Extracellular vesicles from human cardiac progenitor cells inhibit cardiomyocyte apoptosis and improve cardiac function after myocardial infarction

Exosomes Mediate the Intercellular Communication after Myocardial Infarction

The mechanisms of cardiac repair after myocardial infarction (MI) are complicated and not well-understood currently. It is known that exosomes are released from most cells, recognized as new candidates with important roles in intercellular and tissue-level communication. Cells can package proteins and RNA messages into exosome and secret to recipient cells, which regulate gene expression in recipient cells. The research on exosomes in cardiovascular disease is just emerging. It is well-known that exosomes from cardiomyocyte can transfect endothelial cells, stem cells, fibroblasts and smooth muscle cells to induce cellular changes. After myocardial infarction (MI), the exosomes play important roles in local and distant microcommunication. Nowadays, exosomal microRNAs transportation has been found to deliver signals to mediate cardiac repair after MI. However, the exosomes quality and quantities are variable under different pathological conditions. Therefore, we speculate that the monitoring of the quality and quantity of exosomes may serve as diagnosis and prognosis biomarkers of MI, and the study of exosomes will provide insights for the new therapeutics to cardiac remodeling after MI.

Protein contaminations impact quantification and functional analysis of extracellular vesicle preparations from mesenchymal stromal cells

Extracellular vesicles (EV) awakened interest in the research on mesenchymal stromal cells by exploring their paracrine effects. However, many isolation protocols use bovine serum albumin (BSA) during the preparation of the EV. Therefore, we produced ‘sham’ BSA-EV and tested them in comparison to EV derived from mesenchymal stromal cells (MSC-EV). We found that BSA-EV did not express MSC-specific surface markers like CD29 and CD90. However, they were capable of reducing serum-starvation induced apoptosis in vitro in a kidney epithelial cell line to a similar extent as MSC-EV as measured by Annexin V/7-Aminoactinomycin D labeling and flow cytometry.

Exosomes and Their Therapeutic Potentials of Stem Cells

Exosomes, a group of vesicles originating from the multivesicular bodies (MVBs), are released into the extracellular space when MVBs fuse with the plasma membrane. Numerous studies indicate that exosomes play important roles in cell-to-cell communication, and exosomes from specific cell types and conditions display multiple functions such as exerting positive effects on regeneration in many tissues. It is widely accepted that the therapeutic potential of stem cells may be mediated largely by the paracrine factors, so harnessing the paracrine effects of stem and progenitor cells without affecting these living, replicating, and potentially pluripotent cell populations is an advantage in terms of safety and complexity. Ascending evidence indicated that exosomes might be the main components of paracrine factors; thus, understanding the role of exosomes in each subtype of stem cells is far-reaching. In this review, we discuss the functions of exosomes from different types of stem cells and emphasize the therapeutic potentials of exosomes, providing an alternative way of developing strategies to cure diseases.

3D culture for cardiac cells

This review discusses historical milestones, recent developments and challenges in the area of 3D culture models with cardiovascular cell types. Expectations in this area have been raised in recent years, but more relevant in vitro research, more accurate drug testing results, reliable disease models and insights leading to bioartificial organs are expected from the transition to 3D cell culture. However, the construction of organ-like cardiac 3D models currently remains a difficult challenge. The heart consists of highly differentiated cells in an intricate arrangement.Furthermore, electrical “wiring”, a vascular system and multiple cell types act in concert to respond to the rapidly changing demands of the body. Although cardiovascular 3D culture models have been predominantly developed for regenerative medicine in the past, their use in drug screening and for disease models has become more popular recently. Many sophisticated 3D culture models are currently being developed in this dynamic area of life science. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

Acellular approaches for regenerative medicine: on the verge of clinical trials with extracellular membrane vesicles?

Extracellular vesicles (EVs) are a heterogeneous population of naturally occurring secreted small vesicles, with distinct biophysical properties and different functions both in physiology and under pathological conditions. In recent years, a number of studies have demonstrated that EVs might hold remarkable potential in regenerative medicine by acting as therapeutically promising nanodrugs. Understanding their final impact on the biology of specific target cells as well as clarification of their overall therapeutic impact remains a matter of intense debate. Here we review the key principles of EVs in physiological and pathological conditions with a specific highlight on the most recently described mechanisms regulating some of the EV-mediated effects. First, we describe the current debates and the upcoming research on EVs as potential novel therapeutics in regenerative medicine, either as unmodified agents or as functionalized small carriers for targeted drug delivery. Moreover, we address a number of safety aspects and regulatory limitations related to the novel nature of EV-mediated therapeutic applications. Despite the emerging possibilities of EV treatments, these issues need to be overcome in order to allow their safe and successful application in future explorative clinical studies.

Exosomes: Fundamental Biology and Roles in Cardiovascular Physiology

Exosomes are nanosized membrane particles that are secreted by cells that transmit information from cell to cell. The information within exosomes prominently includes their protein and RNA payloads. Exosomal microRNAs in particular can potently and fundamentally alter the transcriptome of recipient cells. Here we summarize what is known about exosome biogenesis, content, and transmission, with a focus on cardiovascular physiology and pathophysiology. We also highlight some of the questions currently under active investigation regarding these extracellular membrane vesicles and their potential in diagnostic and therapeutic applications.

Extracellular Vesicles: Evolving Factors in Stem Cell Biology

Stem cells are proposed to continuously secrete trophic factors that potentially serve as mediators of autocrine and paracrine activities, associated with reprogramming of the tumor microenvironment, tissue regeneration, and repair. Hitherto, significant efforts have been made to understand the level of underlying paracrine activities influenced by stem cell secreted trophic factors, as little is known about these interactions. Recent findings, however, elucidate this role by reporting the effects of stem cell derived extracellular vesicles (EVs) that mimic the phenotypes of the cells from which they originate. Exchange of genetic information utilizing persistent bidirectional communication mediated by stem cell-EVs could regulate stemness, self-renewal, and differentiation in stem cells and their subpopulations. This review therefore discusses stem cell-EVs as evolving communication factors in stem cell biology, focusing on how they regulate cell fates by inducing persistent and prolonged genetic reprogramming of resident cells in a paracrine fashion. In addition, we address the role of stem cell-secreted vesicles in shaping the tumor microenvironment and immunomodulation and in their ability to stimulate endogenous repair processes during tissue damage. Collectively, these functions ensure an enormous potential for future therapies.

The Evolution of the Stem Cell Theory for Heart Failure

Various stem cell-based approaches for cardiac repair have achieved encouraging results in animal experiments, often leading to their rapid proceeding to clinical testing. However, freewheeling evolutionary developments of the stem cell theory might lead to dystopian scenarios where heterogeneous sources of therapeutic cells could promote mixed clinical outcomes in un-stratified patient populations. This review focuses on the lessons that should be learnt from the first generation of stem cell-based strategies and emphasizes the absolute requirement to better understand the basic mechanisms of stem cell biology and cardiogenesis. We will also discuss about the unexpected “big bang” in the stem cell theory, “blasting” the therapeutic cells to their unchallenged ability to release paracrine factors such as extracellular membrane vesicles. Paradoxically, the natural evolution of the stem cell theory for cardiac regeneration may end with the development of cell-free strategies with multiple cellular targets including cardiomyocytes but also other infiltrating or resident cardiac cells.

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Varied sources of therapeutic cells and low repair ability of the failing heart contribute to mixed results in clinical trials.

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Consensus is still lacking concerning the appropriate type of therapeutic stem cells.

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A clear understanding of cardiac development and adult cardiogenesis might increase the efficiency of regenerative therapies.

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Delivery of stem cell-derived paracrine factor alone to the damaged heart may be sufficient to activate repair mechanisms.

Reaching out: junctions between cardiac telocytes and cardiac stem cells in culture

Telocytes (TCs) were previously shown by our group to form a tandem with stem/progenitor cells in cardiac stem cell (CSC) niches, fulfilling various roles in cardiac renewal. Among these, the ability to ‘nurse’ CSCs in situ, both through direct physical contact (junctions) as well as at a distance, by paracrine signalling or through extracellular vesicles containing mRNA. We employed electron microscopy to identify junctions (such as gap or adherens junctions) in a co‐culture of cardiac TCs and CSCs. Gap junctions were observed between TCs, which formed networks, however, not between TCs and CSCs. Instead, we show that TCs and CSCs interact in culture forming heterocellular adherens junctions, as well as non‐classical junctions such as puncta adherentia and stromal synapses. The stromal synapse formed between TCs and CSCs (both stromal cells) was frequently associated with the presence of electron‐dense nanostructures (on average about 15 nm in length) connecting the two opposing membranes. The average width of the synaptic cleft was 30 nm, whereas the average length of the intercellular contact was 5 μm. Recent studies have shown that stem cells fail to adequately engraft and survive in the hostile environment of the injured myocardium, possibly as a result of the absence of the pro‐regenerative components of the secretome (paracrine factors) and/or of neighbouring support cells. Herein, we emphasize the similarities between the junctions described in co‐culture and the junctions identified between TCs and CSCs in situ. Reproducing a CSC niche in culture may represent a viable alternative to mono‐cellular therapies.

Cardioprotective Actions of TGFβRI Inhibition Through Stimulating Autocrine/Paracrine of Survivin and Inhibiting Wnt in Cardiac Progenitors

Heart failure due to myocardial infarction (MI) is a major cause of morbidity and mortality in the world. We found previously that A83-01, a TGFβRI inhibitor, could facilitate cardiac repair in post-MI mice and induce the expansion of a Nkx2.5 + cardiomyoblast population. This study aimed to investigate the key autocrine/paracrine factors regulated by A83-01 in the injured heart and the mechanism of cardioprotection by this molecule. Using a previously described transgenic Nkx2.5 enhancer-green fluorescent protein (GFP) reporter mice, we isolated cardiac progenitor cells (CPC) including Nkx2.5-GFP + (Nkx2.5+), sca1+, and Nkx2.5+/sca1 + cells. A83-01 was found to induce proliferation of these three subpopulations mainly through increasing Birc5 expression in the MEK/ERK-dependent pathway. Survivin, encoded by Birc5, could also directly proliferate Nkx2.5 + cells and enhance cultured cardiomyocytes viability. A83-01 could also reverse the downregulation of Birc5 in postinjured mice hearts (n = 6) to expand CPCs. Moreover, the increased Wnt3a in postinjured hearts could decrease CPCs, which could be reversed by A83-01 via inhibiting Fzd6 and Wnt1-induced signaling protein 1 expressions in CPCs. Next, we used inducible αMHC-cre/mTmG mice to label cardiomyocytes with GFP and nonmyocytes with RFP. We found A83-01 preserved more GFP + myocytes (68.6% ± 3.1% vs. 80.9% ± 3.0%; p < .05, n = 6) and fewer renewed RFP + myocytes (0.026% ± 0.005% vs. 0.062% ± 0.008%; p < .05, n = 6) in parallel with less cardiac fibrosis in isoprenaline-injected mice treated with A83-01. TGFβRI inhibition in an injured adult heart could both stimulate the autocrine/paracrine activity of survivin and inhibit Wnt in CPCs to mediate cardioprotection and improve cardiac function.

Role and Function of MicroRNAs in Extracellular Vesicles in Cardiovascular Biology

Intercellular communication mediated by extracellular vesicles is crucial for preserving vascular integrity and in the development of cardiovascular disease. Extracellular vesicles consist of apoptotic bodies, microvesicles, and exosomes that can be found in almost every fluid compartment of the body like blood, saliva, and urine. In the recent years, a lot of reports came up suggesting that major cardiovascular and metabolic pathologies like atherogenesis, heart failure, or diabetes are highly influenced by transfer of microRNAs via extracellular vesicles leading to altered protein expression and phenotypes of recipient cells. The following review will summarize the fast developing field of intercellular signaling in cardiovascular biology by microRNA-containing extracellular vesicles.

MiR-145 facilitates proliferation and migration of endothelial progenitor cells and recanalization of arterial thrombosis in cerebral infarction mice via JNK signal pathway

Arterial thrombosis in cerebral infarction severely affects patients' lives. Classical treatment including surgery and medication both had significantly adverse effects, making it necessary to find novel strategy. Endothelial progenitor cells (EPCs) have been shown to enhance the recanalization of thrombosis, while leaving its molecular mechanism unclear. EPCs were separated from peripheral blood, and were transfected by microRNA (miR)-145. The growth, proliferation and migration abilities were quantified by MTT, clone formation and Transwell assays, respectively. Cell apoptosis was evaluated by flow cytometry. The activation of JNK signaling pathway was measured by Western blotting, followed by JNK inhibitor SP600125. In a mouse cerebral infarction model, miR-145 transfected EPCs were injected to observe the condition of arterial thrombosis. MiR-145 transfection enhanced growth, migration and proliferation of EPCs without induction of apoptosis. MiR-145 exerts its effects via JNK signaling pathway, as the blocking inhibited cell migration/proliferation. In vivo injection of miR-145 transfected EPCs also potentiated cell proliferation and migration, in addition to the recanalization of arterial thrombosis. MiR-145 facilitates proliferation and migration of EPCs and recanalization of arterial thrombosis in cerebral infarction mice via JNK signal pathway. This study provided new insights regarding infarction treatment.

Stem cell-derived exosomes: roles in stromal remodeling, tumor progression, and cancer immunotherapy

Stem cells are known to maintain stemness at least in part through secreted factors that promote stem-like phenotypes in resident cells. Accumulating evidence has clarified that stem cells release nano-vesicles, known as exosomes, which may serve as mediators of cell-to-cell communication and may potentially transmit stem cell phenotypes to recipient cells, facilitating stem cell maintenance, differentiation, self-renewal, and repair. It has become apparent that stem cell-derived exosomes mediate interactions among stromal elements, promote genetic instability in recipient cells, and induce malignant transformation. This review will therefore discuss the potential of stem cell-derived exosomes in the context of stromal remodeling and their ability to generate cancer-initiating cells in a tumor niche by inducing morphologic and functional differentiation of fibroblasts into tumor-initiating fibroblasts. In addition, the immunosuppressive potential of stem cell-derived exosomes in cancer immunotherapy and their prospective applications in cell-free therapies in future translational medicine is discussed.

Intravenous Cardiac Stem Cell-Derived Exosomes Ameliorate Cardiac Dysfunction in Doxorubicin Induced Dilated Cardiomyopathy

Despite the efficacy of cardiac stem cells (CSCs) for treatment of cardiomyopathies, there are many limitations to stem cell therapies. CSC-derived exosomes (CSC-XOs) have been shown to be responsible for a large portion of the regenerative effects of CSCs. Using a mouse model of doxorubicin induced dilated cardiomyopathy, we study the effects of systemic delivery of human CSC-XOs in mice. Mice receiving CSC-XOs showed improved heart function via echocardiography, as well as decreased apoptosis and fibrosis. In spite of using immunocompetent mice and human CSC-XOs, mice showed no adverse immune reaction. The use of CSC-XOs holds promise for overcoming the limitations of stem cells and improving cardiac therapies.

The secretome of myocardial telocytes modulates the activity of cardiac stem cells

Telocytes (TCs) are interstitial cells that are present in numerous organs, including the heart interstitial space and cardiac stem cell niche. TCs are completely different from fibroblasts. TCs release extracellular vesicles that may interact with cardiac stem cells (CSCs) via paracrine effects. Data on the secretory profile of TCs and the bidirectional shuttle vesicular signalling mechanism between TCs and CSCs are scarce. We aimed to characterize and understand the in vitro effect of the TC secretome on CSC fate. Therefore, we studied the protein secretory profile using supernatants from mouse cultured cardiac TCs. We also performed a comparative secretome analysis using supernatants from rat cultured cardiac TCs, a pure CSC line and TCs-CSCs in co-culture using (i) high-sensitivity on-chip electrophoresis, (ii) surface-enhanced laser desorption/ionization time-of-flight mass spectrometry and (iii) multiplex analysis by Luminex-xMAP. We identified several highly expressed molecules in the mouse cardiac TC secretory profile: interleukin (IL)-6, VEGF, macrophage inflammatory protein 1α (MIP-1α), MIP-2 and MCP-1, which are also present in the proteome of rat cardiac TCs. In addition, rat cardiac TCs secrete a slightly greater number of cytokines, IL-2, IL-10, IL-13 and some chemokines like, GRO-KC. We found that VEGF, IL-6 and some chemokines (all stimulated by IL-6 signalling) are secreted by cardiac TCs and overexpressed in co-cultures with CSCs. The expression levels of MIP-2 and MIP-1α increased twofold and fourfold, respectively, when TCs were co-cultured with CSCs, while the expression of IL-2 did not significantly differ between TCs and CSCs in mono culture and significantly decreased (twofold) in the co-culture system. These data suggest that the TC secretome plays a modulatory role in stem cell proliferation and differentiation.

Exosome enrichment of human serum using multiple cycles of centrifugation

In this work, we compared the use of repeated cycles of centrifugation at conventional speeds for enrichment of exosomes from human serum compared to the use of ultracentrifugation (UC). After removal of cells and cell debris, a speed of 110 000 × g or 40 000 × g was used for the UC or centrifugation enrichment process, respectively. The enriched exosomes were analyzed using the bicinchoninic acid assay, 1D gel separation, transmission electron microscopy, Western blotting, and high-resolution LC-MS/MS analysis. It was found that a five-cycle repetition of UC or centrifugation is necessary for successful removal of nonexosomal proteins in the enrichment of exosomes from human serum. More significantly, 5× centrifugation enrichment was found to provide similar or better performance than 5× UC enrichment in terms of enriched exosome protein amount, Western blot band intensity for detection of CD-63, and numbers of identified exosome-related proteins and cluster of differentiation (CD) proteins. A total of 478 proteins were identified in the LC-MS/MS analyses of exosome proteins obtained from 5× UCs and 5× centrifugations including many important CD membrane proteins. The presence of previously reported exosome-related proteins including key exosome protein markers demonstrates the utility of this method for analysis of proteins in human serum.

Mesenchymal stromal cells for cutaneous wound healing in a rabbit model: pre-clinical study applicable in the pediatric surgical setting

Objective

Mesenchymal stromal cells (MSCs) expanded in vitro have been proposed as a potential therapy for congenital or acquired skin defects in pediatrics. The aim of this pre-clinical study was to investigate the effects of intradermal injections of MSC in experimental cutaneous wound repair comparing allogeneic and autologous adipose stem cells (ASCs) and autologous bone marrow-mesenchymal stromal cells (BM-MSCs).

Methods

Mesenchymal stromal cells were in vitro expanded from adipose and BM tissues of young female New Zealand rabbits. MSCs were characterized for plastic adhesion, surface markers, proliferation and differentiation capacity. When an adequate number of cells (ASCs 10 × 10⁶ and BM-MSCs 3 × 10⁶, because of their low rate of proliferation) was reached, two skin wounds were surgically induced in each animal. The first was topically treated with cell infusions, the second was used as a control. The intradermal inoculation included autologous or allogeneic ASCs or autologous BM-MSCs. For histological examination, animals were sacrificed and wounds were harvested after 11 and 21 days of treatment.

Results

Rabbit ASCs were isolated and expanded in vitro with relative abundance, cells expressed typical surface markers (CD49e, CD90 and CD29). Topically, ASC inoculation provided more rapid wound healing than BM-MSCs and controls. Improved re-epithelization, reduced inflammatory infiltration and increased collagen deposition were observed in biopsies from wounds treated with ASCs, with the best result in the autologous setting. ASCs also improved restoration of skin architecture during wound healing.

Conclusion

The use of ASCs may offer a promising solution to treat extended wounds. Pre-clinical studies are however necessary to validate the best skin regeneration technique, which could be used in pediatric surgical translational research.

Exosomal clusterin, identified in the pericardial fluid, improves myocardial performance following MI through epicardial activation, enhanced arteriogenesis and reduced apoptosis

BACKGROUND

We recently demonstrated that epicardial progenitor cells participate in the regenerative response to myocardial infarction (MI) and factors released in the pericardial fluid (PF) may play a key role in this process. Exosomes are secreted nanovesicles of endocytic origin, identified in most body fluids, which may contain molecules able to modulate a variety of cell functions. Here, we investigated whether exosomes are present in the PF and their potential role in cardiac repair.

METHODS AND RESULTS

Early gene expression studies in 3day-infarcted mouse hearts showed that PF induces epithelial-to-mesenchymal transition (EMT) in epicardial cells. Exosomes were identified in PFs from non-infarcted patients (PFC) and patients with acute MI (PFMI). A shotgun proteomics analysis identified clusterin in exosomes isolated from PFMI but not from PFC. Notably, clusterin has a protective effect on cardiomyocytes after acute MI in vivo and is an important mediator of TGFβ-induced. Clusterin addition to the pericardial sac determined an increase in epicardial cells expressing the EMT marker α-SMA and, interestingly, an increase in the number of epicardial cells ckit(+)/α-SMA(+), 7days following MI. Importantly, clusterin treatment enhanced arteriolar length density and lowered apoptotic rates in the peri-infarct area. Hemodynamic studies demonstrated an improvement in cardiac function in clusterin-treated compared to untreated infarcted hearts.

CONCLUSIONS

Exosomes are present and detectable in the PFs. Clusterin was identified in PFMI-exosomes and might account for an improvement in myocardial performance following MI through a framework including EMT-mediated epicardial activation, arteriogenesis and reduced cardiomyocyte apoptosis.

Exosomes for Intramyocardial Intercellular Communication

Cross-talk between different cell types plays central roles both in cardiac homeostasis and in adaptive responses of the heart to stress. Cardiomyocytes (CMs) send biological messages to the other cell types present in the heart including endothelial cells (ECs) and fibroblasts. In turn, CMs receive messages from these cells. Recent evidence has now established that exosomes, nanosized secreted extracellular vesicles, are crucial mediators of such messages. CMs, ECs, cardiac fibroblasts, and cardiac progenitor cells (CPCs) release exosomes carrying nonrandom subsets of proteins, lipids, and nucleic acids present in their cells of origin. Exosomes secreted from CMs are internalized by fibroblasts and regulate gene expression in these cells as well as in ECs. CPC-derived exosomes protect CMs against apoptosis while also stimulating angiogenesis. They are rich in cardioprotective and proangiogenic microRNAs such as miR-146, miR-210, and miR-132. When injected into infracted hearts in vivo, CPC-derived exosomes reduce infarct size and improve cardiac function. Thus, exosomes are emerging both as key mediators of intercellular communication in the heart and as therapeutic candidates for heart disease.

Extracellular vesicles shuffling intercellular messages: for good or for bad

The release of extracellular vesicles (EVs) is a highly conserved process exploited by diverse organisms as a mode of intercellular communication. Vesicles of sizes ranging from 30 to 1000nm, or even larger, are generated by blebbing of the plasma membrane (microvesicles) or formed in multivesicular endosomes (MVEs) to be secreted by exocytosis as exosomes. Exosomes, microvesicles and other EVs contain membrane and cytosolic components that include proteins, lipids and RNAs, a composition that differs related to their site of biogenesis. Several mechanisms are involved in vesicle formation at the plasma membrane or in endosomes, which is reflected in their heterogeneity, size and composition. EVs have significant promise for therapeutics and diagnostics and for understanding physiological and pathological processes all of which have boosted research to find modulators of their composition, secretion and targeting.

Extracellular vesicle microRNA transfer in cardiovascular disease

microRNAs (miRNAs) are a class of small regulatory RNAs that decrease protein translation to fine-tune cellular function. Recently, miRNAs were found to transfer from a donor cell into a recipient cell via exosomes and microparticles. These microvesicles are found in blood, urine, saliva, and other fluid compartments. miRNAs are delivered with intact functionality and have been repeatedly shown to regulate protein expression in recipient cells in a paracrine fashion. Thus, transported miRNAs are a new class of cell-to-cell regulatory species. Exosomal miRNA transfer is now being reported in cardiovascular systems and disease. In the blood vessels, this transfer modulates atherosclerosis and angiogenesis. In the heart, it modulates heart failure, myocardial infarction, and response to ischemic preconditioning. This review describes our current understanding of extracellular vesicle miRNA transfer, demonstrating the roles of miR-126, miR-146a, miR-143, and other miRNAs being shuttled from endothelial cells, stem cells, fibroblasts and others into myocytes, endothelial cells, and smooth muscle cells to activate cellular changes and modulate disease phenotypes.

Exosomes and exosomal miRNAs in cardiovascular protection and repair

Cell-cell communication between cardiac and vascular cells and from stem and progenitor cells to differentiated cardiovascular cells is both an important and complex process, achieved through a diversity of mechanisms that have an impact on cardiovascular biology, disease and therapeutics. In recent years, evidence has accumulated suggesting that extracellular vesicles (EVs) are a new system of intercellular communication. EVs of different sizes are produced via different biogenesis pathways and have been shown to be released and taken up by most of known cell types, including heart and vascular cells, and stem and progenitor cells. This review will focus on exosomes, the smallest EVs (up to 100nm in diameter) identified so far. Cells can package cargoes consisting of selective lipids, proteins and RNA in exosomes and such cargoes can be shipped to recipient cells, inducing expressional and functional changes. This review focuses on exosomes and microRNAs in the context of cardiovascular disease and repair. We will describe exosome biogenesis and cargo formation and discuss the available information on in vitro and in vivo exosomes-based cell-to-cell communication relevant to cardiovascular science. The methods used in exosome research will be also described. Finally, we will address the promise of exosomes as clinical biomarkers and their impact as a biomedical tool in stem cell-based cardiovascular therapeutics.

Cardiosome mediated regulation of MMP9 in diabetic heart: role of mir29b and mir455 in exercise

'Cardiosomes' (exosomes from cardiomyocytes) have recently emerged as nanovesicles (30-100 nm) released in the cardiosphere by myocytes and cardiac progenitor cells, though their role in diabetes remains elusive. Diabetic cardiovascular complications are unequivocally benefitted from exercise; however, the molecular mechanisms need exploration. This novel study is based on our observation that exercise brings down the levels of activated (Matrix Metalloprotease 9) in db/db mice in a model of type 2 diabetes. We hypothesize that exosomes that are released during exercise contain microRNAs (mir455, mir29b, mir323-5p and mir466) that bind to the 3' region of MMP9 and downregulate its expression, hence mitigating the deleterious downstream effects of MMP9, which causes extracellular matrix remodeling. First, we confirmed the presence of exosomes in the heart tissue and serum by electron microscopy and flow cytometry, respectively, in the four treatment groups: (i) db/control, (ii) db/control+exercise, (iii) db/db and (iv) db/db+exercise. Use of exosomal markers CD81, Flottilin 1, and acetylcholinesterase activity in the isolated exosomes confirmed enhanced exosomal release in the exercise group. The microRNAs isolated from the exosomes contained mir455, mir29b, mir323-5p and mir466 as quantified by qRTPCR, however, mir29b and mir455 showed highest upregulation. We performed 2D zymography which revealed significantly lowered activity of MMP9 in the db/db exercise group as compared to non-exercise group. The immunohistochemical analysis further confirmed the downregulated expression of MMP9 after exercise. Since MMP9 is involved in matrix degradation and leads to fibrosis and myocyte uncoupling, the present study provides a strong evidence how exercise can mitigate these conditions in diabetic patients.

MicroRNA profiling of pericardial fluid samples from patients with heart failure

AIMS

Multicellular organisms maintain vital functions through intercellular communication. Release of extracellular vesicles that carry signals to even distant target organs is one way of accomplishing this communication. MicroRNAs can also be secreted from the cells in exosomes and act as paracrine signalling molecules. In addition, microRNAs have been implicated in the pathogenesis of a large number of diseases, including cardiovascular diseases, and are considered as promising candidate biomarkers due to their relative stability and easy quantification from clinical samples. Pericardial fluid contains hormones secreted by the heart and is known to reflect the cardiac function. In this study, we sought to investigate whether pericardial fluid contains microRNAs and if so, whether they could be used to distinguish between different cardiovascular pathologies and disease stages.

METHODS AND RESULTS

Pericardial fluid was collected from heart failure patients during open-heart surgery. MicroRNA profiles of altogether 51 patients were measured by quantitative real-time PCR (qPCR) using Exiqon human panels I and II. On the average, 256 microRNAs were detected per sample, and 70 microRNAs out of 742 profiled microRNAs were detected in every sample. The five most abundant microRNAs in pericardial fluid were miR-21-5p, miR-451a, miR-125b-5p, let-7b-5p and miR-16-5p. No specific signatures for cardiovascular pathologies or clinically assessed heart failure stages could be detected from the profiles and, overall, microRNA profiles of the samples were found to be very similar despite the heterogeneity in the study population.

CONCLUSION

Measured microRNA profiles did not separate the samples according to the clinical features of the patients. However, several previously identified heart failure marker microRNAs were detected. The pericardial fluid microRNA profile appeared to be a result of an active and selective secretory process indicating that microRNAs may act as paracrine signalling factors by mediating the local crosstalk between cardiac cells.

Stem cells in the management of advanced heart failure

PURPOSE OF REVIEW

Outcomes of stem cell trials in patients with advanced heart failure have been divergent, which has raised some scepticism about this therapy and led to recommending slowing clinical trials until basic issues have been more thoroughly addressed. It is therefore timely and relevant to examine the current data and discuss how recent findings may change the perspectives of stem cell therapy.

RECENT FINDINGS

The most important recent change has been a shift in the mechanistic paradigm. Although the initial objective of stem cells was to physically replace dead cardiomyocytes and build a new electromechanically integrated myocardial tissue, it is now recognized that the unavoidable death of most of the transplanted cells makes this objective unrealistic. Indeed, the primary mechanism of action of the cells seems to be paracrine through the release of factors activating the endogenous signalling pathways, leading to cardioprotection. This hypothesis has several implications. First, it leads to focus on the efficiency of early retention, rather than on sustained survival, which, in turn, implies improving delivery approaches, largely through an increased reliance on adjunctive biomaterials; second, it may rationalize the use of allogeneic cells as long as their rejection is delayed to give them enough time for releasing the signalling biomolecules; and, finally, it raises the possibility that transplantation of cells could be replaced by the delivery of their sole secretome, possibly under the form of microvesicles.

SUMMARY

Put together, these approaches could streamline the translational process and enhance large-scale clinical applications.

Long Noncoding RNAs and MicroRNAs in Cardiovascular Pathophysiology

RNAs not encoding proteins have gained prominence over the last couple of decades as fundamental regulators of cellular function. Not surprisingly, their dysregulation is increasingly being linked to pathology. Here, we review recent reports investigating the pathophysiological relevance of this species of RNA for the cardiovascular system, concentrating mainly on recent findings on long noncoding RNAs and microRNAs in cardiac hypertrophy and failure.

Telocytes transfer extracellular vesicles loaded with microRNAs to stem cells

Telocytes (TCs) are cells ubiquitously distributed in the body and characterized by very long and thin prolongations named telopodes (Tps). Cardiac TCs are the best characterized TCs for the moment. Tps release extracellular vesicles (EVs) in vivo and in vitro suggesting that TCs regulate the activity of other cells by vesicular paracrine signals. TCs have been found within the stem cell niche of several organs. Electron microscopy or electron tomography has shown that Tps are located in close vicinity of stem cells (SC). Since stem cell regulation by niche components involves paracrine signalling, we have investigated if TCs could be part of this mechanism. Using fluorescent labelling of cells and EVs with calcein and Cy5-miR-21 oligos, we provide evidence that TCs can modulate SC through EVs loaded with microRNAs. TCs deliver microRNA to cardiac stem cells (CSCs), as well as to other types of SCs (e.g. hematopoietic SC) indicating that this mechanism is not restricted to cardiac tissue. We also found that CSCs deliver microRNA loaded EVs to TCs, suggesting that there is a continuous, post-transcriptional regulatory signal back and forth between TCs and SC. In conclusion, our data reveal the existence of a reciprocal (bidirectional) epigenetic signalling between TCs and SC.

Extracellular vesicles: potential roles in regenerative medicine

Extracellular vesicles (EV) consist of exosomes, which are released upon fusion of the multivesicular body with the cell membrane, and microvesicles, which are released directly from the cell membrane. EV can mediate cell–cell communication and are involved in many processes, including immune signaling, angiogenesis, stress response, senescence, proliferation, and cell differentiation. The vast amount of processes that EV are involved in and the versatility of manner in which they can influence the behavior of recipient cells make EV an interesting source for both therapeutic and diagnostic applications. Successes in the fields of tumor biology and immunology sparked the exploration of the potential of EV in the field of regenerative medicine. Indeed, EV are involved in restoring tissue and organ damage, and may partially explain the paracrine effects observed in stem cell-based therapeutic approaches. The function and content of EV may also harbor information that can be used in tissue engineering, in which paracrine signaling is employed to modulate cell recruitment, differentiation, and proliferation. In this review, we discuss the function and role of EV in regenerative medicine and elaborate on potential applications in tissue engineering.

miR-133a enhances the protective capacity of cardiac progenitors cells after myocardial infarction

miR-133a and miR-1 are known as muscle-specific microRNAs that are involved in cardiac development and pathophysiology. We have shown that both miR-1 and miR-133a are early and progressively upregulated during in vitro cardiac differentiation of adult cardiac progenitor cells (CPCs), but only miR-133a expression was enhanced under in vitro oxidative stress. miR-1 was demonstrated to favor differentiation of CPCs, whereas miR-133a overexpression protected CPCs against cell death, targeting, among others, the proapoptotic genes Bim and Bmf. miR-133a-CPCs clearly improved cardiac function in a rat myocardial infarction model by reducing fibrosis and hypertrophy and increasing vascularization and cardiomyocyte proliferation. The beneficial effects of miR-133a-CPCs seem to correlate with the upregulated expression of several relevant paracrine factors and the plausible cooperative secretion of miR-133a via exosomal transport. Finally, an in vitro heart muscle model confirmed the antiapoptotic effects of miR-133a-CPCs, favoring the structuration and contractile functionality of the artificial tissue.

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miR-1 and miR-133a have a role in adult cardiac progenitor cells (CPCs)

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miR-133a-CPCs protect cardiac function

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miR-133a-CPCs increase vascularization and protect against hypertrophy

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miR-133a is enriched in CPCs-derived exosomes

Identification of therapeutic covariant microRNA clusters in hypoxia-treated cardiac progenitor cell exosomes using systems biology

RATIONALE

Myocardial infarction is a leading cause of death in developed nations, and there remains a need for cardiac therapeutic systems that mitigate tissue damage. Cardiac progenitor cells (CPCs) and other stem cell types are attractive candidates for treatment of myocardial infarction; however, the benefit of these cells may be as a result of paracrine effects.

OBJECTIVE

We tested the hypothesis that CPCs secrete proregenerative exosomes in response to hypoxic conditions.

METHODS AND RESULTS

The angiogenic and antifibrotic potential of secreted exosomes on cardiac endothelial cells and cardiac fibroblasts were assessed. We found that CPC exosomes secreted in response to hypoxia enhanced tube formation of endothelial cells and decreased profibrotic gene expression in TGF-β-stimulated fibroblasts, indicating that these exosomes possess therapeutic potential. Microarray analysis of exosomes secreted by hypoxic CPCs identified 11 miRNAs that were upregulated compared with exosomes secreted by CPCs grown under normoxic conditions. Principle component analysis was performed to identify miRNAs that were coregulated in response to distinct exosome-generating conditions. To investigate the cue-signal-response relationships of these miRNA clusters with a physiological outcome of tube formation or fibrotic gene expression, partial least squares regression analysis was applied. The importance of each up- or downregulated miRNA on physiological outcomes was determined. Finally, to validate the model, we delivered exosomes after ischemia-reperfusion injury. Exosomes from hypoxic CPCs improved cardiac function and reduced fibrosis.

CONCLUSIONS

These data provide a foundation for subsequent research of the use of exosomal miRNA and systems biology as therapeutic strategies for the damaged heart.

Pathologic function and therapeutic potential of exosomes in cardiovascular disease

The heart is a very complex conglomeration of organized interactions between various different cell types that all aid in facilitating myocardial function through contractility, sufficient perfusion, and cell-to-cell reception. In order to make sure that all features of the heart work effectively, it is imperative to have a well-controlled communication system among the different types of cells. One of the most important ways that the heart regulates itself is by the use of extracellular vesicles, more specifically, exosomes. Exosomes are types of nano-vesicles, naturally released from living cells. They are believed to play a critical role in intercellular communication through the means of certain mechanisms including direct cell-to-cell contact, long-range signals as well as electrical and extracellular chemical molecules. Exosomes contain many unique features like surface proteins/receptors, lipids, mRNAs, microRNAs, transcription factors and other proteins. Recent studies indicate that the exosomal contents are highly regulated by various stress and disease conditions, in turn reflective of the parent cell status. At present, exosomes are well appreciated to be involved in the process of tumor and infection disease. However, the research on cardiac exosomes is just emerging. In this review, we summarize recent findings on the pathologic effects of exosomes on cardiac remodeling under stress and disease conditions, including cardiac hypertrophy, peripartum cardiomyopathy, diabetic cardiomyopathy and sepsis-induced cardiovascular dysfunction. In addition, the cardio-protective effects of stress-preconditioned exosomes and stem cell-derived exosomes are also summarized. Finally, we discuss how to epigenetically reprogram exosome contents in host cells which makes them beneficial for the heart.