Bone marrow mesenchymal stem cells-derived conditioned medium protects cardiomyocytes from hypoxia/reoxygenation-induced injury through Notch2/mTOR/autophagy signaling

The dual role of mesenchymal stem cells in apoptosis regulation

Mesenchymal stem cells (MSCs) are widely distributed pluripotent stem cells with powerful immunomodulatory capacity. MSCs transplantation therapy (MSCT) is widely used in the fields of tissue regeneration and repair, and treatment of inflammatory diseases. Apoptosis is an important way for tissues to maintain cell renewal, but it also plays an important role in various diseases. And many studies have shown that MSCs improves the diseases by regulating cell apoptosis. The regulation of MSCs on apoptosis is double-sided. On the one hand, MSCs significantly inhibit the apoptosis of diseased cells. On the other hand, MSCs also promote the apoptosis of tumor cells and excessive immune cells. Furthermore, MSCs regulate apoptosis through multiple molecules and pathways, including three classical apoptotic signaling pathways and other pathways. In this review, we summarize the current evidence on the regulation of apoptosis by MSCs.

Delta like Non-Canonical Notch Ligand 2 inhibits chondrogenic differentiation and cell proliferation of bone marrow mesenchymal stem cells through the Notch1 signaling pathway

Bone marrow mesenchymal stem cells (BMSCs) is the candidate for the treatment of cartilage defects because of their directional induction potential and natural anti-inflammatory properties. As one of the non-canonical receptors of Notch1, Delta Like Non-Canonical Notch Ligand 2 (DLK2) involves in stem cells' adipogenesis and chondrogenic differentiation. However, the specific regulatory mechanism of DLK2 in the chondrogenic differentiation of BMSCs is still unclear. In this study, we found that the expression of DLK2 was reduced and the expression of Col2a1, Col10a1, Acan, Sox9, and Notch1 was raised in the process of BMSCs chondrogenic differentiation. However, the expression of Col2a1, Col10a1, Acan, and Sox9 reduced significantly, and the signal factor Notch1 and the chondrogenic differentiation capacity of BMSCs turned down in the DLK2 overexpression group. Furthermore, the expression of Col2a1, Col10a1, Acan, and Sox9 significantly enhanced, Notch1 expression was also increased, and the chondrogenic differentiation capacity of BMSCs turned up in the DLK2 suppression group. Concurrently, the proliferation of BMSCs was weakened after overexpression of DLK2, and there was no significant change in cell migration. However, the proliferation and migration of BMSCs were significantly enhanced after the inhibition of DLK2 expression. Therefore, these results suggest that DLK2 negatively regulates chondrogenic differentiation and cell proliferation in BMSCs by inhibiting the Notch1 signaling pathway.

Recent Advances of Using Exosomes as Diagnostic Markers and Targeting Carriers for Cardiovascular Disease

Cardiovascular diseases (CVDs) are the leading cause of human death worldwide. Exosomes act as endogenous biological vectors; they possess advantages of low immunogenicity and low safety risks, also providing tissue selectivity, including the inherent targeting the to heart. Therefore, exosomes not only have been applied as biomarkers for diagnosis and therapeutic outcome confirmation but also showed potential as drug carriers for cardiovascular targeting delivery. This review aims to summarize the progress and challenges of exosomes as novel biomarkers, especially many novel exosomal noncoding RNAs (ncRNAs), and also provides an overview of the improved targeting functions of exosomes by unique engineered approaches, the latest developed administration methods, and the therapeutic effects of exosomes used as the biocarriers of medications for cardiovascular disease treatment. Also, the possible therapeutic mechanisms and the potentials for transferring exosomes to the clinic for CVD treatment are discussed. The advances, in vivo and in vitro applications, modifications, mechanisms, and challenges summarized in this review will provide a general understanding of this promising strategy for CVD treatment.

Redox signaling regulates the skeletal tissue development and regeneration

Skeletal tissue development and regeneration in mammals are intricate, multistep, and highly regulated processes. Various signaling pathways have been implicated in the regulation of these processes, including redox. Redox signaling is the signal transduction by electron transfer reactions involving free radicals or related species. Redox homeostasis is essential to cell metabolic states, as the ROS not only regulates cell biological processes but also mediates physiological processes. Following a bone fracture, redox signaling is also triggered to regulate bone healing and regeneration by targeting resident stromal cells, osteoblasts, osteoclasts and endothelial cells. This review will focus on how the redox signaling impact the bone development and bone regeneration.

Cell Therapy: A New Technology for Cerebral Circulation Restoration after Ischemia/Reperfusion

Cell therapy with mesenchymal stem cells (MSCs) may be a promising technique for cerebral blood flow restoration after transient ischemia. Before a practical application of the cell material, 7-9 days are required for its cultivation. We studied the efficacy of human MSC (hMSC) transplantation performed 7 days after cerebral ischemia/reperfusion (I/R) to help recover cerebral circulation. The intravital micrograph technique was used to comparatively evaluate the vasculature density in the pia mater and the reactivity of the pial arteries in response to acetylcholine (ACh) in rats after I/R (clamping of both carotid arteries and a simultaneous decrease in and strict maintenance of the mean BP at 45 ± 2 mm Hg for 12 min) and with/without hMSC transplantation. Perfusion (P) in the sensorimotor cortex was assessed using laser dopplerography. After 14 and 21 days, the vasculature density in I/R-affected rats was 1.2- to 1.4-fold and 1.2- to 1.3-fold lower, respectively, than that in the controls. The number of ACh-dilated arteries decreased 1.6- to 1.9-fold and 1.2- to 1.7-fold 14 and 21 days after I/R, respectively. After 21 days, the P level decreased 1.6-fold, on average. Administration of hMSCs on day 7 after I/R resulted in complete recovery of the vasculature density by day 14. ACh-mediated dilatation fully recovered only in arteries of less than 40 μm in diameter within 21 days. After 21 days, the P level was 1.2-fold lower than that in the controls but significantly higher than that in rats after I/R without hMSCs. Delayed administration of MSCs after a transient cerebral ischemic attack affords the time for the procedures required to prepare cell material for transplantation and provides a good therapeutic response in the pial microvasculature.

Autophagy impairment in patients with obstructive sleep apnea modulates intermittent hypoxia-induced oxidative stress and cell apoptosis via hypermethylation of the ATG5 gene promoter region

BACKGROUND

Autophagy is a catabolic process that recycles damaged organelles and acts as a pro-survival mechanism, but little is known about autophagy dysfunction and epigenetic regulation in patients with obstructive sleep apnea (OSA).

METHODS

Protein/gene expressions and DNA methylation levels of the autophagy-related genes (ATG) were examined in blood leukocytes from 64 patients with treatment-naïve OSA and 24 subjects with primary snoring (PS).

RESULTS

LC3B protein expression of blood monocytes, and ATG5 protein expression of blood neutrophils were decreased in OSA patients versus PS subjects, while p62 protein expression of cytotoxic T cell was increased, particularly in those with nocturia. ATG5, ULK1, and BECN1 gene expressions of peripheral blood mononuclear cells were decreased in OSA patients versus PS subjects. LC3B gene promoter regions were hypermethylated in OSA patients, particularly in those with excessive daytime sleepiness, while ATG5 gene promoter regions were hypermethylated in those with morning headache or memory impairment. LC3B protein expression of blood monocytes and DNA methylation levels of the LC3B gene promoter region were negatively and positively correlated with apnea hyponea index, respectively. In vitro intermittent hypoxia with re-oxygenation exposure to human THP-1/HUVEC cell lines resulted in LC3B/ATG5/ULK1/BECN1 down-regulations and p62 up-regulation along with increased apoptosis and oxidative stress, while rapamycin and umbilical cord-mesenchymal stem cell treatment reversed these abnormalities through de-methylation of the ATG5 gene promoter.

CONCLUSIONS

Impaired autophagy activity in OSA patients was regulated by aberrant DNA methylation, correlated with clinical phenotypes, and contributed to increased cell apoptosis and oxidative stress. Autophagy enhancers may be novel therapeutics for OSA-related neurocognitive dysfunction.

A Novel 5-Chloro-N-phenyl-1H-indole-2-carboxamide Derivative as Brain-Type Glycogen Phosphorylase Inhibitor: Validation of Target PYGB

Brain-type glycogen phosphorylase (PYGB) inhibitors are recognized as prospective drugs for treating ischemic brain injury. We previously reported compound 1 as a novel glycogen phosphorylase inhibitor with brain-protective properties. In this study, we validated whether PYGB could be used as the therapeutic target for hypoxic-ischemic diseases and investigated whether compound 1 exerts a protective effect against astrocyte hypoxia/reoxygenation (H/R) injury by targeting PYGB. A gene-silencing strategy was initially applied to downregulate PYGB proteins in mouse astrocytes, which was followed by a series of cellular experiments with compound 1. Next, we compared relevant indicators that could prove the protective effect of compound 1 on brain injury, finding that after PYGB knockdown, compound 1 could not obviously alleviate astrocytes H/R injury, as evidenced by cell viability, which was not significantly improved, and lactate dehydrogenase (LDH) leakage rate, intracellular glucose content, and post-ischemic reactive oxygen species (ROS) level, which were not remarkably reduced. At the same time, cellular energy metabolism did not improve, and the degree of extracellular acidification was not downregulated after administration of compound 1 after PYGB knockdown. In addition, it could neither significantly increase the level of mitochondrial aerobic energy metabolism nor inhibit the expression of apoptosis-associated proteins. The above results indicate that compound 1 could target PYGB to exert its protective effect against cellular H/R injury in mouse astrocytes. Simultaneously, we further demonstrated that PYGB could be an efficient therapeutic target for ischemic-hypoxic diseases. This study provides a new reference for further in-depth study of the action mechanism of the efficacy of compound 1.

LPS preconditioning of MSC-CM improves protection against hypoxia/reoxygenation-induced damage in H9c2 cells partly via HMGB1/Bach1 signalling

Mesenchymal stem cell-derived conditioned medium (MSC-CM) improves cardiac function after myocardial infarction; however, this cardioprotective effect is moderate and transient. Lipopolysaccharide (LPS) pretreatment partially improves MSC-CM-mediated cardioprotective effects owing to the presence of paracrine factors. However, the mechanism underlying these improved effects remains unknown. To study the effect of LPS-pretreated MSC-CM on hypoxia/reoxygenation (H/R)-induced injury, MSCs were treated with or without LPS (400 ng/mL) for 48 h, and the supernatant was collected (MSC-CM). Subsequently, H9c2 cells were co-cultured with Nor-CM (CM derived from LPS-untreated MSCs) and LPS-CM (CM derived from LPS-pretreated MSCs) for 24 h and subjected to H/R. MSC-CM inhibited the progression of H/R-induced injury in H9c2 cells, and this protective effect was enhanced via LPS pretreatment as evidenced by the improved apoptosis assessment index (i.e. caspase-3 and B-cell lymphoma-2 [Bcl-2] expression) and decreased levels of lactic dehydrogenase (LDH) and cardiac troponin (cTn). In addition, the results of haematoxylin-eosin staining (H&E), transmission electron microscopy (TEM) and TdT-mediated dUTP nick-end labelling (TUNEL) validated that MSC-CM inhibited H/R-induced injury in H9c2 cardiomyocytes. LPS pretreatment downregulated the expression of high mobility group box-1 (HMGB1) and BTB and CNC homology-1 (Bach1) proteins in MSCs but upregulated the expression of vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF) and insulin-like growth factor (IGF). HMGB1 knockdown (MSC/siHMGB1-CM) significantly decreased the expression of Bach1 and increased the expression of VEGF, HGF and IGF. Bach1 knockdown (MSC/siBach1-CM) did not alter the production of HMGB1 but increased the expression of VEGF and IGF. LPS pretreatment did not alter the expression of the paracrine factors VEGF and HGF in the MSC/siHMGB1 group but increased their expression in the MSC/siBach1 group. The myocyte anti-apoptotic effects of MSCs/siBach1-CM were similar to those of untreated MSCs, which were not enhanced by LPS. LPS-pretreated MSC-CM protects H9c2 cells against H/R-induced injury partly through the HMGB1/Bach1 signalling pathway.

Bone marrow mesenchymal stem cell-derived exosomes shuttling miR-150-5p alleviates mechanical allodynia in rats by targeting NOTCH2 in microglia

Background

This study probes into the function and mechanism of bone marrow mesenchymal stem cell (BMSC)-derived exosomes loaded with miR-150-5p in mechanical allodynia.

Methods

BMSCs were infected with miR-150-5p inhibition lentiviruses to obtain exosomes with low miR-150-5p expression. A L5 spinal nerve ligation (SNL) model was established in rats where exosomes, NOTCH2 overexpression/inhibition plasmids, or microglial cells were intrathecally administered. Hind paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) of rats were measured. TUNEL staining was used to measure the apoptotic rate in rat spinal dorsal horn (SDH), ELISA to evaluate pro-inflammatory factor levels, and RT-qPCR, western blotting, and immunohistochemistry to detect miR-150-5p and NOTCH2 expression. Immunofluorescence was used for localizing exosomes and NOTCH2 and detecting the expression of OX42, a maker for microglia. Dual luciferase reporter and RNA pull down assays were performed to validate the putative binding between miR-150-5p and NOTCH2.

Results

NOTCH2 expressed at a high level and miR-150-5p was downregulated in SDH of SNL rats. Exosomes injected were localized in rat SDH. BMSC-exosomes or NOTCH2 downregulation increased PWT and PWL of SNL rats and reduced apoptosis and inflammation in SDH. In contrast, NOTCH2 overexpression aggravated mechanical allodynia and SDH injury. Moreover, inhibiting miR-150-5p in BMSC-exosomes offset the therapeutic effects of BMSC-exosomes. Microglia activation induced mechanical allodynia in wild rats, while intrathecal injection of microglial cells incubated with BMSC-exosomes showed alleviated mechanical allodynia in SNL rats. NOTCH2 was targeted by miR-150-5p.

Conclusion

BMSC-derived exosomal miR-150-5p alleviates mechanical allodynia by targeting NOTCH2 in microglial cells.

Intravenous injection of SDF-1α-overexpressing bone marrow mesenchymal stem cells has a potential protective effect on myocardial ischemia in mice

Background Neutrophils are involved in the injury of myocytes during myocardial ischemia (MI). Stem cells migrate to the site of myocardial injury under homing signals and play a protective role, such as inhibiting inflammation. Chemokine SDF-1α and its related receptor CXCR4 are upregulated after myocardial infarction, which may play an important role in stem cell homing. Objectives This study aimed to explore the potential therapeutic effect of SDF-1α-modified bone marrow mesenchymal stem cells on myocardial ischemia/reperfusion (I/R) injury. Methods We explored the role of SDF-1α modified bone marrow mesenchymal stem cells in vivo and in vitro. SDF-1α and CXCR4 expression was detected under hypoxia/reoxygenation (H/R) condition. Cell migration was detected by the transwell method. The levels of SDF-1α and IL-1β, IL-6, IL-10, and TNF-α were detected in different groups. Results In vivo, SDF-1α was mainly upregulated and secreted by cardiomyocytes, and cardiomyocytes recruited stem cells through the SDF-1/CXCR4 pathway to reduce the damage of polymorphic mononuclear neutrophils to cardiomyocytes under H/R. Upregulation of SDF-1α increased the migration ability of BMSC Stem Cells to H/R-induced cardiomyocytes. In vitro, intravenous injection of SDF-1α gene-modified BMSC Stem Cells reduced inflammatory infiltration in the injured area as well as the level of systemic inflammatory factors. Conclusions SDF-1α-overexpressing BMSC Stem Cells protected the heart function of mice and significantly reduced I/R-induced myocardial injury, which has a potential protective effect on MI.

Hypoxic Preconditioning Enhances the Efficacy of Mesenchymal Stem Cells-Derived Conditioned Medium in Switching Microglia toward Anti-inflammatory Polarization in Ischemia/Reperfusion

Activation of pro-inflammatory microglia is an important mechanism of the cerebral ischemia-reperfusion (I/R)-induced neuronal injury and dysfunction. Mesenchymal stem cells (MSCs) together with their paracrine factors demonstrated curative potential in immune disorders and inflammatory diseases, as well as in ischemic diseases. However, it remains unclear whether conditioned medium from MSCs could effectively regulate the activation and polarization of microglia exposed to I/R stimulation. In this study, we investigated the effects of conditioned medium from bone marrow MSCs (BMSCs-CM) on I/R-stimulated microglia and the potential mechanism involved, as well as the way to obtain more effective BMSCs-CM. First, cell model of oxygen-glucose deprivation/reoxygenation (OGD/R) was established in microglia to mimic the I/R. BMSCs-CM from different culture conditions (normoxic: 21% O2; hypoxic: 1% O2; hypoxia preconditioning: preconditioning with 1% O2 for 24 h) was used to treat the microglia. Our results showed that BMSCs-CM effectively promoted the survival and alleviated the injury of microglia. Moreover, in microglia exposed to OGD/R, BMSCs-CM inhibited significantly the expression of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6), CD86 and inducible nitric oxide synthase, whereas upregulated the levels of anti-inflammatory cytokine (IL-10), CD206 and Arginase-1. These results suggested that BMSCs-CM promoted the polarization of anti-inflammatory microglia. In particular, BMSCs-CM from cultures with hypoxia preconditioning was more effective in alleviating cell injury and promoting anti-inflammatory microglia polarization than BMSCs-CM from normoxic cultures and from hypoxic cultures. Furthermore, inhibition of exosomes secretion could largely mitigate these effects of BMSCs-CM. In conclusion, our results suggested that hypoxia preconditioning of BMSCs could enhance the efficacy of BMSCs-CM in alleviating OGD/R-induced injury and in promoting the anti-inflammatory polarization of microglia, and these beneficial effects of BMSCs-CM owed substantially to exosomes.

Hypoxia/reoxygenation-induced upregulation of miRNA-542-5p aggravated cardiomyocyte injury by repressing autophagy

MicroRNAs (miRNAs) and autophagy exert an important role in hypoxia/reoxygenation (H/R)-induced cardiomyocyte injury. The current study aimed to explore the role of miRNA and autophagy in H/R-induced cardiomyocyte injury. Cardiomyocyte H9c2 was exposed to H/R to simulate H/R injury in vitro. The differentially expressed miRNAs were identified using quantitative RT-PCR (qPCR). Lactate dehydrogenase (LDH) activity was assayed to assess H/R injury. The role of miRNA and autophagy in regulating the viability and cell apoptosis was evaluated using cell counting kit-8 (CCK-8) assay, flow cytometry (FCM), and western blot. The autophagy activation was assessed through testing the number of light chain 3 (LC3) puncta and LC3-II expression using western blot and immunofluorescence analysis. In the present study, we found that the miR-542-5p expression and the autophagy activation were significantly increased in H9c2 cells after H/R injury. Functionally, forced expression of miR-542-5p further aggravated H/R injury in H9c2 cells, whereas miR-542-5p inhibition alleviated H/R injury as measured by the cell viability, LDH activity and cell apoptosis. miR-542-5p repressed autophagy activation, whereas miR-542-5p inhibition facilitated autophagy activation in H9c2 cells exposed to H/R as measured by the LC3 puncta number, LC3II, and p62 protein level. Especially, autophagy inhibition by specific inhibitor partially lessened the role of miR-542-5p inhibitor in alleviating H/R injury. Finally, the autophagy-related 7 (ATG7) was identified as a novel target gene of miR-542-5p in H9c2 cells. The current data suggest that miR-542-5p/autophagy pathway might be a potential target for the treatment of H/R-related heart diseases.

Oxidative Stress, Inflammation, and Autophagy: Potential Targets of Mesenchymal Stem Cells-Based Therapies in Ischemic Stroke

Ischemic stroke is a leading cause of death worldwide; currently available treatment approaches for ischemic stroke are to restore blood flow, which reduce disability but are time limited. The interruption of blood flow in ischemic stroke contributes to intricate pathophysiological processes. Oxidative stress and inflammatory activity are two early events in the cascade of cerebral ischemic injury. These two factors are reciprocal causation and directly trigger the development of autophagy. Appropriate autophagy activity contributes to brain recovery by reducing oxidative stress and inflammatory activity, while autophagy dysfunction aggravates cerebral injury. Abundant evidence demonstrates the beneficial impact of mesenchymal stem cells (MSCs) and secretome on cerebral ischemic injury. MSCs reduce oxidative stress through suppressing reactive oxygen species (ROS) and reactive nitrogen species (RNS) generation and transferring healthy mitochondria to damaged cells. Meanwhile, MSCs exert anti-inflammation properties by the production of cytokines and extracellular vesicles, inhibiting proinflammatory cytokines and inflammatory cells activation, suppressing pyroptosis, and alleviating blood–brain barrier leakage. Additionally, MSCs regulation of autophagy imbalances gives rise to neuroprotection against cerebral ischemic injury. Altogether, MSCs have been a promising candidate for the treatment of ischemic stroke due to their pleiotropic effect.

H3K27 demethylase KDM6B aggravates ischemic brain injury through demethylation of IRF4 and Notch2-dependent SOX9 activation

Lysine demethylase 6B (KDM6B) is a histone H3 lysine 27 (H3K27) demethylase that serves as a key mediator of gene transcription. Although KDM6B has been reported to modulate neuroinflammation after ischemic stroke, its role in ischemic brain injury is yet to be well elucidated. Therefore, this study aimed to thoroughly demonstrate the molecular mechanism underlying the effect of KDM6B on neurological function and astrocyte response in post-ischemic brain injury. Middle cerebral artery occlusion/reperfusion (MCAO) mouse models were constructed, while the oxygen-glucose deprivation/reperfusion (OGD/R) model was developed in astrocytes to mimic injury conditions. KDM6B was upregulated post-MCAO in mice and in astrocytes following the induction of OGD/R. Silencing of KDM6B resulted in suppressed neurological deficit, reduced cerebral infarction volume, attenuated neuronal cell apoptosis, and disrupted inflammation. Dual-luciferase reporter gene and chromatin immunoprecipitation-quantitative polymerase chain reaction assays revealed that KDM6B inhibited H3K27 trimethylation in the interferon regulatory factor 4 (IRF4) promoter region, resulting in the upregulation of IRF4 expression, which in turn bound to the Notch2 promoter region to induce its downstream factor SRY-related high-mobility group box 9 (SOX9). SOX9 knockdown reversed the effects of KDM6B overexpression on ischemia-triggered brain damage. Based on these findings, we concluded that KDM6B-mediated demethylation of IRF4 contributes to aggravation of ischemic brain injury through SOX9 activation.

To Breathe or Not to Breathe: The Role of Oxygen in Bone Marrow-Derived Mesenchymal Stromal Cell Senescence

Stem cell-based cellular therapy is a promising tool for the treatment of pathological conditions with underlying severe tissue damage or malfunction like in chronic cardiovascular, musculoskeletal, or inflammatory conditions. One of the biggest technical challenges of the use of natural stem cells, however, is the prevention of their premature senescence during therapeutical manipulations. Culturing stem cells under hypoxic conditions is believed to be a possible route to fulfill this goal. Here, we review current literature data on the effects of hypoxia on bone marrow-derived mesenchymal stromal cells, one of the most popular tools of practical cellular therapy, in the context of their senescence.

Circular RNA Involvement in the Protective Effect of Human Umbilical Cord Mesenchymal Stromal Cell-Derived Extracellular Vesicles Against Hypoxia/Reoxygenation Injury in Cardiac Cells

Human umbilical cord mesenchymal stromal cell-derived extracellular vesicles (HuMSC-EVs) can repair damaged tissues. The expression profile of circular RNAs (circRNAs) provides valuable insights into the regulation of the repair process and the exploration of the repair mechanism. AC16 cardiomyocytes were exposed to hypoxia/reoxygenation (H/R) injury and subsequently cultured with or without HuMSC-EVs (Group T and Group C, respectively). High-throughput RNA sequencing was implemented for the two groups. On the basis of the transcriptome data, gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, and network analyses were carried out to determine the differential gene expression profiles between the two groups. After screening the circRNA database, the results were proved by quantitative real-time polymerase chain reaction. The survival rate of cardiomyocytes exposed to H/R was increased by treatment with HuMSC-EVs. RNA-seq analysis showed that 66 circRNAs were differentially expressed in cardiomyocytes in the co-cultured group. The cellular responses to hypoxia and to decreased oxygen levels were at the top of the GO upregulated list for the two groups, while the vascular endothelial growth factor signaling pathway, long-term potentiation, and the glucagon signaling pathway were at the top of the KEGG pathway upregulated list for the two groups. In the same samples, the 10 most aberrantly upregulated circRNAs were chosen for further verification of their RNA sequences. Seven of the 10 most aberrant circRNAs were significantly upregulated in the co-cultured group and in the HuMSC-EVs. Our results revealed that upregulated circRNAs were abundant during the repair of damaged cardiomyocytes by HuMSC-EVs, which provides a new perspective for the repair of H/R by HuMSC-EVs.

Conditioned medium from adipose-derived stem cells attenuates ischemia/reperfusion-induced cardiac injury through the microRNA-221/222/PUMA/ETS-1 pathway

Rationale: Cardiovascular diseases, such as myocardial infarction (MI), are the leading causes of death worldwide. Reperfusion therapy is the common standard treatment for MI. However, myocardial ischemia/reperfusion (I/R) causes cardiomyocyte injury, including apoptosis and fibrosis. We aimed to investigate the effects of conditioned medium from adipose-derived stem cells (ADSC-CM) on apoptosis and fibrosis in I/R-treated hearts and hypoxia/reoxygenation (H/R)-treated cardiomyocytes and the underlying mechanisms.

Methods: ADSC-CM was collected from ADSCs. The effects of intramuscular injection of ADSC-CM on cardiac function, cardiac apoptosis, and fibrosis examined by echocardiography, Evans blue/TTC staining, TUNEL assay, and Masson's trichrome staining in I/R-treated mice. We also examined the effects of ADSC-CM on apoptosis and fibrosis in H/R-treated H9c2 cells by annexin V/PI flow cytometry, TUNEL assay, and immunocytochemistry.

Results: ADSC-CM treatment significantly reduced heart damage and fibrosis of I/R-treated mice and H/R-treated cardiomyocytes. In addition, the expression of apoptosis-related proteins, such as p53 upregulated modulator of apoptosis (PUMA), p-p53 and B-cell lymphoma 2 (BCL2), as well as the fibrosis-related proteins ETS-1, fibronectin and collagen 3, were significantly reduced by ADSC-CM treatment. Moreover, we demonstrated that ADSC-CM contains a large amount of miR-221/222, which can target and regulate PUMA or ETS-1 protein levels. Furthermore, the knockdown of PUMA and ETS-1 decreased the induction of apoptosis and fibrosis, respectively. MiR-221/222 overexpression achieved similar results. We also observed that cardiac I/R markedly increased apoptosis and fibrosis in miR-221/222 knockout (KO) mice, while ADSC-CM decreased these effects. The increased phosphorylation of p38 and NF‐κB not only mediated myocardial apoptosis through the PUMA/p53/BCL2 pathway but also regulated fibrosis through the ETS-1/fibronectin/collagen 3 pathway.

Conclusions: Overall, our results show that ADSC-CM attenuates cardiac apoptosis and fibrosis by reducing PUMA and ETS-1 expression, respectively. The protective effect is mediated via the miR-221/222/p38/NF-κB pathway.

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

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

The Role of MSC Therapy in Attenuating the Damaging Effects of the Cytokine Storm Induced by COVID-19 on the Heart and Cardiovascular System

The global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) has led to 47 m infected cases and 1. 2 m (2.6%) deaths. A hallmark of more severe cases of SARS-CoV-2 in patients with acute respiratory distress syndrome (ARDS) appears to be a virally-induced over-activation or unregulated response of the immune system, termed a "cytokine storm," featuring elevated levels of pro-inflammatory cytokines such as IL-2, IL-6, IL-7, IL-22, CXCL10, and TNFα. Whilst the lungs are the primary site of infection for SARS-CoV-2, in more severe cases its effects can be detected in multiple organ systems. Indeed, many COVID-19 positive patients develop cardiovascular complications, such as myocardial injury, myocarditis, cardiac arrhythmia, and thromboembolism, which are associated with higher mortality. Drug and cell therapies targeting immunosuppression have been suggested to help combat the cytokine storm. In particular, mesenchymal stromal cells (MSCs), owing to their powerful immunomodulatory ability, have shown promise in early clinical studies to avoid, prevent or attenuate the cytokine storm. In this review, we will discuss the mechanistic underpinnings of the cytokine storm on the cardiovascular system, and how MSCs potentially attenuate the damage caused by the cytokine storm induced by COVID-19. We will also address how MSC transplantation could alleviate the long-term complications seen in some COVID-19 patients, such as improving tissue repair and regeneration.

Systemic Mesenchymal Stem Cell-Derived Exosomes Reduce Myocardial Infarct Size: Characterization With MRI in a Porcine Model

The observations that mesenchymal stem cells (MSCs) exert cardiac protection and repair via their secretome with the active component(s) identified as exosomes underpinned our test of the efficacy of MSC exosomes in a porcine model of myocardial infarction (MI) when administered systemically by the convenient method of intravenous (IV) bolus injection. Results show that 7 days of IV exosomes results in clear reduction (30-40%) of infarct size measured at both 7 and 28 days post-MI, despite near identical release of hs Troponin T. Together with reduced infarct size, exosome treatment reduced transmurality and lessened wall thinning in the infarct zone. Exosome treated pigs showed relative preservation of LV function with significant amelioration of falls in fractional wall thickening compared with control. However, global measures of LV function were less protected by exosome treatment. It is possible that greater preservation of global LV function may have been attenuated by increased cardiac fibrosis, as T1 values showed significant increase in the exosome pigs compared to control particularly in the infarct related segments. Taken together, these results show clear effects of IV exosomes administered over 7 days to reduce infarct size with relatively preserved cardiac function compared to control treated infarct pigs.

Macrophage migration inhibitory factor rejuvenates aged human mesenchymal stem cells and improves myocardial repair

The beneficial functions of mesenchymal stem cells (MSCs) decline with age, limiting their therapeutic efficacy for myocardial infarction (MI). Macrophage migration inhibitory factor (MIF) promotes cell proliferation and survival. We investigated whether MIF overexpression could rejuvenate aged MSCs and increase their therapeutic efficacy in MI. Young and aged MSCs were isolated from the bone marrow of young and aged donors. Young MSCs, aged MSCs, and MIF-overexpressing aged MSCs were transplanted into the peri-infarct region in a rat MI model. Aged MSCs exhibited a lower proliferative capacity, lower MIF level, greater cell size, greater senescence-associated-β-galactosidase activity, and weaker paracrine effects than young MSCs. Knocking down MIF in young MSCs induced cellular senescence, whereas overexpressing MIF in aged MSCs reduced cellular senescence. MIF rejuvenated aged MSCs by activating autophagy, an effect largely reversed by the autophagy inhibitor 3-methyladenine. MIF-overexpressing aged MSCs induced angiogenesis and prevented cardiomyocyte apoptosis to a greater extent than aged MSCs, and had improved heart function and cell survival more effectively than aged MSCs four weeks after MI. Thus, MIF rejuvenated aged MSCs by activating autophagy and enhanced their therapeutic efficacy in MI, suggesting a novel MSC-based therapeutic strategy for cardiovascular diseases in the aged population.

MiR-29a in mesenchymal stem cells inhibits FSTL1 secretion and promotes cardiac myocyte apoptosis in hypoxia-reoxygenation injury

BACKGROUND

Mesenchymal stem cells (MSCs) are under consideration for myocardial ischemia-reperfusion (I/R) injury therapy, but their mechanism remains to be evaluated. In this article, we aimed to study the effects of the miR-29a/follistatin-like 1 axis in bone marrow-derived mesenchymal stem cells on modulating myocyte apoptosis after hypoxia-reoxygenation (H/R) injury.

METHODS

An in vitro myocardial ischemia-reperfusion injury model of H9c2 cells was developed by hypoxia-reoxygenation injury. The mRNA levels of follistatin-like 1, Bcl-2, Bax, and miR-29a and the protein levels of Bcl-2, Bax, cleaved caspase-3, and components of the JAK2/STAT3 pathway were detected by qRT-PCR and western blotting, respectively. Secretion of follistatin-like 1 was evaluated by enzyme-linked immunosorbent assay. Cell apoptosis was evaluated by flow cytometry. The interaction between miR-29a and follistatin-like 1 was evaluated by dual luciferase reporter assay.

RESULTS

MiR-29a suppressed the expression and secretion of follistatin-like 1 in bone marrow-derived mesenchymal stem cells. Overexpression of follistatin-like 1 in bone marrow-derived mesenchymal stem cells decreased apoptosis of myocytes induced by hypoxia-reoxygenation. Cell apoptosis in myocytes was promoted by conditioned medium from bone marrow-derived mesenchymal stem cells with ectopic miR-29a expression. Conditioned medium of miR-29a-overexpressing bone marrow-derived mesenchymal stem cells inhibited the JAK2/STAT3 pathway in myocytes to promote apoptosis of myocytes.

CONCLUSIONS

MiR-29a in bone marrow-derived mesenchymal stem cells inhibits follistatin-like 1 secretion and promotes myocyte apoptosis by suppressing the JAK2/STAT3 pathway in hypoxia-reoxygenation injury.