in biomedical bone-related research, emphasizing the problematic issues of the use of calvarial critical and subcritical size defects. Additionally, surgical protocols for the establishment of both defects in rat calvarial bone, as well as the description and exemplification of the most frequently used techniques to access the bone tissue repair, are portrayed.

Bone density and hyperlipidemia: the T-lymphocyte connection

Osteoporosis, which contributes to morbidity and mortality, often coexists with cardiovascular disease, especially atherosclerosis. We have reported recently that in vitro exposure of human T-lymphocytes to oxidized lipids induced expression of a key osteoclastogenic cytokine, receptor activator of NF-κB ligand (RANKL). Our previous studies have shown that mice fed an atherogenic high-fat diet developed osteopenia and that bone marrow preosteoclasts from these hyperlipidemic mice have increased osteoclastic potential. To investigate the role of T-lymphocytes in the diet-induced bone loss, C57BL/6 mice were fed either chow or a high-fat diet, and bone parameters and T-lymphocyte activation were assessed at 6 and 11 months. Consistent with our previous findings, peripheral quantitative computed tomographic (pQCT) analysis showed that mice in the high-fat group had lower bone mineral content than mice in the chow group. Furthermore, histomorphometric analysis showed decreased structural parameters in the high-fat group. Coculture studies showed that bone marrow cells isolated from the high-fat group, which contained increased levels of activated memory T-lymphocytes compared with bone marrow cells from the chow mice, supported osteoclastic differentiation of RAW 264.7 cells. Additionally, RANKL expression was upregulated significantly in the T-lymphocytes isolated from the bone marrow of the high-fat group. Splenic T-lymphocytes isolated from the high-fat group also had increased expression of transcripts for the receptor for oxidized lipids (LOX-1) as well as for inflammatory and osteoclastogenic cytokines, including RANKL, interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), IL-1β, and interferon γ (IFN-γ). Together these findings suggest that T-lymphocytes play a key role in the osteoclastogenesis induced by a high-fat diet and may contribute to the bone loss associated with diet-induced osteopenia.

Biocompatibility of adhesive complex coacervates modeled after the sandcastle glue of Phragmatopoma californica for craniofacial reconstruction

Craniofacial reconstruction would benefit from a degradable adhesive capable of holding bone fragments in three-dimensional alignment and gradually being replaced by new bone without loss of alignment or volume changes. Modeled after a natural adhesive secreted by the sandcastle worm, we studied the biocompatibility of adhesive complex coacervates in vitro and in vivo with two different rat calvarial models. We found that the adhesive was non-cytotoxic and supported the attachment, spreading, and migration of a commonly used osteoblastic cell line over the course of several days. In animal studies we found that the adhesive was capable of maintaining three-dimensional bone alignment in freely moving rats over a 12 week indwelling period. Histological evidence indicated that the adhesive was gradually resorbed and replaced by new bone that became lamellar across the defect without loss of alignment, changes in volume, or changes in the adjacent uninjured bone. The presence of inflammatory cells was consistent with what has been reported with other craniofacial fixation methods including metal plates, screws, tacks, calcium phosphate cements and cyanoacrylate adhesives. Collectively, the results suggest that the new bioadhesive formulation is degradable, osteoconductive and appears suitable for use in the reconstruction of craniofacial fractures.

The immune system and bone

T cells and B cells produce large amounts of cytokines which regulate bone resorption and bone formation. These factors play a critical role in the regulation of bone turnover in health and disease. In addition, immune cells of the bone marrow regulate bone homeostasis by cross-talking with bone marrow stromal cells and osteoblastic cells via cell surface molecules. These regulatory mechanisms are particularly relevant for postmenopausal osteoporosis and hyperparathyroidism, two common forms of bone loss caused primarily by an expansion of the osteoclastic pool only partially compensated by a stimulation of bone formation. This article describes the cytokines and immune factors that regulate bone cells, the immune cells relevant to bone, examines the connection between T cells and bone in health and disease, and reviews the evidence in favor of a link between T cells and the mechanism of action of estrogen and PTH in bone.

A novel T cell cytokine, secreted osteoclastogenic factor of activated T cells, induces osteoclast formation in a RANKL-independent manner

OBJECTIVE

Chronic T cell activation is central to the etiology of rheumatoid arthritis (RA), an inflammatory autoimmune disease that leads to severe focal bone erosions and generalized systemic osteoporosis. Previous studies have shown novel cytokine-like activities in medium containing activated T cells, characterized by potent induction of the osteoblastic production of interleukin-6 (IL-6), an inflammatory cytokine and stimulator of osteoclastogenesis, as well as induction of an activity that directly stimulates osteoclast formation in a manner independent of the key osteoclastogenic cytokine RANKL. This study was undertaken to identify the factors secreted by T cells that are responsible for these activities.

METHODS

Human T cells were activated using anti-human CD3 and anti-human CD28 antibodies for 72 hours in AIM V serum-free medium to obtain T cell-conditioned medium, followed by concentration and fractionation of the medium by fast-protein liquid chromatography. Biologically active fractions were resolved using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Major bands were analyzed by mass spectrometry, and a major candidate protein was identified. This novel cytokine was cloned, and its expression was analyzed using recombinant DNA technologies.

RESULTS

A single novel cytokine that could induce both osteoblastic IL-6 production and functional osteoclast formation in the absence of osteoblasts or RANKL and that was insensitive to the effects of the RANKL inhibitor osteoprotegerin was identified in the activated T cell-conditioned medium; this cytokine was designated secreted osteoclastogenic factor of activated T cells (SOFAT). Further analysis of SOFAT revealed that it was derived from an unusual messenger RNA splice variant coded by the threonine synthase-like 2 gene homolog, which is a conserved gene remnant coding for threonine synthase, an enzyme that functions only in microorganisms and plants.

CONCLUSION

SOFAT may act to exacerbate inflammation and/or bone turnover under inflammatory conditions such as RA or periodontitis and in conditions of estrogen deficiency.

T lymphocytes amplify the anabolic activity of parathyroid hormone through Wnt10b signaling

Intermittent administration of parathyroid hormone (iPTH) is used to treat osteoporosis because it improves bone architecture and strength, but the underlying cellular and molecular mechanisms are unclear. Here, we show that iPTH increases the production of Wnt10b by bone marrow CD8+ T cells and induces these lymphocytes to activate canonical Wnt signaling in preosteoblasts. Accordingly, in responses to iPTH, T cell null mice display diminished Wnt signaling in preosteoblasts and blunted osteoblastic commitment, proliferation, differentiation, and life span, which result in decreased trabecular bone anabolism and no increase in strength. Demonstrating the specific role of lymphocytic Wnt10b, iPTH has no anabolic activity in mice lacking T-cell-produced Wnt10b. Therefore, T-cell-mediated activation of Wnt signaling in osteoblastic cells plays a key permissive role in the mechanism by which iPTH increases bone strength, suggesting that T cell osteoblast crosstalk pathways may provide pharmacological targets for bone anabolism.

Bone resorption in incompletely impacted mandibular third molars and acute pericoronitis

Acute pericoronitis (AP) arises frequently in incompletely impacted mandibular third molars, but it remains unknown whether bone resorption in aging is associated with acute inflammation of the third molar. We conducted an experiment to compare the ratio of bone resorption to root length in the distal surface of the second molar (A), the proximal surface (B), and distal surface (C) in mesio-angular, incompletely impacted third molars in 27 young and 58 older adults with AP and 77 young and 79 older adults without a history of AP. Bone resorption in A, B, and C in older adults with AP demonstrated a significantly higher ratio when compared to those without AP, whereas there was no difference between those with and without AP in young adults except for B in women. However, there were no differences between bone resorption in B with AP in young and older women, and between bone resorption in C with AP in young and older adults. These indicate that AP and bone resorption are associated with incompletely impacted mandibular third molars in older adults.