Notch activation enhances lineage commitment and protective signaling in cardiac progenitor cells

Inhibiting AGTR1 reduces AML burden and protects the heart from cardiotoxicity in mouse models

Clinical treatment of acute myeloid leukemia (AML) largely relies on intensive chemotherapy. However, the application of chemotherapy is often hindered by cardiotoxicity. Patient sequence data revealed that angiotensin II receptor type 1 (AGTR1) is a shared target between AML and cardiovascular disease (CVD). We found that inhibiting AGTR1 sensitized AML to chemotherapy and protected the heart against chemotherapy-induced cardiotoxicity in a human AML cell-transplanted mouse model. These effects were regulated by the AGTR1-Notch1 axis in AML cells and cardiomyocytes from mice. In mouse cardiomyocytes, AGTR1 was hyperactivated by AML and chemotherapy. AML leukemogenesis increased the expression of the angiotensin-converting enzyme and led to increased production of angiotensin II, the ligand of AGTR1, in an MLL-AF9-driven AML mouse model. In this model, the AGTR1-Notch1 axis regulated a variety of genes involved with cell stemness and chemotherapy resistance. AML cell stemness was reduced after Agtr1a deletion in the mouse AML cell transplant model. Mechanistically, Agtr1a deletion decreased γ-secretase formation, which is required for transmembrane Notch1 cleavage and release of the Notch1 intracellular domain into the nucleus. Using multiomics, we identified AGTR1-Notch1 signaling downstream genes and found decreased binding between these gene sequences with Notch1 and chromatin enhancers, as well as increased binding with silencers. These findings describe an AML/CVD association that may be used to improve AML treatment.

The benign nature and rare occurrence of cardiac myxoma as a possible consequence of the limited cardiac proliferative/ regenerative potential: a systematic review

BACKGROUND

Cardiac Myxoma is a primary tumor of heart. Its origins, rarity of the occurrence of primary cardiac tumors and how it may be related to limited cardiac regenerative potential, are not yet entirely known. This study investigates the key cardiac genes/ transcription factors (TFs) and signaling pathways to understand these important questions.

METHODS

Databases including PubMed, MEDLINE, and Google Scholar were searched for published articles without any date restrictions, involving cardiac myxoma, cardiac genes/TFs/signaling pathways and their roles in cardiogenesis, proliferation, differentiation, key interactions and tumorigenesis, with focus on cardiomyocytes.

RESULTS

The cardiac genetic landscape is governed by a very tight control between proliferation and differentiation-related genes/TFs/pathways. Cardiac myxoma originates possibly as a consequence of dysregulations in the gene expression of differentiation regulators including Tbx5, GATA4, HAND1/2, MYOCD, HOPX, BMPs. Such dysregulations switch the expression of cardiomyocytes into progenitor-like state in cardiac myxoma development by dysregulating Isl1, Baf60 complex, Wnt, FGF, Notch, Mef2c and others. The Nkx2-5 and MSX2 contribute predominantly to both proliferation and differentiation of Cardiac Progenitor Cells (CPCs), may possibly serve roles based on the microenvironment and the direction of cell circuitry in cardiac tumorigenesis. The Nkx2-5 in cardiac myxoma may serve to limit progression of tumorigenesis as it has massive control over the proliferation of CPCs. The cardiac cell type-specific genetic programming plays governing role in controlling the tumorigenesis and regenerative potential.

CONCLUSION

The cardiomyocytes have very limited proliferative and regenerative potential. They survive for long periods of time and tightly maintain the gene expression of differentiation genes such as Tbx5, GATA4 that interact with tumor suppressors (TS) and exert TS like effect. The total effect such gene expression exerts is responsible for the rare occurrence and benign nature of primary cardiac tumors. This prevents the progression of tumorigenesis. But this also limits the regenerative and proliferative potential of cardiomyocytes. Cardiac Myxoma develops as a consequence of dysregulations in these key genes which revert the cells towards progenitor-like state, hallmark of CM. The CM development in carney complex also signifies the role of TS in cardiac cells.

The Vascular Niche for Adult Cardiac Progenitor Cells

Research on cardiac progenitor cell populations has generated expectations about their potential for cardiac regeneration capacity after acute myocardial infarction and during physiological aging; however, the endogenous capacity of the adult mammalian heart is limited. The modest efficacy of exogenous cell-based treatments can guide the development of new approaches that, alone or in combination, can be applied to boost clinical efficacy. The identification and manipulation of the adult stem cell environment, termed niche, will be critical for providing new evidence on adult stem cell populations and improving stem-cell-based therapies. Here, we review and discuss the state of our understanding of the interaction of adult cardiac progenitor cells with other cardiac cell populations, with a focus on the description of the B-CPC progenitor population (Bmi1+ cardiac progenitor cell), which is a strong candidate progenitor for all main cardiac cell lineages, both in the steady state and after cardiac damage. The set of all interactions should be able to define the vascular cardiac stem cell niche, which is associated with low oxidative stress domains in vasculature, and whose manipulation would offer new hope in the cardiac regeneration field.

Signaling pathways and targeted therapy for myocardial infarction

Although the treatment of myocardial infarction (MI) has improved considerably, it is still a worldwide disease with high morbidity and high mortality. Whilst there is still a long way to go for discovering ideal treatments, therapeutic strategies committed to cardioprotection and cardiac repair following cardiac ischemia are emerging. Evidence of pathological characteristics in MI illustrates cell signaling pathways that participate in the survival, proliferation, apoptosis, autophagy of cardiomyocytes, endothelial cells, fibroblasts, monocytes, and stem cells. These signaling pathways include the key players in inflammation response, e.g., NLRP3/caspase-1 and TLR4/MyD88/NF-κB; the crucial mediators in oxidative stress and apoptosis, for instance, Notch, Hippo/YAP, RhoA/ROCK, Nrf2/HO-1, and Sonic hedgehog; the controller of myocardial fibrosis such as TGF-β/SMADs and Wnt/β-catenin; and the main regulator of angiogenesis, PI3K/Akt, MAPK, JAK/STAT, Sonic hedgehog, etc. Since signaling pathways play an important role in administering the process of MI, aiming at targeting these aberrant signaling pathways and improving the pathological manifestations in MI is indispensable and promising. Hence, drug therapy, gene therapy, protein therapy, cell therapy, and exosome therapy have been emerging and are known as novel therapies. In this review, we summarize the therapeutic strategies for MI by regulating these associated pathways, which contribute to inhibiting cardiomyocytes death, attenuating inflammation, enhancing angiogenesis, etc. so as to repair and re-functionalize damaged hearts.

E2A ablation enhances proportion of nodal-like cardiomyocytes in cardiac-specific differentiation of human embryonic stem cells

BACKGROUND

Human sinoatrial cardiomyocytes are essential building blocks for cell therapies of conduction system disorders. However, current differentiation protocols for deriving nodal cardiomyocytes from human pluripotent stem cells (hPSCs) are very inefficient.

METHODS

By employing the hPSCs to cardiomyocyte (CM) in vitro differentiation system and generating E2A-knockout hESCs using CRISPR/Cas9 gene editing technology, we analyze the functions of E2A in CM differentiation.

FINDINGS

We found that knockout of the transcription factor E2A substantially increased the proportion of nodal-like cells in hESC-derived CMs. The E2A ablated CMs displayed smaller cell size, increased beating rates, weaker contractile force, and other functional characteristics similar to sinoatrial node (SAN) cells. Transcriptomic analyses indicated that ion channel-encoding genes were up-regulated in E2A ablated CMs. E2A directly bounded to the promoters of genes key to SAN development via conserved E-box motif, and promoted their expression. Unexpect enhanced activity of NOTCH pathway after E2A ablation could also facilate to induct ventricle workingtype CMs reprogramming into SAN-like cells.

INTERPRETATION

Our study revealed a new role for E2A during directed cardiac differentiation of hESCs and may provide new clues for enhancing induction efficiency of SAN-like cardiomyocytes from hPSCs in the future.

FUNDING

This work was supported by the NSFC (No.82070391, N.S.; No.81870175 and 81922006, P.L.), the National Key R&D Program of China (2018YFC2000202, N.S.; 2017YFA0103700, P.L.), the Haiju program of National Children's Medical Center EK1125180102, and Innovative research team of high-level local universities in Shanghai and a key laboratory program of the Education Commission of Shanghai Municipality (ZDSYS14005).

Adding a "Notch" to Cardiovascular Disease Therapeutics: A MicroRNA-Based Approach

Dysregulation of the Notch pathway is implicated in the pathophysiology of cardiovascular diseases (CVDs), but, as of today, therapies based on the re-establishing the physiological levels of Notch in the heart and vessels are not available. A possible reason is the context-dependent role of Notch in the cardiovascular system, which would require a finely tuned, cell-specific approach. MicroRNAs (miRNAs) are short functional endogenous, non-coding RNA sequences able to regulate gene expression at post-transcriptional levels influencing most, if not all, biological processes. Dysregulation of miRNAs expression is implicated in the molecular mechanisms underlying many CVDs. Notch is regulated and regulates a large number of miRNAs expressed in the cardiovascular system and, thus, targeting these miRNAs could represent an avenue to be explored to target Notch for CVDs. In this Review, we provide an overview of both established and potential, based on evidence in other pathologies, crosstalks between miRNAs and Notch in cellular processes underlying atherosclerosis, myocardial ischemia, heart failure, calcification of aortic valve, and arrhythmias. We also discuss the potential advantages, as well as the challenges, of using miRNAs for a Notch-based approach for the diagnosis and treatment of the most common CVDs.

Adult stem cell niches for tissue homeostasis

Adult stem cells are fundamental to maintain tissue homeostasis, growth, and regeneration. They reside in specialized environments called niches. Following activating signals, they proliferate and differentiate into functional cells that are able to preserve tissue physiology, either to guarantee normal turnover or to counteract tissue damage caused by injury or disease. Multiple interactions occur within the niche between stem cell‐intrinsic factors, supporting cells, the extracellular matrix, and signaling pathways. Altogether, these interactions govern cell fate, preserving the stem cell pool, and regulating stem cell proliferation and differentiation. Based on their response to body needs, tissues can be largely classified into three main categories: tissues that even in normal conditions are characterized by an impressive turnover to replace rapidly exhausting cells (blood, epidermis, or intestinal epithelium); tissues that normally require only a basal cell replacement, though able to efficiently respond to increased tissue needs, injury, or disease (skeletal muscle); tissues that are equipped with less powerful stem cell niches, whose repairing ability is not able to overcome severe damage (heart or nervous tissue). The purpose of this review is to describe the main characteristics of stem cell niches in these different tissues, highlighting the various components influencing stem cell activity. Although much has been done, more work is needed to further increase our knowledge of niche interactions. This would be important not only to shed light on this fundamental chapter of human physiology but also to help the development of cell‐based strategies for clinical therapeutic applications, especially when other approaches fail.

Autophagy Promoted Neural Differentiation of Human Placenta-derived Mesenchymal Stem Cells

BACKGROUND/AIM

Human placenta-derived mesenchymal stem cells (hPMSCs) are multipotent and possess neurogenicity. Numerous studies have shown that Notch inhibition and DNA demethylation promote neural differentiation. Here, we investigated the modulation of autophagy during neural differentiation of hPMSCs, induced by DAPT and 5-Azacytidine.

MATERIALS AND METHODS

hPMSCs were treated with DAPT to induce neural differentiation, and the autophagy regulating molecules were used to assess the impact of autophagy on neural differentiation.

RESULTS

The hPMSCs presented with typical mesenchymal stem cell phenotypes, in which the majority of cells expressed CD73, CD90 and CD105. hPMSCs were multipotent, capable of differentiating into mesodermal cells. After treatment with DAPT, hPMSCs upregulated the expression of neuronal genes including SOX2, Nestin, and βIII-tubulin, and the autophagy genes LC3I/II and Beclin. These genes were further increased when 5-Azacytidine was co-supplemented in the culture medium. The inhibition of autophagy by chloroquine impeded the neural differentiation of hPMSCs, marked by the downregulation of βIII-tubulin, while the activation of autophagy by valproic acid (VPA) instigated the emergence of βIII-tubulin-positive cells.

CONCLUSION

During the differentiation process, autophagy was modulated, implying that autophagy could play a significant role during the differentiation of these cells. The blockage and stimulation of autophagy could either hinder or induce the formation of neural-like cells, respectively. Therefore, the refinement of autophagic activity at an appropriate level might improve the efficiency of stem cell differentiation.

Effects of Cardiotoxins on Cardiac Stem and Progenitor Cell Populations

As research and understanding of the cardiotoxic side-effects of anticancer therapy expands further and the affected patient population grows, notably the long-term survivors of childhood cancers, it is important to consider the full range of myocardial cell types affected. While the direct impacts of these toxins on cardiac myocytes constitute the most immediate damage, over the longer term, the myocardial ability to repair, or adapt to this damage becomes an ever greater component of the disease phenotype. One aspect is the potential for endogenous myocardial repair and renewal and how this may be limited by cardiotoxins depleting the cells that contribute to these processes. Clear evidence exists of new cardiomyocyte formation in adult human myocardium, along with the identification in the myocardium of endogenous stem/progenitor cell populations with pro-regenerative properties. Any effects of cardiotoxins on either of these processes will worsen long-term prognosis. While the role of cardiac stem/progenitor cells in cardiomyocyte renewal appears at best limited (although with stronger evidence of this process in response to diffuse cardiomyocyte loss), there are strong indications of a pro-regenerative function through the support of injured cell survival. A number of recent studies have identified detrimental impacts of anticancer therapies on cardiac stem/progenitor cells, with negative effects seen from both long-established chemotherapy agents such as, doxorubicin and from newer, less overtly cardiotoxic agents such as tyrosine kinase inhibitors. Damaging impacts are seen both directly, on cell numbers and viability, but also on these cells' ability to maintain the myocardium through generation of pro-survival secretome and differentiated cells. We here present a review of the identified impacts of cardiotoxins on cardiac stem and progenitor cells, considered in the context of the likely role played by these cells in the maintenance of myocardial tissue homeostasis.

Cardiovascular Complications Associated with COVID-19 and Potential Therapeutic~Strategies

The outbreak of coronavirus disease 2019 (COVID-19), an infectious disease with severe acute respiratory syndrome, has now become a worldwide pandemic. Despite the respiratory complication, COVID-19 is also associated with significant multiple organ dysfunction, including severe cardiac impairment. Emerging evidence reveals a direct interplay between COVID-19 and dire cardiovascular complications, including myocardial injury, heart failure, heart attack, myocarditis, arrhythmias as well as blood clots, which are accompanied with elevated risk and adverse outcome among infected patients, even sudden death. The proposed pathophysiological mechanisms of myocardial impairment include invasion of SARS-CoV-2 virus via angiotensin-converting enzyme 2 to cardiovascular cells/tissue, which leads to endothelial inflammation and dysfunction, de-stabilization of vulnerable atherosclerotic plaques, stent thrombosis, cardiac stress due to diminish oxygen supply and cardiac muscle damage, and myocardial infarction. Several promising therapeutics are under investigation to the overall prognosis of COVID-19 patients with high risk of cardiovascular impairment, nevertheless to date, none have shown proven clinical efficacy. In this comprehensive review, we aimed to highlight the current integrated therapeutic approaches for COVID-19 and we summarized the potential therapeutic options, currently under clinical trials, with their mechanisms of action and associated adverse cardiac events in highly infectious COVID-19 patients.

Macrophage-derived MMP-8 determines smooth muscle cell differentiation from adventitia stem/progenitor cells and promotes neointima hyperplasia

AIMS

Emerging evidence has suggested that adventitia stem/progenitor cells (AdSPCs) migrate into the intima of arteries in response to injury, where they differentiate towards smooth muscle cells (SMCs) and participate in neointimal hyperplasia. We have previously identified matrix metalloproteinase-8 (MMP8) as a key player in atherogenesis. In this study, we aimed to investigate the functional roles of macrophage-derived MMP8 in AdSPC differentiation and injury-induced arterial remodelling.

METHODS AND RESULTS

We first observed an important role for MMP8 in SMC differentiation from embryonic stem cells, but this effect was not seen in AdSPCs. Instead, through macrophages/AdSPCs co-culture and macrophage conditional culture medium studies, we have demonstrated that the MMP8 protein secreted from macrophages promotes SMC differentiation from AdSPCs. Mechanistically, we showed that macrophage-derived MMP8 promotes SMC differentiation from AdSPCs through modulating transforming growth factor-β activity and a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10)/Notch1 signalling. We further demonstrated that the binding site for CBF1, Suppressor of Hairless, and Lag-1 (CSL) within SMC gene promoters is responsible for Notch1 mediated SMC differentiation. Finally, we demonstrated that macrophage-derived MMP8 increased injury-induced neointimal SMC hyperplasia by activating ADAM10/Notch1 signalling.

CONCLUSIONS

We have identified macrophage-derived MMP8 as a regulator in SMC differentiation from AdSPCs and neointimal SMC hyperplasia in response to injury. Our data provide new insights into the roles of MMP8 in AdSPC differentiation and the pathogenesis of neointima formation in the context of angiographic restenosis, and therefore may aid in the development of novel therapeutic agents for the prevention of this disease.

Enhancing myocardial repair with CardioClusters

Cellular therapy to treat heart failure is an ongoing focus of intense research, but progress toward structural and functional recovery remains modest. Engineered augmentation of established cellular effectors overcomes impediments to enhance reparative activity. Such 'next generation' implementation includes delivery of combinatorial cell populations exerting synergistic effects. Concurrent isolation and expansion of three distinct cardiac-derived interstitial cell types from human heart tissue, previously reported by our group, prompted design of a 3D structure that maximizes cellular interaction, allows for defined cell ratios, controls size, enables injectability, and minimizes cell loss. Herein, mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs) and c-Kit⁺ cardiac interstitial cells (cCICs) when cultured together spontaneously form scaffold-free 3D microenvironments termed CardioClusters. scRNA-Seq profiling reveals CardioCluster expression of stem cell-relevant factors, adhesion/extracellular-matrix molecules, and cytokines, while maintaining a more native transcriptome similar to endogenous cardiac cells. CardioCluster intramyocardial delivery improves cell retention and capillary density with preservation of cardiomyocyte size and long-term cardiac function in a murine infarction model followed 20 weeks. CardioCluster utilization in this preclinical setting establish fundamental insights, laying the framework for optimization in cell-based therapeutics intended to mitigate cardiomyopathic damage.

Dysregulation of Notch signaling in cardiac mesenchymal cells of patients with tetralogy of Fallot

BACKGROUND

Tetralogy of Fallot (TF) is a severe congenital defect of heart development. Fine-tuned sequential activation of Notch signaling genes is responsible for proper heart chamber development. Mutations in Notch genes have been associated with TF. The aim of this study was to analyze the activity of the Notch pathway in cardiac mesenchymal cells derived from ventricular tissue of TF patients.

METHODS

Cardiac mesenchymal cells were isolated from 42 TF patients and from 14 patients with ventricular septal defects (VSDs), used as a comparison group. The Notch pathway was analyzed by estimating the expression of Notch-related genes by qPCR. Differentiation and proliferation capacity of the cells was estimated.

RESULTS

The TF-derived cells demonstrated a dysregulated pattern of Notch-related gene expression comparing to VSD-derived cells. Correlation of Notch signaling activation level by HEY1/HES1 expression level with proliferation and cardiogenic-like differentiation of cardiac mesenchymal cells was observed but not with clinical parameters nor with the age of the patients.

CONCLUSIONS

The data suggest a contribution of dysregulated Notch signaling to the pathogenesis of tetralogy of Fallot and importance of Notch signaling level for the functional state of cardiac mesenchymal cells, which could be critical considering these cells for potential cell therapy approaches.

COVID-19 in the heart and the lungs: could we "Notch" the inflammatory storm?

From January 2020, coronavirus disease (COVID-19) originated in China has spread around the world. The disease is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The presence of myocarditis, cardiac arrest, and acute heart failure in COVID-19 patients suggests the existence of a relationship between SARS-CoV-2 infection and cardiac disease. The Notch signalling is a major regulator of cardiovascular function and it is also implicated in several biological processes mediating viral infections. In this report we discuss the possibility to target Notch signalling to prevent SARS-CoV-2 infection and interfere with the progression of COVID-19- associated heart and lungs disease.

Paeonol Reverses Adriamycin Induced Cardiac Pathological Remodeling through Notch1 Signaling Reactivation in H9c2 Cells and Adult Zebrafish Heart

Adriamycin is a commonly prescribed chemotherapeutic drug for a wide range of cancers. Adriamycin causes cardiotoxicity as an adverse effect that limits its clinical application in cancer treatment. Several mechanisms have been proposed to explain the toxicity it causes in heart cells. Disruption of inherent cardiac repair mechanism is the least understood mechanism of Adriamycin-induced cardiotoxicity. Adriamycin induces pathological remodeling in cardiac cells by promoting apoptosis, hypertrophy, and fibrosis. We found that Adriamycin inhibited Notch1 in a time- and dose-dependent manner in H9c2 cells. We used Paeonol, a Notch1 activator, and analyzed the markers of apoptosis, hypertrophy, and fibrosis in H9c2 cells in vitro and in adult zebrafish heart in vivo as model systems to study Adriamycin-induced cardiotoxicity. Paeonol activated Notch1 signaling and expression of its downstream target genes effectively in the Adriamycin-treated condition in vitro and in vivo. Also we detected that Notch activation using Paeonol protected the cells from apoptosis, collagen deposition, and hypertrophy response using functional assays. We conclude that Adriamycin induced cardiotoxicity by promoting the pathological cardiac remodeling through inhibition of Notch1 signaling and that the Notch1 reactivation by Paeonol protected the cells and reversed the cardiotoxicity.

Predicting Functional Responses of Progenitor Cell Exosome Potential with Computational Modeling

Congenital heart disease can lead to severe right ventricular heart failure (RVHF). We have shown that aggregated c‐kit⁺ progenitor cells (CPCs) can improve RVHF repair, likely due to exosome‐mediated effects. Here, we demonstrate that miRNA content from monolayer (2D) and aggregated (3D) CPC exosomes can be related to in vitro angiogenesis and antifibrosis responses using partial least squares regression (PLSR). PLSR reduced the dimensionality of the data set to the top 40 miRNAs with the highest weighted coefficients for the in vitro biological responses. Target pathway analysis of these top 40 miRNAs demonstrated significant fit to cardiac angiogenesis and fibrosis pathways. Although the model was trained on in vitro data, we demonstrate that the model can predict angiogenesis and fibrosis responses to exosome treatment in vivo with a strong correlation with published in vivo responses. These studies demonstrate that PLSR modeling of exosome miRNA content has the potential to inform preclinical trials and predict new promising CPC therapies. stem cells translational medicine2019;8:1212–1221

Aggregation of Child Cardiac Progenitor Cells Into Spheres Activates Notch Signaling and Improves Treatment of Right Ventricular Heart Failure

RATIONALE

Congenital heart disease can lead to life-threatening right ventricular (RV) heart failure. Results from clinical trials support expanding cardiac progenitor cell (CPC) based therapies. However, our recent data show that CPCs lose function as they age, starting as early as 1 year.

OBJECTIVE

To determine whether the aggregation of child (1-5-year-old) CPCs into scaffold-free spheres can improve differentiation by enhancing Notch signaling, a known regulator of CPC fate. We hypothesized that aggregated (3-dimensional [3D]) CPCs will repair RV heart failure better than monolayer (2-dimensional [2D]) CPCs.

METHODS AND RESULTS

Spheres were produced with 1500 CPCs each using a microwell array. CPC aggregation significantly increased gene expression of Notch1 compared with 2D CPCs, accompanied by significant upregulation of cardiogenic transcription factors (GATA4, HAND1, MEF2C, NKX2.5, and TBX5) and endothelial markers (CD31, FLK1, FLT1, VWF). Blocking Notch receptor activation with the γ-secretase inhibitor DAPT (N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester) diminished these effects. To evaluate the therapeutic improvements of CPC aggregation, RV heart failure was induced in athymic rats by pulmonary artery banding, and cells were implanted into the RV free wall. Echocardiographic measurements 28 days postimplantation showed significantly improved RV function with 3D compared with 2D CPCs. Tracking implanted CPCs via DiR (1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbocyanine iodide)-labeling showed improved retention of 3D CPCs. Transducing 3D CPCs with Notch1-shRNA (short hairpin RNA) did not reduce retention, but significantly reduced RV functional improvements. Histological analyses showed 3D treatment reduced RV fibrosis and increased angiogenesis. Although 3D CPCs formed CD31⁺ vessel-like cells in vivo, these effects are more likely because of improved 3D CPC exosome function compared with 2D CPC exosomes.

CONCLUSIONS

Spherical aggregation improves child CPC function in a Notch-dependent manner. The strong reparative ability of CPC spheres warrants further investigation as a treatment for pediatric heart failure, especially in older children where reparative ability may be reduced.

Notch signal pathway - therapeutic target for regulation of reparative processes in the heart

Notch signaling pathway is a universal regulator of cell fate in embryogenesis and in maintaining the cell homeostasis of adult tissue. Through local cell-cell interactions, he controls neighboring cells behavior and determines their capacity for self-renewal, growth, survival, differentiation, and apoptosis. Recent studies have shown that the control of regenerative processes in the heart is also carried out with the participation of Notch system. At the heart of Notch regulates migration bone marrow progenitors and stimulates the proliferation of cardiomyocytes, cardiac progenitor cell activity, limits cardiomyocyte hypertrophy and fibrosis progression and stimulates angiogenesis. Notch signaling pathway may be regarded as a very promising target for the development of drugs for the stimulation of regeneration in the myocardium.

Hypoxia-stressed cardiomyocytes promote early cardiac differentiation of cardiac stem cells through HIF-1α/Jagged1/Notch1 signaling

Hypoxia is beneficial for the differentiation of stem cells transplanted for myocardial injury, but mechanisms underlying this benefit remain unsolved. Here, we report the impact of hypoxia-induced Jagged1 expression in cardiomyocytes (CMs) for driving the differentiation of cardiac stem cells (CSCs). Forced hypoxia-inducible factor 1α (HIF-1α) expression and physical hypoxia (5% O₂) treatment could induce Jagged1 expression in neonatal rat CMs. Pharmacological inhibition of HIF-1α by YC-1 attenuated hypoxia-promoted Jagged1 expression in CMs. An ERK inhibitor (PD98059), but not inhibitors of JNK (SP600125), Notch (DAPT), NF-κB (PTDC), JAK (AG490), or STAT3 (Stattic) suppressed hypoxia-induced Jagged1 protein expression in CMs. c-Kit⁺ CSCs isolated from neonatal rat hearts using a magnetic-activated cell sorting method expressed GATA4, SM22α or vWF, but not Nkx2.5 and cTnI. Moreover, 87.3% of freshly isolated CSCs displayed Notch1 receptor expression. Direct co-culture of CMs with BrdU-labeled CSCs enhanced CSCs differentiation, as evidenced by an increased number of BrdU⁺/Nkx2.5⁺ cells, while intermittent hypoxia for 21 days promoted co-culture-triggered differentiation of CSCs into CM-like cells. Notably, YC-1 and DAPT attenuated hypoxia-induced differentiation. Our results suggest that hypoxia induces Jagged1 expression in CMs primarily through ERK signaling, and facilitates early cardiac lineage differentiation of CSCs in CM/CSC co-cultures via HIF-1α/Jagged1/Notch signaling.

Mesenchymal stem cells attenuate doxorubicin‑induced cellular senescence through the VEGF/Notch/TGF‑β signaling pathway in H9c2 cardiomyocytes

The clinical use of doxorubicin (Dox) is limited by its cardiotoxicity. The fundamental changes it induces include interstitial myocardial fibrosis and the appearance of senescent cardiomyocytes. Mesenchymal stem cell (MSC)‑based therapies have also been reported to modulate cellular senescence, and have been used effectively to treat age‑related cardiovascular diseases. In the present study, the Transwell system was used to coculture H9c2 cells with MSCs, and their proliferation and viability were assessed. The expression of senescence‑related genes p53 and p16, and telomere length were measured using reverse transcription‑quantitative polymerase chain reaction analysis, and the Jagged‑1/Notch‑1 signaling pathway was detected using western blot analysis. The results revealed that Dox induced the senescence of H9c2 cells, characterized by a low proliferation rate, poor viability, reduced telomere length and impaired telomerase activity, and by marked increases in the expression of p53 and p16. By contrast, when cocultured with MSCs in the presence of Dox, H9c2 cell proliferation and viability increased, whereas the expression levels of p53 and p16 decreased, and telomere length and telomerase activity increased. The mechanism underlying the antisenescence function of MSCs was clarified, which involved the vascular endothelial growth factor (VEGF)/Jagged‑1/Notch‑1/transforming growth factor‑β1 (TGF‑β1) signaling pathway. It was confirmed that inhibiting VEGF, or silencing Jagged‑1 or Notch‑1 with small interfering RNA, or using recombinant TGF‑β1 eliminated the antisenescence effects of MSCs on the Dox‑treated H9c2 cells. The results revealed that MSCs rescued H9c2 cells from Dox‑induced senescence through the release of VEGF, which activated the Jagged‑1/Notch‑1 signaling pathway, leading to the inhibition of TGF‑β1 release. Therefore, treatment with MSCs may have important therapeutic implications on the attenuation of cardiotoxicity in patients with cancer treated with Dox.

Beyond cardiomyocyte loss: Role of Notch in cardiac aging

The knowledge of the cellular events occurring in the aging heart has dramatically expanded in the last decade and is expected to further grow in years to come. It is now clear that impaired function and loss of cardiomyocytes are major features of cardiac aging, but other events are likewise important. In particular, accumulating experimental evidence highlights the importance of fibroblast and cardiac progenitor cell (CPC) dysfunction. The Notch pathway regulates cardiomyocyte, fibroblast, and CPC activity and, thus, may be critically involved in heart disease associated with advanced age, especially heart failure. In a translational perspective, thorough investigation of the Notch system in the aging myocardium may lead to the identification of molecular targets for novel therapies for age-related cardiac disease.

Combining cell and gene therapy to advance cardiac regeneration

INTRODUCTION

The characterization of multipotent endogenous cardiac stem cells (eCSCs) and the breakthroughs of somatic cell reprogramming to boost cardiomyocyte replacement have fostered the prospect of achieving functional heart repair/regeneration.

AREAS COVERED

Allogeneic CSC therapy through its paracrine stimulation of the endogenous resident reparative/regenerative process produces functional meaningful myocardial regeneration in pre-clinical porcine myocardial infarction models and is currently tested in the first-in-man human trial. The in vivo test of somatic reprogramming and cardioregenerative non-coding RNAs revived the interest in gene therapy for myocardial regeneration. The latter, together with the advent of genome editing, has prompted most recent efforts to produce genetically-modified allogeneic CSCs that secrete cardioregenerative factors to optimize effective myocardial repair.

EXPERT OPINION

The current war against heart failure epidemics in western countries seeks to find effective treatments to set back the failing hearts prolonging human lifespan. Off-the-shelf allogeneic-genetically-modified CSCs producing regenerative agents are a novel and evolving therapy set to be affordable, safe, effective and available at all times for myocardial regeneration to either prevent or treat heart failure.

Single-cell analysis of the fate of c-kit-positive bone marrow cells

The plasticity of c-kit-positive bone marrow cells (c-kit-BMCs) in tissues different from their organ of origin remains unclear. We tested the hypothesis that c-kit-BMCs are functionally heterogeneous and only a subgroup of these cells possesses cardiomyogenic potential. Population-based assays fall short of identifying the properties of individual stem cells, imposing on us the introduction of single cell-based approaches to track the fate of c-kit-BMCs in the injured heart; they included viral gene-tagging, multicolor clonal-marking and transcriptional profiling. Based on these strategies, we report that single mouse c-kit-BMCs expand clonally within the infarcted myocardium and differentiate into specialized cardiac cells. Newly-formed cardiomyocytes, endothelial cells, fibroblasts and c-kit-BMCs showed in their genome common sites of viral integration, providing strong evidence in favor of the plasticity of a subset of BMCs expressing the c-kit receptor. Similarly, individual c-kit-BMCs, which were infected with multicolor reporters and injected in infarcted hearts, formed cardiomyocytes and vascular cells organized in clusters of similarly colored cells. The uniform distribution of fluorescent proteins in groups of specialized cells documented the polyclonal nature of myocardial regeneration. The transcriptional profile of myogenic c-kit-BMCs and whole c-kit-BMCs was defined by RNA sequencing. Genes relevant for engraftment, survival, migration, and differentiation were enriched in myogenic c-kit-BMCs, a cell subtype which could not be assigned to a specific hematopoietic lineage. Collectively, our findings demonstrate that the bone marrow comprises a category of cardiomyogenic, vasculogenic and/or fibrogenic c-kit-positive cells and a category of c-kit-positive cells that retains an undifferentiated state within the damaged heart.

Notch signaling modulates the electrical behavior of cardiomyocytes

Notch receptor signaling is active during cardiac development and silenced in myocytes after birth. Conversely, outward K⁺ Kv currents progressively appear in postnatal myocytes leading to shortening of the action potential (AP) and acquisition of the mature electrical phenotype. In the present study, we tested the possibility that Notch signaling modulates the electrical behavior of cardiomyocytes by interfering with Kv currents. For this purpose, the effects of Notch receptor activity on electrophysiological properties of myocytes were evaluated using transgenic mice with inducible expression of the Notch1 intracellular domain (NICD), the functional fragment of the activated Notch receptor, and in neonatal myocytes after inhibition of the Notch transduction pathway. By patch clamp, NICD-overexpressing cells presented prolonged AP duration and reduced upstroke amplitude, properties that were coupled with reduced rapidly activating Kv and fast Na⁺ currents, compared with cells obtained from wild-type mice. In cultured neonatal myocytes, inhibition of the proteolitic release of NICD with a γ-secretase antagonist increased transcript levels of the Kv channel-interacting proteins 2 (KChIP2) and enhanced the density of Kv currents. Collectively, these results indicate that Notch signaling represents an important regulator of the electrophysiological behavior of developing and adult myocytes by repressing, at least in part, repolarizing Kv currents. NEW & NOTEWORTHY We investigated the effects of Notch receptor signaling on the electrical properties of cardiomyocytes. Our results indicate that the Notch transduction pathway interferes with outward K⁺ Kv currents, critical determinants of the electrical repolarization of myocytes.

Cardiac Progenitor Cells and the Interplay with Their Microenvironment

The microenvironment plays a crucial role in the behavior of stem and progenitor cells. In the heart, cardiac progenitor cells (CPCs) reside in specific niches, characterized by key components that are altered in response to a myocardial infarction. To date, there is a lack of knowledge on these niches and on the CPC interplay with the niche components. Insight into these complex interactions and into the influence of microenvironmental factors on CPCs can be used to promote the regenerative potential of these cells. In this review, we discuss cardiac resident progenitor cells and their regenerative potential and provide an overview of the interactions of CPCs with the key elements of their niche. We focus on the interaction between CPCs and supporting cells, extracellular matrix, mechanical stimuli, and soluble factors. Finally, we describe novel approaches to modulate the CPC niche that can represent the next step in recreating an optimal CPC microenvironment and thereby improve their regeneration capacity.

Phospholipase Cγ1 Mediates Intima Formation Through Akt-Notch1 Signaling Independent of the Phospholipase Activity

Background

Vascular smooth muscle cell proliferation, migration, and dedifferentiation are critical for vascular diseases. Recently, it was demonstrated that Notch receptors have opposing effects on intima formation after vessel injury. Therefore, it is important to investigate the specific regulatory pathways that activate the different Notch receptors.

Methods and Results

There was a time‐ and dose‐dependent activation of Notch1 by angiotensin II and platelet‐derived growth factor in vascular smooth muscle cells. When phospholipase Cγ1 (PLCγ1) expression was reduced by small interfering RNA, Notch1 activation and Hey2 expression (Notch target gene) induced by angiotensin II or platelet‐derived growth factor were remarkably inhibited, while Notch2 degradation was not affected. Mechanistically, we observed an association of PLCγ1 and Akt, which increased after angiotensin II or platelet‐derived growth factor stimulation. PLCγ1 knockdown significantly inhibited Akt activation. Importantly, PLCγ1 phospholipase site mutation (no phospholipase activity) did not affect Akt activation. Furthermore, PLCγ1 depletion inhibited platelet‐derived growth factor–induced vascular smooth muscle cell proliferation, migration, and dedifferentiation, while it increased apoptosis. In vivo, PLCγ1 and control small interfering RNA were delivered periadventitially in pluronic gel and complete carotid artery ligation was performed. Morphometric analysis 21 days after ligation demonstrated that PLCγ1 small interfering RNA robustly attenuated intima area and intima/media ratio compared with the control group.

Conclusions

PLCγ1‐Akt–mediated Notch1 signaling is crucial for intima formation. This effect is attributable to PLCγ1‐Akt interaction but not PLCγ1 phospholipase activity. Specific inhibition of the PLCγ1 and Akt interaction will be a promising therapeutic strategy for preventing vascular remodeling.

Eat, breathe, ROS: controlling stem cell fate through metabolism

INTRODUCTION

Research reveals cardiac regeneration exists at levels previously deemed unattainable. Clinical trials using stem cells demonstrate promising cardiomyogenic and regenerative potential but insufficient contractile recovery. Incomplete understanding of the biology of administered cells likely contributes to inconsistent patient outcomes. Metabolism is a core component of many well-characterized stem cell types, and metabolic changes fundamentally alter stem cell fate from self-renewal to lineage commitment, and vice versa. However, the metabolism of stem cells currently studied for cardiac regeneration remains incompletely understood. Areas covered: Key metabolic features of stem cells are reviewed and unique stem cell metabolic characteristics are discussed. Metabolic changes altering stem cell fate are considered from quiescence and self-renewal to lineage commitment. Key metabolic concepts are applied toward examining cardiac regeneration through stem cell-based approaches, and clinical implications of current cell therapies are evaluated to identify potential areas of improvement. Expert commentary: The metabolism and biology of stem cells used for cardiac therapy remain poorly characterized. A growing appreciation for the fundamental relationship between stem cell functionality and metabolic phenotype is developing. Future studies unraveling links between cardiac stem cell metabolism and regenerative potential may considerably improve treatment strategies and therapeutic outcomes.

Targeted myocardial delivery of GDF11 gene rejuvenates the aged mouse heart and enhances myocardial regeneration after ischemia-reperfusion injury

Ischemic cardiac injury is the main contributor to heart failure, and the regenerative capacity of intrinsic stem cells plays an important role in tissue repair after injury. However, stem cells in aged individuals have reduced regenerative potential and aged tissues lack the capacity to renew. Growth differentiation factor 11 (GDF11), from the activin-transforming growth factor β superfamily, has been shown to promote stem cell activity and rejuvenation. We carried out non-invasive targeted delivery of the GDF11 gene to the heart using ultrasound-targeted microbubble destruction (UTMD) and cationic microbubble (CMB) to investigate the ability of GDF11 to rejuvenate the aged heart and improve tissue regeneration after injury. Young (3 months) and old (21 months) mice were used to evaluate the expression of GDF11 mRNA in the myocardium at baseline and after ischemia/reperfusion (I/R) and myocardial infarction. GDF11 expression decreased with age and following myocardial injury. UTMD-mediated delivery of the GDF11 plasmid to the aged heart after I/R injury effectively and selectively increased GDF11 expression in the heart, and improved cardiac function and reduced infarct size. Over-expression of GDF11 decreased senescence markers, p16 and p53, as well as the number of p16⁺ cells in old mouse hearts. Furthermore, increased proliferation of cardiac stem cell antigen 1 (Sca-1⁺) cells and increased homing of endothelial progenitor cells and angiogenesis in old ischemic hearts occurred after GDF11 over-expression. Repetitive targeted delivery of the GDF11 gene via UTMD can rejuvenate the aged mouse heart and protect it from I/R injury.

Cardiomyocyte Lineage Specification in Adult Human Cardiac Precursor Cells Via Modulation of Enhancer-Associated Long Noncoding RNA Expression

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Human CPCs produce predominantly smooth muscle cells.

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CPCs can be redirected to the cardiomyocyte fate by transient activation followed by inhibition of NOTCH signaling.

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Inhibition of NOTCH signaling during differentiation represses MIR-143/145 expression and blocks smooth muscle differentiation.

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Expression of the microRNAs is under control of CARMEN, a long noncoding RNA associated with an enhancer located in the MIR-143/145 locus and target of NOTCH signaling.

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The CARMEN/MIR-145/143 locus represents a promising therapeutic target to favor production of cardiomyocytes in cell replacement therapies.

The mechanisms controlling differentiation in adult cardiac precursor cells (CPCs) are still largely unknown. In this study, CPCs isolated from the human heart were found to produce predominantly smooth muscle cells but could be redirected to the cardiomyocyte fate by transient activation followed by inhibition of NOTCH signaling. NOTCH inhibition repressed MIR-143/145 expression, and blocked smooth muscle differentiation. Expression of the microRNAs is under control of CARMEN, a long noncoding RNA associated with an enhancer located in the MIR-143/145 locus and target of NOTCH signaling. The CARMEN/MIR-145/143 axis represents, therefore, a promising target to favor production of cardiomyocytes in cell replacement therapies.

Cross-talk of SFRP4, integrin α1β1, and Notch1 inhibits cardiac differentiation of P19CL6 cells

Signaling pathways play an important role in cardiogenesis. Secreted frizzled-related protein 4 (SFRP4), a member of the Wnt family, contributes to adipogenesis and tumorigenesis. However, how SFRP4 participates in cardiogenesis and the detailed molecular mechanisms involved have not been elucidated. The aim of this work was to determine cross-talk between SFRP4, integrin α1β1, and Notch1 during cardiac differentiation of P19CL6 cells. Using a well-established in vitro P19CL6 cell cardiomyocyte differentiation system, we found that SFRP4 inhibited P19CL6 cell cardiac differentiation via SFRP4 overexpression or knockdown. In addition, the SFRP4 overexpression augmented Notch1 and HES1 production. Further investigation demonstrated that SFRP4 bound to integrin α1β1 to activate the focal adhesion kinase (FAK) pathway and that phosphorylated FAK Y397 (p-FAK Y397) aided Notch intracellular domain 1 (NICD1) nuclear translocation to form a p-FAK Y397-NICD1 complex that activated the Hes1 promoter. Taken together, the cross-talk between SFRP4, integrin α1β1, and Notch1 suppresses the cardiac differentiation of P19CL6 cells.

Empowering Adult Stem Cells for Myocardial Regeneration V2.0: Success in Small Steps

Much has changed since our survey of the landscape for myocardial regeneration powered by adult stem cells 4 years ago.(1) The intervening years since that first review has witnessed an explosive expansion of studies that advance both understanding and implementation of adult stem cells in promoting myocardial repair. Painstaking research from innumerable laboratories throughout the world is prying open doors that may lead to restoration of myocardial structure and function in the wake of pathological injury. This global effort has produced deeper mechanistic comprehension coupled with an evolving appreciation for the complexity of myocardial regeneration in the adult context. Undaunted by both known and (as yet) unknown challenges, pursuit of myocardial regenerative medicine mediated by adult stem cell therapy has gathered momentum fueled by tantalizing clues and visionary goals. This concise review takes a somewhat different perspective than our initial treatise, taking stock of the business sector that has become an integral part of the field while concurrently updating state of affairs in cutting edge research. Looking retrospectively at advancement over the years as all reviews eventually must, the fundamental lesson to be learned is best explained by Jonatan Mårtensson: "Success will never be a big step in the future. Success is a small step taken just now."

Notch1 Pathway Protects against Burn-Induced Myocardial Injury by Repressing Reactive Oxygen Species Production through JAK2/STAT3 Signaling

Oxidative stress plays an important role in burn-induced myocardial injury, but the cellular mechanisms that control reactive oxygen species (ROS) production and scavenging are not fully understood. This study demonstrated that blockade of Notch signaling via knockout of the transcription factor RBP-J or a pharmacological inhibitor aggravated postburn myocardial injury, which manifested as deteriorated serum CK, CK-MB, and LDH levels and increased apoptosis in vitro and in vivo. Interruption of Notch signaling increased intracellular ROS production, and a ROS scavenger reversed the exacerbated myocardial injury after Notch signaling blockade. These results suggest that Notch signaling deficiency aggravated postburn myocardial injury through increased ROS levels. Notch signaling blockade also decreased MnSOD expression in vitro and in vivo. Notably, Notch signaling blockade downregulated p-JAK2 and p-STAT3 expression. Inhibition of JAK2/STAT3 signaling with AG490 markedly decreased MnSOD expression, increased ROS production, and aggravated myocardial injury. AG490 plus GSI exerted no additional effects. These results demonstrate that Notch signaling protects against burn-induced myocardial injury through JAK2/STAT3 signaling, which activates the expression of MnSOD and leads to decreased ROS levels.