Exosomal microRNA-21-5p Mediates Mesenchymal Stem Cell Paracrine Effects on Human Cardiac Tissue Contractility

Modulation of Mesenchymal Stem Cells for Enhanced Therapeutic Utility in Ischemic Vascular Diseases

Mesenchymal stem cells are multipotent stem cells isolated from various tissue sources, including but not limited to bone marrow, adipose, umbilical cord, and Wharton Jelly. Although cell-mediated mechanisms have been reported, the therapeutic effect of MSCs is now recognized to be primarily mediated via paracrine effects through the secretion of bioactive molecules, known as the “secretome”. The regenerative benefit of the secretome has been attributed to trophic factors and cytokines that play neuroprotective, anti-angiogenic/pro-angiogenic, anti-inflammatory, and immune-modulatory roles. The advancement of autologous MSCs therapy can be hindered when introduced back into a hostile/disease environment. Barriers include impaired endogenous MSCs function, limited post-transplantation cell viability, and altered immune-modulatory efficiency. Although secretome-based therapeutics have gained popularity, many translational hurdles, including the heterogeneity of MSCs, limited proliferation potential, and the complex nature of the secretome, have impeded the progress. This review will discuss the experimental and clinical impact of restoring the functional capabilities of MSCs prior to transplantation and the progress in secretome therapies involving extracellular vesicles. Modulation and utilization of MSCs–secretome are most likely to serve as an effective strategy for promoting their ultimate success as therapeutic modulators.

A New Role for Extracellular Vesicles in Cardiac Tissue Engineering and Regenerative Medicine

Cardiovascular diseases are the leading cause of death worldwide. Discovering new therapies to treat heart disease requires improved understanding of cardiac physiology at a cellular level. Extracellular vesicles (EVs) are plasma membrane-bound nano- and microparticles secreted by cells and known to play key roles in intercellular communication, often through transfer of biomolecular cargo. Advances in EV research have established techniques for EV isolation from tissue culture media or biofluids, as well as standards for quantitation and biomolecular characterization. EVs released by cardiac cells are known to be involved in regulating cardiac physiology as well as in the progression of myocardial diseases. Due to difficulty accessing the heart in vivo, advanced in vitro cardiac 'tissues-on-a-chip' have become a recent focus for studying EVs in the heart. These physiologically relevant models are producing new insight into the role of EVs in cardiac physiology and disease while providing a useful platform for screening novel EV-based therapeutics for cardiac tissue regeneration post-injury. Numerous hurdles have stalled the clinical translation of EV therapeutics for heart patients, but tissue-on-a-chip models are playing an important role in bridging the translational gap, improving mechanistic understanding of EV signalling in cardiac physiology, disease, and repair.

Friends and foes: Extracellular vesicles in aging and rejuvenation

Extracellular vesicles (EVs) are released by many different cell types throughout the body and play a role in a diverse range of biological processes. EVs circulating in blood as well as in other body fluids undergo dramatic alterations over an organism's lifespan that are only beginning to be elucidated. The exact nature of these changes is an area of active and intense investigation, but lacks clear consensus due to the substantial heterogeneity in EV subpopulations and insufficiencies in current technologies. Nonetheless, emerging evidence suggests that EVs regulate systemic aging as well as the pathophysiology of age-related diseases. Here, we review the current literature investigating EVs and aging with an emphasis on consequences for the maintenance of human healthspan. Intriguingly, the biological utility of EVs both in vitro and in vivo and across contexts depends on the states of the source cells or tissues. As such, EVs secreted by cells in an aged or pathological state may impose detrimental consequences on recipient cells, while EVs secreted by youthful or healthy cells may promote functional improvement. Thus, it is critical to understand both functions of EVs and tip the balance toward their beneficial effects as an antiaging intervention.

Mesenchymal stem cell-derived exosomes regulate the polarization and inflammatory response of macrophages via miR-21-5p to promote repair after myocardial reperfusion injury

Background

Myocardial ischemia-reperfusion injury is a type of myocardial ischemia that has a significant impact on patients' health. We aimed to explore the protective effect of mesenchymal stem cell-derived exosomes (MSC-EXOs) on myocardial ischemia-reperfusion injury and their specific mechanism.

Methods

The effects of MSC-EXOs on myocardial ischemia-reperfusion injury were recorded. An enzyme-linked immunosorbent assay (ELISA) was used to determine the levels of IL-6 and IL-10 in mouse myocardial tissue or culture supernatant. Co-cultured MSC-EXOs and RAW264.7 cells were used to study the effect of MSC-EXOs on the polarization of macrophages at the cellular level. The ratio of M1 and M2 macrophages were detected by flow cytometry, and RT-qPCR detected the mRNA expression levels of corresponding markers. After transfection with miR-21-5p inhibitors or mimics, flow cytometry and RT-qPCR experiments were performed to explore the specific role of MSC-EXOs in macrophage polarization.

Results

After injection of MSC-EXOs, the mRNA expression of M1 macrophage markers (iNOS, IL-1β, IL-6, and TNFα) in the myocardial tissue of model mice was significantly reduced (P<0.05), and the mRNA expression of M2 macrophage markers was significantly increased (P<0.05). The injection also reduced the inflammation response in the model mice (P<0.05). In the in vitro experiment, lipopolysaccharide (LPS) induced the inflammatory microenvironment. After MSC-EXOs were fixed in the cytoplasm of RAW264.7 cells, the level of IL-6 in the culture supernatant decreased (P<0.05), and the level of IL-10 increased (P<0.05). The addition of MSC-EXOs to LPS-induced RAW264.7 cells promoted their polarization toward the M2 phenotype and upregulated their marker expression levels (P<0.05). Following inhibition of miR-21-5p in MSC cells, the EXOs were collected, and it was found that MSC-EXOs that inhibited the expression of miR-21-5p promoted LPS-induced polarization of RAW264.7 cells to the M1 phenotype and upregulated inflammation in the culture supernatant. Furthermore, transfection with miR-21-5p mimics promoted the polarization of RAW264.7 cells to the M2 phenotype and reduced the level of inflammatory factors in the culture supernatant.

Conclusions

MSC-EXOs promote the polarization of macrophages to the M2 phenotype via miR-21-5p, thereby reducing inflammation and promoting heart repair.

Mesenchymal stem cell-derived exosome microRNA as therapy for cardiac ischemic injury

Cardiovascular diseases (CVD) are a significant cause of human health harm. In the past, stem cell therapy was reported to have functional defects, such as immune rejection, tumorigenicity, and infusion toxicity. Exosomes are extracellular vesicles with lipid bilayer membrane structure, containing proteins, lipids, mRNA, miRNA, DNA, and other molecules, which can mediate various biological functions such as immune response, inflammatory response, cell migration, and differentiation intercellular communication. Exosomal miRNAs have outstanding advantages in disease diagnosis and curative effect prediction. Likewise, paracrine factors could also mediate the main therapeutic effect of mesenchymal stem cells. Research has shown that mesenchymal stem cell-derived micro-exosomes, which may come from stem cells, accumulate in the ischemic tissue and regulate cell proliferation, apoptosis, inflammation, and angiogenesis sites of myocardial injury after being transplanted. This review reviewed the molecular mechanisms of exosomes and internal microRNAs derived from mesenchymal stem cells in cardiac ischemic injury repair.

The Emerging Role of Exosomes in the Treatment of Human Disorders With a Special Focus on Mesenchymal Stem Cells-Derived Exosomes

Extracellular vesicles (EVs) are produced by diverse eukaryotic and prokaryotic cells. They have prominent roles in the modulation of cell-cell communication, inflammation versus immunomodulation, carcinogenic processes, cell proliferation and differentiation, and tissue regeneration. These acellular vesicles are more promising than cellular methods because of the lower risk of tumor formation, autoimmune responses and toxic effects compared with cell therapy. Moreover, the small size and lower complexity of these vesicles compared with cells have made their production and storage easier than cellular methods. Exosomes originated from mesenchymal stem cells has also been introduced as therapeutic option for a number of human diseases. The current review aims at summarization of the role of EVs in the regenerative medicine with a focus on their therapeutic impacts in liver fibrosis, lung disorders, osteoarthritis, colitis, myocardial injury, spinal cord injury and retinal injury.

Biomimetic and immunomodulatory therapeutics as an alternative to natural exosomes for vascular and cardiac applications

Inflammation is a central mechanism in cardiovascular diseases (CVD), where sustained oxidative stress and immune responses contribute to cardiac remodeling and impairment. Exosomes are extracellular vesicles released by cells to communicate with their surroundings and to modulate the tissue microenvironment. Recent evidence indicates their potential as cell-free immunomodulatory therapeutics for CVD, preventing cell death and fibrosis while inducing wound healing and angiogenesis. Biomimetic exosomes are semi-synthetic particles engineered using essential moieties present in natural exosomes (lipids, RNA, proteins) to reproduce their therapeutic effects while improving on scalability and standardization due to the ample range of moieties available to produce them. In this review, we provide an up-to-date description of the use of exosomes for CVD and offer our vision on the areas of opportunity for the development of biomimetic strategies. We also discuss the current limitations to overcome in the process towards their translation into clinic.

RETRACTED: Downregulation of microRNA-21-5p from macrophages-derived exosomes represses ventricular remodeling after myocardial infarction via inhibiting tissue inhibitors of metalloproteinase 3

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Concern was raised about the reliability of the Western blot results in Figs. 1E, 5B and 6B, which appear to have the same eyebrow shaped phenotype as many other publications tabulated here (https://docs.google.com/spreadsheets/d/149EjFXVxpwkBXYJOnOHb6RhAqT4a2llhj9LM60MBffM/edit#gid=0 [docs.google.com]). The journal requested the corresponding author comment on these concerns and provide the raw data. However, the authors were not responsive to the request for comment. Since original data could not be provided, the overall validity of the results could not be confirmed. Therefore, the Editor-in-Chief decided to retract the article.

Macro-encapsulation of mesenchymal stem cells in acute and chronic liver injury animal models

BACKGROUND AND AIM

Stem cell treatments using scaffolds for liver disease have been well studied. However, macro-encapsulation of mesenchymal stem cells (MSCs) to minimize or inhibit stem cell homing has not been evaluated. Here, we conducted a proof-of-concept study using MSCs macro-encapsulated in poly lactic-co-glycolic acid in liver disease models.

METHODS

Poly lactic-co-glycolic acid semipermeable membranes (surface pore size up to 40 μm) were used as the macro-encapsulation system. Macro-encapsulated pouches were loaded with MSCs and sealed. Each pouch was implanted in the subcutaneous region of the dorsum or interlobular space of the liver. Acute liver injury was induced using thioacetamide intraperitoneal injection thrice a week. For the chronic liver fibrosis model, thioacetamide dose was gradually increased, starting from 100 to 400 mg/kg over 16 weeks (thrice a week).

RESULTS

In the acute liver injury model, the treated groups showed decreased liver inflammation and necrosis compared with the control. Hepatic fibrosis decreased in the treated group in the chronic liver fibrosis model compared with that in the control group. Encapsulated MSCs exhibited changed cell morphology and characteristics after implantation, showing increased periodic acid-Schiff staining and CYP2E1 expression. Migration and homing of MSCs into the liver was not observed. Under hypoxic conditions, macro-encapsulated MSCs secreted more growth hormones, including vascular endothelial growth factor, platelet-derived growth factor, angiopoietin-2, and placental growth factor, than monolayered MSCs in vitro.

CONCLUSIONS

Macro-encapsulated MSCs attenuate hepatic inflammation and fibrosis by upregulating hypoxia-induced growth hormone secretion in liver disease models.

Non-Coding RNAs in the Cardiac Action Potential and Their Impact on Arrhythmogenic Cardiac Diseases

Cardiac arrhythmias are prevalent among humans across all age ranges, affecting millions of people worldwide. While cardiac arrhythmias vary widely in their clinical presentation, they possess shared complex electrophysiologic properties at cellular level that have not been fully studied. Over the last decade, our current understanding of the functional roles of non-coding RNAs have progressively increased. microRNAs represent the most studied type of small ncRNAs and it has been demonstrated that miRNAs play essential roles in multiple biological contexts, including normal development and diseases. In this review, we provide a comprehensive analysis of the functional contribution of non-coding RNAs, primarily microRNAs, to the normal configuration of the cardiac action potential, as well as their association to distinct types of arrhythmogenic cardiac diseases.

Cerebrospinal Fluid and Plasma Small Extracellular Vesicles and miRNAs as Biomarkers for Prion Diseases

Diagnosis of transmissible spongiform encephalopathies (TSEs), or prion diseases, is based on the detection of proteinase K (PK)-resistant PrP^Sc in post-mortem tissues as indication of infection and disease. Since PrP^Sc detection is not considered a reliable method for in vivo diagnosis in most TSEs, it is of crucial importance to identify an alternative source of biomarkers to provide useful alternatives for current diagnostic methodology. Ovine scrapie is the prototype of TSEs and has been known for a long time. Using this natural model of TSE, we investigated the presence of PrP^Sc in exosomes derived from plasma and cerebrospinal fluid (CSF) by protein misfolding cyclic amplification (PMCA) and the levels of candidate microRNAs (miRNAs) by quantitative PCR (qPCR). Significant scrapie-associated increase was found for miR-21-5p in plasma-derived but not in CSF-derived exosomes. However, miR-342-3p, miR-146a-5p, miR-128-3p and miR-21-5p displayed higher levels in total CSF from scrapie-infected sheep. The analysis of overexpressed miRNAs in this biofluid, together with plasma exosomal miR-21-5p, could help in scrapie diagnosis once the presence of the disease is suspected. In addition, we found the presence of PrP^Sc in most CSF-derived exosomes from clinically affected sheep, which may facilitate in vivo diagnosis of prion diseases, at least during the clinical stage.

Endothelial extracellular vesicles contain protective proteins and rescue ischemia-reperfusion injury in a human heart-on-chip

Extracellular vesicles (EVs) derived from various stem cell sources induce cardioprotective effects during ischemia-reperfusion injury (IRI). These have been attributed mainly to the antiapoptotic, proangiogenic, microRNA (miRNA) cargo within the stem cell-derived EVs. However, the mechanisms of EV-mediated endothelial signaling to cardiomyocytes, as well as their therapeutic potential toward ischemic myocardial injury, are not clear. EV content beyond miRNA that may contribute to cardioprotection has not been fully illuminated. This study characterized the protein cargo of human vascular endothelial EVs (EEVs) to identify lead cardioactive proteins and assessed the effect of EEVs on human laminar cardiac tissues (hlCTs) exposed to IRI. We mapped the protein content of human vascular EEVs and identified proteins that were previously associated with cellular metabolism, redox state, and calcium handling, among other processes. Analysis of the protein landscape of human cardiomyocytes revealed corresponding modifications induced by EEV treatment. To assess their human-specific cardioprotection in vitro, we developed a human heart-on-a-chip IRI assay using human stem cell-derived, engineered cardiac tissues. We found that EEVs alleviated cardiac cell death as well as the loss in contractile capacity during and after simulated IRI in an uptake- and dose-dependent manner. Moreover, we found that EEVs increased the respiratory capacity of normoxic cardiomyocytes. These results suggest that vascular EEVs rescue hlCTs exposed to IRI possibly by supplementing injured myocytes with cargo that supports multiple metabolic and salvage pathways and therefore may serve as a multitargeted therapy for IRI.

Emerging understanding of apoptosis in mediating mesenchymal stem cell therapy

Mesenchymal stem cell transplantation (MSCT) has been recognized as a potent and promising approach to achieve immunomodulation and tissue regeneration, but the mechanisms of how MSCs exert therapeutic effects remain to be elucidated. Increasing evidence suggests that transplanted MSCs only briefly remain viable in recipients, after which they undergo apoptosis in the host circulation or in engrafted tissues. Intriguingly, apoptosis of infused MSCs has been revealed to be indispensable for their therapeutic efficacy, while recipient cells can also develop apoptosis as a beneficial response in restoring systemic and local tissue homeostasis. It is notable that apoptotic cells produce apoptotic extracellular vesicles (apoEVs), traditionally known as apoptotic bodies (apoBDs), which possess characterized miRnomes and proteomes that contribute to their specialized function and to intercellular communication. Importantly, it has been demonstrated that the impact of apoEVs is long-lasting in health and disease contexts, and they critically mediate the efficacy of MSCT. In this review, we summarize the emerging understanding of apoptosis in mediating MSCT, highlighting the potential of apoEVs as cell-free therapeutics.

iPSCs and Exosomes: Partners in Crime Fighting Cardiovascular Diseases

Cardiovascular diseases are the leading cause of mortality worldwide. Understanding the mechanisms at the basis of these diseases is necessary in order to generate therapeutic approaches. Recently, cardiac tissue engineering and induced pluripotent stem cell (iPSC) reprogramming has led to a skyrocketing number of publications describing cardiovascular regeneration as a promising option for cardiovascular disease treatment. Generation of artificial tissue and organoids derived from induced pluripotent stem cells is in the pipeline for regenerative medicine. The present review summarizes the multiple approaches of heart regeneration with a special focus on iPSC application. In particular, we describe the strength of iPSCs as a tool to study the molecular mechanisms driving cardiovascular pathologies, as well as their potential in drug discovery. Moreover, we will describe some insights into novel discoveries of how stem-cell-secreted biomolecules, such as exosomes, could affect cardiac regeneration, and how the fine tuning of the immune system could be a revolutionary tool in the modulation of heart regeneration.

Bioengineering Technologies for Cardiac Regenerative Medicine

Cardiac regenerative medicine faces big challenges such as a lack of adult cardiac stem cells, low turnover of mature cardiomyocytes, and difficulty in therapeutic delivery to the injured heart. The interaction of bioengineering and cardiac regenerative medicine offers innovative solutions to this field. For example, cell reprogramming technology has been applied by both direct and indirect routes to generate patient-specific cardiomyocytes. Various viral and non-viral vectors have been utilized for gene editing to intervene gene expression patterns during the cardiac remodeling process. Cell-derived protein factors, exosomes, and miRNAs have been isolated and delivered through engineered particles to overcome many innate limitations of live cell therapy. Protein decoration, antibody modification, and platelet membranes have been used for targeting and precision medicine. Cardiac patches have been used for transferring therapeutics with better retention and integration. Other technologies such as 3D printing and 3D culture have been used to create replaceable cardiac tissue. In this review, we discuss recent advancements in bioengineering and biotechnologies for cardiac regenerative medicine.

Mesenchymal stem cell-derived extracellular vesicles in the failing heart: past, present, and future

Cardiovascular disease (CVD) is the leading cause of death globally. Current treatment options include lifestyle changes, medication, and surgical intervention. However, many patients are unsuitable candidates for surgeries due to comorbidities, diffuse coronary artery disease, or advanced stages of heart failure. The search for new treatment options has recently transitioned from cell-based therapies to stem-cell-derived extracellular vesicles (EVs). A number of challenges remain in the EV field, including the effect of comorbidities, characterization, and delivery. However, recent revolutionary developments and insight into the potential of personalizing EV contents by bioengineering methods to alter specific signaling pathways in the ischemic myocardium hold promise. Here, we discuss the past limitations of cell-based therapies and recent EV studies involving in vivo, in vitro, and omics, and future challenges and opportunities in EV-based treatments in CVD.

Translational Animal Models Provide Insight Into Mesenchymal Stromal Cell (MSC) Secretome Therapy

The therapeutic potential of the mesenchymal stromal cell (MSC) secretome, consisting of all molecules secreted by MSCs, is intensively studied. MSCs can be readily isolated, expanded, and manipulated in culture, and few people argue with the ethics of their collection. Despite promising pre-clinical studies, most MSC secretome-based therapies have not been implemented in human medicine, in part because the complexity of bioactive factors secreted by MSCs is not completely understood. In addition, the MSC secretome is variable, influenced by individual donor, tissue source of origin, culture conditions, and passage. An increased understanding of the factors that make up the secretome and the ability to manipulate MSCs to consistently secrete factors of biologic importance will improve MSC therapy. To aid in this goal, we can draw from the wealth of information available on secreted factors from MSC isolated from veterinary species. These translational animal models will inspire efforts to move human MSC secretome therapy from bench to bedside.

Mesenchymal Stem Cell-Derived Exosomes: A Promising Biological Tool in Nanomedicine

As nano-scale biological vesicles, extracellular vesicles (EVs)/exosomes, in particular, exosomes derived from mesenchymal stem cells (MSC-exosomes), have been studied in the diagnosis, prevention, and treatment of many diseases. In addition, through the combination of nanotechnology and biotechnology, exosomes have emerged as innovative tools for the development of nanomedicine. This review focuses on a profound summarization of MSC-exosomes as a powerful tool in bionanomedicine. It systemically summarizes the role of MSC-exosomes as a nanocarrier, drug loading and tissue engineering, and their potential contribution in a series of diseases as well as the advantages of exosomes over stem cells and synthetic nanoparticles and potential disadvantages. The in-depth understanding of the functions and mechanisms of exosomes provides insights into the basic research and clinical transformation in the field of nanomedicine.

Role of Exosomal miRNAs in Heart Failure

Heart failure is the terminal outcome of the majority of cardiovascular diseases, which lacks specific diagnostic biomarkers and therapeutic targets. It contributes to most of cardiovascular hospitalizations and death despite of the current therapy. Therefore, it is important to explore potential molecules improving the diagnosis and treatment of heart failure. MicroRNAs (miRNAs) are small non-coding RNAs that have been reported to be involved in regulating processes of heart failure. After the discovery of miRNAs in exosomes, the subcellular distribution analysis of miRNAs is raising researchers' attention. Growing evidence demonstrates that exosomal miRNAs may be promising diagnostic and therapeutic molecules for heart failure. This review summarizes the role of exosomal miRNAs in heart failure in the prospect of molecular and clinical researches.

Mapping current research and identifying hotspots on mesenchymal stem cells in cardiovascular disease

BACKGROUND

Mesenchymal stem cells (MSCs) have important research value and broad application prospects in the cardiovascular disease. This study provides information on the latest progress, evolutionary path, frontier research hotspots, and future research developmental trends in this field.

METHODS

A knowledge map was generated by CiteSpace and VOSviewer analysis software based on data obtained from the literature on MSCs in the cardiovascular field.

RESULTS

The USA and China ranked at the top in terms of the percentage of articles, accounting for 34.306% and 28.550%, respectively. The institution with the highest number of research publications in this field was the University of Miami, followed by the Chinese Academy of Medical Sciences and Harvard University. The research institution with the highest ACI value was Harvard University, followed by the Mayo Clinic and the University of Cincinnati. The top three subjects in terms of the number of published articles were cell biology, cardiovascular system cardiology, and research experimental medicine. The journal with the most publications in this field was Circulation Research, followed by Scientific Reports and Biomaterials. The direction of research on MSCs in the cardiovascular system was divided into four parts: (1) tissue engineering, scaffolds, and extracellular matrix research; (2) cell transplantation, differentiation, proliferation, and signal transduction pathway research; (3) assessment of the efficacy of stem cells from different sources and administration methods in the treatment of acute myocardial infarction, myocardial hypertrophy, and heart failure; and (4) exosomes and extracellular vesicles research. Tissue research is the hotspot and frontier in this field.

CONCLUSION

MSC research has presented a gradual upward trend in the cardiovascular field. Multidisciplinary intersection is a characteristic of this field. Engineering and materials disciplines are particularly valued and have received attention from researchers. The progress in multidisciplinary research will provide motivation and technical support for the development of this field.

Targeted miR-21 loaded liposomes for acute myocardial infarction

Acute and persistent myocardial ischemia is the main cause of acute myocardial infarction (AMI) and heart failure. MicroRNA-21(miR-21) contributes to the pathophysiological consequences of acute myocardial infarction by targeting downstream crucial regulators. Thus, miR-21 mimics are a promising strategy for the treatment of AMI. However, their poor stability and insufficient cellular uptake are the major challenges. Herein, we encapsulated miR-21 mimics into liposomes modified with the cardiac troponin T (cTnT) antibody for targeted delivery of miR-21(cT-21-LIPs) to the ischemic myocardium. The cT-21-LIPs exhibited enhanced targeting efficiency to hypoxia primary cardiomyocytes in vitro and improved accumulation in the ischemic heart of AMI rats after injection via the tail vein due to the specifical target to overexpressed troponin. The cT-21-LIPs could significantly improve the cardiac function and decrease the infarct size after AMI, while maintaining the viability of cardiomyocytes. This design provides a novel strategy for delivering small nucleotide drugs specifically to the infarcted heart, which may find great potential in clinics.

Exosomal miR-199a-5p promotes hepatic lipid accumulation by modulating MST1 expression and fatty acid metabolism

BACKGROUND AND AIMS

Non-alcoholic fatty liver disease (NAFLD) and its complications has become an expanding health problem worldwide with limited therapeutic approaches. The current study was aiming to identify novel microRNA in the regulation of hepatic lipid metabolism in NAFLD.

APPROCHES AND RESULTS

Systematic screening of microRNA expression by high-throughput small RNA sequencing demonstrated that microRNA 199a-5p (miR-199a-5p) was significantly upregulated in high fat diet-induced steatosis mouse model, with the most abundant expression in adipose tissue. MST1 was further identified as the target gene for miR-199a with specific recognition at the 3' untranslated region with dural luciferase reporter assay. Delivery of miR-199a-5p with exosomes into mice aggravated liver lipid accumulation in hepatocytes, accompanied by down-regulation of hepatic MST1 expression and modulation of hepatic lipogenesis and lipolysis, including SREBP-1c, AMPK signaling cascades and the down-stream CPT1α and FASN. Conversely, administration of exosome containing anti-miR-199a-5p resulted in attenuated steotosis in mice fed on high fat diet. Importanly, miR-199a-5p-induced abnormal cellular lipid accumulation could be markedly reversed by overexpression of MST1.

CONCLUSION

miR-199a-5p might be an essentail regulator for hepatic lipid metabolism, possibly through its interction with MST1 and the subsequent signaling cascade. Thus, miR-199a-5p may serve as an important therapeutic target in the treatment of NAFLD.

Extracellular Vesicles in Cardiac Regeneration: Potential Applications for Tissues-on-a-Chip

Strategies to regenerate cardiac tissue postinjury are limited and heart transplantation remains the only 'cure' for a failing heart. Extracellular vesicles (EVs), membrane-bound cell secretions important in intercellular signaling, have been shown to play a crucial role in regulating heart function. A mechanistic understanding of the role of EVs in the heart remains elusive due to the challenges in studying the native human heart. Tissue-on-a-chip platforms, comprising functional, physiologically relevant human tissue models, are an emerging technology that has yet to be fully applied to the study of EVs. In this review, we summarize recent advances in cardiac tissue-on-a-chip (CTC) platforms and discuss how they are uniquely situated to advance our understanding of EVs in cardiac disease and regeneration.

Exosomal microRNA-23b-3p from bone marrow mesenchymal stem cells maintains T helper/Treg balance by downregulating the PI3k/Akt/NF-κB signaling pathway in intracranial aneurysm

Bone marrow mesenchymal stem cells (BMSCs) are involved in cancer initiation and metastasis, and sometimes mediate cell communication by releasing exosomes and delivering microRNAs (miRNAs). The study aims to investigate the effects of exosomal hsa-miR-23b-3p derived from human BMSCs on intracranial aneurysm (IA). Firstly, human BMSCs-derived exosomes were extracted by ultra-high speed centrifugation. After clinical specimen collection, imbalance of T helper (Th) 17/Treg was found in patients with IA. Then, basilar artery aneurysm models were established and BMSCs-derived exosomes were isolated and identified. The results showed that BMSCs-derived exosomes improved pathological remodeling of IA wall, upregulated the contractile phenotype and inhibited the secretory phenotype of smooth muscle cells and reduced the number of Th17 cells to maintain the balance of Th17/Treg. In addition, human BMSCs-derived exosomes inhibited the activation of the phosphatidylinositol-3 kinase (PI3K)/protein kinase B (Akt)/nuclear factor-kappa B (NF-κB) signaling pathway and maintained Th17/Treg balance, which in turn interfered with aneurysm formation. Finally, the targeting relationship between hsa-miR-23b-3p and KLF5 was confirmed. We further noted that BMSCs-derived exosomal hsa-miR-23b-3p inhibited IA formation by targeting KLF5 through suppression of the PI3k/Akt/NF-κB signaling pathway. All in all, our study concluded that BMSCs-derived exosomal hsa-miR-23b-3p could maintain Th17/Treg balance by targeting KLF5 through suppression of the PI3k/Akt/NF-κB signaling pathway, thus inhibit IA formation.

Biomimetic nanovesicle design for cardiac tissue repair

Cardiovascular disease is a major cause of mortality and morbidity worldwide. Exosome therapies are promising for cardiac repair. Exosomes transfer cargo between cells, have high uptake by native cells and are ideal natural carriers for proteins and nucleic acids. Despite their proreparative potential, exosome production is dependent on parent cell state with typically low yields and cargo variability. Therefore, there is potential value in engineering exosomes to maximize their benefits by delivering customized, potent cargo for cardiovascular disease. Here, we outline several methods of exosome engineering focusing on three important aspects: optimizing cargo, homing to target tissue and minimizing clearance. Finally, we put these methods in context of the cardiac field and discuss the future potential of vesicle design.

Pro-Angiogenic Actions of CMC-Derived Extracellular Vesicles Rely on Selective Packaging of Angiopoietin 1 and 2, but Not FGF-2 and VEGF

While the fundamental mechanism by which cardiac cell therapy mitigates ventricular dysfunction in the post ischemic heart remains poorly defined, donor cell paracrine signaling is presumed to be a chief contributor to the afforded benefits. Of the many bioactive molecules secreted by transplanted cells, extracellular vesicles (EVs) and their proteinaceous, nucleic acid, and lipid rich contents, comprise a heterogeneous assortment of prospective cardiotrophic factors-whose involvement in the activation of endogenous cardiac repair mechanism(s), including reducing fibrosis and promoting angiogenesis, have yet to be fully explained. In the current study we aimed to interrogate potential mechanisms by which cardiac mesenchymal stromal cell (CMC)-derived EVs contribute to the CMC pro-angiogenic paracrine signaling capacity in vitro. Vesicular transmission and biological activity of human CMC-derived EVs was evaluated in in vitro assays for human umbilical vein endothelial cell (HUVEC) function, including EV uptake, cell survival, migration, tube formation, and intracellular pathway activation. HUVECs incubated with EVs exhibited augmented cell migration, tube formation, and survival under peroxide exposure; findings which paralleled enhanced activation of the archetypal pro-survival/pro-angiogenic pathways, STAT3 and PI3K-AKT. Cytokine array analyses revealed preferential enrichment of a subset of prototypical angiogenic factors, Ang-1 and Ang-2, in CMC EVs. Interestingly, pharmacologic inhibition of Tie2 in HUVECs, the cognate receptors of angiopoietins, efficiently attenuated CMC-EV-induced HUVEC migration. Further, in additional assays a Tie2 kinase inhibitor exhibited specificity to inhibit Ang-1-, but not Ang-2-, induced HUVEC migration. Overall, these findings suggest that the pro-angiogenic activities of CMC EVs are principally mediated by Ang-1-Tie2 signaling.

Small but significant: Insights and new perspectives of exosomes in cardiovascular disease

Cardiovascular diseases (CVDs) are a major health problem worldwide, and health professionals are still actively seeking new and effective approaches for CVDs treatment. Presently, extracellular vesicles, particularly exosomes, have gained its popularity for CVDs treatment because of their function as messengers for inter- and extra-cellular communications to promote cellular functions in cardiovascular system. However, as a newly developed field, researchers are still trying to fully understand the role of exosomes, and their mechanism in mediating cardiac repair process. Therefore, a comprehensive review of this topic can be timely and favourable. In this review, we summarized the basic biogenesis and characterization of exosomes and then further extended the focus on the circulating exosomes in cellular communication and stem cell-derived exosomes in cardiac disease treatment. In addition, we covered interactions between the heart and other organs through exosomes, leading to the diagnostic characteristics of exosomes in CVDs. Future perspectives and limitations of exosomes in CVDs were also discussed with a special focus on exploring the potential delivery routes, targeting the injured tissue and engineering novel exosomes, as well as its potential as one novel target in the metabolism-related puzzle.

Cortical Bone Derived Stem Cells Modulate Cardiac Fibroblast Response via miR-18a in the Heart After Injury

The adult heart following injury such as a myocardial infarction forms a fibrotic scar associated with transformation of resident cardiac fibroblasts into myofibroblast, accelerating cardiac remodeling and dysfunction. Cell therapies provide a novel direction for the enhancement of cardiac structure and function but remain poorly described in terms of the effect on resident cardiac fibroblasts. We have shown cortical bone derived stem cells (CBSCs) exhibit an ability to repair the heart after myocardial injury together with reduced scar formation. Nevertheless, whether CBSCs possess ability to modulate resident fibroblast response after myocardial injury remains untested.

Extracellular vesicles from human embryonic stem cell-derived cardiovascular progenitor cells promote cardiac infarct healing through reducing cardiomyocyte death and promoting angiogenesis

Human pluripotent stem cells (hPSCs)-derived cardiovascular progenitor cells (CVPCs) are a promising source for myocardial repair, while the mechanisms remain largely unknown. Extracellular vesicles (EVs) are known to mediate cell–cell communication, however, the efficacy and mechanisms of hPSC-CVPC-secreted EVs (hCVPC-EVs) in the infarct healing when given at the acute phase of myocardial infarction (MI) are unknown. Here, we report the cardioprotective effects of the EVs secreted from hESC-CVPCs under normoxic (EV-N) and hypoxic (EV-H) conditions in the infarcted heart and the long noncoding RNA (lncRNA)-related mechanisms. The hCVPC-EVs were confirmed by electron microscopy, nanoparticle tracking, and immunoblotting analysis. Injection of hCVPC-EVs into acutely infracted murine myocardium significantly improved cardiac function and reduced fibrosis at day 28 post MI, accompanied with the improved vascularization and cardiomyocyte survival at border zones. Consistently, hCVPC-EVs enhanced the tube formation and migration of human umbilical vein endothelial cells (HUVECs), improved the cell viability, and attenuated the lactate dehydrogenase release of neonatal rat cardiomyocytes (NRCMs) with oxygen glucose deprivation (OGD) injury. Moreover, the improvement of the EV-H in cardiomyocyte survival and tube formation of HUVECs was significantly better than these in the EV-N. RNA-seq analysis revealed a high abundance of the lncRNA MALAT1 in the EV-H. Its abundance was upregulated in the infarcted myocardium and cardiomyocytes treated with hCVPC-EVs. Overexpression of human MALAT1 improved the cell viability of NRCM with OGD injury, while knockdown of MALAT1 inhibited the hCVPC-EV-promoted tube formation of HUVECs. Furthermore, luciferase activity assay, RNA pull-down, and manipulation of miR-497 levels showed that MALAT1 improved NRCMs survival and HUVEC tube formation through targeting miR-497. These results reveal that hCVPC-EVs promote the infarct healing through improvement of cardiomyocyte survival and angiogenesis. The cardioprotective effects of hCVPC-EVs can be enhanced by hypoxia-conditioning of hCVPCs and are partially contributed by MALAT1 via targeting the miRNA.

Novel Applications of Mesenchymal Stem Cell-derived Exosomes for Myocardial Infarction Therapeutics

Cardiovascular diseases (CVDs) are the leading cause of mortality and morbidity globally, representing approximately a third of all deaths every year. The greater part of these cases is represented by myocardial infarction (MI), or heart attack as it is better known, which occurs when declining blood flow to the heart causes injury to cardiac tissue. Mesenchymal stem cells (MSCs) are multipotent stem cells that represent a promising vector for cell therapies that aim to treat MI due to their potent regenerative effects. However, it remains unclear the extent to which MSC-based therapies are able to induce regeneration in the heart and even less clear the degree to which clinical outcomes could be improved. Exosomes, which are small extracellular vesicles (EVs) known to have implications in intracellular communication, derived from MSCs (MSC-Exos), have recently emerged as a novel cell-free vector that is capable of conferring cardio-protection and regeneration in target cardiac cells. In this review, we assess the current state of research of MSC-Exos in the context of MI. In particular, we place emphasis on the mechanisms of action by which MSC-Exos accomplish their therapeutic effects, along with commentary on the current difficulties faced with exosome research and the ongoing clinical applications of stem-cell derived exosomes in different medical contexts.

How does temperature play a role in the storage of extracellular vesicles?

Extracellular vesicles (EVs) contain specific proteins, lipids, and nucleic acids that can be passed to other cells as signal molecules to alter their function. However, there are many problems and challenges in the conversion and clinical application of EVs. Storage and protection of EVs is one of the issues that need further research. To adapt to potential clinical applications, this type of problem must be solved. This review summarizes the storage practices of EVs in recent years, and explains the impact of temperature on the quality and stability of EVs during storage based on current research, and explains the potential mechanisms involved in this effect as much as possible.

Knockout of beta-2 microglobulin enhances cardiac repair by modulating exosome imprinting and inhibiting stem cell-induced immune rejection

BACKGROUND AND AIMS

Allogeneic human umbilical mesenchymal stem cells (alloUMSC) are convenient cell source for stem cell-based therapy. However, immune rejection is a major obstacle for clinical application of alloUMSC for cardiac repair after myocardial infarction (MI). The immune rejection is due to the presence of human leukocyte antigen (HLA) class I molecule which is increased during MI. The aim of this study was to knockout HLA light chain β2-microglobulin (B2M) in UMSC to enhance stem cell engraftment and survival after transplantation.

METHODS AND RESULTS

We developed an innovative strategy using CRISPR/Cas9 to generate UMSC with B2M deletion (B2M-UMSC). AlloUMSC injection induced CD8+ T cell-mediated immune rejection in immune competent rats, whereas no CD8+ T cell-mediated killing against B2M-UMSC was observed even when the cells were treated with IFN-γ. Moreover, we demonstrate that UMSC-derived exosomes can inhibit cardiac fibrosis and restore cardiac function, and exosomes derived from B2M-UMSC are more efficient than those derived from UMSC, indicating that the beneficial effect of exosomes can be enhanced by modulating exosome's imprinting. Mechanistically, microRNA sequencing identifies miR-24 as a major component of the exosomes from B2M-UMSCs. Bioinformatics analysis identifies Bim as a putative target of miR-24. Loss-of-function studies at the cellular level and gain-of-function approaches in exosomes show that the beneficial effects of B2M-UMSCs are mediated by the exosome/miR-24/Bim pathway.

CONCLUSION

Our findings demonstrate that modulation of exosome's imprinting via B2M knockout is an efficient strategy to prevent the immune rejection of alloUMSCs. This study paved the way to the development of new strategies for tissue repair and regeneration without the need for HLA matching.

Small extracellular vesicles deliver miR-21 and miR-217 as pro-senescence effectors to endothelial cells

The role of epigenetics in endothelial cell senescence is a cutting-edge topic in ageing research. However, little is known of the relative contribution to pro-senescence signal propagation provided by microRNAs shuttled by extracellular vesicles (EVs) released from senescent cells. Analysis of microRNA and DNA methylation profiles in non-senescent (control) and senescent (SEN) human umbilical vein endothelial cells (HUVECs), and microRNA profiling of their cognate small EVs (sEVs) and large EVs demonstrated that SEN cells released a significantly greater sEV number than control cells. sEVs were enriched in miR-21-5p and miR-217, which target DNMT1 and SIRT1. Treatment of control cells with SEN sEVs induced a miR-21/miR-217-related impairment of DNMT1-SIRT1 expression, the reduction of proliferation markers, the acquisition of a senescent phenotype and a partial demethylation of the locus encoding for miR-21. MicroRNA profiling of sEVs from plasma of healthy subjects aged 40-100 years showed an inverse U-shaped age-related trend for miR-21-5p, consistent with senescence-associated biomarker profiles. Our findings suggest that miR-21-5p/miR-217 carried by SEN sEVs spread pro-senescence signals, affecting DNA methylation and cell replication.

The biology function and biomedical applications of exosomes

The study of extracellular vesicles (EVs) has the potential to identify unknown cellular and molecular mechanisms in intercellular communication and in organ homeostasis and disease. Exosomes, with an average diameter of ~100 nanometers, are a subset of EVs. The biogenesis of exosomes involves their origin in endosomes, and subsequent interactions with other intracellular vesicles and organelles generate the final content of the exosomes. Their diverse constituents include nucleic acids, proteins, lipids, amino acids, and metabolites, which can reflect their cell of origin. In various diseases, exosomes offer a window into altered cellular or tissue states, and their detection in biological fluids potentially offers a multicomponent diagnostic readout. The efficient exchange of cellular components through exosomes can inform their applied use in designing exosome-based therapeutics.

Acute air exposure modulates the microRNA abundance in stress responsive tissues and circulating extracellular vesicles in rainbow trout (Oncorhynchus mykiss)

The hypothalamic-pituitary-interrenal axis is an important regulator of stress and metabolism in teleosts. Cortisol is secreted by the head kidney where it increases gluconeogenesis in the liver to increase circulating glucose levels. MicroRNAs (miRNAs) are small, non-coding RNA molecules that bind to the 3' untranslated region of specific mRNA to regulate their expression. MicroRNAs can also be secreted into circulation by association with extracellular vesicles (EVs) where they can influence the phenotype of other tissues. In this study, adult rainbow trout were exposed to a 3-minute acute air stress and allowed to recover for 1-, 3-, or 24-h to determine how miRNAs were altered. MicroRNAs measured in this study were chosen based on their high relative abundance in tissues that drive the stress response (miR-21a-3p, let-7a-5p, miR-143-3p) or their role in regulating DNA methylation (miR-29a-3p). In general, miRNAs increased in circulating EVs during the recovery period while decreasing in head kidney and liver at the same timepoints. Predicted targets for these miRNAs were analyzed using KEGG and DAVID functional enrichment analysis. Pathways involved in metabolism and cell signaling were predicted to be upregulated. Future studies can use these results to investigate how pathways are regulated after stress. Overall, our results indicate that miRNAs are regulated during teleost stress responses and could be supporting the cortisol-mediated changes that occur.

Preservation techniques of stem cells extracellular vesicles: a gate for manufacturing of clinical grade therapeutic extracellular vesicles and long-term clinical trials

Extracellular vesicles (EVs) are nanosized vesicles released by different cells and have been separated from most of the body fluids. These vesicles play a central role in cell-to-cell communications as carry a distinct cargo including proteins, RNA species, DNAs, and lipids that are meant to be shipped and exchanged between cells at both systemic and paracrine levels. They serve in regulating normal physiological processes. EVs released from stem cells exert similar therapeutic effect to their originating cells. Clinical application of EVs requires the preparation of sufficient and viable active therapeutic EVs as well as implementing suitable methods for long-term preservation to expedite both their clinical and commercial uses. Cryopreservation is the most common method used to preserve decomposable biomaterials. However, cryopreservation causes cryoinjury to cells which therefore necessitate the use of cryoprotectants. Two types of cryoprotectants exist: penetrating and non-penetrating. In freeze drying, the watery content is sublimed from the product after it is frozen. This drying process is pertinent to thermo-liable substances and those unstable in aqueous solutions for prolonged storage periods. In spray drying technique, the solution containing EVs is firstly atomized, then droplets are rapidly converted into a dry powder using heated gas. Even with the exposure to high temperatures of the drying gas, spray drying is considered suitable for heat-sensitive materials. EVs are considered a promising cell-free therapy, but the lack of proper preservation limits its benefits. Preservation of EVs will initiate a vast amount of clinical trials on different species and different clinical problems.

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

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

The Contrasting Role of Extracellular Vesicles in Vascular Inflammation and Tissue Repair

Extracellular vesicles are a heterogeneous family of vesicles, generated from different subcellular compartments and released into the extracellular space. Composed of a lipid bilayer encompassing both soluble cytosolic material and nuclear components, these organelles have been recently described as novel regulators of intercellular communication between adjacent and remote cells. Due to their diversified composition and biological content, they portray specific signatures of cellular activation and pathological processes, their potential as diagnostic and prognostic biomarkers has raised significant interest in cardiovascular diseases. Circulating vesicles, especially those released from platelets, leukocytes, and endothelial cells are found to play a critical role in activating several fundamental cells within the vasculature, including endothelial cells and vascular smooth muscle cells. Their intrinsic activity and immunomodulatory properties lends them to not only promote vascular inflammation, but also enhance tissue regeneration, vascular repair, and indeed resolution. In this review we aim to recapitulate the recent findings concerning the roles played by EVs that originate from different circulating cells, with particular reference to their action on the endothelium. We focus herein, on the interaction of platelet and leukocyte EVs with the endothelium. In addition, their potential biological function in promoting tissue resolution and vascular repair will also be discussed.

Heart Failure with Reduced Ejection Fraction (HFrEF) and Preserved Ejection Fraction (HFpEF): The Diagnostic Value of Circulating MicroRNAs

Circulating microRNAs offer attractive potential as epigenetic disease biomarkers by virtue of their biological stability and ready accessibility in liquid biopsies. Numerous clinical cohort studies have revealed unique microRNA profiles in different disease settings, suggesting utility as markers with diagnostic and prognostic applications. Given the complex network of microRNA functions in modulating gene expression and post-transcriptional modifications, the circulating microRNA landscape in disease may reflect pathophysiological status, providing valuable information for delineating distinct subtypes and/or stages of complex diseases. Heart failure (HF) is an increasingly significant global health challenge, imposing major economic liability and health care burden due to high hospitalization, morbidity, and mortality rates. Although HF is defined as a syndrome characterized by symptoms and findings on physical examination, it may be further differentiated based on left ventricular ejection fraction (LVEF) and categorized as HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF). The presenting clinical syndromes in HFpEF and HFrEF are similar but mortality differs, being somewhat lower in HFpEF than in HFrEF. However, while HFrEF is responsive to an array of therapies, none has been shown to improve survival in HFpEF. Herein, we review recent HF cohort studies focusing on the distinct microRNA profiles associated with HF subtypes to reveal new insights to underlying mechanisms and explore the possibility of exploiting these differences for diagnostic/prognostic applications.

Adult human cardiac stem cell supplementation effectively increases contractile function and maturation in human engineered cardiac tissues

BACKGROUND

Delivery of stem cells to the failing heart is a promising therapeutic strategy. However, the improvement in cardiac function in animal studies has not fully translated to humans. To help bridge the gap between species, we investigated the effects of adult human cardiac stem cells (hCSCs) on contractile function of human engineered cardiac tissues (hECTs) as a species-specific model of the human myocardium.

METHODS

Human induced pluripotent stem cell-derived cardiomyoctes (hCMs) were mixed with Collagen/Matrigel to fabricate control hECTs, with an experimental group of hCSC-supplemented hECT fabricated using a 9:1 ratio of hCM to hCSC. Functional testing was performed starting on culture day 6, under spontaneous conditions and also during electrical pacing from 0.25 to 1.0 Hz, measurements repeated at days 8 and 10. hECTs were then frozen and processed for gene analysis using a Nanostring assay with a cardiac targeted custom panel.

RESULTS

The hCSC-supplemented hECTs displayed a twofold higher developed force vs. hCM-only controls by day 6, with approximately threefold higher developed stress and maximum rates of contraction and relaxation during pacing at 0.75 Hz. The spontaneous beat rate characteristics were similar between groups, and hCSC supplementation did not adversely impact beat rate variability. The increased contractility persisted through days 8 and 10, albeit with some decrease in the magnitude of the difference of the force by day 10, but with developed stress still significantly higher in hCSC-supplemented hECT; these findings were confirmed with multiple hCSC and hCM cell lines. The force-frequency relationship, while negative for both, control (- 0.687 Hz^- 1; p = 0.013 vs. zero) and hCSC-supplemented (- 0.233 Hz^- 1;p = 0.067 vs. zero) hECTs, showed a significant rectification in the regression slope in hCSC-supplemented hECT (p = 0.011 vs. control). Targeted gene exploration (59 genes) identified a total of 14 differentially expressed genes, with increases in the ratios of MYH7/MHY6, MYL2/MYL7, and TNNI3/TNNI1 in hCSC-supplemented hECT versus controls.

CONCLUSIONS

For the first time, hCSC supplementation was shown to significantly improve human cardiac tissue contractility in vitro, without evidence of proarrhythmic effects, and was associated with increased expression of markers of cardiac maturation. These findings provide new insights about adult cardiac stem cells as contributors to functional improvement of human myocardium.

The Art of Intercellular Wireless Communications: Exosomes in Heart Disease and Therapy

Exosomes are nanoscale membrane-bound extracellular vesicles secreted by most eukaryotic cells in the body that facilitates intercellular communication. Exosomes carry several signaling biomolecules, including miRNA, proteins, enzymes, cell surface receptors, growth factors, cytokines and lipids that can modulate target cell biology and function. Due to these capabilities, exosomes have emerged as novel intercellular signaling mediators in both homeostasis and pathophysiological conditions. Recent studies document that exosomes (both circulating or released from heart tissue) have been actively involved in cardiac remodeling in response to stressors. Also, exosomes released from progenitor/stem cells have protective effects in heart diseases and shown to have regenerative potential in the heart. In this review we discuss- the critical role played by circulating exosomes released from various tissues and from cells within the heart in cardiac health; the gap in knowledge that needs to be addressed to promote future research; and exploitation of recent advances in exosome engineering to develop novel therapy.

Electrical Stimulation of pediatric cardiac-derived c-kit+ progenitor cells improves retention and cardiac function in right ventricular heart failure

Nearly 1 in every 120 children born has a congenital heart defect. Although surgical therapy has improved survival, many of these children go on to develop right ventricular heart failure (RVHF). The emergence of cardiovascular regenerative medicine as a potential therapeutic strategy for pediatric HF has provided new avenues for treatment with a focus on repairing or regenerating the diseased myocardium to restore cardiac function. Although primarily tried using adult cells and adult disease models, stem cell therapy is relatively untested in the pediatric population. Here, we investigate the ability of electrical stimulation (ES) to enhance the retention and therapeutic function of pediatric cardiac-derived c-kit+ progenitor cells (CPCs) in an animal model of RVHF. Human CPCs isolated from pediatric patients were exposed to chronic ES and implanted into the RV myocardium of rats. Cardiac function and cellular retention analysis showed electrically stimulated CPCs (ES-CPCs) were retained in the heart at a significantly higher level and longer time than control CPCs and also significantly improved right ventricular functional parameters. ES also induced upregulation of extracellular matrix and adhesion genes and increased in vitro survival and adhesion of cells. Specifically, upregulation of β1 and β5 integrins contributed to the increased retention of ES-CPCs. Lastly, we show that ES induces CPCs to release higher levels of pro-reparative factors in vitro. These findings suggest that ES can be used to increase the retention, survival, and therapeutic effect of human c-kit+ progenitor cells and can have implications on a variety of cell-based therapies. Stem Cells 2019;37:1528-1541.

Knockout of beta-2 microglobulin reduces stem cell-induced immune rejection and enhances ischaemic hindlimb repair via exosome/miR-24/Bim pathway

Generating universal human umbilical mesenchymal stem cells (UMSCs) without immune rejection is desirable for clinical application. Here we developed an innovative strategy using CRISPR/Cas9 to generate B2M^‐UMSCs in which human leucocyte antigen (HLA) light chain β2‐microglobulin (B2M) was deleted. The therapeutic potential of B2M^‐UMSCs was examined in a mouse ischaemic hindlimb model. We show that B2M^‐UMSCs facilitated perfusion recovery and enhanced running capability, without inducing immune rejection. The beneficial effect was mediated by exosomes. Mechanistically, microRNA (miR) sequencing identified miR‐24 as a major component of the exosomes originating from B2M^‐UMSCs. We identified Bim as a potential target of miR‐24 through bioinformatics analysis, which was further confirmed by loss‐of‐function and gain‐of‐function approaches. Taken together, our data revealed that knockout of B2M is a convenient and efficient strategy to prevent UMSCs‐induced immune rejection, and it provides a universal clinical‐scale cell source for tissue repair and regeneration without the need for HLA matching in the future.

Aptamer-functionalized exosomes from bone marrow stromal cells target bone to promote bone regeneration

In elderly people particularly in postmenopausal women, inadequate bone formation by osteoblasts originating from bone marrow mesenchymal stem cells (BMSCs) for compensation of bone resorption by osteoclasts is a major reason for osteoporosis. Enhancing osteoblastic differentiation of BMSCs is a feasible therapeutic strategy for osteoporosis. Here, bone marrow stromal cell (ST)-derived exosomes (STExos) are found to remarkably enhance osteoblastic differentiation of BMSCs in vitro. However, intravenous injection of STExos is inefficient in ameliorating osteoporotic phenotypes in an ovariectomy (OVX)-induced postmenopausal osteoporosis mouse model, which may be because STExos are predominantly accumulated in the liver and lungs, but not in bone. Hereby, the STExo surface is conjugated with a BMSC-specific aptamer, which delivers STExos into BMSCs within bone marrow. Intravenous injection of the STExo-Aptamer complex enhances bone mass in OVX mice and accelerates bone healing in a femur fracture mouse model. These results demonstrate the efficiency of BMSC-specific aptamer-functionalized STExos in targeting bone to promote bone regeneration, providing a novel promising approach for the treatment of osteoporosis and fracture.

Exosomal non-coding RNAs (Exo-ncRNAs) in cardiovascular health

Extracellular vesicles (EVs) play a role in the pathophysiological processes and in different diseases, including cardiovascular disease. Out of several categories of EVs, exosomes (smallest - 30 to 150 nm) are gaining most of the focus as the next generation of biomarkers and in therapeutic strategies. This is because exosomes can be differentiated from other types of EVs based on the expression of tetraspanin molecules on the surface. More importantly, exosomes can be traced back to the cell of origin by identifying the unique cellular marker(s) on the exosomal surface. Recently, several researchs have demonstrated an important and underappreciated mechanism of paracrine cell-cell communication involving exosomal transfer, and its subsequent functional impact on recipient cells. Exosomes are enriched in proteins, mRNAs, miRNAs, and other non-coding RNAs, which can potentially alter myocardial function. Additionally, different stages of tissue damage can also be identified by measuring these bioactive molecules in the circulation. There are several aspects of this new concept still unknown. Therefore, in this review, we have summarized the knowledge we have so far and highlighted the potential of this novel concept of next generation biomarkers and therapeutic intervention.

Exosomes in ischemic heart disease: novel carriers for bioinformation

The occurrence of ischemic heart disease(IHD) is a multi-step chain process from potential risk factors to overt clinical diseases. Vascular cells, blood cells, cardiomyocytes and stem cells are all involved in the pathophysiological links via continual and polynary crosstalk. Exosomes,as powerful vectors for intercellular communication,have been a hotspot for basic and clinical research. Plenty of evidence has shown that exosomes largely participate in the evolution of IHD, including endothelial dysfunction, lipid deposition, atheromatous plaque formation and rupture, myocardial ischemia-reperfusion(I/R) injury,and heart failure (HF), while the rules for detailed communication in the different stages of this continuous disease are still poorly understood. This review will systematically describe characteristics of exosomal crosstalk between different cells in the diverse periods, and also cast light on the potential and challenges for exosome application as therapeutic targets, hoping to offer supporting background for the following research.

Enhancement of therapeutic potential of mesenchymal stem cell-derived extracellular vesicles

After the initial investigations into applications of mesenchymal stem cells (MSCs) for cell therapy, there was increased interest in their secreted soluble factors. Following studies of MSCs and their secreted factors, extracellular vesicles (EVs) released from MSCs have emerged as a new mode of intercellular crosstalk. MSC-derived EVs have been identified as essential signaling mediators under both physiological and pathological conditions, and they appear to be responsible for many of the therapeutic effects of MSCs. In several in vitro and in vivo models, EVs have been observed to have supportive functions in modulating the immune system, mainly mediated by EV-associated proteins and nucleic acids. Moreover, stimulation of MSCs with biophysical or biochemical cues, including EVs from other cells, has been shown to influence the contents and biological activities of subsequent MSC-derived EVs. This review provides on overview of the contents of MSC-derived EVs in terms of their supportive effects, and it provides different perspectives on the manipulation of MSCs to improve the secretion of EVs and subsequent EV-mediated activities. In this review, we discuss the possibilities for manipulating MSCs for EV-based cell therapy and for using EVs to affect the expression of elements of interest in MSCs. In this way, we provide a clear perspective on the state of the art of EVs in cell therapy focusing on MSCs, and we raise pertinent questions and suggestions for knowledge gaps to be filled.

Cardiomyogenesis Modeling Using Pluripotent Stem Cells: The Role of Microenvironmental Signaling

Pluripotent stem cells (PSC) can be used as a model to study cardiomyogenic differentiation. In vitro modeling can reproduce cardiac development through modulation of some key signaling pathways. Therefore, many studies make use of this strategy to better understand cardiomyogenesis complexity and to determine possible ways to modulate cell fate. However, challenges remain regarding efficiency of differentiation protocols, cardiomyocyte (CM) maturation and therapeutic applications. Considering that the extracellular milieu is crucial for cellular behavior control, cardiac niche studies, such as those identifying secreted molecules from adult or neonatal tissues, allow the identification of extracellular factors that may contribute to CM differentiation and maturation. This review will focus on cardiomyogenesis modeling using PSC and the elements involved in cardiac microenvironmental signaling (the secretome - extracellular vesicles, extracellular matrix and soluble factors) that may contribute to CM specification and maturation.

Blockade of miR-140-3p prevents functional deterioration in afterload-enhanced engineered heart tissue

Afterload enhancement (AE) of rat engineered heart tissue (EHT) in vitro leads to a multitude of changes that in vivo are referred to as pathological cardiac hypertrophy: e.g., cardiomyocyte hypertrophy, contractile dysfunction, reactivation of fetal genes and fibrotic changes. Moreover AE induced the upregulation of 22 abundantly expressed microRNAs. Here, we aimed at evaluating the functional effect of inhibiting 7 promising microRNAs (miR-21-5p, miR-146b-5p, miR-31a-5p, miR-322-5p, miR-450a-5p, miR-140-3p and miR-132-3p) in a small-range screen. Singular transfection of locked nucleic acid (LNA)-based anti-miRs at 100 nM (before the one week AE-procedure) led to a powerful reduction of the targeted microRNAs. Pretreatment with anti-miR-146b-5p, anti-miR-322-5p or anti-miR-450a-5p did not alter the AE-induced contractile decline, while anti-miR-31a-5p-pretreatment even worsened it. Anti-miR-21-5p and anti-miR-132-3p partially attenuated the AE-effect, confirming previous reports. LNA-anti-miR against miR-140-3p, a microRNA recently identified as a prognostic biomarker of cardiovascular disease, also attenuated the AE-effect. To simplify future in vitro experiments and to create an inhibitor for in vivo applications, we designed shorter miR-140-3p-inhibitors and encountered variable efficiency. Only the inhibitor that effectively repressed miR-140-3p was also protective against the AE-induced contractile decline. In summary, in a small-range functional screen, miR-140-3p evolved as a possible new target for the attenuation of afterload-induced pathological cardiac hypertrophy.