Modulation of osteoclast function in bone by the immune system

The immune cells in modulating osteoclast formation and bone metabolism

Osteoclasts are pivotal in regulating bone metabolism, with immune cells significantly influencing both physiological and pathological processes by modulating osteoclast functions. This is particularly evident in conditions of inflammatory bone resorption, such as rheumatoid arthritis and periodontitis. This review summarizes and comprehensively analyzes the research progress on the regulation of osteoclast formation by immune cells, aiming to unveil the underlying mechanisms and pathways through which diseases, such as rheumatoid arthritis and periodontitis, impact bone metabolism.

[Progress of research on the relationship between calcitonin gene-related peptide and RANK/RANKL/OPG system in the bone reconstruction]

OBJECTIVE

To summarize the research progress on the calcitonin gene-related peptide (CGRP) and receptor activator of nuclear factor κB (RANK)/receptor activator of nuclear factor κB ligand (RANKL)/osteoprotegerin (OPG) system during bone reconstruction to provide theoretical basis for further research on the prevention and treatment of bone-related diseases.

METHODS

The relevant research results at home and abroad in recent years were analyzed and summarized.

RESULTS

CGRP and RANK/RANKL/OPG system play important regulatory roles in the bone reconstruction.

CONCLUSION

At present, the research on the mechanism of CGRP and RANK/RANKL/OPG system in bone reconstruction is insufficient. Therefore, it is necessary to study further on the process and interrelation of CGRP and RANK/RANKL/OPG system in bone reconstruction to confirm their mechanism, which will bring new ideas and methods for the treatment of bone related diseases in clinic.

Genetic determinants and postorthodontic external apical root resorption in Czech children

OBJECTIVE

Genes, involved in the modulation of inflammatory response and bone remodeling, play a role in the development of postorthodontic external apical root resorption (EARR). The aim of our study was to analyze possible associations between seven single nucleotide polymorphisms (SNPs) in interleukin-17A (IL-17), osteopontin (SPP1), purinoreceptor P2X7 (P2RX7), and tumor necrosis factor receptor superfamily member 11B (TNFRSF11B) genes and EARR in children after orthodontic treatment.

SUBJECTS AND METHODS

This case-control study comprised 99 orthodontically treated patients (69 controls and 30 subjects with EARR). Genotype determinations of rs2275913, rs11730582, rs9138, rs208294, rs1718119, rs3102735, and rs2073618 were based on polymerase chain reaction using 5' nuclease TaqMan^® assays.

RESULTS

While no significant differences were observed in allele or genotype frequencies of all seven studied SNPs, specific haplotype of P2RX7 (rs208294 and rs1718119) modified the risk of EARR development (P < 0.05). In addition, the length of treatment with a fixed orthodontic appliance positively correlated with the presence of EARR (P < 0.05).

CONCLUSIONS

Although the effect of individual SNPs studied on the EARR development was not confirmed in the Czech population, complex analysis suggested that variability in the P2RX7 gene and the length of orthodontic treatment may be important factors contributing to the etiopathogenesis of postorthodontic EARR.

FTY-720P Suppresses Osteoclast Formation by Regulating Expression of Interleukin-6 (IL-6), Interleukin-4 (IL-4), and Matrix Metalloproteinase 2 (MMP-2)

Background

Osteoclast formation is closely related to the immune system. FTY720, a new immunosuppressive agent, has some functions in immune regulation. Its main active ingredients become FTY-720P in vivo by phosphorylation modification. The objective of this study was to determine the effects of FTY-720 with various concentrations on osteoclasts in vitro.

Material/Methods

RAW264.7 cells and bone marrow-derived mononuclear phagocytes (BMMs) were treated with RANKL to obtain osteoclasts in vitro. To investigate the role of FTY-720 in osteoclast formation, trap enzyme staining was performed and the number of osteoclasts was counted. Bone slices were stained with methylene blue, we counted the number of lacunae after bone slices were placed into dishes together with osteoclasts, and we observed the effect and function of FTY-720 in osteoclasts induced by RAW264.7 cells and BMMs. Then, we used a protein array kit to explore the effects of FTY-720P on osteoclasts.

Results

The results of enzyme trap staining and F-actin staining experiments show that, with the increasing concentration of FTY-720P, the number of osteoclast induced by RAW264.7 cells and BMMs gradually decreased (P<0.05), especially when the FTY-720P concentration reached 1000 ng/ml, and the number of osteoclasts formed was the lowest (P<0.05). With bone lacuna toluidine blue staining, the results also show that, with the increasing concentration of FTY-720P, the number of bone lacuna gradually decreased (P<0.05), and the number of lacunae is lowest when the concentration reached 800 ng/ml. Finally, protein array results showed that IL-4, IL-6, IL-12, MMP-2, VEGF-C, GFR, basic FGF, MIP-2, and insulin proteins were regulated after FTY-720P treatment.

Conclusions

FTY-720P can suppress osteoclast formation and function, and FTY-720P induces a series of cytokine changes.

Increased osteoporosis risk in dermatomyositis or polymyositis independent of the treatments: a population-based cohort study with propensity score

We investigated the relationship between dermatomyositis/polymyositis (DM/PM) and the risk of subsequent osteoporosis development. A population-based retrospective cohort analysis was conducted using the National Health Insurance Research Database and the Catastrophic Illness Patients Database of Taiwan. We included 1179 patients and 4716 patients from 1999 to 2008 as the DM/PM cohort and the comparison cohort, respectively, and calculated the incidence rates of newly diagnosed osteoporosis. We used Cox proportional hazards models stratified on matched pair to assess the effect of DM/PM. The Kaplan-Meier method was applied to estimate the cumulative osteoporosis incidence curves. Patients with DM/PM were 2.99 times more likely to experience osteoporosis than those without DM/PM. The risk for osteoporosis in DM/PM patients was higher than comparisons in different propensity score quartiles. DM/PM cohort, no matter treated with or without corticosteroids and immunosuppressant, had a higher risk than the comparison cohort. The incidence of osteoporosis in Taiwan is associated with a priori DM/PM history. This risk was independent of the corticosteroids and immunosuppressant treatment.

The Neutrophil to Lymphocyte Ratio on Admission and Short-Term Outcomes in Orthogeriatric Patients

AIM

To investigate the association of the neutrophil to lymphocyte ratio (NLR) at admission with presence of fracture, comorbid conditions, and its prognostic value for short-term outcomes in orthogeriatric patients.

METHODS

On 415 consecutive patients (mean age 78.8 ±8.7[SD] years, 281 women, 255 with a non-vertebral bone fracture, including 167 with a hip fracture, HF) admitted to the Department of Orthopaedic Surgery at the Canberra hospital (2010 - 2011) data on clinical and laboratory characteristics were collected prospectively. The validation dataset included 294 consecutive patients (mean age 82.1 ± 8.0 years, 72.1% women) with HF.

RESULTS

Multivariate regression revealed four variables, presence of HF, hypoalbuminaemia (<33g/L), anaemia (<120g/L) and hyperparathyroidism (PTH>6.8 pmol/L), as independent determinants of admission NLR≥5.1. There was a dose-graded relationship between presence of fracture, especially HF, postoperative complications and levels of NLR categorized as tertiles. Compared to patients with NLR<5.1(first tertile), patients with NLR 5.1-8.5 (second tertile) had a 1.8-, 3.1-, 2.6-, and 2.5-fold higher risk for presence of any fracture, HF, developing postoperative myocardial injury (troponin I rise) and a high inflammatory response/infection (CRP>100mg/L after the 3rd postoperative day), respectively, while in subjects with NLR>8.5 (third tertile) these risks were 2.6-, 4.9-, 5.9- and 4.5-times higher, respectively; subjects with NLR>8.5 had a 9.7 times higher chance of dying in the hospital compared to patients with NLR 5.1-8.5; the NLR retained its significance on multivariate analyses. The NLR ≥5.1 predicted postoperative myocardial injury with an area under the curve (AUC) of 0.626, CRP>100mg/L with AUC of 0.631 and the NLR >8.5 predicted in-hospital mortality with an AUC of 0.793, showing moderately high sensitivity (86.7%, 80% and 90%, respectively) and negative predictive value (92.9%, 71.2%, 99.6%, respectively), but low specificity. Admission NLR was superior to other, except hypoalbuminaemia, prognostic markers; combined use of both NLR≥5.1 and albumin<33g/L only moderately increased the accuracy of prediction. The validation study confirmed the prognostic value of the admission NLR.

CONCLUSIONS

In orthogeriatric patients, high NLR on admission is an independent indicator of fracture presence, a significant risk factor and moderate predictor of postoperative myocardial injury, high inflammatory response/infection and in-hospital death.

Intercellular cross-talk among bone cells: new factors and pathways

Intercellular communication within the bone microenvironment is critical for the maintenance of normal bone structure. Osteoblast-lineage cells at all stages of differentiation, from pluripotent precursors to matrix-embedded osteocytes, produce regulatory factors that modulate the differentiation and activity of both bone-forming osteoblasts and bone-resorbing osteoclasts. Osteoclasts can also release factors that feed back to regulate osteoblast activity. Intercellular cross-talk within the bone microenvironment is not restricted only to these bone cells. Other cells within the bone marrow microenvironment, including adipocytes, T cells, and macrophages, play key roles that influence the processes of bone formation and resorption. This review discusses recent work that provides new insights into some of these communication networks and the factors involved, including osteocytic production of receptor activator of nuclear factor-κB ligand (RANKL) and sclerostin, osteoblastic production of interleukin-33, osteoclast-derived Semaphorin 4D, ephrin signaling, and signals from T helper cells and resident osteal macrophages (osteomacs).

Immune regulation of osteoclast function in postmenopausal osteoporosis: a critical interdisciplinary perspective

Extensive studies on cross talk between immune and skeletal systems in autoimmune diseases give rise to a new discipline of 'osteoimmunology', which explores the molecular regulation of osteoclasts by immune system. Postmenopausal osteoporosis is recognized as a cytokine driven disease, but the mechanism that how estrogen deficiency interplaying with cytokines to stimulate bone loss remains to be elucidated. Although the effect of individual cytokines on osteoclast formation is well characterized, the major challenge is to fit a multitude of redundant pathways and cytokines into a systemic model of postmenopausal osteoporosis. This review presents current findings and hypothesis to explain estrogen deficiency-stimulated bone loss in a critical interdisciplinary perspective. To better understand the interaction between osteoclasts and immune system in postmenopausal osteoporosis, many of the lessons have been explored in animal models.

Pathology of the distal phalanx in equine laminitis: more than just skin deep

The etiopathogenesis of laminitis is complex and involves multiple tissue types. It may be initiated by biomechanical, traumatic, inflammatory, vascular, toxic, and metabolic factors. Although histopathologic changes occurring within the lamellae of experimental models of laminitis are well described and reported, histopathologic changes occurring in the distal phalanx are not, even though gross and radiographic evidence of disease are often apparent and bony lesions could be considered a significant source of pain. Recent scientific evidence indicates that the microenvironment of bone is an important modulator of inflammatory processes that can both influence, and be influenced by components of other organ systems, including the immune, nervous, gastrointestinal, and integumentary systems. This article describes various laminitis-associated histopathological changes in the distal phalanx, introduces concepts of osteoimmunology with regards to equine laminitis, and provides a rationale for histopathological examination of the distal phalanx, as well as the soft tissue structures of the lamellae and corium in laminitis cases.

Effect of stress on mRNA expression of H+-ATPase in osteoclasts

This study was designed to investigate the effect of various strengths and action times of flow stress on mRNA expression of H+-ATPase in osteoclasts. Osteoclasts were obtained through a classical mechanical-anatomical technique. They were identified by their morphology, tartrate-resistant acid phosphatase (TRAP) staining, and by a test of their ability to form resorption lacunae. Osteoclasts were mechanically loaded by flow stress using a cell-loading system. The stress-loading experiments were divided into various strength groups and action time groups. The morphological changes of osteoclasts after application of loading stress were analyzed using an image analysis system and Image-Pro Plus software. Expression of H+-ATPase mRNA in osteoclasts was detected by real-time fluorescent quantitative polymerase chain reaction. The existence of significant differences between experimental groups was analyzed using SPSS 12.0 software. The cytoplasm of osteoclasts with positive TRAP staining appeared with a characteristic claret-red color. Cells were able to form resorption pits in the surface of dentine slices. Morphological changes of osteoclasts with applied stress assumed an early increasing tendency before reaching a peak value and following a decreasing tendency. A significant difference of H+-ATPase mRNA expression of osteoclasts was seen between any two groups (P < 0.05). H+-ATPase mRNA expression in osteoclasts had a tendency to first increase with increasing stress and was observed to then decrease in one action time group. In this present study, a close relationship between the stress and mRNA expression of H+-ATPase in osteoclasts was observed.