Mesenchymal Stem Cell-Derived Exosomes Promote Fracture Healing in a Mouse Model

Mesenchymal stem cell exosomes in bone regenerative strategies-a systematic review of preclinical studies

The ability of bone for regeneration has long been recognized. However, once beyond a critical size, spontaneous regeneration of bone is limited. Several studies have focused on enhancing bone regeneration by applying mesenchymal stromal/stem cells (MSCs) in the treatment strategies. Despite the therapeutic efficacy of MSCs in bone regeneration, cell-based therapies are impeded by several challenges in maintaining the optimal cell potency and viability during expansion, storage, and final delivery to patients. Recently, there has been a paradigm shift in therapeutic mechanism of MSCs in tissue repair from one based on cellular differentiation and replacement to one based on secretion and paracrine signaling. Among the broad spectrum of trophic factors, extracellular vesicles ​particularly the exosomes have been reported to be therapeutically efficacious in several injury/disease indications, including bone defects and diseases. The current systematic review aims to summarize the results of the existing animal studies which were conducted to evaluate the therapeutic efficacy of MSC exosomes for bone regeneration. Following the Preferred Reporting Items for Systematic Reviews and Meta-analysis ​guidelines, the PubMed and The Cochrane Library database were searched for relevant controlled preclinical animal studies. A total of 23 studies were identified, with the total sample size being 690 rats or mice and 38 rabbits. Generally, MSC exosomes were found to be efficacious for bone regeneration in animal models of bone defects and diseases such as osteonecrosis and osteoporosis. In these studies, MSC exosomes promoted new bone formation with supporting vasculature ​and displayed improved morphological, biomechanical, and histological outcomes, coupled with positive effects on cell survival, proliferation, and migration, osteogenesis, and angiogenesis. Unclear-to-low risk in bias and incomplete reporting in the primary studies highlighted the need for standardization in outcome measurements and reporting. Further studies in large animal models to establish the safety and efficacy would provide useful information on guiding the design of clinical trials.

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Therapeutic efficacy of MSC exosomes in bone regeneration was studied in 23 studies.

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MSC exosomes are therapeutically efficacious in bone regeneration.

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MSC exosomes improve morphological, biomechanical, and histological outcomes.

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MSC exosomes promote a multifaceted mechanism in bone regeneration.

Exosomes: roles and therapeutic potential in osteoarthritis

Exosomes participate in many physiological and pathological processes by regulating cell-cell communication, which are involved in numerous diseases, including osteoarthritis (OA). Exosomes are detectable in the human articular cavity and were observed to change with OA progression. Several joint cells, including chondrocytes, synovial fibroblasts, osteoblasts, and tenocytes, can produce and secrete exosomes that influence the biological effects of targeted cells. In addition, exosomes from stem cells can protect the OA joint from damage by promoting cartilage repair, inhibiting synovitis, and mediating subchondral bone remodeling. This review summarizes the roles and therapeutic potential of exosomes in OA and discusses the perspectives and challenges related to exosome-based treatment for OA patients in the future.

Time Course of Immune Response and Immunomodulation During Normal and Delayed Healing of Musculoskeletal Wounds

Single trauma injuries or isolated fractures are often manageable and generally heal without complications. In contrast, high-energy trauma results in multi/poly-trauma injury patterns presenting imbalanced pro- and anti- inflammatory responses often leading to immune dysfunction. These injuries often exhibit delayed healing, leading to fibrosis of injury sites and delayed healing of fractures depending on the intensity of the compounding traumas. Immune dysfunction is accompanied by a temporal shift in the innate and adaptive immune cells distribution, triggered by the overwhelming release of an arsenal of inflammatory mediators such as complements, cytokines and damage associated molecular patterns (DAMPs) from necrotic cells. Recent studies have implicated this dysregulated inflammation in the poor prognosis of polytraumatic injuries, however, interventions focusing on immunomodulating inflammatory cellular composition and activation, if administered incorrectly, can result in immune suppression and unintended outcomes. Immunomodulation therapy is promising but should be conducted with consideration for the spatial and temporal distribution of the immune cells during impaired healing. This review describes the current state of knowledge in the spatiotemporal distribution patterns of immune cells at various stages during musculoskeletal wound healing, with a focus on recent advances in the field of Osteoimmunology, a study of the interface between the immune and skeletal systems, in long bone fractures. The goals of this review are to (1) discuss wound and fracture healing processes of normal and delayed healing in skeletal muscles and long bones; (2) provide a balanced perspective on temporal distributions of immune cells and skeletal cells during healing; and (3) highlight recent therapeutic interventions used to improve fracture healing. This review is intended to promote an understanding of the importance of inflammation during normal and delayed wound and fracture healing. Knowledge gained will be instrumental in developing novel immunomodulatory approaches for impaired healing.

Administration of Human Non-Diabetic Mesenchymal Stromal Cells to a Murine Model of Diabetic Fracture Repair: A Pilot Study

Individuals living with type 1 diabetes mellitus may experience an increased risk of long bone fracture. These fractures are often slow to heal, resulting in delayed reunion or non-union. It is reasonable to theorize that the underlying cause of these diabetes-associated osteopathies is faulty repair dynamics as a result of compromised bone marrow progenitor cell function. Here it was hypothesized that the administration of non-diabetic, human adult bone marrow-derived mesenchymal stromal cells (MSCs) would enhance diabetic fracture healing. Human MSCs were locally introduced to femur fractures in streptozotocin-induced diabetic mice, and the quality of de novo bone was assessed eight weeks later. Biodistribution analysis demonstrated that the cells remained in situ for three days following administration. Bone bridging was evident in all animals. However, a large reparative callus was retained, indicating non-union. µCT analysis elucidated comparable callus dimensions, bone mineral density, bone volume/total volume, and volume of mature bone in all groups that received cells as compared to the saline-treated controls. Four-point bending evaluation of flexural strength, flexural modulus, and total energy to re-fracture did not indicate a statistically significant change as a result of cellular administration. An ex vivo lymphocytic proliferation recall assay indicated that the xenogeneic administration of human cells did not result in an immune response by the murine recipient. Due to this dataset, the administration of non-diabetic bone marrow-derived MSCs did not support fracture healing in this pilot study.

Preservation of Mesenchymal Stem Cell-Derived Extracellular Vesicles after Abdominal Delivery in the Experiment

Light luminescent microscopy was used to study the distribution of extracellular microvesicles with PKH26-stained membranes secreted by placenta-derived mesenchymal stromal cells in the uterine tissues at different terms after injections to intact rats and after abdominal delivery (a model of cesarian section). Microvesicles migrated through the uterine tissues and were detected for at least 8 days after injection. In some cases, microvesicles were more numerous in the uterus after cesarian section modeling, which can be related to blockade of microcirculation and lymph flow due to inflammation accompanying surgical intervention. The content of microvesicles in the uterine tissues gradually declined due to macrophage phagocytosis and, probably, due to their migration into the vascular bed. Despite their size, properly stained extracellular microvesicles can be detected by light microscopy in tissues after injections.

Effectiveness of mesenchymal stem cell-conditioned medium in bone regeneration in animal and human models: a systematic review and meta-analysis

BACKGROUND

Given the limitations of current therapies for the reconstruction of bone defects, regenerative medicine has arisen as a new therapeutic strategy along with mesenchymal stem cells (MSCs), which, because of their osteogenic potential and immunomodulatory properties, have emerged as a promising alternative for the treatment of bone injuries. In vivo studies have demonstrated that MSCs have a positive effect on regeneration due to their secretion of cytokines and growth factors that, when collected in conditioned medium (MSC-CM) and applied to an injured tissue, can modulate and promote the formation of new tissue.

OBJECTIVE

To evaluate the effectiveness of application of conditioned medium derived from mesenchymal stem cells in bone regeneration in animal and human models.

METHODS

We conducted a systematic review with a comprehensive search through February of 2018 using several electronic databases (MEDLINE, EMBASE, SCOPUS, CENTRAL (Ovid), and LILACS), and we also used the "snowballing technique". Articles that met the inclusion criteria were selected through abstract review and subsequent assessment of the full text. We assessed the risk of bias with the SYRCLE and Cochrane tools, and three meta-analyses were performed.

RESULTS

We included 21 articles, 19 of which used animal models and 2 of which used human models. In animal models, the application of MSC-CM significantly increased the regeneration of bone defects in comparison with control groups. Human studies reported early mineralization in regenerated bones, and no bone resorption, inflammation, nor local or systemic alterations were observed in any case. The meta-analysis showed an overall favorable effect of the application of MSC-CM.

CONCLUSIONS

The application of MSC-CM to bone defects has a positive and favorable effect on the repair and regeneration of bone tissue, particularly in animal models. It is necessary to perform additional studies to support the application of MSC-CM in clinical practice.

Serum outperforms plasma in small extracellular vesicle microRNA biomarker studies of adenocarcinoma of the esophagus

BACKGROUND

Circulating microRNAs (miRNAs) are potential biomarkers for many diseases. However, they can originate from non-disease specific sources, such as blood cells, and compromise the investigations for miRNA biomarkers. While small extracellular vesicles (sEVs) have been suggested to provide a purer source of circulating miRNAs for biomarkers discovery, the most suitable blood sample for sEV miRNA biomarker studies has not been defined.

AIM

To compare the miRNA profiles between matched serum and plasma sEV preparations to determine their suitability for biomarker studies.

METHODS

Matched serum and plasma samples were obtained from 10 healthy controls and 10 patients with esophageal adenocarcinoma. sEV isolates were prepared from serum and plasma using ExoQuick^TM and quantified using NanoSight. RNA was extracted from sEV preparations with the miRNeasy Serum/Plasma kit and profiled using the Taqman Openarray qPCR. The overall miRNA content and the expression of specific miRNAs of reported vesicular and non-vesicular origins were compared between serum and plasma sEV preparations. The diagnostic performance of a previously identified multi-miRNA biomarker panel for esophageal adenocarcinoma was also compared.

RESULTS

The overall miRNA content was higher in plasma sEV preparations (480 miRNAs) and contained 97.5% of the miRNAs found in the serum sEV preparations (412 miRNAs).The expression of commonly expressed miRNAs was highly correlated (Spearman’s R = 0.87, P < 0.0001) between the plasma and serum sEV preparations, but was consistently higher in the plasma sEV preparations. Specific blood-cell miRNAs (hsa-miR-223-3p, hsa-miR-451a, miR-19b-3p, hsa-miR-17-5p, hsa-miR-30b-5p, hsa-miR-106a-5p, hsa-miR-150-5p and hsa-miR-92a-3p) were expressed at 2.7 to 9.6 fold higher levels in the plasma sEV preparations compared to serum sEV preparations (P < 0.05). In plasma sEV preparations, the percentage of protein-associated miRNAs expressed at relatively higher levels (Ct 20-25) was greater than serum sEV preparations (50% vs 31%). While the percentage of vesicle-associated miRNAs expressed at relatively higher levels was greater in the serum sEV preparations than plasma sEV preparations (70% vs 44%). A 5-miRNA biomarker panel produced a higher cross validated accuracy for discriminating patients with esophageal adenocarcinoma from healthy controls using serum sEV preparations compared with plasma sEV preparations (AUROC 0.80 vs 0.54, P < 0.05).

CONCLUSION

Although plasma sEV preparations contained more miRNAs than serum sEV preparations, they also contained more miRNAs from non-vesicle origins. Serum appears to be more suitable than plasma for sEV miRNAs biomarkers studies.

Regulating Osteogenic Differentiation by Suppression of Exosomal MicroRNAs

IMPACT STATEMENT

We investigated the role of exosomes in osteogenesis and the use of miRNA inhibitor-transfected exosomes to control osteogenic differentiation. RNA-sequencing (RNA-seq) of exosomal miRNAs revealed that growth condition of milieu of preosteoblast exosomes harbors high levels of let-7, which plays a critical role in osteogenesis regulation. We modified exosomes by transfecting let-7 inhibitor into exosomes under growth condition in MC3T3-E1 cells and revealed that exosomes whose let-7 was inactivated by engineering lost the ability to recover osteogenic differentiation. Genetically modified exosomes may serve as powerful biomaterials for developmental control, including of osteogenesis regulation.

Human amniotic mesenchymal stromal cells promote bone regeneration via activating endogenous regeneration

Rationale: The effectiveness of stem cell based-therapy for bone regeneration has been demonstrated; yet, clinical application of autologous stem cells is still limited by invasive acquisition, long culture processes, and high cost. Besides, it remains controversial whether autologous stem cells could directly participate in tissue repair after differentiation. Thus, increasing allogeneic stem cells have been developed into drugs to indirectly activate endogenous regeneration and induce tissue regeneration. Human amniotic mesenchymal stromal cells (HAMSCs) have been extensively studied, showing multiple regulatory functions, but mechanisms of HAMSCs in promoting bone regeneration are remain unclear. Methods: Proteome profile of HAMSCs and their functions on vascularized bone regeneration were investigated in vitro, while rabbit cranial defect model was used to further detect the effects of bone formation in vivo. Results: HAMSCs secrete many osteogenic, angiogenic, and immunomodulatory cytokines. In vitro, HAMSCs can promote human bone-marrow mesenchymal stromal cells (HBMSCs) migration and osteogenic differentiation; promote the capillary-tube formation of human umbilical vascular endothelial cells (HUVECs), induce HUVECs migration and pro-angiogenic genes expression, and promote M2 macrophage polarization. Further, in vivo studies suggested that transplanted HAMSCs could survive and induce M2 macrophages to secrete bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) in rabbits' skull defects at an early stage, and, in turn, promote more new bone formation. Conclusion: HAMSCs have good biocompatibility and paracrine function to promote bone repair by stimulating endogenous regeneration.

Mesenchymal Stem Cell Derived Extracellular Vesicles for Tissue Engineering and Regenerative Medicine Applications

Mesenchymal stem cells (MSCs) are being extensively investigated for their potential in tissue engineering and regenerative medicine. However, recent evidence suggests that the beneficial effects of MSCs may be manifest by their released extracellular vesicles (EVs); typically not requiring the administration of MSCs. This evidence, predominantly from pre-clinical in vitro and in vivo studies, suggests that MSC-EVs may exhibit substantial therapeutic properties in many pathophysiological conditions, potentially restoring an extensive range of damaged or diseased tissues and organs. These benefits of MSC EVs are apparently found, regardless of the anatomical or body fluid origin of the MSCs (and include e.g., bone marrow, adipose tissue, umbilical cord, urine, etc). Furthermore, early indications suggest that the favourable effects of MSC-EVs could be further enhanced by modifying the way in which the donor MSCs are cultured (for example, in hypoxic compared to normoxic conditions, in 3D compared to 2D culture formats) and/or if the EVs are subsequently bio-engineered (for example, loaded with specific cargo). So far, few human clinical trials of MSC-EVs have been conducted and questions remain unanswered on whether the heterogeneous population of EVs is beneficial or some specific sub-populations, how best we can culture and scale-up MSC-EV production and isolation for clinical utility, and in what format they should be administered. However, as reviewed here, there is now substantial evidence supporting the use of MSC-EVs in tissue engineering and regenerative medicine and further research to establish how best to exploit this approach for societal and economic benefit is warranted.

[Review for different sources of exosomes in bone tissue engineering research]

Exosomes are 40-100 nm vesicles that are released into the extracellular environment upon the fusion of multivesicular bodies with the plasma membrane. The biologically cargoes transported by exosomes are diverse. Exosomes are important carriers of signal transmission and interaction between cells. Exosomes are believed to play an important role in tissue repair and bone regeneration. Studies have evaluated that exosomes secreted by cells play an increasingly significant roles in bone tissue engineering and have multiple functions, including regulating immunity, promoting cell proliferation and differentiation, enhancing bone regeneration and angiogenesis. The review analyzes the characteristics and biological properties of different cell-derived exosomes in the bone environment, summarizes their research progress in bone repair, and discusses the challenges and future directions for their application in bone tissue engineering.

Growth Factor Gene-Modified Mesenchymal Stem Cells in Tissue Regeneration

There have been marked changes in the field of stem cell therapeutics in recent years, with many clinical trials having been conducted to date in an effort to treat myriad diseases. Mesenchymal stem cells (MSCs) are the cell type most frequently utilized in stem cell therapeutic and tissue regenerative strategies, and have been used with excellent safety to date. Unfortunately, these MSCs have limited ability to engraft and survive, reducing their clinical utility. MSCs are able to secrete growth factors that can support the regeneration of tissues, and engineering MSCs to express such growth factors can improve their survival, proliferation, differentiation, and tissue reconstructing abilities. As such, it is likely that such genetically modified MSCs may represent the next stage of regenerative therapy. Indeed, increasing volumes of preclinical research suggests that such modified MSCs expressing growth factors can effectively treat many forms of tissue damage. In the present review, we survey recent approaches to producing and utilizing growth factor gene-modified MSCs in the context of tissue repair and discuss its prospects for clinical application.

The Role of Bone-Derived Exosomes in Regulating Skeletal Metabolism and Extraosseous Diseases

Bone-derived exosomes are naturally existing nano-sized extracellular vesicles secreted by various cells, such as bone marrow stromal cells, osteoclasts, osteoblasts, and osteocytes, containing multifarious proteins, lipids, and nucleic acids. Accumulating evidence indicates that bone-derived exosomes are involved in the regulation of skeletal metabolism and extraosseous diseases through modulating intercellular communication and the transfer of materials. Following the development of research, we found that exosomes can be considered as a potential candidate as a drug delivery carrier thanks to its ability to transport molecules into targeted cells with high stability, safety, and efficiency. This review aims to discuss the emerging role of bone-derived exosomes in skeletal metabolism and extraosseous diseases as well as their potential role as candidate biomarkers or for developing new therapeutic strategies.

Exosomal miRNA-128-3p from mesenchymal stem cells of aged rats regulates osteogenesis and bone fracture healing by targeting Smad5

Transplantation of mesenchymal stem cells (MSCs) has been considered an effective therapeutic treatment for a variety of diseases including bone fracture. However, there are associated complications along with MSCs transplantation. There is evidence to show that exosomes (Exos) derived from MSCs exert a similar paracrine function. In addition, repair capabilities of MSCs decline with age. Hence, this study aims to confirm whether the Exos protective function on osteogenic differentiation and fracture healing from aged MSCs was attenuated. This information was used in order to investigate the underlying mechanism. MSCs were successfully isolated and identified from young and aged rats, and Exos were then obtained. Aged-Exos exhibited significantly attenuated effects on MSCs osteogenic differentiation in vitro and facture healing in vivo. Using miRNA array analysis, it was shown that miR-128-3p was markedly upregulated in Aged-Exos. In vitro experiments confirmed that Smad5 is a direct downstream target of miR-128-3p, and was inhibited by overexpressed miR-128-3p. A series gain- and loss- function experiment indicated that miR-128-3P serves a suppressor role in the process of fracture healing. Furthermore, effects caused by miR-128-3P mimic/inhibitor were reversed by the application of Smad5/siSmad5. Taken together, these results suggest that the therapeutic effects of MSCs-derived Exos may vary according to differential expression of miRNAs. Exosomal miR-128-3P antagomir may act as a promising therapeutic strategy for bone fracture healing, especially for the elderly.

The Therapeutic Potential of Breast Milk-Derived Extracellular Vesicles

In the past few decades, interest in the therapeutic benefits of exosomes and extracellular vesicles (EVs) has grown exponentially. Exosomes/EVs are small particles which are produced and exocytosed by cells throughout the body. They are loaded with active regulatory and stimulatory molecules from the parent cell including miRNAs and enzymes, making them prime targets in therapeutics and diagnostics. Breast milk, known for years to have beneficial health effects, contains a population of EVs which may mediate its therapeutic effects. This review offers an update on the therapeutic potential of exosomes/EVs in disease, with a focus on EVs present in human breast milk and their remedial effect in the gastrointestinal disease necrotizing enterocolitis. Additionally, the relationship between EV miRNAs, health, and disease will be examined, along with the potential for EVs and their miRNAs to be engineered for targeted treatments.

Serum extracellular vesicles expressing bone activity markers associate with bone loss after HIV antiretroviral therapy

OBJECTIVE

We tested whether bone-related extracellular vesicle phenotypes changed after initiating antiretroviral therapy (ART) and determined whether changes in levels of extracellular vesicles correlated with changes in bone mineral density (BMD).

DESIGN

Extracellular vesicle phenotypes were measured in blinded serum samples from 15 adults with HIV at baseline, 1, 3, 6 and 12 months after ART initiation. Not all samples were available at each time point so we averaged early (TP1, 1-3 months) and late (TP2, 6-12 months) time points.

METHODS

Extracellular vesicles were stained for osteocalcin (OC), RANKL (CD254), RANK (CD265), M-CSF (macrophage colony stimulating factor), and CD34. Serum OC, procollagen type I N-terminal propeptide (P1NP), and C-terminal telopeptide of type 1 collagen (CTx) were also measured.

RESULTS

BMD significantly decreased from baseline to 12 months. Levels of OC+EVs, serum OC, serum P1NP, and CTx were significantly higher at early and late time points compared with baseline. Increases in EVs expressing OC, RANKL, RANK, and CD34 from baseline to TP1 were associated with decreases in total hip BMD from baseline to 12 months. Change in serum OC, P1NP, and CTx from baseline to TP1 or TP2 did not correlate with change in BMD.

CONCLUSION

Early changes in extracellular vesicles expressing markers of bone activity were associated with total hip bone loss 12 months after ART initiation. These data suggest that serum extracellular vesicles may serve as novel biomarkers of bone remodeling. Future studies are required to determine if extracellular vesicles contribute to the effects of ART on changes in bone turnover markers and BMD.

Clinical applications of exosome membrane proteins

Extracellular vesicles (EVs) are small membranous particles that can mediate cell-to-cell communication and which are divided into at least three categories according to their subcellular origin and size: exosomes, microvesicles, and apoptotic bodies. Exosomes are the smallest (30–150 nm) of these EVs, and play an important role in EV-mediated cell-to-cell interactions, by transferring proteins, nucleic acids and, lipids from their parental cells to adjacent or distant cells to alter their phenotypes. Most exosome studies in the past two decades have focused on their nucleic acid composition and their transfer of mRNAs and microRNAs to neighboring cells. However, exosomes also carry specific membrane proteins that can identify the physiological and pathological states of their parental cells or indicate their preferential target cells or tissues. Exosome membrane protein expression can also be directly employed or modified to allow exosomes to serve as drug delivery systems and therapeutic platforms, including in targeted therapy approaches. This review will briefly summarize information on exosome membrane proteins components and their role in exosome–cell interactions, including proteins associated with specific cell-interactions and diseases, and the potential for using exosome membrane proteins in therapeutic targeting approaches.

Lactate in Sarcoma Microenvironment: Much More than just a Waste Product

Sarcomas are rare and heterogeneous malignant tumors relatively resistant to radio- and chemotherapy. Sarcoma progression is deeply dependent on environmental conditions that sustain both cancer growth and invasive abilities. Sarcoma microenvironment is composed of different stromal cell types and extracellular proteins. In this context, cancer cells may cooperate or compete with stromal cells for metabolic nutrients to sustain their survival and to adapt to environmental changes. The strict interplay between stromal and sarcoma cells deeply affects the extracellular metabolic milieu, thus altering the behavior of both cancer cells and other non-tumor cells, including immune cells. Cancer cells are typically dependent on glucose fermentation for growth and lactate is one of the most heavily increased metabolites in the tumor bulk. Currently, lactate is no longer considered a waste product of the Warburg metabolism, but novel signaling molecules able to regulate the behavior of tumor cells, tumor-stroma interactions and the immune response. In this review, we illustrate the role of lactate in the strong acidity microenvironment of sarcoma. Really, in the biological context of sarcoma, where novel targeted therapies are needed to improve patient outcomes in combination with current therapies or as an alternative treatment, lactate targeting could be a promising approach to future clinical trials.

Extracellular Vesicles as Drug Delivery Systems - Methods of Production and Potential Therapeutic Applications

Drug delivery systems are created to achieve the desired therapeutic effect of a specific pharmaceutical compound. Numerous drawbacks and side effects such as unfavorable pharmacokinetics, lack of tissue selectivity, immunogenicity, increased systemic clearance and toxicity, have been observed for currently available drug delivery systems (DDSs). The use of natural and artificial extracellular vesicles (EVs) in drug delivery may help to solve the aforementioned problems faced by different DDSs. Due to their self-origin, small size, flexibility, the presence of multiple adhesive molecules on their surfaces as well as their function as biomolecules carriers, EVs are the perfect candidates for DDSs. Currently, several drug delivery systems based on EVs have been proposed. While the great potential of these particles in targeted drug delivery has been recognized in cancer, hepatitis C, neurodegenerative diseases, inflammatory states etc., this field is still in the early stage of development. Unfortunately, the use of EVs from natural sources (cell cultures, body fluids) results in numerous problems in terms of the heterogeneity of isolated vesicle population as well as the method of isolation thereof, which may influence vesicle composition and properties. Therefore, there is a significant need for the synthesis of artificial EV-based DDSs under strictly controlled laboratory conditions and from well-defined biomolecules (proteins and lipids). Vesicle-mimetic delivery systems, characterized by properties similar to natural EVs, will bring new opportunities to study the mechanisms of DDS internalization and their biological activity after delivering their cargo to a target cell.

Mesenchymal stromal cell-derived exosomes ameliorate peripheral neuropathy in a mouse model of diabetes

AIMS/HYPOTHESIS

Diabetic peripheral neuropathy (DPN) is one of the major complications of diabetes, which contributes greatly to morbidity and mortality. There is currently no effective treatment for this disease. Exosomes are cell-derived nanovesicles and play an important role in intercellular communications. The present study investigated whether mesenchymal stromal cell (MSC)-derived exosomes improve neurological outcomes of DPN.

METHODS

Exosomes were isolated from the medium of cultured mouse MSCs by ultracentrifugation. Diabetic mice (BKS.Cg-m+/+Lepr^db/J, db/db) at the age of 20 weeks were used as DPN models. Heterozygous mice (db/m) of the same age were used as the control. MSC-exosomes were administered weekly via the tail vein for 8 weeks. Neurological function was evaluated by testing motor and sensory nerve conduction velocities, and thermal and mechanical sensitivity. Morphometric analysis was performed by myelin sheath staining and immunohistochemistry. Macrophage markers and circulating cytokines were measured by western blot and ELISA. MicroRNA (miRNA) array and bioinformatics analyses were performed to examine the exosomal miRNA profile and miRNA putative target genes involved in DPN.

RESULTS

Treatment of DPN with MSC-exosomes markedly decreased the threshold for thermal and mechanical stimuli and increased nerve conduction velocity in diabetic mice. Histopathological analysis showed that MSC-exosomes markedly augmented the density of FITC-dextran perfused blood vessels and increased the number of intraepidermal nerve fibres (IENFs), myelin thickness and axonal diameters of sciatic nerves. Western blot analysis revealed that MSC-exosome treatment decreased and increased M1 and M2 macrophage phenotype markers, respectively. Moreover, MSC-exosomes substantially suppressed proinflammatory cytokines. Bioinformatics analysis revealed that MSC-exosomes contained abundant miRNAs that target the Toll-like receptor (TLR)4/NF-κB signalling pathway.

CONCLUSIONS/INTERPRETATION

MSC-derived exosomes alleviate neurovascular dysfunction and improve functional recovery in mice with DPN by suppression of proinflammatory genes.

Exosomes from bone marrow mesenchymal stem cells enhance fracture healing through the promotion of osteogenesis and angiogenesis in a rat model of nonunion

BACKGROUND

As important players in cell-to-cell communication, exosomes (exo) are believed to play a similar role in promoting fracture healing. This study investigated whether exosomes derived from bone marrow mesenchymal stem cells (BMMSC-Exos) could improve fracture healing of nonunion.

METHODS

BMMSC-Exos were isolated and transplanted into the fracture site in a rat model of femoral nonunion (Exo group) every week. Moreover, equal volumes of phosphate-buffered saline (PBS) and exosome-depleted conditioned medium (CM-Exo) were injected into the femoral fracture sites of the rats in the control and CM-Exo groups. Bone healing processes were recorded and evaluated by radiographic methods on weeks 8, 14 and 20 after surgery. Osteogenesis and angiogenesis at the fracture sites were evaluated by radiographic and histological methods on postoperative week 20. The expression levels of osteogenesis- or angiogenesis-related genes were evaluated in vitro by western blotting and immunohistochemistry. The ability to internalize exosomes was assessed using the PKH26 assay. Altered proliferation and migration of human umbilical vein endothelial cells (HUVECs) and mouse embryo osteoblast precursor cells (MC3TE-E1s) treated with BMMSC-Exos were determined by utilizing EdU incorporation, immunofluorescence staining, and scratch wound assay. The angiogenesis ability of HUVECs was evaluated through tube formation assays. Finally, to explore the effect of exosomes in osteogenesis via the BMP-2/Smad1/RUNX2 signalling pathway, the BMP-2 inhibitors noggin and LDN193189 were utilized, and their subsequent effects were observed.

RESULTS

BMMSC-Exos were observed to be spherical with a diameter of approximately 122 nm. CD9, CD63 and CD81 were expressed. Transplantation of BMMSC-Exos obviously enhanced osteogenesis, angiogenesis and bone healing processes in a rat model of femoral nonunion. BMMSC-Exos were taken up by HUVECs and MC3T3-E1 in vitro, and their proliferation and migration were also improved. Finally, experiments with BMP2 inhibitors confirmed that the BMP-2/Smad1/RUNX2 signalling pathway played an important role in the pro-osteogenesis induced by BMMSC-Exos and enhanced fracture healing of nonunion.

CONCLUSIONS

Our findings suggest that transplantation of BMMSC-Exos exerts a critical effect on the treatment of nonunion by promoting osteogenesis and angiogenesis. This promoting effect might be ascribed to the activation of the BMP-2/Smad1/RUNX2 and the HIF-1α/VEGF signalling pathways.

Exosomes derived from human bone marrow mesenchymal stem cells transfer miR-222-3p to suppress acute myeloid leukemia cell proliferation by targeting IRF2/INPP4B

AIM

This study aims to explore the role and mechanism of exosomes derived from human bone marrow mesenchymal stem cells (hBM-MSCs-Exo) in regulating proliferation and apoptosis of acute myeloid leukemia (AML) cell line THP-1.

METHODS

hBM-MSCs-Exo was isolated by ultra-centrifugation and administered into THP-1 cells to elucidate the effects of exosomes in THP-1 cells. Cell proliferation and apoptosis were examined by CCK-8 assay and flow cytometry, respectively. The expression of miR-222-3p, IRF2, and INPP4B were measured by qRT-PCR and western blot. The interaction between miR-222-3p and IRF2 was analyzed by luciferase reporter assay.

RESULTS

Lower cell viability rate, higher apoptosis ratio, higher miR-222-3p expression, and lower IRF1/INPP4B expression were observed in THP-1 cells exposed to BM-MSCs-Exo. The proliferation-inhibitory and pro-apoptotic effects of BM-MSCs-Exo on THP-1 cells were markedly compromised when miR-222-3p expression in BM-MSCs-Exo was inhibited. Furthermore, miR-222-3p directly targeted IRF2 and negatively regulated IRF2/INPP4B signaling in THP-1 cells. Moreover, overexpression of either IRF2 or INPP4B counteracted the proliferation-inhibitory and pro-apoptotic effects mediated by BM-MSCs-Exo.

CONCLUSION

BM-MSCs delivered miR-222-3p via exosomes to inhibit cell proliferation and promote cell apoptosis by targeting IRF2 and negatively regulating IRF2/INPP4B signaling in THP-1 cells.

Are we underutilizing bone marrow and cord blood? Review of their role and potential in the era of cellular therapies

Since the first hematopoietic stem cell transplant, over a million transplants have been performed worldwide. In the last decade, the transplant field has witnessed a progressive decline in bone marrow and cord blood utilization and a parallel increase in peripheral blood as a source of stem cells. Herein, we review the use of bone marrow and cord blood in the hematopoietic stem cell transplant setting, and we describe the recent advances made in different medical fields using cells derived from cord blood and bone marrow.

A Role for Exosomes in Craniofacial Tissue Engineering and Regeneration

Tissue engineering and regenerative medicine utilize mesenchymal stem cells (MSCs) and their secretome in efforts to create or induce functional tissue replacement. Exosomes are specific extracellular vesicles (EVs) secreted by MSCs and other cells that carry informative cargo from the MSC to targeted cells that influence fundamental cellular processes including apoptosis, proliferation, migration, and lineage-specific differentiation. In this report, we review the current knowledge regarding MSC exosome biogenesis, cargo and function. This review summarizes the use of MSC exosomes to control or induce bone, cartilage, dentin, mucosa, and pulp tissue formation. The next-step engineering of exosomes provides additional avenues to enhance oral and craniofacial tissue engineering and regeneration.

Exosomes and Bone Disease

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Exosomes, which mediate cell-to-cell communications and provide a novel insight into information exchange, have drawn increasing attention in recent years. The homeostasis of bone metabolism is critical for bone health. The most common bone diseases such as osteoporosis, osteoarthritis and bone fractures have apparent correlations with exosomes. Accumulating evidence has suggested the potential regenerative capacities of stem cell-derived exosomes. In this review, we summarise the pathophysiological mechanism, clinical picture and therapeutic effects of exosomes in bone metabolism. We introduce the advantages and challenges in the application of exosomes. Although the exact mechanisms remain unclear, miRNAs seem to play major roles in the exosome.

Methods for loading therapeutics into extracellular vesicles and generating extracellular vesicles mimetic-nanovesicles

Extracellular vesicles (EVs) are membrane bound vesicles released into the extracellular environment by eukaryotic and prokaryotic cells. EVs are enriched in active biomolecules and they can horizontally transfer cargo to recipient cells. In recent years EVs have demonstrated promising clinical applications due to their theragnostic potential. Although EVs have promising therapeutic potential, there are several challenges associated with using EVs before transition from the laboratory to clinical use. Some of these challenges include issues around low yield, isolation and purification methodologies, and efficient engineering (loading) of EVs with therapeutic cargo. Also, to achieve higher therapeutic efficiency, EV architecture and cargo may need to be manipulated prior to clinical application. Some of these issues have been addressed by developing biomimetic EVs. EV mimetic-nanovesicles (M-NVs) are a type of artificial EVs which can be generated from all cell types with comparable characteristics as EVs for an alternative therapeutic modality. In this review, we will discuss current techniques for modifying EVs and methodology used to generate and customize EV mimetic-nanovesicles.

The Development of Extracellular Vesicle-Integrated Biomaterials for Bone Regeneration

The clinical need for effective bone regeneration remains in huge demands. Although autologous and allogeneic bone grafts are generally considered "gold standard" treatments for bone defects, these approaches may result in various complications. Furthermore, safety considerations of gene- and cell-based therapies require further clarification and approval from regulatory authorities. Therefore, developing new therapeutic biomaterials that can empower endogenous regenerative properties to accelerate bone repair and regeneration is of great significance. Extracellular vesicles (EVs) comprise a heterogeneous population of naturally derived nanoparticles that play a critical role in mediating cell-cell communication. The vast amount of biological processes that EVs are involved in, such as immune modulation, senescence, and angiogenesis, and the versatility of manner in which they can influence the behavior of recipient cells make EVs an interesting source for both diagnostic and therapeutic applications. Advancement of knowledge in the fields of immunology and cell biology has sparked the exploration of the potential of EVs in the field of regenerative medicine. EVs travel between cells and deliver functional cargoes, such as proteins and RNAs, thereby regulating the recruitment, proliferation, and differentiation of recipient cells. Numerous studies have demonstrated the pivotal role of EVs in tissue regeneration both in vitro and in vivo. In this chapter, we will outline current knowledge surrounding EVs, summarize their functional roles in bone regenerative medicine, and elaborate on potential application and challenges of EV-integrated biomaterials in bone tissue engineering.

Emerging role of stem cell-derived extracellular microRNAs in age-associated human diseases and in different therapies of longevity

Organismal aging involves the progressive decline in organ function and increased susceptibility to age-associated diseases. This has been associated with the aging of stem cell populations within the body that decreases the capacity of stem cells to self-renew, differentiate, and regenerate damaged tissues and organs. This review aims to explore how aging is associated with the dysregulation of stem cell-derived extracellular vesicles (SCEVs) and their corresponding miRNA cargo (SCEV-miRNAs), which are short non-coding RNAs involved in post-transcriptional regulation of target genes. Recent evidence has suggested that in aging stem cells, SCEV-miRNAs may play a vital role regulating various processes that contribute to aging: cellular senescence, stem cell exhaustion, telomere length, and circadian rhythm. Hence, further clarifying the age-dependent molecular mechanisms through which SCEV-miRNAs exert their downstream effects may inform a greater understanding of the biology of aging, elucidate their role in stem cell function, and identify important targets for future regenerative therapies. Additionally, current studies evaluating therapeutic role of SCEVs and SCEV-miRNAs in treating several age-associated diseases are also discussed.

Applications of extracellular vesicles in tissue regeneration

Extracellular vesicles (EVs) can be classified into several types based on their different biosyntheses or release pathways, including exosomes, microvesicles, apoptotic bodies, and large oncosomes. As they contain DNAs, RNAs, proteins, and other bioactive signals, EVs have been utilized in the diagnosis field for a long time. Considering the fact that stem cells have been widely used for tissue regeneration and EVs possess similar biological properties to their source cells, tissue regeneration abilities of EVs have recently attracted much attention in the regenerative medicine field. In this paper, recent advances and challenges of EVs applied in the repair and regeneration of damaged tissues, such as skin, heart, liver, kidney, bone, and central nervous system, have been summarized. Specifically, critical bioactive molecules, which are encapsulated within EVs and play significant roles in the tissue regeneration, have been highlighted. Finally, the prospects and future development directions of the application of EVs in the field of tissue regeneration have been discussed.

Interests of Exosomes in Bone and Periodontal Regeneration: A Systematic Review

Periodontitis is an infectious inflammatory disease characterized by clinical attachment loss and tooth supporting tissue destruction. As exosomes demonstrated pro-regenerative ability, their use in periodontal treatment has been suggested. The aim of this systematic review is to gather and summarize the most recent data regarding exosomes to determine their potential impact in bone and periodontal regeneration. Electronic databases (Pubmed, Web of Science) were searched up to February 2020. Studies assessing the impact of exosomes administration in experimental bone and periodontal defects have been identified according to PRISMA guidelines. Among the 183 identified articles, 16 met the inclusion criteria and were included in this systematic review. Experimental bone defects were mainly surgically induced with a dental bur or distraction tools. All studies considered bone healing after exosomes administration as the primary outcome. Results showed that mesenchymal stem cells derived exosomes administration promoted bone healing and neovascularization. Nevertheless, a dose-effect relationship was observed. Exosomes administration appears to promote significantly the bone healing and periodontal regeneration. However, only a limited number of studies have been carried out so far and the optimized protocols in this context need to be evaluated.

Extracellular Vesicles from Mesenchymal Stem Cells as Novel Treatments for Musculoskeletal Diseases

Mesenchymal stem/stromal cells (MSCs) represent a promising therapy for musculoskeletal diseases. There is compelling evidence indicating that MSC effects are mainly mediated by paracrine mechanisms and in particular by the secretion of extracellular vesicles (EVs). Many studies have thus suggested that EVs may be an alternative to cell therapy with MSCs in tissue repair. In this review, we summarize the current understanding of MSC EVs actions in preclinical studies of (1) immune regulation and rheumatoid arthritis, (2) bone repair and bone diseases, (3) cartilage repair and osteoarthritis, (4) intervertebral disk degeneration and (5) skeletal muscle and tendon repair. We also discuss the mechanisms underlying these actions and the perspectives of MSC EVs-based strategies for future treatments of musculoskeletal disorders.

Regeneration-Related Functional Cargoes in Mesenchymal Stem Cell-Derived Small Extracellular Vesicles

Mesenchymal stem cell-derived small extracellular vesicles (MSC-sEV) are the primary effective source in stem cell-dependent regenerative medicine due to their preponderances over direct MSC implantation. An increasing number of studies have been carried out on MSC-sEV derived from different types of cells, and their function of accelerating tissue repair was proved. However, only a few researches were able to demonstrate the functional cargoes in MSC-sEV or their mechanisms in promoting tissue recovery. In this review, we present current achievements in discovering MSC-sEV-carried RNAs and proteins as promoters in tissue regeneration. Their therapeutic function includes modulating immune reactivity, promoting angiogenesis, and accelerating cell proliferation and migration through orchestrates of cell signaling pathways.

Exosomes and Extracellular RNA in Muscle and Bone Aging and Crosstalk

PURPOSE OF REVIEW

Extracellular vesicles (EV), which include exosomes and microvesicles, are membrane-bound particles shed by most cell types and are important mediators of cell-cell communication by delivering their cargo of proteins, miRNA, and mRNA to target cells and altering their function. Here, we provide an overview of what is currently known about EV composition and function in bone and muscle cells and discuss their role in mediating crosstalk between these two tissues as well as their role in musculoskeletal aging.

RECENT FINDINGS

Recent studies have shown that muscle and bone cells produce EV, whose protein, mRNA, and miRNA cargo reflects the differentiated state of the parental cells. These EV have functional effects within their respective tissues, but evidence is accumulating that they are also shed into the circulation and can have effects on distant tissues. Bone- and muscle-derived EV can alter the differentiation and function of bone and muscle cells. Many of these effects are mediated via small microRNAs that regulate target genes in recipient cells. EV-mediated signaling in muscle and bone is an exciting and emerging field. While considerable progress has been made, much is still to be discovered about the mechanisms regulating EV composition, release, uptake, and function in muscle and bone. A key challenge is to understand more precisely how exosomes function in truly physiological settings.

Mesenchymal Stromal Cell-Based Bone Regeneration Therapies: From Cell Transplantation and Tissue Engineering to Therapeutic Secretomes and Extracellular Vesicles

Effective regeneration of bone defects often presents significant challenges, particularly in patients with decreased tissue regeneration capacity due to extensive trauma, disease, and/or advanced age. A number of studies have focused on enhancing bone regeneration by applying mesenchymal stromal cells (MSCs) or MSC-based bone tissue engineering strategies. However, translation of these approaches from basic research findings to clinical use has been hampered by the limited understanding of MSC therapeutic actions and complexities, as well as costs related to the manufacturing, regulatory approval, and clinical use of living cells and engineered tissues. More recently, a shift from the view of MSCs directly contributing to tissue regeneration toward appreciating MSCs as "cell factories" that secrete a variety of bioactive molecules and extracellular vesicles with trophic and immunomodulatory activities has steered research into new MSC-based, "cell-free" therapeutic modalities. The current review recapitulates recent developments, challenges, and future perspectives of these various MSC-based bone tissue engineering and regeneration strategies.

Exosomes from conditioned media of bone marrow-derived mesenchymal stem cells promote bone regeneration by enhancing angiogenesis

Growth factors in serum-free conditioned media from human bone marrow-derived mesenchymal stem cells (MSC-CM) are known to be effective in bone regeneration. However, the secretomes in MSC-CM that act as active ingredients for bone regeneration, as well as their mechanisms, remains unclear. Exosomes, components of MSC-CM, provide the recipient cells with genetic information and enhance the recipient cellular paracrine stimulation, which contributes to tissue regeneration. We hypothesized that MSC-CM-derived exosomes (MSC-Exo) promoted bone regeneration, and that angiogenesis was a key step. Here, we prepared an MSC-Exo group, MSC-CM group, and Exo-antiVEGF group (MSC-Exo with angiogenesis inhibitor), and examined the osteogenic and angiogenic potential in MSCs. Furthermore, we used a rat model of calvaria bone defect and implanted each sample to evaluate bone formation weekly, until week 4 after treatment. Results showed that MSC-Exo enhanced cellular migration and osteogenic and angiogenic gene expression in MSCs compared to that in other groups. In vivo, early bone formation by MSC-Exo was also confirmed. Two weeks after implantation, the newly formed bone area was 31.5 ± 6.5% in the MSC-Exo group while those in the control and Exo-antiVEGF groups were 15.4 ± 4.4% and 8.7 ± 1.1%, respectively. Four weeks after implantation, differences in the area between the MSC-Exo group and the Exo-antiVEGF or control groups were further broadened. Histologically, notable accumulation of osteoblast-like cells and vascular endothelial cells was observed in the MSC-Exo group; however, fewer cells were found in the Exo-antiVEGF and control groups.

In conclusion, MSC-Exo promoted bone regeneration during early stages, as well as enhanced angiogenesis. Considering the tissue regeneration with transplanted cells and their secretomes, this study suggests that exosomes might play an important role, especially in angiogenesis.

Immunomodulatory Effects of MSCs in Bone Healing

Mesenchymal stem cells (MSCs) are capable of differentiating into multilineage cells, thus making them a significant prospect as a cell source for regenerative therapy; however, the differentiation capacity of MSCs into osteoblasts seems to not be the main mechanism responsible for the benefits associated with human mesenchymal stem cells hMSCs when used in cell therapy approaches. The process of bone fracture restoration starts with an instant inflammatory reaction, as the innate immune system responds with cytokines that enhance and activate many cell types, including MSCs, at the site of the injury. In this review, we address the influence of MSCs on the immune system in fracture repair and osteogenesis. This paradigm offers a means of distinguishing target bone diseases to be treated with MSC therapy to enhance bone repair by targeting the crosstalk between MSCs and the immune system.

Exosomes influence the behavior of human mesenchymal stem cells on titanium surfaces

Mesenchymal stem cells (MSCs) have important roles during osseointegration. This study determined (i) if MSC-derived extracellular vesicles (EVs)/exosomes can be immobilized on titanium (Ti) surfaces and influence the behavior of MSCs, (ii) if the response is differentially affected by EVs from expanded vs differentiated MSCs and (iii) if the EV protein cargos predict the functional features of the exosomes. EVs secreted by human adipose-derived MSCs were isolated by ultracentrifugation and analyzed using nanoparticle tracking analysis, Western blotting and relative quantitative mass spectrometry. Fluorescence microscopy, scanning electron microscopy, cell counting assay and quantitative polymerase chain reaction were used to analyze MSC adhesion, proliferation and differentiation. Exosome immobilization on Ti promoted MSC adhesion and spreading after 24 h and proliferation after 3 and 6 days, irrespective of whether the exosomes were obtained from expansion or differentiation conditions. Immobilized exosomes upregulated stromal cell-derived factor (SDF-1α) gene expression. Cell adhesion molecules and signaling molecules were abundant in the exosomal proteome. The predicted functions of the equally-abundant proteins in both exosome types were in line with the observed biological effects mediated by the exosomes. Thus, exosomes derived from MSCs and immobilized on Ti surfaces interact with MSCs and rapidly promote MSC adhesion and proliferation. These findings provide a novel route for modification of titanium implant surfaces.

Neurogenesis-on-Chip: Electric field modulated transdifferentiation of human mesenchymal stem cell and mouse muscle precursor cell coculture

A number of bioengineering strategies, using biophysical stimulation, are being explored to guide the human mesenchymal stem cells (hMScs) into different lineages. In this context, we have limited understanding on the transdifferentiation of matured cells to another functional-cell type, when grown with stem cells, in a constrained cellular microenvironment under biophysical stimulation. While addressing such aspects, the present work reports the influence of the electric field (EF) stimulation on the phenotypic and functionality modulation of the coculture of murine myoblasts (C2C12) with hMScs [hMSc:C2C12=1:10] in a custom designed polymethylmethacrylate (PMMA) based microfluidic device with in-built metal electrodes. The quantitative and qualitative analysis of the immunofluorescence study confirms that the cocultured cells in the conditioned medium with astrocytic feed, exhibit differentiation towards neural-committed cells under biophysical stimulation in the range of the endogenous physiological electric field strength (8 ± 0.06  mV/mm). The control experiments using similar culture protocols revealed that while C2C12 monoculture exhibited myotube-like fused structures, the hMScs exhibited the neurosphere-like clusters with SOX2, nestin, βIII-tubulin expression. The electrophysiological study indicates the significant role of intercellular calcium signalling among the differentiated cells towards transdifferentiation. Furthermore, the depolarization induced calcium influx strongly supports neural-like behaviour for the electric field stimulated cells in coculture. The intriguing results are explained in terms of the paracrine signalling among the transdifferentiated cells in the electric field stimulated cellular microenvironment. In summary, the present study establishes the potential for neurogenesis on-chip for the coculture of hMSc and C2C12 cells under tailored electric field stimulation, in vitro.

Extracellular vesicles as a novel therapeutic tool for cell-free regenerative medicine in oral rehabilitation

Oral maxillofacial defects may always lead to complicated hard and soft tissue loss, including bone, nerve, blood vessels, teeth and skin, which are difficult to restore and severely influence the life quality of patients. Extracellular vesicles (EVs), including exosomes, microvesicles and apoptotic bodies, are emerging as potential solutions for complex tissue regeneration through cell-free therapies. In this review, we highlight the functional roles of EVs in the regenerative medicine for oral maxillofacial rehabilitation, specifically bone, skin, blood vessels, peripheral nerve and tooth-related tissue regeneration. Publications were reviewed by two researchers independently basing on three databases (PubMed, MEDLINE and Web of Science), until 31 December 2018. Basing on current researches, we classified the origin of EVs for regenerative medicine into four categories: related cells in the regenerative niche, mesenchymal stem cells, immune cells and body fluids. The secretome of different cells are distinct, while the same cells secrete different EVs under varied conditions; therefore, the content profiles of EVs and regulatory mechanisms on target cells are compared and emphasised. By unravelling the regulatory mechanisms of EVs in tissue regeneration, modified cells and tailored EVs with specific target may be produced for precision medicine with high efficacy.

Stem cell derived exosomes: microRNA therapy for age-related musculoskeletal disorders

Age-associated musculoskeletal disorders (MSDs) have been historically overlooked by mainstream biopharmaceutical researchers. However, it has now been recognized that stem and progenitor cells confer innate healing capacity for the musculoskeletal system. Current evidence indicates that exosomes are particularly important in this process as they can mediate sequential and reciprocal interactions between cells to initiate and enhance healing. The present review focuses on stem cells (SCs) derived exosomes as a regenerative therapy for treatment of musculoskeletal disorders. We discuss mechanisms involving exosome-mediated transfer of RNAs and how these have been demonstrated in vitro and in vivo to affect signal transduction pathways in target cells. We envision that standardized protocols for stem cell culture as well as for the isolation and characterization of exosomes enable GMP-compliant large-scale production of SCs-derived exosomes. Hence, potential new treatment for age-related degenerative diseases can be seen in the horizon.

Human perivascular stem cell-derived extracellular vesicles mediate bone repair

The vascular wall is a source of progenitor cells that are able to induce skeletal repair, primarily by paracrine mechanisms. Here, the paracrine role of extracellular vesicles (EVs) in bone healing was investigated. First, purified human perivascular stem cells (PSCs) were observed to induce mitogenic, pro-migratory, and pro-osteogenic effects on osteoprogenitor cells while in non-contact co-culture via elaboration of EVs. PSC-derived EVs shared mitogenic, pro-migratory, and pro-osteogenic properties of their parent cell. PSC-EV effects were dependent on surface-associated tetraspanins, as demonstrated by EV trypsinization, or neutralizing antibodies for CD9 or CD81. Moreover, shRNA knockdown in recipient cells demonstrated requirement for the CD9/CD81 binding partners IGSF8 and PTGFRN for EV bioactivity. Finally, PSC-EVs stimulated bone repair, and did so via stimulation of skeletal cell proliferation, migration, and osteodifferentiation. In sum, PSC-EVs mediate the same tissue repair effects of perivascular stem cells, and represent an 'off-the-shelf' alternative for bone tissue regeneration.

Stem cell-based bone and dental regeneration: a view of microenvironmental modulation

In modern medicine, bone and dental loss and defects are common and widespread morbidities, for which regenerative therapy has shown great promise. Mesenchymal stem cells, obtained from various sources and playing an essential role in organ development and postnatal repair, have exhibited enormous potential for regenerating bone and dental tissue. Currently, mesenchymal stem cells (MSCs)-based bone and dental regeneration mainly includes two strategies: the rescue or mobilization of endogenous MSCs and the application of exogenous MSCs in cytotherapy or tissue engineering. Nevertheless, the efficacy of MSC-based regeneration is not always fulfilled, especially in diseased microenvironments. Specifically, the diseased microenvironment not only impairs the regenerative potential of resident MSCs but also controls the therapeutic efficacy of exogenous MSCs, both as donors and recipients. Accordingly, approaches targeting a diseased microenvironment have been established, including improving the diseased niche to restore endogenous MSCs, enhancing MSC resistance to a diseased microenvironment and renormalizing the microenvironment to guarantee MSC-mediated therapies. Moreover, the application of extracellular vesicles (EVs) as cell-free therapy has emerged as a promising therapeutic strategy. In this review, we summarize current knowledge regarding the tactics of MSC-based bone and dental regeneration and the decisive role of the microenvironment, emphasizing the therapeutic potential of microenvironment-targeting strategies in bone and dental regenerative medicine.

Exosomes Derived from miR-143-Overexpressing MSCs Inhibit Cell Migration and Invasion in Human Prostate Cancer by Downregulating TFF3

Exosomes are membrane-enclosed nanovesicles that shuttle active cargoes, such as mRNAs and microRNAs (miRNAs), between different cells. Mesenchymal stem cells (MSCs) are able to migrate to the tumor sites and exert complex functions over tumor progress. We investigated the effect of human bone marrow-derived MSC (BMSC)-derived exosomal miR-143 on prostate cancer. During the co-culture experiments, we disrupted exosome secretion by the inhibitor GW4869 and overexpressed exosomal miR-143 using miR-143 plasmid. miR-143 was involved in the progression of prostate cancer via trefoil factor 3 (TFF3). Moreover, miR-143 was downregulated while TFF3 was upregulated in prostate cancer cells and tissues, and miR-143 was found to specifically inhibit TFF3 expression. Human MSC-derived exosomes enriched miR-143 and transferred miR-143 to prostate cancer cells. Furthermore, elevated miR-143 or exosome-miR-143 or silencing TFF3 inhibited the expression of TFF3, proliferating cell nuclear antigen (PCNA), matrix metalloproteinase (MMP)-2, and MMP-9 and PC3 cell proliferation, migration, invasion, and tumor growth, whereas it promoted apoptosis. In conclusion, hMSC-derived exosomal miR-143 directly and negatively targets TFF3 to suppress prostate cancer.

The Role of Exosomes in Bone Remodeling: Implications for Bone Physiology and Disease

Bone remodeling represents a physiological phenomenon of continuous bone tissue renewal that requires fine orchestration of multiple cell types, which is critical for the understanding of bone disease but not yet clarified in precise detail. Exosomes, which are cell-secreted nanovesicles drawing increasing attention for their broad biosignaling functions, can shed new light on how multiple heterogeneous cells communicate for the purpose of bone remodeling. In the healthy bone, exosomes transmit signals favoring both bone synthesis and resorption, regulating the differentiation, recruitment, and activity of most cell types involved in bone remodeling and even assuming an active role in extracellular matrix mineralization. Additionally, in the ailing bone, they actively participate in pathogenic processes constituting also potential therapeutic agents and drug vectors. The present review summarizes the current knowledge on bone exosomes and bone remodeling in health and disease.

Immunoregulatory role of exosomes derived from differentiating mesenchymal stromal cells on inflammation and osteogenesis

Bone marrow-derived mesenchymal stem/stromal cells (BMSCs) can differentiate into bone-forming osteoblasts, playing a crucial role in bone regeneration. Exosomes are naturally cell-secreted nanovesicles and are lately regraded as an emerging mediator of cellular communication in physiological and pathological conditions. The present study aimed at investigating the complex cellular communications, especially those among the differentiating BMSCs, immune cells (e.g., macrophages), and newly recruited BMSCs via exosome-mediated pathways. Exosomes were first isolated from osteogenically differentiating BMSCs at various stages (Day 0, Day 3, Day 7, and Day 14, respectively). The cellular uptake of isolated exosomes was examined in macrophages and human BMSCs (hBMSCs). The exosomes collected at various osteogenic differentiation stages (0d-exo, 3d-exo, 7d-exo, and 14d-exo) had no effect on the viability of hBMSCs. The uptake of exosomes (0d-exo, 3d-exo, and 7d-exo) significantly decreased proinflammatory-gene expression and the level of an M1 phenotypic marker. Our results then revealed that 3d-exo, 7d-exo, and 14d-exo led to a remarkable increase in mesenchymal stem/stromal cell migration. In addition, 0d-exo significantly promoted the expression of early osteogenic markers, such as alkaline phosphatase and bone morphogenetic protein 2, indicating a pro-osteogenic role of hBMSC-derived exosomes. Collectively, these results suggest that exosomes derived from differentiating mesenchymal stem/stromal cells play a unique osteoimmunomodulatory role in the regulation of bone dynamics.

Dendritic cells and M2 macrophage play an important role in suppression of Th2-mediated inflammation by adipose stem cells-derived extracellular vesicles

Although stem cell-derived extracellular vesicles (EVs) have been shown to facilitate regeneration of injured tissue, there is no report that evaluates the immune-modulating effect of stem cell-derived EVs on Th2-mediated inflammation. In this study, we evaluated the immunomodulatory effects of adipose stem cells (ASCs)-derived EVs on Th2-mediated inflammation induced by Aspergillus protease antigen in lung epithelial cells. The EVs were isolated from supernatant of ASCs and the diameters of EVs were measured by using dynamic light scattering. The mice primary lung epithelial cells and mouse lung epithelial cell line (MLE12) were pre-treated with 200 ng/ml of Aspergillus protease and then treated with 1 μg/ml of ASC-derived EVs. Real time PCR was performed to determine the expression levels of eotaxin, IL-25, TGF-β, and IL-10 mRNAs after EV treatment. To evaluate the role of EVs in macrophage polarization and dendritic cells (DCs) differentiation, in vitro bone marrow-derived macrophage and DCs stimulation assay was performed. EV treatment significantly decreased the expression of eotaxin and IL-25 and increased TGF-β and IL-10 in both lung epithelial cells. EV treatment significantly increased the expression of co-stimulatory molecules such as CD40, CD80, and CD 86 in immature DCs. Furthermore, EV treatment significantly enhanced the gene expression of M2 macrophage marker such as Arg1, CCL22, IL-10, and TGF-β. In conclusion, EVs of ASCs ameliorated Th2-mediated inflammation induced by Aspergillus protease antigen through the activation of dendritic cells and M2 macrophage, accompanied by down-regulation of eotaxin and IL-25, and up-regulation of TGF-β and IL-10 in mouse lung epithelial cells.

The relationship between molecular content of mesenchymal stem cells derived exosomes and their potentials: Opening the way for exosomes based therapeutics

At least, more than half of our understanding of extracellular vesicles owes to the studies conducted over the past few years. When it became clear that the exosomes have various potentials in medicine, extensive research has focused on these potentials in a variety of areas including cancer, drug delivery and regenerative medicine. The growing understanding of molecular structure and functions of exosomes causes the vision to become brighter in the exosomes complexity, and our attitude toward these vesicles has undergone changes accordingly. Proteomic and transcriptomic studies on exosomes have highlighted their molecular diversity. In this review, we explicitly examine the exosomes composition, molecular structure and their therapeutic potentials in some diseases. Due to the very heterogeneous nature of exosomes, the process of their use as a therapeutic agent in the clinic has been challenged. We are still at the beginning of recognizing the molecular composition of exosomes and mechanisms that affect their physiology and biology. The growing trend of engineering of exosomes has shown a promising future to further utilize them in a different field. Molecular profiling of exosomes and their content for their related potentials in regenerative medicine should be done exactly for further defining a minimum content for specific therapeutic potentials.

3D Printing PLA/Gingival Stem Cells/ EVs Upregulate miR-2861 and -210 during Osteoangiogenesis Commitment

Bone tissue regeneration strategies require approaches that provide an osteogenic and angiogenic microenvironment able to drive the bone growth. Recently, the development of 3D printing biomaterials, including poly(lactide) (3D-PLA), enriched with mesenchymal stem cells (MSCs) and/or their derivatives, such as extracellular vesicles (EVs) has been achieving promising results. In this study, in vitro results showed an increased expression of osteogenic and angiogenic markers, as RUNX2, VEGFA, OPN and COL1A1 in the living construct 3D-PLA/human Gingival MSCs (hGMSCs)/EVs. Considering that EVs carry and transfer proteins, mRNA and microRNA into target cells, we evaluated miR-2861 and miR-210 expression related to osteoangiogenesis commitment. Histological examination of rats implanted with 3D-PLA/hGMSCs/EVs evidenced the activation of bone regeneration and of the vascularization process, confirmed also by MicroCT. In synthesis, an upregulation of miR-2861 and -210 other than RUNX2, VEGFA, OPN and COL1A1 was evident in cells cultured in the presence of the biomaterial and EVs. Then, these results evidenced that EVs may enhance bone regeneration in calvaria defects, in association with an enhanced vascularization offering a novel regulatory system in the osteoangiogenesis evolution. The application of new strategies to improve biomaterial engraftment is of great interest in the regenerative medicine and can represent a way to promote bone regeneration.

Fetal Dermal Mesenchymal Stem Cell-Derived Exosomes Accelerate Cutaneous Wound Healing by Activating Notch Signaling

Fetal dermal mesenchymal stem cells (FDMSCs), isolated from fetal skin, are serving as a novel MSC candidate with great potential in regenerative medicine. More recently, the paracrine actions, especially MSC-derived exosomes, are being focused on the vital role in MSC-based cellular therapy. This study was to evaluate the therapeutic potential of exosomes secreted by FDMSCs in normal wound healing. First, the in vivo study indicated that FDMSC exosomes could accelerate wound closure in a mouse full-thickness skin wound model. Then, we investigated the role of FDMSC-derived exosomes on adult dermal fibroblast (ADFs). The results demonstrated that FDMSC exosomes could induce the proliferation, migration, and secretion of ADFs. We discovered that after treatment of exosomes, the Notch signaling pathway was activated. Then, we found that in FDMSC exosomes, the ligands of the Notch pathway were undetectable expect for Jagged 1, and the results of Jagged 1 mimic by peptide and knockdown by siRNA suggested that Jagged 1 may lead the activation of the Notch signal in ADFs. Collectively, our findings indicated that the FDMSC exosomes may promote wound healing by activating the ADF cell motility and secretion ability via the Notch signaling pathway, providing new aspects for the therapeutic strategy of FDMSC-derived exosomes for the treatment of skin wounds.