Differential effects of interleukin-6 receptor activation on intracellular signaling and bone resorption by isolated rat osteoclasts

Does the rate of orthodontic tooth movement change during the estrus cycle? A systematic review based on animal studies

BACKGROUND

As the fluctuation of sex hormone levels in menstruating women results in periodical effects in bone metabolism, understanding the implications for tooth movement could be of benefit to the orthodontist. This type of research presents practical and ethical problems in humans, but animal models could provide useful information. Our objective was to systematically investigate the available evidence on the question whether the rate of orthodontic tooth movement varies between the different stages of the estrus cycle in animals.

METHODS

Unrestricted searches in 7 databases and manual searching of the reference lists in relevant studies were performed up to February 2021 (Medline [PubMed], CENTRAL [Cochrane Library; includes records from Embase, CINAHL, ClinicalTrials.gov, WHO's ICTRP, KoreaMed, Cochrane Review Groups' Specialized Registers, and records identified by handsearching], Cochrane Database of Systematic Reviews [Cochrane Library], Scopus, Web of Knowledge [including Web of Science Core Collection, KCI Korean Journal Database, Russian Science Citation Index, SciELO Citation Index and Zoological Record], Arab World Research Source [EBSCO] and ProQuest Dissertation and Theses [ProQuest]). Our search focused on prospective controlled animal studies, whose samples included female subjects of any species that were quantitatively comparing the amount of tooth movement in the different stages of the estrus cycle. Following study retrieval and selection, relevant data was extracted, and the risk of bias was assessed using the SYRCLE's Risk of Bias Tool.

RESULTS

From the finally assessed records, 3 studies met the inclusion criteria. Two of the studies experimented on Wistar rats, whereas the other on cats. Tooth movement was induced by expansion or coil springs. The rate of orthodontic tooth movement was increased during the stages of the estrus cycle when oestrogen and/or progesterone levels were lower. The risk of bias in the retrieved studies was assessed to be unclear.

CONCLUSION

Hormonal changes during the estrus cycle may affect the rate of orthodontic tooth movement. Although these animal experiment results should be approached cautiously regarding their translational potential, it could be useful to consider the possible impact of these physiological changes in the clinical setting until more information becomes available. Registration: PROSPERO (CRD42021158069).

EphA2 Is a Clinically Relevant Target for Breast Cancer Bone Metastatic Disease

EphA2 receptor tyrosine kinase (RTK) is highly expressed in breast tumor cells across multiple molecular subtypes and correlates with poor patient prognosis. In this study, the potential role of EphA2 in this clinically relevant phenomenon is investigated as metastasis of breast cancer to bone is a major cause of morbidity and mortality in patients. It was found that the EphA2 function in breast cancer cells promotes osteoclast activation and the development of osteolytic bone disease. Blocking EphA2 function molecularly and pharmacologically in breast tumors reduced the number and size of bone lesions and the degree of osteolytic disease in intratibial and intracardiac mouse models, which correlated with a significant decrease in the number of osteoclasts at the tumor-bone interface. EphA2 loss of function in tumor cells impaired osteoclast progenitor differentiation in coculture, which is mediated, at least in part, by reduced expression of IL-6. EPHA2 transcript levels are enriched in human breast cancer bone metastatic lesions relative to visceral metastatic sites; EphA2 protein expression was detected in breast tumor cells in bone metastases in patient samples, supporting the clinical relevance of the study's findings. These data provide a strong rationale for the development and application of molecularly targeted therapies against EphA2 for the treatment of breast cancer bone metastatic disease. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Effects of Laparoscopic Sleeve Gastrectomy on Bone Mineral Density and Bone Metabolism in Chinese Patients with Obesity

OBJECTIVE

Laparoscopic sleeve gastrectomy (LSG) is one of the most effective therapies to treat obesity. Due to a lack of longitudinal research, we explored the changes in BMD and bone metabolism in Chinese patients with obesity before and after LSG.

MATERIALS AND METHODS

A total of 49 obese Chinese patients with obesity were recruited from the Second Xiangya Hospital of Central South University. All patients underwent LSG, and the metabolic indicators were evaluated, including the serum osteocalcin (OC), total-terminal propeptide of type I procollagen (TPINP) and carboxy terminal telopeptide of collagen type I (CTX) levels at baseline and 2, 6 and 12 months postoperatively. Dual energy X-ray absorptiometry (DEXA) was used to measure body composition and BMD before and 12 months after LSG.

RESULTS

The body mass index (BMI) significantly decreased at 12 months postoperatively, and no patients developed osteoporosis. The BMD of femoral neck and total hip significantly decreased from the baseline to 12 months postoperatively, while the BMD of lumbar spine did not change significantly. The OC, TPINP and CTX levels significantly increased at 12 months postoperatively. The excess BMI loss (EBMIL) was positively related while the reduction in visceral adipose tissue (VAT) mass was negatively related to the decreases in BMD of the femoral neck and total hip at 12 months postoperatively. The increase in OC was negatively correlated with the decrease in BMD of the femoral neck, while the increase in TPINP was positively correlated with the decrease in BMD of total hip.

CONCLUSION

Based on the 12-month follow-up results, the BMD of the femoral neck and total hip was decreased in Chinese patients with obesity after LSG, while bone remodelling was active. This finding suggested that weight loss, a decrease in the VAT mass and an increase in bone remodelling may be correlated with a reduction in BMD.

Increased risk of incident osteoporosis and osteoporotic fracture in tuberculosis patients: a population-based study in a tuberculosis-endemic area

The occurrence of osteoporosis in tuberculosis, a chronic infection, has rarely been evaluated. In this study, we found significantly higher incidence rates of osteoporosis (Adjusted hazard ratio (AHR) 1.82) and osteoporotic fracture (AHR 2.33) in tuberculosis patients than matched cohorts, which suggest that osteoporosis screening should be considered in tuberculosis patients' follow-up program. The aim of this study is to determine the occurrence of incident osteoporosis in patients who completed anti-tuberculosis (TB) treatment.

INTRODUCTION

Chronic inflammatory disorders are associated with an increased risk of osteoporosis. Although TB is an infectious disease characterized by systemic inflammatory responses, the impact of active TB on incident osteoporosis is unclear. We used the Taiwan National Health Insurance Research Database to investigate the association between history of active TB and incident osteoporosis and osteoporotic fracture.

METHODS

In this nationwide retrospective cohort study, active TB patients and their age- and sex-matched controls were identified from the National Health Insurance Research Database in Taiwan during 2000-2012. The occurrence of incident osteoporosis, osteoporotic fractures, and risk factors associated with osteoporosis among TB patients and matched controls were analyzed.

RESULTS

We observed incident osteoporosis in 2.2% (n = 86) of the TB patients and in 1.1% (n = 162) of the matched controls. The incidence rate of osteoporosis was 4.31 and 1.80 per 1000 person-years, which was significantly higher in TB patients (p < 0.001). In multivariate analysis, TB was an independent risk factor for osteoporosis. The other independent factors associated with osteoporosis were older age, female sex, chronic obstructive pulmonary disease, asthma, and lower income. Moreover, we demonstrated that the occurrence of osteoporotic fracture was significantly higher in TB patients.

CONCLUSIONS

Patients with a history of active TB have a higher incidence rate of osteoporosis and osteoporotic fracture.

Role of inflammation in the aging bones

Chronic inflammation in aging is characterized by increased inflammatory cytokines, bone loss, decreased adaptation, and defective tissue repair in response to injury. Aging leads to inherent changes in mesenchymal stem cell (MSC) differentiation, resulting in impaired osteoblastogenesis. Also, the pro-inflammatory cytokines increase with aging, leading to enhanced myelopoiesis and osteoclastogenesis. Bone marrow macrophages (BMMs) play pivotal roles in osteoblast differentiation, the maintenance of hematopoietic stem cells (HSCs), and subsequent bone repair. However, during aging, little is known about the role of macrophages in the differentiation and function of MSC and HSC. Aged mammals have higher circulating pro-inflammatory cytokines than young adults, supporting the hypothesis of increased inflammation with aging. This review will aid in the understanding of the potential role(s) of pro-inflammatory (M1) and anti-inflammatory (M2) macrophages in differentiation and function of osteoblasts and osteoclasts in relation to aging.

The effect of laminin-1-doped nanoroughened implant surfaces: gene expression and morphological evaluation

Aim. This study aimed to observe the morphological and molecular effect of laminin-1 doping to nanostructured implant surfaces in a rabbit model. Materials and Methods. Nanostructured implants were coated with laminin-1 (test; dilution, 100 μg/mL) and inserted into the rabbit tibiae. Noncoated implants were used as controls. After 2 weeks of healing, the implants were removed and subjected to morphological analysis using scanning electron microscopy (SEM) and gene expression analysis using the real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Results. SEM revealed bony tissue attachment for both control and test implants. Real-time RT-PCR analysis showed that the expression of osteoblast markers RUNX-2, osteocalcin, alkaline phosphatase, and collagen I was higher (1.62-fold, 1.53-fold, 1.97-fold, and 1.04-fold, resp.) for the implants modified by laminin-1 relative to the control. All osteoclast markers investigated in the study presented higher expression on the test implants than controls as follows: tartrate-resistant acid phosphatase (1.67-fold), calcitonin receptor (1.35-fold), and ATPase (1.25-fold). The test implants demonstrated higher expression of inflammatory markers interleukin-10 (1.53-fold) and tumour necrosis factor-α (1.61-fold) relative to controls. Conclusion. The protein-doped surface showed higher gene expression of typical genes involved in the osseointegration cascade than the control surface.

Osseous Metaplasia in Castleman's Disease: A Case Report

Background. Castleman's disease is a benign lymphoproliferative disorder. The disease may be localized or multicentric. Three histologic variants are recognized: hyaline vascular, plasma cell, and mixed types. Case. A 20-year-old man presented with large left axillary mass. The histologic examination of the resected mass showed follicular pattern with large nodules of mantle cells arranged concentrically around atrophic and vascularized germinal centers. There was also some benign-appearing bone trabeculae interspersed with lymphoid tissue. The diagnosis of Castleman's disease, hyaline-vascular type with osseous metaplasia, was made.

Clinical significance of interleukin (IL)-6 in cancer metastasis to bone: potential of anti-IL-6 therapies

Metastatic events to the bone occur frequently in numerous cancer types such as breast, prostate, lung, and renal carcinomas, melanoma, neuroblastoma, and multiple myeloma. Accumulating evidence suggests that the inflammatory cytokine interleukin (IL)-6 is frequently upregulated and is implicated in the ability of cancer cells to metastasize to bone. IL-6 is able to activate various cell signaling cascades that include the STAT (signal transducer and activator of transcription) pathway, the PI3K (phosphatidylinositol-3 kinase) pathway, and the MAPK (mitogen-activated protein kinase) pathway. Activation of these pathways may explain the ability of IL-6 to mediate various aspects of normal and pathogenic bone remodeling, inflammation, cell survival, proliferation, and pro-tumorigenic effects. This review article will discuss the role of IL-6: 1) in bone metabolism, 2) in cancer metastasis to bone, 3) in cancer prognosis, and 4) as potential therapies for metastatic bone cancer.

Osteoblasts are a major source of inflammatory cytokines in the tumor microenvironment of bone metastatic breast cancer

Metastatic breast cancer cells co-opt the cells of the bone to increase their production of inflammatory cytokines. Here, we sought to identify key cytokines expressed by osteoblasts in vitro and in vivo in the presence of MDA-MB-231 metastatic breast cancer cells, including a bone-seeking variant. We hypothesized that osteoblast-derived cytokines increase in the presence of metastatic breast cancer cell conditioned medium (CM), act as chemoattractants for cancer cells, and enhance osteoclast formation. We detected increases in the concentrations of osteoblast-derived IL-6, MCP-1, VEGF, MIP-2, and KC in vitro in culture supernatants from MC3T3-E1 cells in the presence of metastatic breast cancer cell CM and from cancer-bearing femurs ex vivo. A comparison of cancer cell- and osteoblast-derived cytokines revealed that while breast cancer cells expressed the same or equivalent cytokines as the osteoblasts, the breast cancer cells only produced picogram quantities of MCP-1; osteoblasts expressed nanogram amounts. Bone-derived MCP-1 increased in the proximal metaphysis, an area where breast cancer cells preferentially trafficked following intracardiac inoculation in athymic mice. An MDA-MB-231 bone-seeking variant was not different from parental lines. Osteoblast CM was a potent chemoattractant for metastatic breast cancer cells. Furthermore, culture supernatants of osteoblasts treated with breast cancer cell CM enhanced osteoclast formation. These findings suggest that bone metastatic breast cancer cells utilize osteoblast-derived cytokines to facilitate breast cancer cell colonization and survival upon arrival in the bone microenvironment.

Bone remodeling

The skeleton is a metabolically active organ that undergoes continuous remodeling throughout life. Bone remodeling involves the removal of mineralized bone by osteoclasts followed by the formation of bone matrix through the osteoblasts that subsequently become mineralized. The remodeling cycle consists of three consecutive phases: resorption, during which osteoclasts digest old bone; reversal, when mononuclear cells appear on the bone surface; and formation, when osteoblasts lay down new bone until the resorbed bone is completely replaced. Bone remodeling serves to adjust bone architecture to meet changing mechanical needs and it helps to repair microdamages in bone matrix preventing the accumulation of old bone. It also plays an important role in maintaining plasma calcium homeostasis. The regulation of bone remodeling is both systemic and local. The major systemic regulators include parathyroid hormone (PTH), calcitriol, and other hormones such as growth hormone, glucocorticoids, thyroid hormones, and sex hormones. Factors such as insulin-like growth factors (IGFs), prostaglandins, tumor growth factor-beta (TGF-beta), bone morphogenetic proteins (BMP), and cytokines are involved as well. As far as local regulation of bone remodeling is concerned, a large number of cytokines and growth factors that affect bone cell functions have been recently identified. Furthermore, through the RANK/receptor activator of NF-kappa B ligand (RANKL)/osteoprotegerin (OPG) system the processes of bone resorption and formation are tightly coupled allowing a wave of bone formation to follow each cycle of bone resorption, thus maintaining skeletal integrity.

Bone Marrow Mesenchymal Stem Cells Provide an Alternate Pathway of Osteoclast Activation and Bone Destruction by Cancer Cells

The bone is the third most common site of cancer metastasis. To invade the bone, tumor cells produce osteoclast-activating factors that increase bone resorption by osteoclasts. Here we report that human neuroblastoma cells that form osteolytic lesions in vivo do not produce osteoclast-activating factors but rather stimulate osteoclast activity in the presence of human bone marrow mesenchymal stem cells. This alternative pathway of osteoclast activation involves a nonadhesive interaction between neuroblastoma cells and bone marrow mesenchymal stem cells. Stimulated bone marrow mesenchymal stem cells express markedly increased levels of interleukin-6, which is then responsible for osteoclast activation. This report describes a critical role of bone marrow mesenchymal stem cells in bone destruction in cancer.

Calcium sensing and cell signaling processes in the local regulation of osteoclastic bone resorption

The skeletal matrix in terrestrial vertebrates undergoes continual cycles of removal and replacement in the processes of bone growth, repair and remodeling. The osteoclast is uniquely important in bone resorption and thus is implicated in the pathogenesis of clinically important bone and joint diseases. Activated osteoclasts form a resorptive hemivacuole with the bone surface into which they release both acid and osteoclastic lysosomal hydrolases. This article reviews cell physiological studies of the local mechanisms that regulate the resorptive process. These used in vitro methods for the isolation, culture and direct study of the properties of neonatal rat osteoclasts. They demonstrated that both local microvascular agents and products of the bone resorptive process such as ambient Ca2+ could complement longer-range systemic regulatory mechanisms such as those that might be exerted through calcitonin (CT). Thus elevated extracellular [Ca2+], or applications of surrogate divalent cation agonists for Ca2+, inhibited bone resorptive activity and produced parallel increases in cytosolic [Ca2+], cell retraction and longer-term inhibition of enzyme release in isolated rat osteoclasts. These changes showed specificity, inactivation, and voltage-dependent properties that implicated a cell surface Ca2+ receptor (CaR) sensitive to millimolar extracellular [Ca2+]. Pharmacological, biophysical and immunochemical evidence implicated a ryanodine-receptor (RyR) type II isoform in this process and localized it to a unique, surface membrane site, with an outward-facing channel-forming domain. Such a surface RyR might function either directly or indirectly in the process of extracellular [Ca2+] sensing and in turn be modulated by cyclic adenosine diphosphate ribose (cADPr) produced by the ADP-ribosyl cyclase, CD38. The review finishes by speculating about possible detailed models for these transduction events and their possible interactions with other systemic mechanisms involved in Ca2+ homeostasis as well as the possible role of the RyR-based signaling mechanisms in longer-term cell regulatory processes.

NFkappaB: a pivotal transcription factor in prostate cancer metastasis to bone

Prostate cancers frequently metastasize to bone and this accounts for substantial morbidity. We investigated the potential role of the transcription factor NFkappaB as a central regulator of prostate cancer metastasis using the prostate adenocarcinoma cell line, PC-3, in a series of in vitro studies. Wild type PC-3 cells (PC-3.WT) have high basal levels of NFkappaB signaling, otherwise absent in PC-3 cells stably expressing a mutant form of the inhibitory kappa B (IkappaB) protein alpha (PC-3.mIkappaB). Although PC-3.WT cells in co-culture with rat bone marrow cells enhance bone resorption, no increase was observed in co-cultures with PC-3.mIkappaB cells. Similarly, although PC-3.WT cells were invasive in a chicken chorioallantoic membrane extravasation model, PC-3.mIkappaB cells lose this capacity to invade. NFkappaB reciprocally regulated genes involved in cellular invasion, with upregulation of MMP-9 and downregulation of its inhibitor, TIMP-1 in PC-3.WT cells, whereas MMP-9 was downregulated and TIMP-1 was upregulated in PC-3.mIkappaB cells. Finally, high basal gene and protein expression of the osteoclast-activating cytokine IL-6, observed in PC-3.WT cells, was absent in PC-3.mIkappaB cells. These in vitro experiments suggest NFkappaB as an important target to prevent prostate cancer bone metastasis and provide a rationale for further study of this transcription factor in metastatic disease.

Osteoclastogenesis, bone resorption, and osteoclast-based therapeutics

Over the past decade, advances in molecular tools, stem cell differentiation, osteoclast and osteoblast signaling mechanisms, and genetically manipulated mice models have resulted in major breakthroughs in understanding osteoclast biology. This review focuses on key advances in our understanding of molecular mechanisms underlying the formation, function, and survival of osteoclasts. These include key signals mediating osteoclast differentiation, including PU.1, RANK, CSF-1/c-fms, and src, and key specializations of the osteoclast including HCl secretion driven by H+-ATPase and the secretion of collagenolytic enzymes including cathepsin K and matrix metalloproteinases (MMPs). These pathways and highly expressed proteins provide targets for specific therapies to modify bone degradation. The main outstanding issues, basic and translational, will be considered in relation to the osteoclast as a target for antiresorptive therapies.

Disordered osteoclast formation and function in a CD38 (ADP-ribosyl cyclase)-deficient mouse establishes an essential role for CD38 in bone resorption

We have evaluated the role of the ADP-ribosyl cyclase, CD38, in bone remodeling, a process by which the skeleton is being renewed constantly through the coordinated activity of osteoclasts and osteoblasts. CD38 catalyzes the cyclization of its substrate, NAD+, to the Ca2+-releasing second messenger, cyclic ADP-ribose (cADPr). We have shown previously that CD38 is expressed both in osteoblasts and osteoclasts. Its activation in the osteoclast triggers Ca2+ release through ryanodine receptors (RyRs), stimulation of interleukin-6 (IL-6), and an inhibition of bone resorption. Here, we have examined the consequences of deleting the CD38 gene in mice on skeletal remodeling. We report that CD38-/- mice displayed a markedly reduced bone mineral density (BMD) at the femur, tibia, and lumbar spine at 3 months and at the lumbar spine at 4 months, with full normalization of the BMD at all sites at 5 months. The osteoporosis at 3 months was accompanied by a reduction in primary spongiosa and increased osteoclast surfaces on histomorphometric analysis. Hematopoetic stem cells isolated ex vivo from CD38-/- mice showed a dramatic approximately fourfold increase in osteoclast formation in response to incubation for 6 days with RANK-L and M-CSF. The osteoclasts so formed in these cultures showed a approximately 2.5-fold increase in resorptive activity compared with wild-type cells. However, when adherent bone marrow stromal cells were allowed to mature into alkaline phosphatase-positive colony-forming units (CFU-Fs), those derived from CD38-/- mice showed a significant reduction in differentiation compared with wild-type cells. Real-time RT-PCR on mRNA isolated from osteoclasts at day 6 showed a significant reduction in IL-6 and IL-6 receptor mRNA, together with significant decreases in the expression of all calcineurin A isoforms, alpha, beta, and gamma. These findings establish a critical role for CD38 in osteoclast formation and bone resorption. We speculate that CD38 functions as a cellular NAD+ "sensor," particularly during periods of active motility and secretion.