T-cell cytokine induction of BMP-2 regulates human mesenchymal stromal cell differentiation and mineralization

Single-cell transcriptome profiling identifies the activation of type I interferon signaling in ossified posterior longitudinal ligament

Ossification of the posterior longitudinal ligament (OPLL) is a condition comprising ectopic bone formation from spinal ligaments. This disease is a leading cause of myelopathy in the Asian population. However, the molecular mechanism underlying OPLL and efficient preventive interventions remain unclear. Here, we performed single-cell RNA sequencing and revealed that type I interferon (IFN) signaling was activated in the ossified ligament of patients with OPLL. We also observed that IFN-β stimulation promoted the osteogenic differentiation of preosteoblasts in vitro and activated the ossification-related gene SPP1, thereby confirming the single-cell RNA sequencing findings. Further, blocking the IFN-α/β subunit 1 receptor (IFNAR1) using an anti-IFNAR1 neutralizing antibody markedly suppressed osteogenic differentiation. Together, these results demonstrated that the type I IFN signaling pathway facilitated ligament ossification, and the blockade of this signaling might provide a foundation for the prevention of OPLL.

Application of nanoparticles as surface modifiers of dental implants for revascularization/regeneration of bone

BACKGROUND

Osseointegrated dental implants are widely established as a first-choice treatment for the replacement of missing teeth. Clinical outcomes are however often compromised by short or longer-term biological complications and pathologies. Nanoparticle-coated materials represent a very active research area with the potential to enhance clinical outcomes and reduce complications of implant therapy. This scoping review aimed to summarize current research on various types of nanoparticles (NPs) used as surface modifiers of dental implants and their potential to promote biological and clinical outcomes.

METHODS

A systematic electronic search was conducted in SCOPUS, PubMed and Google Scholar aiming to identify in vivo, in situ, or in vitro studies published between 2014 and 2024. Inclusion and exclusion criteria were determined and were described in the methods section.

RESULTS

A total of 169 articles (44 original papers from Scopus and PubMed, and 125 articles from Google Scholar) were identified by the electronic search. Finally, 30 studies fit the inclusion criteria and were further used in this review. The findings from the selected papers suggest that nanoparticle-coated dental implants show promising results in enhancing bone regeneration and promoting angiogenesis around the implant site. These effects are due to the unique physicochemical properties of nanoparticle-coated implants and the controlled release of bioactive molecules from nanoparticle-modified surfaces.

CONCLUSION

Nanoscale modifications displayed unique properties which could significantly enhance the properties of dental implants and further accelerate revascularization, and osseointegration while facilitating early implant loading. Yet, since many of these findings were based on in-vitro/in-situ systems, further research is required before such technology reaches clinical application.

The interactions of macrophages, lymphocytes, and mesenchymal stem cells during bone regeneration

Bone regeneration and repair are crucial to ambulation and quality of life. Factors such as poor general health, serious medical comorbidities, chronic inflammation, and ageing can lead to delayed healing and nonunion of fractures, and persistent bone defects. Bioengineering strategies to heal bone often involve grafting of autologous bone marrow aspirate concentrate (BMAC) or mesenchymal stem cells (MSCs) with biocompatible scaffolds. While BMAC shows promise, variability in its efficacy exists due to discrepancies in MSC concentration and robustness, and immune cell composition. Understanding the mechanisms by which macrophages and lymphocytes - the main cellular components in BMAC - interact with MSCs could suggest novel strategies to enhance bone healing. Macrophages are polarized into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, and influence cell metabolism and tissue regeneration via the secretion of cytokines and other factors. T cells, especially helper T1 (Th1) and Th17, promote inflammation and osteoclastogenesis, whereas Th2 and regulatory T (Treg) cells have anti-inflammatory pro-reconstructive effects, thereby supporting osteogenesis. Crosstalk among macrophages, T cells, and MSCs affects the bone microenvironment and regulates the local immune response. Manipulating the proportion and interactions of these cells presents an opportunity to alter the local regenerative capacity of bone, which potentially could enhance clinical outcomes.

Osteoporosis: interferon-gamma-mediated bone remodeling in osteoimmunology

As the world population ages, osteoporosis, the most common disease of bone metabolism, affects more than 200 million people worldwide. The etiology is an imbalance in bone remodeling process resulting in more significant bone resorption than bone remodeling. With the advent of the osteoimmunology field, the immune system's role in skeletal pathologies is gradually being discovered. The cytokine interferon-gamma (IFN-γ), a member of the interferon family, is an important factor in the etiology and treatment of osteoporosis because it mediates bone remodeling. This review starts with bone remodeling process and includes the cellular and key signaling pathways of bone remodeling. The effects of IFN-γ on osteoblasts, osteoclasts, and bone mass are discussed separately, while the overall effects of IFN-γ on primary and secondary osteoporosis are summarized. The net effect of IFN-γ on bone appears to be highly dependent on the environment, dose, concentration, and stage of cellular differentiation. This review focuses on the mechanisms of bone remodeling and bone immunology, with a comprehensive discussion of the relationship between IFN-γ and osteoporosis. Finding the paradoxical balance of IFN-γ in bone immunology and exploring the potential of its clinical application provide new ideas for the clinical treatment of osteoporosis and drug development.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Osteoimmunomodulatory Nanoparticles for Bone Regeneration

Treatment of large bone fractures remains a challenge for orthopedists. Bone regeneration is a complex process that includes skeletal cells such as osteoblasts, osteoclasts, and immune cells to regulate bone formation and resorption. Osteoimmunology, studying this complicated process, has recently been used to develop biomaterials for advanced bone regeneration. Ideally, a biomaterial shall enable a timely switch from early stage inflammatory (to recruit osteogenic progenitor cells) to later-stage anti-inflammatory (to promote differentiation and terminal osteogenic mineralization and model the microstructure of bone tissue) in immune cells, especially the M1-to-M2 phenotype switch in macrophage populations, for bone regeneration. Nanoparticle (NP)-based advanced drug delivery systems can enable the controlled release of therapeutic reagents and the delivery of therapeutics into specific cell types, thereby benefiting bone regeneration through osteoimmunomodulation. In this review, we briefly describe the significance of osteoimmunology in bone regeneration, the advancement of NP-based approaches for bone regeneration, and the application of NPs in macrophage-targeting drug delivery for advanced osteoimmunomodulation.

Bio-Activated PEEK: Promising Platforms for Improving Osteogenesis through Modulating Macrophage Polarization

The attention on orthopedic biomaterials has shifted from their direct osteogenic properties to their osteoimmunomodulation, especially the modulation of macrophage polarization. Presently, advanced technologies endow polyetheretherketone (PEEK) with good osteoimmunomodulation by modifying PEEK surface characteristics or incorporating bioactive substances with regulating macrophage polarization. Recent studies have demonstrated that the fabrication of a hydrophilic surface and the incorporation of bioactive substances into PEEK (e.g., zinc, calcium, and phosphate) are good strategies to promote osteogenesis by enhancing the polarization of M2 macrophages. Furthermore, the modification by other osteoimmunomodulatory composites (e.g., lncRNA-MM2P, IL-4, IL-10, and chitosan) and their controlled and desired release may make PEEK an optimal bio-activated implant for regulating and balancing the osteogenic system and immune system. The purpose of this review is to comprehensively evaluate the potential of bio-activated PEEK in polarizing macrophages into M2 phenotype to improve osteogenesis. For this objective, we retrieved and discussed different kinds of bio-activated PEEK regarding improving osteogenesis through modulating macrophage polarization. Meanwhile, the relevant challenges and outlook were presented. We hope that this review can shed light on the development of bio-activated PEEK with more favorable osteoimmunomodulation.

Osteoimmunomodulatory potential of 3D printed submicron patterns assessed in a direct co-culture model

Modulation of the immune response following the implantation of biomaterials can have beneficial effects on bone regeneration. This involves complex interactions between the inflammatory and osteogenic cells. Therefore, the study of cell-cell interactions using direct co-culture models integrated with biomaterials is of great interest. This research aimed to study the viability, morphology, and osteogenic activity of preosteoblasts (OBs) co-cultured with pro-inflammatory macrophages (M1s) on the 3D printed (non)patterned surfaces. OBs and M1s remained alive and proliferated actively for 14 days in the mixture of Dulbecco's Modified Eagle's Medium (DMEM) and alpha Minimum Essential Medium (α-MEM) (1:1), regardless of the cell ratio in the co-cultures. The spatial organization of the two types of cells changed with the time of culture from an initially uniform cell distribution to the formation of a thick layer of OBs covered by clusters of M1s. On day 7, the expression of PGE2 and TNF-α were upregulated in the co-culture relative to the mono-culture of OBs and M1s. The inflammation decreased differentiation and matrix mineralization of OBs after 28 days of culture. Interestingly, the incorporation of 3D printed submicron pillars into the direct co-culture model enhanced the differentiation of preosteoblasts, as shown by relatively higher RUNX2 expression, thereby revealing the osteoimmunomodulatory potential of such surface patterns.

Current Development of Nano-Drug Delivery to Target Macrophages

Macrophages are the most important innate immune cells that participate in various inflammation-related diseases. Therefore, macrophage-related pathological processes are essential targets in the diagnosis and treatment of diseases. Since nanoparticles (NPs) can be preferentially taken up by macrophages, NPs have attracted most attention for specific macrophage-targeting. In this review, the interactions between NPs and the immune system are introduced to help understand the pharmacokinetics and biodistribution of NPs in immune cells. The current design and strategy of NPs modification for specific macrophage-targeting are investigated and summarized.

The Paget's disease of bone risk gene PML is a negative regulator of osteoclast differentiation and bone resorption

Paget's disease of bone (PDB) is characterized by focal increases in bone remodelling. Genome-wide association studies identified a susceptibility locus for PDB tagged by rs5742915, which is located within the PML gene. Here, we have assessed the candidacy of PML as the predisposing gene for PDB at this locus. We found that the PDB-risk allele of rs5742915 was associated with lower PML expression and that PML expression in blood cells from individuals with PDB was lower than in controls. The differentiation, survival and resorptive activity of osteoclasts prepared from Pml-/- mice was increased compared with wild type. Furthermore, the inhibitory effect of IFN-γ on osteoclast formation from Pml-/- was significantly blunted compared with wild type. Bone nodule formation was also increased in osteoblasts from Pml-/- mice when compared with wild type. Although microCT analysis of trabecular bone showed no differences between Pml-/- mice and wild type, bone histomorphometry showed that Pml-/- mice had high bone turnover with increased indices of bone resorption and increased mineral apposition rate. These data indicate that reduced expression of PML predisposes an individual to PDB and identify PML as a novel regulator of bone metabolism. This article has an associated First Person interview with the first author of the paper.

Malfunction of airway basal stem cells plays a crucial role in pathophysiology of tracheobronchopathia osteoplastica

Understanding disease-associated stem cell abnormality has major clinical implications for prevention and treatment of human disorders, as well as for regenerative medicine. Here we report a multifaceted study on airway epithelial stem cells in Tracheobronchopathia Osteochondroplastica (TO), an under-detected tracheobronchial disorder of unknown etiology and lack of specific treatment. Epithelial squamous metaplasia and heterotopic bone formation with abnormal cartilage proliferation and calcium deposits are key pathological hallmarks of this disorder, but it is unknown whether they are coincident or share certain pathogenic mechanisms in common. By functional evaluation and genome-wide profiling at both transcriptional and epigenetic levels, we reveal a role of airway basal cells in TO progression by acting as a repository of inflammatory and TGFβ-BMP signals, which contributes to both epithelial metaplasia and mesenchymal osteo-chondrogenesis via extracellular signaling and matrix remodeling. Restoration of microenvironment by cell correction or local pathway intervention may provide therapeutic benefits.

Tracheobronchopathia osteoplastica (TO), is an underreported affliction characterized by squamous metaplasia and heterotopic bone formation in trachea and bronchi. Here the authors apply functional, as well as genome-wide transcriptional and epigenetic profiling to identify airway basal cells dysfunction underlying TO.

Intermittent Hypoxic Therapy Inhibits Allogenic Bone-Graft Resorption by Inhibition of Osteoclastogenesis in a Mouse Model

Systemic Intermittent Hypoxic Therapy (IHT) relies on the adaptive response to hypoxic stress. We investigated allogenic bone-graft resorption in the lumbar spine in 48 mice. The mice were exposed to IHT for 1 week before surgery or 1 week after surgery and compared with controls after 1 and 4 weeks. Complete graft resorption was observed in 33-36% of the animals in the control group, but none in the preoperative IHT group. Increased bone-graft volume was demonstrated by micro-computed tomography in the preoperative IHT group after 1 week (p = 0.03) while a non-significant difference was observed after 4 weeks (p = 0.12). There were no significant differences in the postoperative IHT group. Increased concentration of immune cells was localized in the graft area, and more positive tartrate-resistant acid phosphatase (TRAP) staining was found in controls compared with IHT allogenic bone grafts. Systemic IHT resulted in a significant increase of the major osteoclast inhibitor osteoprotegerin as well as osteogenic and angiogenic regulators Tgfbr3, Fst3l, Wisp1, and Vegfd. Inflammatory cytokines and receptor activator of nuclear factor kappa-B ligand (RANKL) stimulators IL-6, IL-17a, IL-17f, and IL-23r increased after 1 and 4 weeks, and serum RANKL expression remained constant while Ccl3 and Ccl5 decreased. We conclude that the adaptive response to IHT activates numerous pathways leading to inhibition of osteoclastic activity and inhibition of allogenic bone-graft resorption.

The response of macrophages and their osteogenic potential modulated by micro/nano-structured Ti surfaces

Current understanding on the interactions between micro/nano-structured Ti surfaces and macrophages is still limited. In this work, TiO₂ nano-structures were introduced onto acid-etched Ti surfaces by alkali-heat treatment, ion exchange and subsequent heat treatment. By adjusting the concentration of NaOH during alkali-heat treatment, nano-flakes, nano-flakes mixed with nano-wires or nano-wires could formed on acid-etched Ti surfaces. The micro- and micro/nano-structured Ti surfaces possessed similar surface chemical and phase compositions. In vitro results indicate that the morphology of macrophages was highly dependent on the morphological features of nano-structures. Nano-flakes and nano-wires were favorable to induce the formation of lamellipodia and filopodia, respectively. Compared to micro-structured Ti surface, micro/nano-structured Ti surfaces polarized macrophages to their M2 phenotype and enhanced the gene expressions of osteogenic growth factors in macrophages. The M2 polarized macrophages promoted the maturation of osteoblasts. Compared to that with nano-flakes or nano-wires, the surface with mixed features of nano-flakes and nano-wires exhibited stronger anti-inflammatory and osteo-immunomodulatory effects. The findings presented in the current work suggest that introducing micro/nano-topographies onto Ti-based implant surfaces is a promising strategy to modulate the inflammatory response and mediate osteogenesis.

Exploring the Biomaterial-Induced Secretome: Physical Bone Substitute Characteristics Influence the Cytokine Expression of Macrophages

In addition to their chemical composition various physical properties of synthetic bone substitute materials have been shown to influence their regenerative potential and to influence the expression of cytokines produced by monocytes, the key cell-type responsible for tissue reaction to biomaterials in vivo. In the present study both the regenerative potential and the inflammatory response to five bone substitute materials all based on β-tricalcium phosphate (β-TCP), but which differed in their physical characteristics (i.e., granule size, granule shape and porosity) were analyzed for their effects on monocyte cytokine expression. To determine the effects of the physical characteristics of the different materials, the proliferation of primary human osteoblasts growing on the materials was analyzed. To determine the immunogenic effects of the different materials on human peripheral blood monocytes, cells cultured on the materials were evaluated for the expression of 14 pro- and anti-inflammatory cytokines, i.e., IL-6, IL-10, IL-1β, VEGF, RANTES, IL-12p40, I-CAM, IL-4, V-CAM, TNF-α, GM-CSF, MIP-1α, Il-8 and MCP-1 using a Bio-Plex^® Multiplex System. The granular shape of bone substitutes showed a significant influence on the osteoblast proliferation. Moreover, smaller pore sizes, round granular shape and larger granule size increased the expression of GM-CSF, RANTES, IL-10 and IL-12 by monocytes, while polygonal shape and the larger pore sizes increased the expression of V-CAM. The physical characteristics of a bone biomaterial can influence the proliferation rate of osteoblasts and has an influence on the cytokine gene expression of monocytes in vitro. These results indicate that the physical structure of a biomaterial has a significant effect of how cells interact with the material. Thus, specific characteristics of a material may strongly affect the regenerative potential in vivo.

Inflammation and biomaterials: role of the immune response in bone regeneration by inorganic scaffolds

The regulatory role of the immune system in maintaining bone homeostasis and restoring its functionality, when disturbed due to trauma or injury, has become evident in recent years. The polarization of macrophages, one of the main constituents of the immune system, into the pro-inflammatory or anti-inflammatory phenotype has great repercussions for cellular crosstalk and the subsequent processes needed for proper bone regeneration such as angiogenesis and osteogenesis. In certain scenarios, the damaged osseous tissue requires the placement of synthetic bone grafts to facilitate the healing process. Inorganic biomaterials such as bioceramics or bioactive glasses are the most widely used due to their resemblance to the mineral phase of bone and superior osteogenic properties. The immune response of the host to the inorganic biomaterial, which is of an exogenous nature, might determine its fate, leading either to active bone regeneration or its failure. Therefore, various strategies have been employed, like the modification of structural/chemical features or the incorporation of bioactive molecules, to tune the interplay with the immune cells. Understanding how these particular modifications impact the polarization of macrophages and further osteogenic and osteoclastogenic events is of great interest in view of designing a new generation of osteoimmunomodulatory materials that support the regeneration of osseous tissue during all stages of bone healing.

The State of the Art and Prospects for Osteoimmunomodulatory Biomaterials

The critical role of the immune system in host defense against foreign bodies and pathogens has been long recognized. With the introduction of a new field of research called osteoimmunology, the crosstalk between the immune and bone-forming cells has been studied more thoroughly, leading to the conclusion that the two systems are intimately connected through various cytokines, signaling molecules, transcription factors and receptors. The host immune reaction triggered by biomaterial implantation determines the in vivo fate of the implant, either in new bone formation or in fibrous tissue encapsulation. The traditional biomaterial design consisted in fabricating inert biomaterials capable of stimulating osteogenesis; however, inconsistencies between the in vitro and in vivo results were reported. This led to a shift in the development of biomaterials towards implants with osteoimmunomodulatory properties. By endowing the orthopedic biomaterials with favorable osteoimmunomodulatory properties, a desired immune response can be triggered in order to obtain a proper bone regeneration process. In this context, various approaches, such as the modification of chemical/structural characteristics or the incorporation of bioactive molecules, have been employed in order to modulate the crosstalk with the immune cells. The current review provides an overview of recent developments in such applied strategies.

Modulating macrophage activities to promote endogenous bone regeneration: Biological mechanisms and engineering approaches

A coordinated interaction between osteogenesis and osteoimmune microenvironment is essential for successful bone healing. In particular, macrophages play a central regulatory role in all stages of bone repair. Depending on the signals they sense, these highly plastic cells can mediate the host immune response against the exterior signals of molecular stimuli and implanted scaffolds, to exert regenerative potency to a varying extent. In this article, we first encapsulate the immunomodulatory functions of macrophages during bone regeneration into three aspects, as sweeper, mediator and instructor. We introduce the phagocytic role of macrophages in different bone healing periods ('sweeper') and overview a variety of paracrine cytokines released by macrophages either mediating cell mobilisation, vascularisation and matrix remodelling ('mediator'), or directly driving the osteogenic differentiation of bone progenitors and bone repair ('instructor'). Then, we systematically classify and discuss the emerging engineering strategies to recruit, activate and modulate the phenotype transition of macrophages, to exploit the power of endogenous macrophages to enhance the performance of engineered bone tissue.

What do we know about bone morphogenetic proteins and osteochondroprogenitors in inflammatory conditions?

Osteochondroprogenitors are crucial for embryonic bone development and postnatal processes such as bone repair in response to fracture injury, and their dysfunction may contribute to insufficient repair of structural damage in inflammatory arthritides. In the fracture healing, the early inflammatory phase is crucial for normal callus development and new bone formation. This process involves a complex interplay of many molecules and cell types, responsible for recruitment, expansion and differentiation of osteochondroprogenitor populations. In inflammatory arthritides, inflammation induces bone resorption and causes insufficient bone formation, which leads to local and systemic bone loss. While bone loss is a predominant feature in rheumatoid arthritis, inflammation also induces pathologic bone formation at enthesial sites in seronegative spondyloarthropathies. Bone morphogenetic proteins (BMP) are involved in cell proliferation, differentiation and apoptosis, and have fundamental roles in maintenance of postnatal bone homeostasis. They are crucial regulators of the osteochondroprogenitor pool and drive their proliferation, differentiation, and lifespan during bone regeneration. In this review, we summarize the effects of inflammation on osteochondroprogenitor populations during fracture repair and in inflammatory arthritides, with special focus on inflammation-mediated modulation of BMP signaling. We also present data in which we describe a population of murine synovial osteochondroprogenitor cells, which are reduced in arthritis, and characterize their expression of genes involved in regulation of bone homeostasis, emphasizing the up-regulation of BMP pathways in early progenitor subset. Based on the presented data, it may be concluded that during an inflammatory response, innate immune cells induce osteochondroprogenitors by providing signals for their recruitment, by producing BMPs and other osteogenic factors for paracrine effects, and by secreting inflammatory cytokines that may positively regulate osteogenic pathways. On the other hand, inflammatory cells may secrete cytokines that interfere with osteogenic pathways, proapoptotic factors that reduce the pool of osteochondroprogenitor cells, as well as BMP and Wnt antagonists. The net effect is strongly context-dependent and influenced by the local milieu of cells, cytokines, and growth factors. Further elucidation of the interplay between inflammatory signals and BMP-mediated bone formation may provide valuable tools for therapeutic targeting.

Effects of Physical, Chemical, and Biological Stimulus on h-MSC Expansion and Their Functional Characteristics

Human adult mesenchymal stem or stromal cells (h-MSC) therapy has gained considerable attention due to the potential to treat or cure diseases given their immunosuppressive properties and tissue regeneration capabilities. Researchers have explored diverse strategies to promote high h-MSC production without losing functional characteristics or properties. Physical stimulus including stiffness, geometry, and topography, chemical stimulus, like varying the surface chemistry, and biochemical stimuli such as cytokines, hormones, small molecules, and herbal extracts have been studied but have yet to be translated to industrial manufacturing practice. In this review, we describe the role of those stimuli on h-MSC manufacturing, and how these stimuli positively promote h-MSC properties, impacting the cell manufacturing field for cell-based therapies. In addition, we discuss other process considerations such as bioreactor design, good manufacturing practice, and the importance of the cell donor and ethics factors for manufacturing potent h-MSC.

The effect of biomimetic calcium deficient hydroxyapatite and sintered β-tricalcium phosphate on osteoimmune reaction and osteogenesis

Biomaterial implantation triggers inflammatory reactions. Understanding the effect of physicochemical features of biomaterials on the release of inflammatory cytokines from immune cells would be of great interest in view of designing bone graft materials to enhance the healing of bone defects. The present work investigated the interactions of two chemically and texturally different calcium phosphate (CaPs) substrates with macrophages, one of the main innate immune cells, and its further impact on osteogenic differentiation of bone forming cells. The behaviour of macrophages seeded on biomimetic calcium deficient hydroxyapatite (CDHA) and sintered β-tricalcium phosphate (β-TCP) was assessed in terms of the release of inflammatory cytokines and osteoclastogenic factors. The osteogenic differentiation of bone progenitor cells (bone marrow stromal cells (BMSCs) and osteoblastic cell line (SaOS-2)) were subsequently studied by incubating with the conditioned medium induced by macrophage-CaPs interaction in order to reveal the effect of immune cell reaction to CaPs on osteogenic differentiation. It was found that the incubation of macrophages with CaPs substrates caused a decrease of pro-inflammatory cytokines, more pronounced for β-TCP compared with CDHA showing significantly decreased IL-6, TNF-a, and iNOS. However, the macrophage-CDHA interaction resulted in a more favourable environment for osteogenic differentiation of osteoblasts with more collagen type I production and osteogenic genes (Runx2, BSP) expression, suggesting that osteogenic differentiation of bone cells is not only determined by the nature of biomaterials, but also significantly influenced by the inflammatory environment generated by the interaction of immune cells and biomaterials. STATEMENT OF SIGNIFICANCE: The field of osteoimmunology highlights the importance of the cross-talk between immune and bone cells for effective bone regeneration. This tight interaction opens the door to new strategies that encompass the development of smart cell-instructive biomaterials which performance covers the events from early inflammation to osteogenesis. The present work links the anti-inflammatory and osteoimmunomodulatory features of synthetic bone grafts to their chemistry and texture, focussing on the cross-talk between macrophages and two major orchestrators of bone healing, namely primary mesenchymal stem cells and osteoblasts. The results emphasize the importance of the microenvironment created through the interaction between the substrate and the immune cells as it can stimulate osteogenic events and subsequently foster bone healing.

Self-mineralizing Ca-enriched methacrylated gellan gum beads for bone tissue engineering

In this study, methacrylated gellan-gum (GG-MA) heteropolysaccharide is proposed as a hydrogel for drug delivery and bone tissue engineering applications. Calcium-enriched beads obtained from the crosslinking of 1% (w/v) GG-MA solutions with 0.1 MCaCl₂ were investigated, considering their intrinsic capacity to promote self-mineralization by ion binding and deposition. Indeed, when immersed in a physiological environment, the Ca-enriched beads promoted the development of a bone-like apatite layer, as confirmed by EDS and XRD chemical analysis. Additionally, the mild production process is compatible with drugs incorporation and release. After encapsulation, Dextran with different molecular weights as well as Dexamethasone 21-phosphate were efficiently released to the surrounding environment. The engineered system was also evaluated considering its biocompatibility, by means of qualitative determination of total complement activation, macrophage proliferation, cytokine release and in vitro cell culture. These experiments showed that the developed hydrogels may not stimulate a disproportionate pro-inflammatory reaction once transplanted. At last, when implanted subcutaneously in CD1 male mice up to 8 weeks, the beads were completely calcified, and no inflammatory reaction was observed. Summing up, these results show that calcium-enriched GG-MA hydrogel beads hold great potential as news tools for bone tissue regeneration and local drug delivery applications. STATEMENT OF SIGNIFICANCE: This work describes a low-cost and straightforward strategy to prepare bioactive methacrylated gellan gum (GG-MA) hydrogels, which can be used as drug delivery systems. GG-MA is a highly anionic polymer, that can be crosslinked with divalent ions, as calcium. Taking advantage of this feature, it was possible to prepare Ca-enriched GG-MA hydrogel beads. These beads display a bioactive behavior, since they promote apatite deposition when placed in physiological conditions. Studies on the immune response suggest that the developed beads do not trigger severe immune responses. Importantly, the mild processing method render these beads compliant with drug delivery strategies, paving the way for the application of dual-functional materials on bone tissue engineering.

TNF-α suppresses osteogenic differentiation of MSCs by accelerating P2Y2 receptor in estrogen-deficiency induced osteoporosis

Tumor Necrosis Factor-α (TNF-α)-inhibited osteogenic differentiation of mesenchymal stem cells (MSCs) contributes to impaired bone formation, which plays a central role in the pathogenesis of postmenopausal osteoporosis. However, the exact mechanisms of TNF-α-inhibited osteoblast differentiation have not been fully elucidated. Multiple P2 purinoceptor subtypes are expressed in several species of osteoblasts and are confirmed to regulate bone metabolism. The purpose of this study is to investigate whether P2 purinoceptors are involved in TNF-α-inhibited osteoblast differentiation. This study shows TNF-α increased P2Y₂ receptor expression in the differentiation of MSCs into osteoblasts in a noticeable manner. Overexpressing or silencing of the P2Y₂ receptor either impaired or promoted osteogenic differentiation of MSCs significantly. Silencing of the P2Y₂ receptor attenuated the inhibitory effects of TNF-α on osteoblastic differentiation of MSCs. In addition, silencing of the P2Y₂ receptor evidently alleviated TNF-α-inhibited MSC proliferation. P2Y₂ receptor expression was mechanistically upregulated by TNF-α mainly through extracellular regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways. Overall, our results revealed a novel function of the P2Y₂ receptor and suggested suppressing the P2Y₂ receptor may be an effective strategy to promote bone formation in estrogen deficiency-induced osteoporosis.

Effect of nano-structural properties of biomimetic hydroxyapatite on osteoimmunomodulation

Immune cells are sensitive to the microstructural and textural properties of materials. Tuning the structural features of synthetic bone grafts could be a valuable strategy to regulate the specific response of the immune system, which in turn modulates the activity of bone cells. The aim of this study was to analyse the effect of the structural characteristics of biomimetic calcium deficient hydroxyapatite (CDHA) on the innate immune response of macrophages and the subsequent impact on osteogenesis and osteoclastogenesis. Murine RAW 264.7 cells were cultured, under standard and inflammatory conditions, on chemically identical CDHA substrates that varied in microstructure and porosity. The impact on osteogenesis was evaluated by incubating osteoblastic cells (SaOS-2) with RAW-CDHA conditioned extracts. The results showed that macrophages were sensitive to different textural and structural properties of CDHA. Under standard conditions, the impact of inflammatory cytokine production by RAW cells cultured on CDHA played a significant role in the degradation of substrates, suggesting the impact of resorptive behaviour of RAW cells on biomimetic surfaces. Osteoblast differentiation was stimulated by the conditioned media collected from RAW cells cultured on needle-like nanostructured CDHA. The results demonstrated that needle-like nanostructured CDHA was able to generate a favourable osteoimmune environment to regulate osteoblast differentiation and osteogenesis. Under inflammatory conditions, the incubation of RAW cells with less porous CDHA resulted in a decreased gene expression and release of pro-inflammatory cytokines.

Nanotopography-based strategy for the precise manipulation of osteoimmunomodulation in bone regeneration

Immune cells play vital roles in regulating bone dynamics. Successful bone regeneration requires a favourable osteo-immune environment. The high plasticity and diversity of immune cells make it possible to manipulate the osteo-immune response of immune cells, thus modulating the osteoimmune environment and regulating bone regeneration. With the advancement in nanotechnology, nanotopographies with different controlled surface properties can be fabricated. On tuning the surface properties, the osteo-immune response can be precisely modulated. This highly tunable characteristic and immunomodulatory effects make nanotopography a promising strategy to precisely manipulate osteoimmunomdulation for bone tissue engineering applications. This review first summarises the effects of the immune response during bone healing to show the importance of regulating the immune response for the bone response. The plasticity of immune cells is then reviewed to provide rationales for manipulation of the osteoimmune response. Subsequently, we highlight the current types of nanotopographies applied in bone biomaterials and their fabrication techniques, and explain how these nanotopographies modulate the immune response and the possible underlying mechanisms. The effects of immune cells on nanotopography-mediated osteogenesis are emphasized, and we propose the concept of "nano-osteoimmunomodulation" to provide a valuable strategy for the development of nanotopographies with osteoimmunomodulatory properties that can precisely regulate bone dynamics.

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

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

Inhibition of TGFβ signaling decreases osteogenic differentiation of fibrodysplasia ossificans progressiva fibroblasts in a novel in vitro model of the disease

Fibrodysplasia ossificans progressiva is a rare genetic disorder characterized by progressive heterotopic ossification. FOP patients develop soft tissue lumps as a result of inflammation-induced flare-ups which leads to the irreversible replacement of skeletal muscle tissue with bone tissue. Classical FOP patients possess a mutation (c.617G>A; R206H) in the ACVR1-encoding gene which leads to dysregulated BMP signaling. Nonetheless, not all FOP patients with this mutation exhibit equal severity in symptom presentation or disease progression which indicates a strong contribution by environmental factors. Given the pro-inflammatory role of TGFβ, we studied the role of TGFβ in the progression of osteogenic differentiation in primary dermal fibroblasts from five classical FOP patients based on a novel method of platelet lysate-based osteogenic transdifferentiation. During the course of transdifferentiation the osteogenic properties of the cells were evaluated by the mRNA expression of Sp7/Osterix, Runx2, Alp, OC and the presence of mineralization. During transdifferentiation the expression of osteoblast markers Runx2 (p<0.05) and Alp were higher in patient cells compared to healthy controls. All cell lines exhibited increase in mineralisation. FOP fibroblasts also expressed higher baseline Sp7/Osterix levels (p<0.05) confirming their higher osteogenic potential. The pharmacological inhibition of TGFβ signaling during osteogenic transdifferentiation resulted in the attenuation of osteogenic transdifferentiation in all cell lines as shown by the decrease in the expression of Runx2 (p<0.05), Alp and mineralization. We suggest that blocking of TGFβ signaling can decrease the osteogenic transdifferentiation of FOP fibroblasts.

Proinflammatory T cells and IL-17 stimulate osteoblast differentiation

The local immune response is important to consider when the aim is to improve bone regeneration. Recently T lymphocytes and their associated cytokines have been identified as regulators in fracture callus formation, but it is not known whether T cells affect bone progenitor cells directly. The goal of this in vitro study was to investigate the role of different T cell subsets and their secreted factors on the osteogenic differentiation of human mesenchymal stem cells (MSCs). Significant increases in the alkaline phosphatase activity and the subsequent matrix mineralization by MSCs were found after their exposure to activated T cells or activated T cell-derived conditioned medium. Blocking IFN-γ in the conditioned medium abolished its pro-osteogenic effect, while blocking TGF-β further enhanced osteogenesis. The relative contribution of an anti- or proinflammatory T cell phenotype in MSC osteogenic differentiation was studied next. Enrichment of the fraction of anti-inflammatory regulatory T cells had no beneficial osteogenic effect. In contrast, soluble factors derived from enriched T helper 17 cells upregulated the expression of osteogenic markers by MSCs. IL-17A, and IL-17F, their main proinflammatory cytokines, similarly exhibited strong osteogenic effects when exposed directly to MSCs. IL-17A in particular showed a synergistic action together with bone morphogenetic protein 2. These results indicate that individual T cell subsets, following their activation, affect osteoblast maturation in a different manner through the production of soluble factors. From all T cells, the proinflammatory T cells, including the T helper 17 cells, are most stimulatory for osteogenesis.

High mobility group box 1-immobilized nanofibrous scaffold enhances vascularization, osteogenesis and stem cell recruitment

An engineered, multi-functional HMGB1-immobilized scaffold is developed. HMGB1 is immobilized on the surface of electrospinning poly-l-lactide (PLLA)/polycaprolactone (PCL) nanofibers via heparin, which is used as a “trigger” signal to make the bone scaffold capable of enhancing vascularization, inducing osteogenesis and recruiting stem cells.

T cells, osteoblasts, and osteocytes: interacting lineages key for the bone anabolic and catabolic activities of parathyroid hormone

Osteoimmunology is a field of research dedicated to the study of the interactions between the immune system and bone. Among the cells of the immune system that regulate bone turnover and the responsiveness of bone cells to calciothropic hormones are bone marrow T lymphocytes. T cells secrete osteoclastogenic cytokines such as RANKL and TNF-α, as well as factors that stimulate bone formation, one of which is Wnt10b. In addition, T cells regulate the differentiation and life span of stromal cells (SCs) and their responsiveness to parathyroid hormone (PTH) via costimulatory molecules expressed on their surface. The conditioning effect of T cells on SCs is inherited by the osteoblastic and osteocytic progeny of SCs. As a result, osteoblastic cells of T cell-deficient mice have functional characteristics different from corresponding cells of T cell-replete mice. These differences include the ratio of RANKL/OPG produced in response to continuous PTH treatment, and the osteoblastogenic response to intermittent PTH treatment. This article reviews the evidence indicating that the effects of PTH are mediated not only by osteoblasts and osteocytes but also by T cells.

Cross-talk between bone morphogenetic proteins and inflammatory pathways

Pro-inflammatory cytokines and bone morphogenetic proteins are generally studied separately and considered to be elements of different worlds, immunology and developmental biology. Varas and colleagues report that these factors show cross-talk in rheumatoid arthritis synoviocytes. They show that pro-inflammatory cytokines not only stimulate the production of bone morphogenetic proteins but that these endogenously produced bone morphogenetic proteins interfere with the effects of pro-inflammatory cytokines on synoviocytes.

Selection of animal models for pre-clinical strategies in evaluating the fracture healing, bone graft substitutes and bone tissue regeneration and engineering

In vitro assays can be useful in determining biological mechanism and optimizing scaffold parameters, however translation of the in vitro results to clinics is generally hard. Animal experimentation is a better approximation than in vitro tests, and usage of animal models is often essential in extrapolating the experimental results and translating the information in a human clinical setting. In addition, usage of animal models to study fracture healing is useful to answer questions related to the most effective method to treat humans. There are several factors that should be considered when selecting an animal model. These include availability of the animal, cost, ease of handling and care, size of the animal, acceptability to society, resistance to surgery, infection and disease, biological properties analogous to humans, bone structure and composition, as well as bone modeling and remodeling characteristics. Animal experiments on bone healing have been conducted on small and large animals, including mice, rats, rabbits, dogs, pigs, goats and sheep. This review also describes the molecular events during various steps of fracture healing and explains different means of fracture healing evaluation including biomechanical, histopathological and radiological assessments.

The immunological contribution to heterotopic ossification disorders

The formation of bone outside the endogenous skeleton is a significant clinical event, rendering affected individuals with immobility and a diminished quality of life. This bone, termed heterotopic ossification (HO), can appear in patients following invasive surgeries and traumatic injuries, as well as progressively manifest in several congenital disorders. A unifying feature of both genetic and nongenetic episodes of HO is immune system involvement at the early stages of disease. Activation of the immune system sets the stage for the downstream anabolic events that eventually result in ectopic bone formation, rendering the immune system a particularly appealing site of early therapeutic intervention for optimal management of disease. In this review, we will discuss the immunological contributions to HO disorders, with specific focus on contributing cell types, signaling pathways, relevant in vivo animal models, and potential therapeutic targets.

Changes of serum cytokines-related Th1/Th2/Th17 concentration in patients with postmenopausal osteoporosis

BACKGROUND

Postmenopausal osteoporosis is now hypothetically considered to be an autoimmune and inflammatory process in which many pro-inflammatory and T cell-derived cytokines play important roles in the loss of bone mass. For instance, interleukin-2 (IL-2), interferon-γ (IFN-γ), and tumor necrosis factor-α (TNF-α) secreted by Th1 and IL-6, IL-4, and IL-10 secreted by Th2 have been shown to be involved in the pathogenesis of osteoporosis. Interleukin-17 (IL-17) is a characteristic cytokine secreted by Th17 cells of the CD4 + subgroup. Although IL-17 has been shown to enhance bone resorption in ovariectomized mouse model, bone cells and genetic research, human-related studies of IL-17 are few.

METHODS

According to WHO classification of osteoporosis by the T scores of BMD, the subjects were divided into the postmenopausal osteoporosis group (T scores≤-2.5), the postmenopausal osteopenia group (-2.5 < T scores<-1), and the postmenopausal normal BMD group (T scores≥-1); 30 subjects in each group. Cytometric bead array (CBA) technique was employed for serum determination of the primary indexes including IL-17A, IL-2, IFN-γ, TNF-α, IL-6, IL-4, and IL-10 concentrations in the 90 volunteers. In the meantime, serum calcium, phosphorus, magnesium, and alkaline phosphatase concentrations were also determined in the patients. One-way analysis of variance (one-way ANOVA) was employed in data analysis to determine whether the testing results of various parameters had significant differences. The bivariate correlation was tested with the Pearson correlation coefficient. When p < 0.05, the difference was considered to have statistical significance.

RESULTS

Serum IL-17A concentration was significantly higher in the postmenopausal osteoporosis group than in the postmenopausal osteopenia group and the postmenopausal normal BMD group, but the difference between the postmenopausal osteopenia group and the postmenopausal normal BMD group had no statistical significance. IL-17A was negatively correlated with BMD. To our knowledge, we discovered for the first time that serum concentrations of IFN-γ and IL-4 were significantly lower in the postmenopausal osteoporosis group than in the postmenopausal normal BMD group; IFN-γ and IL-4 were positively correlated with BMD. In addition, we also determined that BMI was negatively correlated with BMD; IL-17A was positively correlated with serum calcium. However, no significant differences in IL-6, TNF-α, IL-2, and IL-10 were observed among the three groups; these three factors were not correlated with BMD.

CONCLUSIONS

Our experiments have confirmed the roles of IL-17 in the pathogenesis of postmenopausal osteoporosis and in the promotion of bone resorption. Targeted therapy of IL-17, IFN-γ, and IL-4 may be beneficial in the treatment of patients with postmenopausal osteoporosis. Our experiments have also confirmed the roles of IFN-γ and IL-4 in the pathogenesis of postmenopausal osteoporosis and in the inhibition of bone resorption.

Co-cultures of programmable cells of monocytic origin and mesenchymal stem cells do increase osteogenic differentiation

Impaired bone healing can occur with numerous pathologic conditions like trauma, osteoporosis, and infection. Therefore tissue-engineering strategies that aim to enhance osteogenic differentiation of stem cells in order to accelerate bone healing are a major goal of contemporary regenerative research. In this study we cultivated mesenchymal stem cells (MSC) together with the recently patented programmable cells of monocytic origin (PCMO) to test whether co-cultures promote an osteogenic differentiation process. PCMO have recently been shown to have pluripotent characteristics and do support the regeneration processes of liver and heart diseases. Quantitative real time PCR expression profiles of osteogenic marker genes such as alkaline phosphatase in co-cultures of PCMO and MSC showed that MSC differentiated into osteoblast-like cells more rapidly as compared to mono-cultures. Alkaline phosphatase expression and enzyme activity levels were highly increased in co-cultures compared to mono-cultures of MSC. Tests for mineralized matrix formation also indicated that PCMO have a positive effect on co-cultured MSC under osteogenic culture conditions. However, analysis of collagen 1A did not show enhanced expression. In summary, PCMO obviously have the ability to promote osteogenic differentiation of MSC in vitro while their own pluripotent potential is not sufficient to develop osteoblast-like characteristics themselves.

Mesenchymal stromal cells derived from the bone marrow of acute lymphoblastic leukemia patients show altered BMP4 production: correlations with the course of disease

The relevance of tumor microenvironment for the development and progression of tumor cells in hematological malignancies has been extensively reported. Identification of factors involved in the information exchange between the malignant cells and the bone marrow mesenchymal stem cells (BM-MSCs) and the knowledge on their functioning may provide important information to eliminate leukemic cells from protective BM niches. We evaluated changes in BM-MSCs obtained from children with acute lymphoblastic leukemia (ALL) at different times in the course of disease. Whereas ALL-MSCs did not exhibit phenotypic changes compared to BM-derived MSCs isolated from healthy donors, they exhibited increased adipogenic capacity. In addition, the viability of healthy CD34+ hematopoietic progenitors was significantly reduced when co-cultured with ALL-MSCs. ALL-MSCs grow less efficiently, although gradually recover normal growth with treatment. Accordingly, proliferation is particularly low in MSCs obtained at diagnosis and in the first days of treatment (+15 days), recovering to control levels after 35 days of treatment. Correlating these results with bone morphogenetic protein 4 (BMP4) production, a molecule demonstrated to affect MSC biology, we found higher production of BMP4 in ALL-MSCs derived from patients over the course of disease but not in those free of leukemia. However, no significant differences in the expression of different members of the BMP4 signaling pathway were observed. Furthermore, an inverse correlation between high levels of BMP4 production in the cultures and MSC proliferation was found, as observed in MSCs derived from patients at diagnosis that produce high BMP4 levels. In addition, co-culturing ALL-MSC with the REH leukemia cell line, but not CD34+ hematopoietic progenitors, powerfully enhanced BMP4 production, suggesting an intimate crosstalk among ALL-MSCs isolated from BM colonized by ALL cells that presumably also occurs in situ conditions. Our data may support the participation of BMP4 in BM niche, but the mechanism remains to be elucidated.

Nutrient element-based bioceramic coatings on titanium alloy stimulating osteogenesis by inducing beneficial osteoimmmunomodulation

Nutrient element-based Sr₂ZnSi₂O₇ coatings induce favorable osteoimmunomodulation. Material chemistry of Sr₂ZnSi₂O₇ coating modulates the immune environment to induce osteogenic differentiation of BMSCs by activating BMP2 signalling pathway.

Osteoimmunology and bone homeostasis: relevance to spondyloarthritis

The seronegative spondyloarthopathies (SpA) share certain common articular and peri-articular features that differ from rheumatoid arthritis (RA) and other forms of inflammatory arthritis. These include the tendency of the SpAs to involve the axial skeleton in addition to the diarthrodial joints, and the prominent involvement of the extra-articular entheses (sites of ligamentous and tendon insertion), which are not common sites of primary pathology in RA and other inflammatory arthropathies. The differential anatomic sites of bone pathology in the SpAs in comparison to the other forms of arthritis suggest that the underlying pathogenic processes and cellular and molecular mechanisms that account for the peri-articular bone pathology involve different underlying disease mechanisms. This review will highlight the molecular and cellular processes that are involved in the pathogenesis of the skeletal pathology in the SpAs, and provide evidence that many of the factors involved in regulation of bone cell function exhibit potent immune-regulatory activity, providing support for the general concept of osteoimmunology.

Role of T cells in the modulation of PTH action: physiological and clinical significance

Osteoimmunology is new field of research dedicated to the study of the interactions between the immune system and bone. Among the cells of the immune system that regulate bone and hemopoietic cells are T lymphocytes. These cells secrete osteoclastogenic cytokines such as RANKL and TNF, as well as factors that stimulate bone formation and hemopoietic cells, one of which is Wnt10b. This article will review the evidence that T cells are implicated in the mechanism of action of parathyroid hormone (PTH) in bone and on the hemopoietic system.

Monocyte exosomes stimulate the osteogenic gene expression of mesenchymal stem cells

Inflammation and regeneration at the implant-bone interface are intimately coupled via cell-cell communication. In contrast to the prevailing view that monocytes/macrophages orchestrate mesenchymal stem cells (MSCs) and progenitor cells via the secretion of soluble factors, we examined whether communication between these different cell types also occurs via exosomes. LPS-stimulated human monocytes released exosomes, positive for CD9, CD63, CD81, Tsg101 and Hsp70, as determined by flow cytometry and Western blot. These exosomes also contained wide size distribution of RNA, including RNA in the size of microRNAs. The exosomes were shown to interact with human mesenchymal stem cells. After 24 h of culture, a considerable portion of the MSCs had internalised PKH67-labelled exosomes. Furthermore, after 72 h, the gene expression of the osteogenic markers runt-related transcription factor 2 (RUNX2) and bone morphogenetic protein-2 (BMP-2) had increased in comparison with control medium, whereas no significant difference in osteocalcin (OC) expression was demonstrated. The present results show that, under given experimental conditions, monocytes communicate with MSCs via exosomes, resulting in the uptake of exosomes in MSCs and the stimulation of osteogenic differentiation. The present observations suggest that exosomes constitute an additional mode of cell-cell signalling with an effect on MSC differentiation during the transition from injury and inflammation to bone regeneration.

Traumatized and inflamed--but resilient: glial aromatization and the avian brain

Steroids like estrogens have potent effects on the vertebrate brain, and are provided to neural targets from peripheral and central sources. Estradiol synthesized within the vertebrate CNS modulates neural structure and function, including the pathways involved in neuroprotection, and perhaps, neural repair. Specifically, aromatase; the enzyme responsible for the conversion of testosterone to estradiol, is upregulated in the avian and mammalian brain following disruption of the neuropil by multiple forms of perturbation including mechanical injury, ischemia and excitotoxicity. This injury induced aromatase expression is somewhat unique in that it occurs in astroglia rather than neurons, and is stimulated in response to factors associated with brain damage. In this review, we focus on the induction, expression and consequences of glial aromatization in the songbird brain. We begin with a review of the anatomical consequences of glial estrogen provision followed by a discussion of the cellular mechanisms whereby glial aromatization may affect injury-induced neuroplasticity. We then present the current status of our understanding regarding the inductive role of inflammatory processes in the transcription and translation of astrocytic aromatase. We consider the functional aspects of glial aromatization before concluding with unanswered questions and suggestions for future studies. Birds have long informed us about fundamental questions in endocrinology, immunology, and neuroplasticity; and their unique anatomical and physiological characteristics continue to provide an excellent system in which to learn about brain trauma, inflammation, and neuroprotection.

Adjunct teriparatide therapy with monitoring of bone turnover markers and bone scintigraphy for bisphosphonate-related osteonecrosis of the jaw

The management of bisphosphonate-related osteonecrosis of the jaw (BRONJ) is still difficult in many cases that do not respond to conservative treatments. We report a case of BRONJ treated by adjunctive teriparatide therapy for 6 months with monitoring of bone turnover markers (at baseline, at 1, 3, and 6 months of treatment, and after 9 months off therapy) and bone scintigraphy (at baseline, 3 and 6 months, and after 9 months off therapy). The patient was a 78-year-old woman with osteoporosis and BRONJ. She had not responded to previous conventional treatment. Teriparatide was added for resolution of BRONJ. The pain disappeared after 1 month, and remarkable bone regeneration was obtained after 6 months, with significantly increasing bone formation and resorption markers. Bone scintigraphy showed regression of the uptake area. This case suggests the usefulness of monitoring bone turnover markers and using bone scintigraphy to increase the effectiveness of teriparatide therapy.