Molecular signatures of mesenchymal stem cell-derived extracellular vesicle-mediated tissue repair

Understanding molecular characteristics of extracellular vesicles derived from different types of mesenchymal stem cells for therapeutic translation

Mesenchymal stem cells (MSCs) have been studied for decades as candidates for cellular therapy, and their secretome, including secreted extracellular vesicles (EVs), has been identified to contribute significantly to regenerative and reparative functions. Emerging evidence has suggested that MSC-EVs alone, could be used as therapeutics that emulate the biological function of MSCs. However, just as with MSCs, MSC-EVs have been shown to vary in composition, depending on the tissue source of the MSCs as well as the protocols employed in culturing the MSCs and obtaining the EVs. Therefore, the importance of careful choice of cell sources and culture environments is receiving increasing attention. Many factors contribute to the therapeutic potential of MSC-EVs, including the source tissue, isolation technique, and culturing conditions. This review illustrates the molecular landscape of EVs derived from different types of MSC cells along with culture strategies. A thorough analysis of publicly available omic datasets was performed to advance the precision understanding of MSC-EVs with unique tissue source-dependent molecular characteristics. The tissue-specific protein and miRNA-driven Reactome ontology analysis was used to reveal distinct patterns of top Reactome ontology pathways across adipose, bone marrow, and umbilical MSC-EVs. Moreover, a meta-analysis assisted by an AI technique was used to analyze the published literature, providing insights into the therapeutic translation of MSC-EVs based on their source tissues.

miRNA profiling of B16F10 melanoma cell exosomes reveals melanin synthesis-related genes

This study investigates the communication between skin cells, specifically melanocytes, keratinocytes, and fibroblasts, which is crucial for the process of melanin production known as melanogenesis. We aimed to understand the role of melanocyte exosomes in regulating melanogenesis and to uncover the microRNAs influencing this process. We isolated exosomes and characterized them using advanced microscopy and protein analysis to achieve this. We conducted experiments on melanoma cells to study melanin production regulation and examined how exosomes influenced gene expression related to melanogenesis. The results revealed that melanocyte exosomes increased certain types of tyrosinases, thereby enhancing melanin production. Furthermore, we acquired the miRNA profile of exosomes and hypothesized that specific siRNAs, such as miR-21a-5p, could potentially facilitate melanin synthesis. Our findings shed light on the importance of exosomes in skin health and provide valuable insights into intercellular communication mechanisms. Understanding these processes can pave the way for innovative therapies to treat melanin-related disorders and maintain healthy skin.

Mesenchymal stem cells and their derived exosomes for the treatment of COVID-19

Coronavirus disease 2019 (COVID-19) is an acute respiratory infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 infection typically presents with fever and respiratory symptoms, which can progress to severe respiratory distress syndrome and multiple organ failure. In severe cases, these complications may even lead to death. One of the causes of COVID-19 deaths is the cytokine storm caused by an overactive immune response. Therefore, suppressing the overactive immune response may be an effective strategy for treating COVID-19. Mesenchymal stem cells (MSCs) and their derived exosomes (MSCs-Exo) have potent homing abilities, immunomodulatory functions, regenerative repair, and antifibrotic effects, promising an effective tool in treating COVID-19. In this paper, we review the main mechanisms and potential roles of MSCs and MSCs-Exo in treating COVID-19. We also summarize relevant recent clinical trials, including the source of cells, the dosage and the efficacy, and the clinical value and problems in this field, providing more theoretical references for the clinical use of MSCs and MSCs-Exo in the treatment of COVID-19.

Efficient preparation of high-purity and intact mesenchymal stem cell-derived extracellular vesicles

Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have shown great promise for regeneration and immunomodulation. However, efficient and scalable methods for their preparation are still lacking. In this study, we present the adoption of a label-free technique known as "EXODUS" to isolate and purify MSC-EVs from the conditioned medium. Our findings indicate that EXODUS can rapidly isolate EVs from 10 mL of conditioned medium with a 5-fold higher yield compared to conventional approaches, including ultracentrifugation (UC) and polyethylene glycol precipitation (PEG) methods. Additionally, pre-storing the conditioned medium at 4°C for 1 week resulted in a ~2-fold higher yield of MSC-EVs compared to the freshly prepared medium. However, storing the purified EV particles at 4°C for 1 month led to a 2-fold reduction in particle concentration. Furthermore, we found that MSC-EVs isolated using EXODUS exhibit higher expression levels of EV markers such as Alix, Flotillin1, CD81, and TSG101 in comparison to PEG and UC methods. We also discovered that MSC-EVs isolated using EXODUS are enriched in response to cytokine, collagen-containing extracellular matrix, and calcium ion binding compared to PEG method and enriched in extracellular structure organization, extracellular matrix, and extracellular matrix structure constituents compared to UC. Finally, we demonstrated that MSC-EVs isolated using EXODUS exhibit greater potential in animal organ development, tissue development, and anatomical structure morphogenesis compared to the UC. These findings suggest that EXODUS is a suitable method for the large-scale preparation of high-quality MSC-EVs for various clinical applications.

Osteogenic human MSC-derived extracellular vesicles regulate MSC activity and osteogenic differentiation and promote bone regeneration in a rat calvarial defect model

BACKGROUND

There is growing evidence that extracellular vesicles (EVs) play a crucial role in the paracrine mechanisms of transplanted human mesenchymal stem cells (hMSCs). Little is known, however, about the influence of microenvironmental stimuli on the osteogenic effects of EVs. This study aimed to investigate the properties and functions of EVs derived from undifferentiated hMSC (Naïve-EVs) and hMSC during the early stage of osteogenesis (Osteo-EVs). A further aim was to assess the osteoinductive potential of Osteo-EVs for bone regeneration in rat calvarial defects.

METHODS

EVs from both groups were isolated using size-exclusion chromatography and characterized by size distribution, morphology, flow cytometry analysis and proteome profiling. The effects of EVs (10 µg/ml) on the proliferation, migration, and osteogenic differentiation of cultured hMSC were evaluated. Osteo-EVs (50 µg) or serum-free medium (SFM, control) were combined with collagen membrane scaffold (MEM) to repair critical-sized calvarial bone defects in male Lewis rats and the efficacy was assessed using µCT, histology and histomorphometry.

RESULTS

Although Osteo- and Naïve-EVs have similar characteristics, proteomic analysis revealed an enrichment of bone-related proteins in Osteo-EVs. Both groups enhance cultured hMSC proliferation and migration, but Osteo-EVs demonstrate greater efficacy in promoting in vitro osteogenic differentiation, as evidenced by increased expression of osteogenesis-related genes, and higher calcium deposition. In rat calvarial defects, MEM with Osteo-EVs led to greater and more consistent bone regeneration than MEM loaded with SFM.

CONCLUSIONS

This study discloses differences in the protein profile and functional effects of EVs obtained from naïve hMSC and hMSC during the early stage of osteogenesis, using different methods. The significant protein profile and cellular function of EVs derived from hMSC during the early stage of osteogenesis were further verified by a calvarial bone defect model, emphasizing the importance of using differentiated MSC to produce EVs for bone therapeutics.

Extracellular vesicles: powerful candidates in nano-drug delivery systems

Extracellular vesicles (EVs), which are nanoparticles that are actively released by cells, contain a variety of biologically active substances, serve as significant mediators of intercellular communication, and participate in many processes, in health and pathologically. Compared with traditional nanodrug delivery systems (NDDSs), EVs have unique advantages due to their natural physiological properties, such as their biocompatibility, stability, ability to cross barriers, and inherent homing properties. A growing number of studies have reported that EVs deliver therapeutic proteins, small-molecule drugs, siRNAs, miRNAs, therapeutic proteins, and nanomaterials for targeted therapy in various diseases. However, due to the lack of standardized techniques for isolating, quantifying, and characterizing EVs; lower-than-anticipated drug loading efficiency; insufficient clinical production; and potential safety concerns, the practical application of EVs still faces many challenges. Here, we systematically review the current commonly used methods for isolating EVs, summarize the types and methods of loading therapeutic drugs into EVs, and discuss the latest progress in applying EVs as NDDs. Finally, we present the challenges that hinder the clinical application of EVs.

Pharmacological Agents and Potential New Therapies in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by an imbalance between vasoactive mediators, which causes vascular remodeling, increased pulmonary vascular resistance, and right ventricular overload, ultimately leading to heart failure and death. A metabolic theory has been suggested to explain the pathophysiology of PAH whereby abnormalities in mitochondrial biogenesis can trigger a hyperproliferative and apoptosis-resistant phenotype in cardiopulmonary and malignant cells, leading to mitochondrial dysfunction, which in turn causes the Warburg effect. This can culminate in the mitophagy of pulmonary vessels and cardiomyocytes. The present narrative review focuses on the pathophysiology of PAH, the pharmacological agents currently available for its treatment, and promising and challenging areas of therapeutic investigation.

The Application of MicroRNAs in Glaucoma Research: A Bibliometric and Visualized Analysis

Glaucoma is similar to a neurodegenerative disorder and leads to global irreversible loss of vision. Despite extensive research, the pathophysiological mechanisms of glaucoma remain unclear, and no complete cure has yet been identified for glaucoma. Recent studies have shown that microRNAs can serve as diagnostic biomarkers or therapeutic targets for glaucoma; however, there are few bibliometric studies that focus on using microRNAs in glaucoma research. Here, we have adopted a bibliometric analysis in the field of microRNAs in glaucoma research to manifest the current tendencies and research hotspots and to present a visual map of the past and emerging tendencies in this field. In this study, we retrieved publications in the Web of Science database that centered on this field between 2007 and 2022. Next, we used VOSviewer, CiteSpace, Scimago Graphica, and Microsoft Excel to present visual representations of a co-occurrence analysis, co-citation analysis, tendencies, hotspots, and the contributions of authors, institutions, journals, and countries/regions. The United States was the main contributor. Investigative Ophthalmology and Visual Science has published the most articles in this field. Over the past 15 years, there has been exponential growth in the number of publications and citations in this field across various countries, organizations, and authors. Thus, this study illustrates the current trends, hotspots, and emerging frontiers and provides new insight and guidance for searching for new diagnostic biomarkers and clinical trials for glaucoma in the future. Furthermore, international collaborations can also be used to broaden and deepen the field of microRNAs in glaucoma research.

Using Pre-Clinical Studies to Explore the Potential Clinical Uses of Exosomes Secreted from Induced Pluripotent Stem Cell-Derived Mesenchymal Stem cells

Recent studies of exosomes derived from mesenchymal stem cells (MSCs) have indicated high potential clinical applications in many diseases. However, the limited source of MSCs impedes their clinical research and application. Most recently, induced pluripotent stem cells (iPSCs) have become a promising source of MSCs. Exosome therapy based on iPSC-derived MSCs (iMSCs) is a novel technique with much of its therapeutic potential untapped. Compared to MSCs, iMSCs have proved superior in cell proliferation, immunomodulation, generation of exosomes capable of controlling the microenvironment, and bioactive paracrine factor secretion, while also theoretically eliminating the dependence on immunosuppression drugs. The therapeutic effects of iMSC-derived exosomes are explored in many diseases and are best studied in wound healing, cardiovascular disease, and musculoskeletal pathology. It is pertinent clinicians have a strong understanding of stem cell therapy and the latest advances that will eventually translate into clinical practice. In this review, we discuss the various applications of exosomes derived from iMSCs in clinical medicine.

Preventive Effects of Exosome-Rich Conditioned Medium From Amniotic Membrane-Derived Mesenchymal Stem Cells for Diabetic Retinopathy in Rats

Purpose

Diabetic retinopathy (DR) is an important disease that causes vision loss in many diabetic patients. Stem cell therapy has been attempted for treatment of this disease; however, it has some limitations. This study aimed to evaluate the preventive efficacy of exosome-rich conditioned medium (ERCM) derived from amniotic membrane stem cells for DR in rats.

Methods

Twenty-eight 8-week-old male Sprague-Dawley rats were divided into three groups: group 1, normal control (Con) group; group 2, diabetes mellitus (DM) group; and group 3, DM with ERCM-treated (DM-ERCM) group. DM was induced by intraperitoneal injection of streptozotocin. The DM-ERCM group received ERCM containing 1.2 × 10⁹ exosomes into subconjunctival a total of four times every 2 weeks.

Results

On electroretinogram, the DM-ERCM group had significantly higher b-wave and flicker amplitudes than those in the DM group. In fundoscopy, retinal vascular attenuation was found in both the DM and DM-ERCM groups; however, was more severe in the DM group. On histology, the ganglion cell and nerve fiber layer rates of the total retinal layer significantly increased in the DM group compared with the Con group, whereas the DM-ERCM group showed no significant difference compared with the Con group. Cataracts progressed significantly more in the DM group than that in the DM-ERCM group and there was no uveitis in the DM-ERCM group.

Conclusions

Subconjunctival ERCM delayed the progression of DR and cataracts and significantly reduced the incidence of uveitis.

Translational Relevance

Our study shows the clinical potential of minimally invasive exosome-rich conditioned medium treatment to prevent diabetic retinopathy.

Small extracellular vesicles derived from human adipose-derived mesenchymal stromal cells cultured in a new chemically-defined contaminate-free media exhibit enhanced biological and therapeutic effects on human chondrocytes in vitro and in a mouse osteoarthritis model

Human small extracellular vesicles (sEVs) derived from adipose-derived mesenchymal stromal cells (ASC) have been reported to suppress the progression of osteoarthritis (OA) in animal studies and subsequently, translation of this potential to assess their clinical efficacy is anticipated. However, fabrication protocols for sEVs to eliminate potential contamination by culture medium-derived components need to be established prior to their clinical use. The purpose of the present studies was to elucidate the influence of medium-derived contaminants on the biological effects of sEVs, and to establish isolation methods for sEVs using a new clinical grade chemically-defined media (CDM). The quantity and purity of ASC-derived sEVs cultured in four different CDMs (CDM1, 2, 3 and 4) were evaluated. The concentrates of the four media incubated without cells were used as the background (BG) control for each set of sEVs. The biological effect of sEVs fabricated in the four different CDMs on normal human articular chondrocytes (hACs) were evaluated in vitro using a variety of methodological assessments. Finally, the sEVs with the highest purity were tested for their ability to suppress the progression of knee OA mouse model. Analysis of the BG controls revealed that CDM1-3 contained detectable particles, while there was no visible contamination of culture media-derived components detected with CDM4. Accordingly, the sEVs fabricated with CDM4 (CDM4-sEVs) exhibited the highest purity and yield. Notably, the CDM4-sEVs were the most efficient in promoting the cellular proliferation, migration, chondrogenic differentiation, and anti-apoptotic activity of hACs. Furthermore, CDM4-sEVs significantly suppressed the osteochondral degeneration in vivo model. Small EVs derived from ASCs cultured in a CDM without detectable contaminants demonstrated enhanced biological effects on hACs and the progression of OA. Thus, sEVs isolated with CDM4 most optimally meet the requirements of efficacy and safety for assessment in their future clinical applications.

Wound-Healing Effects of Mesenchymal Stromal Cell Secretome in the Cornea and the Role of Exosomes

Mesenchymal stromal/stem cells (MSCs) and their secreted factors have been shown to have immunomodulatory and regenerative effects. In this study, we investigated human bone-marrow-derived MSC secretome (MSC-S) for the treatment of corneal epithelial wounds. Specifically, we evaluated the role of MSC extracellular vesicles (EV)/exosomes in mediating the wound-healing effects of the MSC-S. In vitro studies using human corneal epithelial cells showed that MSC-CM increased cell proliferation in HCEC and HCLE cells, while EV-depleted MSC-CM showed lower cell proliferation in both cell lines compared to the MSC-CM group. In vitro and in vivo experiments revealed that 1X MSC-S consistently promoted wound healing more effectively than 0.5X MSC-S, and MSC-CM promoted wound healing in a dose-dependent manner, while exosome deprivation delayed wound healing. We further evaluated the incubation period of MSC-CM on corneal wound healing and showed that MSC-S collected for 72 h is more effective than MSC-S collected for 48 h. Finally, we evaluated the stability of MSC-S under different storage conditions and found that after one cycle of freeze-thawing, MSC-S is stable at 4 °C for up to 4 weeks. Collectively, we identified the following: (i) MSC-EV/Exo as the active ingredient in MSC-S that mediates the wound-healing effects in the corneal epithelium, providing a measure to optimize its dosing for a potential clinical product; (ii) Treatment with EV/Exo-containing MSC-S resulted in an improved corneal barrier and decreased corneal haze/edema relative to EV/Exo-depleted MSC-S; (iii) The stability of MSC-CM for up to 4 weeks showed that the regular storage condition did not significantly impact its stability and therapeutic functions.

Mesenchymal Stem Cell-Derived Extracellular Vesicles: Hype or Hope for Skeletal Muscle Anti-Frailty

Steadily rising population ageing is a global demographic trend due to the advancement of new treatments and technologies in the medical field. This trend also indicates an increasing prevalence of age-associated diseases, such as loss of muscle mass (sarcopenia), which tends to afflict the older population. The deterioration in muscle function can cause severe disability and seriously affects a patient's quality of life. Currently, there is no treatment to prevent and reverse age-related skeletal muscle ageing frailty. Existing interventions mainly slow down and control the signs and symptoms. Mesenchymal stem cell-derived extracellular vesicle (MSC-EV) therapy is a promising approach to attenuate age-related skeletal muscle ageing frailty. However, more studies, especially large-scale randomised clinical trials need to be done in order to determine the adequacy of MSC-EV therapy in treating age-related skeletal muscle ageing frailty. This review compiles the present knowledge of the causes and changes regarding skeletal muscle ageing frailty and the potential of MSC-EV transplantation as a regenerative therapy for age-related skeletal muscle ageing frailty and its clinical trials.

Apoptotic vesicles resist oxidative damage in noise-induced hearing loss through activation of FOXO3a-SOD2 pathway

BACKGROUND

Mesenchymal stem cell (MSC) transplantation is a promising therapeutic approach for noise-induced hearing loss (NIHL). As the indispensable role of apoptosis in MSC transplantation was raised, the benefits of MSC-derived apoptotic vesicles (apoVs) in several disease models have been proved. However, whether apoVs benefit in NIHL have not been studied yet.

METHODS

Female CBA/J mice and HEI-OC1 cells were used in this study. Flow cytometry, nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM) were used to characterize apoVs. Proteomic analysis was used to identify function proteins in apoVs. Immunofluorescence was used to reveal distribution pattern. Auditory brainstem response (ABR) test was used to measure the effect of apoVs treatment. DCFH-DA staining and MitoSOX staining were used to indicate oxidative damage. Western-blot and qRT-PCR were used to study the signaling pathways.

RESULTS

We found that apoVs can be endocytosed by hair cells through systemic administration. Importantly, apoVs administration effectively attenuated NIHL and reduced hair cell loss by resisting oxidative damage in vivo. Further, apoVs application activated forkhead box o3 (FOXO3a)-mitochondrial superoxide dismutase 2(SOD2) pathway, which may relate to signal transduction and activators of transcription 3 (STAT3) in apoVs.

CONCLUSIONS

These findings uncovered the role of apoVs in preventing NIHL and resisting oxidative damage, indicating that apoVs is a promising way for inner ear delivery and a prospective cell-free therapy for NIHL.

Amniotic Mesenchymal-Derived Extracellular Vesicles and Their Role in the Prevention of Persistent Post-Breeding Induced Endometritis

Persistent post-breeding induced endometritis (PPBIE) is considered a major cause of subfertility in mares. It consists of persistent or delayed uterine inflammation in susceptible mares. There are many options for the treatment of PPBIE, but in this study, a novel approach aimed at preventing the onset of PPBIE was investigated. Stallion semen was supplemented with extracellular vesicles derived from amniotic mesenchymal stromal cells (AMSC-EVs) at the time of insemination to prevent or limit the development of PPBIE. Before use in mares, a dose–response curve was produced to evaluate the effect of AMSC-EVs on spermatozoa, and an optimal concentration of 400 × 106 EVs with 10 × 106 spermatozoa/mL was identified. At this concentration, sperm mobility parameters were not negatively affected. Sixteen susceptible mares were enrolled and inseminated with semen (n = 8; control group) or with semen supplemented with EVs (n = 8; EV group). The supplementation of AMSC-EVs to semen resulted in a reduction in polymorphonuclear neutrophil (PMN) infiltration as well as intrauterine fluid accumulation (IUF; p < 0.05). There was a significant reduction in intrauterine cytokine levels (p < 0.05) for TNF-α and IL-6 and an increase in anti-inflammatory IL-10 in mares in the EV group, suggesting successful modulation of the post-insemination inflammatory response. This procedure may be useful for mares susceptible to PPBIE.

miR-1260b inhibits periodontal bone loss by targeting ATF6β mediated regulation of ER stress

The expression profiles of exosomal microRNAs (miRNAs) are regulated by the microenvironment, and appropriate priming with mesenchymal stem cells (MSCs) is one of the strategies to enhance the paracrine potency of MSCs. Our previous work demonstrated that exosomes from tumor necrosis factor (TNF)-α-primed human gingiva-derived MSCs (GMSCs) could be a therapeutic tool against periodontitis, and that TNFα-inducible exosomal miR-1260b is essential for the inhibition of alveolar bone loss. However, the precise molecular mechanism underlying miR-1260b-mediated inhibition of osteoclastogenesis is not yet fully understood. Here, we found that the activating transcription factor (ATF)-6β, a novel miR-1260b-targeting gene, is critical for the regulation of osteoclastogenesis under endoplasmic reticulum (ER) stress. An experimental periodontal mouse model demonstrated that induction of ER stress was accompanied by enhanced ATF6β expression, and local administration of miR-1260b and ATF6β siRNA using polyethylenimine nanoparticles (PEI-NPs) significantly suppressed the periodontal bone resorption. In periodontal ligament (PDL) cells, the ER stress inducer, tunicamycin, enhanced the expression of the receptor activator of NF-κB ligand (RANKL), while miR-1260b-mediated downregulation of ATF6β caused RANKL inhibition. Furthermore, the secretome from miR-1260b/ATF6β-axis-activated PDL cells inhibited osteoclastogenesis in human CD14+ peripheral blood-derived monocytes. These results indicate that the miR-1260b/ATF6β axis mediates the regulation of ER stress, which may be used as a novel therapeutic strategy to treat periodontal disease.

Perivascular Mesenchymal Stem/Stromal Cells, an Immune Privileged Niche for Viruses?

Mesenchymal stem cells (MSCs) play a critical role in response to stress such as infection. They initiate the removal of cell debris, exert major immunoregulatory activities, control pathogens, and lead to a remodeling/scarring phase. Thus, host-derived ‘danger’ factors released from damaged/infected cells (called alarmins, e.g., HMGB1, ATP, DNA) as well as pathogen-associated molecular patterns (LPS, single strand RNA) can activate MSCs located in the parenchyma and around vessels to upregulate the expression of growth factors and chemoattractant molecules that influence immune cell recruitment and stem cell mobilization. MSC, in an ultimate contribution to tissue repair, may also directly trans- or de-differentiate into specific cellular phenotypes such as osteoblasts, chondrocytes, lipofibroblasts, myofibroblasts, Schwann cells, and they may somehow recapitulate their neural crest embryonic origin. Failure to terminate such repair processes induces pathological scarring, termed fibrosis, or vascular calcification. Interestingly, many viruses and particularly those associated to chronic infection and inflammation may hijack and polarize MSC’s immune regulatory activities. Several reports argue that MSC may constitute immune privileged sanctuaries for viruses and contributing to long-lasting effects posing infectious challenges, such as viruses rebounding in immunocompromised patients or following regenerative medicine therapies using MSC. We will herein review the capacity of several viruses not only to infect but also to polarize directly or indirectly the functions of MSC (immunoregulation, differentiation potential, and tissue repair) in clinical settings.

Exosomes: a new way of protecting and regenerating optic nerve after injury

As an important part of the central nervous system (CNS), the optic nerve usually cannot regenerate directly after injury. Therefore, treating the injury and restoring the function of the optic nerve are a historical problem in the medical field. Due to the special anatomical position of the optic nerve, the microenvironment needed for protection and regeneration after injury is lacking. Therefore, preventing the continued loss of neurons, protecting the functional nerves, and promoting the effective protection of nerves are the main ways to solve the problem. Exosomes are nano-sized vesicles with a diameter of 30-150 nm, composed of lipid bilayers, proteins, and genetic material. They have key functions in cell-to-cell communication, immune regulation, inflammation, and regeneration. More and more shreds of evidence show that exosomes not only play an important role in systemic diseases such as cancer, cardiovascular diseases, and brain diseases; they also play a key role in ophthalmological diseases. This article reviews the role of exosomes in the protection and regeneration of the optic nerve after optic nerve injury in related experimental studies and clinical treatment methods. GRAPHICAL ABSTARCT: .

Enhancement strategies for mesenchymal stem cells and related therapies

Cell therapy, particularly mesenchymal stem/stromal (MSC) therapy, has been investigated for a wide variety of disease indications, particularly those with inflammatory pathologies. However, recently it has become evident that the MSC is far from a panacea. In this review we will look at current and future strategies that might overcome limitations in efficacy. Many of these take their inspiration from stem cell niche and the mechanism of MSC action in response to the injury microenvironment, or from previous gene therapy work which can now benefit from the added longevity and targeting ability of a live cell vector. We will also explore the nascent field of extracellular vesicle therapy and how we are already seeing enhancement protocols for this exciting new drug. These enhanced MSCs will lead the way in more difficult to treat diseases and restore potency where donors or manufacturing practicalities lead to diminished MSC effect.

Mesenchymal Stem Cell-Derived Extracellular Vesicles: Immunomodulatory Effects and Potential Applications in Intervertebral Disc Degeneration

Intervertebral disc (IVD) degenerative disease is a common health problem worldwide. Administration of mesenchymal stem cells (MSCs) in intervertebral disc degeneration (IVDD) has been widely explored in recent years. However, transplantation of MSCs is restricted by several factors. Currently, paracrine signaling is one of the main mechanisms by which MSCs play a therapeutic role in disc regeneration. Extracellular vehicles (EVs) are the main paracrine products of MSCs. They show great potential as an effective alternative to MSCs and play immunomodulation roles such as anti-inflammatory effects, antioxidative stress, antiapoptosis, and antiextracellular matrix (ECM) degradation during treatment of IVDD. This review focuses on the immunomodulatory effect of MSC EVs and their potential applications.

Role of MSC-derived small extracellular vesicles in tissue repair and regeneration

Mesenchymal stem cells (MSCs) are crucial for tissue homeostasis and repair, secreting vesicles to the extracellular environment. Isolated exosomes were shown to affect angiogenesis, immunomodulation and tissue regeneration. Numerous efforts have been dedicated to describe the mechanism of action of these extracellular vesicles (EVs) and guarantee their safety, since the final aim is their therapeutic application in the clinic. The major advantage of applying MSC-derived EVs is their low or inexistent immunogenicity, prompting their use as drug delivery or therapeutic agents, as well as wound healing, different cancer types, and inflammatory processes in the neurological and cardiovascular systems. MSC-derived EVs display no vascular obstruction effects or apparent adverse effects. Their nano-size ensures their passage through the blood-brain barrier, demonstrating no cytotoxic or immunogenic effects. Several in vitro tests have been conducted with EVs obtained from different sources to understand their biology, molecular content, signaling pathways, and mechanisms of action. Application of EVs to human therapies has recently become a reality, with clinical trials being conducted to treat Alzheimer's disease, retina degeneration, and COVID-19 patients. Herein, we describe and compare the different extracellular vesicles isolation methods and therapeutic applications regarding the tissue repair and regeneration process, presenting the latest clinical trial reports.

Treatment of ischemic stroke with modified mesenchymal stem cells

Ischemic stroke is one of the leading causes of death and disability. Ischemia triggers a cascade of events leading to cell death and cerebral infarction. Mesenchymal stem cell (MSC) therapy is a promising treatment modality to promote the development of nerve and blood vessels and improve nerve function. However, MSCs have a limited therapeutic effect in the harsh microenvironment of ischemic brain tissue. Modified MSC therapy shows better therapeutic effect under different pathological conditions, and is expected to be translated into clinical practice. In this article, we review the latest advances in the development of modified MSCs for the treatment of cerebral ischemia. In particular, we summarize the targets involved in migration, homing, antioxidant stress, anti-inflammatory, nerve and vascular regeneration, providing new ideas for clinical transformation.

Exosomes-loaded thermosensitive hydrogels for corneal epithelium and stroma regeneration

Corneal damage forms scar tissue and manifests as permanent corneal opacity, which is the main cause of visual impairment caused by corneal diseases. To treat these diseases, herein, we developed a novel approach based on the exosome derived from induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) combined with a thermosensitive hydrogel, which reduces scar formation and accelerates the healing process. We found that a thermosensitive chitosan-based hydrogels (CHI hydrogel) sustained-release iPSC-MSC exosomes can effectively promote the repair of damaged corneal epithelium and stromal layer, downregulating mRNA expression coding for the three most enriched collagens (collagen type I alpha 1, collagen type V alpha 1 and collagen type V alpha 2) in corneal stroma and reducing scar formation in vivo. Furthermore, iPSC-MSCs secrete exosomes that contain miR-432-5p, which suppresses translocation-associated membrane protein 2 (TRAM2), a vital modulator of the collagen biosynthesis in the corneal stromal stem cells to avert the deposition of extracellular matrix (ECM). Our findings indicate that iPSC-MSCs secrete miRNA-containing exosomes to promote corneal epithelium and stroma regeneration, and that miR-432-5p can prevent ECM deposition via a mechanism most probably linked to direct repression of its target gene TRAM2. Overall, our exosomes-based thermosensitive CHI hydrogel, is a promising technology for clinical therapy of various corneal diseases.

Therapeutic effects of mesenchymal stem cells-derived extracellular vesicles' miRNAs on retinal regeneration: a review

Extracellular vesicles (EVs), which consist of microvesicles and exosomes, are secreted from all cells to transform vital information in the form of lipids, proteins, mRNAs and small RNAs such as microRNAs (miRNAs). Many studies demonstrated that EVs' miRNAs have effects on target cells. Numerous people suffer from the blindness caused by retinal degenerations. The death of retinal neurons is irreversible and creates permanent damage to the retina. In the absence of acceptable cures for retinal degenerative diseases, stem cells and their paracrine agents including EVs have become a promising therapeutic approach. Several studies showed that the therapeutic effects of stem cells are due to the miRNAs of their EVs. Considering the effects of microRNAs in retinal cells development and function and studies which provide the possible roles of mesenchymal stem cells-derived EVs miRNA content on retinal diseases, we focused on the similarities between these two groups of miRNAs that could be helpful for promoting new therapeutic techniques for retinal degenerative diseases.

A comprehensive review of COVID-19 biology, diagnostics, therapeutics, and disease impacting the central nervous system

The ongoing COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a highly transmissible disease. SARS-CoV-2 is estimated to have infected over 153 million people and to have caused over 3.2 million global deaths since its emergence in December 2019. SARS-CoV-2 is the seventh coronavirus known to infect humans, and like other coronaviruses, SARS-CoV-2 infection is characterized by a variety of symptoms including general flu-like symptoms such as a fever, sore throat, fatigue, and shortness of breath. Severe cases often display signs of pneumonia, lymphopenia, acute kidney injury, cardiac injury, cytokine storms, lung damage, acute respiratory distress syndrome (ARDS), multiple organ failure, sepsis, and death. There is evidence that around 30% of COVID-19 cases have central nervous system (CNS) or peripheral nervous system (PNS) symptoms along with or in the absence of the previously mentioned symptoms. In cases of CNS/PNS impairments, patients display dizziness, ataxia, seizure, nerve pain, and loss of taste and/or smell. This review highlights the neurological implications of SARS-CoV-2 and provides a comprehensive summary of the research done on SARS-CoV-2 pathology, diagnosis, therapeutics, and vaccines up to May 5.

Intravenous injection of adult human bone marrow mesenchymal stromal cells attenuates spinal cord ischemia/reperfusion injury in a murine aortic arch crossclamping model

OBJECTIVE

We sought to investigate the efficacy of human bone marrow mesenchymal stem/stromal cell (hBM-MSC) in a murine spinal cord ischemia/reperfusion (SCIR) model.

METHODS

C57BL/6J mice were subjected to SCIR by crossclamping the aortic arch and left subclavian artery for 5.5 minutes. Two hours after reperfusion, hBM-MSCs (hBM-MSC group) or phosphate-buffered saline (control group) were intravenously injected without immunosuppressant. Hindlimb motor function was assessed until day 28 after reperfusion using the Basso Mouse Scale (BMS). The lumbar spinal cord was harvested at hour 24 and day 28, and the histologic number of NeuN-positive motor neurons in 3 cross-sections of each lumbar spinal cord and the gene expression were evaluated.

RESULTS

BMS score was 0 throughout the study period in all control mice. BMS score was significantly greater in the hBM-MSC group than the control group from hour 8 (P < .05) to day 28 (P < .01). The numbers of motor neurons at hour 24 (P < .01) and day 28 (P < .05) were significantly preserved in the hBM-MSC group than the control group. mRNA expression levels of proinflammatory cytokines were significantly lower (P < .05), and those of insulin-like growth factor-1 (P < .01) and proangiogenic factors (P < .05) were significantly greater in the hBM-MSC group than the control group at hour 24.

CONCLUSIONS

hBM-MSC therapy may attenuate SCIR injury by preserving motor neurons, at least in part, through inhibition of proinflammatory cytokines and upregulation of proangiogenic factors in the reperfusion-injured spinal cord.

Extracellular Vesicles-The Next Frontier in Endocrinology

Extracellular vesicles (EVs), including exosomes, are emerging as important carriers of signals in normal and pathological physiology. As EVs are a long-range communication or signaling modality-just like hormones are-the field of endocrinology is uniquely poised to offer insight into their functional biology and regulation. EVs are membrane-bound particles secreted by many different cell types and can have local or systemic effects, being transported in body fluids. They express transmembrane proteins, some of which are shared between EVs and some being specific to the tissue of origin, that can interact with target cells directly (much like hormones can). They also contain cargo within them that includes DNA, RNA, miRNA, and various metabolites. They can fuse with target cells to empty their cargo and alter their target cell physiology in this way also. Similar to the endocrine system, the EV system is likely to be under homeostatic control, making the regulation of their biogenesis and secretion important aspects to study. In this review, we briefly highlight select examples of how EVs are implicated in normal physiology and disease states. We also discuss what is known about their biogenesis and regulation of secretion. We hope that this paper inspires the endocrinology field to use our collective expertise to explore these new multimodal "hormones."

Dynamic regulation of mitochondrial-endoplasmic reticulum crosstalk during stem cell homeostasis and aging

Cellular therapy exerts profound therapeutic potential for curing a broad spectrum of diseases. Adult stem cells reside within a specified dynamic niche in vivo, which is essential for continuous tissue homeostatic maintenance through balancing self-renewal with lineage selection. Meanwhile, adult stem cells may be multipotent or unipotent, and are present in both quiescent and actively dividing states in vivo of the mammalians, which may switch to each other state in response to biophysical cues through mitochondria-mediated mechanisms, such as alterations in mitochondrial respiration and metabolism. In general, stem cells facilitate tissue repair after tissue-specific homing through various mechanisms, including immunomodulation of local microenvironment, differentiation into functional cells, cell "empowerment" via paracrine secretion, immunoregulation, and intercellular mitochondrial transfer. Interestingly, cell-source-specific features have been reported between different tissue-derived adult stem cells with distinct functional properties due to the different microenvironments in vivo, as well as differential functional properties in different tissue-derived stem cell-derived extracellular vehicles, mitochondrial metabolism, and mitochondrial transfer capacity. Here, we summarized the current understanding on roles of mitochondrial dynamics during stem cell homeostasis and aging, and lineage-specific differentiation. Also, we proposed potential unique mitochondrial molecular signature features between different source-derived stem cells and potential associations between stem cell aging and mitochondria-endoplasmic reticulum (ER) communication, as well as potential novel strategies for anti-aging intervention and healthy aging.

Transplantation of engineered exosomes derived from bone marrow mesenchymal stromal cells ameliorate diabetic peripheral neuropathy under electrical stimulation

Diabetic peripheral neuropathy (DPN) is a long-term complication associated with nerve dysfunction and uncontrolled hyperglycemia. In spite of new drug discoveries, development of effective therapy is much needed to cure DPN. Here, we have developed a combinatorial approach to provide biochemical and electrical cues, considered to be important for nerve regeneration. Exosomes derived from bone marrow mesenchymal stromal cells (BMSCs) were fused with polypyrrole nanoparticles (PpyNps) containing liposomes to deliver both the cues in a single delivery vehicle. We developed DPN rat model and injected intramuscularly the fused exosomal system to understand its long-term therapeutic effect. We found that the fused system along with electrical stimulation normalized the nerve conduction velocity (57.60 ± 0.45 m/s) and compound muscle action potential (16.96 ± 0.73 mV) similar to healthy control (58.53 ± 1.10 m/s; 18.19 ± 1.45 mV). Gastrocnemius muscle morphology, muscle mass, and integrity were recovered after treatment. Interestingly, we also observed paracrine effect of delivered exosomes in controlling hyperglycemia and loss in body weight and also showed attenuation of damage to the tissues such as the pancreas, kidney, and liver. This work provides a promising effective treatment and also contribute cutting edge therapeutic approach for the treatment of DPN.

hucMSC-derived exosomes attenuate colitis by regulating macrophage pyroptosis via the miR-378a-5p/NLRP3 axis

Background

Human umbilical cord mesenchymal stem cell (hucMSC)-derived exosomes are recognized as novel cell-free therapeutic agents for inflammatory bowel disease (IBD), a condition caused by dysregulated intestinal mucosal immunity. In this event, macrophage pyroptosis, a process of cell death following the activation of NLRP3 (NOD-like receptor family, pyrin domain-containing 3) inflammasomes, is believed to partially account for inflammatory reactions. However, the role of macrophage pyroptosis in the process of hucMSC-derived exosomes alleviating colitis remains unknown. This study aimed at exploring the therapeutic effect and mechanism of hucMSC-derived exosomes on colitis repair.

Methods

In vivo, we used BALB/c mice to establish a dextran sulfate sodium (DSS)-induced colitis model and administrated hucMSC-derived exosomes intravenously to estimate its curative effect. Human myeloid leukemia mononuclear (THP-1) cells and mouse peritoneal macrophages (MPMs) were stimulated with lipopolysaccharides (LPS) and Nigericin to activate NLRP3 inflammasomes, which simulated an inflammation environment in vitro. A microRNA mimic was used to verify the role of miR-378a-5p/NLRP3 axis in the colitis repair.

Results

hucMSC-derived exosomes inhibited the activation of NLRP3 inflammasomes in the mouse colon. The secretion of interleukin (IL)-18, IL-1β, and Caspase-1 cleavage was suppressed, resulting in reduced cell pyroptosis. The same outcome was observed in the in vitro cell experiments, where the co-culture of THP-1 cells and MPMs with hucMSC-derived exosomes caused decreased expression of NLRP3 inflammasomes and increased cell survival. Furthermore, miR-378a-5p was highly expressed in hucMSC-derived exosomes and played a vital function in colitis repair.

Conclusion

hucMSC-derived exosomes carrying miR-378a-5p inhibited NLRP3 inflammasomes and abrogated cell pyroptosis to protect against DSS-induced colitis.

Stem-Cell Derived Exosomes for the Treatment of Osteoarthritis

Osteoarthritis(OA) is a common degenerative orthopedic disease with multiple pathologic changes in joints affecting large populations worldwide. No treatment can reverse the progress of OA. Since exosomes were first reported in 1983, researches have been conducted to explore the mechanisms and therapeutic potential of exosomes in treating OA. Exosomes derived from Mesenchymal stem cells have attracted increasing attention in tackling the disease. This article summarizes the current advances and challenges in exosomes for OA, which may providea reference for further research.

SHED aggregate exosomes shuttled miR-26a promote angiogenesis in pulp regeneration via TGF-β/SMAD2/3 signalling

OBJECTIVES

Pulp regeneration brings big challenges for clinicians, and vascularization is considered as its determining factor. We previously accomplished pulp regeneration with autologous stem cells from deciduous teeth (SHED) aggregates implantation in teenager patients, however, the underlying mechanism needs to be clarified for regenerating pulp in adults. Serving as an important effector of mesenchymal stem cells (MSCs), exosomes have been reported to promote angiogenesis and tissue regeneration effectively. Here, we aimed to investigate the role of SHED aggregate-derived exosomes (SA-Exo) in the angiogenesis of pulp regeneration.

MATERIALS AND METHODS

We extracted exosomes from SHED aggregates and utilized them in the pulp regeneration animal model. The pro-angiogenetic effects of SA-Exo on SHED and human umbilical vein endothelial cells (HUVECs) were evaluated. The related mechanisms were further investigated.

RESULTS

We firstly found that SA-Exo significantly improved pulp tissue regeneration and angiogenesis in vivo. Next, we found that SA-Exo promoted SHED endothelial differentiation and enhanced the angiogenic ability of HUVECs, as indicated by the in vitro tube formation assay. Mechanistically, miR-26a, which is enriched in SA-Exo, improved angiogenesis both in SHED and HUVECs via regulating TGF-β/SMAD2/3 signalling.

CONCLUSIONS

In summary, these data reveal that SA-Exo shuttled miR-26a promotes angiogenesis via TGF-β/SMAD2/3 signalling contributing to SHED aggregate-based pulp tissue regeneration. These novel insights into SA-Exo may facilitate the development of new strategies for pulp regeneration.

Mesenchymal stromal cell-derived extracellular vesicles for bone regeneration therapy

Purpose

To analyze preclinical bone regeneration studies employing mesenchymal stromal cell (MSC)- derived extracellular vesicles (EVs) and highlight any commonalities in EV biomarker expression, miRNA cargo(s) or pathway activation that will aid in understanding the underlying therapeutic mechanisms.

Methods

Articles employing EVs derived from either MSCs or MSC-like osteogenic stromal cells in preclinical bone regeneration studies are included in this review.

Results

EVs derived from a variety of MSC types were able to successfully induce bone formation in preclinical models. Many studies failed to perform in-depth EV characterization. The studies with detailed EV characterization data report very different miRNA cargos, even in EVs isolated from the same species and cell types. Few preclinical studies have analyzed the underlying mechanisms of MSC-EV therapeutic action.

Conclusion

There is a critical need for mechanistic preclinical studies with thorough EV characterization to determine the best therapeutic MSC-EV source for bone regeneration therapies. Issues including controlled EV delivery, large scale production, and proper storage also need to be addressed before EV-based bone regeneration therapies can be translated for clinical bone repair.

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EVs from different MSC sources successfully regenerate bone in preclinical models.

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Studies were reviewed to find commonalities in EV cargo(s)/pathways activated in MSC-EV-based bone regeneration therapies.

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Issues that need to be overcome to enable clinical translation of EV-based therapies were addressed.

Biomaterial-based extracellular vesicle delivery for therapeutic applications

Extracellular vesicle (EV)- based therapies have been successfully tested in preclinical models for several biomedical applications, including tissue engineering, drug delivery and cancer therapy. However, EVs are most commonly delivered via local or systemic injection, which results in rapid clearance. In order to prolong the retention of EVs at target site and improve their therapeutic efficacy, biomaterial-based delivery systems are being investigated. This review discusses the various biomaterial-based systems that have been used to deliver EVs for therapeutic applications, specifically highlighting any strategies for controlled release. Further, challenges to clinical translation of biomaterial-based EV delivery systems are also discussed.

Characterization of Extracellular Vesicles from Preconditioned Human Adipose-Derived Stromal/Stem Cells

Cell-free therapy using extracellular vesicles (EVs) from adipose-derived mesenchymal stromal/stem cells (ASCs) seems to be a safe and effective therapeutic option to support tissue and organ regeneration. The application of EVs requires particles with a maximum regenerative capability and hypoxic culture conditions as an in vitro preconditioning regimen has been shown to alter the molecular composition of released EVs. Nevertheless, the EV cargo after hypoxic preconditioning has not yet been comprehensively examined. The aim of the present study was the characterization of EVs from hypoxic preconditioned ASCs. We investigated the EV proteome and their effects on renal tubular epithelial cells in vitro. While no effect of hypoxia was observed on the number of released EVs and their protein content, the cargo of the proteins was altered. Proteomic analysis showed 41 increased or decreased proteins, 11 in a statistically significant manner. Furthermore, the uptake of EVs in epithelial cells and a positive effect on oxidative stress in vitro were observed. In conclusion, culture of ASCs under hypoxic conditions was demonstrated to be a promising in vitro preconditioning regimen, which alters the protein cargo and increases the anti-oxidative potential of EVs. These properties may provide new potential therapeutic options for regenerative medicine.

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

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.

Biomimetic Culture Strategies for the Clinical Expansion of Mesenchymal Stromal Cells

Mesenchymal stromal/stem cells (MSCs) typically require significant ex vivo expansion to achieve the high cell numbers required for research and clinical applications. However, conventional MSC culture on planar (2D) plastic surfaces has been shown to induce MSC senescence and decrease cell functionality over long-term proliferation, and usually, it has a high labor requirement, a high usage of reagents, and therefore, a high cost. In this Review, we describe current MSC-based therapeutic strategies and outline the important factors that need to be considered when developing next-generation cell expansion platforms. To retain the functional value of expanded MSCs, ex vivo culture systems should ideally recapitulate the components of the native stem cell microenvironment, which include soluble cues, resident cells, and the extracellular matrix substrate. We review the interplay between these stem cell niche components and their biological roles in governing MSC phenotype and functionality. We discuss current biomimetic strategies of incorporating biochemical and biophysical cues in MSC culture platforms to grow clinically relevant cell numbers while preserving cell potency and stemness. This Review summarizes the current state of MSC expansion technologies and the challenges that still need to be overcome for MSC clinical applications to be feasible and sustainable.

Extracellular Vesicles From Liver Progenitor Cells Downregulates Fibroblast Metabolic Activity and Increase the Expression of Immune-Response Related Molecules

Extracellular vesicles (EVs) mediate cell-to-cell crosstalk whose content can induce changes in acceptor cells and their microenvironment. MLP29 cells are mouse liver progenitor cells that release EVs loaded with signaling cues that could affect cell fate. In the current work, we incubated 3T3-L1 mouse fibroblasts with MLP29-derived EVs, and then analyzed changes by proteomics and transcriptomics. Results showed a general downregulation of protein and transcript expression related to proliferative and metabolic routes dependent on TGF-beta. We also observed an increase in the ERBB2 interacting protein (ERBIN) and Cxcl2, together with an induction of ribosome biogenesis and interferon-related response molecules, suggesting the activation of immune system signaling.

Introduction to the Community of Extracellular Vesicles

Since the discovery that extracellular vesicles (EVs) mediate intercellular communication, there is an exponential increase in the interest on EVs, especially in pathological settings. EVs are membranous vesicles that are secreted by various cell types and the release of EVs is conserved in every prokaryotic and eukaryotic organism tested to date. These vesicles were initially thought to be garbage disposal vehicles and subsequent studies over the past 4 decades have attributed several functional roles to EVs, some of which are critical for homeostasis. The molecular cargo of nucleic acids, proteins, lipids and metabolites packaged in EVs often mirror the host cells phenotypic status. EVs can be taken up by recipient cells and upon uptake, EVs through its molecular cargo, can induce a cascade of signal transduction events in recipient cells. EVs are categorised into several subtypes depending on their biogenesis and secretion. Due to several subtypes, differing sizes within a subtype and varying cargo, EVs are heterogenous in nature and the biophysical and biochemical properties of EVs often overlap between EV subtypes. Hence, it is important to be cautious when selecting the method of EV isolation and characterisation. This chapter provides a brief introduction to EVs and their subtypes.

Exosomes from β-Cells Promote Differentiation of Induced Pluripotent Stem Cells into Insulin-Producing Cells Through microRNA-Dependent Mechanisms

OBJECTIVE

Exosomes have emerged as potential tools for the differentiation of induced pluripotent stem cells (iPSCs) into insulin-producing cells (IPCs). Exosomal microRNAs are receiving increasing attention in this process. Here, we aimed at investigating the role of exosomes derived from a murine pancreatic β-cell line and identifying signature exosomal miRNAs on iPSCs differentiation.

METHODS

Exosomes were isolated from MIN6 cells and identified with TEM, NTA and Western blot. PKH67 tracer and transwell assay were used to confirm exosome delivery into iPSCs. qRT-PCR was applied to detect key pancreatic transcription gene expression and exosome-derived miRNA expression. Insulin secretion was determined using FCM and immunofluorescence. The specific exosomal miRNAs were determined via RNA-interference of Ago2. The therapeutic effect of 21 day-exosome-induced IPCs was validated in T1D mice induced by STZ.

RESULTS

iPSCs cultured in medium containing exosomes showed sustained higher expression of MAFA, Insulin1, Insulin2, Isl1, Neuroud1, Nkx6.1 and NGN3 compared to control iPSCs. In FCM analysis, approximately 52.7% of the differentiated cells displayed insulin expression at the middle stage. Consistent with the gene expression data, immunofluorescence assays showed that Nkx6.1 and insulin expression in iPSCs were significantly upregulated. Intriguingly, the expression of pancreatic markers and insulin was significantly decreased in iPSCs cultured with siAgo2 exosomes. Transplantation of 21 day-induced IPCs intoT1D mice efficiently enhanced glucose tolerance and partially controlled hyperglycemia. The therapeutic effect was significantly attenuated in T1D mice that received iPSCs cultured with siAgo2 exosomes. Of the seven exosomal microRNAs selected for validation, miR-706, miR-709, miR-466c-5p, and miR-423-5p showed dynamic expression during 21 days in culture.

CONCLUSION

These data indicate that differentiation of exosome-induced iPSCs into functional cells is crucially dependent on the specific miRNAs encased within exosomes, whose functional analysis is likely to provide insight into novel regulatory mechanisms governing iPSCs differentiation into IPCs.

Extracellular vesicles derived from human dental pulp stem cells promote osteogenesis of adipose-derived stem cells via the MAPK pathway

Recent studies have shown that co-culture systems play an important role in bone tissue engineering. In this study, human dental pulp stem cells (hDPSCs) were co-cultured with human adipose-derived stem cells (hADSCs), and osteoblastic phenotypes were found to be enhanced in co-cultures compared with monocultures of hDPSCs or hADSCs. Furthermore, GW4869, an inhibitor of extracellular vesicle (EV) formation, suppressed the mineralization of co-cultured cells. Studies indicate that the therapeutic potential of DPSCs is realized through paracrine action, in which EVs play an important role. To study their role, we successfully obtained and identified hDPSC-derived extracellular vesicles (hDPSC-EVs), and further investigated their effects on hADSCs and the underlying mechanism. hADSCs were stimulated with hDPSC-EVs, which were found to promote the migration and mineralization of hADSCs. Moreover, hDPSC-EVs promoted osteogenic differentiation by enhancing the phosphorylation of ERK 1/2 and JNK in hADSCs. To investigate the specific proteins in EVs that might play a role in hADSC osteogenic differentiation, we performed proteomic analysis of hDPSC-EVs. We determined the top 30 enriched pathways, which notably included the insulin signaling pathway. The number of genes enriched in the insulin signaling pathway was the largest, in addition to the “protein processing in endoplasmic reticulum” term. The MAPK cascade is a typical downstream pathway mediating insulin signaling. To further study the effects of hDPSC-EVs on maxillofacial bone regeneration, we used hDPSC-EVs as a cell-free biomaterial in a model of mandibular defects in rats. To assess the therapeutic potential of EVs, we analyzed their proteome. Animal experiments demonstrated that hDPSC-EVs promoted the regeneration of bone defects. Overall, these results highlight the potential of hDPSC-EVs to induce lineage specific differentiation of hADSCs. The results also indicated the importance of considering hDPSC-EVs as biomimetic materials for clinical translation of treatments for oral maxillofacial defects.

Effect of Mesenchymal Stem Cell-Derived Exosomes on Retinal Injury: A Review of Current Findings

In recent years, various studies have followed in the literature on the therapeutic effects of mesenchymal stem cells (MSC) on damage in retinal cells. The evidence that MSCs exert their regenerative and damage reduction effect in a paracrine way, through the release of soluble factors and exosomes, is now consolidated. Exosomes are microvesicles formed by a double layer of phospholipid membrane and carry proteins and RNA, through which they play a therapeutic role on target cells. Scientific research has recently focused on the use of exosomes derived from MSC in various models of retinal damage in vitro and in vivo as they, compared to MSCs, have similar functions and at the same time have different advantages such as greater stability and handling, a lower chance of immunological rejection and no risk of malignant transformation. The purpose of this review is to summarize current knowledge on the therapeutic use of exosomes derived from MSCs in retinal damage and to stimulate new clinical perspectives regarding their use.

[Problems and prospects of cell therapy for critical ischaemia of lower limbs]

BACKGROUND

Cell therapy was proposed as a procedure of indirect revascularization for patients with critical ischaemia of lower extremities for whom endovascular and surgical revascularization is impossible. We present herein a review of the state of the art of studies in the field of cell therapy of this cohort of patients.

BASIC PROVISIONS

Cell therapy has proved safe, however, the results of studies of efficacy are relatively ambiguous and unconvincing. The number of patients in separately taken clinical trials is minimal. The reviewed studies differed not only by heterogeneity of the cell types used but by the routes of administration of cells (cells were delivered either intramuscularly (predominantly) or intraarterially) and the duration of follow up (time of assessment and duration of follow up varied from 1 month to 2 years). One of the problems became the lack of the routine study of the angiogenic potential of stem cells prior to their clinical application. It is known that the angiogenic activity of multipotent cells of apparently healthy patients may differ from that of patients suffering from atherosclerosis, chronic renal failure, diabetes.

CONCLUSIONS

It is supposed that treatment with stem cells or precursor cells is more efficient as compared to protein or gene therapy not only owing to direct vasculogenic properties but a paracrine action through excretion of proangiogenic biologically active substances. More studies with larger cohorts are necessary to provide stronger safety and efficacy data on cell therapy. Besides, a promising trend in the field of cellular approaches is modulation of regenerative capability of stem cells, which may help overcome difficulties in understanding the place of cell therapy in therapeutic angiogenesis.

Mesenchymal stem cell-derived small extracellular vesicles and bone regeneration

Mesenchymal stem cells (MSCs) and MSC‐derived small extracellular vesicles (sEVs) are promising candidates for cell‐based and cell‐free regenerative medicine, respectively. By virtue of their multiple lineage differentiation capacity, MSCs have been implicated as an ideal tool for bone and cartilage regeneration. However, later observations attributed such regenerative effects to MSC‐secreted paracrine factors. Exosomes, endosomal originated sEVs carrying lipid, protein and nucleic acid cargoes, were identified as components of the MSC secretome and propagated the key regenerative and immunoregulatory characteristics of parental MSCs. Here, exosome biogenesis, the molecular composition of exosomes, sEV‐cell interactions and the effects on key bone homeostasis cells are reviewed. MSC‐derived sEVs show to promote neovascularization and bone and cartilage regeneration in preclinical disease models. The mechanisms include the transfer of molecules, including microRNAs, mRNAs and proteins, to other key cells. MSC‐derived sEVs are interesting candidates as biopharmaceuticals for drug delivery and for the engineering of biologically functionalized materials. Although major exploratory efforts have been made for therapeutic development, the secretion, distribution and biological effects of MSC‐derived sEVs in bone and cartilage regeneration are not fully understood. Moreover, techniques for high‐yield production, purity and storage need to be optimized before effective and safe MSC‐derived sEVs therapies are realized.

Potential of Extracellular Vesicle-Associated TSG-6 from Adipose Mesenchymal Stromal Cells in Traumatic Brain Injury

Multipotent mesenchymal stromal cells (MSC) represent a promising strategy for a variety of medical applications. Although only a limited number of MSC engraft and survive after in vivo cellular infusion, MSC have shown beneficial effects on immunomodulation and tissue repair. This indicates that the contribution of MSC exists in paracrine signaling, rather than a cell-contact effect of MSC. In this review, we focus on current knowledge about tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) and mechanisms based on extracellular vesicles (EV) that govern long-lasting immunosuppressive and regenerative activity of MSC. In this context, in particular, we discuss the very robust set of findings by Jha and colleagues, and the opportunity to potentially extend their research focus on EV isolated in concentrated conditioned media (CCM) from adipose tissue derived MSC (ASC). Particularly, the authors showed that ASC-CCM mitigated visual deficits after mild traumatic brain injury in mice. TSG-6 knockdown ASC were, then, used to generate TSG-6-depleted CCM that were not able to replicate the alleviation of abnormalities in injured animals. In light of the presented results, we envision that the infusion of much distilled ASC-CCM could enhance the alleviation of visual abnormalities. In terms of EV research, the advantages of using size-exclusion chromatography are also highlighted because of the enrichment of purer and well-defined EV preparations. Taken together, this could further delineate and boost the benefit of using MSC-based regenerative therapies in the context of forthcoming clinical research testing in diseases that disrupt immune system homeostasis.

Dose-effect relationship and molecular mechanism by which BMSC-derived exosomes promote peripheral nerve regeneration after crush injury

Background

The development of new treatment strategies to improve peripheral nerve repair after injury, especially those that accelerate axonal nerve regeneration, is very important. The aim of this study is to elucidate the molecular mechanisms of how bone marrow stromal cell (BMSC)-derived exosomes (EXOs) participate in peripheral nerve regeneration and whether the regenerative effect of EXOs is correlated with dose.

Method

BMSCs were transfected with or without an siRNA targeting Ago2 (SiAgo2). EXOs extracted from the BMSCs were administered to dorsal root ganglion (DRG) neurons in vitro. After 48 h of culture, the neurite length was measured. Moreover, EXOs at four different doses were injected into the gastrocnemius muscles of rats with sciatic nerve crush injury. The sciatic nerve functional index (SFI) and latency of thermal pain (LTP) of the hind leg sciatic nerve were measured before the operation and at 7, 14, 21, and 28 days after the operation. Then, the number and diameter of the regenerated fibers in the injured distal sciatic nerve were quantified. Seven genes associated with nerve regeneration were investigated by qRT-PCR in DRG neurons extracted from rats 7 days after the sciatic nerve crush.

Results

We showed that after 48 h of culture, the mean number of neurites and the length of cultured DRG neurons in the SiAgo2-BMSC-EXO and SiAgo2-BMSC groups were smaller than that in the untreated and siRNA control groups. The average number and diameter of regenerated axons, LTP, and SFI in the group with 0.9 × 10¹⁰ particles/ml EXOs were better than those in other groups, while the group that received a minimum EXO dose (0.4 × 10¹⁰ particles/ml) was not significantly different from the PBS group. The expression of PMP22, VEGFA, NGFr, and S100b in DRGs from the EXO-treated group was significantly higher than that in the PBS control group. No significant difference was observed in the expression of HGF and Akt1 among the groups.

Conclusions

These results showed that BMSC-derived EXOs can promote the regeneration of peripheral nerves and that the mechanism may involve miRNA-mediated regulation of regeneration-related genes, such as VEGFA. Finally, a dose-effect relationship between EXO treatment and nerve regeneration was shown.

Small Extracellular Vesicles from Human Fetal Dermal Cells and Their MicroRNA Cargo: KEGG Signaling Pathways Associated with Angiogenesis and Wound Healing

The use of cell secreted factors in clinical settings could be an alternative to conventional cell therapy, with the advantage of limiting concerns generally associated with traditional cell transplantation, such as tumorigenicity, immunoreactivity, and carrying of infections. Based on our published data, we predict a potential role for extracellular vesicles (EVs) in contributing to the proangiogenic activity of human fetal dermal cell secretome. Depletion of nanosized EVs from secretome significantly impaired its ability to induce formation of mesh-like structures in vitro. The isolated EVs were characterized for size and concentration by nanoparticle tracking analysis, and for protein markers (Rab5⁺, Alix⁺, CD63⁺, and calnexin⁻). The microRNA profile of EVs revealed 87 microRNAs significantly upregulated (≥15-fold increase) in fetal compared to adult dermal cell-derived EVs. Interestingly, these upregulated microRNAs included microRNAs with a validated role in angiogenesis according to literature. Moreover, the DIANA-TarBase v7.0 analysis confirmed enrichment in the KEGG signaling pathways associated with angiogenesis and wound healing, with the identification of putative target genes including thrombospondin 1. To validate the in silico data, EVs were also characterized for total protein contents. When tested in in vitro angiogenesis, fetal dermal cell-derived EVs were more effective than their adult counterpart in inducing formation of complete mesh-like structures. Furthermore, treatment of fibroblasts with fetal dermal-derived EVs determined a 4-fold increase of thrombospondin 1 protein amounts compared with the untreated fibroblasts. Finally, visualization of CSFE-labeled EVs in the cytosol of target cells suggested a successful uptake of these particles at 4-8 hours of incubation. We conclude that EVs are important contributors of the proangiogenic effect of fetal dermal cell secretome. Hence, EVs could also serve as vehicle for a successful delivery of microRNAs or other molecules of therapeutic interest to target cells.

Intracellular prodrug gene therapy for cancer mediated by tumor cell suicide gene exosomes

Recently, we reported about exosomes possessing messenger RNA (mRNA) of suicide gene secreted from mesenchymal stem/stromal cells (MSCs) engineered to express the suicide gene-fused yeast cytosine deaminase::uracil phosphoribosyltransferase (yCD::UPRT). The yCD::UPRT-MSC exosomes are internalized by tumor cells and intracellularly convert prodrug 5-fluorocytosine (5-FC) to cytotoxic drug 5-fluorouracil (5-FU). Human tumor cells with the potential to metastasize release exosomes involved in the creation of a premetastatic niche at the predicted organs. We found that cancer cells stably transduced with yCD::UPRT gene by retrovirus infection released exosomes acting similarly like yCD::UPRT-MSC exosomes. Different types of tumor cells were transduced with the yCD::UPRT gene. The homogenous cell population of yCD::UPRT-transduced tumor cells expressed the yCD::UPRT suicide gene and secreted continuously exosomes with suicide gene mRNA in their cargo. All tumor cell suicide gene exosomes upon internalization into the recipient tumor cells induced the cell death by intracellular conversion of 5-FC to 5-FU and to 5-FUMP in a dose-dependent manner. Most of tumor cell-derived suicide gene exosomes were tumor tropic, in 5-FC presence they killed tumor cells but did not inhibit the growth of human skin fibroblast as well as DP-MSCs. Tumor cell-derived suicide gene exosomes home to their cells of origin and hold an exciting potential to become innovative specific therapy for tumors and potentially for metastases.

MSC-derived exosomal miR-34a/c-5p and miR-29b-3p improve intestinal barrier function by targeting the Snail/Claudins signaling pathway

AIMS

Mesenchymal stem cell (MSC)-derived exosomes (MSCs-exos) regulate biological functions in different diseases, such as liver fibrosis, diabetes, and ischaemic heart injury. However, the function of MSC-derived exosomes on the intestinal barrier and the underlying mechanisms are poorly characterized.

MAIN METHODS

The expression of miR-34a/c-5p, miR-29b-3p and Claudin-3 in human normal intestinal tissues and damaged intestinal tissues was evaluated by RT-qPCR. The effect of MSC-secreted exosomes on Claudins in Caco-2 cells was measured by using confocal microscopy, RT-qPCR and Western blot. Dual luciferase reporter assays and RNA immunoprecipitation (RIP) assays were performed to study the interaction between miR-34a/c-5p, miR-29b-3p and Snail. I/R-induced intestinal damage in rats was used to determine the in vivo effect of MSC-exos on intestinal barrier function.

KEY FINDINGS

In this study, we found that miR-34a/c-5p, miR-29b-3p and Claudin-3 were downregulated in damaged human intestinal tissues. MSC-exos increased the expression of Claudin-3, Claudin-2 and ZO-1 in Caco-2 cells. Further studies demonstrated that MSC-exos promoted Claudin-3, Claudin-2 and ZO-1 expression in Caco-2 cells by Snail, which was targeted by miR-34a/c-5p and miR-29b-3p. In vivo experiments showed that MSC-derived exosomes could improve I/R-induced intestinal damage through the Snail/Claudins signaling pathway.

SIGNIFICANCE

The findings here suggest a novel molecular basis for the therapy of intestinal barrier dysfunction.