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

Human placenta mesenchymal stem cells promote axon survival following optic nerve compression through activation of NF-κB pathway

Different damage factors are known to trigger cell death in the optic nerves. Use of mesenchymal stem cells is a possible treatments option for traumatic optic nerve injury due to their ability to secrete protective cytokines and recovery factors. In this study, we investigated the neuroprotective effects of human placenta-derived mesenchymal stem cells (hPMSCs) using an established optic nerve compression model and model of R28 cells that were exposed to hypoxia. Forty percent of axon death was seen in induced in vivo optic nerve injury model (p < .05), and 70% of R28 cells exposed to cobalt chloride (CoCl₂ ), leading to hypoxia, underwent apoptosis (p < .05). After intravenous injection of hPMSCs into tail vein, there was 25% improvement of axon survival in vivo (p < .05). R28 cells incubated with hPMSCs after exposure to hypoxic condition resulted in 50% increased cell survival compared with R28 cells without hPMSC exposure (p < .05), suggesting the active release of multiple factors related to cell survival. In addition, we found that Nf-κb protein mediates neuroprotection pathway via up-regulation of target proteins regulated by hPMSCs. Therefore, we assert that Nf-κb was one of the mediator proteins in a recovery pathway induced by hPMSCs. In conclusion, these indicate that transactivation of Nf-κb protein has a critical role in recovery mechanism by hPMSCs. We suggest that hPMSCs have abilities to recover neuronal damages by up-regulating the expression of genes associated with axon survival and can a better understanding of the possible role of hPMSCs in the treatment modalities of optic nerve injury.

Human amniotic epithelial cells regulate osteoblast differentiation through the secretion of TGFβ1 and microRNA-34a-5p

Since the beginning of the use of stem cells in tissue regenerative medicine, there has been a search for optimal sources of stem cells. Human amniotic epithelial cells (hAECs) are derived from human amnions, which are typically discarded as medical waste, but were recently found to include cells with trilineage differentiation potential in vitro. Previous study has focused on the osteogenic differentiation ability of hAECs as seed cells in bone regeneration; however, their paracrine effects on osteoblasts (OBs) are yet to be elucidated. In the present study, conditioned medium (CM) derived from hAECs was used to determine their paracrine effects on the human fetal OB cell line (hFOB1.19), and the potential bioactive factors involved in this process were investigated. The results suggested that hAEC-CM markedly promoted the proliferation, migration and osteogenic differentiation of hFOB1.19 cells. Expression of transforming growth factor β₁ (TGFβ₁) and microRNA 34a-5p (miR-34a-5p) were detected in hAECs. Furthermore, it was demonstrated that TGFβ₁ and miR-34a-5p stimulated the differentiation of hFOB1.19 cells, and that TGFβ₁ promoted cell migration. Moreover, the effects of hAEC-CM were downregulated following the depletion of either TGFβ₁ or miR-34a-5p. These results demonstrated that hAECs promote OB differentiation through the secretion of TGFβ₁ and miR-34a-5p, and that hAECs may be an optimal cell source in bone regenerative medicine.

Stem cell-based bone regeneration in diseased microenvironments: Challenges and solutions

Restoration of extensive bone loss and defects remain as an unfulfilled challenge in modern medicine. Given the critical contributions to bone homeostasis and diseases, mesenchymal stem cells (MSCs) have shown great promise to jumpstart and facilitate bone healing, with immense regenerative potential in both pharmacology-based endogenous MSC rescue/mobilization in skeletal diseases and emerging application of MSC transplantation in bone tissue engineering and cytotherapy. However, efficacy of MSC-based bone regeneration was not always achieved; particularly, fulfillment of MSC-mediated bone healing in diseased microenvironments of host comorbidities remains as a major challenge. Indeed, impacts of diseased microenvironments on MSC function rely not only on the dynamic regulation of resident MSCs by surrounding niche to convoy pathological signals of bone, but also on the profound interplay between transplanted MSCs and recipient components that mediates and modulates therapeutic effects on skeletal conditions. Accordingly, novel solutions have recently been developed, including improving resistance of MSCs to diseased microenvironments, recreating beneficial microenvironments to guarantee MSC-based regeneration, and usage of subcellular vesicles of MSCs in cell-free therapies. In this review, we summarize state-of-the-art knowledge regarding applications and challenges of MSC-mediated bone healing, further offering principles and effective strategies to optimize MSC-based bone regeneration in aging and diseases.

Extracellular vesicles are integral and functional components of the extracellular matrix

Extracellular vesicles (EV) are small plasma membrane-derived particles released into the extracellular space by virtually all cell types. Recently, EV have received increased interest because of their capability to carry nucleic acids, proteins, lipids and signaling molecules and to transfer their cargo into the target cells. Less attention has been paid to their role in modifying the composition of the extracellular matrix (ECM), either directly or indirectly via regulating the ability of target cells to synthesize or degrade matrix molecules. Based on recent results, EV can be considered one of the structural and functional components of the ECM that participate in matrix organization, regulation of cells within it, and in determining the physical properties of soft connective tissues, bone, cartilage and dentin. This review addresses the relevance of EV as specific modulators of the ECM, such as during the assembly and disassembly of the molecular network, signaling through the ECM and formation of niches suitable for tissue regeneration, inflammation and tumor progression. Finally, we assess the potential of these aspects of EV biology to translational medicine.

Exosomes from embryonic mesenchymal stem cells alleviate osteoarthritis through balancing synthesis and degradation of cartilage extracellular matrix

Background

Mesenchymal stem cell therapy for osteoarthritis (OA) has been widely investigated, but the mechanisms are still unclear. Exosomes that serve as carriers of genetic information have been implicated in many diseases and are known to participate in many physiological processes. Here, we investigate the therapeutic potential of exosomes from human embryonic stem cell-induced mesenchymal stem cells (ESC-MSCs) in alleviating osteoarthritis (OA).

Methods

Exosomes were harvested from conditioned culture media of ESC-MSCs by a sequential centrifugation process. Primary mouse chondrocytes treated with interleukin 1 beta (IL-1β) were used as an in vitro model to evaluate the effects of the conditioned medium with or without exosomes and titrated doses of isolated exosomes for 48 hours, prior to immunocytochemistry or western blot analysis. Destabilization of the medial meniscus (DMM) surgery was performed on the knee joints of C57BL/6 J mice as an OA model. This was followed by intra-articular injection of either ESC-MSCs or their exosomes. Cartilage destruction and matrix degradation were evaluated with histological staining and OARSI scores at the post-surgery 8 weeks.

Results

We found that intra-articular injection of ESC-MSCs alleviated cartilage destruction and matrix degradation in the DMM model. Further in vitro studies illustrated that this effect was exerted through ESC-MSC-derived exosomes. These exosomes maintained the chondrocyte phenotype by increasing collagen type II synthesis and decreasing ADAMTS5 expression in the presence of IL-1β. Immunocytochemistry revealed colocalization of the exosomes and collagen type II-positive chondrocytes. Subsequent intra-articular injection of exosomes derived from ESC-MSCs successfully impeded cartilage destruction in the DMM model.

Conclusions

The exosomes from ESC-MSCs exert a beneficial therapeutic effect on OA by balancing the synthesis and degradation of chondrocyte extracellular matrix (ECM), which in turn provides a new target for OA drug and drug-delivery system development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0632-0) contains supplementary material, which is available to authorized users.

Stem cell-derived exosomes: A promising strategy for fracture healing

OBJECTIVES

To describe the biological characteristics of exosomes and to summarize the current status of stem cell-derived exosomes on fracture healing. Meanwhile, future challenges, limitations and perspectives are also discussed.

METHODS

Search and analyze the related articles in pubmed database through the multi-combination of keywords like "stem cells","exosomes","bone regeneration" and "fracture healing".

CONCLUSION

Stem cell-derived exosome therapy for fracture healing has been enjoying popularity and is drawing increasing attention. This strategy helps to promote proliferation and migration of cells, as well as osteogenesis and angiogenesis, in the process of bone formation. Although the exact mechanisms remain elusive, exosomal miRNAs seem to play vital roles. Future studies are required to solve multiple problems before clinical application, including comprehensive and thorough understanding of exosomes, the exact roles of exosomes in regulating bone formation, and the optimal source, dose and frequency of treatment, as well as technical and safety issues. Moreover, studies based on fracture models of large animals are could offer guidance and are in demand.

Stem Cell-Derived Extracellular Vesicles as a Novel Potential Therapeutic Tool for Tissue Repair

Stem cells, with their therapeutic potential in tissue repair and regeneration, have been widely used in translational medicine. Recent evidence suggests that the beneficial effects are mediated largely by their paracrine actions rather than the engraftment and differentiation at the injured sites. Extracellular vesicles (EVs), actively released from cells, play important roles in cell‐to‐cell communication and display multiple functions in tissue regeneration. In the present report, we will briefly review the current knowledge related to the therapeutic potential of EVs, particularly stem cell or progenitor cell‐derived ones for promoting tissue repair and regeneration, and focus on the restorative properties of exosomes/microvesicles in cutaneous wound healing, bone regeneration, hindlimb ischemia, and vascular injury repair. Stem Cells Translational Medicine2017;6:1753–1758

Effect of parathyroid hormone on healing in osteoporotic fractures via a phospholipase C-independent pathway

Objective

This study was performed to investigate the effect of parathyroid hormone (PTH) on healing in osteoporotic fractures via a phospholipase C (PLC)-independent pathway and explore the mechanism of PTH-mediated bone formation.

Methods

Ninety-six 12-week-old C57BL/6J female mice underwent bilateral ovariectomy. One month later, the lower third of the femur was fractured and the mice were treated using saline, PTH(1-28), PTH(1-34), zoledronic acid (ZA), PTH(1-28)+ZA, and PTH(1-34)+ZA. The mice were killed at weeks 2 and 4 in each group. Biomechanical testing and micro-computed tomography were performed.

Results

The formation and strength of the callus increased in all but the saline group. The mice treated with PTH(1-34) showed a significantly higher ultimate bending force, bending rigidity, bone mineral density, percent bone volume, and trabecular thickness than those treated with PTH(1-28). The PTH(1-34)+ZA group demonstrated the greatest improvements in the ultimate bending force, bending rigidity, bone mineral density, and relative bone volume.

Conclusions

PTH can promote fracture healing and callus hardness in ovariectomized mice by increasing callus formation and reconstructing trabecular bone via a PLC-independent pathway. PTH combined with ZA has a cumulative effect on the healing of fractures in ovariectomized mice.

Dendritic Cell-derived Extracellular Vesicles mediate Mesenchymal Stem/Stromal Cell recruitment

Orchestration of bone repair processes requires crosstalk between different cell populations, including immune cells and mesenchymal stem/stromal cells (MSC). Extracellular vesicles (EV) as mediators of these interactions remain vastly unexplored. Here, we aimed to determine the mechanism of MSC recruitment by Dendritic Cells (DC), hypothesising that it would be mediated by EV. Primary human DC-secreted EV (DC-EV), isolated by ultracentrifugation, were characterized for their size, morphology and protein markers, indicating an enrichment in exosomes. DC-EV were readily internalized by human bone marrow-derived MSC, without impacting significantly their proliferation or influencing their osteogenic/chondrogenic differentiation. Importantly, DC-EV significantly and dose-dependently promoted MSC recruitment across a transwell system and enhanced MSC migration in a microfluidic chemotaxis assay. DC-EV content was analysed by chemokine array, indicating the presence of chemotactic mediators. Osteopontin and matrix metalloproteinase-9 were confirmed inside EV. In summary, DC-EV are naturally loaded with chemoattractants and can contribute to cell recruitment, thus inspiring the development of new tissue regeneration strategies.

Extracellular vesicles of ETV2 transfected fibroblasts stimulate endothelial cells and improve neovascularization in a murine model of hindlimb ischemia

Ischemia are common conditions related to lack of blood supply to tissues. Depending on the ischemic sites, ischemia can cause different diseases, such as hindlimb ischemia, heart infarction and stroke. This study aims to evaluate how extracellular vesicles (EVs) derived from ETV2 transfected fibroblasts affect endothelial cell proliferation and neovascularization in a murine model of hindlimb ischemia. Human fibroblasts were isolated and cultured under standard conditions and expanded to the 3th passage before use in experiments. Human fibroblasts were transduced with a viral vector containing the ETV2 gene. Transduced cells were selected by puromycin treatment. These cells were further cultured for collection of EVs, which were isolated from culture supernatant. Following co-culture with endothelial cells, EVs were evaluated for their effect on endothelial cell proliferation and were directly injected into ischemic tissues of a murine model of hindlimb ischemia. The results showed that EVs could induce endothelial cell proliferation in vitro and improved neovascularization in a murine model of hindlimb ischemia. Our results suggest that EVs derived from ETV2-transfected fibroblasts can be promising non-cellular products for the regeneration of blood vessels.

Priming Adipose Stem Cells with Tumor Necrosis Factor-Alpha Preconditioning Potentiates Their Exosome Efficacy for Bone Regeneration

Mesenchymal stem cells (MSCs) have been widely used for tissue repair and regeneration. However, the inherent drawbacks, including limited cell survival after cell transplantation, have hindered direct MSC transplantation for tissue repair and regeneration. The aim of this study was to investigate if exosomes isolated from MSCs can promote the proliferation and differentiation of human primary osteoblastic cells (HOBs) and be potentially used for bone tissue regeneration. We showed that adipose tissue-derived MSC (ASC)-derived exosomes (ASC-EXO) were able to promote the proliferation and osteogenic differentiation in HOBs; and the trophic effects of ASC-EXO on HOBs were further harnessed when ASCs were preconditioned with tumor necrosis factor-alpha (TNF-α) for 3 days, which mimics the acute inflammatory phase upon bone injury. In addition, we showed that Wnt-3a content was elevated in ASC-EXO when ASCs were preconditioned by TNF-α, and inhibiting Wnt signaling decreased the osteogenic gene expression levels in HOBs which were cultured in TNF-α preconditioned ASCs conditioned medium. In conclusion, it was demonstrated that ASC-EXO, especially primed by TNF-α preconditioning on ASCs, offer a promising approach to replace direct stem cell transplantation for bone repair and regeneration.

Concise Review: MSC-Derived Exosomes for Cell-Free Therapy

Mesenchymal stem cell transplantation is undergoing extensive evaluation as a cellular therapy in human clinical trials. Because MSCs are easily isolated and amenable to culture expansion in vitro there is a natural desire to test MSCs in many diverse clinical indications. This is exemplified by the rapidly expanding literature base that includes many in vivo animal models. More recently, MSC-derived extracellular vesicles (EVs), which include exosomes and microvesicles (MV), are being examined for their role in MSC-based cellular therapy. These vesicles are involved in cell-to-cell communication, cell signaling, and altering cell or tissue metabolism at short or long distances in the body. The exosomes and MVs can influence tissue responses to injury, infection, and disease. MSC-derived exosomes have a content that includes cytokines and growth factors, signaling lipids, mRNAs, and regulatory miRNAs. To the extent that MSC exosomes can be used for cell-free regenerative medicine, much will depend on the quality, reproducibility, and potency of their production, in the same manner that these parameters dictate the development of cell-based MSC therapies. However, the MSC exosome's contents are not static, but rather a product of the MSC tissue origin, its activities and the immediate intercellular neighbors of the MSCs. As such, the exosome content produced by MSCs appears to be altered when MSCs are cultured with tumor cells or in the in vivo tumor microenvironment. Therefore, careful attention to detail in producing MSC exosomes may provide a new therapeutic paradigm for cell-free MSC-based therapies with decreased risk. Stem Cells 2017;35:851-858.

Systemic administration of mesenchymal stem cells combined with parathyroid hormone therapy synergistically regenerates multiple rib fractures

Background

A devastating condition that leads to trauma-related morbidity, multiple rib fractures, remain a serious unmet clinical need. Systemic administration of mesenchymal stem cells (MSCs) has been shown to regenerate various tissues. We hypothesized that parathyroid hormone (PTH) therapy would enhance MSC homing and differentiation, ultimately leading to bone formation that would bridge rib fractures.

Methods

The combination of human MSCs (hMSCs) and a clinically relevant PTH dose was studied using immunosuppressed rats. Segmental defects were created in animals’ fifth and sixth ribs. The rats were divided into four groups: a negative control group, in which animals received vehicle alone; the PTH-only group, in which animals received daily subcutaneous injections of 4 μg/kg teriparatide, a pharmaceutical derivative of PTH; the hMSC-only group, in which each animal received five injections of 2 × 10⁶ hMSCs; and the hMSC + PTH group, in which animals received both treatments. Longitudinal in vivo monitoring of bone formation was performed biweekly using micro-computed tomography (μCT), followed by histological analysis.

Results

Fluorescently-dyed hMSCs were counted using confocal microscopy imaging of histological samples harvested 8 weeks after surgery. PTH significantly augmented the number of hMSCs that homed to the fracture site. Immunofluorescence of osteogenic markers, osteocalcin and bone sialoprotein, showed that PTH induced cell differentiation in both exogenously administered cells and resident cells. μCT scans revealed a significant increase in bone volume only in the hMSC + PTH group, beginning by the 4^th week after surgery. Eight weeks after surgery, 35% of ribs in the hMSC + PTH group had complete bone bridging, whereas there was complete bridging in only 6.25% of ribs (one rib) in the PTH-only group and in none of the ribs in the other groups. Based on the μCT scans, biomechanical analysis using the micro-finite element method demonstrated that the healed ribs were stiffer than intact ribs in torsion, compression, and bending simulations, as expected when examining bone callus composed of woven bone.

Conclusions

Administration of both hMSCs and PTH worked synergistically in rib fracture healing, suggesting this approach may pave the way to treat multiple rib fractures as well as additional fractures in various anatomical sites.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0502-9) contains supplementary material, which is available to authorized users.