MicroRNA-10b promotes the migration of mouse bone marrow-derived mesenchymal stem cells and downregulates the expression of E-cadherin

Limbal Epithelial Stem Cells in the Diabetic Cornea

Continuous replenishment of the corneal epithelium is pivotal for maintaining optical transparency and achieving optimal visual perception. This dynamic process is driven by limbal epithelial stem cells (LESCs) located at the junction between the cornea and conjunctiva, which is otherwise known as the limbus. In patients afflicted with diabetes, hyperglycemia-induced impairments in corneal epithelial regeneration results in persistent epithelial and other defects on the ocular surface, termed diabetic keratopathy (DK), which progressively diminish vision and quality of life. Reports of delayed corneal wound healing and the reduced expression of putative stem cell markers in diabetic relative to healthy eyes suggest that the pathogenesis of DK may be associated with the abnormal activity of LESCs. However, the precise role of these cells in diabetic corneal disease is poorly understood and yet to be comprehensively explored. Herein, we review existing literature highlighting aberrant LESC activity in diabetes, focusing on factors that influence their form and function, and emerging therapies to correct these defects. The consequences of malfunctioning or depleted LESC stocks in DK and limbal stem cell deficiency (LSCD) are also discussed. These insights could be exploited to identify novel targets for improving the management of ocular surface complications that manifest in patients with diabetes.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

Biology and therapeutic potential of mesenchymal stem cell extracellular vesicles in axial spondyloarthritis

Axial spondyloarthritis (AxSpA) is a chronic, inflammatory, autoimmune disease that predominantly affects the joints of the spine, causes chronic pain, and, in advanced stages, may result in spinal fusion. Recent developments in understanding the immunomodulatory and tissue-differentiating properties of mesenchymal stem cell (MSC) therapy have raised the possibility of applying such treatment to AxSpA. The therapeutic effectiveness of MSCs has been shown in numerous studies spanning a range of diseases. Several studies have been conducted examining acellular therapy based on MSC secretome. Extracellular vesicles (EVs) generated by MSCs have been proven to reproduce the impact of MSCs on target cells. These EVs are associated with immunological regulation, tissue remodeling, and cellular homeostasis. EVs' biological effects rely on their cargo, with microRNAs (miRNAs) integrated into EVs playing a particularly important role in gene expression regulation. In this article, we will discuss the impact of MSCs and EVs generated by MSCs on target cells and how these may be used as unique treatment strategies for AxSpA.

Macrophages and Bone Marrow-Derived Mesenchymal Stem Cells Work in Concert to Promote Fracture Healing: A Brief Review

Bone marrow-derived mesenchymal stem cell (BMSC)-based and macrophage-based cell therapy are regarded as promising strategies to promote fracture healing because of incredible osteogenic potential of BMSCs and typical immunomodulatory function of macrophages. Apart from their respective key roles, accumulative evidence has also demonstrated the importance of cross talk between these two cell types in fracture healing process. This review takes a deep insight into the recent research progress of the synergic performance of BMSCs and macrophages by discussing not only the cells own functions but also the relevant impact factors and mechanisms (ambient microenvironment stimulus, miRNAs, etc). The aim of this review is to provide some valuable cues and technique support for the macrophage- and BMSC-related research, which will be helpful to propel BMSC/macrophage-based combined cell therapy for bone fracture treatment.

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

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

MicroRNAs in Serum Exosomes as Circulating Biomarkers for Postmenopausal Osteoporosis

Postmenopausal osteoporosis (PMOP) is the most common skeletal disease in postmenopausal women and has become a global public health issue. Emerging evidence demonstrated the important relationship between microRNAs and PMOP. However, miRNAs have not yet been reported in PMOP. Hence, the present study aimed to investigate the differences in miRNA expression profiles in PMOP with fragility fractures to identify the key circulating miRNAs in serum exosomes and to validate these molecules as potential biomarkers. Postmenopausal women with osteoporotic fracture and normal bone mass were enrolled. Serum exosomes were isolated by traditional differential ultracentrifugation from participants. Isolated exosomes were identified by electron microscopy, western blotting and nanoparticle-tracking analysis and then examined for exosomal small RNA sequencing. The expression of miRNAs was compared by sRNA deep sequencing and bioinformatics analysis. Three miRNAs (mir-324-3p, mir-766-3p and mir-1247-5p) were found to be associated with BMD of L1-L4, FN (femur neck) and TH (total hip), while mir-330-5p and mir-3124-5p were associated with BMD of FN and TH. Furthermore, mir-330-5p was found to promote the ALP activity of hBMSCs, while mir-3124-5p showed the opposite result. The results showed that serum exosomal miRNAs were differentially expressed in postmenopausal osteoporosis patients with fragility fractures. Our study provides the first evidence that exosomal miRNA profiling revealed aberrant circulating miRNA in postmenopausal osteoporosis. Mir-324-3p, mir-766-3p, mir-1247-5p, mir-330-5p and mir-3124-5p, which were associated with bone mineral density (BMD), may serve as candidate diagnostic biomarkers as well as potentially contribute to pathophysiology of PMOP.

Cell-free exosome-laden scaffolds for tissue repair

With the development of regenerative medicine, tissue repair at the molecular, cellular, tissue, and organ level has seen continuous improvements over traditional techniques. As the core of tissue repair, seed cells are widely used in various fields of regenerative medicine. However, their use is still associated with problems such as decreased cell survival and regeneration capacity after transplantation, immune rejection, and ethical concerns. Therefore, it is difficult to universally and safely apply stem cell banks for regenerative medicine. The paracrine effects of cells, especially secretion of exosomes, play vital roles in cell communication, immune response, angiogenesis, scar formation, tissue repair, and other biological functions. Exosomes are a type of nanoscale extracellular vesicle that contain biologically active molecules such as RNA and proteins; therefore, exosomes can replicate the functions of their parental cells. Meanwhile, exosomes can be used as nanocarriers to deliver active factors or small molecules to promote tissue repair. Preclinical studies of exosomes in tissue engineering and regenerative medicine have been carried in the fields of bone/cartilage repair, nerve regeneration, liver and kidney regeneration, skin repair, vascular tissue regeneration, etc. This review introduces exosomes from the aspects of biogenesis, composition, identification, and isolation, and focuses on the development status of scaffold materials for exosome delivery. In addition, we highlight examples of exosome-laden scaffolds for preclinical applications in tissue repair. We look forward to the broad application prospects of exosome-laden scaffolds.

Mesenchymal stem cells secretome: The cornerstone of cell-free regenerative medicine

Mesenchymal stem cells (MSCs) are the most frequently used stem cells in clinical trials due to their easy isolation from various adult tissues, their ability of homing to injury sites and their potential to differentiate into multiple cell types. However, the realization that the beneficial effect of MSCs relies mainly on their paracrine action, rather than on their engraftment in the recipient tissue and subsequent differentiation, has opened the way to cell-free therapeutic strategies in regenerative medicine. All the soluble factors and vesicles secreted by MSCs are commonly known as secretome. MSCs secretome has a key role in cell-to-cell communication and has been proven to be an active mediator of immune-modulation and regeneration both in vitro and in vivo. Moreover, the use of secretome has key advantages over cell-based therapies, such as a lower immunogenicity and easy production, handling and storage. Importantly, MSCs can be modulated to alter their secretome composition to better suit specific therapeutic goals, thus, opening a large number of possibilities. Altogether these advantages now place MSCs secretome at the center of an important number of investigations in different clinical contexts, enabling rapid scientific progress in this field.

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.

Endogenous cell recruitment strategy for articular cartilage regeneration

In the absence of timely and proper treatments, injuries to articular cartilage (AC) can lead to cartilage degeneration and ultimately result in osteoarthritis. Regenerative medicine and tissue engineering techniques are emerging as promising approaches for AC regeneration and repair. Although the use of cell-seeded scaffolds prior to implantation can regenerate and repair cartilage lesions to some extent, these approaches are still restricted by limited cell sources, excessive costs, risks of disease transmission and complex manufacturing practices. Recently developed acellular scaffold approaches that rely on the recruitment of endogenous cells to the injured sites avoid these drawbacks and offer great promise for in situ AC regeneration. Multiple endogenous stem/progenitor cells (ESPCs) are found in joint-resident niches and have the capability to migrate to sites of injury to participate in AC regeneration. However, the natural recruitment of ESPCs is insufficient, and the local microenvironment is hostile after injury. Hence, an endogenous cell recruitment strategy based on the combination of chemoattractants and acellular scaffolds to effectively and specifically recruit ESPCs and improve local microenvironment may provide new insights into in situ AC regeneration. This review provides a brief overview of: (1) the status of endogenous cell recruitment strategy; (2) the subpopulations, potential migration routes (PMRs) of joint-resident ESPCs and their immunomodulatory and reparative effects; (3) chemoattractants and their potential adverse effects; (4) scaffold-based drug delivery systems (SDDSs) that are utilized for in situ AC regeneration; and (5) the challenges and future perspectives of endogenous cell recruitment strategy for AC regeneration. STATEMENT OF SIGNIFICANCE: Although the endogenous cell recruitment strategy for articular cartilage (AC) regeneration has been investigated for several decades, much work remains to be performed in this field. Future studies should have the following aims: (1) reporting the up-to-date progress in the endogenous cell recruitment strategies; (2) determining the subpopulations of ESPCs, the cellular and molecular mechanisms underlying the migration of these cells and their anti-inflammatory, immunomodulatory and reparative effects; (3) elucidating the chemoattractants that enhance ESPC recruitment and their potential adverse effects; and (4) developing advanced SDDSs for chemoattractant dispatch. Herein, we present a systematic overview of the aforementioned issues to provide a better understanding of endogenous cell recruitment strategies for AC regeneration and repair.

MicroRNA-126 promotes proliferation, migration, invasion and endothelial differentiation while inhibits apoptosis and osteogenic differentiation of bone marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (BMSCs) are widely used for the treatment of inflammatory and immune diseases, and microRNA-126 (miR-126) is a critical regulator in inflammation as well as immunity. However, the mediating role of miR-126 in BMSCs is still not clear. Thus, this study aimed to preliminarily investigate the effect of miR-126 on proliferation, apoptosis, migration, invasion, differentiation, and its potential regulating pathways in BMSCs. Human BMSCs were obtained and infected with miR-126 overexpression lentivirus, control overexpression lentivirus, miR-126 knock-down lentivirus and control knock-down lentivirus, then cell functions, the PI3 K/AKT pathway and MEK1/ERK1 pathway were evaluated. Subsequently, PI3 K overexpression plasmid and MEK1 overexpression plasmid were transfected into BMSCs with miR-126 knockdown, then the cell functions were assessed as well. BMSCs with miR-126 overexpression displayed elevated proliferation, migration and invasion while decreased apoptosis; however, BMSCs with miR-126 knockdown presented with decreased proliferation, migration, invasion but increased apoptosis. As for differentiation, BMSCs with miR-126 overexpression showed higher levels of CD31, eNOS and VE-cadherin but lower expressions of ALP, OPN and RUNX2, while BMSCs with miR-126 knockdown disclosed the opposite results. Additionally, BMSCs with miR-126 overexpression showed elevated PI3 K, pAKT, MEK1 and pERK1 expressions, while BMSCs with miR-126 knockdown displayed opposite results. Furthermore, PI3 K overexpression and MEK1 overexpression both reversed the effects of miR-126 on cell functions in BMSCs. In conclusion, miR-126 is a genetic regulator in BMSCs via modulating multiple cell functions through the PI3 K/AKT and MEK1/ERK1 signaling pathways.

MicroRNAs in the Migration of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) represent a promising source of cell-based therapies for treatment of a wide variety of injuries and diseases. Their tropism and migration to the damaged sites, which are elicited by cytokines secreted from tissues around pathology, are the prerequisite for tissue repair and regeneration. Better understanding of the elicited-migration of MSCs and discovering conditions that elevate their migration ability, will help to increase their homing to pathologies and improve therapeutic efficacy. It is increasingly recognized that microRNAs are important regulators of cell migration. Here we summarize current understanding of the microRNA-regulated migration of MSCs.

Functional and histological evaluation of bone marrow stem cell-derived exosomes therapy on the submandibular salivary gland of diabetic Albino rats through TGFβ/ Smad3 signaling pathway

BACKGROUND

To prevail over diabetes mellitus and its numerous complications, researchers are seeking new therapies. Exosomes are natural cargo of functional proteins and can be used as a therapeutic delivery of these molecules.

OBJECTIVE

The aim of this study was to evaluate the effect of exosomes derived from bone marrow mesenchymal stem cells (BM-MSCs) as a therapeutic intervention in salivary gland diabetic complications.

METHODS

Ten adult healthy male Albino rats, weighing about 150-200 g were grouped into 2 groups. Diabetic group I: consisted of 5 streptozotocin (STZ)-induced diabetic rats. Exosomes treated group II: consisted of 5 STZ-induced diabetic rats, each animal received a single injection of exosomes (100 μg/kg/dose suspended in 0.2 ml PBS) through the tail vein. All animals were sacrificed after 5 weeks from the beginning of the experiment. Submandibular salivary gland samples were excised and processed for histological, ultrastructural examination and PCR for TGFβ, Smad2 and Smad3. Blood glucose level was monitored weekly, salivary IgA and serum amylase were evaluated before and after diabetes induction and at the end of the experiment.

RESULTS

Histological and ultrastructural results of the exosomes treated group were promising regarding the glandular and ductal elements with less fibrosis observed. Results of PCR supported the role of exosomes to inhibit the diabetic sequalae in salivary gland and its complications through inhibiting TGFβ and its related pathway via Smad2 and Smad3. Blood glucose levels were reduced. In addition, salivary glands' function was improved as evidenced by reduction in serum amylase and salivary IgA.

CONCLUSION

BM-MSC-derived exosomes could be a novel therapeutic strategy for diabetic complications involving salivary glands.

Post-production modifications of murine mesenchymal stem cell (mMSC) derived extracellular vesicles (EVs) and impact on their cellular interaction

In regards to their key role in intercellular communication, extracellular vesicles (EVs) have a strong potential as bio-inspired drug delivery systems (DDS). With the aim of circumventing some of their well-known issues (production yield, drug loading yield, pharmacokinetics), we specifically focused on switching the biological vision of these entities to a more physico-chemical one, and to consider and fine-tune EVs as synthetic vectors. To allow a rational use, we first performed a full physico-chemical (size, concentration, surface charge, cryoTEM), biochemical (western blot, proteomics, lipidomics, transcriptomics) and biological (cell internalisation) characterisation of murine mesenchymal stem cell (mMSC)-derived EVs. A stability study based on evaluating the colloidal behaviour of obtained vesicles was performed in order to identify optimal storage conditions. We evidenced the interest of using EVs instead of liposomes, in regards to target cell internalisation efficiency. EVs were shown to be internalised through a caveolae and cholesterol-dependent pathway, following a different endocytic route than liposomes. Then, we characterised the effect of physical methods scarcely investigated with EVs (extrusion through 50 nm membranes, freeze-drying, sonication) on EV size, concentration, structure and cell internalisation properties. Our extensive characterisation of the effect of these physical processes highlights their promise as loading methods to make EVs efficient delivery vehicles.

Genetically Engineered-MSC Therapies for Non-unions, Delayed Unions and Critical-size Bone Defects

The normal bone regeneration process is a complex and coordinated series of events involving different cell types and molecules. However, this process is impaired in critical-size/large bone defects, with non-unions or delayed unions remaining a major clinical problem. Novel strategies are needed to aid the current therapeutic approaches. Mesenchymal stem/stromal cells (MSCs) are able to promote bone regeneration. Their beneficial effects can be improved by modulating the expression levels of specific genes with the purpose of stimulating MSC proliferation, osteogenic differentiation or their immunomodulatory capacity. In this context, the genetic engineering of MSCs is expected to further enhance their pro-regenerative properties and accelerate bone healing. Herein, we review the most promising molecular candidates (protein-coding and non-coding transcripts) and discuss the different methodologies to engineer and deliver MSCs, mainly focusing on in vivo animal studies. Considering the potential of the MSC secretome for bone repair, this topic has also been addressed. Furthermore, the promising results of clinical studies using MSC for bone regeneration are discussed. Finally, we debate the advantages and limitations of using MSCs, or genetically-engineered MSCs, and their potential as promoters of bone fracture regeneration/repair.

miRNA-seq analysis of human vertebrae provides insight into the mechanism underlying GIOP

High-throughput sequencing (HTS) was recently applied to detect microRNA (miRNA) regulation in age-related osteoporosis. However, miRNA regulation has not been reported in glucocorticoid-induced osteoporosis (GIOP) patients and the mechanism of GIOP remains elusive. To comprehensively analyze the role of miRNA regulation in GIOP based on human vertebrae and to explore the molecular mechanism, a high-throughput sequencing strategy was employed to identify miRNAs involved in GIOP. Twenty-six patients undergoing spinal surgery were included in this study. Six vertebral samples were selected for miRNA sequencing (miRNA-seq) analysis and 26 vertebral samples were verified by qRT-PCR. Bioinformatics was utilized for target prediction, to investigate the regulation of miRNA-mRNA networks, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Six significantly up-regulated miRNAs (including one novel miRNA) and three significantly down-regulated miRNAs were verified via miRNA-seq and verified in the vertebrae of GIOP patients. Up-regulated miRNAs included hsa-miR-214-5p, hsa-miR-10b-5p, hsa-miR-21-5p, hsa-miR-451a, hsa-miR-186-5p, and hsa-miR-novel-chr3_49,413 while down-regulated miRNAs included hsa-let-7f-5p, hsa-let-7a-5p, and hsa-miR-27a-3p. Bioinformatics analysis revealed 5983 and 23,463 predicted targets in the up-regulated and down-regulated miRNAs respectively, using the miRanda, miRBase and TargetScan databases. The target genes of these significantly altered miRNAs were enriched to 1939 GO terms and 84 KEGG pathways. GO terms revealed that up-regulated targets were most enriched in actin filament-based processes (BP), anchoring junction (CC), and cytoskeletal protein binding (MF). Conversely, the down-regulated targets were mostly enriched in multicellular organismal development (BP), intracellular membrane-bounded organelles (CC), and protein binding (MF). Top-10 pathway analysis revealed that the differentially expressed miRNAs in GIOP were closely related to bone metabolism-related pathways such as FoxO, PI3K-Akt, MAPK and Notch signaling pathway. These results suggest that significantly altered miRNAs may play an important role in GIOP by targeting mRNA and regulating biological processes and bone metabolism-related pathways such as MAPK, FoxO, PI3K-Akt and Notch signaling, which provides novel insight into the mechanism of GIOP and lays a good foundation for the prevention and treatment of GIOP.

Intranasal administration of exosomes derived from mesenchymal stem cells ameliorates autistic-like behaviors of BTBR mice

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by three core symptoms that include social interaction deficits, cognitive inflexibility, and communication disorders. They have been steadily increasing in children over the past several years, with no effective treatment. BTBR T+tf/J (BTBR) mice are an accepted model of evaluating autistic-like behaviors as they present all core symptoms of ASD. We have previously shown that transplantation of human bone marrow mesenchymal stem cells (MSC) to the lateral ventricles of BTBR mice results in long lasting improvement in their autistic behavioral phenotypes. Recent studies point exosomes as the main mediators of the therapeutic effect of MSC. Here, we tested whether treatment with the exosomes secreted from MSC (MSC-exo) will show similar beneficial effects. We found that intranasal administration of MSC-exo increased male to male social interaction and reduced repetitive behaviors. Moreover, the treatment led to increases of male to female ultrasonic vocalizations and significant improvement in maternal behaviors of pup retrieval. No negative symptoms were detected following MSC-exo intranasal treatments in BTBR or healthy C57BL mice. The marked beneficial effects of the exosomes in BTBR mice may translate to a novel, non-invasive, and therapeutic strategy to reduce the symptoms of ASD.

Mesenchymal stem cell-derived exosomes have altered microRNA profiles and induce osteogenic differentiation depending on the stage of differentiation

Human mesenchymal stem cell (hMSC)-derived exosomes have shown regenerative effects, but their role in osteogenesis and the underlying mechanism are yet to be determined. In this study, we examined the time-course secretion of exosomes by hMSCs during the entire process of osteogenic differentiation. Exosomes derived from hMSCs in various stages of osteogenic differentiation committed homotypic cells to differentiate towards osteogenic lineage, but only exosomes from late stages of osteogenic differentiation induced extracellular matrix mineralisation. Exosomes from expansion and early and late stages of osteogenic differentiation were internalised by a subpopulation of hMSCs. MicroRNA profiling revealed a set of differentially expressed exosomal microRNAs from the late stage of osteogenic differentiation, which were osteogenesis related. Target prediction demonstrated that these microRNAs enriched pathways involved in regulation of osteogenic differentiation and general mechanisms how exosomes exert their functions, such as "Wnt signalling pathway" and "endocytosis". Taken together, the results show that MSCs secrete exosomes with different biological properties depending on differentiation stage of their parent cells. The exosomal cargo transferred from MSCs in the late stage of differentiation induces osteogenic differentiation and mineralisation. Moreover, it is suggested that the regulatory effect on osteogenesis by exosomes is at least partly exerted by exosomal microRNA.

MiR-375 inhibits the hepatocyte growth factor-elicited migration of mesenchymal stem cells by downregulating Akt signaling

The migration of mesenchymal stem cells (MSCs) is critical for their use in cell-based therapies. Accumulating evidence suggests that microRNAs are important regulators of MSC migration. Here, we report that the expression of miR-375 was downregulated in MSCs treated with hepatocyte growth factor (HGF), which strongly stimulates the migration of these cells. Overexpression of miR-375 decreased the transfilter migration and the migration velocity of MSCs triggered by HGF. In our efforts to determine the mechanism by which miR-375 affects MSC migration, we found that miR-375 significantly inhibited the activation of Akt by downregulating its phosphorylation at T308 and S473, but had no effect on the activity of mitogen-activated protein kinases. Further, we showed that 3'phosphoinositide-dependent protein kinase-1 (PDK1), an upstream kinase necessary for full activation of Akt, was negatively regulated by miR-375 at the protein level. Moreover, miR-375 suppressed the phosphorylation of focal adhesion kinase (FAK) and paxillin, two important regulators of focal adhesion (FA) assembly and turnover, and decreased the number of FAs at cell periphery. Taken together, our results demonstrate that miR-375 inhibits HGF-elicited migration of MSCs through downregulating the expression of PDK1 and suppressing the activation of Akt, as well as influencing the tyrosine phosphorylation of FAK and paxillin and FA periphery distribution.

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

OBJECTIVES

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

METHODS

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

CONCLUSION

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

Genome-wide analysis suggests a differential microRNA signature associated with normal and diabetic human corneal limbus

Small non-coding RNAs, in particular microRNAs (miRNAs), regulate fine-tuning of gene expression and can impact a wide range of biological processes. However, their roles in normal and diseased limbal epithelial stem cells (LESC) remain unknown. Using deep sequencing analysis, we investigated miRNA expression profiles in central and limbal regions of normal and diabetic human corneas. We identified differentially expressed miRNAs in limbus vs. central cornea in normal and diabetic (DM) corneas including both type 1 (T1DM/IDDM) and type 2 (T2DM/NIDDM) diabetes. Some miRNAs such as miR-10b that was upregulated in limbus vs. central cornea and in diabetic vs. normal limbus also showed significant increase in T1DM vs. T2DM limbus. Overexpression of miR-10b increased Ki-67 staining in human organ-cultured corneas and proliferation rate in cultured corneal epithelial cells. MiR-10b transfected human organ-cultured corneas showed downregulation of PAX6 and DKK1 and upregulation of keratin 17 protein expression levels. In summary, we report for the first time differential miRNA signatures of T1DM and T2DM corneal limbus harboring LESC and show that miR-10b could be involved in the LESC maintenance and/or their early differentiation. Furthermore, miR-10b upregulation may be an important mechanism of corneal diabetic alterations especially in the T1DM patients.

Overexpression of miR-10b in colorectal cancer patients: Correlation with TWIST-1 and E-cadherin expression

MicroRNAs are emergent players of epigenetics that function as oncogenes or tumor suppressors and that have been implicated in regulating diverse cellular pathways. MiR-10b is an oncogenic microRNA involved in tumor invasion and metastasis in various cancers. Our data have shown that miR-10b is overexpressed in colorectal cancer samples in comparison with non-tumorous adjacent mucosa (p = 0.0025) and that it is associated with severe features such as tumor size >5 cm (p = 0.023), distant metastasis (p = 0.0022), non-differentiated tumors (p = 0.016), and vascular invasion (p = 0.01). Regarding the regulation of its expression, positive correlation between the loss of miR-10b and aberrant DNA methylation (p = 0.02) as well as a loss of TWIST-1 messenger RNA (p = 0.018) have been observed. Furthermore, expression analysis of the downstream miR-10b targets has shown that there are associations between low HOXD10 messenger RNA and E-cadherin protein levels (p < 0.0001, p = 0.0008, respectively) and overexpression of miR-10b. Our data suggests that overexpression of miR-10b results from high levels of TWIST-1 and may induce a decrease of E-cadherin membranous protein levels, thus contributing to the acquisition of metastatic phenotypes in colorectal cancer.

MiR-124 suppresses the chemotactic migration of rat mesenchymal stem cells toward HGF by downregulating Wnt/β-catenin signaling

Mesenchymal stem cells (MSCs) exhibit the potential to repair a wide variety of injured adult tissues. The migration capability of MSCs is an important determinant of the efficiency of MSC transplant therapy. MicroRNAs (miRNAs) are increasingly implicated in regulating the migration of MSCs. Herein, we show that the expression of miR-124 was downregulated in rat MSCs (rMSCs) treated with hepatocyte growth factor (HGF). Overexpression of miR-124 significantly reduced the chemotactic migration of rMSCs toward HGF, while inhibition of endogenous miR-124 promoted the chemotactic migration. A further study revealed that miR-124 directly targeted FZD4 and LRP6, which encode a receptor and co-receptor of the Wnt/β-catenin signaling pathway, respectively, thus reducing the activity of this signaling. Consistently, activation of the Wnt/β-catenin signaling pathway by LiCl and ΔN89β-catenin rescued the inhibitory effect of miR-124 on the chemotactic migration of rMSCs toward HGF, while inhibition of Wnt/β-catenin signaling by FH535 abrogated the enhanced chemotactic response achieved by the miR-124 inhibitor. Collectively, our study demonstrates that miR-124 downregulates Wnt/β-catenin signaling via targeting FZD4 and LRP6 and thus suppresses the chemotactic migration of rMSCs toward HGF.

Autotaxin-LPA axis regulates hMSC migration by adherent junction disruption and cytoskeletal rearrangement via LPAR1/3-dependent PKC/GSK3β/β-catenin and PKC/Rho GTPase pathways

Bioactive molecules and stem cell-based regenerative engineering is emerging a promising approach for regenerating tissues. Autotaxin (ATX) is a key enzyme that regulates lysophosphatidic acid (LPA) levels in biological fluids, which exerts a wide range of cellular functions. However, the biological role of ATX in human umbilical cord blood-derived mesenchymal stem cells (hMSCs) migration remains to be fully elucidated. In this study, we observed that hMSCs, which were stimulated with LPA, accelerated wound healing, and LPA increased the migration of hMSCs into a wound site in a mouse skin wound healing model. In an experiment to investigate the effect of LPA on hMSC migration, ATX and LPA increased hMSC migration in a dose-dependent manner, and LPA receptor 1/3 siRNA transfections inhibited the ATX-induced cell migration. Furthermore, LPA increased Ca(2+) influx and PKC phosphorylation, which were blocked by Gαi and Gαq knockdown as well as by Ptx pretreatment. LPA increased GSK3β phosphorylation and β-catenin activation. LPA induced the cytosol to nuclear translocation of β-catenin, which was inhibited by PKC inhibitors. LPA stimulated the binding of β-catenin on the E-box located in the promoter of the CDH-1 gene and decreased CDH-1 promoter activity. In addition, the ATX and LPA-induced increase in hMSC migration was blocked by β-catenin siRNA transfection. LPA-induced PKC phosphorylation is also involved in Rac1 and CDC42 activation, and Rac1 and CDC42 knockdown abolished LPA-induced F-actin reorganization. In conclusion, ATX/LPA stimulates the migration of hMSCs through LPAR1/3-dependent E-cadherin reduction and cytoskeletal rearrangement via PKC/GSK3β/β-catenin and PKC/Rho GTPase pathways.

cAMP Promotes Cell Migration Through Cell Junctional Complex Dynamics and Actin Cytoskeleton Remodeling: Implications in Skin Wound Healing

Stem cells have attracted great interest for their therapeutic capacity in tissue regeneration. Cyclic adenosine 3',5'-monophosphate (cAMP), existing in high concentration at wound sites, mediated various signaling pathways such as cytoskeleton dynamics, cell adhesion, and cell migration in stem cells, which suggest the critical roles of cAMP in the wound healing process through functional regulation of stem cells. However, the mechanisms behind the effect of cAMP on mouse embryonic stem cell (mESC) motility and its roles on skin wound healing remain to be fully elucidated. In the present study, 8-Bromo cAMP-treated mESCs showed significant wound closure and improved neovascularization. Moreover, 8-Bromo cAMP stimulated mESC migration into the wound bed. 8-Bromo cAMP also increased ESC motility in in vitro migration assay. 8-Bromo cAMP induced myosin light chain phosphorylation through Rac1 and Cdc42 signaling, which were involved in 8-Bromo cAMP-induced decrease in expression of junction proteins (connexin 43, E-cadherin, and occludin) at the plasma membrane. Subsequently, 8-Bromo cAMP induced the disruption of cell junctions (including gap junctions, adherens junctions, and tight junctions), which reduced the function of the gap junctions and cell adhesion. In addition, 8-Bromo cAMP-induced Rac1 and Cdc42 activation increased Arp3, TOCA, PAK, and N-WASP expression, but decreased cofilin phosphorylation level, which elicited actin cytoskeleton remodeling. In contrast to the control, 8-Bromo cAMP evoked a substantial migration of cells into the denuded area, which was blocked by the small interfering RNAs of the signaling pathway-related molecules or by inhibitors. In conclusion, cAMP enhanced the migration of mESCs through effective coordination of junctional disruption and actin cytoskeleton remodeling, which increased the wound healing capacity of ESCs.

Human bone marrow- and adipose-mesenchymal stem cells secrete exosomes enriched in distinctive miRNA and tRNA species

Introduction

Administration of mesenchymal stem cells (MSCs) represents a promising treatment option for patients suffering from immunological and degenerative disorders. Accumulating evidence indicates that the healing effects of MSCs are mainly related to unique paracrine properties, opening opportunities for secretome-based therapies. Apart from soluble factors, MSCs release functional small RNAs via extracellular vesicles (EVs) that seem to convey essential features of MSCs. Here we set out to characterize the full small RNAome of MSC-produced exosomes.

Methods

We set up a protocol for isolating exosomes released by early passage adipose- (ASC) and bone marrow-MSCs (BMSC) and characterized them via electron microscopy, protein analysis and small RNA-sequencing. We developed a bioinformatics pipeline to define the exosome-enclosed RNA species and performed the first complete small RNA characterization of BMSCs and ASCs and their corresponding exosomes in biological replicates.

Results

Our analysis revealed that primary ASCs and BMSCs have highly similar small RNA expression profiles dominated by miRNAs and snoRNAs (together 64-71 %), of which 150–200 miRNAs are present at physiological levels. In contrast, the miRNA pool in MSC exosomes is only 2-5 % of the total small RNAome and is dominated by a minor subset of miRNAs. Nevertheless, the miRNAs in exosomes do not merely reflect the cellular content and a defined set of miRNAs are overrepresented in exosomes compared to the cell of origin. Moreover, multiple highly expressed miRNAs are precluded from exosomal sorting, consistent with the notion that these miRNAs are involved in functional repression of RNA targets. While ASC and BMSC exosomes are similar in RNA class distribution and composition, we observed striking differences in the sorting of evolutionary conserved tRNA species that seems associated with the differentiation status of MSCs, as defined by Sox2, POU5F1A/B and Nanog expression.

Conclusions

We demonstrate that primary MSCs release small RNAs via exosomes, which are increasingly implicated in intercellular communications. tRNAs species, and in particular tRNA halves, are preferentially released and their specific sorting into exosomes is related to MSC tissue origin and stemness. These findings may help to understand how MSCs impact neighboring or distant cells with possible consequences for their therapeutic usage.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0116-z) contains supplementary material, which is available to authorized users.

TGF-β1 induces apoptosis of bone marrow-derived mesenchymal stem cells via regulation of mitochondrial reactive oxygen species production

Bone marrow-derived mesenchymal stem cells (BMSCs) are the most promising seed cells in regenerative medicine. Our previous study demonstrated that transforming growth factor (TGF)-β1 induced BMSC senescence in vitro. Whether TGF-β1 affects the apoptosis of BMSCs has not been examined; therefore the aim of the present study was to investigate this effect. BMSCs were isolated from mouse bone marrow, and the third-passage cells were exposed to 0, 10 and 20 ng/ml TGF-β1 for 24 h. Cell proliferation was measured by MTT assay; apoptosis was assessed using DAPI staining; and the apoptotic signals Annexin V, B-cell lymphoma (Bcl)-2 and Bcl-2-associated X protein (Bax) were measured using western blotting. Mitochondrial reactive oxygen species (ROS) were measured by flow cytometry following staining with MitoSOX™ Red mitochondrial superoxide indicator. The MTT assay showed that 10 and 20 ng/ml TGF-β1 inhibited BMSC proliferation. DAPI staining demonstrated that 10 and 20 ng/ml TGF-β1 promoted BMSC apoptosis, which was further confirmed by a western blotting assay showing a significant increase in the pro-apoptotic signals Annexin V and Bax but a decrease in the anti-apoptotic signal Bcl-2. It was also found that TGF-β1 markedly increased the mitochondrial ROS levels in BMSCs. It is well known that mitochondrial ROS are strong stimulators of cell apoptosis. These findings indicate that TGF-β1 can induce BMSC apoptosis, and the mechanism may involve mitochondrial ROS generation.

Interactions between E-cadherin and microRNA deregulation in head and neck cancers: the potential interplay

E-cadherin expression in the head and neck epithelium is essential for the morphogenesis and homeostasis of epithelial tissues. The cadherin-mediated cell-cell contacts are required for the anchorage-dependent growth of epithelial cells. Further, survival and proliferation require physical tethering created by proper cell-cell adhesion. Otherwise, the squamous epithelial cells will undergo programmed cell death. Head and neck cancers can escape from anoikis and enter into the epithelial-mesenchymal transition stages via the modulation of E-cadherin expression with epigenetic mechanisms. At epigenetic level, gene expression control is not dependent on the DNA sequence. In the context of E-cadherin regulation in head and neck cancers, 2 major mechanisms including de novo promoter hypermethylation and microRNA dysregulation are most extensively studied. Both of them control E-cadherin expression at transcription level and subsequently hinder the overall E-cadherin protein level in the head and neck cancer cells. Increasing evidence suggested that microRNA mediated E-cadherin expression in the head and neck cancers by directly/indirectly targeting the transcription suppressors of E-cadherin, ZEB1 and ZEB2.

Downregulation of β-catenin and Akt signaling is responsible for poor proliferation of the late passage of bone marrow mesenchymal stem cells

It is well established that mesenchymal stem cells (MSCs) will partially lose their proliferative ability with continuous expansion. However, the specific mechanisms underlying this effect remain unclear. In the present study, it was identified that β-catenin was downregulated in the late passage (passage 8) of bone marrow mesenchymal stem cells (bmMSCs). Following β-catenin expression, the expression of phospho-Akt was also significantly decreased in the late passage of bmMSCs. More notably, overexpression of β-catenin in passage 8 of bmMSCs by transfection with pMXs-β-catenin plasmids, significantly increased cell proliferation and Akt expression. These results indicate that the downregulation of β-catenin and Akt signaling may be a critical factor for the proliferation of the late passage of bmMSCs.

Concise review: MicroRNA function in multipotent mesenchymal stromal cells

Multipotent mesenchymal stromal cells (MSCs) are ideal candidates for different cellular therapies due to their simple isolation, extensive expansion potential, and low immunogenicity. For various therapeutic approaches, such as bone and cartilage repair, MSCs are expected to contribute by direct differentiation to replace the damaged tissue, while many other applications rely on the secretion of paracrine factors which modulate the immune response and promote angiogenesis. MicroRNAs (miRNAs), which target messenger RNA for cleavage or translational repression, have recently been shown to play critical functions in MSC to regulate differentiation, paracrine activity, and other cellular properties such as proliferation, survival, and migration. The global miRNA expression profile of MSC varies according to the tissue of origin, species, and detection methodology, while also certain miRNAs are consistently found in all types of MSC. The function in MSC of more than 60 different miRNAs has been recently described, which is the subject of this review. A special emphasis is given to miRNAs that have demonstrated a function in MSC in vivo. We also present in detail miRNAs with overlapping effects (i.e., common target genes) and discuss future directions to deepen our understanding of miRNA biology in MSC. These recent discoveries have opened the possibility of modulating miRNAs in MSC, in order to enhance their proregenerative, therapeutic potential.

Aspirin attenuates angiotensin II-induced inflammation in bone marrow mesenchymal stem cells via the inhibition of ERK1/2 and NF-κB activation

Angiotensin II (Ang II) is a peptide hormone that plays a critical role in numerous physiological and pathophysiological processes. It is also commonly used as an inducer for the directional differentiation of bone marrow mesenchymal stem cells (bmMSCs). Previous studies demonstrated that Ang II induces inflammatory responses in endothelial cells, smooth muscle cells and fibroblasts. Aspirin is generally used as analgesic, antipyretic and occasionally anti-inflammatory medication. Whether aspirin suppresses inflammatory responses in bmMSCs has not been elucidated. In this study, we investigated the effect of aspirin on Ang II-induced inflammation in bmMSCs. Our results demonstrated that Ang II (10 nM-10 μM) increased the secretion of tumor necrosis factor (TNF)-α and interleukin (IL)-6 from bmMSCs in a dose-dependent manner. This result was further confirmed by a reverse transcription-polymerase chain reaction (RT-PCR) assay, which demonstrated a dose-dependent increase in the mRNA expression of TNF-α, IL-6, IL-1β and monocyte chemotactic protein-1 (MCP-1) in bmMSCs following exposure to Ang II. Furthermore, it was also observed that Ang II increased the expression of phospho-extracellular signal-regulated kinase 1/2 (ERK1/2) and phospho-nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB)-p65 in bmMSCs. The application of aspirin (0.1 mM) significantly inhibited the activation of ERK1/2 and NF-κB, the expression of TNF-α, IL-6, IL-1β and MCP-1 genes and the secretion of TNF-α and IL-6. Our findings indicated that aspirin may attenuate Ang II-induced inflammation in bmMSCs via the inhibition of ERK1/2 and NF-κB activation.