Knockout of the murine prostaglandin EP2 receptor impairs osteoclastogenesis in vitro

Osteocyte-mediated mechanical response controls osteoblast differentiation and function

Low bone mass is a pervasive global health concern, with implications for osteoporosis, frailty, disability, and mortality. Lifestyle factors, including sedentary habits, metabolic dysfunction, and an aging population, contribute to the escalating prevalence of osteopenia and osteoporosis. The application of mechanical load to bone through physical activity and exercise prevents bone loss, while sufficient mechanical load stimulates new bone mass acquisition. Osteocytes, cells embedded within the bone, receive mechanical signals and translate these mechanical cues into biological signals, termed mechano-transduction. Mechano-transduction signals regulate other bone resident cells, such as osteoblasts and osteoclasts, to orchestrate changes in bone mass. This review explores the mechanisms through which osteocyte-mediated response to mechanical loading regulates osteoblast differentiation and bone formation. An overview of bone cell biology and the impact of mechanical load will be provided, with emphasis on the mechanical cues, mechano-transduction pathways, and factors that direct progenitor cells toward the osteoblast lineage. While there are a wide range of clinically available treatments for osteoporosis, the majority act through manipulation of the osteoclast and may have significant disadvantages. Despite the central role of osteoblasts to the deposition of new bone, few therapies directly target osteoblasts for the preservation of bone mass. Improved understanding of the mechanisms leading to osteoblastogenesis may reveal novel targets for translational investigation.

Associations of Neutrophil-to-Lymphocyte Ratio, Platelet-to-Lymphocyte Ratio and Monocyte-to-Lymphocyte Ratio with Osteoporosis and Incident Vertebral Fracture in Postmenopausal Women with Rheumatoid Arthritis: A Single-Center Retrospective Cohort Study

Background and Objectives: We investigated whether nutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphoycte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR) are associated with the presence of osteoporosis (OP) and vertebral fractures in patients with rheumatoid arthritis (RA). Materials and Methods: This retrospective cohort study included 413 postmenopausal patients with RA and 200 healthy controls who underwent dual-energy X-ray absorptiometry (DEXA) between January 2005 and December 2017. DEXA examination data were defined as the index date, and all laboratory values were measured within one month from the index date. OP was defined as a T-score < −2.5, and incident vertebral fractures were defined as the first occurrence of non-traumatic fractures after the index date. NLR, PLR, and MLR measures were dichotomized by a median split (low vs. high). Results: The median NLR, PLR, and MLR in RA patients were significantly higher than those in controls. The frequencies of OP of the lumbar spine, hip, and either site in postmenopausal patients with RA were 24.7%, 15.5%, and 32%, respectively, and were significantly higher than those in controls. After adjusting for confounding factors, a high baseline NLR was significantly associated with OP at either site (OR = 1.61, p = 0.041). In addition, high baseline NLR (OR = 2.11, p = 0.025) and PLR (OR = 2.3, p = 0.011) were related with the presence OP at hip. During the follow-up period, 53 (12.8%) patients with RA developed vertebral fractures incidentally. In multivariable Cox regression models, a high baseline NLR (HR = 4.72, p < 0.001), PLR (HR = 1.96, p = 0.024), and MLR (HR = 2.64, p = 0.002) were independently associated with a higher risk of incidental vertebral fractures. Conclusions: Our data suggest that NLR, PLR, and MLR can be used as potential markers of systemic bone loss among individuals with RA.

Pharmacological antagonism of EP2 receptor does not modify basal cardiovascular and respiratory function, blood cell counts, and bone morphology in animal models

The EP2 receptor has emerged as a therapeutic target with exacerbating role in disease pathology for a variety of peripheral and central nervous system disorders. We and others have recently demonstrated beneficial effects of EP2 antagonists in preclinical models of neuroinflammation and peripheral inflammation. However, it was earlier reported that mice with global EP2 knockout (KO) display adverse phenotypes on fertility and blood pressure. Other studies indicated that EP2 activation with an agonist has a beneficial effect of healing fractured bone in animal models. These results impeded the development of EP2 antagonists, and EP2 antagonism as therapeutic strategy. To determine whether treatment with EP2 antagonist mimics the adverse phenotypes of the EP2 global KO mouse, we tested two EP2 antagonists TG11-77. HCl and TG6-10-1 in mice and rats while they are on normal or high-salt diet, and by two different administration protocols (acute and chronic). There were no adverse effects of the antagonists on systolic and diastolic blood pressure, heart rate, respiratory function in mice and rats regardless of rodents being on a regular or high salt diet. Furthermore, chronic exposure to TG11-77. HCl produced no adverse effects on blood cell counts, bone-volume and bone-mineral density in mice. Our findings argue against adverse effects on cardiovascular and respiratory systems, blood counts and bone structure in healthy rodents from the use of small molecule reversible antagonists for EP2, in contrast to the genetic ablation model. This study paves the way for advancing therapeutic applications of EP2 antagonists against diseases involving EP2 dysfunction.

Investigating global gene expression changes in a murine model of cherubism

Cherubism is a rare genetic disorder caused primarily by mutations in SH3BP2 resulting in excessive bone resorption and fibrous tissue overgrowth in the lower portions of the face. Bone marrow derived cell cultures derived from a murine model of cherubism display poor osteogenesis and spontaneous osteoclast formation. To develop a deeper understanding for the potential underlying mechanisms contributing to these phenotypes in mice, we compared global gene expression changes in hematopoietic and mesenchymal cell populations between cherubism and wild type mice. In the hematopoietic population, not surprisingly, upregulated genes were significantly enriched for functions related to osteoclastogenesis. However, these upregulated genes were also significantly enriched for functions associated with inflammation including arachidonic acid/prostaglandin signaling, regulators of coagulation and autoinflammation, extracellular matrix remodeling, and chemokine expression. In the mesenchymal population, we observed down regulation of osteoblast and adventitial reticular cell marker genes. Regulators of BMP and Wnt pathway associated genes showed numerous changes in gene expression, likely implicating the down regulation of BMP signaling and possibly the activation of certain Wnt pathways. Analyses of the cherubism derived mesenchymal population also revealed interesting changes in gene expression related to inflammation including the expression of distinct granzymes, chemokines, and sulfotransferases. These studies reveal complex changes in gene expression elicited from a cherubic mutation in Sh3bp2 that are informative to the mechanisms responding to inflammatory stimuli and repressing osteogenesis. The outcomes of this work are likely to have relevance not only to cherubism, but other inflammatory conditions impacting the skeleton.

Therapeutic potentials and modulatory mechanisms of fatty acids in bone

Bone metabolism is a lifelong process that includes bone formation and resorption. Osteoblasts and osteoclasts are the predominant cell types associated with bone metabolism, which is facilitated by other cells such as bone marrow mesenchymal stem cells (BMMSCs), osteocytes and chondrocytes. As an important component in our daily diet, fatty acids are mainly categorized as long‐chain fatty acids including polyunsaturated fatty acids (LCPUFAs), monounsaturated fatty acids (LCMUFAs), saturated fatty acids (LCSFAs), medium‐/short‐chain fatty acids (MCFAs/SCFAs) as well as their metabolites. Fatty acids are closely associated with bone metabolism and associated bone disorders. In this review, we summarized the important roles and potential therapeutic implications of fatty acids in multiple bone disorders, reviewed the diverse range of critical effects displayed by fatty acids on bone metabolism, and elucidated their modulatory roles and mechanisms on specific bone cell types. The evidence supporting close implications of fatty acids in bone metabolism and disorders suggests fatty acids as potential therapeutic and nutritional agents for the treatment and prevention of metabolic bone diseases.

In Vivo Bone Effects of a Novel Bisphosphonate-EP4a Conjugate Drug (C3) for Reversing Osteoporotic Bone Loss in an Ovariectomized Rat Model

Pathological bone loss is a regular feature of postmenopausal osteoporosis, and the microstructural changes along with the bone loss make the individual prone to getting hip, spine, and wrist fractures. We have developed a new conjugate drug named C3, which has a synthetic, stable EP4 agonist (EP4a) covalently linked to an inactive alendronate (ALN) that binds to bone and allows physiological remodeling. After losing bone for 12 weeks, seven groups of rats were treated for 8 weeks via tail‐vein injection. The groups were: C3 conjugate at low and high doses, vehicle‐treated ovariectomy (OVX) and sham, C1 (a similar conjugate, but with active ALN at high dose), inactive ALN alone, and a mixture of unconjugated ALN and EP4a to evaluate the conjugation effects. Bone turnover was determined by dynamic and static histomorphometry; μCT was employed to determine bone microarchitecture; and bone mechanical properties were evaluated via biomechanical testing. Treatment with C3 significantly increased trabecular bone volume and vertebral BMD versus OVX controls. There was also significant improvement in the vertebral load‐bearing abilities and stimulation of bone formation in femurs after C3 treatment. This preclinical research revealed that C3 resulted in significant anabolic effects on trabecular bone, and EP4a and ALN conjugation components are vital to conjugate anabolic efficacy. A combined therapy using an EP4 selective agonist anabolic agent linked to an inactive ALN is presented here that produces significant anabolic effects, allows bone remodeling, and has the potential for treating postmenopausal osteoporosis or other diseases where bone strengthening would be beneficial. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Omega-3 fatty acids and meloxicam supplementation and the incidence and histopathological changes associated with femoral head syndrome in broilers

Femoral head separation (FHS) is one of the problems commonly found in fast growing-type broilers that resulted in joint inflammation leading to lameness and poor animal welfare. This study aimed to examine the alimentary effects of omega-3 fatty acids (DHA) and meloxicam on the incidence of FHS in relation with changes in pathological features and serum concentrations of TNFα and IL1β in broilers. A total number of 1152 male day-old Cobb 500 broilers were divided into four groups. The chicks in T1 (Control) received the basal diet. Chicks in T2 to T4 were given burden of a modified speed bump, in which the chicks in T2 received the basal diet, and the chicks in T3 and T4 received 2% All-G-Rich (16% DHA) in the basal diet and meloxicam in drinking water (0.5 mg/kg BW) during Days 22–43 of age, respectively. It was demonstrated that the incidence of FHS in T4 was the smallest (P &lt; 0.05) among groups although the incidence of FHS was not increased by modified speed bump itself. Although BW (and average daily gain) in T3 was the smallest, but the incidence of FHS was not decreased. An osteochondrosis cleft during histopathological examination could be detected even in the normal gross lesions. Serum concentrations in TNFα and IL1β were not different among groups. In conclusion, meloxicam as an anti-inflammatory drug was useful to alleviate the gross pathological changes of FHS whereas DHA was not effective at the used dosage. Studies on histopathological changes at the beginning of FHS lesion are necessary.

TNFα Increases RANKL Expression via PGE₂-Induced Activation of NFATc1

Tumor necrosis factor α (TNFα) is known to upregulate the expression of receptor activator of NF-κB ligand (RANKL). We investigated the role of the calcineurin/nuclear factor of activated T-cells (NFAT) signaling pathway in TNFα-induced RANKL expression in C2C12 and primary cultured mouse calvarial cells. TNFα-induced RANKL expression was blocked by the calcineurin/NFAT pathway inhibitors. TNFα increased NFAT transcriptional activity and subsequent RANKL promoter binding. Mutations in the NFAT-binding element (MT(N)) suppressed TNFα-induced RANKL promoter activity. TNFα increased prostaglandin E2 (PGE₂) production, which in turn enhanced NFAT transcriptional activity and binding to the RANKL promoter. MT(N) suppressed PGE₂-induced RANKL promoter activity. TNFα and PGE₂ increased the expression of RANKL, NFAT cytoplasmic-1 (NFATc1), cAMP response element-binding protein (CREB), and cyclooxygenase 2 (COX2); which increment was suppressed by indomethacin, a COX inhibitor. Mutations in the CRE-like element blocked PGE₂-induced RANKL promoter activity. PGE₂ induced the binding of CREB to the RANKL promoter, whereas TNFα increased the binding of both CREB and NFATc1 to this promoter through a process blocked by indomethacin. The PGE₂ receptor antagonists AH6809 and AH23848 blocked TNFα-induced expression of RANKL, NFATc1, and CREB; transcriptional activity of NFAT; and binding of NFATc1 or CREB to the RANKL promoter. These results suggest that TNFα-induced RANKL expression depends on PGE₂ production and subsequent transcriptional activation/enhanced binding of NFATc1 and CREB to the RANKL promoter.

Phospholipase A2-activating protein is associated with a novel form of leukoencephalopathy

Leukoencephalopathies are a group of white matter disorders related to abnormal formation, maintenance, and turnover of myelin in the central nervous system. These disorders of the brain are categorized according to neuroradiological and pathophysiological criteria. Herein, we have identified a unique form of leukoencephalopathy in seven patients presenting at ages 2 to 4 months with progressive microcephaly, spastic quadriparesis, and global developmental delay. Clinical, metabolic, and imaging characterization of seven patients followed by homozygosity mapping and linkage analysis were performed. Next generation sequencing, bioinformatics, and segregation analyses followed, to determine a loss of function sequence variation in the phospholipase A₂-activating protein encoding gene (PLAA). Expression and functional studies of the encoded protein were performed and included measurement of prostaglandin E₂ and cytosolic phospholipase A₂ activity in membrane fractions of fibroblasts derived from patients and healthy controls. Plaa-null mice were generated and prostaglandin E₂ levels were measured in different tissues. The novel phenotype of our patients segregated with a homozygous loss-of-function sequence variant, causing the substitution of leucine at position 752 to phenylalanine, in PLAA, which causes disruption of the protein's ability to induce prostaglandin E₂ and cytosolic phospholipase A₂ synthesis in patients' fibroblasts. Plaa-null mice were perinatal lethal with reduced brain levels of prostaglandin E₂ The non-functional phospholipase A₂-activating protein and the associated neurological phenotype, reported herein for the first time, join other complex phospholipid defects that cause leukoencephalopathies in humans, emphasizing the importance of this axis in white matter development and maintenance.

Bone Remodeling in Post-menopausal Osteoporosis

Bone mass in the skeleton is dependent on the coordinated activities of bone-forming osteoblasts and bone-resorbing osteoclasts in discrete bone multi-cellular units. Remodeling of bone in these units is important not only for maintaining bone mass, but also to repair microdamage, to prevent accumulation of too much old bone, and for mineral homeostasis. The activities of osteoblasts and osteoclasts are controlled by a variety of hormones and cytokines, as well as by mechanical loading. Most importantly, sex hormones are very crucial for keeping bone mass in balance, and the lack of either estrogen or testosterone leads to decreased bone mass and increased risk for osteoporosis. The prevalence of osteoporotic fractures is increasing dramatically in the Western part of the world and is a major health problem in many countries. In the present review, the cellular and molecular mechanisms controlling bone remodeling and the influence of sex hormones on these processes are summarized. In a separate paper in this issue, the pathogenesis of post-menopausal osteoporosis will be compared with that of inflammation-induced bone remodeling, including the evidence for and against the hypothesis that concomitant post-menopausal osteoporotic disease influences the progression of periodontal disease.

In vivo effects of two novel ALN-EP4a conjugate drugs on bone in the ovariectomized rat model for reversing postmenopausal bone loss

Two alendronate-EP4 agonist (ALN-EP4a) conjugate drugs, C1 and C2, which differ in structure by a short linker molecule, were evaluated in ovariectomized (OVX) rats for their anabolic effects. We showed that C1 led to significant anabolic effects on cortical and trabecular bone while anabolic effects associated with C2 were minimal.

INTRODUCTION

EP4as were covalently linked to ALN to create ALN-EP4a conjugate anabolic bone drugs, C1 and C2, which differ in structure by a short linker molecule in C1. When administered systemically, C1 and C2 are delivered to bone through targeted binding of ALN, where local hydrolytic enzymes liberate EP4a from ALN to exert anabolic effects. Here, we compare effects of C1 to C2 in a curative in vivo study.

METHODS

Three-month-old female Sprague Dawley rats were OVX or sham operated and allowed to lose bone for 3 months. Animals were then treated via tail vein injections for 3 months and sacrificed. Treatment groups were as follows: C1L (5 mg/kg biweekly), C1H (5 mg/kg weekly), C2L (15 mg/kg monthly), C2H (15 mg/kg biweekly), OVX and sham control (phosphate-buffered saline (PBS) biweekly), and ALN/EP4a-unconjugated mixture (0.75 mg/kg each biweekly).

RESULTS

MicroCT analysis showed that C1H treatment significantly increased vertebral bone mineral density (vBMD) and trabecular bone volume versus OVX controls while C2 treatments did not. Biomechanical testing showed that C1H treatment but not C2 treatments led to significant improvement in the load bearing abilities of the vertebrae compared to OVX controls. C1 stimulated endocortical bone formation and increased load bearing in femurs, while C2 did not.

CONCLUSIONS

We showed that C1 led to significant anabolic effects on cortical and trabecular bone while anabolic effects associated with C2 were minimal. These results led us to hypothesize a mode of action by which presence of a linker is crucial in facilitating the anabolic effects of EP4a when dosed as a prodrug with ALN.

Activation of Protein Kinase A in Mature Osteoblasts Promotes a Major Bone Anabolic Response

Protein kinase A (PKA) regulates osteoblast cell function in vitro and is activated by important bone mass modulating agents. We determined whether PKA activation in osteoblasts is sufficient to mediate a bone anabolic response. Thus, a mouse model conditionally expressing a constitutively active PKA (CA-PKA) in osteoblasts (CA-PKA-OB mouse) was developed by crossing a 2.3-kb α1 (I)-collagen promoter-Cre mouse with a floxed-CA-PKA mouse. Primary osteoblasts from the CA-PKA-OB mice exhibited higher basal PKA activity than those from control mice. Microcomputed tomographic analysis revealed that CA-PKA-OB female mice had an 8.6-fold increase in femoral but only 1.16-fold increase in lumbar 5 vertebral bone volume/total volume. Femur cortical thickness and volume were also higher in the CA-PKA-OB mice. In contrast, alterations in many femoral microcomputed tomographic parameters in male CA-PKA-OB mice were modest. Interestingly, the 3-dimensional structure model index was substantially lower both in femur and lumbar 5 of male and female CA-PKA-OB mice, reflecting an increase in the plate to rod-like structure ratio. In agreement, femurs from female CA-PKA-OB mice had greater load to failure and were stiffer compared with those of control mice. Furthermore, the CA-PKA-OB mice had higher levels of serum bone turnover markers and increased osteoblast and osteoclast numbers per total tissue area compared with control animals. In summary, constitutive activation of PKA in osteoblasts is sufficient to increase bone mass and favorably modify bone architecture and improve mechanical properties. PKA activation in mature osteoblasts is, therefore, an important target for designing anabolic drugs for treating diseases with bone loss.

PTGER4 gene variant rs76523431 is a candidate risk factor for radiological joint damage in rheumatoid arthritis patients: a genetic study of six cohorts

Introduction

Prostaglandin E receptor 4 (PTGER4) is implicated in immune regulation and bone metabolism. The aim of this study was to analyze its role in radiological joint damage in rheumatoid arthritis (RA).

Methods

Six independent cohorts of patients with RA of European or North American descent were included, comprising 1789 patients with 5083 sets of X-rays. The Hospital Clínico San Carlos Rheumatoid Arthritis, Princesa Early Arthritis Register Longitudinal study, and Hospital Universitario de La Paz early arthritis (Spain) cohorts were used as discovery cohorts, and the Leiden Early Arthritis Clinic (The Netherlands), Wichita (United States), and National Databank for Rheumatic Diseases (United States and Canada) cohorts as replication cohorts. First, the PTGER4 rs6896969 single-nucleotide polymorphism (SNP) was genotyped using TaqMan assays and available Illumina Immunochip data and studied in the discovery and replication cohorts. Second, the PTGER4 gene and adjacent regions were analyzed using Immunochip genotyping data in the discovery cohorts. On the basis of pooled p values, linkage disequilibrium structure of the region, and location in regions with transcriptional properties, SNPs were selected for replication. The results from discovery, replication, and overall cohorts were pooled using inverse-variance–weighted meta-analysis. Influence of the polymorphisms on the overall radiological damage (constant effect) and on damage progression over time (time-varying effect) was analyzed.

Results

The rs6896969 polymorphism showed a significant association with radiological damage in the constant effect pooled analysis of the discovery cohorts, although no significant association was observed in the replication cohorts or the overall pooled analysis. Regarding the analysis of the PTGER4 region, 976 variants were analyzed in the discovery cohorts. From the constant and time-varying effect analyses, 12 and 20 SNPs, respectively, were selected for replication. Only the rs76523431 variant showed a significant association with radiographic progression in the time-varying effect pooled analysis of the discovery, replication, and overall cohorts. The overall pooled effect size was 1.10 (95 % confidence interval 1.05–1.14, p = 2.10 × 10⁻⁵), meaning that radiographic yearly progression was 10 % greater for each copy of the minor allele.

Conclusions

The PTGER4 gene is a candidate risk factor for radiological progression in RA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0830-z) contains supplementary material, which is available to authorized users.

Production and Functional Characterization of Murine Osteoclasts Differentiated from ER-Hoxb8-Immortalized Myeloid Progenitor Cells

In vitro differentiation into functional osteoclasts is routinely achieved by incubation of embryonic stem cells, induced pluripotent stem cells, or primary as well as cryopreserved spleen and bone marrow-derived cells with soluble receptor activator of nuclear factor kappa-B ligand and macrophage colony-stimulating factor. Additionally, osteoclasts can be derived from co-cultures with osteoblasts or by direct administration of soluble receptor activator of nuclear factor kappa-B ligand to RAW 264.7 macrophage lineage cells. However, despite their benefits for osteoclast-associated research, these different methods have several drawbacks with respect to differentiation yields, time and animal consumption, storage life of progenitor cells or the limited potential for genetic manipulation of osteoclast precursors. In the present study, we therefore established a novel protocol for the differentiation of osteoclasts from murine ER-Hoxb8-immortalized myeloid stem cells. We isolated and immortalized bone marrow cells from wild type and genetically manipulated mouse lines, optimized protocols for osteoclast differentiation and compared these cells to osteoclasts derived from conventional sources. In vitro generated ER-Hoxb8 osteoclasts displayed typical osteoclast characteristics such as multi-nucleation, tartrate-resistant acid phosphatase staining of supernatants and cells, F-actin ring formation and bone resorption activity. Furthermore, the osteoclast differentiation time course was traced on a gene expression level. Increased expression of osteoclast-specific genes and decreased expression of stem cell marker genes during differentiation of osteoclasts from ER-Hoxb8-immortalized myeloid progenitor cells were detected by gene array and confirmed by semi-quantitative and quantitative RT-PCR approaches. In summary, we established a novel method for the quantitative production of murine bona fide osteoclasts from ER-Hoxb8 stem cells generated from wild type or genetically manipulated mouse lines. These cells represent a standardized and theoretically unlimited source for osteoclast-associated research projects.

Enterococcus faecalis promotes osteoclastogenesis and semaphorin 4D expression

Enterococcus faecalis is considered a major bacterial pathogen implicated in endodontic infections and contributes considerably to periapical periodontitis. This study aimed to investigate the potential mechanisms by which E. faecalis accounts for the bone destruction in periapical periodontitis in vitro. Osteoclast precursor RAW264.7 cells were treated with E. faecalis ATCC 29212 and a wild strain of E. faecalis derived clinically from an infected root canal. The results showed that, to some extent, E. faecalis induced the RAW264.7 cells to form tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclast-like cells. This pathogen markedly stimulated RAW264.7 cells to express semaphorin 4D (Sema4D), which inhibits bone formation. Once RAW264.7 cells were primed by low-dose receptor activator of nuclear factor-kappa B ligand (RANKL), E. faecalis could significantly increase the production of TRAP-positive multinucleated cells and up-regulate the expression of osteoclast-specific markers, including NFATc1, TRAP and cathepsin K. Both p38 and ERK1/2 MAPK signaling pathways were activated by E. faecalis in RANKL-primed RAW264.7 cells, and meanwhile the expression of Sema4D was highly increased. In conclusion, E. faecalis may greatly contribute to the bone resorption in periapical periodontitis by promoting RANKL-dependent osteoclastogenesis and expression of Sema4D through activation of p38 and ERK1/2 MAPK signaling pathways.

RANKL inhibition blocks osteolytic lesions and reduces skeletal tumor burden in models of non-small-cell lung cancer bone metastases

INTRODUCTION

Bone metastasis is a serious complication in patients with lung cancer, occurring in up to 40% of patients. Tumor cell-mediated osteolysis occurs ultimately through induction of RANK ligand (RANKL) within the bone stroma although this hypothesis has not been tested extensively in the setting of non-small-cell lung cancer (NSCLC). By using two novel NSCLC bone metastasis mouse models, we examined the effects of RANKL inhibition on osteolysis and tumor progression.

METHODS

We treated mice bearing skeletal NSCLC tumors with osteoprotegerin-Fc (OPG-Fc) to assess whether osteoclast inhibition through RANKL inhibition would affect bone metastases at early or late stages of bone colonization. Progression of skeletal tumor was determined by radiography, longitudinal bioluminescent imaging, and histological analyses.

RESULTS

OPG-Fc reduced development and progression of radiographically evident osteolytic lesions and also significantly reduced skeletal tumor progression in both NSCLC bone metastasis models. In the H1299 human NSCLC bone metastasis model, OPG-Fc plus docetaxel in combination resulted in significantly greater inhibition of skeletal tumor growth compared with either single agent alone. The observed ability of RANKL inhibition to reduce NSCLC osteolytic bone destruction or skeletal tumor burden was associated with decreases in tumor-associated osteoclasts.

CONCLUSIONS

These results demonstrate that RANKL is required for the development of tumor-induced osteolytic bone destruction caused by NSCLC cells in vivo. RANKL inhibition also reduced skeletal tumor burden, presumably through the indirect mechanism of blocking tumor-induced osteoclastogenesis and resultant production of growth factors and calcium from the bone microenvironment. RANKL inhibition also provided an additive benefit to docetaxel treatment by augmenting the reduction of tumor burden.

The protocol for the isolation and cryopreservation of osteoclast precursors from mouse bone marrow and spleen

Osteoclasts are responsible for physiological bone remodeling as well as pathological bone destruction in osteoporosis, periodontitis and rheumatoid arthritis, and thus represent a pharmacological target for drug development. We aimed to characterize and compare the cytokine-induced osteoclastogenesis of bone marrow and spleen precursors. Established protocols used to generate osteoclasts from bone marrow were modified to examine osteoclastogenesis of the spleen cells of healthy mice. Osteoclast formation was successfully induced from spleen precursors using receptor activator of nuclear factor κB ligand (50 ng/ml) and macrophage colony stimulating factor (50 ng/ml). Compared to bone marrow cultures, differentiation from spleen required a longer cultivation time (9 days for spleen, as compared to 5 days for marrow cultures) and a higher plating density of non-adherent cells (75,000/cm(2) for spleen, as compared to 50,000/cm(2) for bone marrow). Osteoclasts generated from spleen precursors expressed osteoclast marker genes calcitonin receptor, cathepsin K and matrix metalloproteinase 9 and were capable of resorbing hydroxyapatite. The differentiation capacity of spleen and bone marrow precursors was comparable for BALB/c, C57BL/6 and FVB mice. We also developed and tested a cryopreservation protocol for the osteoclast precursors. While 70-80 % of cells were lost during the first week of freezing, during the subsequent 5 weeks the losses were within 2-5 % per week. Osteoclastogenesis from the recovered bone marrow precursors was successful up to 5 weeks after freezing. Spleen precursors retained their osteoclastogenic capacity for 1 week after freezing, but not thereafter. The described protocol is useful for the studies of genetically modified animals as well as for screening new osteoclast-targeting therapeutics.

Prostaglandin E2 acts via bone marrow macrophages to block PTH-stimulated osteoblast differentiation in vitro

Intermittent PTH is the major anabolic therapy for osteoporosis while continuous PTH causes bone loss. PTH acts on the osteoblast (OB) lineage to regulate bone resorption and formation. PTH also induces cyclooxygenase-2 (COX-2), producing prostaglandin E2 (PGE(2)) that can act on both OBs and osteoclasts (OCs). Because intermittent PTH is more anabolic in Cox-2 knockout (KO) than wild type (WT) mice, we hypothesized COX-2 might contribute to the effects of continuous PTH by suppressing PTH-stimulated differentiation of mesenchymal stem cells into OBs. We compared effects of continuous PTH on bone marrow stromal cells (BMSCs) and primary OBs (POBs) from Cox-2 KO mice, mice with deletion of PGE(2) receptors (Ptger(4) and Ptger(2) KO mice), and WT controls. PTH increased OB differentiation in BMSCs only in the absence of COX-2 expression or activity. In the absence of COX-2, PTH stimulated differentiation if added during the first week of culture. In Cox-2 KO BMSCs, PTH-stimulated differentiation was prevented by adding PGE(2) to cultures. Co-culture of POBs with M-CSF-expanded bone marrow macrophages (BMMs) showed that the inhibition of PTH-stimulated OB differentiation required not only COX-2 or PGE(2) but also BMMs. Sufficient PGE(2) to mediate the inhibitory effect was made by either WT POBs or WT BMMs. The inhibitory effect mediated by COX-2/PGE(2) was transferred by conditioned media from RANKL-treated BMMs and could be blocked by osteoprotegerin, which interferes with RANKL binding to its receptor on OC lineage cells. Deletion of Ptger(4), but not Ptger(2), in BMMs prevented the inhibition of PTH-stimulated OB differentiation. As expected, PGE(2) also stimulated OB differentiation, but when given in combination with PTH, the stimulatory effects of both were abrogated. These data suggest that PGE(2), acting via EP4R on BMMs committed to the OC lineage, stimulated secretion of a factor or factors that acted to suppress PTH-stimulated OB differentiation. This suppression of OB differentiation could contribute to the bone loss seen with continuous PTH in vivo.

Hydrogen sulphide-releasing diclofenac derivatives inhibit breast cancer-induced osteoclastogenesis in vitro and prevent osteolysis ex vivo

BACKGROUND AND PURPOSE

Hydrogen sulphide (H(2)S) and prostaglandins are both involved in inflammation, cancer and bone turnover, and non-steroidal anti-inflammatory drugs (NSAIDs) and H(2)S donors exhibit anti-inflammatory and anti-tumour properties. H(2)S-releasing diclofenac (S-DCF) derivatives are a novel class of NSAIDs combining the properties of a H(2)S donor with those of a conventional NSAID.

EXPERIMENTAL APPROACH

We studied the effects of the S-DCF derivatives ACS15 and ACS32 on osteoclast and osteoblast differentiation and activity in vitro, human and mouse breast cancer cells support for osteoclast formation and signalling in vitro, and osteolysis ex vivo.

KEY RESULTS

The S-diclofenac derivatives ACS15 and ACS32 inhibited the increase in osteoclast formation induced by human MDA-MB-231 and MCF-7 and mouse 4T1 breast cancer cells without affecting breast cancer cell viability. Conditioned media from human MDA-MB-231 cells enhanced IκB phosphorylation and osteoclast formation and these effects were significantly inhibited following treatment by ACS15 and ACS32, whereas the parent compound diclofenac had no effects. ACS15 and ACS32 inhibited receptor activator of NFκB ligand-induced osteoclast formation and resorption, and caused caspase-3 activation and apoptosis in mature osteoclasts via a mechanism dependent on IKK/NFκB inhibition. In calvaria organ culture, human MDA-MB-231 cells caused osteolysis, and this effect was completely prevented following treatment with ACS15 and ACS32.

CONCLUSIONS AND IMPLICATIONS

S-diclofenac derivatives inhibit osteoclast formation and activity, suppress breast cancer cell support for osteoclastogenesis and prevent osteolysis. This suggests that H(2)S-releasing diclofenac derivatives exhibit anti-resorptive properties, which might be of clinical value in the treatment of osteolytic bone disease.

The effect of enamel matrix derivative (Emdogain®) on gene expression profiles of human primary alveolar bone cells

Emdogain® is frequently used in regenerative periodontal treatment. Understanding its effect on gene expression of bone cells would enable new products and pathways promoting bone formation to be established. The aim of the study was to analyse the effect of Emdogain® on expression profiles of human-derived bone cells with the help of the micro-array, and subsequent validation. Bone was harvested from non-smoking patients during dental implant surgery. After outgrowth, cells were cultured until subconfluence, treated for 24 h with either Emdogain® (100 µg/ml) or control medium, and subsequently RNA was isolated and micro-array was performed. The most important genes demonstrated by micro-array data were confirmed by qPCR and ELISA tests. Emdogain tipped the balance between genes expressed for bone formation and bone resorption towards a more anabolic effect, by interaction of the PGE2 pathway and inhibition of IL-7 production. In addition the results of the present study indicate that Emdogain possibly has an effect on gene expression for extracellular matrix formation of human bone cells, in particular on bone matrix formation and on proliferation and differentiation. With the micro-array and the subsequent validation, the genes possibly involved in Emdogain action on bone cells were identified. These results can contribute to establishing new products and pathways promoting bone formation.

Cyclic nucleotides and phosphodiesterases in monocytic differentiation

Monocytes are immune cells that can differentiate into a number of cell types including macrophages, dendritic cells, and osteoclasts upon exposure to various cytokines. The phenotypes of these differentiated cells are highly heterogeneous and their differentiation can be affected by the cyclic nucleotides, 3'-5'-cyclic adenosine monophosphate (cAMP) and 3'-5'-cyclic guanosine monophosphate (cGMP). The intracellular levels of cAMP and cGMP are controlled through regulation of production by adenylyl and guanylyl cyclases and through degradation by cyclic nucleotide phosphodiesterases (PDEs). PDE inhibition and subsequent changes in cyclic nucleotide levels can alter the final phenotype of a differentiating monocyte with regards to surface marker expression, gene expression, or changes in secreted chemokine and cytokine levels. The differentiation process itself can also be either inhibited or augmented by changes in cyclic nucleotide levels, depending on the system being studied and the timing of cyclic nucleotide elevation. This chapter explores the effects of PDE inhibition and increases in cGMP and cAMP on monocytic differentiation into osteoclasts, dendritic cells, and macrophages.

Microsomal prostaglandin E synthase-1 enhances bone cancer growth and bone cancer-related pain behaviors in mice

AIMS

Nonsteroidal anti-inflammatory drugs are a therapeutic modality for chronic cancer pain arising from bone metastases. Chronic administration of a cyclooxygenase (COX)-2 inhibitor is effective to bone cancer-related pain. However, adverse cardiovascular effects have limited COX-2 inhibitor therapy, and elucidation of better targets for blocking prostaglandin (PG) biosynthesis is necessary. Microsomal PGE synthase-1 (mPGES-1) is an inducible enzyme that catalyzes isomerization of the endoperoxide PGH(2) to PGE(2). To investigate the validity of mPGES-1 as a therapeutic target, we evaluated bone cancer pain-related behaviors in mPGES-1 knockout (PGES-1-/-) mice.

MAIN METHODS

Lewis lung carcinoma cells (LLCCs) were injected into the intramedullary space of the femur of wild-type (WT) and PGES-1-/- mice. Pain-related behaviors were evaluated.

KEY FINDINGS

PGES-1-/- mice exhibited reduced tumor growth in bone marrow compared to WT. The expression of pro-calcitonin gene-related peptide (CGPR) in the dorsal root ganglia of L(1-5) was significantly higher in WT mice at day 14, whereas it was unchanged in mPGES-1 mice. In the observation of pain-related behaviors, mPGES-1-/- mice exhibited significantly fewer spontaneous flinches and their onset was several days later than WT. The appearance of other pain-related behaviors in mPGES-1-/- mice was also delayed as compared to WT. LLCC-injected WT mice treated with a COX-2 inhibitor, celecoxib, exhibited similar temporal changes to mPGES1-/-.

SIGNIFICANCE

The present results suggest that mPGES-1 plays a crucial role in the enhancement of bone cancer growth and bone cancer pain, and that inhibition of mPGES-1 may have clinical utility in the management of bone cancer pain.

Sodium butyrate induces the production of cyclooxygenases and prostaglandin E₂ in ROS 17/2.8 osteoblastic cells

OBJECTIVE

Sodium butyrate (butyric acid; BA) is a major metabolic by-product of the anaerobic periodontopathic bacteria present in subgingival plaque. We examined the effects of BA and/or indomethacin on cell proliferation, the expression of cyclooxygenases (COXs), prostaglandin (PG) receptors (EP1-4), extracellular matrix proteins, such as type I collagen and osteopontin, and PGE(2) production, using ROS17/2.8 cells as osteoblasts.

METHODS

The rat clonal cell line ROS 17/2.8 was cultured with 0, 10(-5), 10(-4), and 10(-3)M BA in the presence or absence of 0.5 μM indomethacin, for up to 7 days. The expression of COX-1, COX-2, EP1, EP2, EP3, EP4, type I collagen, and osteopontin was examined at the mRNA and protein levels using real-time PCR and Western blotting, respectively. The amount of PGE(2) in the culture medium was measured by ELISA.

RESULTS

Proliferation of ROS 17/2.8 cells was not affected by the addition of BA. However, PGE(2) production and the expression of COX-1 and COX-2 increased with the addition of BA. In contrast, indomethacin, an inhibitor of COX, blocked the stimulatory effect of BA. Furthermore, EP2 expression increased with BA treatment, whereas EP1 expression was not affected and the expression of EP3 and EP4 was not detected. The addition of BA also increased the expression of type I collagen and osteopontin. Indomethacin blocked about 50% of the stimulatory effect of BA on type I collagen, whereas it did not block the effect on osteopontin.

CONCLUSIONS

These results suggest that BA induces PGE(2) production by increasing the expression of COX-1 and COX-2 in osteoblasts, and that an autocrine action of the produced PGE(2), via EP1 or BA-induced EP2, is related to an increase in type I collagen expression by BA.

Compressive force induces osteoclast differentiation via prostaglandin E(2) production in MC3T3-E1 cells

In orthodontic tooth movement, prostaglandin E(2) (PGE(2)) released from osteoblasts can alter the normal process of bone remodeling. We previously showed that compressive force (CF) controls bone formation by stimulating the production of PGE(2) and Ep2 and/or Ep4 receptors in osteoblasts. The present study was undertaken to examine the effect of CF on the production of PGE(2), cyclooxygenase-2 (COX-2), macrophage colony-stimulating factor (M-CSF), receptor activator of NF-kappaB ligand (RANKL), and osteoprotegerin (OPG) using osteoblastic MC3T3-E1 cells and to examine the indirect effect of CF on osteoclast differentiation using RAW264.7 cells as osteoclast precursors. MC3T3-E1 cells were cultured with or without continuous CF (1.0 or 3.0 g/cm(2)) for 24 hr, and PGE(2) production was determined using ELISA. The expression of COX-2, M-CSF, RANKL, and OPG genes and proteins was determined using real-time PCR and ELISA, respectively. Osteoclast differentiation was estimated using tartrate-resistant acid phosphatase (TRAP) staining of RAW 264.7 cells cultured for 10 days with conditioned medium from CF-treated MC3T3-E1 cells and soluble RANKL. As CF increased, PGE(2) production and the expression of COX-2, M-CSF, and RANKL increased, whereas OPG expression decreased. The number of TRAP-positive cells increased as CF increased. Celecoxib, a specific inhibitor of COX-2, blocked the stimulatory effect of CF on TRAP staining and the production of PGE(2), M-CSF, RANKL, and OPG. These results suggest that CF induces osteoclast differentiation by increasing M-CSF production and decreasing OPG production via PGE(2) in osteoblasts.

Diabetes and skeletal health

Osteoporosis and diabetes affect a large proportion of the elderly population. The prevalence of diabetes and osteoporosis is increasing. Compared with individuals without diabetes, both men and women with diabetes have a higher risk of fractures, particularly at the hip, with consequent significant morbidity and mortality. Type 1 diabetes is associated with decreased bone mass and although bone mass data for Type 2 diabetes may or may not be decreased, there is evidence of altered bone quality in diabetes. The mechanisms involved include effects of insulin, insulin-like growth factor 1, cytokines, advanced glycation end products, and altered calcium homeostasis. In addition, a drug-induced increase in the incidence of fractures has been noted with the use of thiazolidinediones (TZDs). TZDs improve insulin sensitivity and have multitude other beneficial effects. Osteoblasts and adipocytes are derived from a common multipotential mesenchymal stem cell progenitor, with activation of peroxisome proliferator-activated receptor γ2 by both currently available TZDs (i.e. rosiglitazone and pioglitazone) stimulating adipogenesis and inhibiting osteoblastogenesis. The use of both rosiglitazone and pioglitazone is associated with an increased fracture risk, with changes in bone turnover markers and decreased bone mineral density.

PGE2 signaling through the EP4 receptor on fibroblasts upregulates RANKL and stimulates osteolysis

Periprosthetic osteolysis is the most common cause of aseptic loosening in total joint arthroplasty. The role of inflammatory mediators such as prostaglandin E2 (PGE2) and osteoclast promoting factors including RANKL in the pathogenesis of osteolysis has been well characterized. However, the PGE2 receptor (EP1, EP2, or EP4), and cell type in which it is expressed, which is responsible for PGE2 induction of RANKL during wear debris-induced osteolysis, has yet to be elucidated. To address this, we used mice genetically deficient in these EP receptors to assess PGE2 and wear debris responses in vitro and in vivo. Wear debris-induced osteolysis and RANKL expression were observed at similar levels in WT, EP1(-/-), and EP2(-/-) mice, indicating that these receptors do not mediate PGE2 signals in this process. A conditional knockout approach was used to eliminate EP4 expression in FSP1(+) fibroblasts that are the predominant source of RANKL. In the absence of EP4, fibroblasts do not express RANKL after stimulation with particles or PGE2, nor do they exhibit high levels of osteoclasts and osteolysis. These results show that periprosthetic fibroblasts are important mediators of osteolysis through the expression of RANKL, which is induced after PGE2 signaling through the EP4 receptor.

Bone morphogenetic protein 2 enhances PGE(2)-stimulated osteoclast formation in murine bone marrow cultures

Bone morphogenetic protein 2 (BMP-2) is used clinically to stimulate bone formation and accelerate fracture repair. Adding prostaglandin (PG) E(2) or PGE(2) receptor agonists to BMP-2 has been proposed to improve BMP-2 efficacy. However, this may enhance bone resorption, since PGE(2) can increase receptor activator of NF-kappaB ligand (RANKL) expression and decrease osteoprotegerin (OPG) expression in osteoblasts, and the RANKL:OPG ratio is critical for osteoclast formation. We used bone marrow (BM) cultures and BM macrophage (BMM) cultures from outbred CD1 mice to examine effects on osteoclast formation of BMP-2 and PGE(2). In BM cultures, which contain both osteoblastic and osteoclastic lineage cells, BMP-2 (100 ng/ml) alone did not increase osteoclast formation but enhanced the peak response to PGE(2) by 1.6-9.6-fold. In BMM cultures, which must be treated with RANKL because they do not contain osteoblastic cells, BMP-2 did not increase osteoclast formation, with or without PGE(2). Our results suggest that BMP-2 can increase osteoclast formation in response to PGE(2) by increasing the RANKL:OPG ratio in osteoblasts, which may have therapeutic implications for the use of BMP-2.

Rescue of impaired fracture healing in COX-2-/- mice via activation of prostaglandin E2 receptor subtype 4

Although the essential role of cyclooxygenase (COX)-2 in fracture healing is known, the targeted genes and molecular pathways remain unclear. Using prostaglandin E2 receptor (EP)2 and EP4 agonists, we examined the effects of EP receptor activation in compensation for the lack of COX-2 during fracture healing. In a fracture-healing model, COX-2(-/-) mice showed delayed initiation and impaired endochondral bone repair, accompanied by a severe angiogenesis deficiency. The EP4 agonist markedly improved the impaired healing in COX-2(-/-) mice, as evidenced by restoration of bony callus formation on day 14, a near complete reversal of bone formation, and an approximately 70% improvement of angiogenesis in the COX-2(-/-) callus. In comparison, the EP2 agonist only marginally enhanced bone formation in COX-2(-/-) mice. To determine the differential roles of EP2 and EP4 receptors on COX-2-mediated fracture repair, the effects of selective EP agonists on chondrogenesis were examined in E11.5 long-term limb bud micromass cultures. Only the EP4 agonist significantly increased cartilage nodule formation similar to that observed during prostaglandin E2 treatment. The prostaglandin E2/EP4 agonist also stimulated MMP-9 expression in bone marrow stromal cell cultures. The EP4 agonist further restored the reduction of MMP-9 expression in the COX-2(-/-) fracture callus. Taken together, our studies demonstrate that EP2 and EP4 have differential functions during endochondral bone repair. Activation of EP4, but not EP2 rescued impaired bone fracture healing in COX-2(-/-) mice.

EP4 agonist accelerates osteoinduction and degradation of beta-tricalcium phosphate by stimulating osteoclastogenesis

Porous beta-tricalcium phosphate (TCP) has been known to have osteoinductive potential in ectopic site implantation in canine models without the use of osteoinductive substances or cell transplantation. Prostaglandin E2 receptors, particularly EP4, are known to play an important role in osteogenesis. EP4 agonists have been demonstrated to have positive effects on bone remodeling and bone morphogenic protein-induced ectopic bone formation in rodent models. We examined the efficiency of porousbeta-TCP-induced osteoinduction in beagles by the graded-release EP4 agonist, which was injected at their buttocks intramuscularly. Newly formed bone was observed on and after 3 weeks in the EP4 agonist-injected, while on and after 6 weeks in control groups, respectively. After that the bone resorption and the beta-TCP degradation was accelerated in EP4 agonist-injected group. Tartarate-resistant acid phosphatase-positive cells appeared in each group before bone formation, and the number of these cells reduced gradually; however, more multinucleated and larger cells appeared, particularly in the injected group. Injection of an EP4 agonist was proved to accelerate the osteoinduction and degradation of beta-TCP in canine model. Histological analysis revealed that the EP4 agonist stimulated osteoclastogenesis before bone formation.

Proteinase-activated receptor (PAR)-2 activation impacts bone resorptive properties of human osteoarthritic subchondral bone osteoblasts

INTRODUCTION

In osteoarthritis (OA), the subchondral bone undergoes a remodelling process involving several factors synthesized by osteoblasts. In this study, we investigated the expression, production, modulation, and role of PAR-2 in human OA subchondral bone osteoblasts.

MATERIALS AND METHODS

PAR-2 expression and production were determined by real-time PCR and flow cytometry, respectively. PAR-2 modulation was investigated in OA subchondral bone osteoblasts treated with IL-1 beta (100 pg/ml), TNF-alpha (5 ng/ml), TGF-beta1 (10 ng/ml), PGE(2) (500 nM), IL-6 (10 ng/ml) and IL-17 (10 ng/ml). Membranous RANKL protein was assessed by flow cytometry, and OPG, MMP-1, MMP-9, MMP-13, IL-6 and intracellular signalling pathways by specific ELISAs. Bone resorptive activity was measured by using a co-culture model of human PBMC and OA subchondral bone osteoblasts.

RESULTS

PAR-2 expression and production (p<0.05) were markedly increased when human OA subchondral bone osteoblasts were compared to normal. On OA osteoblasts, PAR-2 production was significantly increased by IL-1 beta, TNF-alpha and PGE(2). Activation of PAR-2 with a specific agonist, SLIGKV-NH(2), induced a significant up-regulation of MMP-1, MMP-9, IL-6, and membranous RANKL, but had no effect on MMP-13 or OPG production. Interestingly, bone resorptive activity was also significantly enhanced following PAR-2 activation. The PAR-2 effect was mediated by activation of the MAP kinases Erk1/2 and JNK.

CONCLUSION

This study is the first to demonstrate that PAR-2 activation plays a role in OA subchondral bone resorption via an up-regulation of major bone remodelling factors. These results shed new light on the potential of PAR-2 as a therapeutic target in OA.

Pathophysiology of cyclooxygenase inhibition in animal models

Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid into prostaglandins (PGs), which play a significant role in health and disease in the gastrointestinal tract (GI) and in the renal, skeletal, and ocular systems. COX-1 is constitutively expressed and found in most normal tissues, whereas COX-2 can be expressed at low levels in normal tissues and is highly induced by pro-inflammatory mediators. Inhibitors of COX activity include: (1) conventional nonselective, nonsteroidal anti-inflammatory drugs (ns-NSAIDs) and (2) COX-2 selective nonsteroidal anti-inflammatory drugs (COX-2 s-NSAIDs). Inhibition of COX-1 often elicits GI toxicity in animals and humans. Therefore, COX-2 s-NSAIDs were developed to provide a selective COX-2 agent, while minimizing the attendant COX-1-mediated GI toxicities. Rats and dogs overpredict COX inhibition for renal effects such as renal handling of electrolytes in humans. COX inhibitors are shown to have both beneficial and detrimental effects, such as on healing of ligament or tendon tears, on the skeletal system in animal models. Certain ophthalmic conditions such as glaucoma and keratitis are associated with increased COX-2 expression, suggesting a potential role in their pathophysiology.

Clinical significance of aberrant methylation of prostaglandin E receptor 2 (PTGER2) in nonsmall cell lung cancer: association with prognosis, PTGER2 expression, and epidermal growth factor receptor mutation

BACKGROUND

The expression of prostaglandin E receptor 2 (PTGER2) affects the biologic behavior of various types of malignant tumors. Recently, transactivation of both PTGER2 and epidermal growth factor receptor (EGFR) has been reported in some tumors.

METHODS

PTGER2 gene expression and possible aberrant methylation of the PTGER2 gene were investigated in 10 nonsmall cell lung cancer (NSCLC) cell lines, 233 primary tumors, and 168 adjacent nonmalignant lung tissues. They were analyzed with reference to an association with EGFR mutation in 133 clinical lung adenocarcinomas and were correlated with patient survival.

RESULTS

Down-regulation of PTGER2 expression was observed in 8 of 10 NSCLC cell lines. Demethylation of 5 expression-negative cell lines restored the expression of PTGER2. Aberrant methylation of the PTGER2 gene was reversely concordant with its messenger RNA expression. PTGER2 methylation was detected in 137 of 233 NSCLC specimens (58%) but was detected in only 2 of 168 nonmalignant lung tissues (1%). Both NSCLCs and adenocarcinomas that had PTGER2 methylation predicted a significantly better prognosis than those without PTGER2 methylation (P = .0051 and P = .0171, respectively). PTGER2 methylation was present with greater frequency in tumors with EGFR mutation than in non-EGFR mutated tumors (P = .0095), and the significance of the correlation was independent after adjusting for sex and smoking status (P = .0144).

CONCLUSIONS

Aberrant methylation of the PTGER2 gene was observed frequently in NSCLC tissues and was associated with the presence of EGFR mutation and a better prognosis.

Staphylococcus aureus induces expression of receptor activator of NF-kappaB ligand and prostaglandin E2 in infected murine osteoblasts

Osteomyelitis is an inflammatory disease of the bone that is characterized by the presence of necrotic bone tissue and increased osteoclast activity. Staphylococcus aureus is responsible for approximately 80% of all cases of human osteomyelitis. While the disease is especially difficult to treat, the pathogenesis of S. aureus-induced osteomyelitis is poorly understood. Elucidating the molecular mechanisms by which S. aureus induces osteomyelitis could lead to a better understanding of the disease and its progression and development of new treatments. Osteoblasts can produce several soluble factors that serve to modulate the activity or formation of osteoclasts. Receptor activator of NF-kappaB ligand (RANK-L) and prostaglandin E(2) (PGE(2)) are two such molecules which can promote osteoclastogenesis and stimulate bone resorption. In addition, previous studies in our laboratory have shown that osteoblasts produce inflammatory cytokines, such as interleukin 6, following infection with S. aureus, which could induce COX-2 and in turn PGE(2), further modulating osteoclast recruitment and differentiation. Therefore, we hypothesized that following infection with S. aureus, osteoblasts will express increased levels of RANK-L and PGE(2). The results presented in this study provide evidence for the first time that RANK-L mRNA and protein and PGE(2) expression are upregulated in S. aureus-infected primary osteoblasts. In addition, through the use of the specific COX-2 inhibitor NS 398, we show that when PGE(2) production is inhibited, RANK-L production is decreased. These data suggest a mechanism whereby osteoblasts regulate the production of RANK-L during infection.

The Remarkable Mechanism of Prostaglandin E2 on Synaptic Plasticity

Prostanoids have a broad spectrum of biological activities in a variety of organs including the brain. However, their effects on synaptic plasticity in the brain, which have been recently revealed, are ambiguous in comparison to those in the other organs. Prostaglandin E2 (PGE2) is a prostanoid produced from arachidonic acid in the cellular membrane, and knowledge about its functions is increasing. Recently, a novel function of PGE2 in the brain has shed light on aspects of synaptic plasticity such as long-term potentiation (LTP). More recently, we have proposed a hypothesis for the mechanisms of this PGE2-related form of synaptic plasticity in the visual cortex. This involves the dynamics of two subtypes of PGE2 receptors that have opposing functions in intracellular signal transduction. Consequently, mechanisms that increase the level of cyclic AMP in the cytosol may explain for the mechanisms of LTP in the visual cortex. The current notion of bidirectional trafficking of PGE2 receptors under this hypothesis is reminiscent of the “silent synapse” mechanism of LTP on the trafficking of the AMPA receptors between the membrane and cytosol. Moreover, we propose the hypothesis that PGE2 acts as a “post-to-postsynaptic messenger” for the induction of LTP in the visual cortex. This review describes a complex mode of action of PGE2 receptors in synaptic plasticity in the brain.

Effect of deletion of the prostaglandin EP2 receptor on the anabolic response to prostaglandin E2 and a selective EP2 receptor agonist

Studies using prostaglandin E receptor (EP) agonists indicate that prostaglandin (PG) E(2) can have anabolic effects through both EP4 and EP2 receptors. We previously found that the anabolic response to a selective EP4 receptor agonist (EP4A, Ono Pharmaceutical) was substantially greater than to a selective EP2 receptor agonist (EP2A) in cultured murine calvarial osteoblastic cells. To further define the role of the EP2 receptor in PG-mediated effects on bone cells, we examined the effects of EP2A and PGE(2) on both calvarial primary osteoblasts (POB) and marrow stromal cells (MSC) cultured from mice with deletion of one (Het) or both (KO) alleles of the EP2 receptor compared to their wild-type (WT) littermates. Deletion of EP2 receptor was confirmed by quantitative real-time PCR, Western blot and immunohistochemistry. The 1 month-old mice used to provide cells in these studies did not show any significant differences in their femurs by static histomorphometry. EP2A was found to enhance osteoblastic differentiation as measured by alkaline phosphatase mRNA expression and activity as well as osteocalcin mRNA expression and mineralization in the WT cell cultures from both marrow and calvariae. The effects were somewhat diminished in cultures from Het mice and abrogated in cultures from KO mice. PGE(2) effects were greater than those of EP2A, particularly in POB cultures and were only moderately diminished in Het and KO cell cultures. We conclude that activation of the EP2 receptor is able to enhance differentiation of osteoblasts, that EP2A is a true selective agonist for this receptor and that PGE(2) has an additional anabolic effect likely mediated by the EP4 receptor.

Micro-CT imaging analysis for the effect of celecoxib, a cyclooxygenase-2 inhibitor, on inflammatory bone destruction in adjuvant arthritis rats

Cyclooxygenase (COX)-2 is known to play an important role in the differentiation and maturation of osteoclasts. However, the role of COX-1 in bone metabolism has not been well explored. In this study, the bone-conserving effects of COX-2-specific (celecoxib), COX-nonselective (loxoprofen), and COX-1-specific agents (SC-58560) were compared using an adjuvant-induced arthritis (AIA) rat model. Arthritis was induced by injecting 50 microl liquid paraffin containing 1 mg Mycobacterium butyricum into the left footpad of Lewis rats. Drugs were given orally twice daily for 10 days beginning 15 days after adjuvant injection. Celecoxib was administered at the rate of 3 mg/kg per day, loxoprofen at 3 mg/kg per day, and SC-58560 at 10 mg/kg per day. The therapeutic effects on 3-D architectural bone changes in the arthritic condition, e.g., the bone volume/total tissue volume ratio and the amount of trabecular bone pattern factor, were determined by analyzing the hindpaw calcaneus of AIA rats using microcomputed tomography (micro-CT). In addition, dual-energy X-ray absorptiometry 2-D bone analysis was performed to compare with micro-CT analysis. AIA rats are prone to substantial bone erosion, which allows for significant changes in the 3-D architectural index. This inflammatory bone destruction was suppressed potently by celecoxib, only moderately by loxoprofen, and not at all by SC-58560. These data suggest that COX-2 plays an important role in the inflammatory bone destruction that occurs with rheumatoid arthritis. The results also suggest that COX-2 is more effective than COX-1 at suppressing the destruction of bone associated with arthritis.

Effect of etidronate on COX-2 expression and PGE(2) production in macrophage-like RAW 264.7 cells stimulated by titanium particles

BACKGROUND

The most common failure of total joint replacement is aseptic loosening in association with osteolysis. Previous reports have shown that prostaglandin E(2) (PGE(2)) secreted from macrophages that phagocytosed wear debris induced periprosthetic osteolysis. Many clinical studies have reported that bisphosphonate therapy reduced periprosthetic bone loss and loosening of the implants after total joint replacements. Bisphosphonates are synthetic compounds with the ability to decrease bone resorption. In addition, some bisphosphonates have been reported to have anti-inflammatory effects by reducing the secretion of pro-inflammatory cytokines. However, the mechanism of bisphosphonates that reduces periprosthetic bone resorption remains unclear. The purpose of this study was to investigate one of the mechanisms by which etidronate (EHDP) inhibits periprosthetic bone resorption.

METHODS

Macrophage-like RAW 264.7 cells were treated with EHDP at concentrations of 0.001, 0.01, 0.1, 1, 10, and 100 microM together with the titanium particles at a concentration of 1 mg/ml. After a 24-h culture period, total mRNA was isolated and reverse transcription-polymerase chain reaction (RT-PCR) was done to examine the expression of cyclooxygenase-2 (COX-2). The supernatants were also collected and production of PGE(2), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) were quantified using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Analyses showed that COX-2 expression and PGE(2) production were suppressed by EHDP in a dose-dependent manner. By 100 microM of EHDP, PGE(2) production of the cells was suppressed approximately to the level of the nonstimulated cells. Production of IL-1beta, IL-6, and TNF-alpha in the supernatant was also suppressed by EHDP.

CONCLUSIONS

The blockage effect of pro-inflammatory cytokines is a possible etidronate mechanism that reduces bone resorption around implants.

Skeletal abnormalities and extra-skeletal ossification in mice with restricted Gsalpha deletion caused by a renin promoter-Cre transgene

We have recently generated a transgenic mouse line (termed hRen-Cre) that expresses Cre-recombinase under the control of a 12.2-kb fragment of the human renin promoter. In the present study, we have crossed hRen-Cre mice with a mouse strain in which exon 1 of the Gnas gene is flanked by loxP sites. Gnas encodes the alpha-subunit of the stimulatory G protein (Gs alpha). Our aim has been to generate a mouse model with locally restricted inactivation of Gs alpha to extend studies of the role of Gs alpha function in vivo. Mice with local Cre-mediated inactivation of Gs alpha (rCre-Gs alpha) are viable and fertile. Their most obvious phenotype consists of marked skeletal malformations of the forelimbs in which computer-tomography scans reveal shortened and fused extremity bones. Extraskeletal ossifications occur in the subcutis and in skeletal muscles associated with the affected long bones. Plasma calcium, phosphate and parathyroid hormone are normal. Skin histology has demonstrated diffuse mineralization and ossification associated with the basal cells of hair follicles. This phenotype in part resembles syndromes in humans associated with loss-of-function of Gs alpha, such as Albright hereditary osteodystrophy and progressive osseous heteroplasia. The renal phenotype of rCre-Gs alpha mice is inconspicuous. Plasma renin concentration, ambient urine osmolarity, and the glomerular filtration rate of rCre-Gs alpha mice do not differ from controls. The absence of measurable functional changes in the renin-angiotensin system indicates insufficient Cre expression in juxtaglomerular granular cells in this strain of mice. Nevertheless, the present report reaffirms the importance of Gs alpha signaling for bone development and the suppression of ectopic ossification.

Hypoxia regulates PGE(2) release and EP1 receptor expression in osteoblastic cells

Changes in regional O(2) tension that occur during fracture and skeletal unloading may stimulate local bone cell activity and ultimately regulate bone maintenance and repair. The mechanisms by which bone cells sense and respond to changes in O(2) tension are unclear. In this study we investigated the effects of low O(2) on activation of the hypoxia response element (HRE), prostaglandin E(2) (PGE(2)) production, PGE(2) receptor (EP) expression and proliferation in MC3T3-E1 osteoblastic cells. Cells were cultured for up to 72 h in 2% O(2) (considered hypoxic), 5% O(2) (in the range of normal O(2) tension in vivo) or 21% O(2) (commonly used for cell culture). Cells cultured in 2% O(2) showed activation of the HRE, increased PGE(2) release, increased EP1 expression, and reduced cell proliferation compared to cells grown at 21% O(2). Similarly, cells cultured in 5% O(2) showed increased expression of EP1 and a trend toward a decrease in proliferation, but no activation of the HRE or increase in PGE(2) levels. Expression of EP2, EP3 and EP4 were not affected by O(2) tension. The differences in EP receptor profile observed in cells grown at 5% compared to 21% O(2) suggest that bone cell phenotype may be altered under routine cell culture conditions. Furthermore, our data suggest that hypoxia-dependent PGE(2) production and EP1 expression in bone cells may play a role in bone remodeling and repair in regions of compromised or damaged bone, where O(2) tension is low.

Cyclooxygenase-2 gene disruption promotes proliferation of murine calvarial osteoblasts in vitro

Cyclooxygenase-2 (COX-2) is highly expressed in osteoblasts, and COX-2 produced prostaglandins (PGs) can increase osteoblastic differentiation in vitro. The goal of this study was to examine effects of COX-2 expression on calvarial osteoblastic proliferation and apoptosis. Primary osteoblasts (POBs) were cultured from calvariae of COX-2 wild-type (WT) and knockout (KO) mice. POB proliferation was evaluated by (3)H-thymidine incorporation and analysis of cell replication and cell cycle distribution by flow cytometry. POB apoptosis was evaluated by annexin and PI staining on flow cytometry. As expected, PGE(2) production and alkaline phosphatase (ALP) activity were increased in WT cultures compared to KO cultures. In contrast, cell numbers were decreased in WT compared to KO cells by day 4 of culture. Proliferation, measured on days 3-7 of culture, was 2-fold greater in KO than in WT POBs and associated with decreased Go/G1 and increased S cell cycle distribution. There was no significant effect of COX-2 genotype on apoptosis under basal culture conditions on day 5 of culture. Cell growth was decreased in KO POBs by the addition of PGE(2) or a protein kinase A agonist and increased in WT POBs by the addition of NS398, a selective COX-2 inhibitor. In contrast, differentiation and cell growth in marrow stromal cell (MSC) cultures, evaluated by ALP and crystal violet staining respectively, were increased in MSCs from WT mice compared to MSCs from KO mice, and exogenous PGE(2) increased cell growth in KO MSC cultures. We conclude that PGs secondary to COX-2 expression decrease osteoblastic proliferation in cultured calvarial cells but increase growth of osteoblastic precursors in MSC cultures.

Prostaglandin E(2) receptors in bone formation

Prostaglandins, PGE(2) in particular, have diverse actions on various organs, including inflammation, bone healing, bone formation, embryo implantation, induction of labour and vasodilatation, among others. However, systemic side effects have limited their clinical utility. The pharmacological activities of PGE(2) are mediated through four G protein-coupled receptor subtypes, EP1-EP4. Recent studies have shown that EP2 and EP4 receptors play important roles in regulating bone formation and resorption. EP2 and EP4 receptor-selective agonists have been shown to stimulate local or systemic bone formation, augment bone mass and accelerate the healing of fractures or bone defects in animal models upon local or systemic administration, thus, potentially offering new therapeutic options for enhancing bone formation and bone repair in humans. This review will focus on the studies related to bone formation and bone healing in the EP receptor knockout (KO) mice and the EP2 or EP4 receptor-selective agonist treated animal models.

Macrophage inflammatory protein-1alpha (MIP-1alpha) enhances a receptor activator of nuclear factor kappaB ligand (RANKL) expression in mouse bone marrow stromal cells and osteoblasts through MAPK and PI3K/Akt pathways

Osteolytic lesions are rapidly progressive during the terminal stages of myeloma, and the bone pain or bone fracture that occurs at these lesions decreases the patients' quality of life to a notable degree. In relation to the etiology of this bone destruction, it has been reported recently that MIP-1alpha, produced in large amounts in myeloma patients, acts indirectly on osteoclastic precursor cells, and activates osteoclasts by way of bone-marrow stromal cells or osteoblasts, although the details of this process remain obscure. In the present study, our group investigated the mechanism by which RANKL expression is induced by MIP-1alpha and the effects of MIP-1alpha on the activation of osteoclasts. RANKL mRNA and RANKL protein expressions increased in both ST2 cells and MC3T3-E1 cells in a MIP-1alpha concentration-dependent manner. RANKL mRNA expression began to increase at 1 h after the addition of MIP-1alpha; the increase became remarkable at 2 h, and continuous expression was observed subsequently. Both ST2 and MC3T3-E1 cells showed similar levels of increased RANKL protein expression at 1, 2, and 3 days after the addition of MIP-1alpha. After the addition of MIP-1alpha, the amount of phosphorylated ERK1/2 and Akt protein expressions showed an increase, as compared to the corresponding amount in the control group. On the other hand, the amount of phosphorylated p38MAPK protein expression showed a decrease from the amount in the control group after the addition of MIP-1alpha. U0126 (a MEK1/2 inhibitor) or LY294002 (a PI3K inhibitor) was added to ST2 and MC3T3-E1 cells, and was found to inhibit RANKL mRNA and RANKL protein expression in these cells. When SB203580, a p38MAPK inhibitor, was added, RANKL mRNA and RANKL protein expression were increased in these cells. MIP-1alpha was found to promote osteoclastic differentiation of C7 cells, an osteoclastic precursor cell line, in a MIP-1alpha concentration-dependent manner. MIP-1alpha promoted differentiation into osteoclasts more extensively in C7 cells incubated together with ST2 and MC3T3-E1 cells than in C7 cells incubated alone. These results suggested that MIP-1alpha directly acts on the osteoclastic precursor cells and induces osteoclastic differentiation. This substance also indirectly induces osteoclastic differentiation through the promotion of RANKL expression in bone-marrow stromal cells and osteoblasts. The findings of this investigation suggested that activation of the MEK/ERK and the PI3K/Akt pathways and inhibition of p38MAPK pathway were involved in RANKL expression induced by MIP-1alpha in bone-marrow stromal cells and osteoblasts. This finding may be useful in the development of an osteoclastic inhibitor that targets intracellular signaling factors.

Rolipram, a phosphodiesterase 4 inhibitor, suppresses PGE2-induced osteoclast formation by lowering osteoclast progenitor cell viability

We have previously shown that phosphodiesterase (PDE) inhibitors induce osteoclast formation by suppressing the degradation of intracellular cAMP. To determine the regulatory roles of PDE inhibitors on PGE2-induced osteoclastogenesis, we investigated the effect of PDE inhibitors on osteoclast formation in the presence of PGE2. We found that IBMX, a nonselective PDE inhibitor, and rolipram, a specific PDE4 inhibitor, decreased PGE2-induced osteoclast formation in cocultures of mouse bone marrow cells and osteoblastic cells. These suppressive effects were observed only when cocultures were treated with PDE inhibitors in the presence of PGE2 at an early stage of differentiation. Northern blot analysis revealed that the PDE4 inhibitor works synergistically with PGE2 to increase the ratio of TRANCE/OPG mRNA in osteoblasts, suggesting that suppression of osteoclast formation by PGE2 and the PDE4 inhibitor is not attributable to their indirect effect on calvarial osteoblasts. We further demonstrated that the PDE4 inhibitor augments the inhibitory effect of PGE2 on osteoclast progenitor cell viability, showing that combined treatment with PGE2 and rolipram suppresses osteoclast formation by directly reducing osteoclast progenitor cell viability.

Prostaglandin E receptors

Prostaglandin (PG) E(2) exerts its actions by acting on a group of G-protein-coupled receptors (GPCRs). There are four GPCRs responding to PGE(2) designated subtypes EP1, EP2, EP3, and EP4 and multiple splicing isoforms of the subtype EP3. The EP subtypes exhibit differences in signal transduction, tissue localization, and regulation of expression. This molecular and biochemical heterogeneity of PGE receptors leads to PGE(2) being the most versatile prostanoid. Studies on knock-out mice deficient in each EP subtype have defined PGE(2) actions mediated by each subtype and identified the role each EP subtype plays in various physiological and pathophysiological responses. Here we review recent advances in PGE receptor research.

Night eating and obesity in the EP3R-deficient mouse

Adult mice carrying a null mutation of the prostanoid receptor EP3R (EP3R(-/-) mice) exhibit increased frequency of feeding during the light cycle of the day and develop an obese phenotype under a normal fat diet fed ad libitum. EP3R(-/-) mice show increased motor activity, which is not sufficient to offset the increased feeding leading to increased body weight. Altered "nocturnal" activity and feeding behavior is present from a very early age and does not seem to require age-dependent factors for the development of obesity. Obesity in EP3R(-/-) mice is characterized by elevated leptin and insulin levels and >20% higher body weight compared with WT littermates. Abdominal and subcutaneous fat and increased liver weight account for the weight increase in EP3R(-/-) mice. These observations expand the roles of prostaglandin E(2) signaling in metabolic regulation beyond the reported stimulation of leptin release from adipose tissue to involve actions mediated by EP3R in the regulation of sleep architecture and feeding behavior. The findings add to the growing literature on links between inflammatory signaling and obesity.