Severe hypoxia exerts parallel and cell-specific regulation of gene expression and alternative splicing in human mesenchymal stem cells

Small extracellular vesicles from hypoxia-preconditioned bone marrow mesenchymal stem cells attenuate spinal cord injury via miR-146a-5p-mediated regulation of macrophage polarization

JOURNAL/nrgr/04.03/01300535-202410000-00027/figure1/v/2024-02-06T055622Z/r/image-tiff Spinal cord injury is a disabling condition with limited treatment options. Multiple studies have provided evidence suggesting that small extracellular vesicles (SEVs) secreted by bone marrow mesenchymal stem cells (MSCs) help mediate the beneficial effects conferred by MSC transplantation following spinal cord injury. Strikingly, hypoxia-preconditioned bone marrow mesenchymal stem cell-derived SEVs (HSEVs) exhibit increased therapeutic potency. We thus explored the role of HSEVs in macrophage immune regulation after spinal cord injury in rats and their significance in spinal cord repair. SEVs or HSEVs were isolated from bone marrow MSC supernatants by density gradient ultracentrifugation. HSEV administration to rats via tail vein injection after spinal cord injury reduced the lesion area and attenuated spinal cord inflammation. HSEVs regulate macrophage polarization towards the M2 phenotype in vivo and in vitro. MicroRNA sequencing and bioinformatics analyses of SEVs and HSEVs revealed that miR-146a-5p is a potent mediator of macrophage polarization that targets interleukin-1 receptor-associated kinase 1. Reducing miR-146a-5p expression in HSEVs partially attenuated macrophage polarization. Our data suggest that HSEVs attenuate spinal cord inflammation and injury in rats by transporting miR-146a-5p, which alters macrophage polarization. This study provides new insights into the application of HSEVs as a therapeutic tool for spinal cord injury.

Alternative pre-mRNA splicing in stem cell function and therapeutic potential: A critical review of current evidence

Alternative splicing is a crucial regulator in stem cell biology, intricately influencing the functions of various biological macromolecules, particularly pre-mRNAs and the resultant protein isoforms. This regulatory mechanism is vital in determining stem cell pluripotency, differentiation, and proliferation. Alternative splicing's role in allowing single genes to produce multiple protein isoforms facilitates the proteomic diversity that is essential for stem cells' functional complexity. This review delves into the critical impact of alternative splicing on cellular functions, focusing on its interaction with key macromolecules and how this affects cellular behavior. We critically examine how alternative splicing modulates the function and stability of pre-mRNAs, leading to diverse protein expressions that govern stem cell characteristics, including pluripotency, self-renewal, survival, proliferation, differentiation, aging, migration, somatic reprogramming, and genomic stability. Furthermore, the review discusses the therapeutic potential of targeting alternative splicing-related pathways in disease treatment, particularly focusing on the modulation of RNA and protein interactions. We address the challenges and future prospects in this field, underscoring the need for further exploration to unravel the complex interplay between alternative splicing, RNA, proteins, and stem cell behaviors, which is crucial for advancing our understanding and therapeutic approaches in regenerative medicine and disease treatment.

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

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

Hypoxic-preconditioned mesenchymal stem cell-derived small extracellular vesicles promote the recovery of spinal cord injury by affecting the phenotype of astrocytes through the miR-21/JAK2/STAT3 pathway

BACKGROUND

Secondary injury after spinal cord injury (SCI) is a major obstacle to their neurological recovery. Among them, changes in astrocyte phenotype regulate secondary injury dominated by neuroinflammation. Hypoxia-preconditioned mesenchymal stem cells (MSCs)-derived extracellular vesicle (H-EV) plays a multifaceted role in secondary injury by interacting with cellular components and signaling pathways. They possess anti-inflammatory properties, regulate oxidative stress, and modulate apoptotic pathways, promoting cell survival and reducing neuronal loss. Given the unique aspects of secondary injury, H-EV shows promise as a therapeutic approach to mitigate its devastating consequences. Our study aimed to determine whether H-EV could promote SCI repair by altering the phenotype of astrocytes.

METHODS

Rat bone marrow MSCs (BMSCs) and EVs secreted by them were extracted and characterized. After the SCI model was successfully constructed, EV and H-EV were administered into the tail vein of the rats, respectively, and then their motor function was evaluated by the Basso-Beattie-Bresnahan (BBB) score, Catwalk footprint analysis, and electrophysiological monitoring. The lesion size of the spinal cord was evaluated by hematoxylin-eosin (HE) staining. The key point was to use glial fibrillary acidic protein (GFAP) as a marker of reactive astrocytes to co-localize with A1-type marker complement C3 and A2-type marker S100A10, respectively, to observe phenotypic changes in astrocytes within tissues. The western blot (WB) of the spinal cord was also used to verify the results. We also compared the efficacy differences in apoptosis and inflammatory responses using terminal deoxynucleotidyl transferase dUTP terminal labeling (TUNEL) assay, WB, and enzyme-linked immunosorbent assay (ELISA). Experiments in vitro were also performed to verify the results. Subsequently, we performed microRNA (miRNA) sequencing analysis of EV and H-EV and carried out a series of knockdown and overexpression experiments to further validate the mechanism by which miRNA in H-EV plays a role in promoting astrocyte phenotypic changes, as well as the regulated signaling pathways, using WB both in vivo and in vitro.

RESULTS

Our findings suggest that H-EV is more effective than EV in the recovery of motor function, anti-apoptosis, and anti-inflammatory effects after SCI, both in vivo and in vitro. More importantly, H-EV promoted the conversion of A1 astrocytes into A2 astrocytes more than EV. Moreover, miR-21, which was found to be highly expressed in H-EV by miRNA sequencing results, was also demonstrated to influence changes in astrocyte phenotype through a series of knockdown and overexpression experiments. At the same time, we also found that H-EV might affect astrocyte phenotypic alterations by delivering miR-21 targeting the JAK2/STAT3 signaling pathway.

CONCLUSION

H-EV exerts neuroprotective effects by delivering miR-21 to promote astrocyte transformation from the A1 phenotype to the A2 phenotype, providing new targets and ideas for the treatment of SCI.

Hypoxic bone marrow mesenchymal stem cell exosomes promote angiogenesis and enhance endometrial injury repair through the miR-424-5p-mediated DLL4/Notch signaling pathway

Background

Currently, bone marrow mesenchymal stem cells (BMSCs) have been reported to promote endometrial regeneration in rat models of mechanically injury-induced uterine adhesions (IUAs), but the therapeutic effects and mechanisms of hypoxic BMSC-derived exosomes on IUAs have not been elucidated.

Objective

To investigate the potential mechanism by which the BMSCS-derived exosomal miR-424-5p regulates IUA angiogenesis through the DLL4/Notch signaling pathway under hypoxic conditions and promotes endometrial injury repair.

Methods

The morphology of the exosomes was observed via transmission electron microscopy, and the expression of exosome markers (CD9, CD63, CD81, and HSP70) was detected via flow cytometry and Western blotting. The expression of angiogenesis-related genes (Ang1, Flk1, Vash1, and TSP1) was detected via RT‒qPCR, and the expression of DLL4/Notch signaling pathway-related proteins (DLL4, Notch1, and Notch2) was detected via Western blotting. Cell proliferation was detected by a CCK-8 assay, and angiogenesis was assessed via an angiogenesis assay. The expression of CD3 was detected by immunofluorescence. The endometrial lesions of IUA rats were observed via HE staining, and the expression of CD3 and VEGFA was detected via immunohistochemistry.

Results

Compared with those in exosomes from normoxic conditions, miR-424-5p was more highly expressed in the exosomes from hypoxic BMSCs. Compared with those in normoxic BMSC-derived exosomes, the proliferation and angiogenesis of HUVECs were significantly enhanced after treatment with hypoxic BMSC-derived exosomes, and these effects were weakened after inhibition of miR-424-5p. miR-424-5p can target and negatively regulate the expression of DLL4, promote the expression of the proangiogenic genes Ang1 and Flk1, and inhibit the expression of the antiangiogenic genes Vash1 and TSP1. The effect of miR-424-5p can be reversed by overexpression of DLL4. In IUA rats, treatment with hypoxic BMSC exosomes and the miR-424-5p mimic promoted angiogenesis and improved endometrial damage.

Conclusion

The hypoxic BMSC-derived exosomal miR-424-5p promoted angiogenesis and improved endometrial injury repair by regulating the DLL4/Notch signaling pathway, which provides a new idea for the treatment of IUAs.

Beyond Traditional Medicine: EVs-Loaded Hydrogels as a Game Changer in Disease Therapeutics

Extracellular vesicles (EVs), especially exosomes, have shown great therapeutic potential in the treatment of diseases, as they can target cells or tissues. However, the therapeutic effect of EVs is limited due to the susceptibility of EVs to immune system clearance during transport in vivo. Hydrogels have become an ideal delivery platform for EVs due to their good biocompatibility and porous structure. This article reviews the preparation and application of EVs-loaded hydrogels as a cell-free therapy strategy in the treatment of diseases. The article also discusses the challenges and future outlook of EVs-loaded hydrogels.

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

Biomimetic synthesis and optimization of extracellular vesicles for bone regeneration

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

Hypoxia-tolerant apical-out intestinal organoids to model host-microbiome interactions

Microbiome is an integral part of the gut and is essential for its proper function. Imbalances of the microbiota can be devastating and have been linked with several gastrointestinal conditions. Current gastrointestinal models do not fully reflect the in vivo situation. Thus, it is important to establish more advanced in vitro models to study host-microbiome/pathogen interactions. Here, we developed for the first time an apical-out human small intestinal organoid model in hypoxia, where the apical surface is directly accessible and exposed to a hypoxic environment. These organoids mimic the intestinal cell composition, structure and functions and provide easy access to the apical surface. Co-cultures with the anaerobic strains Lactobacillus casei and Bifidobacterium longum showed successful colonization and probiotic benefits on the organoids. These novel hypoxia-tolerant apical-out small intestinal organoids will pave the way for unraveling unknown mechanisms related to host-microbiome interactions and serve as a tool to develop microbiome-related probiotics and therapeutics.

Human Mesenchymal Stem Cell Secretome Driven T Cell Immunomodulation Is IL-10 Dependent

The Human Mesenchymal Stem Cell (hMSC) secretome has pleiotropic effects underpinning its therapeutic potential. hMSC serum-free conditioned media (SFCM) contains a variety of cytokines, with previous studies linking a changed secretome composition to physoxia. The Jurkat T cell model allowed the efficacy of SFCM vs. serum-free media (SFM) in the suppression of immunological aspects, including proliferation and polarisation, to be explored. Cell growth in SFM was higher [(21% O2 = 5.3 × 105 ± 1.8 × 104 cells/mL) and (2% O2 = 5.1 × 105 ± 3.0 × 104 cells/mL)], compared to SFCM [(21% O2 = 2.4 × 105 ± 2.5 × 104 cells/mL) and (2% O2 = 2.2 × 105 ± 5.8 × 103 cells/mL)]. SFM supported IL-2 release following activation [(21% O2 = 5305 ± 211 pg/mL) and (2% O2 = 5347 ± 327 pg/mL)] whereas SFCM suppressed IL-2 secretion [(21% O2 = 2461 ± 178 pg/mL) and (2% O2 = 1625 ± 159 pg/mL)]. Anti-inflammatory cytokines, namely IL-4, IL-10, and IL-13, which we previously confirmed as components of hMSC SFCM, were tested. IL-10 neutralisation in SFCM restored proliferation in both oxygen environments (SFM/SFCM+antiIL-10 ~1-fold increase). Conversely, IL-4/IL-13 neutralisation showed no proliferation restoration [(SFM/SFM+antiIL-4 ~2-fold decrease), and (SFM/SFCM+antiIL-13 ~2-fold decrease)]. Present findings indicate IL-10 played an immunosuppressive role by reducing IL-2 secretion. Identification of immunosuppressive components of the hMSC secretome and a mechanistic understanding of their action allow for the advancement and refinement of potential future cell-free therapies.

Hypoxic ASCs-derived Exosomes Attenuate Colitis by Regulating Macrophage Polarization via miR-216a-5p/HMGB1 Axis

BACKGROUND

Exosomes derived from mesenchymal stem cells have shown therapeutic effects for colitis. As a more clinically accessible resource, the therapeutic potential of exosomes from adipose-derived stem cells (ASCs) has not been fully elucidated, and whether hypoxia precondition could improve the therapeutic effect of ASC-derived exosomes in colitis remains elusive.

METHODS

In this study, exosomes were derived from ASCs under normoxia (NExos) and hypoxia (HExos) and were identified by detecting their morphology, size distribution, and exosome surface markers. The concentration of inflammation-related cytokines was detected by ELISA, and macrophage phenotype-related genes were determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), western blot, and immunofluorescence. A miRNA microarray sequencing analysis was conducted to confirm the differentially expressed miRNAs. Dextran sulfate sodium-induced colitis was employed as an in vivo assay.

RESULTS

Administration of NExos alleviated inflammation by modulating the balance of macrophages both in cellular assays and in vivo experiments, and HExos showed higher therapeutic efficiency than NExos. The miR-216a-5p in HExos was significantly enriched and promoted macrophage M2 polarization through transfer to macrophages by exosomes. The miR-216a-5p was confirmed to target the 3'-UTR of HMGB1. Mechanistically, hypoxia-induced ASCs release miR-216a-5p in an exosomal way that induced macrophage M2 polarization by regulating the HMGB1/TLR4/NF-κB signaling pathway.

CONCLUSIONS

Exosomal miR-216a-5p released from hypoxia-prime ASCs showed higher therapeutic efficiency than NExos in experimental colitis by promoting the M2 macrophage phenotype, which indicated that hypoxia prime may represent a promising approach to optimizing the function of ASC-derived exosomes.

Breakthrough of extracellular vesicles in pathogenesis, diagnosis and treatment of osteoarthritis

Osteoarthritis (OA) is a highly prevalent whole-joint disease that causes disability and pain and affects a patient's quality of life. However, currently, there is a lack of effective early diagnosis and treatment. Although stem cells can promote cartilage repair and treat OA, problems such as immune rejection and tumorigenicity persist. Extracellular vesicles (EVs) can transmit genetic information from donor cells and mediate intercellular communication, which is considered a functional paracrine factor of stem cells. Increasing evidences suggest that EVs may play an essential and complex role in the pathogenesis, diagnosis, and treatment of OA. Here, we introduced the role of EVs in OA progression by influencing inflammation, metabolism, and aging. Next, we discussed EVs from the blood, synovial fluid, and joint-related cells for diagnosis. Moreover, we outlined the potential of modified and unmodified EVs and their combination with biomaterials for OA therapy. Finally, we discuss the deficiencies and put forward the prospects and challenges related to the application of EVs in the field of OA.

Exosomes secreted by hypoxia-stimulated bone-marrow mesenchymal stem cells promote grafted tendon-bone tunnel healing in rat anterior cruciate ligament reconstruction model

Background

After anterior cruciate ligament (ACL) reconstruction in clinic, firm and rapid integration of the grafted tendon into the bone tunnel remains a challenge. Exosomes from hypoxia-treated stem cells are beneficial for promoting angiogenesis and then coupling with osteogenesis. Therefore, exosomes from hypoxia-cultured bone-marrow mesenchymal stem cells (Hypo-Exos) may be a cell-free therapy for enhancing graft-bone incorporation after ACL reconstruction.

Methods

Exosomes from normoxia-cultured bone-marrow mesenchymal stem cells (Norm-Exos) or Hypo-Exos were respectively cultured with human umbilical vein endothelial cells (HUVECs) for in-vitro evaluating their functions in HUVECs proliferation, migration, and tube formation. A total of 87 rats with single-bundle ACL reconstructions in the right knee were randomly allocated into 3 different treatments: phosphate-buffered saline (PBS) with the adhesive hydrogel injection as control (Ctrl), Norm-Exos with the adhesive hydrogel injection (Norm-Exos), and Hypo-Exos with the adhesive hydrogel injection (Hypo-Exos). At postoperative weeks 2, 4, or 8, the ACL graft-bone integrations were evaluated.

Results

Hypo-Exos was a better stimulator for in-vitro HUVECs proliferation, migration, and tube formation compared to PBS or Norm-Exos. Hypo-Exos within the adhesive hydrogel could be sustained-released at least 14 days around the peri-graft site. Radiologically, at week 4 or 8, femoral or tibial bone tunnel areas (BTA), as well as bone volume/total volume ratio (BV/TV) of the femoral or tibial peri-graft bone in the Hypo-Exos group, improved significantly better than these parameters of the Ctrl and Norm-Exos groups (P<0.05 for all). Histologically, the grafted tendon-bone interface in the Hypo-Exos group showed significantly higher histologic scores at week 4 or 8 as compared with the other groups (P<0.05 for all). Immunofluorescent staining verified that type H vessels were more abundant in the Hypo-Exos group when compared to the Ctrl or Norm-Exos group at week 2. Biomechanically, the Hypo-Exos group exhibited a significantly heightened failure load compared with the Ctrl and Norm-Exos groups (P<0.05 for all) at 8 weeks. Meanwhile, the stiffness in the Hypo-Exos group was the greatest among the three groups.

Conclusion

Peri-graft Hypo-Exos injection accelerates grafted tendon-bone tunnel integration after ACL reconstruction by improving peri-graft bone microarchitecture.

Characteristics of culture-condition stimulated exosomes or their loaded hydrogels in comparison with other extracellular vesicles or MSC lysates

Recently, it has become popular to study the use of extracellular vesicles (EVs) secreted by stem cells to repair damaged tissues or lost cells. Various cell types and physiological fluids release EVs, and they play an important role in cell-to-cell communication. Moreover, EVs have been implicated in important processes, such as immune responses, homeostasis maintenance, coagulation, inflammation, cancer progression, angiogenesis, and antigen presentation. Thus, EVs participate in both physiological and pathological progression. The main classes of EVs include exosomes, microvesicles (MVs), and apoptotic bodies (ApoBDs). Exosomes, which carry a mass of signal molecules such as RNA, DNA, proteins, and lipids, are the most important of these EVs subsets. Currently, exosomes are generating substantial interest in the scientific community. Exosomes loaded hydrogels or under different cultural environments exhibit different properties and functions. Therefore, the exosomes obtained from different sources and conditions are worth reviewing. More importantly, no review article has compared the different EVs, such as exosomes, MVs, ApoBDs, and mesenchymal stem cell (MSC) lysates, which are special soluble substances. The differentiation between EVs and MSC lysates is a logical approach. Accordingly, this review provides an update on the latest progress in studying the roles of culture-condition stimulated exosomes or their loaded hydrogels and the differentiation between exosomes, MVs, ApoBDs, and MSC lysates. Published studies were retrieved from the PubMed® database for review.

Small extracellular vesicles derived from hypoxic mesenchymal stem cells promote vascularized bone regeneration through the miR-210-3p/EFNA3/PI3K pathway

Angiogenesis is closely coupled with osteogenesis and has equal importance. Thus, promoting angiogenesis during the bone repair process is vital for ideal bone regeneration. As important mediators of cell-cell communication and biological homeostasis, mesenchymal stem cell-derived small extracellular vesicles (MSC-sEVs) have been proved to be highly involved in bone and vascular regeneration. Because hypoxia microenvironment promotes the proangiogenic activity of MSCs, in the present study, we investigate the effect and underlying molecular mechanisms of sEVs from hypoxia-preconditioned MSCs (hypo-sEVs) on angiogenesis and develop an effective strategy to promote vascularized bone regeneration. Compared to sEVs from normoxia MSCs (nor-sEVs), hypo-sEVs promoted the proliferation, migration, and angiogenesis of HUVECs and ultimately enhanced bone regeneration and new blood vessel reconstruction in a critical-size calvarial bone defect model. miRNA sequence and the verified results showed that miR-210-3p in hypo-sEVs was increased via HIF-1α under hypoxia. The upregulated miR-210-3p in hypo-sEVs promoted angiogenesis by downregulating EFNA3 expression and enhancing the phosphorylation of the PI3K/AKT pathway. Thus, this study suggests a successful strategy to enhance vascularized bone regeneration by utilizing hypo-sEVs via the miR-210-3p/EFNA3/PI3K/AKT pathway. STATEMENT OF SIGNIFICANCE: Considering the significance of vascularization in ideal bone regeneration, strategies to promote angiogenesis during bone repair are required. Hypoxia microenvironment can promote the proangiogenic potential of mesenchymal stem cells (MSCs). Nonetheless, the therapeutic effect of small extracellular vesicles (sEVs) from hypoxia-preconditioned MSCs on cranio-maxillofacial bone defect remains unknown, and the underlying mechanism is poorly understood. This study shows that hypo-sEVs significantly enhance the proliferation, migration, and angiogenesis of HUVECs as well as promote vascularized bone formation. Moreover, this work indicates that HIF-1α can induce overexpression of miR-210-3p under hypoxia, and miR-210-3p can hinder EFNA3 expression and subsequently activate the PI3K/AKT pathway. The application of hypo-sEVs provides a facile and promising strategy to promote vascularized bone regeneration in a critical-size bone defect model.

Hypoxia-induced mesenchymal stem cells inhibit corneal fibroblast proliferation by regulating the WWP2/Notch1 axis

Aim: This study aimed to explore the role of hypoxic mesenchymal stem cells (MSCs) in corneal alkali burns and the underlying mechanism. Materials & methods: Rat corneal fibroblasts were incubated with IL-6, followed by treatment with hypoxic MSC supernatant. A rat corneal alkali burn model was implemented and processed with hypoxic MSCs. The associated factors were detected by corresponding methods. Results: Hypoxic MSCs reduced the Notch1 level and the proliferation of rat corneal fibroblasts. Hypoxic MSCs or WWP2 overexpression in MSCs enhanced ubiquitination of Notch1. WWP2 interacted with Notch1, and WWP2 silencing reversed the effects of the hypoxic MSCs. Hypoxic MSC treatment in vivo decreased the corneal neovascularization scores and opacity scores. Conclusion: Hypoxic MSCs inhibited inflammation and alleviated corneal injury in alkali burns via the WWP2/Notch1 axis.

Effects of BMSC-Derived EVs on Bone Metabolism

Extracellular vesicles (EVs) are small membrane vesicles that can be secreted by most cells. EVs can be released into the extracellular environment through exocytosis, transporting endogenous cargo (proteins, lipids, RNAs, etc.) to target cells and thereby triggering the release of these biomolecules and participating in various physiological and pathological processes. Among them, EVs derived from bone marrow mesenchymal stem cells (BMSC-EVs) have similar therapeutic effects to BMSCs, including repairing damaged tissues, inhibiting macrophage polarization and promoting angiogenesis. In addition, BMSC-EVs, as efficient and feasible natural nanocarriers for drug delivery, have the advantages of low immunogenicity, no ethical controversy, good stability and easy storage, thus providing a promising therapeutic strategy for many diseases. In particular, BMSC-EVs show great potential in the treatment of bone metabolic diseases. This article reviews the mechanism of BMSC-EVs in bone formation and bone resorption, which provides new insights for future research on therapeutic strategies for bone metabolic diseases.

Constructing Tissue-Engineered Dressing Membranes with Adipose-Derived Stem Cells and Acellular Dermal Matrix for Diabetic Wound Healing: A Comparative Study of Hypoxia- or Normoxia-Culture Modes

Diabetes foot ulcer (DFU) is a serious complication of diabetes, characterized by impaired vascular function, limited angiogenesis, and chronic inflammation. Direct stem cell injection on treating DFU is far from satisfactory in clinical practice, as this therapy neither protects nor localizes the injected cell suspension at the chronic ulcer site. Meanwhile, most of injected cells gradually perished within several days due to senescence or apoptosis. Acellular dermal matrix (ADM) has the potential to act as excellent cell delivery vehicles, considering it is highly biomimetic to native dermal tissue, has low immunogenicity, and suitable for stem cell attachment and proliferation. Hypoxia culture has significantly enhanced effects on the survival ability of in vitro cultured stem cells, indicating this culture mode is a suitable way for inhibiting the senescence or apoptosis of transplanted cells. In the current study, we, respectively, culture adipose-derived stem cells (ADSCs) on an ADM membrane under a hypoxia or normoxia condition to construct two kinds of tissue-engineered dressing membranes (H-ADSCs/ADM and N-ADSCs/ADM) and then comparatively evaluated their efficacy on DFU healing using a diabetic rat model. In vitro results showed that hypoxia precondition could stimulate the ADSCs secreting VEGF-A, and the culture medium from hypoxia-preconditioned ADSCs could enhance the proliferation, migration, and angiogenesis of HUVECs. In vivo results indicated that compared to the N-ADSCs/ADM membrane, the transplanted cells in the H-ADSCs/ADM membrane can survive longer at the chronic ulcer site, consequently improve angiogenesis, inhibit inflammation, and increase extracellular matrix remodeling, eventually accelerating DFU closure. This study provides an innovative covering graft for the treatment of DFU in the clinic.

Exosomes derived from hypoxia preconditioned mesenchymal stem cells laden in a silk hydrogel promote cartilage regeneration via the miR-205-5p/PTEN/AKT pathway

Tissue engineering has promising prospects for cartilage regeneration. However, there remains an urgent need to harvest high quality seed cells. Bone marrow mesenchymal cells (BMSCs), and in particular their exosomes, might promote the function of articular chondrocytes (ACs) via paracrine mechanisms. Furthermore, preconditioned BMSCs could provide an enhanced therapeutic effect. BMSCs naturally exist in a relatively hypoxic environment (1%-5% O₂); however, they are usually cultured under higher oxygen concentrations (21% O₂). Herein, we hypothesized that hypoxia preconditioned exosomes (H-Exos) could improve the quality of ACs and be more conducive to cartilage repair. In our study, we compared the effects of exosomes derived from BMSCs preconditioned with hypoxia and normoxia (N-Exos) on ACs, demonstrating that H-Exos significantly promoted the proliferation, migration, anabolism and anti-inflammation effects of ACs. Furthermore, we confirmed that hypoxia preconditioning upregulated the expression of miR-205-5p in H-Exos, suggesting that ACs were promoted via the miR-205-5p/PTEN/AKT pathway. Finally, an injectable silk fibroin (SF) hydrogel containing ACs and H-Exos (SF/ACs/H-Exos) was utilized to repair cartilage defects and effectively promote cartilage regeneration in vivo. The application of SF/ACs/H-Exos hydrogel in cartilage regeneration therefore has promising prospects. STATEMENT OF SIGNIFICANCE: Cartilage tissue engineering (CTE) has presented a promising prospect. However, the quality of seed cells is an important factor affecting the repair efficiency. Our study demonstrates for the first time that the exosomes derived from hypoxia preconditioned BMSCs (H-Exos) effectively promote the proliferation, migration and anabolism of chondrocytes and inhibit inflammation through miR-205-5p/PTEN/AKT pathway. Furthermore, we fabricated an injectable silk fibrion (SF) hydrogel to preserve and sustained release H-Exos. A complex composed of SF hydrogel, H-Exos and chondrocytes can effectively promote the regeneration of cartilage defects. Therefore, this study demonstrates that hypoxia pretreatment could optimize the therapeutic effects of BMSCs-derived exosomes, and the combination of exosomes and SF hydrogel could be a promising therapeutic method for cartilage regeneration.

The Application of Extracellular Vesicles Mediated miRNAs in Osteoarthritis: Current Knowledge and Perspective

Osteoarthritis (OA) is a whole joint disease characterized by synovitis, cartilage destruction, and subchondral bone sclerosis and cyst. Despite decades’ study, effective treatment is rare for this chronic disease. Extracellular vesicles (EVs), including exosomes, microvesicles, and apoptosis bodies, are nano-sized vesicles with a cargo containing biologically active agents, such as nucleic acids, lipids, and proteins. As a group of short non-coding RNAs, microRNAs (miRNAs) can be delivered by parental cells secreted EVs. Negatively regulate the target mRNAs at the posttranscriptional level and regulate gene expression in recipient cells without modifying gene sequence. Recently, most studies focused on the function of EVs mediated miRNAs in the pathophysiological process of OA. However, all kinds of EVs specific and OA specific factors might influence the administration of EVs-miRNAs, especially the precise quantitative management. As a result, the flourishing of current research about EVs in the laboratory might not promote the relevant clinical transformation in OA treatment. In this review, we reviewed the present application of EVs-miRNAs in the therapeutic of OA and further analyzed the potential factors that might influence its application. Further progress in the quantitative management of EVs-miRNAs would accelerate the clinical transformation of miRNAs enriched EVs in the OA field.

Extracellular vesicle-derived miR-511-3p from hypoxia preconditioned adipose mesenchymal stem cells ameliorates spinal cord injury through the TRAF6/S1P axis

Extracellular vesicle (EV) from hypoxic adipose tissue-derived mesenchymal stem cells (AD-MSCs) play critical roles in spinal cord injury (SCI) by transferring miRNAs to target cells through fusion with the cell membrane. However, the role of miR-511-3p within the AD-MSCs -derived EV in SCI is largely unknown. Western blotting results demonstrated the secretion of EVs derived from AD-MSCs under hypoxia (Hyp-EVs) was more than those under normoxia (Nor-EVs), and miR-511-3p expression was more enriched in Hyp-EVs. PC12 cells were stimulated with lipopolysaccharide (LPS) to induce cell damage. AD-MSCs were transfected with miR-511-3p mimic or miR-511-3p inhibitor to induce EVs-miR-511-3p overexpression or silencing. Cells treated with Hyp-EVs-miR-511-3p mimic reduced LPS-induced apoptosis, alleviated inflammation and promoted proliferation, while cells treated with Hyp-EVs-miR-511-3p inhibitor aggravated LPS-induced apoptosis and inflammation, and suppressed proliferation. Luciferase reporter gene assay revealed tumor necrosis factor receptor-associated factor 6 (TRAF6) was a target downstream gene of miR-511-3p. A series of gain- and loss-of-function experiments verified that TRAF6 could antagonize the effects of Hyp-EVs-miR-511-3p on inflammation, cell apoptosis and viability. Furthermore, cells treated with CYM5541, an agonist of sphingosine-1-phosphate receptor 3 (S1PR3), reversed the inhibitory effect of Hyp-EVs-miR-511-3p mimic on S1PR3 expression, inflammation and cell apoptosis. Finally, intravenously injection of Hyp-EVs-miR-511-3p mimic into SCI model rats obviously reduced inflammation and promoted neurological function recovery. In conclusion, EVs-derived miR-511-3p from hypoxia preconditioned AD-MSCs ameliorates SCI via TRAF6/S1P/NF-κB pathway, which indicates that miR-511-3p may be a potential therapeutic target for SCI.

Exosomes secreted by hypoxia-preconditioned adipose-derived mesenchymal stem cells reduce neuronal apoptosis in rats with spinal cord injury

Neuronal death is the main cause of nerve function impairment after spinal cord injury (SCI). Exosome-based therapy has become a novel strategy for tissue injury repair. We designed a method to treat SCI using exosomes secreted by adipose tissue-derived stromal cells (ADSCs) under hypoxic conditions. We established a neuronal oxygen-glucose deprivation and reperfusion (OGD/R) model in vitro to simulate the hypoxic environment after SCI. We observed that exosomes derived from hypoxia-conditioned ADSCs (Hypo-exos) significantly reduced neuronal apoptosis after OGD. By establishing a rat SCI model, we found that Hypo-exos can significantly reduce the formation of cavities in the injured area and improve the functional recovery of the hind limbs of rats after injury. To explore the molecular mechanism, we conducted miRNA sequencing analysis of exosomes. Through RT-PCR, dual luciferase reporter assays and signaling pathway chip analysis, we determined that miR-499a-5p regulates the JNK3/c-jun-apoptotic signaling pathway by targeting JNK3. Furthermore, we verified the expression of the key proteins in the JNK3/c-jun-apoptotic signaling pathway by immunofluorescence and western blotting. These results support the hypothesis that Hypo-exos can reduce neuronal apoptosis after SCI and may provide new methods to treat SCI.

Physoxia alters human mesenchymal stem cell secretome

The human mesenchymal stem cell (hMSC) secretome has pleiotropic effects which underpin their therapeutic potential. hMSC serum-free conditioned media (SFCM) has been determined to contain a variety of cytokines with roles in regeneration and suppression of inflammation. Physiological oxygen (physoxia) has been demonstrated to impact upon a number of facets of hMSC biology and we hypothesized that the secretome would be similarly modified. We tested a range of oxygen conditions; 21% O₂ (air oxygen (AO)), 2% O₂ (intermittent hypoxia (IH)) and 2% O₂ Workstation (physoxia (P)) to evaluate their effect on hMSC secretome profiles. Total protein content of secretome was upregulated in IH and P (>3 fold vs AO) and IH (>1 fold vs P). Focused cytokine profiling indicated global upregulation in IH of all 31 biomolecules tested in comparison to AO and P with basic-nerve growth factor (bNGF) and granulocyte colony-stimulating factor (GCSF) (>3 fold vs AO) and bNGF and Rantes (>3 fold vs P) of note. Similarly, upregulation of interferon gamma-induced protein 10 (IP10) was noted in P (>3 fold vs AO). Interleukin-2 (IL2) and Rantes (in AO and P) and adiponectin, IL17a, and epidermal growth factor (EGF) (in AO only) were entirely absent or below detection limits. Quantitative analysis validated the pattern of IH-induced upregulation in vascular endothelial growth factor (VEGF), placental growth factor-1 (PIGF1), Tumor necrosis factor alpha (TNFa), IL2, IL4, and IL10 when compared to AO and P. In summary, modulation of environmental oxygen alters both secretome concentration and composition. This consideration will likely impact on delivering improved mechanistic understanding and potency effects of hMSC-based therapeutics.

Secreted Protein Acidic and Cysteine Rich Matricellular Protein is Enriched in the Bioactive Fraction of the Human Vascular Pericyte Secretome

Aims: To ascertain if human pericytes produce SPARC (acronym for Secreted Protein Acidic and Cysteine Rich), a matricellular protein implicated in the regulation of cell proliferation, migration, and cell-matrix interactions; clarify if SPARC expression in cardiac pericytes is modulated by hypoxia; and determine the functional consequences of SPARC silencing. Results: Starting from the recognition that the conditioned media (CM) of human pericytes promote proliferation and migration of cardiac stromal cells, we screened candidate mediators by mass-spectrometry analysis. Of the 14 high-confidence proteins (<1% FDR) identified in the bioactive fractions of the pericyte CM, SPARC emerged as the top-scored matricellular protein. SPARC expression was validated using ELISA and found to be upregulated by hypoxia/starvation in pericytes that express platelet-derived growth factor receptor α (PDGFRα). This subfraction is acknowledged to play a key role in extracellular matrix remodeling. Studies in patients with acute myocardial infarction showed that peripheral blood SPARC correlates with the levels of creatine kinase Mb, a marker of cardiac damage. Immunohistochemistry analyses of infarcted hearts revealed that SPARC is expressed in vascular and interstitial cells. Silencing of SPARC reduced the pericyte ability to secrete collagen1a1, without inhibiting the effects of CM on cardiac and endothelial cells. These data indicate that SPARC is enriched in the bioactive fraction of the pericyte CM, is induced by hypoxia and ischemia, and is essential for pericyte ability to produce collagen. Innovation: This study newly indicates that pericytes are a source of the matricellular protein SPARC. Conclusion: Modulation of SPARC production by pericytes may have potential implications for postinfarct healing.

Exploration of Alternative Splicing Events in Mesenchymal Stem Cells from Human Induced Pluripotent Stem Cells

Although comparative genome-wide transcriptomic analysis has provided insight into the biology of human induced pluripotent stem cell-derived mesenchymal stem cells (iMSCs), the distinct alternative splicing (AS) signatures of iMSCs remain elusive. Here, we performed Illumina RNA sequencing analysis to characterize AS events in iMSCs compared with tissue-derived MSCs. A total of 4586 differentially expressed genes (|FC| > 2) were identified between iMSCs and umbilical cord blood-derived MSCs (UCB-MSCs), including 2169 upregulated and 2417 downregulated genes. Of these, 164 differentially spliced events (BF > 20) in 112 genes were identified between iMSCs and UCB-MSCs. The predominant type of AS found in iMSCs was skipped exons (43.3%), followed by retained introns (19.5%), alternative 3′ (15.2%) and 5′ (12.8%) splice sites, and mutually exclusive exons (9.1%). Functional enrichment analysis showed that the differentially spliced genes (|FC| > 2 and BF > 20) were mainly enriched in functions associated with focal adhesion, extracellular exosomes, extracellular matrix organization, cell adhesion, and actin binding. Splice isoforms of selected genes including TRPT1, CNN2, and AP1G2, identified in sashimi plots, were further validated by RT-PCR analysis. This study provides valuable insight into the biology of iMSCs and the translation of mechanistic understanding of iMSCs into therapeutic applications.

Hypoxic pretreatment of small extracellular vesicles mediates cartilage repair in osteoarthritis by delivering miR-216a-5p

Osteoarthritis (OA) is a regressive joint disease that mainly affects the cartilage and surrounding tissues. Mounting studies have confirmed that the paracrine effect is related to the potential mechanism of mesenchymal stem cell (MSC) transplantation and that small extracellular vesicles (sEVs) play an imperative role in this paracrine signaling. In fact, hypoxia can significantly improve the effectiveness of MSC transplantation in various disease models. However, it remains unknown whether MSCs in the state of a hypoxic environment can enhance OA cartilage repair and whether this enhancement is mediated by sEV signaling. The primary aim of the present study was to determine whether sEVs from MSCs in the state of hypoxia (Hypo-sEVs) have a superior effect on OA cartilage repair relative to sEVs from MSCs in the normoxia (Nor-sEVs) state. By using an OA model and performing in vitro studies, we verified that Hypo-sEV treatment facilitated the proliferation, migration, and apoptosis suppression of chondrocytes to a greater extent than Nor-sEV treatment. Furthermore, we verified the functional role of sEV miR-216a-5p in the OA cartilage repair process. We also identified JAK2 as the target gene of sEV miR-216a-5p through a series of experiments. Our findings indicated that HIF-1α induces hypoxic BMSCs to release sEVs, which promote the proliferation, migration, and apoptosis inhibition of chondrocytes through the miR-216a-5p/JAK2/STAT3 signaling pathway. Therefore, hypoxic pretreatment is a prospective and effective method to maximize the therapeutic effect of MSC-derived sEVs on OA.

Mesenchymal Stem Cell-Derived Extracellular Vesicles: Regenerative Potential and Challenges

Simple Summary

Mesenchymal stem cell extracellular vesicles (MSCEVs) obtained from MSCs can have numerous therapeutic applications via regeneration of various body tissues. There are certain approaches by which the therapeutic effect of MSCEVs can be further potentiated. Translation of MSCEVs from the preclinical to clinical level presents several challenges to investigators. Thus, knowledge of isolation, culturing, application, and various challenges faced during clinical applications of MSCEVs are the important aspects highlighted in the present review.

Abstract

Evidence suggests that stem cells exert regenerative potential via the release of extracellular vesicles. Mesenchymal stem cell extracellular vesicles (MSCEVs) offer therapeutic benefits for various pathophysiological ailments by restoring tissues. Facts suggest that MSCEV action can be potentiated by modifying the mesenchymal stem cells culturing methodology and bioengineering EVs. Limited clinical trials of MSCEVs have questioned their superiority, culturing quality, production scale-up and isolation, and administration format. Translation of preclinically successful MSCEVs into a clinical platform requires paying attention to several critical matters, such as the production technique, quantification/characterization, pharmacokinetics/targeting/transfer to the target site, and the safety profile. Keeping these issues as a priority, the present review was designed to highlight the challenges in translating preclinical MSCEV research into clinical platforms and provide evidence for the regenerative potential of MSCEVs in various conditions of the liver, kidney, heart, nervous system, bone, muscle, cartilage, and other organs/tissues.

Mechanism of mesenchymal stem cells in spinal cord injury repair through macrophage polarization

Treatment and rehabilitation of spinal cord injury (SCI) is a major problem in clinical medicine. Modern medicine has achieved minimal progress in improving the functions of injured nerves in patients with SCI, mainly due to the complex pathophysiological changes that present after injury. Inflammatory reactions occurring after SCI are related to various functions of immune cells over time at different injury sites. Macrophages are important mediators of inflammatory reactions and are divided into two different subtypes (M1 and M2), which play important roles at different times after SCI. Mesenchymal stem cells (MSCs) are characterized by multi-differentiation and immunoregulatory potentials, and different treatments can have different effects on macrophage polarization. MSC transplantation has become a promising method for eliminating nerve injury caused by SCI and can help repair injured nerve tissues. Therapeutic effects are related to the induced formation of specific immune microenvironments, caused by influencing macrophage polarization, controlling the consequences of secondary injury after SCI, and assisting with function recovery. Herein, we review the mechanisms whereby MSCs affect macrophage-induced specific immune microenvironments, and discuss potential avenues of investigation for improving SCI treatment.

Extracellular vesicles derived from mesenchymal stem cells: A platform that can be engineered

Mesenchymal stem cells play an important role in tissue damage and repair. This role is mainly due to a paracrine mechanism, and extracellular vesicles (EVs) are an important part of the paracrine function. EVs play a vital role in many aspects of cell homeostasis, physiology, and pathology, and EVs can be used as clinical biomarkers, vaccines, or drug delivery vehicles. A large number of studies have shown that EVs derived from mesenchymal stem cells (MSC-EVs) play an important role in the treatment of various diseases. However, the problems of low production, low retention rate, and poor targeting of MSC-EVs are obstacles to current clinical applications. The engineering transformation of MSC-EVs can make up for those shortcomings, thereby improving treatment efficiency. This review summarizes the latest research progress of MSC-EV direct and indirect engineering transformation from the aspects of improving MSC-EV retention rate, yield, targeting, and MSC-EV visualization research, and proposes some feasible MSC-EV engineering methods of transformation.

The influence of oxygen deprivation and donor age on the effect of statins on human mesenchymal stromal cells

To date, no study evaluated the effect of oxygen deprivation together with statins pretreatment on human mesenchymal stromal cells (MSCs). The aim of our study was to establish the influence of atorvastatin and rosuvastatin on MSC proliferation and cytotoxicity in different oxygenic conditions. Human MSCs isolated from the bone marrow (n = 12) were incubated with statins. The proliferation rate and cytotoxic effect were evaluated in normoxic (21 %O₂) and hypoxic (2%O₂) conditions, also in relation to donor age. The treatment with atorvastatin was associated with significantly higher proliferation rate compared to control, both in hypoxic (19 % median increase) and normoxic conditions (20 %), p = 0.02 and p = 0.04, respectively. Atorvastatin had no significant cytotoxic effect on MSCs. Treatment with rosuvastatin in hypoxia resulted in significantly higher proliferation rate (15 %, p = 0.02) comparing to control with no significant cytotoxicity. In atmospheric oxygen concentration, rosuvastatin was associated with no significant change in proliferation and higher cytotoxicity compared to untreated control (p = 0.042 and p = 0.015, for 0.04 μM and 1 μM solutions respectively). There were no differences in the effect of statins on MSC from young donors vs. aged donors. These results suggest that statins could support MSC-based therapy of acute myocardial infarction.

Hypoxia-induced alternative splicing: the 11th Hallmark of Cancer

Hypoxia-induced alternative splicing is a potent driving force in tumour pathogenesis and progression. In this review, we update currents concepts of hypoxia-induced alternative splicing and how it influences tumour biology. Following brief descriptions of tumour-associated hypoxia and the pre-mRNA splicing process, we review the many ways hypoxia regulates alternative splicing and how hypoxia-induced alternative splicing impacts each individual hallmark of cancer. Hypoxia-induced alternative splicing integrates chemical and cellular tumour microenvironments, underpins continuous adaptation of the tumour cellular microenvironment responsible for metastatic progression and plays clear roles in oncogene activation and autonomous tumour growth, tumor suppressor inactivation, tumour cell immortalization, angiogenesis, tumour cell evasion of programmed cell death and the anti-tumour immune response, a tumour-promoting inflammatory response, adaptive metabolic re-programming, epithelial to mesenchymal transition, invasion and genetic instability, all of which combine to promote metastatic disease. The impressive number of hypoxia-induced alternative spliced protein isoforms that characterize tumour progression, classifies hypoxia-induced alternative splicing as the 11th hallmark of cancer, and offers a fertile source of potential diagnostic/prognostic markers and therapeutic targets.

Muscleblind-like 2 controls the hypoxia response of cancer cells

Hypoxia is a hallmark of solid cancers, supporting proliferation, angiogenesis, and escape from apoptosis. There is still limited understanding of how cancer cells adapt to hypoxic conditions and survive. We analyzed transcriptome changes of human lung and breast cancer cells under chronic hypoxia. Hypoxia induced highly concordant changes in transcript abundance, but divergent splicing responses, underlining the cell type-specificity of alternative splicing programs. While RNA-binding proteins were predominantly reduced, hypoxia specifically induced muscleblind-like protein 2 (MBNL2). Strikingly, MBNL2 induction was critical for hypoxia adaptation by controlling the transcript abundance of hypoxia response genes, such as vascular endothelial growth factor A (VEGFA) MBNL2 depletion reduced the proliferation and migration of cancer cells, demonstrating an important role of MBNL2 as cancer driver. Hypoxia control is specific for MBNL2 and not shared by its paralog MBNL1. Thus, our study revealed MBNL2 as central mediator of cancer cell responses to hypoxia, regulating the expression and alternative splicing of hypoxia-induced genes.

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.

Exosome-shuttled miR-216a-5p from hypoxic preconditioned mesenchymal stem cells repair traumatic spinal cord injury by shifting microglial M1/M2 polarization

Background

Spinal cord injury (SCI) can lead to severe motor and sensory dysfunction with high disability and mortality. In recent years, mesenchymal stem cell (MSC)-secreted nano-sized exosomes have shown great potential for promoting functional behavioral recovery following SCI. However, MSCs are usually exposed to normoxia in vitro, which differs greatly from the hypoxic micro-environment in vivo. Thus, the main purpose of this study was to determine whether exosomes derived from MSCs under hypoxia (HExos) exhibit greater effects on functional behavioral recovery than those under normoxia (Exos) following SCI in mice and to seek the underlying mechanism.

Methods

Electron microscope, nanoparticle tracking analysis (NTA), and western blot were applied to characterize differences between Exos and HExos group. A SCI model in vivo and a series of in vitro experiments were performed to compare the therapeutic effects between the two groups. Next, a miRNA microarray analysis was performed and a series of rescue experiments were conducted to verify the role of hypoxic exosomal miRNA in SCI. Western blot, luciferase activity, and RNA-ChIP were used to investigate the underlying mechanisms.

Results

Our results indicate that HExos promote functional behavioral recovery by shifting microglial polarization from M1 to M2 phenotype in vivo and in vitro. A miRNA array showed miR-216a-5p to be the most enriched in HExos and potentially involved in HExos-mediated microglial polarization. TLR4 was identified as the target downstream gene of miR-216a-5p and the miR-216a-5p/TLR4 axis was confirmed by a series of gain- and loss-of-function experiments. Finally, we found that TLR4/NF-κB/PI3K/AKT signaling cascades may be involved in the modulation of microglial polarization by hypoxic exosomal miR-216a-5p.

Conclusion

Hypoxia preconditioning represents a promising and effective approach to optimize the therapeutic actions of MSC-derived exosomes and a combination of MSC-derived exosomes and miRNAs may present a minimally invasive method for treating SCI.

Hypoxic mesenchymal stem cell-derived exosomes promote bone fracture healing by the transfer of miR-126

Increasing evidence has suggested that paracrine mechanisms might be involved in the underlying mechanism of mesenchymal stem cells (MSCs) transplantation, and exosomes are an important component of this paracrine role. However, MSCs are usually exposed to normoxia (21% O₂) in vitro but experience large differences in oxygen concentration in the body under hypoxia. Indeed, hypoxic precondition of MSCs can enhance their paracrine effects. The main purpose of this study was to determine whether exosomes derived from MSCs under hypoxia (Hypo-Exos) exhibit greater effects on bone fracture healing than those under normoxia (Exos). Using in vivo bone fracture model and in vitro experiments including cell proliferation assay, cell migration assay and so on, we confirmed that Hypo-Exos administration promoted angiogenesis, proliferation and migration to a greater extent when compared to Exos. Furthermore, utilizing a series in vitro and in vivo gain and loss of function experiments, we confirmed a functional role for exosomal miR-126 in the process of bone fracture healing. Meanwhile, we found that knockdown of hypoxia inducible factor 1 (HIF-1α) resulted in a significant decrease of miR-126 in MSCs and exosomes, thereby abolishing the effects of Hypo-Exos. In conclusion, our results demonstrated a mechanism by which Hypo-Exos promote bone fracture healing through exosomal miR-126. Moreover, hypoxia preconditioning mediated enhanced production of exosomal miR-126 through the activation of HIF-1α. Hypoxia preconditioning represents an effective and promising method for the optimization of the therapeutic actions of MSC-derived exosomes for bone fracture healing. STATEMENT OF SIGNIFICANCE: Studies have confirmed that transplantation of exosomes exhibit similar therapeutic effects and functional properties to directly-transplanted stem cells but have less significant adverse effects. However, during in vitro culture conditions, MSCs are usually exposed to normoxia (21% O₂) which is very different to the oxygen concentrations found in the body under natural physiological conditions. Our results demonstrated a mechanism by which Hypo-Exos promote bone fracture healing through exosomal miR-126 and the SPRED1/Ras/Erk signaling pathway. Moreover, hypoxia preconditioning mediated enhanced production of exosomal miR-126 through the activation of HIF-1α. Hypoxia preconditioning represents an effective and promising method for the optimization of the therapeutic actions of MSC-derived exosomes for bone fracture healing.

A review on transcriptional regulation responses to hypoxia in mesenchymal stem cells

Mesenchymal stem cells (MSCs), which are known for having therapeutic applications, reside in stem cell niches where the oxygen concentration is low. At the molecular level, the master regulator of the cellular reaction to hypoxia is hypoxia-inducible transcription factor (HIF). The transcriptional response of a cell to hypoxia is affected by two major components; first, the structure of hypoxia-response elements (HREs), which primarily define how much of the HIF signal is integrated into the transcriptional output of individual genes. Second, the availability of other transcriptional factors cooperating with HIF in the context of HRE. In MSCs, the expression of a single gene by hypoxia depends on elements such as factors influencing the HIF activity, metabolic pathways, the real oxygen concentration in the cellular microenvironment, and duration of culture. In addition, specific growth factors and pro-infection cytokines, hormones, oncogenic signaling, as well as ultrasound are potent regulators of HIF in MSCs. Altogether, the response of MSCs to hypoxia is complex and mediated by several genes and molecular agents. Regarding the influence of hypoxia on MSCs, oxygen concentration must be taken into consideration based on the cell type and the aim of culture before a particular MSCs culture.

Cardioprotective microRNAs: Lessons from stem cell-derived exosomal microRNAs to treat cardiovascular disease. Atherosclerosis. 2019;285:1-9. [PMID: 30939341 DOI: 10.1016/j.atherosclerosis.2019.03.016]

The stem cell-based therapy has emerged as a promising therapeutic strategy for treating cardiovascular ischemic diseases (CVIDs), such as myocardial infarction (MI). However, some important functional shortcomings of stem cell transplantation, such as immune rejection, tumorigenicity and infusional toxicity, have overshadowed stem cell therapy in the setting of cardiovascular diseases (CVDs). Accumulating evidence suggests that the therapeutic effects of transplanted stem cells are predominately mediated by secreting paracrine factors, importantly, microRNAs (miRs) present in the secreted exosomes. Therefore, novel cell-free therapy based on the stem cell-secreted exosomal miRs can be considered as a safe and effective alternative tool to stem cell therapy for the treatment of CVDs. Stem cell-derived miRs have recently been found to transfer, via exosomes, from a transplanted stem cell into a recipient cardiac cell, where they regulate various cellular process, such as proliferation, apoptosis, stress responses, as well as differentiation and angiogenesis. The present review aimed to summarize cardioprotective exosomal miRs secreted by transplanted stem cells from various sources, including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), mesenchymal stem cells (MSCs), and cardiac stem/progenitor cells, which showed beneficial modulatory effects on the myocardial infracted heart. In summary, stem cell-exosomal miRs, including miR-19a, mirR-21, miR-21-5p, miR-21-a5p, miR-22 miR-24, miR-26a, miR-29, miR-125b-5p, miR-126, miR-201, miR-210, and miR-294, have been shown to have cardioprotective effects by enhancing cardiomyocyte survival and function and attenuating cardiac fibrosis. Additionally, MCS-exosomal miRs, including miR-126, miR-210, miR-21, miR-23a-3p and miR-130a-3p, are found to exert cardioprotective effects through induction of angiogenesis in ischemic heart after MI.

Hypoxia-Regulated miRNAs in Human Mesenchymal Stem Cells: Exploring the Regulatory Effects in Ischemic Disorders

Human mesenchymal/stromal stem cells (hMSC) are the most promising cell source for adult cell therapies in regenerative medicine. Many clinical trials have reported the use of autologous transplantation of hMSCs in several disorders, but with limited results. To exert their potential, hMSCs could exhibit efficient homing and migration toward lesion sites among other effects, but the underlying process is not clear enough. To further increase the knowledge, we studied the co-regulation between hypoxia-regulated genes and miRNAs. To this end, we investigated the miRNA expression profile of healthy hMSCs in low oxygen/nutrient conditions to mimic ischemia and compared with cells of patients suffering from critical limb ischemia (CLI). miRNAs are small, highly conserved, non-coding RNAs, skilled in the control of the target’s expression level in a fine-tuned way. After analyzing the miRNOme in CLI-derived hMSC cells and healthy controls, and intersecting the results with the mRNA expression dataset under hypoxic conditions, we identified two miRNAs potentially relevant to the disease: miR-29b as a pathological marker of the disease and miR-638 as a therapeutic target. This study yielded a deeper understanding of stem cell biology and ischemic disorders, opening new potential treatments in the future.

Hypoxic BMSC-derived exosomal miRNAs promote metastasis of lung cancer cells via STAT3-induced EMT

Background

Metastasis is the main cause of lung cancer mortality. Bone marrow-derived mesenchymal stem cells (BMSCs) are a component of the cancer microenvironment and contribute to cancer progression. Intratumoral hypoxia affects both cancer and stromal cells. Exosomes are recognized as mediators of intercellular communication. Here, we aim to further elucidate the communication between BMSC-derived exosomes and cancer cells in the hypoxic niche.

Methods

Exosomal miRNA profiling was performed using a microRNA array. Lung cancer cells and an in vivo mouse syngeneic tumor model were used to evaluate the effects of select exosomal microRNAs. Hypoxic BMSC-derived plasma exosomal miRNAs were assessed for their capacity to discriminate between cancer patients and non-cancerous controls and between cancer patients with or without metastasis.

Results

We demonstrate that exosomes derived from hypoxic BMSCs are taken by neighboring cancer cells and promote cancer cell invasion and EMT. Exosome-mediated transfer of select microRNAs, including miR-193a-3p, miR-210-3p and miR-5100, from BMSCs to epithelial cancer cells activates STAT3 signaling and increases the expression of mesenchymal related molecules. The diagnostic accuracy of individual microRNA showed that plasma exosomal miR-193a-3p can discriminate cancer patients from non-cancerous controls. A panel of these three plasma exosomal microRNAs showed a better diagnostic accuracy to discriminate lung cancer patients with or without metastasis than individual exosomal microRNA.

Conclusions

Exosome-mediated transfer of miR-193a-3p, miR-210-3p and miR-5100, could promote invasion of lung cancer cells by activating STAT3 signalling-induced EMT. These exosomal miRNAs may be promising noninvasive biomarkers for cancer progression.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-0959-5) contains supplementary material, which is available to authorized users.

The Role of Hypoxia on the Neuronal Differentiation of Gingival Mesenchymal Stem Cells: A Transcriptional Study

Mesenchymal stem cells (MSCs) are widely used in stem cell therapy for regenerative purposes. Oral-derived MSCs, such as gingival MSCs (GMSCs), deriving from the neural crest seem more suitable to differentiate toward the neuronal lineage. In addition, the preconditioning of MSCs may improve their beneficial effects. Since it is known that hypoxia may influence stem cell properties, we were interested in evaluating the effects of hypoxia preconditioning on the neuronal differentiation of GMSCs. With this aim, we evaluated the transcriptional profile of GMSCs exposed to basal and neuroinductive medium both in normoxia and in cells preconditioned for 48 h in hypoxia. We compared their transcriptional profile using Next Generation Sequencing. At first we observed that hypoxia did not alter cell morphology compared with the GMSCs cultured in a normoxic condition. In order to understand hypoxia preconditioning effects on neuronal differentiation, we screened genes with Log2 fold change ≥2 using the database Cortecon, that collects gene expression data set of in vitro corticogenesis. We observed that hypoxia preconditioning induced the expression of more genes associated with different stages of cortical development. The common genes, expressed both in normoxia and hypoxia preconditioning, were involved in developmental and neuronal processes. Interestingly, a larger number of genes associated with development biology and neuronal process was expressed in GMSCs differentiated after hypoxia preconditioning compared with those in normoxia. In addition, hypoxic-preconditioned differentiated GMSCs showed a higher expression of nestin, PAX6, and GAP43. Our data demonstrated that hypoxia preconditioning enhanced the differentiation potential of GMSCs and induced the activation of a higher number of genes associated with neuronal development. In conclusion, hypoxia may be used to improve MSCs’ properties for stem cell therapy.

Comparing atmospheric and hypoxic cultured mesenchymal stem cell transcriptome: implication for stem cell therapies targeting intervertebral discs

Background

Mesenchymal stem cells (MSCs) represent an attractive avenue for cellular therapies targeting degenerative diseases. MSC in vitro expansion is required in order to obtain therapeutic numbers during the manufacturing process. It is known that culture conditions impact cellular properties and behavior after in vivo transplantation. In this study, we aimed at evaluating the benefit of hypoxic culturing of human bone marrow derived mesenchymal stem cells on cell fitness and whole genome expression and discussed its implication on cellular therapies targeting orthopedic diseases such as chronic lower back pain.

Methods

Human bone marrow mesenchymal stem cells (hBMMSCs) were isolated from fresh human anticoagulated whole bone marrow and were cultured side by side in atmospheric (20% O₂) and hypoxic (5% O₂) oxygen partial pressure for up to 3 passages. Stem cell fitness was assessed by clonogenic assay, cell surface marker expression and differentiation potential. Whole genome expression was performed by mRNA sequencing. Data from clonogenic assays, cell surface marker by flow cytometry and gene expression by quantitative PCR were analyzed by two-tailed paired Student’s t-test. Data from mRNA sequencing were aligned to hg19 using Tophat-2.0.13 and analyzed using Cufflinks-2.1.1.

Results

Hypoxic culturing of hBMMSCs had positive effects on cell fitness, as evidenced by an increased clonogenicity and improved differentiation potential towards adipocyte and chondrocyte lineages. No difference in osteoblast differentiation or in cell surface markers were observed. Only a small subset of genes (34) were identified by mRNA sequencing to be significantly dysregulated by hypoxia. When clustered by biological function, these genes were associated with chondrogenesis and cartilage metabolism, inflammation and immunomodulation, cellular survival, migration and proliferation, vasculogenesis and angiogenesis.

Conclusions

Hypoxic culturing positively impacted hBMMSCs fitness and transcriptome, potentially improving inherent properties of these cells that are critical for the development of successful cellular therapies. Hypoxic culturing should be considered for the in vitro expansion of hBMMSCs during manufacturing of cellular therapies targeting orthopedic disorders such as lower back pain.

Necrotizing enterocolitis is associated with acute brain responses in preterm pigs

Background

Necrotizing enterocolitis (NEC) is an acute gut inflammatory disorder that occurs in preterm infants in the first weeks after birth. Infants surviving NEC often show impaired neurodevelopment. The mechanisms linking NEC lesions with later neurodevelopment are poorly understood but may include proinflammatory signaling in the immature brain. Using preterm pigs as a model for preterm infants, we hypothesized that severe intestinal NEC lesions are associated with acute effects on the developing hippocampus.

Methods

Cesarean-delivered preterm pigs (n = 117) were reared for 8 days and spontaneously developed variable severity of NEC lesions. Neonatal arousal, physical activity, and in vitro neuritogenic effects of cerebrospinal fluid (CSF) were investigated in pigs showing NEC lesions in the colon (Co-NEC) or in the small intestine (Si-NEC). Hippocampal transcriptome analysis and qPCR were used to assess gene expressions and their relation to biological processes, including neuroinflammation, and neural plasticity. Microglia activation was quantified by stereology. The neuritogenic response to selected proteins was investigated in primary cultures of hippocampal neurons.

Results

NEC development rapidly reduced the physical activity of pigs, especially when lesions occurred in the small intestine. Si-NEC and Co-NEC were associated with 27 and 12 hippocampal differentially expressed genes (DEGs), respectively. These included genes related to neuroinflammation (i.e., S100A8, S100A9, IL8, IL6, MMP8, SAA, TAGLN2) and hypoxia (i.e., PDK4, IER3, TXNIP, AGER), and they were all upregulated in Si-NEC pigs. Genes related to protection against oxidative stress (HBB, ALAS2) and oligodendrocytes (OPALIN) were downregulated in Si-NEC pigs. CSF collected from NEC pigs promoted neurite outgrowth in vitro, and the S100A9 and S100A8/S100A9 proteins may mediate the neuritogenic effects of NEC-related CSF on hippocampal neurons. NEC lesions did not affect total microglial cell number but markedly increased the proportion of Iba1-positive amoeboid microglial cells.

Conclusions

NEC lesions, especially when present in the small intestine, are associated with changes to hippocampal gene expression that potentially mediate neuroinflammation and disturbed neural circuit formation via enhanced neuronal differentiation. Early brain-protective interventions may be critical for preterm infants affected by intestinal NEC lesions to reduce their later neurological dysfunctions.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1201-x) contains supplementary material, which is available to authorized users.

Mathematical modelling of interacting mechanisms for hypoxia mediated cell cycle commitment for mesenchymal stromal cells

Background

Existing experimental data have shown hypoxia to be an important factor affecting the proliferation of mesenchymal stromal cells (MSCs), but the contrasting observations made at various hypoxic levels raise the questions of whether hypoxia accelerates proliferation, and how. On the other hand, in order to meet the increasing demand of MSCs, an optimised bioreactor control strategy is needed to enhance in vitro production.

Results

A comprehensive, single-cell mathematical model has been constructed in this work, which combines cellular oxygen sensing with hypoxia-mediated cell cycle progression to predict cell cycle commitment as a proxy to proliferation rate. With oxygen levels defined for in vitro cell culture, the model predicts enhanced proliferation under intermediate (2–8%) and mild (8–15%) hypoxia and cell quiescence under severe (< 2%) hypoxia. Global sensitivity analysis and quasi-Monte Carlo simulation revealed that within a certain range (+/− 100%), model parameters affect (with varying significance) the minimum commitment time, but the existence of a range of optimal oxygen tension could be preserved with the hypothesized effects of Hif2α and reactive oxygen species (ROS). It appears that Hif2α counteracts Hif1α and ROS-mediated protein deactivation under intermediate hypoxia and normoxia (20%), respectively, to regulate the response of cell cycle commitment to oxygen tension.

Conclusion

Overall, this modelling study offered an integrative framework to capture several interacting mechanisms and allowed in silico analysis of their individual and collective roles in shaping the hypoxia-mediated commitment to cell cycle. The model offers a starting point to the establishment of a suitable mechanism that can satisfactorily explain the different existing experimental observations from different studies, and warrants future extension and dedicated experimental validation to eventually support bioreactor optimisation.

Electronic supplementary material

The online version of this article (10.1186/s12918-018-0560-3) contains supplementary material, which is available to authorized users.

Hypoxia stimulates microenvironment in human embryonic stem cell through inflammatory signalling: An integrative analysis

Despite, several lines of evidence suggesting the possible role of hypoxia in stem cell development and differentiation its significance in conferring the stemness and pluripotency remains elusive. In the present study we sought to delineate the candidate genes and molecular pathways imposed during hypoxic microenvironment and its physiological relevance in tipping the balance between the niche and cellular differentiation. Integrated meta-analysis was performed between the hypoxia exposed and normal human embryonic stem cells, employing three transcriptomic cohorts (GSE35819, GSE9510 and GSE37761) retrieved from Gene expression omnibus (GEO) database. Results reveal that a total number of 12 genes were consistently differentially expressed (6up regulated and 6 down regulated) with FDR <0.05 and fold change >1.5. The Gene Ontology (GO) functions and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis was performed using DAVID. The GO analysis showed DEG significantly enriched in terms of Cellular process (GO:0009987), protein binding (GO:0005515) and cell part (GO:0044464). KEGG analysis indicated participation of genes associated with circadian rthyum regulation and PPAR signalling pathway. Further, gene-set signature (MsigDB) enrichment analysis showed positive regulation with inflammatory signals and negative association with PPAR and p53 pathway. Protein-protein network of gene modules suggests significant hub proteins viz. CTTNB1 (Degree = 18), IL8 (Degree = 15), NFKB1 (Degree = 15) and RELA (Degree = 15) in the PPI network. MCODE algorithm was used for subnetworks of the PPI network. Our integrative analysis documents the potential candidate genes which serves distinct roles influencing metabolic shift and induce inflammatory effectors contributing to hypoxic mediated stem cell niche.

Concise Review: Optimized Strategies for Stem Cell-Based Therapy in Myocardial Repair: Clinical Translatability and Potential Limitation

Ischemic heart diseases (IHDs) remain major public health problems with high rates of morbidity and mortality worldwide. Despite significant advances, current therapeutic approaches are unable to rescue the extensive and irreversible loss of cardiomyocytes caused by severe ischemia. Over the past 16 years, stem cell-based therapy has been recognized as an innovative strategy for cardiac repair/regeneration and functional recovery after IHDs. Although substantial preclinical animal studies using a variety of stem/progenitor cells have shown promising results, there is a tremendous degree of skepticism in the clinical community as many stem cell trials do not confer any beneficial effects. How to accelerate stem cell-based therapy toward successful clinical application attracts considerate attention. However, many important issues need to be fully addressed. In this Review, we have described and compared the effects of different types of stem cells with their dose, delivery routes, and timing that have been routinely tested in recent preclinical and clinical findings. We have also discussed the potential mechanisms of action of stem cells, and explored the role and underlying regulatory components of stem cell-derived secretomes/exosomes in myocardial repair. Furthermore, we have critically reviewed the different strategies for optimizing both donor stem cells and the target cardiac microenvironments to enhance the engraftment and efficacy of stem cells, highlighting their clinical translatability and potential limitation. Stem Cells 2018;36:482-500.

Myocardial reparative functions of exosomes from mesenchymal stem cells are enhanced by hypoxia treatment of the cells via transferring microRNA-210 in an nSMase2-dependent way

Hypoxia treatment enhances paracrine effect of mesenchymal stem cells (MSCs). The aim of this study was to investigate whether exosomes from hypoxia-treated MSCs (Exo^H) are superior to those from normoxia-treated MSCs (Exo^N) for myocardial repair. Mouse bone marrow-derived MSCs were cultured under hypoxia or normoxia for 24 h, and exosomes from conditioned media were intramyocardially injected into infarcted heart of C57BL/6 mouse. Exo^H resulted in significantly higher survival, smaller scar size and better cardiac functions recovery. Exo^H conferred increased vascular density, lower cardiomyocytes (CMs) apoptosis, reduced fibrosis and increased recruitment of cardiac progenitor cells in the infarcted heart relative to Exo^N. MicroRNA analysis revealed significantly higher levels of microRNA-210 (miR-210) in Exo^H compared with Exo^N. Transfection of a miR-210 mimic into endothelial cells (ECs) and CMs conferred similar biological effects as Exo^H. Hypoxia treatment of MSCs increased the expression of neutral sphingomyelinase 2 (nSMase2) which is crucial for exosome secretion. Blocking the activity of nSMase2 resulted in reduced miR-210 secretion and abrogated the beneficial effects of Exo^H. In conclusion, hypoxic culture augments miR-210 and nSMase2 activities in MSCs and their secreted exosomes, and this is responsible at least in part for the enhanced cardioprotective actions of exosomes derived from hypoxia-treated cells.

Protein profiling and angiogenic effect of hypoxia-cultured human umbilical cord blood-derived mesenchymal stem cells in hindlimb ischemia

The aim of the present study was to investigate protein profiles of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) cultured in normoxic (21% O₂) and hypoxic (1% O₂) conditions, and evaluate oxygenation effects on angiogenesis in an ischemic hindlimb mouse model using a modified ischemic scoring system. Hypoxic conditions did not change the expression of phenotypic markers and increased adipogenesis and chondrogenesis. Epidermal growth factor (EGF), transforming growth factor alpha (TGF-α), TGF-β RII, and vascular endothelial growth factor (VEGF) were upregulated in the conditioned medium of hypoxic hUCB-MSCs, which are commonly related to angiogenesis and proliferation of biological processes by Gene Ontology. In the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, significant enrichment of the phosphorylation of abelson murine leukemia viral oncogene homolog 1 (ABL1) (Phospho-Tyr204) and B-cell lymphoma-extra large (BCL-XL) (Phospho-Thr47) as anti-apoptotic pathways was observed in hypoxic hUCB-MSCs. Furthermore, hypoxic conditions induced proliferation and migration, and reduced apoptosis of hUCB-MSCs in vitro. Based on the results of protein antibody array, we evaluated the angiogenic effects of injecting normoxic or hypoxic hUCB-MSCs (1×10⁶) into the ischemic hindlimb muscles of mice. Ischemic scores and capillary generation were significantly greater in the hypoxic hUCB-MSC injection group than in the normoxic hUCB-MSC group. Our findings demonstrate that culturing hUCB-MSCs in hypoxic conditions not only significantly enriches phosphorylation in the anti-apoptosis pathway and enhances the secretion of several angiogenic proteins from cells, but also alleviates ischemic injury of hindlimb of mice.

Hypoxic Stress Decreases c-Myc Protein Stability in Cardiac Progenitor Cells Inducing Quiescence and Compromising Their Proliferative and Vasculogenic Potential

Cardiac progenitor cells (CPCs) have been shown to promote cardiac regeneration and improve heart function. However, evidence suggests that their regenerative capacity may be limited in conditions of severe hypoxia. Elucidating the mechanisms involved in CPC protection against hypoxic stress is essential to maximize their cardioprotective and therapeutic potential. We investigated the effects of hypoxic stress on CPCs and found significant reduction in proliferation and impairment of vasculogenesis, which were associated with induction of quiescence, as indicated by accumulation of cells in the G0-phase of the cell cycle and growth recovery when cells were returned to normoxia. Induction of quiescence was associated with a decrease in the expression of c-Myc through mechanisms involving protein degradation and upregulation of p21. Inhibition of c-Myc mimicked the effects of severe hypoxia on CPC proliferation, also triggering quiescence. Surprisingly, these effects did not involve changes in p21 expression, indicating that other hypoxia-activated factors may induce p21 in CPCs. Our results suggest that hypoxic stress compromises CPC function by inducing quiescence in part through downregulation of c-Myc. In addition, we found that c-Myc is required to preserve CPC growth, suggesting that modulation of pathways downstream of it may re-activate CPC regenerative potential under ischemic conditions.