Exosomes secreted by endothelial progenitor cells accelerate bone regeneration during distraction osteogenesis by stimulating angiogenesis

The Angiogenic Repertoire of Stem Cell Extracellular Vesicles: Demystifying the Molecular Underpinnings for Wound Healing Applications

Stem cells-derived extracellular vesicles (SC-EVs) have emerged as promising therapeutic agents for wound repair, recapitulating the biological effects of parent cells while mitigating immunogenic and tumorigenic risks. These EVs orchestrate wound healing processes, notably through modulating angiogenesis-a critical event in tissue revascularization and regeneration. This study provides a comprehensive overview of the multifaceted mechanisms underpinning the pro-angiogenic capacity of EVs from various stem cell sources within the wound microenvironment. By elucidating the molecular intricacies governing their angiogenic prowess, we aim to unravel the mechanistic repertoire underlying their remarkable potential to accelerate wound healing. Additionally, methods to enhance the angiogenic effects of SC-EVs, current limitations, and future perspectives are highlighted, emphasizing the significant potential of this rapidly advancing field in revolutionizing wound healing strategies.

Global scientific trends on exosomes therapy for osteoporosis from 2004 to 2023: A bibliometric and visualized analysis

BACKGROUND

Exosomes have emerged as pivotal mediators in modulating physiological and pathological processes implicated in osteoporosis (OP) through their distinctive mode of intracellular communication. The use of exosomes has evoked considerable interest, catalyzing a surge in research endeavors on a global scale. This study endeavors to scrutinize contemporary landscapes and burgeoning trends in this realm.

METHODS

The Web of Science Core Collection was used to retrieve publications on exosomes therapy for OP within the time frame of January 1, 2004 to December 31, 2023. The bibliometric methodology was applied to study and index the collected data. VOSviewer and citespace software were used to conduct visualization, co-authorship, co-occurrence, and publication trend analyses of exosome therapy in OP.

RESULTS

A total of 610 publications (443 articles and 167 reviews) from 51 countries and 911 institutions were included in this study. Shanghai Jiao Tong University, Central South University, Sichuan University, and Zhejiang University are leading research institutions in this field. Stem Cell Research Therapy published the highest number of articles and has emerged as the most cited journal. Of the 4077 scholars who participated in the study, Xie, Hui, Zhang, Yan, Tan, and Yi-Juan had the largest number of articles. Furthermore, according to the cluster analysis of external keywords, future research hotspots can be categorized into 3 directions: research status of exosomes for the treatment of OP, treatment of OP through exosome-regulated signaling pathways, and exosomes as targeted drug delivery systems.

CONCLUSION

This study suggests that the number of future publications on exosome therapy for OP will increase, with a focus on fundamental investigations into drug-loading capacities and molecular mechanisms. In summary, this study presents the first systematic bibliometric analysis of exosome therapy publications in OP, providing an objective and comprehensive overview of the field and a valuable reference for researchers in this domain.

Endothelial progenitor cell-derived extracellular vesicles: the world of potential prospects for the treatment of cardiovascular diseases

Cardiovascular diseases (CVDs) have emerged as a predominant threat to human health, surpassing the incidence and mortality rates of neoplastic diseases. Extracellular vesicles (EVs) serve as vital mediators in intercellular communication and material exchange. Endothelial progenitor cells (EPCs), recognized as precursors of vascular endothelial cells (ECs), have garnered considerable attention in recent years due to the potential therapeutic value of their derived extracellular vesicles (EPC-EVs) in the context of CVDs. This comprehensive review systematically explores the origins, characteristics, and functions of EPCs, alongside the classification, properties, biogenesis, and extraction techniques of EVs, with particular emphasis on their protective roles in CVDs. Additionally, we delve into the essential bioactive components of EPC-EVs, including microRNAs, long non-coding RNAs, and proteins, analyzing their beneficial effects in promoting angiogenesis, anti-inflammatory and anti-oxidant activities, anti-fibrosis, anti-apoptosis, and myocardial regeneration. Furthermore, this review comprehensively investigates the therapeutic potential of EPC-EVs across various CVDs, encompassing acute myocardial infarction, myocardial ischemia-reperfusion injury, atherosclerosis, non-ischemic cardiomyopathies, and diabetic cardiovascular disease. Lastly, we summarize the potential challenges associated with the clinical application of EPC-EVs and outline future directions, aiming to offer a valuable resource for both theoretical insights and practical applications of EPC-EVs in managing CVDs.

Extracellular vesicles in nanomedicine and regenerative medicine: A review over the last decade

Small extracellular vesicles (sEVs) are known to be secreted by a vast majority of cells. These sEVs, specifically exosomes, induce specific cell-to-cell interactions and can activate signaling pathways in recipient cells through fusion or interaction. These nanovesicles possess several desirable properties, making them ideal for regenerative medicine and nanomedicine applications. These properties include exceptional stability, biocompatibility, wide biodistribution, and minimal immunogenicity. However, the practical utilization of sEVs, particularly in clinical settings and at a large scale, is hindered by the expensive procedures required for their isolation, limited circulation lifetime, and suboptimal targeting capacity. Despite these challenges, sEVs have demonstrated a remarkable ability to accommodate various cargoes and have found extensive applications in the biomedical sciences. To overcome the limitations of sEVs and broaden their potential applications, researchers should strive to deepen their understanding of current isolation, loading, and characterization techniques. Additionally, acquiring fundamental knowledge about sEVs origins and employing state-of-the-art methodologies in nanomedicine and regenerative medicine can expand the sEVs research scope. This review provides a comprehensive overview of state-of-the-art exosome-based strategies in diverse nanomedicine domains, encompassing cancer therapy, immunotherapy, and biomarker applications. Furthermore, we emphasize the immense potential of exosomes in regenerative medicine.

Proteomic Analysis of Umbilical Cord Mesenchymal Stem Cell-Derived Extracellular Vesicles: A Systematic Review

Numerous challenges remain within conventional cell-based therapy despite the growing trend of stem cells used to treat various life-debilitating diseases. These limitations include batch-to-batch heterogeneity, induced alloreactivity, cell survival and integration, poor scalability, and high cost of treatment, thus hindering successful translation from lab to bedside. However, recent pioneering technology has enabled the isolation and enrichment of small extracellular vesicles (EVs), canonically known as exosomes. EVs are described as a membrane-enclosed cargo of functional biomolecules not limited to lipids, nucleic acid, and proteins. Interestingly, studies have correlated the biological role of MSC-EVs to the paracrine activity of MSCs. This key evidence has led to rigorous studies on MSC-EVs as an acellular alternative. Using EVs as a therapy was proposed as a model leading to improvements through increased safety; enhanced bioavailability due to size and permeability; reduced heterogeneity by selective and quantifiable properties; and prolonged shelf-life via long-term freezing or lyophilization. Yet, the identity and potency of EVs are still relatively unknown due to various methods of preparation and to qualify the final product. This is reflected by the absence of regulatory strategies overseeing manufacturing, quality control, clinical implementation, and product registration. In this review, the authors review the various production processes and the proteomic profile of MSC-EVs.

Advancing Tissue Damage Repair in Geriatric Diseases: Prospects of Combining Stem Cell-Derived Exosomes with Hydrogels

Geriatric diseases are a group of diseases with unique characteristics related to senility. With the rising trend of global aging, senile diseases now mainly include endocrine, cardiovascular, neurodegenerative, skeletal, and muscular diseases and cancer. Compared with younger populations, the structure and function of various cells, tissues and organs in the body of the elderly undergo a decline as they age, rendering them more susceptible to external factors and diseases, leading to serious tissue damage. Tissue damage presents a significant obstacle to the overall health and well-being of older adults, exerting a profound impact on their quality of life. Moreover, this phenomenon places an immense burden on families, society, and the healthcare system.In recent years, stem cell-derived exosomes have become a hot topic in tissue repair research. The combination of these exosomes with biomaterials allows for the preservation of their biological activity, leading to a significant improvement in their therapeutic efficacy. Among the numerous biomaterial options available, hydrogels stand out as promising candidates for loading exosomes, owing to their exceptional properties. Due to the lack of a comprehensive review on the subject matter, this review comprehensively summarizes the application and progress of combining stem cell-derived exosomes and hydrogels in promoting tissue damage repair in geriatric diseases. In addition, the challenges encountered in the field and potential prospects are presented for future advancements.

Mesenchymal Stem Cell-Derived Extracellular Vesicles in Bone-Related Diseases: Intercellular Communication Messengers and Therapeutic Engineering Protagonists

Extracellular vesicles (EVs) can deliver various bioactive molecules among cells, making them promising diagnostic and therapeutic alternatives in diseases. Mesenchymal stem cell-derived EVs (MSC-EVs) have shown therapeutic potential similar to MSCs but with drawbacks such as lower yield, reduced biological activities, off-target effects, and shorter half-lives. Improving strategies utilizing biotechniques to pretreat MSCs and enhance the properties of released EVs, as well as modifying MSC-EVs to enhance targeting abilities and achieve controlled release, shows potential for overcoming application limitations and enhancing therapeutic effects in treating bone-related diseases. This review focuses on recent advances in functionalizing MSC-EVs to treat bone-related diseases. Firstly, we underscore the significance of MSC-EVs in facilitating crosstalk between cells within the skeletal environment. Secondly, we highlight strategies of functional-modified EVs for treating bone-related diseases. We explore the pretreatment of stem cells using various biotechniques to enhance the properties of resulting EVs, as well as diverse approaches to modify MSC-EVs for targeted delivery and controlled release. Finally, we address the challenges and opportunities for further research on MSC-EVs in bone-related diseases.

Tibial cortex transverse transport promotes ischemic diabetic foot ulcer healing via enhanced angiogenesis and inflammation modulation in a novel rat model

BACKGROUND

Tibial Cortex Transverse Transport (TTT) represents an innovative surgical method for treating lower extremity diabetic foot ulcers (DFUs), yet its underlying mechanisms remain elusive. Establishing an animal model that closely mirrors clinical scenarios is both critical and novel for elucidating the mechanisms of TTT.

METHODS

We established a diabetic rat model with induced hindlimb ischemia to mimic the clinical manifestation of DFUs. TTT was applied using an external fixator for regulated bone movement. Treatment efficacy was evaluated through wound healing assessments, histological analyses, and immunohistochemical techniques to elucidate biological processes.

RESULTS

The TTT group demonstrated expedited wound healing, improved skin tissue regeneration, and diminished inflammation relative to controls. Marked neovascularization and upregulation of angiogenic factors were observed, with the HIF-1α/SDF-1/CXCR4 pathway and an increase in EPCs being pivotal in these processes. A transition toward anti-inflammatory M2 macrophages indicated TTT's immunomodulatory capacity.

CONCLUSION

Our innovative rat model effectively demonstrates the therapeutic potential of TTT in treating DFUs. We identified TTT's roles in promoting angiogenesis and modulating the immune system. This paves the way for further in-depth research and potential clinical applications to improve DFU management strategies.

The Exosome-Mediated Bone Regeneration: An Advanced Horizon Toward the Isolation, Engineering, Carrying Modalities, and Mechanisms

Exosomes, nanoparticles secreted by various cells, composed of a bilayer lipid membrane, and containing bioactive substances such as proteins, nucleic acids, metabolites, etc., have been intensively investigated in tissue engineering owing to their high biocompatibility and versatile biofunction. However, there is still a lack of a high-quality review on bone defect regeneration potentiated by exosomes. In this review, the biogenesis and isolation methods of exosomes are first introduced. More importantly, the engineered exosomes of the current state of knowledge are discussed intensively in this review. Afterward, the biomaterial carriers of exosomes and the mechanisms of bone repair elucidated by compelling evidence are presented. Thus, future perspectives and concerns are revealed to help devise advanced modalities based on exosomes to overcome the challenges of bone regeneration. It is totally believed this review will attract special attention from clinicians and provide promising ideas for their future works.

Non-bone-derived exosomes: a new perspective on regulators of bone homeostasis

Accumulating evidence indicates that exosomes help to regulate bone homeostasis. The roles of bone-derived exosomes have been well-described; however, recent studies have shown that some non-bone-derived exosomes have better bone targeting ability than bone-derived exosomes and that their performance as a drug delivery vehicle for regulating bone homeostasis may be better than that of bone-derived exosomes, and the sources of non-bone-derived exosomes are more extensive and can thus be better for clinical needs. Here, we sort non-bone-derived exosomes and describe their composition and biogenesis. Their roles and specific mechanisms in bone homeostasis and bone-related diseases are also discussed. Furthermore, we reveal obstacles to current research and future challenges in the practical application of exosomes, and we provide potential strategies for more effective application of exosomes for the regulation of bone homeostasis and the treatment of bone-related diseases. Video Abstract.

Clinical applications of stem cell-derived exosomes

Although stem cell-based therapy has demonstrated considerable potential to manage certain diseases more successfully than conventional surgery, it nevertheless comes with inescapable drawbacks that might limit its clinical translation. Compared to stem cells, stem cell-derived exosomes possess numerous advantages, such as non-immunogenicity, non-infusion toxicity, easy access, effortless preservation, and freedom from tumorigenic potential and ethical issues. Exosomes can inherit similar therapeutic effects from their parental cells such as embryonic stem cells and adult stem cells through vertical delivery of their pluripotency or multipotency. After a thorough search and meticulous dissection of relevant literature from the last five years, we present this comprehensive, up-to-date, specialty-specific and disease-oriented review to highlight the surgical application and potential of stem cell-derived exosomes. Exosomes derived from stem cells (e.g., embryonic, induced pluripotent, hematopoietic, mesenchymal, neural, and endothelial stem cells) are capable of treating numerous diseases encountered in orthopedic surgery, neurosurgery, plastic surgery, general surgery, cardiothoracic surgery, urology, head and neck surgery, ophthalmology, and obstetrics and gynecology. The diverse therapeutic effects of stem cells-derived exosomes are a hierarchical translation through tissue-specific responses, and cell-specific molecular signaling pathways. In this review, we highlight stem cell-derived exosomes as a viable and potent alternative to stem cell-based therapy in managing various surgical conditions. We recommend that future research combines wisdoms from surgeons, nanomedicine practitioners, and stem cell researchers in this relevant and intriguing research area.

Enhanced Bone Regeneration through Regulation of Mechanoresponsive FAK-ERK1/2 Signaling by ZINC40099027 during Distraction Osteogenesis

Background: Focal adhesion kinase (FAK) is activated by mechanical stimulation and plays a vital role in distraction osteogenesis (DO), a well-established but lengthy procedure for repairing large bone defects. Both angiogenesis and osteogenesis contribute to bone regeneration during DO. However, the effects of ZINC40099027 (ZN27), a potent FAK activator, on angiogenesis, osteogenesis, and bone regeneration in DO remain unknown. Methods: The angiogenic potential of human umbilical vein endothelial cells (HUVECs) was evaluated using transwell migration and tube formation assays. The osteogenic activity of bone marrow mesenchymal stem cells (BMSCs) was assessed using alkaline phosphatase (ALP) and alizarin red s (ARS) staining. Additionally, quantitative real-time polymerase chain reaction (qRT-PCR), western blot, and immunofluorescence staining were used to assay angiogenic markers, osteogenic markers, and FAK-extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. In vivo, a rat tibia DO model was established to verify the effects of ZN27 on neovascularization and bone regeneration using radiological and histological analyses. Results: ZN27 promoted the migration and angiogenesis of HUVECs. Additionally, ZN27 facilitated the osteogenic differentiation of BMSCs, as revealed by increased ALP activity, calcium deposition, and expression of osteogenesis-specific markers. The ERK1/2-specific inhibitor PD98059 significantly hindered the effects of ZN27, suggesting the participation of FAK-ERK1/2 signaling in ZN27-enhanced angiogenesis and osteogenesis. As indicated by improved radiological and histological features, ZN27 induced active angiogenesis within the distraction area and accelerated bone regeneration in a rat DO model. Conclusion: Our results show that ZN27 targets FAK-ERK1/2 signaling to stimulate both angiogenesis and osteogenesis, and ZN27 accelerates bone regeneration in DO, suggesting the therapeutic potential of ZN27 for repairing large bone defects in the mechanobiological environment during DO.

Micellized protein transduction domain-bone morphogenetic protein-2 accelerates bone healing in a rat tibial distraction osteogenesis model

The clinical application of growth factors such as recombinant human bone morphogenetic protein-2 (rh-BMP-2), for functional bone regeneration remains challenging due to limited in vivo efficacy and adverse effects of previous modalities. To overcome the instability and short half-life of rh-BMP-2 in vivo, we developed a novel osteogenic supplement by fusing a protein transduction domain (PTD) with BMP-2, effectively creating a prodrug of BMP-2. In this study, we first created an improved PTD-BMP-2 formulation using lipid nanoparticle (LNP) micellization, resulting in downsizing from micrometer to nanometer scale and achieving a more even distribution. The micellized PTD-BMP-2 (mPTD-BMP-2) demonstrated improved distribution and aggregation profiles. As a prodrug of BMP-2, mPTD-BMP-2 successfully activated Smad1/5/8 and induced mineralization with osteogenic gene induction in vitro. In vivo pharmacokinetic analysis revealed that mPTD-BMP-2 had a much more stable pharmacokinetic profile than rh-BMP-2, with a 7.5-fold longer half-life. The in vivo BMP-responsive element (BRE) reporter system was also successfully activated by mPTD-BMP-2. In the in vivo rat tibia distraction osteogenesis (DO) model, micro-computed tomography (micro-CT) scan findings indicated that mPTD-BMP-2 significantly increased bone volume, bone surface, axis moment of inertia (MOI), and polar MOI. Furthermore, it increased the expression of osteogenesis-related genes, and induced bone maturation histologically. Based on these findings, mPTD-BMP-2 could be a promising candidate for the next-generation osteogenesis drug to promote new bone formation in DO surgery. STATEMENT OF SIGNIFICANCE: This study introduces micellized bone morphogenetic protein-2 (mPTD-BMP-2), a next-generation osteogenic supplement that combines protein transduction domain (PTD) and nano-sized micelle formulation technique to improve transduction efficiency and stability. The use of PTD represents a novel approach, and our results demonstrate the superiority of mPTD-BMP-2 over rh-BMP-2 in terms of in vivo pharmacokinetic profile and osteogenic potential, particularly in a rat tibial model of distraction osteogenesis. These findings have significant scientific impact and potential clinical applications in the treatment of bone defects that require distraction osteogenesis. By advancing the field of osteogenic supplements, our study has the potential to contribute to the development of more effective treatments for musculoskeletal disorders.

MiRNAs regulate cell communication in osteogenesis-angiogenesis coupling during bone regeneration

Bone regeneration is a complex process that requires not only the participation of multiple cell types, but also signal communication between cells. The two basic processes of osteogenesis and angiogenesis are closely related to bone regeneration and bone homeostasis. H-type vessels are a subtype of bone vessels characterized by high expression of CD31 and EMCN. These vessels play a key role in the regulation of bone regeneration and are important mediators of coupling between osteogenesis and angiogenesis. Molecular regulation between different cell types is important for coordination of osteogenesis and angiogenesis that promotes bone regeneration. MiRNAs are small non-coding RNAs that predominantly regulate gene expression at the post-transcriptional level and are closely related to cell communication. Specifically, miRNAs transduce external stimuli through various cell signaling pathways and cause a series of physiological and pathological effects. They are also deeply involved in the bone repair process. This review focuses on three signaling pathways related to osteogenesis-angiogenesis coupling, as well as the miRNAs involved in these pathways. Elucidation of the molecular mechanisms governing osteogenesis and angiogenesis is of great significance for bone regeneration.

Novel scaffold platforms for simultaneous induction osteogenesis and angiogenesis in bone tissue engineering: a cutting-edge approach

Despite the recent advances in the development of bone graft substitutes, treatment of critical size bone defects continues to be a significant challenge, especially in the elderly population. A current approach to overcome this challenge involves the creation of bone-mimicking scaffolds that can simultaneously promote osteogenesis and angiogenesis. In this context, incorporating multiple bioactive agents like growth factors, genes, and small molecules into these scaffolds has emerged as a promising strategy. To incorporate such agents, researchers have developed scaffolds incorporating nanoparticles, including nanoparticulate carriers, inorganic nanoparticles, and exosomes. Current paper provides a summary of the latest advancements in using various bioactive agents, drugs, and cells to synergistically promote osteogenesis and angiogenesis in bone-mimetic scaffolds. It also discusses scaffold design properties aimed at maximizing the synergistic effects of osteogenesis and angiogenesis, various innovative fabrication strategies, and ongoing clinical studies.

The accordion technique enhances bone regeneration via angiogenesis factor in a rat distraction osteogenesis model

Objective: The purpose of this study was to observe the effect of the accordion technique (AT) during the distraction phase on chondrogenesis and bone regeneration in a rat femoral distraction osteogenesis (DO) model, and investigate its potential mechanism for reducing the total treatment time of DO. Methods: Fifty-four male Sprague-Dawley (SD) rats that were specific-pathogen-free (SPF) were subjected to DO surgery on the right femur. The distraction rate was 0.5 mm/day for 10 days, following a latency period of 5 days. Rats were randomly divided into Control (no AT, n = 18), Group LA (low amplitude with AT, n = 18), and Group HA (high amplitude with AT, n = 18) according to different AT protocols in the distraction phase. Rats were respectively euthanized by anesthesia overdose at 2, 4 and 6 weeks of the consolidation phase, and the femurs were harvested. Digital radiography, micro-computed tomography (micro-CT), biomechanical tests, and histomorphological analysis were used to assess the quality of regenerated bone in the distraction area. Results: Digital radiographic, micro-CT, biomechanical tests, and histological analysis revealed an increase in early-stage callus formation (p < 0.05) and improved blood supply to the callus tissue in Group LA, as compared to both the Control and Group HA. The enhanced differentiation of fibrous and cartilaginous tissue into bone tissue was also observed in Group LA, leading to improved strength and stiffness (p < 0.05) of the regenerated bone at 6 weeks of the consolidation phase. The angiogenic (hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF), p < 0.05) and osteogenic (runt-related transcription factor 2 (RUNX2), osteocalcin (OCN) and osteopontin (OPN), p < 0.05) biomarkers were higher expressed in Group LA at 2 and 4 weeks of consolidation phase, whereas decreased at 6 weeks of consolidation phase. Conclusion: The application of AT with low amplitude during the distraction phase can enhance chondrogenesis and bone regeneration by activating the angiogenesis factor pathway and upregulating the expression of osteogenic-related biomarkers such as HIF-1α, VEGF, RUNX2, OCN, and OPN.

Extracellular vesicles: From bone development to regenerative orthopedics

Regenerative medicine aims to promote the replacement of tissues lost to damage or disease. While positive outcomes have been observed experimentally, challenges remain in their clinical translation. This has led to growing interest in applying extracellular vesicles (EVs) to augment or even replace existing approaches. Through the engineering of culture environments or direct/indirect manipulation of EVs themselves, multiple avenues have emerged to modulate EV production, targeting, and therapeutic potency. Drives to modulate release using material systems or functionalize implants for improved osseointegration have also led to outcomes that could have real-world impact. The purpose of this review is to highlight advantages in applying EVs for the treatment of skeletal defects, outlining the current state of the art in the field and emphasizing avenues for further investigation. Notably, the review identifies inconsistencies in EV nomenclature and outstanding challenges in defining a reproducible therapeutic dose. Challenges also remain in the scalable manufacture of a therapeutically potent and pure EV product, with a need to address scalable cell sources and optimal culture environments. Addressing these issues will be critical if we are to develop regenerative EV therapies that meet the demands of regulators and can be translated from bench to bedside.

Endocrine modulation of brain-skeleton axis driven by neural stem cell-derived perilipin 5 in the lipid metabolism homeostasis for bone regeneration

Factors released from the nervous system always play crucial roles in modulating bone metabolism and regeneration. How the brain-driven endocrine axes maintain bone homeostasis, especially under metabolic disorders, remains obscure. Here, we found that neural stem cells (NSCs) residing in the subventricular zone participated in lipid metabolism homeostasis of regenerative bone through exosomal perilipin 5 (PLIN5). Fluorescence-labeled exosomes tracing and histological detection identified that NSC-derived exosomes (NSC-Exo) could travel from the lateral ventricle into bone injury sites. Homocysteine (Hcy) led to osteogenic and angiogenic impairment, whereas the NSC-Exo were confirmed to restore it. Mecobalamin, a clinically used neurotrophic drug, further enhanced the protective effects of NSC-Exo through increased PLIN5 expression. Mechanistically, NSC-derived PLIN5 reversed excessive Hcy-induced lipid metabolic imbalance and aberrant lipid droplet accumulation through lipophagy-dependent intracellular lipolysis. Intracerebroventricular administration of mecobalamin and/or AAV-shPlin5 confirmed the effects of PLIN5-driven endocrine modulations on new bone formation and vascular reconstruction in hyperhomocysteinemic and high-fat diet models. This study uncovered a novel brain-skeleton axis that NSCs in the mammalian brain modulated bone regeneration through PLIN5-driven lipid metabolism modulation, providing evidence for lipid- or bone-targeted medicine development.

Molecular events in the jaw vascular unit: A traditional review of the mechanisms involved in inflammatory jaw bone diseases

Inflammatory jaw bone diseases are common in stomatology, including periodontitis, peri-implantitis, medication-related osteonecrosis of the jaw, radiation osteomyelitis of the jaw, age-related osteoporosis, and other specific infections. These diseases may lead to tooth loss and maxillofacial deformities, severely affecting patients' quality of life. Over the years, the reconstruction of jaw bone deficiency caused by inflammatory diseases has emerged as a medical and socioeconomic challenge. Therefore, exploring the pathogenesis of inflammatory diseases associated with jaw bones is crucial for improving prognosis and developing new targeted therapies. Accumulating evidence indicates that the integrated bone formation and dysfunction arise from complex interactions among a network of multiple cell types, including osteoblast-associated cells, immune cells, blood vessels, and lymphatic vessels. However, the role of these different cells in the inflammatory process and the 'rules' with which they interact are still not fully understood. Although many investigations have focused on specific pathological processes and molecular events in inflammatory jaw diseases, few articles offer a perspective of integration. Here, we review the changes and mechanisms of various cell types in inflammatory jaw diseases, with the hope of providing insights to drive future research in this field.

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.

Stem cell-derived exosomes in bone healing: focusing on their role in angiogenesis

Fractures in bone, a tissue critical in protecting other organs, affect patients' quality of life and have a heavy economic burden on societies. Based on regenerative medicine and bone tissue engineering approaches, stem cells have become a promising and attractive strategy for repairing bone fractures via differentiation into bone-forming cells and production of favorable mediators. Recent evidence suggests that stem cell-derived exosomes could mediate the therapeutic effects of their counterpart cells and provide a cell-free therapeutic strategy in bone repair. Since bone is a highly vascularized tissue, coupling angiogenesis and osteogenesis is critical in bone fracture healing; thus, developing therapeutic strategies to promote angiogenesis will facilitate bone regeneration and healing. To this end, stem cell-derived exosomes with angiogenic potency have been developed to improve fracture healing. This review summarizes the effects of stem cell-derived exosomes on the repair of bone tissue, focusing on the angiogenesis process.

Biomimetic synthesis and optimization of extracellular vesicles for bone regeneration

Critical-size bone defect repair is in high demand but is difficult to treat. Modern therapies, such as autograft and cell-based treatments, face limitations, including potential immunological rejection and tumorigenesis. Therefore, extracellular vesicle (EV)-based strategies have been proposed as a novel approach for tissue regeneration owing to EVs' complex composition of lipids, proteins, and nucleic acids, as well as their low immunogenicity and congenital cell-targeting features. Despite these remarkable features of EVs, biomimetic synthesis and optimization of natural EVs can lead to enhanced bioactivity, increased cellular uptake, and specific cell targeting, aiming to achieve optimal therapeutic efficacy. To maximize their function, these nanoparticles can be integrated into bone graft biomaterials for superior bone regeneration. Herein, we summarize the role of naturally occurring EVs from distinct cell types in bone regeneration, the current strategies for optimizing biomimetic synthetic EVs in bone regeneration, and discuss the recent advances in applying bone graft biomaterials for the delivery of EVs to bone defect repair. We focused on distinct strategies for optimizing EVs with different functions and the most recent research on achieving time-controlled release of nanoparticles from EV-loaded biomaterials. Furthermore, we thoroughly discuss several current challenges and proposed solutions, aiming to provide insight into current progress, inspiration for future development directions, and incentives for clinical application in this field.

Exosomes for angiogenesis induction in ischemic disorders

Ischaemic disorders are leading causes of morbidity and mortality worldwide. While the current therapeutic approaches have improved life expectancy and quality of life, they are unable to "cure" ischemic diseases and instate regeneration of damaged tissues. Exosomes are a class of extracellular vesicles with an average size of 100-150 nm, secreted by many cell types and considered a potent factor of cells for paracrine effects. Since exosomes contain multiple bioactive components such as growth factors, molecular intermediates of different intracellular pathways, microRNAs and nucleic acids, they are considered as cell-free therapeutics. Besides, exosomes do not rise cell therapy concerns such as teratoma formation, alloreactivity and thrombotic events. In addition, exosomes are stored and utilized more convenient. Interestingly, exosomes could be an ideal complementary therapeutic tool for ischemic disorders. In this review, we discussed therapeutic functions of exosomes in ischemic disorders including angiogenesis induction through various mechanisms with specific attention to vascular endothelial growth factor pathway. Furthermore, different delivery routes of exosomes and different modification strategies including cell preconditioning, gene modification and bioconjugation, were highlighted. Finally, pre-clinical and clinical investigations in which exosomes were used were discussed.

Functional Approaches in Promoting Vascularization and Angiogenesis in Bone Critical-Sized Defects via Delivery of Cells, Growth Factors, Drugs, and Particles

Critical-sized bone defects, or CSDs, are defined as bone defects that cannot be regenerated by themselves and require surgical intervention via employing specific biomaterials and a certain regenerative strategy. Although a variety of approaches can be used to treat CSDs, poor angiogenesis and vascularization remain an obstacle in these methods. The complex biological healing of bone defects depends directly on the function of blood flow to provide sufficient oxygen and nutrients and the removal of waste products from the defect site. The absence of vascularization can lead to non-union and delayed-union defect development. To overcome this challenge, angiogenic agents can be delivered to the site of injury to stimulate vessel formation. This review begins by introducing the treatment methods for CSDs. The importance of vascularization in CSDs is subsequently highlighted. Delivering angiogenesis agents, including relevant growth factors, cells, drugs, particles, cell secretion substances, their combination, and co-delivery to CSDs are fully explored. Moreover, the effects of such agents on new bone formation, followed by vessel formation in defect areas, are evaluated.

Modification of adipose mesenchymal stem cells-derived small extracellular vesicles with fibrin-targeting peptide CREKA for enhanced bone repair

The process of bone repair is highly regulated by a large number of bioactive factors. Thus, a “cocktail” of bioactive factors supplemented to the defect sites is desirable for bone repair. In this regard, small extracellular vesicles (sEVs) derived from mesenchymal stem cells hold great potential in tissue repair. Nevertheless, the poor homing and retention of sEVs greatly limited their possible clinical application. In the present work, DMPE-PEG-CREKA was inserted into the membrane of sEVs released from adipose-derived mesenchymal stem cells to obtain CREKA functionalized sEVs (CREKA-sEVs), which could target fibrin to accumulate and retain in bone defects. Our results showed that CREKA-sEVs, like sEVs, promoted the osteogenic differentiation of BMSCs, the angiogenic property of HUVECs, and modulated the polarization of macrophages in vitro. Furthermore, due to the improved fibrin-binding and retention capacity of CREKA-sEVs, they enhanced the bone repair substantially in the rat femoral defect model. This study provided a new strategy to improve the therapeutic efficiency of sEVs and showed that CREKA-sEVs had great application value in bone tissue repair.

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The poor homing and retention capacity greatly limited the possible clinical application of sEVs derived from MSCs.

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CREKA modification enabled sEVs to bind fibrin effectively and promoted their accumulation and retention in bone defects.

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CREKA-sEVs enhanced bone repair substantially in the rat femoral defect model.

Exercise-induced skeletal muscle angiogenesis: impact of age, sex, angiocrines and cellular mediators

Exercise-induced skeletal muscle angiogenesis is a well-known physiological adaptation that occurs in humans in response to exercise training and can lead to endurance performance benefits, as well as improvements in cardiovascular and skeletal tissue health. An increase in capillary density in skeletal muscle improves diffusive oxygen exchange and waste extraction, and thus greater fatigue resistance, which has application to athletes but also to the general population. Exercise-induced angiogenesis can significantly contribute to improvements in cardiovascular and metabolic health, such as the increase in muscle glucose uptake, important for the prevention of diabetes. Recently, our understanding of the mechanisms by which angiogenesis occurs with exercise has grown substantially. This review will detail the biochemical, cellular and biomechanical signals for exercise-induced skeletal muscle angiogenesis, including recent work on extracellular vesicles and circulating angiogenic cells. In addition, the influence of age, sex, exercise intensity/duration, as well as recent observations with the use of blood flow restricted exercise, will also be discussed in detail. This review will provide academics and practitioners with mechanistic and applied evidence for optimising training interventions to promote physical performance through manipulating capillarisation in skeletal muscle.

The potential therapeutic role of extracellular vesicles in critical-size bone defects: Spring of cell-free regenerative medicine is coming

In recent years, the incidence of critical-size bone defects has significantly increased. Critical-size bone defects seriously affect patients' motor functions and quality of life and increase the need for additional clinical treatments. Bone tissue engineering (BTE) has made great progress in repairing critical-size bone defects. As one of the main components of bone tissue engineering, stem cell-based therapy is considered a potential effective strategy to regenerate bone tissues. However, there are some disadvantages including phenotypic changes, immune rejection, potential tumorigenicity, low homing efficiency and cell survival rate that restrict its wider clinical applications. Evidence has shown that the positive biological effects of stem cells on tissue repair are largely mediated through paracrine action by nanostructured extracellular vesicles (EVs), which may overcome the limitations of traditional stem cell-based treatments. In addition to stem cell-derived extracellular vesicles, the potential therapeutic roles of nonstem cell-derived extracellular vesicles in critical-size bone defect repair have also attracted attention from scholars in recent years. Currently, the development of extracellular vesicles-mediated cell-free regenerative medicine is still in the preliminary stage, and the specific mechanisms remain elusive. Herein, the authors first review the research progress and possible mechanisms of extracellular vesicles combined with bone tissue engineering scaffolds to promote bone regeneration via bioactive molecules. Engineering modified extracellular vesicles is an emerging component of bone tissue engineering and its main progression and clinical applications will be discussed. Finally, future perspectives and challenges of developing extracellular vesicle-based regenerative medicine will be given. This review may provide a theoretical basis for the future development of extracellular vesicle-based biomedicine and provide clinical references for promoting the repair of critical-size bone defects.

Periosteum-inspired in situ CaP generated nanocomposite hydrogels with strong bone adhesion and superior stretchability for accelerated distraction osteogenesis

BACKGROUND

Distraction osteogenesis (DO) is an efficacious but lengthy procedure to reconstruct segmental bone defects under the principle of tension-stress, during which the periosteum-mediated mechanical stimulation plays a pivotal role. Inspired by the dynamic process of DO and the mechanical stimulation of periosteum, a new design of bionic periosteum was developed to simulate the mechanical transduction of natural periosteum for the application in DO procedure.

METHODS

In this study, an injectable organic-inorganic hybrid hydrogel was developed based on a novel combination of the PEGylated poly (glycerol sebacate) (PEGS) polymer network and in situ formed CaP nanoparticles (ICPNs). Rat bone marrow mesenchymal stem cells (rBMSCs) and human umbilical vein endothelial cells (HUVECs) were cultured and tested in vitro to evaluate biocompatibility, cell adhesion, proliferation, and pro-osteogenic and pro-angiogenic activity. In vivo experiments were conducted in the rat tibial model of distraction osteogenesis.

RESULTS

The developed nanocomposite hydrogels exhibited excellent injectability, robust bone adhesion, superior stretchability, and enhanced osteogenic activity. The results of in vitro and in vivo studies showed that PEGS/ICPN hydrogels could promote new bone formation and mineralization during the dynamic distraction process through the synergistic effects of angiogenesis and osteogenesis.

CONCLUSIONS

This periosteum-inspired nanocomposite hydrogel represents a mechanobiology approach for effectively restoring large bone defects through the dynamic DO process.

Endothelial progenitor cell-derived small extracellular vesicles for myocardial angiogenesis and revascularization

BACKGROUND

Endothelial progenitor cells (EPCs) have been well-studied for their differentiation potential and paracrine activity in vitro and in experimental animal studies. EPCs are the precursors of endothelial cells (ECs) and a rich source of pro-angiogenic factors, and hence, possess enormous potential to treat ischemic heart through myocardial angiogenesis. Their proven safety and efficacy observed during the pre-clinical and clinical studies have portrayed them as a near ideal cell type for cell-based therapy of ischemic heart disease.In response to the chemical cues from the ischemic heart, EPCs from the bone marrow and peripheral circulation home-in to the ischemic myocardium and participate in the intrinsic repair process at the molecular and cellular levels through paracrine activity and EC differentiation. EPCs also release small extracellular vesicles (sEVs) loaded with bioactive molecules as part of their paracrine activity for intercellular communication to participate in the reparative process in the heart.

AIM

This literature review is based on the published data regarding the characteristic features of EPC-derived sEVs and their proteomic and genomic payload, besides facilitating safe and effective repair of the ischemic myocardium. In light of the encouraging published data, translational and clinical assessment of EPC-derived sEVs is warranted. We report the recent experimental animal studies and their findings using EPC-derived sEVs on cardiac angiogenesis and preservation of cardiac function.

RELEVANCE FOR PATIENTS

With the promising results from pre-clinical studies, clinical trials should be conducted to assess the clinical utility of EPC-derived sEVs in the treatment of the ischemic myocardium.

Engineering exosomes for bone defect repair

Currently, bone defect repair is still an intractable clinical problem. Numerous treatments have been performed, but their clinical results are unsatisfactory. As a key element of cell-free therapy, exosome is becoming a promising tool of bone regeneration in recent decades, because of its promoting osteogenesis and osteogenic differentiation function in vivo and in vitro. However, low yield, weak activity, inefficient targeting ability, and unpredictable side effects of natural exosomes have limited the clinical application. To overcome the weakness, various approaches have been applied to produce engineering exosomes by regulating their production and function at present. In this review, we will focus on the engineering exosomes for bone defect repair. By summarizing the exosomal cargos affecting osteogenesis, the strategies of engineering exosomes and properties of exosome-integrated biomaterials, this work will provide novel insights into exploring advanced engineering exosome-based cell-free therapy for bone defect repair.

Hsp20 Promotes Endothelial Progenitor Cell Angiogenesis via Activation of PI3K/Akt Signaling Pathway under Hypoxia

BACKGROUND

Mandibular distraction osteogenesis (MDO) is a kind of endogenous tissue engineering technology that lengthens the jaw and opens airway so that a patient can breathe safely and comfortably on his or her own. Endothelial progenitor cells (EPCs) are crucial for MDO-related angiogenesis. Moreover, emerging evidence suggests that heat shock protein 20 (Hsp20) modulates angiogenesis under hypoxic conditions. However, the specific role of Hsp20 in EPCs, in the context of MDO, is not yet known. The aim of this study was to explore the expression of Hsp20 during MDO and the effects of Hsp20 on EPCs under hypoxia.

METHODS

Mandibular distraction osteogenesis and mandibular bone defect (MBD) canine model were established. The expression of CD34, CD133, HIF-1α, and Hsp20 in callus was detected by immunofluorescence on day 14 after surgery. Canine bone marrow EPCs were cultured, with or without optimal cobalt chloride (CoCl2) concentration. Hypoxic effects, caused by CoCl2, were evaluated by means of the cell cycle, cell apoptosis, transwell cell migration, and tube formation assays. The Hsp20/KDR/PI3K/Akt expression levels were evaluated via immunofluorescence, RT-qPCR, and western blot. Next, EPCs were incorporated with either Hsp20-overexpression or Hsp20-siRNA lentivirus. The resulting effects were evaluated as described above.

RESULTS

CD34, CD133, HIF-1α, and Hsp20 were displayed more positive in the callus of MDO compared with MBD. In addition, hypoxic conditions, generated by 0.1 mM CoCl2, in canine EPCs, accelerated cell proliferation, migration, tube formation, and Hsp20 expression. Hsp20 overexpression in EPCs significantly stimulated cell proliferation, migration, and tube formation, whereas Hsp20 inhibition produced the opposite effect. Additionally, the molecular mechanism was partly dependent on the KDR/PI3K/Akt pathway.

CONCLUSION

In summary, herein, we present a novel mechanism of Hsp20-mediated regulation of canine EPCs via Akt activation in a hypoxic microenvironment.

Potential of extracellular space for tissue regeneration in dentistry

With the proven relationship between oral and general health and the growing aging population, it is pivotal to provide accessible therapeutic approaches to regenerate oral tissues and restore clinical function. However, despite sharing many core concepts with medicine, dentistry has fallen behind the progress in precision medicine and regenerative treatments. Stem cell therapies are a promising avenue for tissue regeneration, however, ethical, safety and cost issues may limit their clinical use. With the significance of paracrine signalling in stem cell and tissue regeneration, extracellular space comprising of the cell secretome, and the extracellular matrix can serve as a potent source for tissue regeneration. Extravesicles are secreted and naturally occurring vesicles with biologically active cargo that can be harvested from the extracellular space. These vesicles have shown great potential as disease biomarkers and can be used in regenerative medicine. As a cell free therapy, secretome and extracellular vesicles can be stored and transferred easily and pose less ethical and safety risks in clinical application. Since there are currently many reviews on the secretome and the biogenesis, characterization and function of extracellular vesicles, here we look at the therapeutic potential of extracellular space to drive oral tissue regeneration and the current state of the field in comparison to regenerative medicine.

[Effect of modified titanium loaded with endothelial progenitor cells-exosomes on osteogenic and angiogenic differentiations of adipose-derived stem cells]

OBJECTIVE

To investigate the effects of titanium modified by ultrasonic acid etching/anodic oxidation (UAT) loaded with endothelial progenitor cells-exosome (EPCs-exo) on proliferation and osteogenic and angiogenic differentiations of adipose-derived stem cells (ADSCs).

METHODS

The adipose tissue and bone marrow of 10 Sprague Dawley rats were harvested. Then the ADSCs and EPCs were isolated and cultured by collagenase digestion method and density gradient centrifugation method, respectively, and identified by flow cytometry. Exo was extracted from the 3rd to 5th generation EPCs using extraction kit, and CD9 and CD81 were detected by Western blot for identification. The three-dimensional printed titanium was modified by ultrasonic acid etching and anodic oxidation to prepare the UAT. The surface characteristics of UAT before and after modification was observed by scanning electron microscopy; UAT was placed in EPCs-exo solutions of different concentrations (100, 200 ng/mL), and the in vitro absorption and release capacity of EPCs-exo was detected by BCA method. Then, UAT was placed in DMEM medium containing different concentrations of EPCs-exo (0, 100, 200 ng/mL), and co-cultured with the 3rd generation ADSCs to construct UAT-ADSCs-exo. Cell morphology by laser confocal microscopy, live/dead cell staining, and cell proliferation were observed to evaluate biocompatibility; alkaline phosphatase (ALP) staining and alizarin red staining, RT-PCR detection of osteogenesis-related genes [osteocalcin (OCN), RUNT-related transcription factor 2 (Runx2), ALP, collagen type 1 (COL-1)] and angiogenesis-related gene [vascular endothelial growth factor (VEGF)], immunofluorescence staining for osteogenesis (OCN)- and angiogenesis (VEGF)-related protein expression were detected to evaluate the effect on the osteogenic and angiogenic differentiation ability of ADSCs.

RESULTS

Scanning electron microscopy showed that micro-nano multilevel composite structures were formed on the surface of UAT. About 77% EPCs-exo was absorbed by UAT within 48 hours, while EPCs-exo absorbed on the surface of UAT showed continuous and stable release within 8 days. The absorption and release amount of 200 ng/mL group were significantly higher than those of 100 ng/mL group ( P<0.05). Biocompatibility test showed that the cells in all concentration groups grew well after culture, and the 200 ng/mL group was better than the other groups, with fully spread cells and abundant pseudopodia, and the cell count and cell activity were significantly higher than those in the other groups ( P<0.05). Compared with the other groups, 200 ng/mL group showed enhanced ALP activity and mineralization ability, increased expressions of osteogenic and angiogenic genes (OCN, Runx2, COL-1, ALP, and VEGF), as well as increased expressions of OCN and VEGF proteins, with significant differences ( P<0.05).

CONCLUSION

EPCs-exo can effectively promote the adhesion, proliferation, and osteogenic and angiogenic differentiation of ADSCs on UAT surface, the effect is the most significant when the concentration is 200 ng/mL.

Infarct-preconditioning exosomes of umbilical cord mesenchymal stem cells promoted vascular remodeling and neurological recovery after stroke in rats

Background

Stroke is the leading cause of disability worldwide, resulting in severe damage to the central nervous system and disrupting neurological functions. There is no effective therapy for promoting neurological recovery. Growing evidence suggests that the composition of exosomes from different microenvironments may benefit stroke. Therefore, it is reasonable to assume that exosomes secreted in response to infarction microenvironment could have further therapeutic effects.

Methods

In our study, cerebral infarct tissue extracts were used to pretreat umbilical cord mesenchymal stem cells (UCMSC). Infarct-preconditioned exosomes were injected into rats via tail vein after middle cerebral artery occlusion (MCAO). The effect of infarct-preconditioned exosomes on the neurological recovery of rats was examined using Tunel assay, 2,3,5-triphenyltetrazolium chloride (TTC) assay, magnetic resonance imaging (MRI) analyses, modified Neurological Severity Score (mNSS), Morris water maze (MWM), and vascular remodeling analysis. Mi-RNA sequencing and functional enrichment analysis were used to validate the signal pathway involved in the effect of infarct-preconditioned exosomes. Human umbilical vein endothelial cells (HUVECs) were co-cultured with the isolated exosomes. Cell Counting Kit-8 (CCK-8) assay, scratch healing, and Western blot analysis were used to detect the biological behavior of HUVECs.

Results

The results showed that compared with normal exosomes, infarct-preconditioned exosomes further promoted vascular remodeling and recovery of neurological function after stroke. The function of upregulated miRNAs and their target genes which is beneficial to vascular smooth muscle cells verified the importance of vascular remodeling in improving stroke. Better resistance to oxygen–glucose deprivation/reoxygenation (OGD/R), reduced apoptosis, and enhanced migration were observed in infarct-preconditioned exosomes-treated umbilical vein endothelial cells.

Conclusions

Our results demonstrated that infarct-preconditioned exosomes promoted neurological recovery after stroke by enhancing vascular endothelial remodeling, suggested that infarct-preconditioned exosomes could be a novel way to alleviate brain damage following a stroke.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03083-9.

Total flavonoids of Rhizoma Drynariae enhances CD31hiEmcnhi vessel formation and subsequent bone regeneration in rat models of distraction osteogenesis by activating PDGF‑BB/VEGF/RUNX2/OSX signaling axis

Total flavonoids of Rhizoma Drynariae (TFRD), extracted from the kidney-tonifying Traditional Chinese medicine Rhizoma Drynariae, can be effective in treating osteoporosis, bone fractures and defects. However, the pharmacological effects of TFRD on the specific vessel subtype CD31^hiEmcn^hi during distraction osteogenesis (DO) remains unclear. The present study aimed to investigate the effects of TFRD on CD31^hiEmcn^hi vessels in a rat model of DO. In the present study, tibial DO models were established using 60 rats with a distraction rate of 0.2 mm per day for 20 days. Co-immunofluorescence staining of CD31 and endomucin (Emcn) was conducted to determine CD31^hiEmcn^hi vessels. Radiographic, angiographic and histological analyses were performed to assess bone and vessel formation. Tube formation, alkaline phosphatase (ALP) and Von Kossa staining assays were performed to test angiogenesis of endothelial precursor cells (EPCs) and osteogenesis of bone marrow-derived mesenchymal stem cells (BMSCs). Additionally, expression levels of platelet-derived growth factor (PDGF)-BB, VEGF, runt-related transcription factor 2 (RUNX2) and Osterix (OSX) were determined by western blotting and reverse transcription-quantitative PCR. The in vivo assays demonstrated that TFRD markedly promoted CD31^hiEmcn^hi vessel formation during DO, whereas PDGF-BB neutralizing antibody suppressed vessel formation. Furthermore, the ALP, Von Kossa staining and tube formation assays indicated that TFRD notably elevated the angiogenic capacity of EPCs and osteogenic capacity of BMSCs under stress conditions, which was significantly suppressed by blocking PDGF-BB. The protein and mRNA levels of PDGF-BB, VEGF, RUNX2 and OSX were upregulated by TFRD, but downregulated by blocking PDGF-BB. Thus, TFRD could facilitate CD31^hiEmcn^hi vessel formation and subsequently enhance angiogenic-osteogenic coupling to regenerate bone defects during DO via the PDGF-BB/VEGF/RUNX2/OSX signaling axis, which indicated that CD31^hiEmcn^hi vessels could be a potential novel therapeutic target for DO, and TFRD may represent a promising drug for promoting bone regeneration in DO by increasing CD31^hiEmcn^hi vessels.

Bioactive extracellular vesicles from a subset of endothelial progenitor cells rescue retinal ischemia and neurodegeneration

Disruption of the neurovascular unit (NVU) underlies the pathophysiology of various CNS diseases. One strategy to repair NVU dysfunction uses stem/progenitor cells to provide trophic support to the NVU's functionally coupled and interdependent vasculature and surrounding CNS parenchyma. A subset of endothelial progenitor cells, endothelial colony-forming cells (ECFCs) with high expression of the CD44 hyaluronan receptor (CD44hi), provides such neurovasculotrophic support via a paracrine mechanism. Here, we report that bioactive extracellular vesicles from CD44hi ECFCs (EVshi) are paracrine mediators, recapitulating the effects of intact cell therapy in murine models of ischemic/neurodegenerative retinopathy; vesicles from ECFCs with low expression levels of CD44 (EVslo) were ineffective. Small RNA sequencing comparing the microRNA cargo from EVshi and EVslo identified candidate microRNAs that contribute to these effects. EVshi may be used to repair NVU dysfunction through multiple mechanisms to stabilize hypoxic vasculature, promote vascular growth, and support neural cells.

A Review Into the Insights of the Role of Endothelial Progenitor Cells on Bone Biology

In addition to its important transport functions, the skeletal system is involved in complex biological activities for the regulation of blood vessels. Endothelial progenitor cells (EPCs), as stem cells of endothelial cells (ECs), possess an effective proliferative capacity and a powerful angiogenic capacity prior to their differentiation. They demonstrate synergistic effects to promote bone regeneration and vascularization more effectively by co-culturing with multiple cells. EPCs demonstrate a significant therapeutic potential for the treatment of various bone diseases by secreting a combination of growth factors, regulating cellular functions, and promoting bone regeneration. In this review, we retrospect the definition and properties of EPCs, their interaction with mesenchymal stem cells, ECs, smooth muscle cells, and immune cells in bone regeneration, vascularization, and immunity, summarizing their mechanism of action and contribution to bone biology. Additionally, we generalized their role and potential mechanisms in the treatment of various bone diseases, possibly indicating their clinical application.

Comprehensive insight into endothelial progenitor cell-derived extracellular vesicles as a promising candidate for disease treatment

Endothelial progenitor cells (EPCs), which are a type of stem cell, have been found to have strong angiogenic and tissue repair capabilities. Extracellular vesicles (EVs) contain many effective components, such as cellular proteins, microRNAs, messenger RNAs, and long noncoding RNAs, and can be secreted by different cell types. The functions of EVs depend mainly on their parent cells. Many researchers have conducted functional studies of EPC-derived EVs (EPC-EVs) and showed that they exhibit therapeutic effects on many diseases, such as cardiovascular disease, acute kidney injury, acute lung injury, and sepsis. In this review article, we comprehensively summarized the biogenesis and functions of EPCs and EVs and the potent role of EPC-EVs in the treatment of various diseases. Furthermore, the current problems and future prospects have been discussed, and further studies are needed to compare the therapeutic effects of EVs derived from various stem cells, which will contribute to the accelerated translation of these applications in a clinical setting.

Thymoquinone-loaded mesenchymal stem cell-derived exosome as an efficient nano-system against breast cancer cells

OBJECTIVES

Exosomes became the subject of extensive research in drug delivery approach due to their potential applicability as therapeutic tools for cancer therapy. Thymoquinone (Tq) is an anti-cancer agent due to its great anti-proliferative effect. However, poor solubility and weak bioavailability restrict its therapeutic applications. In this study, exosomes secreted from human adipocyte-derived mesenchymal stem cells (AdMSCs) were isolated and the efficacy of a novel encapsulation method for loading of Tq was investigated. Finally, the cytotoxic effect of Tq incorporated exosomes against cancer cells was evaluated.

MATERIALS AND METHODS

Exosomes secreted from AdMSCs were isolated via ultracentrifugation and characterized by electron microscopy and western blotting. Then, through a novel encapsulation approach, Tq was loaded into exosomes by the combination of three methods including incubation, freeze-thawing, and surfactant treatment. Then, the encapsulation efficiency, in vitro cellular uptake, and cytotoxicity of Tq incorporated exosomes (Tq@EXOs) in MCF7 and L929 cells were estimated.

RESULTS

Tq loading into exosomes through our novel method caused a significant improvement in encapsulation efficiency of about 60%. The fluorescent microscopy and flow cytometry outcomes indicated the efficient uptake of Tq@EXOs-FITC by cells throughout 4 hr. Furthermore, MTT results displayed the ability of Tq@EXOs in effectively decreasing the cell viability of MCF7 without causing any obvious cytotoxicity on L929 as normal cells.

CONCLUSION

The results suggest that our approach provides effective loading of Tq into exosomes which offer a valuable and safe platform for drug delivery to cancer cells thus having a great potential for clinical studies.

Identification of the key exosomal lncRNAs/mRNAs in the serum during distraction osteogenesis

Background

Distraction osteogenesis (DO), a kind of bone regenerative process, is not only extremely effective, but the osteogenesis rate is far beyond ordinary bone fracture (BF) healing. Exosomes (Exo) are thought to play a part in bone regeneration and healing as key players in cell-to-cell contact. The object of this work was to determine whether exosomes derived from DO and BF serum could stimulate the Osteogenic Differentiation in these two processes, and if so, which genes could be involved.

Methods

The osteogenesis in DO-gap or BF-gap was evaluated using radiographic analysis and histological analysis. On the 14th postoperative day, DO-Exos and BF-Exos were isolated and cocultured with the jaw of bone marrow mesenchymal stem cells (JBMMSCs). Proliferation, migration and osteogenic differentiation of JBMMSCs were ascertained, after which exosomes RNA-seq was performed to identify the relevant gene.

Results

Radiographic and histological analyses manifested that osteogenesis was remarkably accelerated in DO-gap in comparison with BF-gap. Both of the two types of Exos were taken up by JBMMSCs, and their migration and osteogenic differentiation were also seen to improve. However, the proliferation showed no significant difference. Finally, exosome RNA-seq revealed that the lncRNA MSTRG.532277.1 and the mRNA F-box and leucine-rich repeat protein 14(FBXL14) may play a key role in DO.

Conclusions

Our findings suggest that exosomes from serum exert a critical effect on the rapid osteogenesis in DO. This promoting effect might have relevance with the co-expression of MSTRG.532277.1 and FBXL14. On the whole, these findings provide new insights into bone regeneration, thereby outlining possible therapeutic targets for clinical intervention.

Research Progress on Transorgan Regulation of the Cardiovascular and Motor System through Cardiogenic Exosomes

The heart is the core organ of the circulatory system. Through the blood circulation system, it has close contact with all tissues and cells in the body. An exosome is an extracellular vesicle enclosed by a phospholipid bilayer. A variety of heart tissue cells can secrete and release exosomes, which transfer RNAs, lipids, proteins, and other biomolecules to adjacent or remote cells, mediate intercellular communication, and regulate the physiological and pathological activities of target cells. Cardiogenic exosomes play an important role in regulating almost all pathological and physiological processes of the heart. In addition, they can also reach distant tissues and organs through the peripheral circulation, exerting profound influence on their functional status. In this paper, the composition and function of cardiogenic exosomes, the factors affecting cardiogenic exosomes and their roles in cardiovascular physiology and pathophysiology are discussed, and the close relationship between cardiovascular system and motor system is innovatively explored from the perspective of exosomes. This study provides a reference for the development and application of exosomes in regenerative medicine and sports health, and also provides a new idea for revealing the close relationship between the heart and other organ systems.

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.

Bone Cell Exosomes and Emerging Strategies in Bone Engineering

Bone tissue remodeling is a highly regulated process balancing bone formation and resorption through complex cellular crosstalk between resident bone and microenvironment cells. This cellular communication is mediated by direct cell and cell–matrix contact, autocrine, endocrine, and paracrine receptor mediated mechanisms such as local soluble signaling molecules and extracellular vesicles including nanometer sized exosomes. An impairment in this balanced process leads to development of pathological conditions. Bone tissue engineering is an emerging interdisciplinary field with potential to address bone defects and disorders by synthesizing three-dimensional bone substitutes embedded with cells for clinical implantation. However, current cell-based therapeutic approaches have faced hurdles due to safety and ethical concerns, challenging their clinical translation. Recent studies on exosome-regulated bone homeostasis and regeneration have gained interest as prospective cell free therapy in conjugation with tissue engineered bone grafts. However, exosome research is still in its nascent stages of bone tissue engineering. In this review, we specifically describe the role of exosomes secreted by cells within bone microenvironment such as osteoblasts, osteocytes, osteoclasts, mesenchymal stem cell cells, immune cells, endothelial cells, and even tumor cells during bone homeostasis and crosstalk. We also review exosome-based osteoinductive functionalization strategies for various bone-based biomaterials such as ceramics, polymers, and metals in bone tissue engineering. We further highlight biomaterials as carrier agents for exosome delivery to bone defect sites and, finally, the influence of various biomaterials in modulation of cell exosome secretome.

Hypoxia During the Consolidation Phase of Distraction Osteogenesis Promotes Bone Regeneration

Background

Hypoxia is the critical driving force for angiogenesis and can trigger the osteogenic-angiogenic coupling followed by the enhancement of bone regeneration. While lots of studies showed that hypoxia administration can accelerate bone formation during distraction osteogenesis (DO), the therapeutic timing for the osteogenic purpose was concentrated on the distraction phase. The outcomes of hypoxia administration in the consolidation phase stay uncertain. The purpose of this study was to determine the osteogenic effectiveness of hypoxia therapy during the consolidation phase, if any, to enhance bone regeneration in a rat femoral DO model.

Methods

A total of 42 adult male Sprague-Dawley rats underwent right femoral mid-diaphysis transverse osteotomy and were randomly divided into Control (NS administration, n = 21) and Group1 (deferoxamine therapy, n = 21) after distraction. During the consolidation phase, Group1 was treated with local deferoxamine (DFO) injection into the distraction zone, while the Control underwent the same dosage of NS. Animals were sacrificed after 2, 4, and 6 weeks of consolidation. The process of bone formation and remodeling was monitored by digital radiographs, and the regenerated bone was evaluated by micro-computed tomography (micro-CT), biomechanical test, and histological analysis. The serum content of hypoxia-inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF) were measured by enzyme linked immunosorbent assay (ELISA) for further analysis.

Results

Bone regeneration was significantly enhanced after hypoxia therapy during the consolidation phase. The digital radiograph, micro-CT, and biomechanical evaluation showed better effects regarding volume, continuity, and mechanical properties of the regenerated bone in Group1. The histomorphological evaluation also revealed the hypoxia treatment contributed to accelerate bone formation and remodeling during DO. The higher positive expression of angiogenic and osteogenic markers were observed in Group1 after hypoxia administration according to the immunohistochemical analysis. The serum content of HIF-1α and VEGF was also increased after hypoxia therapy as evidenced from ELISA.

Conclusion

Hypoxia administration during the consolidation phase of distraction osteogenesis has benefits in enhancing bone regeneration, including accelerates the bone formation and remodeling.

M2 macrophagy-derived exosomal miRNA-26a-5p induces osteogenic differentiation of bone mesenchymal stem cells

BACKGROUND

Bone marrow mesenchymal stem cells have always been a heated research topic in bone tissue regeneration and repair because of their self-renewal and multi-differentiation potential. A large number of studies have been focused on finding the inducing factors that will promote the osteogenic differentiation of bone marrow mesenchymal stem cells. Previous studies have shown that macrophage exosomes or miRNA-26a-5p can make it work, but the function of this kind of substance on cell osteogenic differentiation has not been public.

METHODS

M2 macrophages are obtained from IL-4 polarized bone marrow-derived macrophages. Exosomes were isolated from the supernatant of M2 macrophages and identified via transmission electron microscopy (TEM), western blotting, and DLS. Chondrogenic differentiation potential was detected by Alcian blue staining. Oil red O staining was used to detect the potential for lipogenic differentiation. And MTT would detect the proliferative capacity of cells. Western blot was performed to detect differential expression of osteogenic differentiation-related proteins.

RESULTS

The results showed that M2 macrophage exosomes will promote bone differentiation and at the same time inhibit lipid differentiation. In addition, M2 macrophage-derived exosomes have the function of promoting the expression of SOX and Aggrecan suppressing the level of MMP13. The exosome inhibitor GW4689 suppresses miRNA-26a-5p in M2 macrophage exosomes, and the treated exosomes do not play an important role in promoting bone differentiation. Moreover, miRNA-26a-5p can enable to promote bone differentiation and inhibit lipid differentiation. miRNA-26a-5p can promote the expression of ALP (alkaline phosphatase), RUNX-2 (Runt-related transcription factor 2), OPN(osteopontin), and Col-2(collagen type II). Therefore, it is speculated that exosomal miRNA-26a-5p is indispensable in osteogenic differentiation.

CONCLUSIONS

The present study indicated that M2 macrophage exosomes carrying miRNA-26a-5p can induce osteogenic differentiation of bone marrow-derived stem cells to inhibit lipogenic differentiation, and miRNA-26a-5p will also promote the expression of osteogenic differentiation-related proteins ALP, RUNX-2, OPN, and Col-2.

EPC-EXs improve astrocyte survival and oxidative stress through different uptaking pathways in diabetic hypoxia condition

Background

Hyperglycemia contributes to cardiovascular complications in patients with type 2 diabetes. We confirmed that high glucose (HG) induces endothelial dysfunction and cerebral ischemic injury is enlarged in diabetic mice. Stem cell-released exosomes have been shown to protect the brain from ischemic stroke. We have previously shown that endothelial progenitor cells (EPCs)-released exosomes (EPC-EXs) can protect endothelial cells from hypoxia/reoxygenation (H/R) and HG-induced injury. Here, we aim to investigate the effects of EPC-EXs on astrocytes under H/R and HG-induced injury and whether miR-126 enriched EPC-EXs (miR126-EPC-EXs) have enhanced efficacy.

Methods

EPC-EX uptake and co-localization were measured by fluorescent microscopy using PKH26 and DAPI staining. miR-126 enrichment was achieved by transfecting with miR-126 mimics and quantified with real-time PCR. After co-incubation, cell death or injury was measured by using LDH (Lactate Dehydrogenase) assay. Oxidative stress/ROS (reactive oxygen species) generation was measured by DHE (Dihydroethidium) staining and lipid peroxidation assay.

Results

The EPC-EXs were effectively taken up by the astrocytes in a concentration as well as time-dependent manners and were co-localized within the nucleus as well as the cytoplasm. Pathway uptake inhibitors revealed that the EPC-EXs are effectively taken up by the clathrin-mediated, caveolin-dependent, and micropinocytosis via PI3K/Akt pathway. H/R and HG-induced a cell injury which could be protected by EPC-EXs evidenced by decreased cell cytotoxicity, oxidative stress, and lipid peroxidation. Moreover, miR-126 overexpression could increase the level of miR-126 in astrocytes and enhance the protective effects of EPC-EXs.

Conclusions

These results collectively indicate that the EPC-EXs could protect astrocytes against the HG plus H/R-induced damage.

[Application of Extracellular Vesicles Derived from Vascular Endothelial/Endothelial Progenitor Cells in Tissue Regeneration and Repair]

Extracellular vesicles can be released by almost all types of cells and are important mediators of intercellular signal transmssion. Extracellular vesicles regulate the function and activity of recipient cells by delivering biologically active molecules such as proteins and nucleic acids, which is of great significance in tissue repair and regeneration. According to numerous studies, extracellular vesicles derived from endothelial/endothelial progenitor cells can induce cell proliferation and differentiation, inhibit cell apoptosis, and promote angiogenesis, playing an increasingly important role in regenerative medicine. We reported in this review the latest findings on applying extracellular vesicles derived from endothelial/endothelial progenitor cells in tissue regeneration and repair, and discussed the challenges and future development directions of their application in the field of regenerative medicine.

SHED‐derived exosomes improve the repair capacity and osteogenesis potential of hPDLCs

OBJECTIVE

Exosomes secreted by stem cells are recognized as a critical component in tissue regeneration during stem cell-based therapy. Considering the limited sources and bone regeneration efficiency of human periodontal ligament cells (hPDLCs), we explored whether exosomes secreted by stem cells from human exfoliated deciduous teeth (SHED-exo) could improve the pluripotency and regenerative potential of hPDLCs.

METHODS AND MATERIALS

In hPDLCs, cell proliferation, migration, cell cycle, apoptosis, and osteogenic differentiation were detected after cells were exposed to SHED-exo (SHED-exo group), blank (control group), or control supernatant without exo (Csup group), via CCK-8, scratch analysis, flow cytometric, real-time PCR, and so on. Exosomes sequencing was performed to compare and analyze miRNAs contented in SHED-exo and hPDLC-exo.

RESULTS

As compared to control or Csup, SHED-exo significantly increased migration, apoptosis, and proliferation, promoted cell cycle transition from G1 to S phase in hPDLCs, and enhanced Runx2 expression and mineralization. In addition, it may be explained by the significant differences in miRNA contented in SHED-exo and hPDLC-exo.

CONCLUSION

Exosomes from SHED can improve cell proliferation, migration, cell cycle, apoptosis, and osteogenic differentiation of hPDLCs, which highlights the therapeutic value of this bioactive component in the regeneration of periodontal tissues using hPDLCs in clinical practice.

Educating EVs to Improve Bone Regeneration: Getting Closer to the Clinic

The incidence of bone-related disorders is continuously growing as the aging of the population in developing countries continues to increase. Although therapeutic interventions for bone regeneration exist, their effectiveness is questioned, especially under certain circumstances, such as critical size defects. This gap of curative options has led to the search for new and more effective therapeutic approaches for bone regeneration; among them, the possibility of using extracellular vesicles (EVs) is gaining ground. EVs are secreted, biocompatible, nano-sized vesicles that play a pivotal role as messengers between donor and target cells, mediated by their specific cargo. Evidence shows that bone-relevant cells secrete osteoanabolic EVs, whose functionality can be further improved by several strategies. This, together with the low immunogenicity of EVs and their storage advantages, make them attractive candidates for clinical prospects in bone regeneration. However, before EVs reach clinical translation, a number of concerns should be addressed. Unraveling the EVs’ mode of action in bone regeneration is one of them; the molecular mediators driving their osteoanabolic effects in acceptor cells are now beginning to be uncovered. Increasing the functional and bone targeting abilities of EVs are also matters of intense research. Here, we summarize the cell sources offering osteoanabolic EVs, and the current knowledge about the molecular cargos that mediate bone regeneration. Moreover, we discuss strategies under development to improve the osteoanabolic and bone-targeting potential of EVs.