Influence of inflammatory conditions provided by macrophages on osteogenic ability of mesenchymal stem cells

Combined application of mesenchymal stem cells and different glucocorticoid dosing alleviates osteoporosis in SLE murine models

OBJECTIVE

Bone mesenchymal stem cells (BMSCs) have been tentatively applied in the treatment of glucocorticoid-induced osteoporosis (GIOP) and systemic lupus erythematosus (SLE). However, the effects of BMSCs on osteoporosis within the context of glucocorticoid (GC) application in SLE remain unclear. Our aim was to explore the roles of BMSCs and different doses of GC interventions on osteoporosis in SLE murine models.

METHODS

MRL/MpJ-Faslpr mice were divided into eight groups with BMSC treatment and different dose of GC intervention. Three-dimensional imaging analysis and hematoxylin and eosin (H&E) staining were performed to observe morphological changes. The concentrations of osteoprotegerin (OPG) and receptor activator of nuclear factor κB ligand (RANKL) in serum were measured by enzyme-linked immunosorbent assay (ELISA). The subpopulation of B cells and T cells in bone marrows and spleens were analyzed by flow cytometry. Serum cytokines and chemokines were assessed using Luminex magnetic bead technology.

RESULTS

BMSCs ameliorated osteoporosis in murine SLE models by enhancing bone mass, improving bone structure, and promoting bone formation through increased bone mineral content and optimization of trabecular morphology. BMSC and GC treatments reduced the number of B cells in bone marrows, but the effect was not significant in spleens. BMSCs significantly promoted the expression of IL-10 while reducing IL-18. Moreover, BMSCs exert immunomodulatory effects by reducing Th17 expression and rectifying the Th17/Treg imbalance.

CONCLUSION

BMSCs effectively alleviate osteoporosis induced by SLE itself, as well as osteoporosis resulting from SLE combined with various doses of GC therapy. The therapeutic effects of BMSCs appear to be mediated by their influence on bone marrow B cells, T cell subsets, and associated cytokines. High-dose GC treatment exerts a potent anti-inflammatory effect but may hinder the immunotherapeutic potential of BMSCs. Our research may offer valuable guidance to clinicians regarding the use of BMSC treatment in SLE and provide insights into the judicious use of GCs in clinical practice.

Interplay between mesenchymal stem cells and macrophages: Promoting bone tissue repair

The repair of bone tissue damage is a complex process that is well-orchestrated in time and space, a focus and difficulty in orthopedic treatment. In recent years, the success of mesenchymal stem cells (MSCs)-mediated bone repair in clinical trials of large-area bone defects and bone necrosis has made it a candidate in bone tissue repair engineering and regenerative medicine. MSCs are closely related to macrophages. On one hand, MSCs regulate the immune regulatory function by influencing macrophages proliferation, infiltration, and phenotype polarization, while also affecting the osteoclasts differentiation of macrophages. On the other hand, macrophages activate MSCs and mediate the multilineage differentiation of MSCs by regulating the immune microenvironment. The cross-talk between MSCs and macrophages plays a crucial role in regulating the immune system and in promoting tissue regeneration. Making full use of the relationship between MSCs and macrophages will enhance the efficacy of MSCs therapy in bone tissue repair, and will also provide a reference for further application of MSCs in other diseases.

Platelets: A Potential Factor that Offers Strategies for Promoting Bone Regeneration

Bone defects represent a prevalent category of clinical injuries, causing significant pain and escalating health care burdens. Effectively addressing bone defects is thus of paramount importance. Platelets, formed from megakaryocyte lysis, have emerged as pivotal players in bone tissue repair, inflammatory responses, and angiogenesis. Their intracellular storage of various growth factors, cytokines, and membrane protein receptors contributes to these crucial functions. This article provides a comprehensive overview of platelets' roles in hematoma structure, inflammatory responses, and angiogenesis throughout the process of fracture healing. Beyond their application in conjunction with artificial bone substitute materials for treating bone defects, we propose the potential future use of anticoagulants such as heparin in combination with these materials to regulate platelet number and function, thereby promoting bone healing. Ultimately, we contemplate whether manipulating platelet function to modulate bone healing could offer innovative ideas and directions for the clinical treatment of bone defects.

Osteogenic properties of bioactive titanium in inflammatory environment

OBJECTIVES

It is very important that the effects of surface modified titanium on osteogenic differentiation of bone marrow mesenchymal stem cells in the process of bone regeneration. The bio-function of modified titanium could be affected by the inflammatory micro-environment. The aim of this study was to investigate the effects of modified titanium on osteogenic differentiation in the inflammatory conditions and the osteogenic properties of the modified titanium dental implant in vivo.

METHODS

The medical pure titanium metals (PT-Ti) subjected to Anodic Oxidation (AO-Ti), Sand Blasting/acid etching (SLA-Ti) and Plasma-sprayed HA coating (HA coating-Ti) were used for regulating the osteogenic properties of MSCs in the normal and inflammatory conditions.

RESULTS

The amount of the MSCs in the inflammatory environment were more similar to that in the non-inflammatory environment after cultured on AO-Ti samples for 7D. However, the proliferation of the MSCs was obviously inhibited on the other groups in the inflammatory condition. The morphology of MSC cells on the modified titanium surface was affected in the inflammatory conditions and the AO-Ti was more conducive to maintain the skeletal morphology of MSCs. The results of osteogenic related proteins expression showed that the amount of BMP-2 on AO-Ti group was the highest in the inflammatory conditions, and followed the order of AO-Ti > HA coating-Ti > SLA-Ti > PT-Ti. What's more, the AO-Ti samples were more beneficial to promote the expression of osteogenic genes ALP, OCN, COL-I and Runx2 in the inflammatory conditions. The results of osteogenic properties in vivo showed that the gingival depth of the AO-Ti group was smaller than that on the other groups. Some new bone could be observed around the AO-Ti implant at two weeks. The bone binding rates on AO-Ti group was the highest of 81.3% after implanted for one year.

SIGNIFICANCE

The AO-Ti was beneficial to osteogenic differentiation than other modified titanium metals in inflammatory condition. The anodic oxidation is an effective surface modification method on titanium to promote bone regeneration.

Macrophages-bone marrow mesenchymal stem cells crosstalk in bone healing

Bone healing is associated with many orthopedic conditions, including fractures and osteonecrosis, arthritis, metabolic bone disease, tumors and periprosthetic particle-associated osteolysis. How to effectively promote bone healing has become a keen topic for researchers. The role of macrophages and bone marrow mesenchymal stem cells (BMSCs) in bone healing has gradually come to light with the development of the concept of osteoimmunity. Their interaction regulates the balance between inflammation and regeneration, and when the inflammatory response is over-excited, attenuated, or disturbed, it results in the failure of bone healing. Therefore, an in-depth understanding of the function of macrophages and bone marrow mesenchymal stem cells in bone regeneration and the relationship between the two could provide new directions to promote bone healing. This paper reviews the role of macrophages and bone marrow mesenchymal stem cells in bone healing and the mechanism and significance of their interaction. Several new therapeutic ideas for regulating the inflammatory response in bone healing by targeting macrophages and bone marrow mesenchymal stem cells crosstalk are also discussed.

Mechanical force induces macrophage-derived exosomal UCHL3 promoting bone marrow mesenchymal stem cell osteogenesis by targeting SMAD1

BACKGROUND

Orthodontic tooth movement (OTM), a process of alveolar bone remodelling, is induced by mechanical force and regulated by local inflammation. Bone marrow-derived mesenchymal stem cells (BMSCs) play a fundamental role in osteogenesis during OTM. Macrophages are mechanosensitive cells that can regulate local inflammatory microenvironment and promote BMSCs osteogenesis by secreting diverse mediators. However, whether and how mechanical force regulates osteogenesis during OTM via macrophage-derived exosomes remains elusive.

RESULTS

Mechanical stimulation (MS) promoted bone marrow-derived macrophage (BMDM)-mediated BMSCs osteogenesis. Importantly, when exosomes from mechanically stimulated BMDMs (MS-BMDM-EXOs) were blocked, the pro-osteogenic effect was suppressed. Additionally, compared with exosomes derived from BMDMs (BMDM-EXOs), MS-BMDM-EXOs exhibited a stronger ability to enhance BMSCs osteogenesis. At in vivo, mechanical force-induced alveolar bone formation was impaired during OTM when exosomes were blocked, and MS-BMDM-EXOs were more effective in promoting alveolar bone formation than BMDM-EXOs. Further proteomic analysis revealed that ubiquitin carboxyl-terminal hydrolase isozyme L3 (UCHL3) was enriched in MS-BMDM-EXOs compared with BMDM-EXOs. We went on to show that BMSCs osteogenesis and mechanical force-induced bone formation were impaired when UCHL3 was inhibited. Furthermore, mothers against decapentaplegic homologue 1 (SMAD1) was identified as the target protein of UCHL3. At the mechanistic level, we showed that SMAD1 interacted with UCHL3 in BMSCs and was downregulated when UCHL3 was suppressed. Consistently, overexpression of SMAD1 rescued the adverse effect of inhibiting UCHL3 on BMSCs osteogenesis.

CONCLUSIONS

This study suggests that mechanical force-induced macrophage-derived exosomal UCHL3 promotes BMSCs osteogenesis by targeting SMAD1, thereby promoting alveolar bone formation during OTM.

Mesenchymal stem cells and macrophages and their interactions in tendon-bone healing

Tendon-bone insertion injuries (TBI), such as anterior cruciate ligament (ACL) and rotator cuff injuries, are common degenerative or traumatic pathologies with a negative impact on the patient's daily life, and they cause huge economic losses every year. The healing process after an injury is complex and is dependent on the surrounding environment. Macrophages accumulate during the entire process of tendon and bone healing and their phenotypes progressively transform as they regenerate. As the "sensor and switch of the immune system", mesenchymal stem cells (MSCs) respond to the inflammatory environment and exert immunomodulatory effects during the tendon-bone healing process. When exposed to appropriate stimuli, they can differentiate into different tissues, including chondrocytes, osteocytes, and epithelial cells, promoting reconstruction of the complex transitional structure of the enthesis. It is well known that MSCs and macrophages communicate with each other during tissue repair. In this review, we discuss the roles of macrophages and MSCs in TBI injury and healing. Reciprocal interactions between MSCs and macrophages and some biological processes utilizing their mutual relations in tendon-bone healing are also described. Additionally, we discuss the limitations in our understanding of tendon-bone healing and propose feasible ways to exploit MSC-macrophage interplay to develop an effective therapeutic strategy for TBI injuries.

The Translational potential of this article

This paper reviewed the important functions of macrophages and mesenchymal stem cells in tendon-bone healing and described the reciprocal interactions between them during the healing process. By managing macrophage phenotypes, mesenchymal stem cells and the interactions between them, some possible novel therapies for tendon-bone injury may be proposed to promote tendon-bone healing after restoration surgery.

Augmented effect of fibroblast growth factor 18 in bone morphogenetic protein 2-induced calvarial bone healing by activation of CCL2/CCR2 axis on M2 macrophage polarization

Fibroblast growth factor (FGF) signaling plays essential roles in various biological events. FGF18 is one of the ligands to be associated with osteogenesis, chondrogenesis and bone healing. The mouse critical-sized calvarial defect healing induced by the bone morphogenetic protein 2 (BMP2)-hydrogel is stabilized when FGF18 is added. Here, we aimed to investigate the role of FGF18 in the calvarial bone healing model. We first found that FGF18 + BMP2 hydrogel application to the calvarial bone defect increased the expression of anti-inflammatory markers, including those related to tissue healing M2 macrophage (M2-Mø) prior to mineralized bone formation. The depletion of macrophages with clodronate liposome hindered the FGF18 effect. We then examined how FGF18 induces M2-Mø polarization by using mouse primary bone marrow (BM) cells composed of macrophage precursors and BM stromal cells (BMSCs). In vitro studies demonstrated that FGF18 indirectly induces M2-Mø polarization by affecting BMSCs. Whole transcriptome analysis and neutralizing antibody treatment of BMSC cultured with FGF18 revealed that chemoattractant chemokine (c-c motif) ligand 2 (CCL2) is the major mediator for M2-Mø polarization. Finally, FGF18-augmented activity toward favorable bone healing with BMP2 was diminished in the calvarial defect in Ccr2-deleted mice. Altogether, we suggest a novel role of FGF18 in M2-Mø modulation via stimulation of CCL2 production in calvarial bone healing.

Fracture Healing in the Setting of Endocrine Diseases, Aging, and Cellular Senescence

More than 2.1 million age-related fractures occur in the United States annually, resulting in an immense socioeconomic burden. Importantly, the age-related deterioration of bone structure is associated with impaired bone healing. Fracture healing is a dynamic process which can be divided into four stages. While the initial hematoma generates an inflammatory environment in which mesenchymal stem cells and macrophages orchestrate the framework for repair, angiogenesis and cartilage formation mark the second healing period. In the central region, endochondral ossification favors soft callus development while next to the fractured bony ends, intramembranous ossification directly forms woven bone. The third stage is characterized by removal and calcification of the endochondral cartilage. Finally, the chronic remodeling phase concludes the healing process. Impaired fracture healing due to aging is related to detrimental changes at the cellular level. Macrophages, osteocytes, and chondrocytes express markers of senescence, leading to reduced self-renewal and proliferative capacity. A prolonged phase of "inflammaging" results in an extended remodeling phase, characterized by a senescent microenvironment and deteriorating healing capacity. Although there is evidence that in the setting of injury, at least in some tissues, senescent cells may play a beneficial role in facilitating tissue repair, recent data demonstrate that clearing senescent cells enhances fracture repair. In this review, we summarize the physiological as well as pathological processes during fracture healing in endocrine disease and aging in order to establish a broad understanding of the biomechanical as well as molecular mechanisms involved in bone repair.

The osteogenetic activities of mesenchymal stem cells in response to Mg2+ ions and inflammatory cytokines: a numerical approach using fuzzy logic controllers

Magnesium (Mg²⁺) ions are frequently reported to regulate osteogenic activities of mesenchymal stem cells (MSCs). In this study, we propose a numerical model to study the regulatory importance of Mg²⁺ ions on MSCs osteoblastic differentiation in the presence of an inflammatory response. A fuzzy logic controller was formulated to receive the concentrations of Mg²⁺ ions and the inflammatory cytokines of TNF-α, IL-10, IL-1β, and IL-8 as cellular inputs and predict the cells’ early and late differentiation rates. Five sets of empirical data obtained from published cell culture experiments were used to calibrate the model. The model successfully reproduced the empirical data regarding the concentration- and phase-dependent effect of Mg²⁺ ions on the differentiation process. In agreement with the experiments, the model showed the stimulatory role of Mg²⁺ ions on the early differentiation phase, once administered at low concentration, and their inhibitory role on the late differentiation phase. The numerical approach used in this study suggested 6–8 mM as the most effective concentration of Mg²⁺ ions in promoting the early differentiation process. Also, the proposed model sheds light on the fundamental differences in the behavioral properties of cells cultured in different experiments, e.g. differentiation rate and the sensitivity of the cultured cells to stimulatory signals such as Mg²⁺ ions. Thus, it can be used to interpret and compare different empirical findings. Moreover, the model successfully reproduced the nonlinearities in the concentration-dependent role of the inflammatory cytokines in early and late differentiation rates. Overall, the proposed model can be employed in studying the osteogenic properties of Mg-based implants in the presence of an inflammatory response.

Magnesium (Mg) is an attractive material for bone implants as it fully degrades after implantation, saving pain and cost of the second surgery for implant removal. To advance its application in the orthopedic industry, it is paramount to fully understand the biological impact of the degradation products, in particular Mg²⁺ ions. Here, we propose a computer model to study the effects of Mg²⁺ ions on bone regeneration. The model focuses on stem cells and includes both the direct stimulation effects of Mg²⁺ ions on cells and the indirect stimulus through the inflammatory system. The proposed model successfully reproduced the experimental data of five different studies. The model additionally highlighted differences amongst different experiments in terms of the cellular response to Mg²⁺ ions. The proposed system therefore provides an important addition to the field of Mg implant research.

Synovial membrane-derived mesenchymal progenitor cells from osteoarthritic joints in dogs possess lower chondrogenic-, and higher osteogenic capacity compared to normal joints

Background

Synovial membrane-derived mesenchymal progenitor cells (SM-MPCs) are a promising candidate for the cell-based treatment of osteoarthritis (OA) considering their in vitro and in vivo capacity for cartilage repair. However, the OA environment may adversely impact their regenerative capacity. There are no studies for canine (c)SM-MPCs that compare normal to OA SM-MPCs, even though dogs are considered a relevant animal model for OA. Therefore, this study compared cSM-MPCs from normal and OA synovial membrane tissue to elucidate the effect of the OA environment on MPC numbers, indicated by CD marker profile and colony-forming unit (CFU) capacity, and the impact of the OA niche on tri-lineage differentiation.

Methods

Normal and OA synovial membrane were collected from the knee joints of healthy dogs and dogs with rupture of the cruciate ligaments. The synovium was assessed by histopathological OARSI scoring and by RT-qPCR for inflammation/synovitis-related markers. The presence of cSM-MPCs in the native tissue was further characterized with flow cytometry, RT-qPCR, and immunohistochemistry, using the MPC markers; CD90, CD73, CD44, CD271, and CD34. Furthermore, cells isolated upon enzymatic digestion were characterized by CFU capacity, and a population doublings assay. cSM-MPCs were selected based on plastic adherence, expanded to passage 2, and evaluated for the expression of MPC-related surface markers and tri-lineage differentiation capacity.

Results

Synovial tissue collected from the OA joints had a significantly higher OARSI score compared to normal joints, and significantly upregulated inflammation/synovitis markers S100A8/9, IL6, IL8, and CCL2. Both normal and OA synovial membrane contained cells displaying MPC properties, including a fibroblast-like morphology, CFU capacity, and maintained MPC marker expression over time during expansion. However, OA cSM-MPCs were unable to differentiate towards the chondrogenic lineage and had low adipogenic capacity in contrast to normal cSM-MPCs, whereas they possessed a higher osteogenic capacity. Furthermore, the OA synovial membrane contained significantly lower percentages of CD90+, CD44+, CD34+, and CD271+ cells.

Conclusions

The OA environment had adverse effects on the regenerative potential of cSM-MPCs, corroborated by decreased CFU, population doubling, and chondrogenic capacity compared to normal cSM-MPCs. OA cSM-MPCs may be a less optimal candidate for the cell-based treatment of OA than normal cSM-MPCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03144-z.

Microsphere-Gel Composite System with Mesenchymal Stem Cell Recruitment, Antibacterial, and Immunomodulatory Properties Promote Bone Regeneration via Sequential Release of LL37 and W9 Peptides

Various types of biomaterials have been widely used to treat complex bone defects. However, potential infection risks and inappropriate host immune responses induced by biomaterials can adversely affect the final bone repair outcome. Therefore, the development of novel bone biomaterials with antibacterial and immunomodulatory capabilities is conducive to achieving a good interaction between the host and material, thereby creating a local microenvironment favorable for osteogenesis and ultimately accelerating bone regeneration. In this study, we fabricated a porcine small intestinal submucosa (SIS) hydrogel containing LL37 peptides and polylactic-glycolic acid (PLGA) microspheres encapsulated with WP9QY(W9) peptide (LL37-W9/PLGA-SIS), which can fill irregular bone defects and exhibits excellent mechanical properties. In vitro experiments showed that the microsphere-gel composite system had sequential drug release characteristics. The LL37 peptide released first had good antibacterial performance and BMSC recruitment ability, which could prevent infection at an early stage and increase the number of BMSCs at the injured site. In addition, it also has immunomodulatory properties, showing both pro-inflammatory and anti-inflammatory activities, but its early pro-inflammatory properties are more inclined to activate the M1 phenotype of macrophages. Moreover, the subsequently released W9 peptide not only reduced the expression of pro-inflammatory genes to alleviate inflammation and induced more macrophages to convert to M2 phenotypes but also promoted the osteogenic differentiation of BMSCs. This finely regulated immune response is considered to be more closely related to the physiological bone healing process. When studying the interaction between macrophages and BMSCs mediated by the material, it was found that the immunomodulatory and osteogenic effects were enhanced. In vivo experiments, we constructed rat skull defect models, which further proved that LL37-W9/PLGA-SIS gel can properly regulate the immune response, and has a good ability to promote osteogenesis in situ. In conclusion, the LL37-W9/PLGA-SIS hydrogel has great application prospects in immune regulation and bone therapy.

Photo-thermic mineralized collagen coatings and their modulation of macrophages polarization

Macrophages polarization in bone immune microenvironment is crucial in bone regeneration. In this work, mineralized collagen (MC) coatings with photo-thermal effect were prepared through incorporation of polydopamine (PDA). MC coatings with different thicknesses were deposited on titanium substrate through electrochemical deposition. PDA preformed on the substrate, acting as a photo-thermal agent. The effects of light illumination, i.e., different thermal effects, on the polarization of mouse bone marrow-derived macrophages were explored. It was found that heat can promote the M1 polarization of macrophages and inhibit the M2 polarization. Also, gene expression results revealed that such photo illumination based macrophage modulation is effective and safe. It provides a possible way for the design of functional materials to regulate the bone immune microenvironment.

Physically Cross-Linked DNA Hydrogel-Based Sustained Cytokine Delivery for In Situ Diabetic Alveolar Bone Rebuilding

The development of a biodegradable and shape-adaptable bioscaffold that can enhance local cytokine retention and bioactivity is essential for the application of immunotherapy in periodontal diseases. Here, we report a biodegradable, anti-inflammatory, and osteogenic ILGel that uses a physically cross-linked DNA hydrogel as a soft bioscaffold for the long-term sustained release of cytokine interleukin-10 (IL-10) to accelerate diabetic alveolar bone rebuilding. Porous microstructures of ILGel favored the encapsulation of IL-10 and maintained IL-10 bioactivity for at least 7 days. ILGel can be gradually degraded or hydrolyzed under physiological conditions, avoiding the potential undesired side effects on dental tissues. Long-term sustained release of bioactive IL-10 from ILGel not only promoted M2 macrophage polarization and attenuated periodontal inflammation but also triggered osteogenesis of mesenchymal stem cells (MSCs), leading to accelerated alveolar bone formation and healing of alveolar bone defects under diabetic conditions in vivo. ILGel treatment significantly accelerated the defect healing rate of diabetic alveolar injury up to 93.42 ± 4.6% on day 21 post treatment compared to that of free IL-10 treatment (63.30 ± 7.39%), with improved trabecular architectures. Our findings imply the potential application of the DNA hydrogel as the bioscaffold for cytokine-based immunotherapy in diabetic alveolar bone injury and other periodontal diseases.

Mesenchymal Stem Cell Mechanisms of Action and Clinical Effects in Osteoarthritis: A Narrative Review

With the insufficient satisfaction rates and high cost of operative treatment for osteoarthritis (OA), alternatives have been sought. Furthermore, the inability of current medications to arrest disease progression has led to rapidly growing clinical research relating to mesenchymal stem cells (MSCs). The availability and function of MSCs vary according to tissue source. The three primary sources include the placenta, bone marrow, and adipose tissue, all of which offer excellent safety profiles. The primary mechanisms of action are trophic and immunomodulatory effects, which prevent the further degradation of joints. However, the function and degree to which benefits are observed vary significantly based on the exosomes secreted by MSCs. Paracrine and autocrine mechanisms prevent cell apoptosis and tissue fibrosis, initiate angiogenesis, and stimulate mitosis via growth factors. MSCs have even been shown to exhibit antimicrobial effects. Clinical results incorporating clinical scores and objective radiological imaging have been promising, but a lack of standardization in isolating MSCs prevents their incorporation in current guidelines.

Regulation of osteogenic differentiation by the pro-inflammatory cytokines IL-1β and TNF-α: current conclusions and controversies

Treatment of complex bone fracture diseases is still a complicated problem that is urged to be solved in orthopedics. In bone tissue engineering, the use of mesenchymal stromal/stem cells (MSCs) for tissue repair brings hope to the medical field of bone diseases. MSCs can differentiate into osteoblasts and promote bone regeneration. An increasing number of studies show that the inflammatory microenvironment affects the osteogenic differentiation of MSCs. It is shown that TNF-α and IL-1β play different roles in the osteogenic differentiation of MSCs via different signal pathways. The main factors that affect the role of TNF-α and IL-1β in osteogenic differentiation of MSCs include concentration and the source of stem cells (different species and different tissues). This review in-depth analyzes the roles of pro-inflammatory cytokines in the osteogenic differentiation of MSCs and reveals some current controversies to provide a reference of comprehensively understanding.

Exendin-4 and eldecalcitol synergistically promote osteogenic differentiation of bone marrow mesenchymal stem cells through M2 macrophages polarization via PI3K/AKT pathway

Background

The incidence of diabetic osteoporosis is increasing. This article evaluates the effect of combination treatment with the hypoglycemic drug exendin-4 (Ex-4) and the vitamin D analog eldecalcitol (ED-71) on improving diabetic osteoporosis and explores the relevant mechanism of action.

Method

Micro-CT, HE staining, immunohistochemistry, qPCR and ELISA were used to evaluate the impact of Ex-4 and ED-71 on bone formation and macrophage polarization in a mouse model of diabetic osteoporosis in vivo. Immunofluorescence, flow cytometry and qPCR were used to characterize the polarization type of macrophages treated with Ex-4 and ED-71 in vitro. A co-culture system of BMSCs and macrophages was established. Subsequently, crystal violet staining, alkaline phosphatase staining and alizarin red staining were used to evaluate the migration and osteogenesis differentiation of BMSCs.

Results

Ex-4 combined with ED-71 significantly reduced blood glucose levels and enhanced bone formation in mice with diabetic osteoporosis. In addition, Ex-4 synergized with ED-71 to induce the polarization of macrophages into M2 through the PI3K/AKT pathway. Macrophages treated with the combination of Ex-4 and ED-71 can significantly induce the osteogenic differentiation of BMSCs.

Conclusion

Ex-4 synergized with ED-71 to reduce blood glucose levels significantly. And this combination therapy can synergistically induce osteogenic differentiation of BMSCs by promoting M2 macrophages polarization, thereby improving diabetic osteoporosis. Therefore, the combination of Ex-4 and ED-71 may be a new strategy for the treatment of diabetic osteoporosis.

Macrophages and Bone Marrow-Derived Mesenchymal Stem Cells Work in Concert to Promote Fracture Healing: A Brief Review

Bone marrow-derived mesenchymal stem cell (BMSC)-based and macrophage-based cell therapy are regarded as promising strategies to promote fracture healing because of incredible osteogenic potential of BMSCs and typical immunomodulatory function of macrophages. Apart from their respective key roles, accumulative evidence has also demonstrated the importance of cross talk between these two cell types in fracture healing process. This review takes a deep insight into the recent research progress of the synergic performance of BMSCs and macrophages by discussing not only the cells own functions but also the relevant impact factors and mechanisms (ambient microenvironment stimulus, miRNAs, etc). The aim of this review is to provide some valuable cues and technique support for the macrophage- and BMSC-related research, which will be helpful to propel BMSC/macrophage-based combined cell therapy for bone fracture treatment.

Macrophage-Derived Exosomes Promote Bone Mesenchymal Stem Cells Towards Osteoblastic Fate Through microRNA-21a-5p

The effective healing of a bone defect is dependent on the careful coordination of inflammatory and bone-forming cells. In the current work, pro-inflammatory M1 and anti-inflammatory M2 macrophages were co-cultured with primary murine bone mesenchymal stem cells (BMSCs), in vitro, to establish the cross-talk among polarized macrophages and BMSCs, and as well as their effects on osteogenesis. Meanwhile, macrophages influence the osteogenesis of BMSCs through paracrine forms such as exosomes. We focused on whether exosomes of macrophages promote osteogenic differentiation. The results indicated that M1 and M2 polarized macrophage exosomes all can promote osteogenesis of BMSCs. Especially, M1 macrophage-derived exosomes promote osteogenesis of BMSCs through microRNA-21a-5p at the early stage of inflammation. This research helps to develop an understanding of the intricate interactions among BMSCs and macrophages, which can help to improve the process of bone healing as well as additional regenerative processes by local sustained release of exosomes.

Time-dependently Appeared Microenvironmental Changes and Mechanism after Cartilage or Joint Damage and the Influences on Cartilage Regeneration

Cartilage and joint damage easily degenerates cartilage and turns into osteoarthritis (OA), which seriously affects human life and work, and has no cure currently. The temporal and spatial changes of multiple microenvironments upon the damage of cartilage and joint are noticed, including the emergences of inflammation, bone remodeling, blood vessels, and nerves, as well as alterations of extracellular and pericellular matrix, oxygen tension, biomechanics, underneath articular cartilage tissues, and pH value. This review summarizes the existing literatures on microenvironmental changes, mechanisms, and their negative effects on cartilage regeneration following cartilage and joint damage. We conclude that time-dependently rebuilding the multiple normal microenvironments of damaged cartilage is the key for cartilage regeneration after systematic studies for the timing and correlations of various microenvironment changes.

Interaction between Macrophages and Human Mesenchymal Stromal Cells Derived from Bone Marrow and Wharton's Jelly-A Comparative Study

Despite intensive clinical research on the use of mesenchymal stromal cells (MSCs), further basic research in this field is still required. Herein, we compared human bone marrow MSCs (BM-MSCs, n = 6) and Wharton’s jelly MSCs (WJ-MSCs, n = 6) in their ability to interact with human primary macrophages. Evaluation of secretory potential revealed that under pro-inflammatory stimulation, WJ-MSCs secreted significantly more IL-6 than BM-MSCs (2-fold). This difference did not translate into the effect of MSCs on macrophages: both types of MSCs significantly directed M1-like macrophages toward the M2 phenotype (based on CD206 expression) to a similar extent. This observation was consistent both in flow cytometry analysis and immunocytochemical assessment. The effect of MSCs on macrophages was sustained when IL-6 signaling was blocked with Tocilizumab. Macrophages, regardless of polarization status, enhanced chemotaxis of both BM-MSCs and WJ-MSCs (p < 0.01; trans-well assay), with WJ-MSCs being significantly more responsive to M1-derived chemotactic signals than BM-MSCs. Furthermore, WJ-MSCs increased their motility (scratch assay) when exposed to macrophage-conditioned medium while BM-MSCs did not. These results indicate that although both BM-MSCs and WJ-MSCs have the ability to reciprocally interact with macrophages, the source of MSCs could slightly but significantly modify the response under clinical settings.

DNA Damage-Induced Inflammatory Microenvironment and Adult Stem Cell Response

Adult stem cells ensure tissue homeostasis and regeneration after injury. Due to their longevity and functional requirements, throughout their life stem cells are subject to a significant amount of DNA damage. Genotoxic stress has recently been shown to trigger a cascade of cell- and non-cell autonomous inflammatory signaling pathways, leading to the release of pro-inflammatory factors and an increase in the amount of infiltrating immune cells. In this review, we discuss recent evidence of how DNA damage by affecting the microenvironment of stem cells present in adult tissues and neoplasms can affect their maintenance and long-term function. We first focus on the importance of self-DNA sensing in immunity activation, inflammation and secretion of pro-inflammatory factors mediated by activation of the cGAS-STING pathway, the ZBP1 pathogen sensor, the AIM2 and NLRP3 inflammasomes. Alongside cytosolic DNA, the emerging roles of cytosolic double-stranded RNA and mitochondrial DNA are discussed. The DNA damage response can also initiate mechanisms to limit division of damaged stem/progenitor cells by inducing a permanent state of cell cycle arrest, known as senescence. Persistent DNA damage triggers senescent cells to secrete senescence-associated secretory phenotype (SASP) factors, which can act as strong immune modulators. Altogether these DNA damage-mediated immunomodulatory responses have been shown to affect the homeostasis of tissue-specific stem cells leading to degenerative conditions. Conversely, the release of specific cytokines can also positively impact tissue-specific stem cell plasticity and regeneration in addition to enhancing the activity of cancer stem cells thereby driving tumor progression. Further mechanistic understanding of the DNA damage-induced immunomodulatory response on the stem cell microenvironment might shed light on age-related diseases and cancer, and potentially inform novel treatment strategies.

The promise(s) of mesenchymal stem cell therapy in averting preclinical diabetes: lessons from in vivo and in vitro model systems

Obesity (Ob) poses a significant risk factor for the onset of metabolic syndrome with associated complications, wherein the Mesenchymal Stem Cell (MSC) therapy shows pre-clinical success. Here, we explore the therapeutic applications of human Placental MSCs (P-MSCs) to address Ob-associated Insulin Resistance (IR) and its complications. In the present study, we show that intramuscular injection of P-MSCs homed more towards the visceral site, restored HOMA-IR and glucose homeostasis in the WNIN/GR-Ob (Ob-T2D) rats. P-MSC therapy was effective in re-establishing the dysregulated cytokines. We report that the P-MSCs activates PI3K-Akt signaling and regulates the Glut4-dependant glucose uptake and its utilization in WNIN/GR-Ob (Ob-T2D) rats compared to its control. Our data reinstates P-MSC treatment's potent application to alleviate IR and restores peripheral blood glucose clearance evidenced in stromal vascular fraction (SVF) derived from white adipose tissue (WAT) of the WNIN/GR-Ob rats. Gaining insights, we show the activation of the PI3K-Akt pathway by P-MSCs both in vivo and in vitro (palmitate primed 3T3-L1 cells) to restore the insulin sensitivity dysregulated adipocytes. Our findings suggest a potent application of P-MSCs in  pre-clinical/Ob-T2D management.

Modulating immune microenvironment during bone repair using biomaterials: Focusing on the role of macrophages

Bone is a self-regenerative tissue that can repair small defects and fractures. In large defects, bone tissue is unable to provide nutrients and oxygen for repair, and autologous grafting is used as the gold standard. As an alternative method, the bone tissue regeneration approach uses osteoconductive biomaterials to overcome bone graft disadvantages. However, biomaterials are considered as foreign components that can stimulate host immune responses. Although traditional principles have been aimed to minimize immune reactions, the design of biomaterials has steadily shifted toward creating an immunomodulatory microenvironment to harness immune cells and responses to repair damaged tissue. Among immune cells, macrophages secrete various immunomodulatory mediators and crosstalk with bone-forming cells and play key roles in bone tissue engineering. Macrophage polarization toward M1 and M2 subtypes mediate pro-inflammatory and anti-inflammatory responses, respectively, which are crucial for bone repairing at different stages. This review provides an overview of the crosstalk between various immune cells and biomaterials, macrophage polarization, and the effect of physicochemical properties of biomaterials on the immune responses, especially macrophages, in bone tissue engineering.

Integrating Bioinformatic Strategies with Real-World Data to Infer Distinctive Immunocyte Infiltration Landscape and Immunologically Relevant Transcriptome Fingerprints in Ossification of Ligamentum Flavum

Purpose

Ossification of the ligamentum flavum (OLF) is a multifactorial disease characterized by an insidious and debilitating process of abnormal bone formation in ligamentum tissues. However, its definite pathogenesis has not been fully elucidated. Potential links between the immune system and various forms of heterotopic ossification have been discussed for many years, whereas no research investigated the immune effects on the initiation and development of OLF. Therefore, we attempt to shed light on this issue.

Methods

A series of bioinformatic algorithms were integrated to evaluate the immune score and the immunocyte infiltration patterns between OLF and normal samples, screen OLF-related and immune-related differentially expressed genes (OIDEGs), and analyze their biological functions. Correlation analysis inferred OIDEGs-related differentially expressed lncRNAs (OIDELs) and infiltrating immune cells (OIICs) to construct an immunoregulatory network.

Results

Differential immune score and immune cell infiltration were determined between two groups, and 10 OIDEGs with diverse biological function annotations were identified and verified. A lncRNA-gene-immunocyte regulatory network further revealed 10 OIDEGs, 41 OIDELs and 7 OIICs that were highly correlated. Among them, CD1E and STAT3 were predicted as hub genes whether at the expression level or interaction level. cDCs emerged as having the most prominent differences and the highest degree of connectivity. FO393414.3, AC096734.1, LINC01137 and DLX6-AS1 with the greatest number of OIDEGs were thought to be more likely to participate in immunoregulation of OLF.

Conclusion

This is the first research to preliminarily elucidate OLF-related immunocyte infiltration landscape and immune-associated transcriptome signatures based on bioinformatic strategies and real-world data, which may provide compelling insights into the pathogenesis and therapeutic targets of OLF.

METTL3 induces bone marrow mesenchymal stem cells osteogenic differentiation and migration through facilitating M1 macrophage differentiation

Despite the crucial role of m⁶A methyltransferase METTL3 in multiple diseases onset and progression, there are still lacking hard evidence proving that METTL3 could affect macrophage polarization in the stage of bone repair. Here, we aimed to explore the potential involvement of METTL3 in bone repair through modulating macrophage polarization and decipher the underlying cellular/molecular mechanisms. Here we treated RAW 264.7 cells and BM-derived primary macrophages (BMDM) with lipopolysaccharide (LPS) to induce M1 differentiation. METTL3 expression was upregulated in pro-inflammatory macrophages (M1) as compared with macrophages (M0). And overexpression of METTL3 promoted the expression of IL-6 and iNOS secretion by M1 macrophage. In the coculture condition, M1 macrophages with forced expression of METTL3 significantly enhanced migration ability of BMSCs, and also remarkably facilitated osteogenesis ability of BMSCs; the opposite was true when expression of METTL3 was knockdown. In addition, the m⁶A-RIP microarray suggested that METTL3 silencing significantly reduce the m⁶A modification of DUSP14, HDAC5 and Nfam1. Furthermore, the findings showed that expression of HADC5 was downregulated in M1 macrophages with METTL3 knockdown, while the DUSP14 expression had slight change and Nfam1 expression was very low. In contrast, METTL3 overexpression promoted HDAC5 expression, indicating that HDAC5 is the critical target gene of METTL3. Under such a theme, we proposed that METTL3 overexpression might be a new approach of replacement therapy for the treatment of bone repair.

Injectable bone cement with magnesium-containing microspheres enhances osteogenesis via anti-inflammatory immunoregulation

Injectable bone cement is especially useful in minimally invasive surgeries to repair small and irregular bone defects. Amongst different kinds of injectable bone cements, bioactive calcium phosphate bone cement (CPC) has been widely studied due to its biological activity. However, its dense structure and poor biodegradability prevent the ingrowth of living tissue, which leads to undesirable bone regeneration and clinical translation. To address this issue, we prepared bone cement based on Magnesium-containing microspheres (MMSs) that can not only be cured into a 3D porous scaffold but also have controllable biodegradability that continuously provides space for desired tissue ingrowth. Interestingly, magnesium ions released from MMSs cement (MMSC) trigger positive immunomodulation via upregulation of the anti-inflammatory genes IL-10 and M2 macrophage polarization with increased expression of CD206, which is beneficial to osteogenesis. Moreover, the physicochemical properties of MMSC, including heat release, rheology and setting time, can be tuned to meet the requirements of injectable bone cement for clinical application. Using a rat model, we have demonstrated that MMSC promoted osteogenesis via mediation of tissue ingrowth and anti-inflammatory immunomodulation. The study provides a paradigm for the design and preparation of injectable bone cements with 3D porous structures, biodegradability and anti-inflammatory immunoregulation to efficiently promote osteogenesis.

Designing biomaterials for the delivery of RNA therapeutics to stimulate bone healing

Ribonucleic acids (small interfering RNA, microRNA, and messenger RNA) have been emerging as a promising new class of therapeutics for bone regeneration. So far, however, research has mostly focused on stability and complexation of these oligonucleotides for systemic delivery. By comparison, delivery of RNA nanocomplexes from biomaterial carriers can facilitate a spatiotemporally controlled local delivery of osteogenic oligonucleotides. This review provides an overview of the state-of-the-art in the design of biomaterials which allow for temporal and spatial control over RNA delivery. We correlate this concept of spatiotemporally controlled RNA delivery to the most relevant events that govern bone regeneration to evaluate to which extent tuning of release kinetics is required. In addition, inspired by the physiological principles of bone regeneration, potential new RNA targets are presented. Finally, considerations for clinical translation and upscaled production are summarized to stimulate the design of clinically relevant RNA-releasing biomaterials.

Wear of hip prostheses increases serum IGFBP-1 levels in patients with aseptic loosening

The biological mechanisms involved in aseptic loosening include inflammation-associated and bone resorption-associated processes. Coordinated cellular actions result in biochemical imbalances with devastating consequences for the joint. Given that this condition is not known for showing systemic signs, we investigated whether circulating levels of inflammation-related proteins are altered in patients with aseptic loosening. Our study included 37 patients who underwent revision surgery due to hip osteolysis and aseptic loosening and 31 patients who underwent primary total hip arthroplasty. Using antibody arrays, we evaluated the serum levels of 320 proteins in four patients from each group. The results showed differences in insulin-like growth factor-binding protein 1 (IGFBP-1) concentrations, which we then quantified using enzyme-linked immunosorbent assay tests in all study patients. The results confirmed that serum IGFBP-1 concentrations were higher in the revision surgery patients than in the hip arthroplasty patients. In vitro studies showed that exposure of human osteoblasts to titanium particles induced an IGFBP-1 release that further increased when exposure to particles was performed in media conditioned by human M1 macrophages. These findings suggest that elevated serum IGFBP-1 levels in patients with aseptic loosening can arise from increased local IGFBP-1 production in the inflammatory environment of the periprosthetic bed.

Modeling Sympathetic Hyperactivity in Alzheimer's Related Bone Loss

BACKGROUND

A significant subset of patients with Alzheimer's disease (AD) exhibit low bone mineral density and are therefore more fracture-prone, relative to their similarly aged neurotypical counterparts. In addition to chronic immune hyperactivity, behavioral dysregulation of effector peripheral sympathetic neurons-which densely innervate bone and potently modulate bone remodeling-is implicated in this pathological bone reformation.

OBJECTIVE

Thus, there exists a pressing need for a robust in vitro model which allows interrogation of the paracrine interactions between the putative mediators of AD-related osteopenia: sympathetic neurons (SNs) and mesenchymal stem cells (MSCs).

METHODS

Toward this end, activated SN-like PC12 cells and bone marrow derived MSCs were cultured in poly(ethylene glycol) diacrylate (PEGDA) hydrogels in the presence or absence of the AD-relevant inflammatory cytokine tumor necrosis factor alpha (TNF-α) under mono- and co-culture conditions.

RESULTS

PC12s and MSCs exposed separately to TNF-α displayed increased expression of pro-inflammatory mediators and decreased osteopontin (OPN), respectively. These data indicate that TNF-α was capable of inducing a dysregulated state in both cell types consistent with AD. Co-culture of TNF-α-activated PC12s and MSCs further exacerbated pathological behaviors in both cell types. Specifically, PC12s displayed increased secretion of interleukin 6 relative to TNF-α stimulated monoculture controls. Similarly, MSCs demonstrated a further reduction in osteogenic capacity relative to TNF-α stimulated monoculture controls, as illustrated by a significant decrease in OPN and collagen type I alpha I chain.

CONCLUSION

Taken together, these data may indicate that dysregulated sympathetic activity may contribute to AD-related bone loss.

Nesfatin-1 Promotes the Osteogenic Differentiation of Tendon-Derived Stem Cells and the Pathogenesis of Heterotopic Ossification in Rat Tendons via the mTOR Pathway

Heterotopic ossification (HO) is a pathological condition involved in tendinopathy. Adipokines are known to play a key role in HO of tendinopathy. Nesfatin-1, an 82-amino acid adipokine is closely reportedly associated with diabetes mellitus (DM), which, in turn, is closely related to tendinopathy. In the present study, we aimed to investigate the effects of nesfatin-1 on the osteogenic differentiation of tendon-derived stem cells (TDSCs) and the pathogenesis of tendinopathy in rats. In vitro, TDSCs were incubated in osteogenic induction medium for 14 days with different nesfatin-1 concentration. In vivo, Sprague Dawley rats underwent Achilles tenotomy to evaluate the effect of nesfatin-1 on tendinopathy. Our results showed that the expression of nesfatin-1 expression in tendinopathy patients was significantly higher than that in healthy subjects. Nesfatin-1 affected the cytoskeleton and reduced the migration ability of TDSCs in vitro. Furthermore, nesfatin-1 inhibited the expression of Scx, Mkx, and Tnmd and promoted the expression of osteogenic genes, such as COL1a1, ALP, and RUNX2; these results suggested that nesfatin-1 inhibits cell migration, adversely impacts tendon phenotype, promotes osteogenic differentiation of TDSCs and the pathogenesis of HO in rat tendons. Moreover, we observed that nesfatin-1 suppressed autophagy and activated the mammalian target of rapamycin (mTOR) pathway both in vitro and in vivo. The suppression of the mTOR pathway alleviated nesfatin-1-induced HO development in rat tendons. Thus, nesfatin-1 promotes the osteogenic differentiation of TDSC and the pathogenesis of HO in rat tendons via the mTOR pathway; these findings highlight a new potential therapeutic target for tendinopathy.

Applications of Graphene and Its Derivatives in Bone Repair: Advantages for Promoting Bone Formation and Providing Real-Time Detection, Challenges and Future Prospects

During continuous innovation in the preparation, characterization and application of various bone repair materials for several decades, nanomaterials have exhibited many unique advantages. As a kind of representative two-dimensional nanomaterials, graphene and its derivatives (GDs) such as graphene oxide and reduced graphene oxide have shown promising potential for the application in bone repair based on their excellent mechanical properties, electrical conductivity, large specific surface area (SSA) and atomic structure stability. Herein, we reviewed the updated application of them in bone repair in order to present, as comprehensively, as possible, their specific advantages, challenges and current solutions. Firstly, how their advantages have been utilized in bone repair materials with improved bone formation ability was discussed. Especially, the effects of further functionalization or modification were emphasized. Then, the signaling pathways involved in GDs-induced osteogenic differentiation of stem cells and immunomodulatory mechanism of GDs-induced bone regeneration were discussed. On the other hand, their applications as contrast agents in the field of bone repair were summarized. In addition, we also reviewed the progress and related principles of the effects of GDs parameters on cytotoxicity and residues. At last, the future research was prospected.