Exosomes Derived From M2 Macrophages Facilitate Osteogenesis and Reduce Adipogenesis of BMSCs

The Role of Extracellular Vesicles in Bone Regeneration and Associated Bone Diseases

Extracellular vesicles (EVs) are nanoscale particles with a lipid bilayer membrane structure secreted by various cell types. Nearly all human cells secrete EVs, primarily mediating intercellular communication. In recent years, scientists have discovered that EVs can carry multiple biological cargos, such as DNA, non-coding RNAs (ncRNAs), proteins, cytokines, and lipids, and mediate intercellular signal transduction. Bone is a connective tissue with a nerve supply and high vascularization. The repair process after injury is highly complex, involving interactions among multiple cell types and biological signaling pathways. Bone regeneration consists of a series of coordinated osteoconductive and osteoinductive biological processes. As mediators of intercellular communication, EVs can promote bone regeneration by regulating osteoblast-mediated bone formation, osteoclast-mediated bone resorption, and other pathways. This review summarizes the biogenesis of EVs and the mechanisms by which EV-mediated intercellular communication promotes bone regeneration. Additionally, we focus on the research progress of EVs in various diseases related to bone regeneration. Finally, based on the above research, we explore the clinical applications of engineered EVs in the diagnosis and treatment of bone regeneration-related diseases.

Role of aptamer technology in extracellular vesicle biology and therapeutic applications

Extracellular vesicles (EVs) are cell-derived nanosized membrane-bound vesicles that are important intercellular signalling regulators in local cell-to-cell and distant cell-to-tissue communication. Their inherent capacity to transverse cell membranes and transfer complex bioactive cargo reflective of their cell source, as well as their ability to be modified through various engineering and modification strategies, have attracted significant therapeutic interest. Molecular bioengineering strategies are providing a new frontier for EV-based therapy, including novel mRNA vaccines, antigen cross-presentation and immunotherapy, organ delivery and repair, and cancer immune surveillance and targeted therapeutics. The revolution of EVs, their diversity as biocarriers and their potential to contribute to intercellular communication, is well understood and appreciated but is ultimately dependent on the development of methods and techniques for their isolation, characterization and enhanced targeting. As single-stranded oligonucleotides, aptamers, also known as chemical antibodies, offer significant biological, chemical, economic, and therapeutic advantages in terms of their size, selectivity, versatility, and multifunctional programming. Their integration into the field of EVs has been contributing to the development of isolation, detection, and analysis pipelines associated with bioengineering strategies for nano-meets-molecular biology, thus translating their use for therapeutic and diagnostic utility.

Modulation of adipose tissue metabolism by exosomes in obesity

Obesity and its related metabolic complications represent a significant global health challenge. Central to this is the dysregulation of glucolipid metabolism, with a predominant focus on glucose metabolic dysfunction in the current research, whereas adipose metabolism impairment garners less attention. Exosomes (EXs), small extracellular vesicles (EVs) secreted by various cells, have emerged as important mediators of intercellular communication and have the potential to be biomarkers, targets, and therapeutic tools for diverse diseases. In particular, EXs have been found to play a role in adipose metabolism by transporting cargoes such as noncoding RNAs (ncRNA), proteins, and other factors. This review article summarizes the current understanding of the role of EXs in mediating adipose metabolism disorders in obesity. It highlights their roles in adipogenesis (encompassing adipogenic differentiation and lipid synthesis), lipid catabolism, lipid transport, and white adipose browning. The insights provided by this review offer new avenues for developing exosome-based therapies to treat obesity and its associated comorbidities.

Macrophage-derived exosomes rescue the TNF-ɑ-suppressed osteo-/cementogenic differentiation of hPDLCs

OBJECTIVE

Inflammatory stimuli compromise the differentiation potency of human periodontal ligament cells (hPDLCs). Macrophage-derived exosomes (M-Exo) play a role in several aspects of cellular activity. This study investigated how M-Exo contributes to the osteo-/cementogenic differentiation of hPDLCs under inflammation and the mechanism involved.

METHODS

M-Exo was identified by transmission electron microscopy, western blotting (WB), and dynamic light scattering. The internalization of M-Exo by hPDLCs was observed. After M-Exo treatment, the osteo-/cementogenic markers were detected by RT-qPCR and WB, and alkaline phosphatase (ALP) activity by ALP staining. Tumor necrosis factor alpha (TNF-ɑ) was applied to simulate inflammation. The rescue effect of M-Exo on TNF-ɑ-suppressed differentiation was validated. The p38 MAPK pathway activity was tested and a specific inhibitor was applied to explore the mechanism.

RESULTS

M-Exo was successfully isolated, identified and internalized by hPDLCs. M-Exo enhanced the osteo-/cementogenic differentiation of hPDLCs, as indicated by upregulated osteo-/cementogenic markers and elevated ALP activity. Moreover, TNF-ɑ inhibited the differentiation capabilities of hPDLCs, on which M-Exo showed a rescue effect. M-Exo activated the p38 MAPK pathway and SB203580 attenuated its promotion effect.

CONCLUSION

This study showed that M-Exo ameliorated the TNF-ɑ-suppressed osteo-/cementogenic differentiation of hPDLCs partly through the p38 MAPK pathway.

M2 macrophage-derived exosomes carry miR-142-3p to restore the differentiation balance of irradiated BMMSCs by targeting TGF-β1

Radiotherapy is essential to cancer treatment, while it inevitably injures surrounding normal tissues, and bone tissue is one of the most common sites prone to irradiation. Bone marrow mesenchymal stem cells (BMMSCs) are sensitive to irradiation and the irradiated dysfunction of BMMSCs may be closely related to irradiation-induced bone damage. Macropahges play important role in regulating stem cell function, bone metabolic balance and irradiation response, but the effects of macrophages on irradiated BMMSCs are still unclear. This study aimed to investigate the role of macrophages and macrophage-derived exosomes in restoring irradiated BMMSCs function. The effects of macrophage conditioned medium (CM) and macrophage-derived exosomes on osteogenic and fibrogenic differentiation capacities of irradiated BMMSCs were detected. The key microribonucleic acids (miRNAs) and targeted proteins in exosomes were also determined. The results showed that irradiation significantly inhibited the proliferation of BMMSCs, and caused differentiation imbalance of BMMSCs, with decreased osteogenic differentiation and increased fibrogenic differentiation. M2 macrophage-derived exosomes (M2D-exos) inhibited the fibrogenic differentiation and promoted the osteogenic differentiation of irradiated BMMSCs. We identified that miR-142-3p was significantly overexpressed in M2D-exos and irradiated BMMSCs treated with M2D-exos. After inhibition of miR-142-3p in M2 macrophage, the effects of M2D-exos on irradiated BMMSCs differentiation were eliminated. Furthermore, transforming growth factor beta 1 (TGF-β1), as a direct target of miR-142-3p, was significantly decreased in irradiated BMMSCs treated with M2D-exos. This study indicated that M2D-exos could carry miR-142-3p to restore the differentiation balance of irradiated BMMSCs by targeting TGF-β1. These findings pave a new way for promising and cell-free method to treat irradiation-induced bone damage.

Interaction between immuno-stem dual lineages in jaw bone formation and injury repair

The jawbone, a unique structure in the human body, undergoes faster remodeling than other bones due to the presence of stem cells and its distinct immune microenvironment. Long-term exposure of jawbones to an oral environment rich in microbes results in a complex immune balance, as shown by the higher proportion of activated macrophage in the jaw. Stem cells derived from the jawbone have a higher propensity to differentiate into osteoblasts than those derived from other bones. The unique immune microenvironment of the jaw also promotes osteogenic differentiation of jaw stem cells. Here, we summarize the various types of stem cells and immune cells involved in jawbone reconstruction. We describe the mechanism relationship between immune cells and stem cells, including through the production of inflammatory bodies, secretion of cytokines, activation of signaling pathways, etc. In addition, we also comb out cellular interaction of immune cells and stem cells within the jaw under jaw development, homeostasis maintenance and pathological conditions. This review aims to eclucidate the uniqueness of jawbone in the context of stem cell within immune microenvironment, hopefully advancing clinical regeneration of the jawbone.

Macrophage exosomes modified by miR-365-2-5p promoted osteoblast osteogenic differentiation by targeting OLFML1

In the bone immune microenvironment, immune cells can regulate osteoblasts through a complex communication network. Macrophages play a central role in mediating immune osteogenesis, exosomes derived from them have osteogenic regulation and can be used as carriers in bone tissue engineering. However, there are problems with exosomal therapy alone, such as poor targeting, and the content of loaded molecules cannot reach the therapeutic concentration. In this study, macrophage-derived exosomes modified with miR-365-2-5p were developed to accelerate bone healing. MC3T3-E1 cells were incubated with the culture supernatants of M0, M1 and M2 macrophages, and it was found that the culture medium of M2 macrophages had the most significant effects in contributing to osteogenesis. High-throughput sequencing identified that miR-365-2-5p was significantly expressed in exosomes derived from M2 macrophages. We incubated MC3T3-E1 with exosomes overexpressing or knocking down miR-365-2-5p to examine the biological function of exosome miR-365-2-5p on MC3T3-E1 differentiation. These findings suggested that miR-365-2-5p secreted by exosomes increased the osteogenesis of MC3T3-E1. Moreover, miR-365-2-5p had a direct influence over osteogenesis for MC3T3-E1. Sequencing analysis combined with dual luciferase detection indicated that miR-365-2-5p binded to the 3'-UTR of OLFML1. In summary, exosomes secreted by M2 macrophages targeted OLFML1 through miR-365-2-5p to facilitate osteogenesis.

Multifunctional Exosomes Derived from M2 Macrophages with Enhanced Odontogenesis, Neurogenesis and Angiogenesis for Regenerative Endodontic Therapy: An In Vitro and In Vivo Investigation

INTRODUCTION

Exosomes derived from M2 macrophages (M2-Exos) exhibit tremendous potential for inducing tissue repair and regeneration. Herein, this study was designed to elucidate the biological roles of M2-Exos in regenerative endodontic therapy (RET) compared with exosomes from M1 macrophages (M1-Exos).

METHODS

The internalization of M1-Exos and M2-Exos by dental pulp stem cells (DPSCs) and human umbilical vein endothelial cells (HUVECs) was detected by uptake assay. The effects of M1-Exos and M2-Exos on DPSC and HUVEC behaviors, including migration, proliferation, odonto/osteogenesis, neurogenesis, and angiogenesis were determined in vitro. Then, Matrigel plugs incorporating M2-Exos were transplanted subcutaneously into nude mice. Immunostaining for vascular endothelial growth factor (VEGF) and CD31 was performed to validate capillary-like networks.

RESULTS

M1-Exos and M2-Exos were effectively absorbed by DPSCs and HUVECs. Compared with M1-Exos, M2-Exos considerably facilitated the proliferation and migration of DPSCs and HUVECs. Furthermore, M2-Exos robustly promoted ALP activity, mineral nodule deposition, and the odonto/osteogenic marker expression of DPSCs, indicating the powerful odonto/osteogenic potential of M2-Exos. In sharp contrast with M1-Exos, which inhibited the neurogenic capacity of DPSCs, M2-Exos contributed to a significantly augmented expression of neurogenic genes and the stronger immunostaining of Nestin. Consistent with remarkably enhanced angiogenic markers and tubular structure formation in DPSCs and HUVECs in vitro, the employment of M2-Exos gave rise to more abundant vascular networks, dramatically higher VEGF expression, and widely spread CD31+ tubular lumens in vivo, supporting the enormous pro-angiogenic capability of M2-Exos.

CONCLUSIONS

The multifaceted roles of M2-Exos in ameliorating DPSC and HUVEC functions potentially contribute to complete functional pulp-dentin complex regeneration.

Immune Cell-Derived Exosomes in Inflammatory Disease and Inflammatory Tumor Microenvironment: A Review

Inflammation is a common feature of many inflammatory diseases and tumors, and plays a decisive role in their development. Exosomes are extracellular vesicles unleashed by assorted types of cells, and it is widely known that exosomes of different immune cell sources play different functions. Exosome production has recently been reported for immune cells comprising macrophages, T cells, B cells, and dendritic cells (DCs). Immune cell-derived exosomes are involved in a variety of inflammatory responses.Herein, we summarize and review the role of macrophages, T cells, B cells, and dendritic cells (DC) in inflammatory diseases, with a focus on the role of immune cell-derived exosomes in osteoarthritis, rheumatoid arthritis, and the inflammatory tumor microenvironment (TME).These findings are expected to be important for developing new treatments for inflammatory diseases and ameliorating tumor-related inflammation.

Macrophage-derived exosomal miRNA-141 triggers endothelial cell pyroptosis by targeting NLRP3 to accelerate sepsis progression

Sepsis, critical condition marked by severe organ dysfunction from uncontrolled infection, involves the endothelium significantly. Macrophages, through paracrine actions, play a vital role in sepsis, but their mechanisms in sepsis pathogenesis remain elusive. Objective: We aimed to explore how macrophage-derived exosomes with low miR-141 expression promote pyroptosis in endothelial cells (ECs). Exosomes from THP-1 cell supernatant were isolated and characterized. The effects of miR-141 mimic/inhibitor on apoptosis, proliferation, and invasion of Human Umbilical Vein Endothelial Cells (HUVECs) were assessed using flow cytometry, CCK-8, and transwell assays. Key pyroptosis-related proteins, including caspase-1, IL-18, IL-1β, NLR Family Pyrin Domain Containing 3 (NLRP3), ASC, and cleaved-GSDMD, were analyzed via Western blot. The interaction between miR-141 and NLRP3 was studied using RNAhybrid v2.2 and dual-Luciferase reporter assays. The mRNA and protein level of NLRP3 after exosomal miR-141 inhibitor treatment was detected by qPCR and Western blot, respectively. Exosomes were successfully isolated. miR-141 mimic reduced cell death and pyroptosis-related protein expression in HUVECs, while the inhibitor had opposite effects, increasing cell death, and enhancing pyroptosis protein expression. Additionally, macrophage-derived exosomal miR-141 inhibitor increased cell death and pyroptosis-related proteins in HUVECs. miR-141 inhibits NLRP3 transcription. Macrophages facilitate sepsis progression by secreting miR-141 decreased exosomes to activate NLRP3-mediated pyroptosis in ECs, which could be a potentially valuable target of sepsis therapy.

Regulation of the immune microenvironment by pioglitazone-loaded polylactic glycolic acid nanosphere composite scaffolds to promote vascularization and bone regeneration

Osteogenesis is caused by multiple factors, and the inflammatory response, osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), regeneration of blood vessels, and other factors must be considered in bone tissue engineering. To effectively repair bone defect, it is important to decrease excessive inflammation, enhance the differentiation of mesenchymal stem cells into osteoblasts, and stimulate angiogenesis. Herein, nano-attapulgite (ATP), polyvinyl alcohol (PVA), and gelatin (GEL) scaffolds were produced using 3D printing technology and pioglitazone (PIO)-containing polylactic acid-glycolic acid (PLGA) nanospheres were added. In both in vitro and in vivo studies, material scaffolds with PIO-loaded polylactic acid-glycolic acid nanospheres could reduce the inflammatory response by encouraging macrophage polarization from M1 to M2 and promoting the osteogenic differentiation of BMSCs by activating the BMP2/Smad/RUNX2 signal pathway to repair bone defects. The vascularization of human umbilical vein endothelial cells (HUVECs) through the PI3K/AKT/HIF1-/VEGF pathway was also encouraged. In vivo research using PIO-containing PLGA nanospheres revealed massive collagen deposition in skin models. These findings indicate a potentially effective scaffold for bone healing, when PLGA nanospheres-which contain the drug PIO-are combined with ATP/PVA/GEL scaffolds.

Exosomal non-coding RNAs: Emerging insights into therapeutic potential and mechanisms in bone healing

Exosomes are nano-sized extracellular vesicles (EVs) released by diverse types of cells, which affect the functions of targeted cells by transporting bioactive substances. As the main component of exosomes, non-coding RNA (ncRNA) is demonstrated to impact multiple pathways participating in bone healing. Herein, this review first introduces the biogenesis and secretion of exosomes, and elucidates the role of the main cargo in exosomes, ncRNAs, in mediating intercellular communication. Subsequently, the potential molecular mechanism of exosomes accelerating bone healing is elucidated from the following four aspects: macrophage polarization, vascularization, osteogenesis and osteoclastogenesis. Then, we systematically introduce construction strategies based on modified exosomes in bone regeneration field. Finally, the clinical trials of exosomes for bone healing and the challenges of exosome-based therapies in the biomedical field are briefly introduced, providing solid theoretical frameworks and optimization methods for the clinical application of exosomes in orthopedics.

Engineered exosomes for tissue regeneration: from biouptake, functionalization and biosafety to applications

Exosomes are increasingly recognized as important effector molecules that regulate intercellular signaling pathways. Notably, certain types of exosomes can induce therapeutic responses, including cell proliferation, angiogenesis, and tissue repair. The use of exosomes in therapy is a hot spot in current research, especially in regenerative medicine. Despite the therapeutic potential, problems have hindered their success in clinical applications. These shortcomings include low concentration, poor targeting and limited loading capability. To fully realize their therapeutic potential, certain modifications are needed in native exosomes. In the present review, we summarize the exosome modification and functionalization strategies. In addition, we provide an overview of potential clinical applications and highlight the issues associated with the biosafety and biocompatibility of engineered exosomes in applications.

M2 macrophage-derived exosomal miR-486-5p influences the differentiation potential of bone marrow mesenchymal stem cells and osteoporosis

BACKGROUND

An imbalance between osteogenesis and adipogenesis in bone marrow mesenchymal stem cells (BMMSCs) can cause osteoporosis. Macrophage-derived exosomes (MD-Exos) and microRNAs (miRNAs) enriched in exosomes participate in the differentiation of BMMSCs.

METHODS

Bioinformatics methods were used to analyze differentially expressed miRNAs. We cocultured M2 macrophages and BMMSCs to examine the biological function of exosomal microRNA-486-5p (miR-486-5p) on BMMSCs differentiation. Gain-of-function experiments related to osteogenesis were designed to investigate the effects of exosomes carrying miR-486-5p on an ovariectomized (OVX) mice model and the direct impact of miR-486-5p on BMMSCs. A dual luciferase experiment was performed to demonstrate the target gene of miR-486-5p.

RESULTS

Bioinformatics analysis identified high expression of miRNA-486 in M2 macrophage-derived exosomes (M2D-Exos). The in vitro results demonstrated that M2 macrophage-derived exosomal miR-486-5p enhanced osteogenic capacity but inhibited the adipogenesis of BMMSCs. The direct effect of miR-486-5p on BMMSCs showed the same effects. Animal experiments revealed that exosomal miR-486-5p rescued bone loss of OVX mice. SMAD2 was characterized as a target gene of miR-486-5p. Pathway analysis showed that M2 macrophage-derived exosomal miR-486-5p stimulated osteogenic differentiation via the TGF-β/SMAD2 signalling pathway.

CONCLUSIONS

Taken together, M2 macrophage-derived exosomal miR-486-5p influences the differentiation potential of BMMSCs through the miR-486-5p/SMAD2/TGF-β signalling pathway and osteoporosis.

Exercise-regulated white adipocyte differentitation: An insight into its role and mechanism

White adipocytes play a key role in the regulation of fat mass amount and energy balance. An appropriate level of white adipocyte differentiation is important for maintaining metabolic homeostasis. Exercise, an important way to improve metabolic health, can regulate white adipocyte differentiation. In this review, the effect of exercise on the differentiation of white adipocytes is summarized. Exercise could regulate adipocyte differentiation in multiple ways, such as exerkines, metabolites, microRNAs, and so on. The potential mechanism underlying the role of exercise in adipocyte differentiation is also reviewed and discussed. In-depth investigation of the role and mechanism of exercise in white adipocyte differentiation would provide new insights into exercise-mediated improvement of metabolism and facilitate the application of exercise-based strategy against obesity.

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.

Stimulating factors for regulation of osteogenic and chondrogenic differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs), distributed in many tissues in the human body, are multipotent cells capable of differentiating in specific directions. It is usually considered that the differentiation process of MSCs depends on specialized external stimulating factors, including cell signaling pathways, cytokines, and other physical stimuli. Recent findings have revealed other underrated roles in the differentiation process of MSCs, such as material morphology and exosomes. Although relevant achievements have substantially advanced the applicability of MSCs, some of these regulatory mechanisms still need to be better understood. Moreover, limitations such as long-term survival in vivo hinder the clinical application of MSCs therapy. This review article summarizes current knowledge regarding the differentiation patterns of MSCs under specific stimulating factors.

Bioengineering extracellular vesicles: smart nanomaterials for bone regeneration

In the past decade, extracellular vesicles (EVs) have emerged as key regulators of bone development, homeostasis and repair. EV-based therapies have the potential to circumnavigate key issues hindering the translation of cell-based therapies including functional tissue engraftment, uncontrolled differentiation and immunogenicity issues. Due to EVs' innate biocompatibility, low immunogenicity, and high physiochemical stability, these naturally-derived nanoparticles have garnered growing interest as potential acellular nanoscale therapeutics for a variety of diseases. Our increasing knowledge of the roles these cell-derived nanoparticles play, has made them an exciting focus in the development of novel pro-regenerative therapies for bone repair. Although these nano-sized vesicles have shown promise, their clinical translation is hindered due to several challenges in the EV supply chain, ultimately impacting therapeutic efficacy and yield. From the biochemical and biophysical stimulation of parental cells to the transition to scalable manufacture or maximising vesicles therapeutic response in vivo, a multitude of techniques have been employed to improve the clinical efficacy of EVs. This review explores state of the art bioengineering strategies to promote the therapeutic utility of vesicles beyond their native capacity, thus maximising the clinical potential of these pro-regenerative nanoscale therapeutics for bone repair.

Hyaluronic acid-based hydrogels: As an exosome delivery system in bone regeneration

Exosomes are extracellular vesicles (EVs) containing various ingredients such as DNA, RNA, lipids and proteins, which play a significant role in intercellular communication. Numerous studies have demonstrated the important role of exosomes in bone regeneration through promoting the expression of osteogenic-related genes and proteins in mesenchymal stem cells. However, the low targeting ability and short circulating half-life of exosomes limited their clinical application. In order to solve those problems, different delivery systems and biological scaffolds have been developed. Hydrogel is a kind of absorbable biological scaffold composed of three-dimensional hydrophilic polymers. It not only has excellent biocompatibility and superior mechanical strength but can also provide a suitable nutrient environment for the growth of the endogenous cells. Thus, the combination between exosomes and hydrogels can improve the stability and maintain the biological activity of exosomes while achieving the sustained release of exosomes in the bone defect sites. As an important component of the extracellular matrix (ECM), hyaluronic acid (HA) plays a critical role in various physiological and pathological processes such as cell differentiation, proliferation, migration, inflammation, angiogenesis, tissue regeneration, wound healing and cancer. In recent years, hyaluronic acid-based hydrogels have been used as an exosome delivery system for bone regeneration and have displayed positive effects. This review mainly summarized the potential mechanism of HA and exosomes in promoting bone regeneration and the application prospects and challenges of hyaluronic acid-based hydrogels as exosome delivery devices in bone regeneration.

The Applications and Potentials of Extracellular Vesicles from Different Cell Sources in Periodontal Regeneration

Periodontitis is a chronic infectious disease worldwide that can cause damage to periodontal supporting tissues including gingiva, bone, cementum and periodontal ligament (PDL). The principle for the treatment of periodontitis is to control the inflammatory process. Achieving structural and functional regeneration of periodontal tissues is also essential and remains a major challenge. Though many technologies, products, and ingredients were applied in periodontal regeneration, most of the strategies have limited outcomes. Extracellular vesicles (EVs) are membranous particles with a lipid structure secreted by cells, containing a large number of biomolecules for the communication between cells. Numerous studies have demonstrated the beneficial effects of stem cell-derived EVs (SCEVs) and immune cell-derived EVs (ICEVs) on periodontal regeneration, which may be an alternative strategy for cell-based periodontal regeneration. The production of EVs is highly conserved among humans, bacteria and plants. In addition to eukaryocyte-derived EVs (CEVs), a growing body of literature suggests that bacterial/plant-derived EVs (BEVs/PEVs) also play an important role in periodontal homeostasis and regeneration. The purpose of this review is to introduce and summarize the potential therapeutic values of BEVs, CEVs and PEVs in periodontal regeneration, and discuss the current challenges and prospects for EV-based periodontal regeneration.

Gold nanoparticles: promising biomaterials for osteogenic/adipogenic regulation in bone repair

Bone defects are a common bone disease, which are usually caused by accidents, trauma and tumors. However, the treatment of bone defects is still a great clinical challenge. In recent years, research on bone repair materials has continued with great success, but there are few reports on the repair of bone defects at a high lipid level. Hyperlipidemia is a risk factor in the process of bone defect repair, which has a negative impact on the process of osteogenesis, increasing the difficulty of bone defect repair. Therefore, it is necessary to find materials that can promote bone defect repair under the condition of hyperlipidemia. Gold nanoparticles (AuNPs) have been applied in the fields of biology and clinical medicine for many years and developed to modulate osteogenic differentiation and adipogenic differentiation. In vitro and vivo studies displayed that they promoted bone formation and inhibited fat accumulation. Further, the metabolism and mechanisms of AuNPs acting on osteogenesis/adipogenesis were partially revealed by researchers. This review further clarifies the role of AuNPs in osteogenic/adipogenic regulation during the process of osteogenesis and bone regeneration by summarizing the related in vitro and in vivo research, discussing the advantages and challenges of AuNPs and highlighting several possible directions for future research, with the aim to provide a new strategy for dealing with bone defects in hyperlipidemic patients.

Dental pulp stem cells induce anti-inflammatory phenotypic transformation of macrophages to enhance osteogenic potential via IL-6/GP130/STAT3 signaling

Background

Periodontitis is a major oral condition and current treatment outcomes can be unsatisfactory. Macrophages are essential to the regeneration process, so we investigated the influence of human dental pulp stem cells (hDPSCs) on macrophage differentiation and the microenvironment and the underlying mechanism.

Methods

hDPSCs were isolated from healthy third molars extracted from patients undergoing maxillofacial surgery. The surface antigens CD73, CD45, CD90 and CD11b of the hDPSCs were detected using flow cytometry. hDPSCs were induced for osteogenic and adipogenic differentiation, and the outcome was assessed by alizarin red staining or Oil Red O staining. The IL-6 level released by hDPSCs was measured by enzyme linked immunosorbent assay (ELISA). Tohoku Hospital Pediatrics-1 (THP-1) cells were cultured and induced into macrophages by phorbol-12-myristate-13-acetate. After coculture of THP-1-derived macrophages with hDPSCs, interleukin 6 (IL-6), Argininase-1 (Arg-1), Mannose receptor C-1 (Mrc-1), inducible nitric oxide synthase (iNOS), and tumor necrosis factor-α (TNF-α) levels in the medium were measured using ELISA and quantificational RT-PCR (qRT-PCR). The numbers of CD80⁺ and CD163⁺ macrophages were counted by immunofluorescence, and GP130/STAT3 signaling protein expression was detected. After coculturing the culture medium of hDPSCs with human bone marrow stem cells (BMSCs), scratch assays and transwell assays were performed to evaluate cell migration and invasion.

Results

Alkaline phosphatase (ALP) staining, alizarin red staining, and western blots were performed to assess osteoblast differentiation. The hDPSCs were positive for surface antigens CD73 and CD90 and negative for CD45 and CD11b expression. The level of IL-6 secreted by hDPSCs significantly increased the number of CD80⁺ cells as well as the levels of Arg-1 and Mrc-1. It also promoted M2 macrophage polarization and activated GP130/STAT3 signaling. However, the medium cocultured with THP-1-derived macrophages by hDPSCs facilitated the migration, invasion, and osteogenic abilities of human bone marrow-derived stem cells (hBMSCs).

Conclusions

hDPSCs can regulate the periodontal microenvironment through IL-6 by inducing phenotypic transformation of M2 macrophages and stimulating osteogenic differentiation of BMSCs.

Long Non-Coding RNAs Within Macrophage-Derived Exosomes Promote BMSC Osteogenesis in a Bone Fracture Rat Model

Purpose

To investigate the effect of macrophage exosomal long non-coding (lnc)RNAs on bone mesenchymal stem cell (BMSC) osteogenesis and the associated mechanism.

Methods

Rat BMSCs and spleen macrophages were co-cultured with serum derived from the fracture microenvironment of rat tibia. BMSC osteogenesis was evaluated using Alizarin red staining and the expression of BMP-2, RUNX2, OPN, and OC mRNA. BMSC osteogenesis was evaluated after co-culture with macrophages stimulated using hypoxic conditions or colony-stimulating factor (CSF). The uptake of macrophage-derived exosomes by BMSCs was evaluated using the exosome uptake assay. High-throughput sequencing and bioinformatics analyses were performed to identify key lncRNAs in the macrophage exosomes. The effect of lncRNA expression levels on BMSC osteogenesis was also assessed using a lncRNA overexpression plasmid and siRNA technology. M1 and M2 macrophages were distinguished using flow cytometry and the key exosomal lncRNA was detected by in situ hybridization.

Results

In the fracture microenvironment, macrophages (stimulated using either hypoxia or CSF) significantly increased the osteogenic ability of BMSCs. We showed that BMSCs assimilated macrophage-derived vesicles and that the inhibition of exosomal secretion significantly attenuated the macrophage-mediated induction of BMSC osteogenesis. The hypoxia condition led to the up-regulation of 310 lncRNAs and the down-regulation of 575 lncRNAs in macrophage exosomes, while CSF stimulation caused the up-regulation of 557 lncRNAs and the down-regulation of 407 lncRNAs. In total, 108 lncRNAs were co-up-regulated and 326 lncRNAs were co-down-regulated under both conditions. We eventually identified LOC103691165 as a key lncRNA that promoted BMSC osteogenesis and was expressed at similar levels in both M1 and M2 macrophages.

Conclusion

In the fracture microenvironment, M1 and M2 macrophages promoted BMSC osteogenesis by secreting exosomes containing LOC103691165.

Osteoimmune Interactions and Therapeutic Potential of Macrophage-Derived Small Extracellular Vesicles in Bone-Related Diseases

Due to the aging of the global population, the burden of bone-related diseases has increased sharply. Macrophage, as indispensable components of both innate immune responses and adaptive immunity, plays a considerable role in maintaining bone homeostasis and promoting bone establishment. Small extracellular vesicles (sEVs) have attracted increasing attention because they participate in cell cross-talk in pathological environments and can serve as drug delivery systems. In recent years, an increasing number of studies have expanded our knowledge about the effects of macrophage-derived sEVs (M-sEVs) in bone diseases via different forms of polarization and their biological functions. In this review, we comprehensively describe on the application and mechanisms of M-sEVs in various bone diseases and drug delivery, which may provide new perspectives for treating and diagnosing human bone disorders, especially osteoporosis, arthritis, osteolysis, and bone defects.

CD301b+ Macrophages as Potential Target to Improve Orthodontic Treatment under Mild Inflammation

Due to improvements of quality of life and the demand for aesthetics, more and more people are choosing orthodontic treatments, resulting in a surge in adult orthodontic patients in recent years. However, a large amount of clinical evidence shows that many orthodontic patients have mild periodontitis in the periodontal tissues, which affects the efficacy of the orthodontic treatment or aggravates the periodontal condition. Therefore, it is important to identify the key factors that affect orthodontic treatments in this inflammatory environment. The aim of this study was to investigate the role of macrophages in orthodontic treatments under inflammatory environments. By analyzing the functional groups of macrophages in the orthodontic rat model of periodontitis, we found that macrophages with high expression levels of CD301b could improve the periodontal microenvironment and improve the efficiency of the orthodontic tooth movement. CD301b+ macrophages transplanted into the model can promote osteogenesis around orthodontic moving teeth, improve bone remodeling during orthodontic treatment, and accelerate orthodontic tooth movement. Considered together, these results suggest that CD301b+ macrophages may play an active role in orthodontic treatments in inflammatory environments and may serve as potential regulatory targets.

The role of the immune microenvironment in bone, cartilage, and soft tissue regeneration: from mechanism to therapeutic opportunity

Bone, cartilage, and soft tissue regeneration is a complex spatiotemporal process recruiting a variety of cell types, whose activity and interplay must be precisely mediated for effective healing post-injury. Although extensive strides have been made in the understanding of the immune microenvironment processes governing bone, cartilage, and soft tissue regeneration, effective clinical translation of these mechanisms remains a challenge. Regulation of the immune microenvironment is increasingly becoming a favorable target for bone, cartilage, and soft tissue regeneration; therefore, an in-depth understanding of the communication between immune cells and functional tissue cells would be valuable. Herein, we review the regulatory role of the immune microenvironment in the promotion and maintenance of stem cell states in the context of bone, cartilage, and soft tissue repair and regeneration. We discuss the roles of various immune cell subsets in bone, cartilage, and soft tissue repair and regeneration processes and introduce novel strategies, for example, biomaterial-targeting of immune cell activity, aimed at regulating healing. Understanding the mechanisms of the crosstalk between the immune microenvironment and regeneration pathways may shed light on new therapeutic opportunities for enhancing bone, cartilage, and soft tissue regeneration through regulation of the immune microenvironment.

Effects of PAMK on lncRNA, miRNA, and mRNA expression profiles of thymic epithelial cells

Polysaccharides from Atractylodes macrocephala Koidz (PAMK) can promote the proliferation of thymocytes and improve the body's immunity. However, the effect of PAMK on thymic epithelial cells has not been reported. Studies have shown that miRNAs and lncRNAs are key factors in regulating cell proliferation. In this study, we found that PAMK could promote the proliferation of mouse medullary thymic epithelial cell line 1 (MTEC1) cells through CCK-8 and EdU experiments. To further explore its mechanism, we detected the effect of PAMK on the expression profiles of lncRNAs, miRNAs, and mRNAs in MTEC1 cells. The results showed that PAMK significantly affected the expression of 225 lncRNAs, 29 miRNAs, and 800 mRNAs. Functional analysis showed that these differentially expressed genes were significantly enriched in cell cycle, cell division, NF-kappaB signaling, apoptotic process, and MAPK signaling pathway. Finally, we used Cytoscape to visualize lncRNA-miRNA-mRNA(14 lncRNAs, 17 miRNAs, 171 mRNAs) networks based on ceRNA theory. These results suggest that lncRNAs and miRNAs may be involved in the effect of PAMK on the proliferation of MTEC1 cells, providing a new research direction for exploring the molecular mechanism of PAMK promoting the proliferation of thymic epithelial cells.

Remotely Temporal Scheduled Macrophage Phenotypic Transition Enables Optimized Immunomodulatory Bone Regeneration

Precise timing of macrophage polarization plays a pivotal role in immunomodulation of tissue regeneration, yet most studies mainly focus on M2 macrophages for their anti-inflammatory and regenerative effects while the essential proinflammatory role of the M1 phenotype on the early inflammation stage is largely underestimated. Herein, a superparamagnetic hydrogel capable of timely controlling macrophage polarization is constructed by grafting superparamagnetic nanoparticles on collagen nanofibers. The magnetic responsive hydrogel network enables efficient polarization of encapsulated macrophage to the M2 phenotype through the podosome/Rho/ROCK mechanical pathway in response to static magnetic field (MF) as needed. Taking advantage of remote accessibility of magnetic field together with the superparamagnetic hydrogels, a temporal engineered M1 to M2 transition course preserving the essential role of M1 at the early stage of tissue healing, as well as enhancing the prohealing effect of M2 at the middle/late stages is established via delayed MF switch. Such precise timing of macrophage polarization matching the regenerative process of injured tissue eventually leads to optimized immunomodulatory bone healing in vivo. Overall, this study offers a remotely time-scheduled approach for macrophage polarization, which enables precise manipulation of inflammation progression during tissue healing.

Trehalose improves palmitic acid-induced apoptosis of osteoblasts by regulating SIRT3-medicated autophagy via the AMPK/mTOR/ULK1 pathway

Accumulation of lipid substances decreased the activity of osteoblasts. Trehalose is a typical stress metabolite to form a protective membrane on cell surface which has been demonstrated to regulate lipid metabolism. This activity of Trehalose indicates the potential effect of osteoporosis treatment. Our study aimed to determine the therapeutic effect of Trehalose in high fat-induced osteoporosis. We used palmitic acid (PA) to mimic the state of high fat and observed the apoptosis ratio of osteoblasts increased. After adding Trehalose, the apoptosis ratio decreased obviously. Autophagy is a regulatory means involved in the process of apoptosis. We detected the autophagy protein and found that the expression of Beclin-1, Atg5, and LC3 II increased, and p62 decreased after Trehalose treatment. When adding an autophagy inhibitor (3-MA), the expression of Beclin-1, Atg5, and LC3 II decreased, and p62 increased. These results indicated autophagy was an important factor involved in the preventive effect of Trehalose in PA-induced apoptosis. SIRT3 is a mitochondrial gene that can inhibit apoptosis, which has been reported to promote autophagy. We used SIRT3-siRNA to silence the expression of SIRT3 and found the effect of Trehalose was counteracted. The apoptosis ratio increased and the expression of Beclin-1, Atg5, and LC3 II decreased, p62 increased. Additionally, we also fed the mice with a high-fat diet (HFD) and intragastrical Trehalose. The results showed that Trehalose could inhibit the bone mass loss with HFD. Our study revealed the effect and mechanism of Trehalose in the treatment of osteoporosis.

The promising roles of macrophages in geriatric hip fracture

As aging becomes a global burden, the incidence of hip fracture (HF), which is the most common fracture in the elderly population and can be fatal, is rapidly increasing, and its extremely high fatality rate places significant medical and financial burdens on patients. Fractures trigger a complex set of immune responses, and recent studies have shown that with aging, the immune system shows decreased activity or malfunctions in a process known as immune senescence, leading to disease and death. These phenomena are the reasons why elderly individuals typically exhibit chronically low levels of inflammation and increased rates of infection and chronic disease. Macrophages, which are key players in the inflammatory response, are critical in initiating the inflammatory response, clearing pathogens, controlling the innate and adaptive immune responses and repairing damaged tissues. Tissue-resident macrophages (TRMs) are widely present in tissues and perform immune sentinel and homeostatic functions. TRMs are combinations of macrophages with different functions and phenotypes that can be directly influenced by neighboring cells and the microenvironment. They form a critical component of the first line of defense in all tissues of the body. Immune system disorders caused by aging could affect the biology of macrophages and thus the cascaded immune response after fracture in various ways. In this review, we outline recent studies and discuss the potential link between monocytes and macrophages and their potential roles in HF in elderly individuals.

The Roles of Exosomes upon Metallic Ions Stimulation in Bone Regeneration

Metallic ions have been widely investigated and incorporated into bone substitutes for bone regeneration owing to their superior capacity to induce angiogenesis and osteogenesis. Exosomes are key paracrine mediators that play a crucial role in cell-to-cell communication. However, the role of exosomes in metallic ion-induced bone formation and their underlying mechanisms remain unclear. Thus, this review systematically analyzes the effects of metallic ions and metallic ion-incorporated biomaterials on exosome secretion from mesenchymal stem cells (MSCs) and macrophages, as well as the effects of secreted exosomes on inflammation, angiogenesis, and osteogenesis. In addition, possible signaling pathways involved in metallic ion-mediated exosomes, followed by bone regeneration, are discussed. Despite limited investigation, metallic ions have been confirmed to regulate exosome production and function, affecting immune response, angiogenesis, and osteogenesis. Although the underlying mechanism is not yet clear, these insights enrich our understanding of the mechanisms of the metallic ion-induced microenvironment for bone regeneration, benefiting the design of metallic ion-incorporated implants.

Extracellular Vesicles in Bone Homeostasis: Emerging Mediators of Osteoimmune Interactions and Promising Therapeutic Targets

An imbalance in bone homeostasis results in bone loss and poor healing in bone diseases and trauma. Osteoimmune interactions, as a key contributor to bone homeostasis, depend on the crosstalk between mesenchymal stem cell-osteoblast (MSC-OB) and monocyte-macrophage (MC-Mφ) lineages. Currently, extracellular vesicles (EVs) are considered to be involved in cell-to-cell communication and represent a novel avenue to enhance our understanding of bone homeostasis and to develop novel diagnostic and therapeutic options. In this comprehensive review, we aim to present recent advances in the study of the effect of MC-Mφ-derived EVs on osteogenesis and the regulatory effects of MSC-OB-derived EVs on the differentiation, recruitment and efferocytosis of Mφ. Furthermore, we discuss the role of EVs as crucial mediators of the communication between these cell lineages involved in the development of common bone diseases, with a focus on osteoporosis, osteoarthritis, bone fracture, and periodontal disease. Together, this review focuses on the apparent discrepancies in current research findings and future directions for translating fundamental insights into clinically relevant EV-based therapies for improving bone health.

Bone Tissue Engineering in the Treatment of Bone Defects

Bones play an important role in maintaining exercise and protecting organs. Bone defect, as a common orthopedic disease in clinics, can cause tremendous damage with long treatment cycles. Therefore, the treatment of bone defect remains as one of the main challenges in clinical practice. Today, with increased incidence of bone disease in the aging population, demand for bone repair material is high. At present, the method of clinical treatment for bone defects including non-invasive therapy and invasive therapy. Surgical treatment is the most effective way to treat bone defects, such as using bone grafts, Masquelet technique, Ilizarov technique etc. In recent years, the rapid development of tissue engineering technology provides a new treatment strategy for bone repair. This review paper introduces the current situation and challenges of clinical treatment of bone defect repair in detail. The advantages and disadvantages of bone tissue engineering scaffolds are comprehensively discussed from the aspect of material, preparation technology, and function of bone tissue engineering scaffolds. This paper also summarizes the 3D printing technology based on computer technology, aiming at designing personalized artificial scaffolds that can accurately fit bone defects.

An Emerging Frontier in Intercellular Communication: Extracellular Vesicles in Regeneration

Regeneration requires cellular proliferation, differentiation, and other processes that are regulated by secreted cues originating from cells in the local environment. Recent studies suggest that signaling by extracellular vesicles (EVs), another mode of paracrine communication, may also play a significant role in coordinating cellular behaviors during regeneration. EVs are nanoparticles composed of a lipid bilayer enclosing proteins, nucleic acids, lipids, and other metabolites, and are secreted by most cell types. Upon EV uptake by target cells, EV cargo can influence diverse cellular behaviors during regeneration, including cell survival, immune responses, extracellular matrix remodeling, proliferation, migration, and differentiation. In this review, we briefly introduce the history of EV research and EV biogenesis. Then, we review current understanding of how EVs regulate cellular behaviors during regeneration derived from numerous studies of stem cell-derived EVs in mammalian injury models. Finally, we discuss the potential of other established and emerging research organisms to expand our mechanistic knowledge of basic EV biology, how injury modulates EV biogenesis, cellular sources of EVs in vivo, and the roles of EVs in organisms with greater regenerative capacity.

Research Progress of Exosomes in Bone Diseases: Mechanism, Diagnosis and Therapy

With the global escalation of the aging process, the number of patients with bone diseases is increasing year by year. Currently, there are limited effective treatments for bone diseases. Exosome, as a vital medium in cell-cell communication, can mediate tissue metabolism through the paracrine transmission of various cargos (proteins, nucleic acids, lipids, etc.) carried by itself. Recently, an increasing number of researchers have proven that exosomes play essential roles in the formation, metabolism, and pathological changes of bone and cartilage. Because exosomes have the advantages of small size, rich sources, and low immunogenicity, they can be used not only as substitutes for the traditional treatment of bone diseases, but also as biomarkers for the diagnosis of bone diseases. This paper reviews the research progress of several kinds of cells derived-exosomes in bone diseases and provides a theoretical basis for further research and clinical application of exosomes in bone diseases in the future.

Beneficial roles of the AhR ligand FICZ on the regenerative potentials of BMSCs and primed cartilage templates

Bone marrow-derived mesenchymal stem cells (BMSCs) are commonly used seed cells, and BMSC-derived primed cartilage templates have been shown to achieve bone regeneration in bone tissue engineering. Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor involved in various cellular processes such as osteogenesis and immune regulation. This study investigated the effects of the AhR endogenous ligand 6-formyl (3,2-b) carbazole (FICZ) on the behavior of BMSCs and cartilage templates as well as the possible underlying molecular mechanisms. AhR expressions in rat bone marrow and isolated BMSCs were detected via immunohistochemistry (IHC) and immunofluorescent staining. Alkaline phosphatase staining and alizarin red staining showed that FICZ treatment enhanced the osteogenic potential of BMSCs without influencing their proliferation. FICZ was shown to alleviate the LPS-induced inflammatory cytokines IL-1β, 6 and TNF-α via the quantitative polymerase chain reaction (qPCR). In the chondrogenic process from BMSCs to primed cartilage templates, the expressions of AhR and its target gene cytochrome P450 subfamily B member 1 (CYP1B1) were inhibited. However, IHC staining demonstrated that AhR was still involved in the subcutaneous ossification of cartilage templates. Then, the effects of FICZ on cartilage templates were investigated. The osteogenic markers were upregulated by FICZ administration. The RAW 264.7 treated by condition medium of FICZ-treated cartilage templates exhibited an anti-inflammatory phenotype. Finally, high-throughput sequencing was applied to analyze the differentially expressed genes (DEGs) in the FICZ-treated cartilage templates. The upregulation of cytochrome P450 subfamily A member 1 (CYP1A1) and sphingomyelin phosphodiesterase 3 (Smpd3) were verified by qPCR, which might be the downstream targets of AhR in the cartilage templates promoting osteogenesis and macrophage polarization. These data implied a beneficial role of FICZ in the regenerative potentials of both BMSCs and primed cartilage templates. The FICZ/AhR axis might be a practical target to achieve optimal bone regeneration.

The emerging roles and mechanisms of exosomal non-coding RNAs in the mutual regulation between adipose tissue and other related tissues in obesity and metabolic diseases

Exosomes (EXs) are the major types of extracellular vesicles (EVs) of 30-100 nm diameter that can be secreted by most cells to the extracellular environment. EXs transport endogenous cargoes (proteins, lipids, RNAs, etc.) to target cells and thereby triggers the release of these bioactive components, which then play important roles in regulating numerous biological processes under both physiological and pathological conditions. Throughout the studies in recent years, growing evidences have shown that EXs-derived non-coding RNAs (EXs-ncRNAs) are emerging as key players in cell-to-cell communication between adipose tissue and other related tissues in obesity and metabolic diseases. In this review, we will summarize the recent findings about EXs-ncRNAs, especially focus on the following aspects: 1) the biogenesis of EXs and emerging roles of EXs-ncRNAs, 2) the role of EXs-ncRNAs (EXs-miRNAs, EXs-lncRNAs, EXs-circRNAs, etc.) that were secreted by adipose-related tissues in promoting the differentiation of preadipocytes into mature and fully functional adipocytes, and 3) the crosstalk between the adipose tissue derived EXs-ncRNAs and the development of insulin resistance, obesity and various cancers. This review aims to reveal the emerging roles and mechanisms of EXs-ncRNAs in the mutual regulation of adipose tissue and its related tissues in obesity and metabolic diseases, so as to provide references for elucidating the etiology of obesity and related metabolic diseases and screening novel therapeutic targets.