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

Numerical analysis of coil designs to expedite fracture healing using dielectrophoresis with S method

BACKGROUND

Classical methods for speeding up fracture healing usually rely on direct electrical stimulation and electromagnetic fields to boost the levels of growth factors at the fracture site. However, these techniques often concentrate on bone cells themselves rather than addressing the critical blood flow dynamics necessary for effective healing. This study introduces a mathematical model designed to explore the potential of dielectrophoretic forces (DEPFs) in improving blood flow at the fracture site. By adjusting blood flow, the model seeks to enhance the delivery of vital nutrients, hormones, and growth factors, including endothelial cells (ECs), vascular endothelial growth factor (VEGF) and oxygen, which are essential for accelerating the fracture healing process.

METHOD

The proposed approach includes a new technique, termed the S method, which assesses the non-uniformity of DEPFs by algebraically analyzing the electric field lines associated with positive and negative dielectrophoresis. We developed analytical equations to simulate various coil configurations, focusing on long bone fractures where blood flow is vertically oriented. The DEPF Factor (χDEPF) was used to measure the ratio of blood flow velocity in the presence of DEPFs compared to the absence of DEPFs, thus indicating the effectiveness of DEPF in enhancing blood flow.

RESULTS

The simulation results revealed that DEPF reaches its peak efficacy at the gamma dispersion band, with the most significant enhancement occurring at a frequency of 15 MHz. Specifically, the average values of χDEPF were 1.8, 3.2, and 7.9 for the catenary, lintearia, and valeria coils, respectively. Our computational model, which incorporated VEGF, ECs, and oxygen tension, demonstrated that the catenary coil slightly improved healing rates in impaired fractures, the lintearia coil normalized healing times between impaired and normal fractures, and the valeria coil not only accelerated healing in impaired fractures but also enhanced healing in normal fractures.

CONCLUSIONS

This paper's findings suggest that the valeria coil exhibits the best DEPF functionality, making it the optimal configuration for future experimental studies aimed at evaluating the efficacy of DEPF in promoting fracture healing. The ability of DEPFs to significantly enhance blood flow could represent a substantial advancement in the treatment of both normal and impaired fractures.

Nanomaterial-based scaffolds for bone regeneration with piezoelectric properties

For proper cellular growth, to prepare tissue scaffold mimicking the tissue properties is a significant challenge. Bone is a vital organ supporting the whole human body for its function. The efficiencies in its structure for a variety of reasons should properly be remedied. Bone tissue engineering (BTE) is an emerging field addressing to develop or repair bone tissue for its proper function. The bone is naturally a piezoelectric material and generates electrical stimuli because of mechanical stress. Thus, the use of piezoelectric materials to build bone tissue is of great interest in BTE. Both piezoelectric polymers and nanomaterials (NMs) are investigated for this goal. In this review, we give an overview of the recent advances in piezoelectric NMs to construct piezoelectric scaffolds in BTE.

Targeting EP2 Receptor Improves Muscle and Bone Health in Dystrophin-/-/Utrophin-/- Double-Knockout Mice

Duchenne muscular dystrophy (DMD) is a severe genetic muscle disease occurring due to mutations of the dystrophin gene. There is no cure for DMD. Using a dystrophin-/-utrophin-/- (DKO-Hom) mouse model, we investigated the PGE2/EP2 pathway in the pathogenesis of dystrophic muscle and its potential as a therapeutic target. We found that Ep2, Ep4, Cox-2, 15-Pgdh mRNA, and PGE2 were significantly increased in DKO-Hom mice compared to wild-type (WT) mice. The EP2 and EP4 receptors were mainly expressed in CD68+ macrophages and were significantly increased in the muscle tissues of both dystrophin-/- (mdx) and DKO-Hom mice compared to WT mice. Osteogenic and osteoclastogenic gene expression in skeletal muscle also increased in DKO-Hom mice, which correlates with severe muscle heterotopic ossification (HO). Treatment of DKO-Hom mice with the EP2 antagonist PF04418948 for 2 weeks increased body weight and reduced HO and muscle pathology by decreasing both total macrophages (CD68+) and senescent macrophages (CD68+P21+), while increasing endothelial cells (CD31+). PF04418948 also increased bone volume/total volume (BV/TV), the trabecular thickness (Tb.Th) of the tibia trabecular bone, and the cortical bone thickness of both the femur and tibia without affecting spine trabecular bone microarchitecture. In summary, our results indicate that targeting EP2 improves muscle pathology and improves bone mass in DKO mice.

Cause and chondroprotective effects of prostaglandin E2 secretion during mesenchymal stromal cell chondrogenesis

Mesenchymal stromal cells (MSCs) that are promising for cartilage tissue engineering secrete high amounts of prostaglandin E2 (PGE2), an immunoactive mediator involved in endochondral bone development. This study aimed to identify drivers of PGE2 and its role in the inadvertent MSC misdifferentiation into hypertrophic chondrocytes. PGE2 release, which rose in the first three weeks of MSC chondrogenesis, was jointly stimulated by endogenous BMP, WNT, and hedgehog activity that supported the exogenous stimulation by TGF-β1 and insulin to overcome the PGE2 inhibition by dexamethasone. Experiments with PGE2 treatment or the inhibitor celecoxib or specific receptor antagonists demonstrated that PGE2, although driven by prohypertrophic signals, exerted broad autocrine antihypertrophic effects. This chondroprotective effect makes PGE2 not only a promising option for future combinatorial approaches to direct MSC tissue engineering approaches into chondral instead of endochondral development but could potentially have implications for the use of COX-2-selective inhibitors in osteoarthritis pain management.

Crosstalk Between the Neuroendocrine System and Bone Homeostasis

The homeostasis of bone microenvironment is the foundation of bone health and comprises 2 concerted events: bone formation by osteoblasts and bone resorption by osteoclasts. In the early 21st century, leptin, an adipocytes-derived hormone, was found to affect bone homeostasis through hypothalamic relay and the sympathetic nervous system, involving neurotransmitters like serotonin and norepinephrine. This discovery has provided a new perspective regarding the synergistic effects of endocrine and nervous systems on skeletal homeostasis. Since then, more studies have been conducted, gradually uncovering the complex neuroendocrine regulation underlying bone homeostasis. Intriguingly, bone is also considered as an endocrine organ that can produce regulatory factors that in turn exert effects on neuroendocrine activities. After decades of exploration into bone regulation mechanisms, separate bioactive factors have been extensively investigated, whereas few studies have systematically shown a global view of bone homeostasis regulation. Therefore, we summarized the previously studied regulatory patterns from the nervous system and endocrine system to bone. This review will provide readers with a panoramic view of the intimate relationship between the neuroendocrine system and bone, compensating for the current understanding of the regulation patterns of bone homeostasis, and probably developing new therapeutic strategies for its related disorders.

Market Needs and Methodologies Associated with Patient Lipidomic Diagnoses and Analyses

This chapter conducts an in-depth exploration of the impact of musculoskeletal (MSK) disorders and injuries, with a specific emphasis on their consequences within the older population demographic. It underscores the escalating demand for innovative interventions in MSK tissue engineering. The chapter also highlights the fundamental role played by lipid signaling mediators (LSMs) in tissue regeneration, with relevance to bone and muscle recovery. Remarkably, Prostaglandin E2 (PGE2) emerges as a central orchestrator in these regenerative processes. Furthermore, the chapter investigates the complex interplay between bone and muscle tissues, explaining the important influence exerted by LSMs on their growth and differentiation. The targeted modulation of LSM pathways holds substantial promise as a beneficial way for addressing muscle disorders. In addition to these conceptual understandings, the chapter provides a comprehensive overview of methodologies employed in the identification of LSMs, with a specific focus on the Liquid Chromatography-Mass Spectrometry (LC-MS). Furthermore, it introduces a detailed LC MS/MS-based protocol tailored for the detection of PGE2, serving as an invaluable resource for researchers immersed in this dynamic field of study.

Increased Osteoblast GαS Promotes Ossification by Suppressing Cartilage and Enhancing Callus Mineralization During Fracture Repair in Mice

GαS, the stimulatory G protein α-subunit that raises intracellular cAMP levels by activating adenylyl cyclase, plays a vital role in bone development, maintenance, and remodeling. Previously, using transgenic mice overexpressing GαS in osteoblasts (GS-Tg), we demonstrated the influence of osteoblast GαS level on osteogenesis, bone turnover, and skeletal responses to hyperparathyroidism. To further investigate whether alterations in GαS levels affect endochondral bone repair, a postnatal bone regenerative process that recapitulates embryonic bone development, we performed stabilized tibial osteotomy in male GS-Tg mice at 8 weeks of age and examined the progression of fracture healing by micro-CT, histomorphometry, and gene expression analysis over a 4-week period. Bone fractures from GS-Tg mice exhibited diminished cartilage formation at the time of peak soft callus formation at 1 week post-fracture followed by significantly enhanced callus mineralization and new bone formation at 2 weeks post-fracture. The opposing effects on chondrogenesis and osteogenesis were validated by downregulation of chondrogenic markers and upregulation of osteogenic markers. Histomorphometric analysis at times of increased bone formation (2 and 3 weeks post-fracture) revealed excess fibroblast-like cells on newly formed woven bone surfaces and elevated osteocyte density in GS-Tg fractures. Coincident with enhanced callus mineralization and bone formation, GS-Tg mice showed elevated active β-catenin and Wntless proteins in osteoblasts at 2 weeks post-fracture, further substantiated by increased mRNA encoding various canonical Wnts and Wnt target genes, suggesting elevated osteoblastic Wnt secretion and Wnt/β-catenin signaling. The GS-Tg bony callus at 4 weeks post-fracture exhibited greater mineral density and decreased polar moment of inertia, resulting in improved material stiffness. These findings highlight that elevated GαS levels increase Wnt signaling, conferring an increased osteogenic differentiation potential at the expense of chondrogenic differentiation, resulting in improved mechanical integrity. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Reduced angiogenesis and delayed endochondral ossification in CD163-/- mice highlights a role of M2 macrophages during bone fracture repair

While recent studies showed that macrophages are critical for bone fracture healing, and lack of M2 macrophages have been implicated in models of delayed union, functional roles for specific M2 receptors have yet to be defined. Moreover, the M2 scavenger receptor CD163 has been identified as a target to inhibit sepsis following implant-associated osteomyelitis, but potential adverse effects on bone healing during blockage therapy have yet to be explored. Thus, we investigated fracture healing in C57BL/6 versus CD163-/- mice using a well-established closed, stabilized, mid-diaphyseal femur fracture model. While gross fracture healing in CD163-/- mice was similar to that of C57BL/6, plain radiographs revealed persistent fracture gaps in the mutant mice on Day 14, which resolved by Day 21. Consistently, 3D vascular micro-CT demonstrated delayed union on Day 21, with reduced bone volume (74%, 61%, and 49%) and vasculature (40%, 40%, and 18%) compared to C57BL/6 on Days 10, 14, and 21 postfracture, respectively (p < 0.01). Histology confirmed large amounts of persistent cartilage in CD163-/- versus C57BL/6 fracture callus on Days 7 and 10 that resolves over time, and immunohistochemistry demonstrated deficiencies in CD206+ M2 macrophages. Torsion testing of the fractures confirmed the delayed early union in CD163-/- femurs, which display decreased yield torque on Day 21, and a decreased rigidity with a commensurate increase in rotation at yield on Day 28 (p < 0.01). Collectively, these results demonstrate that CD163 is required for normal angiogenesis, callus formation, and bone remodeling during fracture healing, and raise potential concerns about CD163 blockade therapy.

Prostaglandin E2/EP4 axis is upregulated in Spondyloarthritis and contributes to radiographic progression

Ankylosing spondylitis (AS) is an inflammatory disease leading to spine ankylosis; however, the mechanisms behind new bone formation are still not fully understood. Single Nucleotide Polymorphisms (SNPs) in PTGER4, encoding for the receptor EP4 of prostaglandin E2 (PGE2), are associated with AS. Since the PGE2-EP4 axis participates in inflammation and bone metabolism, this work aims at investigating the influence of the prostaglandin-E2 axis on radiographic progression in AS. In 185 AS (97 progressors), baseline serum PGE2 predicted progression, and PTGER4 SNP rs6896969 was more frequent in progressors. Increased EP4/PTGER4 expression was observed in AS circulating immune cells, synovial tissue, and bone marrow. CD14highEP4 + cells frequency correlated with disease activity, and when monocytes were cocultured with mesenchymal stem cells, the PGE2/EP4 axis induced bone formation. In conclusion, the Prostaglandin E2 axis is involved in bone remodelling and may contribute to the radiographic progression in AS due to genetic and environmental upregulation.

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.

Estrogen Receptor α Signaling in Osteoblasts is Required for Mechanotransduction in Bone Fracture Healing

Biomechanical stimulation by whole-body low-magnitude high-frequency vibration (LMHFV) has demonstrated to provoke anabolic effects on bone metabolism in both non-osteoporotic and osteoporotic animals and humans. However, preclinical studies reported that vibration improved fracture healing and bone formation in osteoporotic, ovariectomized (OVX) mice representing an estrogen-deficient hormonal status, but impaired bone regeneration in skeletally healthy non-OVX mice. These effects were abolished in general estrogen receptor α (ERα)-knockout (KO) mice. However, it remains to be elucidated which cell types in the fracture callus are targeted by LMHFV during bone healing. To answer this question, we generated osteoblast lineage-specific ERα-KO mice that were subjected to ovariectomy, femur osteotomy and subsequent vibration. We found that the ERα specifically on osteoblastic lineage cells facilitated the vibration-induced effects on fracture healing, because in osteoblast lineage-specific ERα-KO (ERαfl/fl; Runx2Cre) mice the negative effects in non-OVX mice were abolished, whereas the positive effects of vibration in OVX mice were reversed. To gain greater mechanistic insights, the influence of vibration on murine and human osteogenic cells was investigated in vitro by whole genome array analysis and qPCR. The results suggested that particularly canonical WNT and Cox2/PGE2 signaling is involved in the mechanotransduction of LMHFV under estrogen-deficient conditions. In conclusion, our study demonstrates a critical role of the osteoblast lineage-specific ERα in LMHFV-induced effects on fracture healing and provides further insights into the molecular mechanism behind these effects.

The periosteum: a simple tissue with many faces, with special reference to the antler-lineage periostea

Periosteum is a thin membrane covering bone surfaces and consists of two layers: outer fibrous layer and inner cambium layer. Simple appearance of periosteum has belied its own complexity as a composite structure for physical bone protection, mechano-sensor for sensing mechanical loading, reservoir of biochemical molecules for initiating cascade signaling, niche of osteogenic cells for bone formation and repair, and "umbilical cord" for nourishing bone tissue. Periosteum-derived cells (PDCs) have stem cell attributes: self-renewal (no signs of senescence until 80 population doublings) and multipotency (differentiate into fibroblasts, osteoblasts, chondrocytes, adipocytes and skeletal myocytes). In this review, we summarized the currently available knowledge about periosteum and with special references to antler-lineage periostea, and demonstrated that although periosteum is a type of simple tissue in appearance, with multiple faces in functions; antler-lineage periostea add another dimension to the properties of somatic periostea: capable of initiation of ectopic organ formation upon transplantation and full mammalian organ regeneration when interacted with the covering skin. Very recently, we have translated this finding into other mammals, i.e. successfully induced partial regeneration of the amputated rat legs. We believe further refinement along this line would greatly benefit human health.

Role of prostaglandin E2 in tissue repair and regeneration

Tissue regeneration following injury from disease or medical treatment still represents a challenge in regeneration medicine. Prostaglandin E2 (PGE2), which involves diverse physiological processes via E-type prostanoid (EP) receptor family, favors the regeneration of various organ systems following injury for its capabilities such as activation of endogenous stem cells, immune regulation, and angiogenesis. Understanding how PGE2 modulates tissue regeneration and then exploring how to elevate the regenerative efficiency of PGE2 will provide key insights into the tissue repair and regeneration processes by PGE2. In this review, we summarized the application of PGE2 to guide the regeneration of different tissues, including skin, heart, liver, kidney, intestine, bone, skeletal muscle, and hematopoietic stem cell regeneration. Moreover, we introduced PGE2-based therapeutic strategies to accelerate the recovery of impaired tissue or organs, including 15-hydroxyprostaglandin dehydrogenase (15-PGDH) inhibitors boosting endogenous PGE2 levels and biomaterial scaffolds to control PGE2 release.

Complexity of enthesitis and new bone formation in ankylosing spondylitis: current understanding of the immunopathology and therapeutic approaches

Despite increasing availability of treatments for spondyloarthritis (SpA) including tumour necrosis factor (TNF) and interleukin-17 (IL-17) inhibitors, there is no established treatment that abates new bone formation (NBF) in ankylosing spondylitis (AS), a subset of SpA. Recent research on TNF has revealed the increased level of transmembrane TNF in the joint tissue of SpA patients compared to that of rheumatoid arthritis patients, which appears to facilitate TNF-driven osteo-proliferative changes in AS. In addition, there is considerable interest in the central role of IL-23/IL-17 axis in type 3 immunity and the therapeutic potential of blocking this axis to ameliorate enthesitis and NBF in AS. AS immunopathology involves a variety of immune cells, including both innate and adoptive immune cells, to orchestrate the immune response driving type 3 immunity. In response to external stimuli of inflammatory cytokines, local osteo-chondral progenitor cells activate intra-cellular anabolic molecules and signals involving hedgehog, bone morphogenetic proteins, receptor activator of nuclear factor kappa-B ligand, and Wnt pathways to promote NBF in AS. Here, we provide an overview of the current immunopathology and future directions for the treatment of enthesitis and NBF associated with AS.

The Effect of Nonsteroidal Anti-inflammatory Drugs and Selective COX-2 Inhibitors on Bone Healing

A recently published study, "Risk of Nonunion With Nonselective NSAIDs, COX-2 Inhibitors, and Opioids" by George et al (J Bone Joint Surg Am. 2020;102:1230-1238), assesses whether the use of nonselective nonsteroidal anti-inflammatory drugs (NSAIDs), selective cyclooxygenase 2 (COX-2) enzyme inhibitors, or opioids was associated with a risk of long bone fracture nonunion in Optum's deidentified private health database. This review analyzes the study, including strengths, weaknesses, and areas for future research. The study found an association between COX-2 inhibitor and opioid use with fracture nonunion but not with nonselective NSAID use. Although the literature on this topic is varied, these results are at least partially aligned with several animal studies that show COX-2 inhibitors to be associated with fracture nonunion. The George et al study design has several important limitations, indicating that further research is needed on this topic.

A network analysis of angiogenesis/osteogenesis-related growth factors in bone tissue engineering based on in-vitro and in-vivo data: A systems biology approach

The principal purpose of tissue engineering is to stimulate the injured or unhealthy tissues to revive their primary function through the simultaneous use of chemical agents, cells, and biocompatible materials. Still, choosing the appropriate protein as a growth factor (GF) for tissue engineering is vital to fabricate artificial tissues and accelerate the regeneration procedure. In this study, the angiogenesis and osteogenesis-related proteins' interactions are studied using their related network. Three major biological processes, including osteogenesis, angiogenesis, and angiogenesis regulation, were investigated by creating a protein-protein interaction (PPI) network (45 nodes and 237 edges) of bone regeneration efficient proteins. Furthermore, a gene ontology and a centrality analysis were performed to identify essential proteins within a network. The higher degree in this network leads to higher interactions between proteins and causes a considerable effect. The most highly connected proteins in the PPI network are the most remarkable for their employment. The results of this study showed that three significant proteins including prostaglandin endoperoxide synthase 2 (PTGS2), TEK receptor tyrosine kinase (TEK), and fibroblast growth factor 18 (FGF18) were involved simultaneously in osteogenesis, angiogenesis, and their positive regulatory. Regarding the available literature, the results of this study confirmed that PTGS2 and FGF18 could be used as a GF in bone tissue engineering (BTE) applications to promote angiogenesis and osteogenesis. Nevertheless, TEK was not used in BTE applications until now and should be considered in future works to be examined in-vitro and in-vivo.

Wnt/β-catenin signalling promotes more effective fracture healing in aged mice than in adult mice by inducing angiogenesis and cell differentiation

To investigate whether activating the Wnt/β-catenin signalling pathway differentially promotes fracture healing in aged and adult individuals. CatnbTM2Kem, Catnblox(ex3) and wild-type adult and aged mice were used in this study. The femur was electroporated through a hole with a diameter of 0.6 mm. On the 7th, 14th and 21st days after fracture establishment, repair of the femoral diaphyseal bone was examined using X-ray and CT, the levels of mRNAs related to Wnt/β-catenin signalling were detected using real-time polymerase chain reaction (RT-PCR), and angiogenesis and cell differentiation were observed using immunohistochemistry. The numbers of osteoclasts were determined by TRAP staining. Wnt/β-catenin activation accelerated fracture healing in adult mice, with more pronounced effects on aged mice. Compared with wild-type mice at the corresponding ages, Wnt/β-catenin signalling activation induced higher levels of angiogenesis and cell differentiation in aged mice than in adult mice and promoted fracture healing. The administration of medications targeting Wnt/β-catenin signalling to aged patients may accelerate fracture healing to a greater extent.

Cytokine "fine tuning" of enthesis tissue homeostasis as a pointer to spondyloarthritis pathogenesis with a focus on relevant TNF and IL-17 targeted therapies

A curious feature of axial disease in ankylosing spondylitis (AS) and related non-radiographic axial spondyloarthropathy (nrAxSpA) is that spinal inflammation may ultimately be associated with excessive entheseal tissue repair with new bone formation. Other SpA associated target tissues including the gut and the skin have well established paradigms on how local tissue immune responses and proven disease relevant cytokines including TNF and the IL-23/17 axis contribute to tissue repair. Normal skeletal homeostasis including the highly mechanically stressed entheseal sites is subject to tissue microdamage, micro-inflammation and ultimately repair. Like the skin and gut, healthy enthesis has resident immune cells including ILCs, γδ T cells, conventional CD4+ and CD8+ T cells and myeloid lineage cells capable of cytokine induction involving prostaglandins, growth factors and cytokines including TNF and IL-17 that regulate these responses. We discuss how human genetic studies, animal models and translational human immunology around TNF and IL-17 suggest a largely redundant role for these pathways in physiological tissue repair and homeostasis. However, disease associated immune system overactivity of these cytokines with loss of tissue repair “fine tuning” is eventually associated with exuberant tissue repair responses in AS. Conversely, excessive biomechanical stress at spinal enthesis or peripheral enthesis with mechanically related or degenerative conditions is associated with a normal immune system attempts at cytokine fine tuning, but in this setting, it is commensurate to sustained abnormal biomechanical stressing. Unlike SpA, where restoration of aberrant and excessive cytokine “fine tuning” is efficacious, antagonism of these pathways in biomechanically related disease may be of limited or even no value.

New Surgical Model for Bone-Muscle Injury Reveals Age and Gender-Related Healing Patterns in the 5 Lipoxygenase (5LO) Knockout Mouse

Signaling lipid mediators released from 5 lipoxygenase (5LO) pathways influence both bone and muscle cells, interfering in their proliferation and differentiation capacities. A major limitation to studying inflammatory signaling pathways in bone and muscle healing is the inadequacy of available animal models. We developed a surgical injury model in the vastus lateralis (VL) muscle and femur in 129/SvEv littermates mice to study simultaneous musculoskeletal (MSK) healing in male and female, young (3 months) and aged (18 months) WT mice compared to mice lacking 5LO (5LOKO). MSK defects were surgically created using a 1-mm punch device in the VA muscle followed by a 0.5-mm round defect in the femur. After days 7 and 14 post-surgery, the specimens were removed for microtomography (microCT), histopathology, and immunohistochemistry analyses. In addition, non-injured control skeletal muscles along with femur and L5 vertebrae were analyzed. Bones were microCT phenotyped, revealing that aged female WT mice presented reduced BV/TV and trabecular parameters compared to aged males and aged female 5LOKO mice. Skeletal muscles underwent a customized targeted lipidomics investigation for profiling and quantification of lipid signaling mediators (LMs), evidencing age, and gender related-differences in aged female 5LOKO mice compared to matched WT. Histological analysis revealed a suitable bone-healing process with osteoid deposition at day 7 post-surgery, followed by woven bone at day 14 post-surgery, observed in all young mice. Aged WT females displayed increased inflammatory response at day 7 post-surgery, delayed bone matrix maturation, and increased TRAP immunolabeling at day 14 post-surgery compared to 5LOKO females. Skeletal muscles of aged animals showed higher levels of inflammation in comparison to young controls at day 14 post-surgery; however, inflammatory process was attenuated in aged 5LOKO mice compared to aged WT. In conclusion, this new model shows that MSK healing is influenced by age, gender, and the 5LO pathway, which might serve as a potential target to investigate therapeutic interventions and age-related MSK diseases. Our new model is suitable for bone-muscle crosstalk studies.

Different effects of Wnt/β-catenin activation and PTH activation in adult and aged male mice metaphyseal fracture healing

Background

Fractures in older men are not uncommon and need to be healed as soon as possible to avoid related complications. Anti-osteoporotic drugs targeting Wnt/β-catenin and PTH (parathyroid hormone) to promote fracture healing have become an important direction in recent years. The study is to observe whether there is a difference in adult and aged situations by activating two signal paths.

Methods

A single cortical hole with a diameter of 0.6 mm was made in the femoral metaphysis of Catnb^lox(ex3) mice and wild-type mice. The fracture healing effects of CA (Wnt/β-catenin activation) and PTH (activated by PTH (1–34) injections) were assessed by X-ray and CT imaging on days 7, 14, and 21 after fracture. The mRNA levels of β-catenin, PTH1R(Parathyroid hormone 1 receptor), and RUNX2(Runt-related transcription factor 2) in the fracture defect area were detected using RT-PCR. Angiogenesis and osteoblasts were observed by immunohistochemistry and osteoclasts were observed by TRAP (Tartrate-resistant Acid Phosphatase).

Result

Adult CA mice and adult PTH mice showed slightly better fracture healing than adult wild-type (WT) mice, but there was no statistical difference. Aged CA mice showed better promotion of angiogenesis and osteoblasts and better fracture healing than aged PTH mice.

Conclusion

The application of Wnt/β-catenin signaling pathway drugs for fracture healing in elderly patients may bring better early effects than PTH signaling pathway drugs, but the long-term effects need to be observed.

Dose-dependent roles of aspirin and other non-steroidal anti-inflammatory drugs in abnormal bone remodeling and skeletal regeneration

The failure of remodeling process that constantly regenerates effete, aged bone is highly associated with bone nonunion and degenerative bone diseases. Numerous studies have demonstrated that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) activate cytokines and mediators on osteoclasts, osteoblasts and their constituent progenitor cells located around the remodeling area. These cells contribute to a complex metabolic scenario, resulting in degradative or synthetic functions for bone mineral tissues. The spatiotemporal effects of aspirin and NSAIDs in the bone remodeling are controversial according the specific therapeutic doses used for different clinical conditions. Herein, we review in vitro, in vivo, and clinical studies on the dose-dependent roles of aspirin and NSAIDs in bone remodeling. Our results show that low-dose aspirin (< 100 μg/mL), which is widely recommended for prevention of thrombosis, is very likely to be benefit for maintaining bone mass and qualities by activation of osteoblastic bone formation and inhibition of osteoclast activities via cyclooxygenase-independent manner. While, the roles of high-dose aspirin (150-300 μg/mL) and other NSAIDs in bone self-regeneration and fracture-healing process are difficult to elucidate owing to their dual effects on osteoclast activity and bone formation of osteoblast. In conclusion, this study highlighted the potential clinical applications of low-dose aspirin in abnormal bone remodeling as well as the risks of high-dose aspirin and other NSAIDs for relieving pain and anti-inflammation in fractures and orthopedic operations.

Osteoimmunology: Inflammatory osteolysis and regeneration of the alveolar bone

AIM

Osteoimmunology covers the cellular and molecular mechanisms responsible for inflammatory osteolysis that culminates in the degradation of alveolar bone. Osteoimmunology also focuses on the interplay of immune cells with bone cells during bone remodelling and regeneration. The aim of this review was to provide insights into how osteoimmunology affects alveolar bone health and disease.

METHOD

This review is based on a narrative approach to assemble mouse models that provide insights into the cellular and molecular mechanisms causing inflammatory osteolysis and on the impact of immune cells on alveolar bone regeneration.

RESULTS

Mouse models have revealed the molecular pathways by which microbial and other factors activate immune cells that initiate an inflammatory response. The inflammation-induced alveolar bone loss occurs with the concomitant suppression of bone formation. Mouse models also showed that immune cells contribute to the resolution of inflammation and bone regeneration, even though studies with a focus on alveolar socket healing are rare.

CONCLUSIONS

Considering that osteoimmunology is evolutionarily conserved, osteolysis removes the cause of inflammation by provoking tooth loss. The impact of immune cells on bone regeneration is presumably a way to reinitiate the developmental mechanisms of intramembranous and endochondral bone formation.

Cyclooxygenase 2 augments osteoblastic but suppresses chondrocytic differentiation of CD90+ skeletal stem cells in fracture sites

Cyclooxygenase 2 (COX-2) is essential for normal tissue repair. Although COX-2 is known to enhance the differentiation of mesenchymal stem cells (MSCs), how COX-2 regulates MSC differentiation into different tissue-specific progenitors to promote tissue repair remains unknown. Because it has been shown that COX-2 is critical for normal bone repair and local COX-2 overexpression in fracture sites accelerates fracture repair, this study aimed to determine the MSC subsets that are targeted by COX-2. We showed that CD90⁺ mouse skeletal stem cells (mSSCs; i.e., CD45^-Tie2^-AlphaV⁺ MSCs) were selectively recruited by macrophage/monocyte chemoattractant protein 1 into fracture sites following local COX-2 overexpression. In addition, local COX-2 overexpression augmented osteoblast differentiation and suppressed chondrocyte differentiation in CD90⁺ mSSCs, which depended on canonical WNT signaling. CD90 depletion data demonstrated that local COX-2 overexpression targeted CD90⁺ mSSCs to accelerate fracture repair. In conclusion, CD90⁺ mSSCs are promising targets for the acceleration of bone repair.

Prostaglandin receptor EP4 expression by Th17 cells is associated with high disease activity in ankylosing spondylitis

BACKGROUND

Th17 cells are involved in the pathogenesis of ankylosing spondylitis (AS). However, the mechanism underlying enhanced Th17 cell accumulation in AS remains unknown. The prostaglandin E₂ receptor EP2/EP4 signaling pathway plays a critical role in the development of autoimmune Th17 cells. Interestingly, recent genome-wide association studies (GWAS) have identified five risk alleles for AS in PTGER4, the gene encoding for EP4. The aim of this study was to reveal a possible link between EP4 and disease activity in patients with AS.

METHODS

Th17 cells from patients with AS were analyzed for the transcriptional expression of prostaglandin receptor genes by quantitative RT-PCR. Th17 cells from patients with rheumatoid arthritis (RA) and from healthy individuals served as controls. EP4 receptor expression in Th17 cells was assessed ex vivo by flow cytometry and by western blot. Functional analysis using EP4-specific agonists was performed to reveal how EP4 regulates Th17 cells.

RESULTS

EP4 is significantly overexpressed in Th17 cells from patients with AS compared to Th17 cells from healthy individuals or patients with RA or psoriatic arthritis (PsA). EP4 upregulation is unique to Th17 cells and is not found in other CD4⁺ T cell subsets. Specific activation of EP4 drives Th17 cell development and promotes EP4 expression in a positive feedback loop in AS but not in RA or PsA. Mechanistically, EP4 acts via upregulation of the interleukin-23 receptor (IL-23R), by suppressing the RORγt inhibitor FoxO1 and by enhancing STAT3 phosphorylation. Increased EP4 expression levels in Th17 cells from AS patients correlate with high disease activity as defined by a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score ≥ 4 (r = 0.7591, p = 0.0016).

CONCLUSIONS

EP4 is a potential marker of disease activity in patients with AS. Aberrant EP4 expression might contribute to pathogenic Th17 cell accumulation and represent a new target for the treatment of AS.

Dysfunctional stem and progenitor cells impair fracture healing with age

Successful fracture healing requires the simultaneous regeneration of both the bone and vasculature; mesenchymal stem cells (MSCs) are directed to replace the bone tissue, while endothelial progenitor cells (EPCs) form the new vasculature that supplies blood to the fracture site. In the elderly, the healing process is slowed, partly due to decreased regenerative function of these stem and progenitor cells. MSCs from older individuals are impaired with regard to cell number, proliferative capacity, ability to migrate, and osteochondrogenic differentiation potential. The proliferation, migration and function of EPCs are also compromised with advanced age. Although the reasons for cellular dysfunction with age are complex and multidimensional, reduced expression of growth factors, accumulation of oxidative damage from reactive oxygen species, and altered signaling of the Sirtuin-1 pathway are contributing factors to aging at the cellular level of both MSCs and EPCs. Because of these geriatric-specific issues, effective treatment for fracture repair may require new therapeutic techniques to restore cellular function. Some suggested directions for potential treatments include cellular therapies, pharmacological agents, treatments targeting age-related molecular mechanisms, and physical therapeutics. Advanced age is the primary risk factor for a fracture, due to the low bone mass and inferior bone quality associated with aging; a better understanding of the dysfunctional behavior of the aging cell will provide a foundation for new treatments to decrease healing time and reduce the development of complications during the extended recovery from fracture healing in the elderly.

Biological factors involved in alveolar bone regeneration: Consensus report of Working Group 1 of the 15th European Workshop on Periodontology on Bone Regeneration

BACKGROUND AND AIMS

To describe the biology of alveolar bone regeneration.

MATERIAL AND METHODS

Four comprehensive reviews were performed on (a) mesenchymal cells and differentiation factors leading to bone formation; (b) the critical interplay between bone resorbing and formative cells; (c) the role of osteoimmunology in the formation and maintenance of alveolar bone; and (d) the self-regenerative capacity following bone injury or tooth extraction were prepared prior to the workshop.

RESULTS AND CONCLUSIONS

This summary information adds to the fuller understanding of the alveolar bone regenerative response with implications to reconstructive procedures for patient oral rehabilitation. The group collectively formulated and addressed critical questions based on each of the reviews in this consensus report to advance the field. The report concludes with identified areas of future research.

GIT1 is critical for formation of the CD31hiEmcnhi vessel subtype in coupling osteogenesis with angiogenesis via modulating preosteoclasts secretion of PDGF-BB

G protein-coupled receptor kinase 2 interacting protein-1 (GIT1) is a scaffold protein that plays a vital role in bone modeling and remodeling during osteogenesis coupled with angiogenesis. Recent studies have shown that a specialized subset of vascular endothelium strongly positive for CD31 and Endomucin (CD31^hiEmcn^hi) is coupled with anabolic bone formation. Based on our previous finding that GIT1 knockout (GIT1 KO) mice have impaired angiogenesis and bone formation, we hypothesized that GIT1 affects formation of the CD31^hiEmcn^hi vessel subtype. In the current study, GIT1 knockout (GIT1 KO) mice displayed a significant decrease in trabecular bone mass and CD31^hiEmcn^hi vessel number, compared to their wild-type counterparts. In the fracture healing mouse model, GIT1 KO mice contained a lower number of CD31^hiEmcn^hi vessels in fracture callus at days 7 and 14. However, no significant differences in the number of preosteoclasts in bone marrow, trabecular bone and callus in GIT1 KO mice were observed, compared with wild-type mice. Notably, concentrations of serum platelet-derived growth factor-BB(PDGF-BB) secreted by preosteoclasts associated with CD31^hiEmcn^hi vessel formation were lower in GIT1 KO mice. In addition, PDGF-BB-associated expression of phosphorylated extracellular signal-regulated kinase- 1/2 (ERK1/2) and specificity protein 1 (SP1) was significantly decreased in preosteoclasts of GIT1 KO mice. These results collectively suggest that GIT1 is a critical participant in formation of the CD31^hiEmcn^hi vessel subtype, highlighting a novel biologic function of this scaffold protein in preosteoclasts.

Inhibition of the Prostaglandin EP-1 Receptor in Periosteum Progenitor Cells Enhances Osteoblast Differentiation and Fracture Repair

Fracture healing is a complex and integrated process that involves mesenchymal progenitor cell (MPC) recruitment, proliferation and differentiation that eventually results in bone regeneration. Prostaglandin E2 (PGE2) is an important regulator of bone metabolism and has an anabolic effect on fracture healing. Prior work from our laboratory showed EP1^-/- mice have enhanced fracture healing, stronger cortical bones, higher trabecular bone volume and increased in vivo bone formation. We also showed that bone marrow MSCs from EP1^-/- mice exhibit increased osteoblastic differentiation in vitro. In this study we investigate the changes in the periosteal derived MPCs (PDMPCs), which are crucial for fracture repair, upon EP1 deletion. EP1^-/- PDMPCs exhibit increased numbers of total (CFU-F) and osteoblastic colonies (CFU-O) as well as enhanced osteoblastic and chondrogenic differentiation. Moreover, we tested the possible therapeutic application of a specific EP1 receptor antagonist to accelerate fracture repair. Our findings showed that EP1 antagonist administration to wild type mice in the early stages of repair similarly resulted in enhanced CFU-F, CFU-O, and osteoblast differentiation in PDMPCs and resulted in enhanced fracture callus formation at 10 days post fracture and increased bone volume and improved biomechanical healing of femur fractures at 21 days post fracture.

CREB/Wnt10b mediates the effect of COX-2 on promoting BMP9-induced osteogenic differentiation via reducing adipogenic differentiation in mesenchymal stem cells

Bone morphogenetic protein 9 (BMP9) is one of the most potent osteogenic factors, which may be a potential candidate for bone tissue engineering. However, the osteogenic capacity of BMP9 still need to be further enhanced. In this study, we determined the effect of Wnt10b on BMP9-induced osteogenic differentiation in mesenchymal stem cell (MSCs) and the possible mechanism underlying this process. We introduced the polymerase chain reaction (PCR), Western blot analysis, histochemical stain, ectopic bone formation, and microcomputed tomography analysis to evaluate the effect of Wnt10b on BMP9-induced osteogenic differentiation. Meanwhile, PCR, Western blot analysis, chromatin immunoprecipitation, and immunoprecipitation were used to analyze the possible relationship between BMP9 and Wnt10b. We found that BMP9 upregulates Wnt10b in C3H10T1/2 cells. Wnt10b increases the osteogenic markers and bone formation induced by BMP9 in C3H10T1/2 cells, and silencing Wnt10b decreases these effects of BMP9. Meanwhile, Wnt10b enhances the level of phosphorylated Smad1/5/8 (p-Smad1/5/8) induced by BMP9, which can be reduced by silencing Wnt10b. On the contrary, Wnt10b inhibits adipogenic markers induced by BMP9, which can be decreased by silencing Wnt10b. Further analysis indicated that BMP9 upregulates cyclooxygenase-2 (COX-2) and phosphorylation of cAMP-responsive element binding (p-CREB) simultaneously. COX-2 potentiates the effect of BMP9 on increasing p-CREB and Wnt10b, while silencing COX-2 decreases these effects. p-CREB interacts with p-Smad1/5/8 to bind the promoter of Wnt10b in C3H10T1/2 cells. Our findings suggested that Wnt10b can promote BMP9-induced osteogenic differentiation in MSCs, which may be mediated through enhancing BMP/Smad signal and reducing adipogenic differentiation; BMP9 may upregulate Wnt10b via the COX-2/p-CREB-dependent manner.

MiR-92 suppresses proliferation and induces apoptosis by targeting EP4/Notch1 axis in gastric cancer

MiR-92a has been shown to be dysregulated in various cancers and exhibited differential role in carcinogenesis. In this study, we sought to delineate the functional role of miR-92a and its regulatory pathway in gastric cancer. MiR-92a expression were underexpressed in tissues of gastric cancer patients with the area under curve (AUC) of 0.78. Low expression in plasma was due to the increased promoter DNA methylation of miR-92a. Overexpression of miR-92a inhibited cell proliferation and invasion, and induced apoptosis. Furthermore, miR-92a reduced tumor growth in xenograft model. EP4 and Notch 1 were identified to be negatively regulated by miR-92a, and involved in cell growth. Moreover, NF-κB expression was inversely correlated with miR-92a in gastric cancer tissues and suppressed the expression of miR-92. This study unravels the tumor suppressive role of miR-92a involving EP4/Notch 1 signaling regulated by NF-κB in gastric cancer. Further studies on miR-92a and EP4/Notch1 may provide a new treatment strategy for gastric cancer.

Ageing: Is there a role for arachidonic acid and other bioactive lipids? A review

Ageing is inevitable. Recent studies suggest that it could be delayed. Low-grade systemic inflammation is seen in type 2 diabetes mellitus, hypertension and endothelial dysfunction that are common with increasing age. In all these conditions, an alteration in arachidonic acid (AA) metabolism is seen in the form of increased formation of pro-inflammatory eicosanoids and decreased production of anti-inflammatory lipoxins, resolvins, protectins and maresins and decreased activity of desaturases. Calorie restriction, exercise and parabiosis delay age-related changes that could be related to enhanced proliferation of stem cells, decrease in inflammation and transfer of GDF-11 (growth differentiation factor-11) and other related molecules from the young to the old, increase in the formation of lipoxin A4, resolvins, protectins and maresins, hydrogen sulfide (H2S) and nitric oxide (NO); inhibition of ageing-related hypothalamic or brain IKK-β and NF-kB activation, decreased gonadotropin-releasing hormone (GnRH) release resulting in increased neurogenesis and consequent decelerated ageing. This suggests that hypothalamus participates in ageing process. N-acylethanolamines (NAEs) and lipid-derived signalling molecules can be tuned favorably under dietary restriction to extend lifespan and/or prevent advanced age associated diseases in an mTOR dependent pathway manner. Sulfur amino acid (SAA) restriction increased hydrogen sulfide (H2S) production and protected tissues from hypoxia and tissue damage. Anti-inflammatory metabolites formed from AA such as LXA4, resolvins, protectins and maresins enhance production of NO, CO, H2S; suppress NF-kB expression and alter mTOR expression and thus, may aid in delaying ageing process. Dietary restriction and exercise enhance AA metabolism to form LXA4, resolvins, protectins and maresins that have anti-inflammatory actions. AA and their metabolites also influence stem cell biology, enhance neurogenesis to improve memory and augment autophagy to prolong life span. Thus, AA and other PUFAs and their anti-inflammatory metabolites inhibit inflammation, augment stem cell proliferation, restore to normal lipid-derived signaling molecules and NO and H2S production, enhance autophagy and prolong life span.

Teriparatide (human PTH1-34) compensates for impaired fracture healing in COX-2 deficient mice

Genetic ablation of cyclooxygenase-2 (COX-2) in mice is known to impair fracture healing. To determine if teriparatide (human PTH_1-34) can promote healing of Cox-2-deficient fractures, we performed detailed in vivo analyses using a murine stabilized tibia fracture model. Periosteal progenitor cell proliferation as well as bony callus formation was markedly reduced in Cox-2^-/- mice at day 10 post-fracture. Remarkably, intermittent PTH_1-34 administration increased proliferation of periosteal progenitor cells, restored callus formation on day 7, and enhanced bone formation on days 10, 14 and 21 in Cox-2-deficient mice. PTH_1-34 also increased biomechanical torsional properties at days 10 or 14 in all genotypes, consistent with enhanced bony callus formation by radiologic examinations. To determine the effects of intermittent PTH_1-34 for callus remodeling, TRAP staining was performed. Intermittent PTH_1-34 treatment increased the number of TRAP positive cells per total callus area on day 21 in Cox-2^-/- fractures. Taken together, the present findings indicate that intermittent PTH_1-34 treatment could compensate for COX-2 deficiency and improve impaired fracture healing in Cox-2-deficient mice.

Cyclooxygenase-2 deficiency causes delayed ossification of lumbar vertebral endplates

Based on previous findings that cyclooxygenase-2 (COX-2) is a critical molecule in chondrocyte differentiation and skeletal repair, we hypothesized that COX-2 deficiency or inhibition affects the ossification of vertebral endplates (VEP) and degeneration of intervertebral discs (IVD) and thus is involved in the pathogenesis of low back pain (LBP). We aimed to delineate the COX-2 working mechanism and its interacting molecules, and to explore the effect of NSAIDs and selective COX-2 inhibitor on degenerative spinal diseases. Here, lumbar spinal samples harvested from Cox-2 mutant (Cox-2-/-) and wild type (WT) mice were used for histological examinations. Nucleus pulposus (NP) cells isolated from rat were treated with PGE-2. Mouse endplate chondrocytes (mEC) isolated from mice were treated with a recombinant sonic hedgehog (Shh) protein. A mouse IVD organ culture system was established and treated COX-2 inhibitor Celecoxib. Human lumbar endplate chondrocytes were cultured and treated with Celecoxib. Immunohistochemical (IHC) studies were done in the human and mouse VEP samples. Radiographic and histological examinations revealed delayed VEP ossification in Cox-2-/- mice compared to WT ones. Decreased PGE-2 expression was found to promote Shh expression in rat NP cells, while Shh increased noggin expression in mEC. IHC showed that noggin expression was increased while pSmad1 expression decreased in the VEP of Cox-2-/- mice. Human VEP samples from patients with severe IVD degeneration showed decreased expression of Shh and noggin and increased expression of COX-2 and pSmad1 compared with milder cases. In cultured mouse IVDs and human endplate chondrocytes, Celecoxib enhanced expression of Shh and noggin and decreased Smad1 phosphorylation. In conclusion, COX-2/PGE-2 axis plays an important role in VEP ossification and IVD degeneration through crosstalk with Shh and BMP signaling pathways. These findings may facilitate clinical use of COX-2 inhibitor to prevent LBP progression.

Nonsteroidal Anti-Inflammatory Drugs and Bone-Healing: A Systematic Review of Research Quality

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) are often avoided by orthopaedic surgeons because of their possible influence on bone-healing. This belief stems from multiple studies, in particular animal studies, that show delayed bone-healing or nonunions associated with NSAID exposure. The purpose of this review was to critically analyze the quality of published literature that evaluates the impact of NSAIDs on clinical bone-healing.

METHODS

A MEDLINE and Embase search was conducted to identify all articles relating to bone and fracture-healing and the utilization of NSAIDs. All human studies, including review articles, were identified for further analysis. Non-English-language manuscripts and in vitro and animal studies were excluded. A total of twelve clinical articles and twenty-four literature reviews were selected for analysis. The quality of the clinical studies was assessed with a modified Coleman Methodology Score with emphasis on the NSAID utilization. Review articles were analyzed with regard to variability in the cited literature and final conclusions.

RESULTS

The mean modified Coleman Methodology Score (and standard deviation) was significantly lower (p = 0.032) in clinical studies that demonstrated a negative effect of NSAIDs on bone-healing (40.0 ± 14.3 points) compared with those that concluded that NSAIDs were safe (58.8 ± 10.3 points). Review articles also demonstrated substantial variability in the number of cited clinical studies and overall conclusions. There were only two meta-analyses and twenty-two narrative reviews. The mean number (and standard deviation) of clinical studies cited was significantly greater (p = 0.008) for reviews that concluded that NSAIDs were safe (8.0 ± 4.8) compared with those that recommended avoiding them (2.1 ± 2.1). Unanimously, all reviews admitted to the need for prospective randomized controlled trials to help clarify the effects of NSAIDs on bone-healing.

CONCLUSIONS

This systematic literature review highlights the great variability in the interpretation of the literature addressing the impact of NSAIDs on bone-healing. Unfortunately, there is no consensus regarding the safety of NSAIDs following orthopaedic procedures, and future studies should aim for appropriate methodological designs to help to clarify existing discrepancies to improve the quality of care for orthopaedic patients.

CLINICAL RELEVANCE

This systematic review highlights the limitations in the current understanding of the effects of NSAIDs on bone healing. Thus, withholding these medications does not have any proven scientific benefit to patients and may even cause harm by increasing narcotic requirements in cases in which they could be beneficial for pain management. This review should encourage further basic-science and clinical studies to clarify the risks and benefits of anti-inflammatory medications in the postoperative period, with the aim of improving patient outcomes.

In vitro functional characterization of prostaglandin-endoperoxide synthase 2 during chondrocyte hypertrophic differentiation

Cyclooxygenase 2 (Cox-2) has been implicated an essential role during bone repair, but the mechanisms remain elusive. Bone repair healing is known to include processes similar to endochondral ossification. In this study, we investigated the in vitro effect of Cox-2 on Col10a1 expression and chondrocyte hypertrophy, two critical components of endochondral ossification. Using quantitative RT-PCR, we detected increased mRNA levels of Cox-2 and Col10a1 in hypertrophic MCT cells, while cells treated with Cox-2 inhibitor, NS398, showed decreased mRNA and protein levels of Cox-2 and Col10a1. Increased Cox-2 also correlated with significantly upregulated Col10a1 in hypertrophic ATDC5 cells, whereas inhibition of Cox-2 significantly decreased Col10a1 expression. We further generated a Cox-2-expressing ATDC5 stable cell line. Compared with the controls, Cox-2 over-expression significantly increased Col10a1 as early as day 7 of continuous culturing, but not at days 14 and 21. Enhanced Alp staining was also observed in day 7 stable cell line. Correspondingly, we detected significantly increased levels of Runx2, Alp, Bcl-2, Bax, Col1a1, Osterix, and Bsp in day 7 stable line. Most of these genes have been associated with chondrocyte maturation and apoptosis. Together, our results support that Cox-2 promotes Col10a1 expression and chondrocyte hypertrophy in vitro, possibly through upregulation of Runx2 and other relevant transcription factors.

Preconditioning of murine mesenchymal stem cells synergistically enhanced immunomodulation and osteogenesis

Background

Mesenchymal stem cells (MSCs) are capable of immunomodulation and tissue regeneration, highlighting their potential translational application for treating inflammatory bone disorders. MSC-mediated immunomodulation is regulated by proinflammatory cytokines and pathogen-associated molecular patterns such as lipopolysaccharide (LPS). Previous studies showed that MSCs exposed to interferon gamma (IFN-γ) and the proinflammatory cytokine tumor necrosis factor alpha (TNF-α) synergistically suppressed T-cell activation.

Methods

In the current study, we developed a novel preconditioning strategy for MSCs using LPS plus TNF-α to optimize the immunomodulating ability of MSCs on macrophage polarization.

Results

Preconditioned MSCs enhanced anti-inflammatory M2 macrophage marker expression (Arginase 1 and CD206) and decreased inflammatory M1 macrophage marker (TNF-α/IL-1Ra) expression using an in-vitro coculture model. Immunomodulation of MSCs on macrophages was significantly increased compared to the combination of IFN-γ plus TNF-α or single treatment controls. Increased osteogenic differentiation including alkaline phosphate activity and matrix mineralization was only observed in the LPS plus TNF-α preconditioned MSCs. Mechanistic studies showed that increased prostaglandin E2 (PGE2) production was associated with enhanced Arginase 1 expression. Selective cyclooxygenase-2 inhibition by Celecoxib decreased PGE2 production and Arginase 1 expression in cocultured macrophages.

Conclusions

The novel preconditioned MSCs have increased immunomodulation and bone regeneration potential and could be applied to the treatment of inflammatory bone disorders including periprosthetic osteolysis, fracture healing/nonunions, and osteonecrosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0730-z) contains supplementary material, which is available to authorized users.

Osteoimmunology in Bone Fracture Healing

PURPOSE OF REVIEW

In the process of bone fracture healing, inflammation is thought to be an essential process that precedes bone formation and remodeling. We review recent studies on bone fracture healing from an osteoimmunological point of view.

RECENT FINDINGS

Based on previous observations that many types of immune cells infiltrate into the bone injury site and release a variety of molecules, recent studies have addressed the roles of specific immune cell subsets. Macrophages and interleukin (IL)-17-producing γδ T cells enhance bone healing, whereas CD8⁺ T cells impair bone repair. Additionally, IL-10-producing B cells may contribute to bone healing by suppressing excessive and/or prolonged inflammation. Although the involvement of other cells and molecules has been suggested, the precise underlying mechanisms remain elusive. Accumulating evidence has begun to reveal the deeper picture of bone fracture healing. Further studies are required for the development of novel therapeutic strategies for bone fracture.

Overexpression of RANKL in osteoblasts: a possible mechanism of susceptibility to bone disease in cystic fibrosis

Bone fragility and loss are a significant cause of morbidity in patients with cystic fibrosis (CF), and the lack of effective therapeutic options means that treatment is more often palliative rather than curative. A deeper understanding of the pathogenesis of CF-related bone disease (CFBD) is necessary to develop new therapies. Defective CF transmembrane conductance regulator (CFTR) protein and chronic inflammation in bone are important components of the CFBD development. The receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) drive the regulation of bone turnover. To investigate their roles in CFBD, we evaluated the involvement of defective CFTR in their production level in CF primary human osteoblasts with and without inflammatory stimulation, in the presence or not of pharmacological correctors of the CFTR. No major difference in cell ultrastructure was noted between cultured CF and non-CF osteoblasts, but a delayed bone matrix mineralization was observed in CF osteoblasts. Strikingly, resting CF osteoblasts exhibited strong production of RANKL protein, which was highly localized at the cell membrane and was enhanced in TNF (TNF-α) or IL-17-stimulated conditions. Under TNF stimulation, a defective response in OPG production was observed in CF osteoblasts in contrast to the elevated OPG production of non-CF osteoblasts, leading to an elevated RANKL-to-OPG protein ratio in CF osteoblasts. Pharmacological inhibition of CFTR chloride channel conductance in non-CF osteoblasts replicated both the decreased OPG production and the enhanced RANKL-to-OPG ratio. Interestingly, using CFTR correctors such as C18, we significantly reduced the production of RANKL by CF osteoblasts, in both resting and TNF-stimulated conditions. In conclusion, the overexpression of RANKL and high membranous RANKL localization in osteoblasts are related to defective CFTR, and may worsen bone resorption, leading to bone loss in patients with CF. Targeting osteoblasts with CFTR correctors may represent an effective strategy to treat CFBD. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

In Vivo Tracking of Streptococcal Infections of Subcutaneous Origin in a Murine Model

PURPOSE

Generation of plasmin in vivo by Streptococcus pyogenes is thought to localize the active protease complexes to the pathogen surface to aid in tissue dissemination. Here, we chose to follow cutaneous streptococcal infections by the use of non-invasive bioluminescence imaging to determine if this pathogen can be followed by this approach and the extent of bacterial spread in the absence of canonical plasminogen activation by streptokinase.

PROCEDURES

Mice were injected subcutaneously with either bioluminescent strains of streptococci, namely Xen20 and Xen10 or S. pyogenes ALAB49. Bioluminescence imaging was performed daily and results were correlated with microbiological and histological analyses.

RESULTS

Comparative analysis of chronologic non-invasive datasets indicated that Xen20 did not disseminate from the initial infection site. Contrary to this, microbiological and histological analyses of Xen20 mice for total bacterial burden indicated sepsis and widespread pathogen involvement.

CONCLUSIONS

The use of bioluminescence in microbe-based studies requires genomic and pathologic characterization to correlate imaging results with underlying pathology.

Cyclooxygenase-2 deficiency impairs muscle-derived stem cell-mediated bone regeneration via cellular autonomous and non-autonomous mechanisms

This study investigated the role of cyclooxygenase-2 (COX-2) expression by donor and host cells in muscle-derived stem cell (MDSC)-mediated bone regeneration utilizing a critical size calvarial defect model. We found that BMP4/green fluorescent protein (GFP)-transduced MDSCs formed significantly less bone in COX-2 knock-out (Cox-2KO) than in COX-2 wild-type (WT) mice. BMP4/GFP-transduced Cox-2KO MDSCs also formed significantly less bone than transduced WT MDSCs when transplanted into calvarial defects created in CD-1 nude mice. The impaired bone regeneration in the Cox-2KO MDSCBMP4/GFP group is associated with downregulation of BMP4-pSMAD1/5 signaling, decreased osteogenic differentiation and lowered proliferation capacity after transplantation, compared with WT MDSCBMP4/GFP cells. The Cox-2KO MDSCBMP4/GFP group demonstrated a reduction in cell survival and direct osteogenic differentiation in vitro These effects were mediated in part by the downregulation of Igf1 and Igf2. In addition, the Cox-2KO MDSCBMP4/GFP cells recruited fewer macrophages than the WT MDSC/BMP4/GFP cells in the early phase after injury. We concluded that the bone regeneration capacity of Cox-2KO MDSCs was impaired because of a reduction in cell proliferation and survival capacities, reduction in osteogenic differentiation and a decrease in the ability of the cells to recruit host cells to the injury site.

Bone disease in cystic fibrosis: new pathogenic insights opening novel therapies

Mutations within the gene encoding for the chloride ion channel cystic fibrosis transmembrane conductance regulator (CFTR) results in cystic fibrosis (CF), the most common lethal autosomal recessive genetic disease that causes a number of long-term health problems, as the bone disease. Osteoporosis and increased vertebral fracture risk associated with CF disease are becoming more important as the life expectancy of patients continues to improve. The etiology of low bone density is multifactorial, most probably a combination of inadequate peak bone mass during puberty and increased bone losses in adults. Body mass index, male sex, advanced pulmonary disease, malnutrition and chronic therapies are established additional risk factors for CF-related bone disease (CFBD). Consistently, recent evidence has confirmed that CFTR plays a major role in the osteoprotegerin (OPG) and COX-2 metabolite prostaglandin E2 (PGE2) production, two key regulators in the bone formation and regeneration. Several others mechanisms were also recognized from animal and cell models contributing to malfunctions of osteoblast (cell that form bone) and indirectly of bone-resorpting osteoclasts. Understanding such mechanisms is crucial for the development of therapies in CFBD. Innovative therapeutic approaches using CFTR modulators such as C18 have recently shown in vitro capacity to enhance PGE2 production and normalized the RANKL-to-OPG ratio in human osteoblasts bearing the mutation F508del-CFTR and therefore potential clinical utility in CFBD. This review focuses on the recently identified pathogenic mechanisms leading to CFBD and potential future therapies for treating CFBD.

Profiling microRNA expression during fracture healing

BACKGROUND

The discovery of microRNA (miRNA) has revealed a novel type of regulatory control for gene expression. Increasing evidence suggests that miRNA regulates chondrocyte, osteoblast, and osteoclast differentiation and function, indicating miRNA as key regulators of bone formation, resorption, remodeling, and repair. We hypothesized that the functions of certain miRNAs and changes to their expression pattern may play crucial roles during the process of fracture healing.

METHODS

Standard healing fractures and unhealing fractures produced by periosteal cauterization at the fracture site were created in femurs of seventy rats, with half assigned to the standard healing fracture group and half assigned to the nonunion group. At post-fracture days 3, 7, 10, 14, 21, and 28, total RNA including miRNA was extracted from the newly generated tissue at the fracture site. Microarray analysis was performed with miRNA samples from each group on post-fracture day 14. For further analysis, we selected highly up-regulated five miRNAs in the standard healing fracture group from the microarray data. Real-time PCR was performed with miRNA samples at each time point above mentioned to compare the expression levels of the selected miRNAs between standard healing fractures and unhealing fractures and investigate their time-course changes.

RESULTS

Microarray and real-time polymerase chain reaction (PCR) analyses on day 14 revealed that five miRNAs, miR-140-3p, miR-140-5p, miR-181a-5p, miR-181d-5p, and miR-451a, were significantly highly expressed in standard healing fractures compared with unhealing fractures. Real-time PCR analysis further revealed that in standard healing fractures, the expression of all five of these miRNAs peaked on day 14 and declined thereafter.

CONCLUSION

Our results suggest that the five miRNAs identified using microarray and real-time PCR analyses may play important roles during fracture healing. These findings provide valuable information to further understand the molecular mechanism of fracture healing and may lead to the development of miRNA-based tissue engineering strategies to promote fracture healing.

HIF-1α-induced microRNA-210 reduces hypoxia-induced osteoblast MG-63 cell apoptosis

To better understand the ischemic-hypoxia-induced fracture healing impairment, we determined in this study the microRNA-210 expression in broken bone specimens and in osteoblasts under hypoxia and then determined the influence of microRNA-210 overexpression on the osteoblast cell proliferation and apoptosis. Results demonstrated that microRNA-210 expression was upregulated with an association with HIF-1α overexpression in clinical human catagmatic tissues and was upregulated HIF-1α-dependently in response to hypoxia in osteoblast MG-63 cells. CCK-8 assay indicated that microRNA-210 upregulation by microRNA-210 mimics reduced the chemotherapeutic 5-FU-induced osteoblast cell death, and colony formation assay demonstrated that microRNA-210 mimics promoted osteoblast cells growth. Moreover, the microRNA-210 mimics transfection inhibited the hypoxia-induced MG-63 cell apoptosis via inhibiting the activation of caspase 3 and caspase 9. Therefore, our research indicated a protective role of microRNA-210 in response to hypoxia. And microRNA-210 might serve as a protective role in bone fracture healing.

Hypoxia promotes AMP-activated protein kinase (AMPK) and induces apoptosis in mouse osteoblasts

The hypoxic environment around the fracture site develops post the blood flow disruption and leads to osteoblast cell death and further impairs fracture healing. Hypoxia usually leads to the mitochondrial dysfunction and then results in apoptotic cell death. AMPK is ubiquitously expressed and functions as an intracellular fuel sensor by maintaining energy balance, as is potentially activated by hypoxia, ischemia, and ROS, however, the regulatory role of AMPK in hypoxia-induced apoptosis in osteoblasts and in the fracture healing has not been identified. In present study, we firstly determined the apoptosis induction by hypoxia in mouse osteoblastic MC3T3-E1 cells via examining the apoptotic cells and the activation of apoptosis-related molecules, then investigated the activation of AMPK signaling by hypoxia via analyzing the phosphorylation of AMPKα and ACC1, finally we explored the association of the AMPK activation with the hypoxia-induced apoptosis using loss-of-function strategy. Results demonstrated that hypoxia induced apoptosis in MC3T3-E1 cells and activated the AMPK signaling. And the knockdown of AMPK via chemical treatment or RNA interfering significantly decreased the hypoxia-induced apoptosis in MC3T3-E1 cells. Taken together, present study unveiled the regulatory role of AMPK signaling in the hypoxia-induced osteoblast apoptosis.