Notch1 signaling stimulates proliferation of immature cardiomyocytes

ErbB2-NOTCH1 axis controls autophagy in cardiac cells

Although the epidermal growth factor receptor 2 (ErbB2) and Notch1 signaling pathways have both significant roles in regulating cardiac biology, their interplay in the heart remains poorly investigated. Here, we present evidence of a crosstalk between ErbB2 and Notch1 in cardiac cells, with effects on autophagy and proliferation. Overexpression of ErbB2 in H9c2 cardiomyoblasts induced Notch1 activation in a post-transcriptional, p38-dependent manner, while ErbB2 inhibition with the specific inhibitor, lapatinib, reduced Notch1 activation. Moreover, incubation of H9c2 cells with lapatinib resulted in stalled autophagic flux and decreased proliferation, consistent with the established cardiotoxicity of this and other ErbB2-targeting drugs. Confirming the findings in H9c2 cells, exposure of primary neonatal mouse cardiomyocytes to exogenous neuregulin-1, which engages ErbB2, stimulated proliferation, and this effect was abrogated by concomitant inhibition of the enzyme responsible for Notch1 activation. Furthermore, the hearts of transgenic mice specifically overexpressing ErbB2 in cardiomyocytes had increased levels of active Notch1 and of Notch-related genes. These data expand the knowledge of ErbB2 and Notch1 functions in the heart and may allow better understanding the mechanisms of the cardiotoxicity of ErbB2-targeting cancer treatments.

Signaling Pathways Governing Cardiomyocyte Differentiation

Cardiomyocytes are the largest cell type that make up the heart and confer beating activity to the heart. The proper differentiation of cardiomyocytes relies on the efficient transmission and perception of differentiation cues from several signaling pathways that influence cardiomyocyte-specific gene expression programs. Signaling pathways also mediate intercellular communications to promote proper cardiomyocyte differentiation. We have reviewed the major signaling pathways involved in cardiomyocyte differentiation, including the BMP, Notch, sonic hedgehog, Hippo, and Wnt signaling pathways. Additionally, we highlight the differences between different cardiomyocyte cell lines and the use of these signaling pathways in the differentiation of cardiomyocytes from stem cells. Finally, we conclude by discussing open questions and current gaps in knowledge about the in vitro differentiation of cardiomyocytes and propose new avenues of research to fill those gaps.

Non-Coding Ribonucleic Acids as Diagnostic and Therapeutic Targets in Cardiac Fibrosis

PURPOSE OF REVIEW

Cardiac fibrosis is a crucial juncture following cardiac injury and a precursor for many clinical heart disease manifestations. Epigenetic modulators, particularly non-coding RNAs (ncRNAs), are gaining prominence as diagnostic and therapeutic tools.

RECENT FINDINGS

miRNAs are short linear RNA molecules involved in post-transcriptional regulation; lncRNAs and circRNAs are RNA sequences greater than 200 nucleotides that also play roles in regulating gene expression through a variety of mechanisms including miRNA sponging, direct interaction with mRNA, providing protein scaffolding, and encoding their own products. NcRNAs have the capacity to regulate one another and form sophisticated regulatory networks. The individual roles and disease relevance of miRNAs, lncRNAs, and circRNAs to cardiac fibrosis have been increasingly well described, though the complexity of their interrelationships, regulatory dynamics, and context-specific roles needs further elucidation. This review provides an overview of select ncRNAs relevant in cardiac fibrosis as a surrogate for many cardiac disease states with a focus on crosstalk and regulatory networks, variable actions among different disease states, and the clinical implications thereof. Further, the clinical feasibility of diagnostic and therapeutic applications as well as the strategies underway to advance ncRNA theranostics is explored.

Low expression of Notch1 may be associated with acute myocardial infarction

Background

The transmembrane protein Notch1 is associated with cell growth, development, differentiation, proliferation, apoptosis, adhesion, and the epithelial mesenchymal transition. Proteomics, as a research method, uses a series of sequencing techniques to study the composition, expression levels, and modifications of proteins. Here, the association between Notch1 and acute myocardial infarction (AMI) was investigated using proteomics, to assess the possibility of using Notch1 as a biomarker for the disease.

Methods

Fifty-five eligible patients with AMI and 74 with chronic coronary syndrome (CCS) were enrolled, representing the experimental and control groups, respectively. The mRNA levels were assessed using RT-qPCR and proteins were measured using ELISA, and the results were compared and analyzed.

Results

Notch1 mRNA levels were 0.52 times higher in the peripheral blood mononuclear cells of the AMI group relative to the CCS group (p < 0.05) while Notch1 protein levels were 0.63 times higher in peripheral blood plasma in AMI patients (p < 0.05). Notch1 levels were not associated with older age, hypertension, smoking, high abdominal-blood glucose, high total cholesterol, and high LDL in AMI. Logistic regression indicated associations between AMI and reduced Notch1 expression, hypertension, smoking, and high fasting glucose.

Conclusions

Notch1 expression was reduced in the peripheral blood of patients with AMI relative to those with CCS. The low expression of Notch1 was found to be an independent risk factor for AMI and may thus be an indicator of the disease.

A review on regulation of DNA methylation during post-myocardial infarction

Myocardial infarction (MI) imposes a huge medical and economic burden on society, and cardiac repair after MI involves a complex series of processes. Understanding the key mechanisms (such as apoptosis, autophagy, inflammation, and fibrosis) will facilitate further drug development and patient treatment. Presently, a substantial body of evidence suggests that the regulation of epigenetic processes contributes to cardiac repair following MI, with DNA methylation being among the notable epigenetic factors involved. This article will review the research on the mechanism of DNA methylation regulation after MI to provide some insights for future research and development of related drugs.

Regulation of endogenous cardiomyocyte proliferation: The known unknowns

Myocardial regeneration in patients with cardiac damage is a long-sought goal of clinical medicine. In animal species in which regeneration occurs spontaneously, as well as in neonatal mammals, regeneration occurs through the proliferation of differentiated cardiomyocytes, which re-enter the cell cycle and proliferate. Hence, the reprogramming of the replicative potential of cardiomyocytes is an achievable goal, provided that the mechanisms that regulate this process are understood. Cardiomyocyte proliferation is under the control of a series of signal transduction pathways that connect extracellular cues to the activation of specific gene transcriptional programmes, eventually leading to the activation of the cell cycle. Both coding and non-coding RNAs (in particular, microRNAs) are involved in this regulation. The available information can be exploited for therapeutic purposes, provided that a series of conceptual and technical barriers are overcome. A major obstacle remains the delivery of pro-regenerative factors specifically to the heart. Improvements in the design of AAV vectors to enhance their cardiotropism and efficacy or, alternatively, the development of non-viral methods for nucleic acid delivery in cardiomyocytes are among the challenges ahead to progress cardiac regenerative therapies towards clinical application.

Impaired Human Cardiac Cell Development due to NOTCH1 Deficiency

BACKGROUND

NOTCH1 pathogenic variants are implicated in multiple types of congenital heart defects including hypoplastic left heart syndrome, where the left ventricle is underdeveloped. It is unknown how NOTCH1 regulates human cardiac cell lineage determination and cardiomyocyte proliferation. In addition, mechanisms by which NOTCH1 pathogenic variants lead to ventricular hypoplasia in hypoplastic left heart syndrome remain elusive.

METHODS

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas9 genome editing was utilized to delete NOTCH1 in human induced pluripotent stem cells. Cardiac differentiation was carried out by sequential modulation of WNT signaling, and NOTCH1 knockout and wild-type differentiating cells were collected at day 0, 2, 5, 10, 14, and 30 for single-cell RNA-seq.

RESULTS

Human NOTCH1 knockout induced pluripotent stem cells are able to generate functional cardiomyocytes and endothelial cells, suggesting that NOTCH1 is not required for mesoderm differentiation and cardiovascular development in vitro. However, disruption of NOTCH1 blocks human ventricular-like cardiomyocyte differentiation but promotes atrial-like cardiomyocyte generation through shortening the action potential duration. NOTCH1 deficiency leads to defective proliferation of early human cardiomyocytes, and transcriptomic analysis indicates that pathways involved in cell cycle progression and mitosis are downregulated in NOTCH1 knockout cardiomyocytes. Single-cell transcriptomic analysis reveals abnormal cell lineage determination of cardiac mesoderm, which is manifested by the biased differentiation toward epicardial and second heart field progenitors at the expense of first heart field progenitors in NOTCH1 knockout cell populations.

CONCLUSIONS

NOTCH1 is essential for human ventricular-like cardiomyocyte differentiation and proliferation through balancing cell fate determination of cardiac mesoderm and modulating cell cycle progression. Because first heart field progenitors primarily contribute to the left ventricle, we speculate that pathogenic NOTCH1 variants lead to biased differentiation of first heart field progenitors, blocked ventricular-like cardiomyocyte differentiation, and defective cardiomyocyte proliferation, which collaboratively contribute to left ventricular hypoplasia in hypoplastic left heart syndrome.

Cardiac regeneration: Options for repairing the injured heart

Cardiac regeneration is one of the grand challenges in repairing injured human hearts. Numerous studies of signaling pathways and metabolism on cardiac development and disease pave the way for endogenous cardiomyocyte regeneration. New drug delivery approaches, high-throughput screening, as well as novel therapeutic compounds combined with gene editing will facilitate the development of potential cell-free therapeutics. In parallel, progress has been made in the field of cell-based therapies. Transplantation of human pluripotent stem cell (hPSC)-derived cardiomyocytes (hPSC-CMs) can partially rescue the myocardial defects caused by cardiomyocyte loss in large animals. In this review, we summarize current cell-based and cell-free regenerative therapies, discuss the importance of cardiomyocyte maturation in cardiac regenerative medicine, and envision new ways of regeneration for the injured heart.

The negative regulation of gene expression by microRNAs as key driver of inducers and repressors of cardiomyocyte differentiation

Cardiac muscle damage-induced loss of cardiomyocytes (CMs) and dysfunction of the remaining ones leads to heart failure, which nowadays is the number one killer worldwide. Therapies fostering effective cardiac regeneration are the holy grail of cardiovascular research to stop the heart failure epidemic. The main goal of most myocardial regeneration protocols is the generation of new functional CMs through the differentiation of endogenous or exogenous cardiomyogenic cells. Understanding the cellular and molecular basis of cardiomyocyte commitment, specification, differentiation and maturation is needed to devise innovative approaches to replace the CMs lost after injury in the adult heart. The transcriptional regulation of CM differentiation is a highly conserved process that require sequential activation and/or repression of different genetic programs. Therefore, CM differentiation and specification have been depicted as a step-wise specific chemical and mechanical stimuli inducing complete myogenic commitment and cell-cycle exit. Yet, the demonstration that some microRNAs are sufficient to direct ESC differentiation into CMs and that four specific miRNAs reprogram fibroblasts into CMs show that CM differentiation must also involve negative regulatory instructions. Here, we review the mechanisms of CM differentiation during development and from regenerative stem cells with a focus on the involvement of microRNAs in the process, putting in perspective their negative gene regulation as a main modifier of effective CM regeneration in the adult heart.

Inhibition of the NOTCH1 Pathway in the Stressed Heart Limits Fibrosis and Promotes Recruitment of Non-Myocyte Cells into the Cardiomyocyte Fate

Cardiac pathologies lead to an acute or gradual loss of cardiomyocytes. Because of the limited regenerative capacity of the mammalian heart, cardiomyocytes are only replaced by fibrotic tissue. Excessive fibrosis contributes to the deterioration of cardiac function and the transition to heart failure, which is the leading cause of morbidity and mortality worldwide. Currently, no treatments can promote replenishment of the injured heart with newly formed cardiomyocytes. In this context, regenerative strategies explore the possibility to promote recovery through induction of cardiomyocyte production from pre-existing cardiomyocytes. On the other hand, cardiac non-myocyte cells can be directly reprogrammed into induced cardiac precursor cells and cardiomyocytes, suggesting that these cells could be exploited to produce cardiomyocytes in vivo. Here, we provide evidence that the sequential activation and inhibition of the NOTCH1 signaling pathway in the stressed heart decreases fibrosis and improves cardiac function in the stressed heart. This is accompanied by the emergence of new cardiomyocytes from non-myocyte origin. Overall, our data show how a developmental pathway such as the NOTCH pathway can be manipulated to provide therapeutic benefit in the damaged heart.

Comprehensive profile of circRNAs in formaldehyde induced heart development

Circular RNAs (circRNAs) are a novel type of long non-coding RNAs that can regulate gene expression in heart development and heart disease. However, the expression pattern of circRNAs in congenital heart disease (CHD) induced by formaldehyde exposure is still unknown. We detected circRNAs expression profiles in heart tissue taken from six neonatal rat pups with formaldehyde exposure group and normal group using RNA-sequencing. Results revealed that a total of 54 circRNAs were dysregulated in the formaldehyde exposure group compared to the normal group. Among them, 31 were upregulated and 23 were downregulated (fold change = 2.0, p < 0.0 5). The qRT-qPCR results showed that expressions of 12:628708|632694, 18:77477060|77520779, 5:167486001|167526275 were significantly upregulated, while that of 7:41167312|4116775 and 20:50659751|5068786 were notably downregulated; the expression pattern was consistent with the RNA sequencing data. Bioinformatics analysis shows that the pathogenesis of formaldehyde exposure-induced CHD may involve Hippo-YAP pathway、Notch signaling pathway and other pathways. A key miRNA (rno-miR-665) was identified by constructing a circRNA-miRNA-mRNA co-expression network. In summary, the study illustrated that circRNAs differentially expressed in fetal heart tissues during formaldehyde exposure has potential biological functions and may be a biomarker or therapeutic target for CHD.

Heart regeneration: 20 years of progress and renewed optimism

Cardiovascular disease is a leading cause of death worldwide, and thus there remains great interest in regenerative approaches to treat heart failure. In the past 20 years, the field of heart regeneration has entered a renaissance period with remarkable progress in the understanding of endogenous heart regeneration, stem cell differentiation for exogenous cell therapy, and cell-delivery methods. In this review, we highlight how this new understanding can lead to viable strategies for human therapy. For the near term, drugs, electrical and mechanical devices, and heart transplantation will remain mainstays of cardiac therapies, but eventually regenerative therapies based on fundamental regenerative biology may offer more permanent solutions for patients with heart failure.

Reawakening the Intrinsic Cardiac Regenerative Potential: Molecular Strategies to Boost Dedifferentiation and Proliferation of Endogenous Cardiomyocytes

Despite considerable efforts carried out to develop stem/progenitor cell-based technologies aiming at replacing and restoring the cardiac tissue following severe damages, thus far no strategies based on adult stem cell transplantation have been demonstrated to efficiently generate new cardiac muscle cells. Intriguingly, dedifferentiation, and proliferation of pre-existing cardiomyocytes and not stem cell differentiation represent the preponderant cellular mechanism by which lower vertebrates spontaneously regenerate the injured heart. Mammals can also regenerate their heart up to the early neonatal period, even in this case by activating the proliferation of endogenous cardiomyocytes. However, the mammalian cardiac regenerative potential is dramatically reduced soon after birth, when most cardiomyocytes exit from the cell cycle, undergo further maturation, and continue to grow in size. Although a slow rate of cardiomyocyte turnover has also been documented in adult mammals, both in mice and humans, this is not enough to sustain a robust regenerative process. Nevertheless, these remarkable findings opened the door to a branch of novel regenerative approaches aiming at reactivating the endogenous cardiac regenerative potential by triggering a partial dedifferentiation process and cell cycle re-entry in endogenous cardiomyocytes. Several adaptations from intrauterine to extrauterine life starting at birth and continuing in the immediate neonatal period concur to the loss of the mammalian cardiac regenerative ability. A wide range of systemic and microenvironmental factors or cell-intrinsic molecular players proved to regulate cardiomyocyte proliferation and their manipulation has been explored as a therapeutic strategy to boost cardiac function after injuries. We here review the scientific knowledge gained thus far in this novel and flourishing field of research, elucidating the key biological and molecular mechanisms whose modulation may represent a viable approach for regenerating the human damaged myocardium.

Bioengineering Systems for Modulating Notch Signaling in Cardiovascular Development, Disease, and Regeneration

The Notch intercellular signaling pathways play significant roles in cardiovascular development, disease, and regeneration through modulating cardiovascular cell specification, proliferation, differentiation, and morphogenesis. The dysregulation of Notch signaling leads to malfunction and maldevelopment of the cardiovascular system. Currently, most findings on Notch signaling rely on animal models and a few clinical studies, which significantly bottleneck the understanding of Notch signaling-associated human cardiovascular development and disease. Recent advances in the bioengineering systems and human pluripotent stem cell-derived cardiovascular cells pave the way to decipher the role of Notch signaling in cardiovascular-related cells (endothelial cells, cardiomyocytes, smooth muscle cells, fibroblasts, and immune cells), and intercellular crosstalk in the physiological, pathological, and regenerative context of the complex human cardiovascular system. In this review, we first summarize the significant roles of Notch signaling in individual cardiac cell types. We then cover the bioengineering systems of microfluidics, hydrogel, spheroid, and 3D bioprinting, which are currently being used for modeling and studying Notch signaling in the cardiovascular system. At last, we provide insights into ancillary supports of bioengineering systems, varied types of cardiovascular cells, and advanced characterization approaches in further refining Notch signaling in cardiovascular development, disease, and regeneration.

The roles of signaling pathways in cardiac regeneration

In recent years, knowledge of cardiac regeneration mechanisms has dramatically expanded. Regeneration can replace lost parts of organs, common among animal species. The heart is commonly considered an organ with terminal development, which has no reparability potential during post-natal life; however, some intrinsic regeneration capacity has been reported for cardiac muscle, which opens novel avenues in cardiovascular disease treatment. Different endogenous mechanisms were studied for cardiac repairing and regeneration in recent decades. Survival, proliferation, inflammation, angiogenesis, cell-cell communication, cardiomyogenesis, and anti-aging pathways are the most important mechanisms that have been studied in this regard. Several in vitro and animal model studies focused on proliferation induction for cardiac regeneration reported promising results. These studies have mainly focused on promoting proliferation signaling pathways and demonstrated various signaling pathways such as Wnt, PI3K/Akt, IGF-1, TGF-β, Hippo, and VEGF signaling cardiac regeneration. Therefore, in this review, we intended to discuss the connection between different critical signaling pathways in cardiac repair and regeneration.

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.

Posttranslational Modifications: Emerging Prospects for Cardiac Regeneration Therapy

Heart failure (HF) following ischemic heart disease (IHD) remains a hard nut to crack and a leading cause of death worldwide. Cardiac regeneration aims to promote cardiomyocyte (CM) proliferation by transitioning the cell cycle state of CMs from arrest to re-entry. Protein posttranslational modifications (PTMs) have recently attracted extensive attention in the field of cardiac regeneration due to their reversibility and effects on the stability, activity, and subcellular localization of target proteins. The balance of PTMs is disrupted when neonatal CMs withdraw from the cell cycle, resulting in significant dysfunction of downstream substrate protein localization, expression, and activity, ultimately limiting the maintenance of cardiac regeneration ability. In this review, we summarize recent research concerning the role of PTMs in cardiac regeneration, while focusing on phosphorylation, acetylation, ubiquitination, glycosylation, methylation, and neddylation, and the effects of these modifications on CM proliferation, which may provide potential targets for future treatments for IHD.

Molecular regulation of myocardial proliferation and regeneration

Heart regeneration is a fascinating and complex biological process. Decades of intensive studies have revealed a sophisticated molecular network regulating cardiac regeneration in the zebrafish and neonatal mouse heart. Here, we review both the classical and recent literature on the molecular and cellular mechanisms underlying heart regeneration, with a particular focus on how injury triggers the cell-cycle re-entry of quiescent cardiomyocytes to replenish their massive loss after myocardial infarction or ventricular resection. We highlight several important signaling pathways for cardiomyocyte proliferation and propose a working model of how these injury-induced signals promote cardiomyocyte proliferation. Thus, this concise review provides up-to-date research progresses on heart regeneration for investigators in the field of regeneration biology.

Targets and regulation of microRNA-652-3p in homoeostasis and disease

microRNA are small non-coding RNA molecules which inhibit gene expression by binding mRNA, preventing its translation. As important regulators of gene expression, there is increasing interest in microRNAs as potential diagnostic biomarkers and therapeutic targets. Studies investigating the role of one of the miRNA-miR-652-3p-detail diverse roles for this miRNA in normal cell homoeostasis and disease states, including cancers, cardiovascular disease, mental health, and central nervous system diseases. Here, we review recent literature surrounding miR-652-3p, discussing its known target genes and their relevance to disease progression. These studies demonstrate that miR-652-3p targets LLGL1 and ZEB1 to modulate cell polarity mechanisms, with impacts on cancer metastasis and asymmetric cell division. Inhibition of the NOTCH ligand JAG1 by miR-652-3p can have diverse effects on angiogenesis and immune cell regulation. Investigation of miR-652-3p and other dysregulated miRNAs identified a number of pathways potentially regulated by miR-652-3p. This review demonstrates that miR-652-3p has great promise as a diagnostic or therapeutic target due to its activity across multiple cellular systems.

Non-coding RNA therapeutics for cardiac regeneration

A growing body of evidence indicates that cardiac regeneration after myocardial infarction can be achieved by stimulating the endogenous capacity of cardiomyocytes (CMs) to replicate. This process is controlled, both positively and negatively, by a large set of non-coding RNAs (ncRNAs). Some of the microRNAs (miRNAs) that can stimulate CM proliferation is expressed in embryonic stem cells and is required to maintain pluripotency (e.g. the miR-302∼367 cluster). Others also govern the proliferation of different cell types, including cancer cells (e.g. the miR-17∼92 cluster). Additional miRNAs were discovered through systematic screenings (e.g. miR-199a-3p and miR-590-3p). Several miRNAs instead suppress CM proliferation and are involved in the withdrawal of CMs from the cell cycle after birth (e.g. the let-7 and miR-15 families). Similar regulatory roles on CM proliferation are also exerted by a few long ncRNAs. This body of information has obvious therapeutic implications, as miRNAs with activator function or short antisense oligonucleotides against inhibitory miRNAs or lncRNAs can be administered to stimulate cardiac regeneration. Expression of miRNAs can be achieved by gene therapy using adeno-associated vectors, which transduce CMs with high efficiency. More effective and safer for therapeutic purposes, small nucleic acid therapeutics can be obtained as chemically modified, synthetic molecules, which can be administered through lipofection or inclusion in lipid or polymer nanoparticles for efficient cardiac delivery. The notion that it is possible to reprogramme CMs into a regenerative state and that this property can be enhanced by ncRNA therapeutics remains exciting, however extensive experimentation in large mammals and rigorous assessment of safety are required to advance towards clinical application.

Regulation of cardiomyocyte fate plasticity: a key strategy for cardiac regeneration

With the high morbidity and mortality rates, cardiovascular diseases have become one of the most concerning diseases worldwide. The heart of adult mammals can hardly regenerate naturally after injury because adult cardiomyocytes have already exited the cell cycle, which subseqently triggers cardiac remodeling and heart failure. Although a series of pharmacological treatments and surgical methods have been utilized to improve heart functions, they cannot replenish the massive loss of beating cardiomyocytes after injury. Here, we summarize the latest research progress in cardiac regeneration and heart repair through altering cardiomyocyte fate plasticity, which is emerging as an effective strategy to compensate for the loss of functional cardiomyocytes and improve the impaired heart functions. First, residual cardiomyocytes in damaged hearts re-enter the cell cycle to acquire the proliferative capacity by the modifications of cell cycle-related genes or regulation of growth-related signals. Additionally, non-cardiomyocytes such as cardiac fibroblasts, were shown to be reprogrammed into cardiomyocytes and thus favor the repair of damaged hearts. Moreover, pluripotent stem cells have been shown to transform into cardiomyocytes to promote heart healing after myocardial infarction (MI). Furthermore, in vitro and in vivo studies demonstrated that environmental oxygen, energy metabolism, extracellular factors, nerves, non-coding RNAs, etc. play the key regulatory functions in cardiac regeneration. These findings provide the theoretical basis of targeting cellular fate plasticity to induce cardiomyocyte proliferation or formation, and also provide the clues for stimulating heart repair after injury.

The effect of gestational diabetes on identification of key genes and pathways in human umbilical vein endothelial cell by integrated bioinformatics analysis

Maternal diabetes may lead to long-term risks for the offspring. The study aims at identifying the potential crucial genes and pathways associated with foetal metabolism and malformation of gestational diabetes mellitus (GDM). Gene Expression Series 49524 and 87295 were downloaded from Gene Expression Omnibus database, including eight from GDM and eight from non-GDM. A total of 35 differentially expressed genes were identified. Gene ontology functional annotation and signalling pathway analyses were performed. Four hub genes were identified by protein-protein interaction network: SHH, E2F1, STAT1, and HOXA9. The four hub genes were assessed by western blot and real-time quantitative PCR in clinical samples. The results of this data mining and integration help to reveal the pathophysiologic and molecular mechanism imprinted in primary umbilical cord-derived cells from GDM offspring. These genes and pathways identified are potential stratification biomarkers and provide further insight for developing therapeutic intervention for the offspring of diabetic mothers.Impact statementWhat is already known on this subject? Maternal diabetes may lead to long-term risks for the offspring. A high glucose environment might change the umbilical cord expression of genes implicated in foetal metabolism and development. However, underlying molecular mechanisms have not been investigated thoroughly.What do the results of this study add? GO functional annotation showed that the biological functions of differentially expressed genes mainly involved in metanephros development, salivary gland morphogenesis, fat cell differentiation, vasculogenesis, muscle cell proliferation, heart morphogenesis and Wnt signalling pathway. Signalling pathway analyses found that these differentially expressed genes mainly implicated in the apoptosis, cell cycle, Hedgehog, P53, and NOTCH signalling pathway. Four hub genes were identified by protein-protein interaction network: SHH, E2F1, STAT1 and HOXA9.What are the implications of these findings for clinical practice and/or further research? The genes and pathways identified in the present study are potential stratification biomarkers and provide further insight for developing therapeutic intervention for the offspring of diabetic mothers.

Cardiomyocyte Proliferation and Maturation: Two Sides of the Same Coin for Heart Regeneration

In the past few decades, cardiac regeneration has been the central target for restoring the injured heart. In mammals, cardiomyocytes are terminally differentiated and rarely divide during adulthood. Embryonic and fetal cardiomyocytes undergo robust proliferation to form mature heart chambers in order to accommodate the increased workload of a systemic circulation. In contrast, postnatal cardiomyocytes stop dividing and initiate hypertrophic growth by increasing the size of the cardiomyocyte when exposed to increased workload. Extracellular and intracellular signaling pathways control embryonic cardiomyocyte proliferation and postnatal cardiac hypertrophy. Harnessing these pathways could be the future focus for stimulating endogenous cardiac regeneration in response to various pathological stressors. Meanwhile, patient-specific cardiomyocytes derived from autologous induced pluripotent stem cells (iPSCs) could become the major exogenous sources for replenishing the damaged myocardium. Human iPSC-derived cardiomyocytes (iPSC-CMs) are relatively immature and have the potential to increase the population of cells that advance to physiological hypertrophy in the presence of extracellular stimuli. In this review, we discuss how cardiac proliferation and maturation are regulated during embryonic development and postnatal growth, and explore how patient iPSC-CMs could serve as the future seed cells for cardiac cell replacement therapy.

Designing Biomaterials to Modulate Notch Signaling in Tissue Engineering and Regenerative Medicine

The design of cell-instructive biomaterials for tissue engineering and regenerative medicine is at a crossroads. Although the conventional tissue engineering approach is top-down (cells seeded to macroporous scaffolds and mature to form tissues), bottom-up tissue engineering strategies are becoming appealing. With such developments, we can study cell signaling events, thus enabling functional tissue assembly in physiologic and diseased models. Among many important signaling pathways, the Notch signaling pathway is the most diverse in its influence during tissue morphogenesis and repair following injury. Although Notch signaling is extensively studied in developmental biology and cancer biology, our knowledge of designing biomaterial-based Notch signaling platforms and incorporating Notch signaling components into engineered tissue systems is limited. By incorporating Notch signaling to tissue engineering scaffolds, we can direct cell-specific responses and improve engineered tissue maturation. This review will discuss recent progress in the development of Notch signaling biomaterials as a promising target to control cellular fate decisions, including the influences of ligand identity, biophysical material cues, ligand presentation strategies, and mechanotransduction. Notch signaling is consequently of interest to direct, control, and reprogram cellular behavior on a biomaterial surface. We anticipate that discussions in this article will allow for enhanced knowledge and insight into designing Notch targeted biomaterials for various tissue engineering and cell fate determinations. Impact statement Notch signaling is recognized as an important pathway in tissue engineering and regenerative medicine; however, there is no systematic review on this topic. The comprehensive review and perspectives presented here provide an in-depth discussion on ligand presentation strategies both in 2D and in 3D cell culture environments involving biomaterials/scaffolds. In addition, this review article provides insight into the challenges in designing cell surrogate biomaterials capable of providing Notch signals. To the best of the authors' knowledge, this is the first review relevant to the fields of tissue engineering.

LRP6 downregulation promotes cardiomyocyte proliferation and heart regeneration

The adult mammalian heart is thought to be a terminally differentiated organ given the postmitotic nature of cardiomyocytes. Consequently, the potential for cardiac repair through cardiomyocyte proliferation is extremely limited. Low-density lipoprotein receptor-related protein 6 (LRP6) is a Wnt co-receptor that is required for embryonic heart development. In this study we investigated the role of LRP6 in heart repair through regulation of cardiomyocyte proliferation. Lrp6 deficiency increased cardiomyocyte cell cycle activity in neonatal, juvenile and adult mice. Cardiomyocyte-specific deletion of Lrp6 in the mouse heart induced a robust regenerative response after myocardial infarction (MI), led to reduced MI area and improvement in left ventricular systolic function. In vivo genetic lineage tracing revealed that the newly formed cardiomyocytes in Lrp6-deficient mouse hearts after MI were mainly derived from resident cardiomyocytes. Furthermore, we found that the pro-proliferative effect of Lrp6 deficiency was mediated by the ING5/P21 signaling pathway. Gene therapy using the adeno-associated virus (AAV)9 miRNAi-Lrp6 construct promoted the repair of heart injury in mice. Lrp6 deficiency also induced the proliferation of human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Our study identifies LRP6 as a critical regulator of cardiomyocyte proliferation, which may lead to the development of a novel molecular strategy to promote myocardial regeneration and repair.

Cardiac Regeneration After Myocardial Infarction: an Approachable Goal

Purpose of Review

Until recently, cardiac regeneration after myocardial infarction has remained a holy grail in cardiology. Failure of clinical trials using adult stem cells and scepticism about the actual existence of such cells has reinforced the notion that the heart is an irreversibly post-mitotic organ. Recent evidence has drastically challenged this conclusion.

Recent Findings

Cardiac regeneration can successfully be obtained by at least two strategies. First, new cardiomyocytes can be generated from embryonic stem cells or induced pluripotent stem cells and administered to the heart either as cell suspensions or upon ex vivo generation of contractile myocardial tissue. Alternatively, the endogenous capacity of cardiomyocytes to proliferate can be stimulated by the delivery of individual genes or, more successfully, of selected microRNAs.

Summary

Recent experimental success in large animals by both strategies now fuels the notion that cardiac regeneration is indeed possible. Several technical hurdles, however, still need to be addressed and solved before broad and successful clinical application is achieved.

Common Regulatory Pathways Mediate Activity of MicroRNAs Inducing Cardiomyocyte Proliferation

Loss of functional cardiomyocytes is a major determinant of heart failure after myocardial infarction. Previous high throughput screening studies have identified a few microRNAs (miRNAs) that can induce cardiomyocyte proliferation and stimulate cardiac regeneration in mice. Here, we show that all of the most effective of these miRNAs activate nuclear localization of the master transcriptional cofactor Yes-associated protein (YAP) and induce expression of YAP-responsive genes. In particular, miR-199a-3p directly targets two mRNAs coding for proteins impinging on the Hippo pathway, the upstream YAP inhibitory kinase TAOK1, and the E3 ubiquitin ligase β-TrCP, which leads to YAP degradation. Several of the pro-proliferative miRNAs (including miR-199a-3p) also inhibit filamentous actin depolymerization by targeting Cofilin2, a process that by itself activates YAP nuclear translocation. Thus, activation of YAP and modulation of the actin cytoskeleton are major components of the pro-proliferative action of miR-199a-3p and other miRNAs that induce cardiomyocyte proliferation.

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A few microRNAs can stimulate cardiac myocyte proliferation

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The most effective of these microRNAs activate YAP

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Several pro-proliferative microRNAs also inhibit actin depolymerization

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miR-199a-3p directly targets TAOK1, b-TrCP, and Cofilin2 to achieve its effects

Gene Therapy for the Heart Lessons Learned and Future Perspectives

While clinical gene therapy celebrates its first successes, with several products already approved for clinical use and several hundreds in the final stages of the clinical approval pipeline, there is not a single gene therapy approach that has worked for the heart. Here, we review the past experience gained in the several cardiac gene therapy clinical trials that had the goal of inducing therapeutic angiogenesis in the ischemic heart and in the attempts at modulating cardiac function in heart failure. Critical assessment of the results so far achieved indicates that the efficiency of cardiac gene delivery remains a major hurdle preventing success but also that improvements need to be sought in establishing more reliable large animal models, choosing more effective therapeutic genes, better designing clinical trials, and more deeply understanding cardiac biology. We also emphasize a few areas of cardiac gene therapy development that hold great promise for the future. In particular, the transition from gene addition studies using protein-coding cDNAs to the modulation of gene expression using small RNA therapeutics and the improvement of precise gene editing now pave the way to applications such as cardiac regeneration after myocardial infarction and gene correction for inherited cardiomyopathies that were unapproachable until a decade ago.

Delta-1 Functionalized Hydrogel Promotes hESC-Cardiomyocyte Graft Proliferation and Maintains Heart Function Post-Injury

Current cell transplantation techniques are hindered by small graft size, requiring high cell doses to achieve therapeutic cardiac remuscularization. Enhancing the proliferation of transplanted human embryonic stem cell-derived cardiomyocytes (hESC-CMs) could address this, allowing an otherwise subtherapeutic cell dose to prevent disease progression after myocardial infarction. In this study, we designed a hydrogel that activates Notch signaling through 3D presentation of the Notch ligand Delta-1 to use as an injectate for transplanting hESC-CMs into the infarcted rat myocardium. After 4 weeks, hESC-CM proliferation increased 2-fold and resulted in a 3-fold increase in graft size with the Delta-1 hydrogel compared to controls. To stringently test the effect of Notch-mediated graft expansion on long-term heart function, a normally subtherapeutic dose of hESC-CMs was implanted into the infarcted myocardium and cardiac function was evaluated by echocardiography. Transplantation of the Delta-1 hydrogel + hESC-CMs augmented heart function and was significantly higher at 3 months compared to controls. Graft size and hESC-CM proliferation were also increased at 3 months post-implantation. Collectively, these results demonstrate the therapeutic approach of a Delta-1 functionalized hydrogel to reduce the cell dose required to achieve functional benefit after myocardial infarction by enhancing hESC-CM graft size and proliferation.

miRNAs that Induce Human Cardiomyocyte Proliferation Converge on the Hippo Pathway

Understanding the mechanisms that control human cardiomyocyte proliferation might be applicable to regenerative medicine. We screened a whole genome collection of human miRNAs, identifying 96 to be capable of increasing proliferation (DNA synthesis and cytokinesis) of human iPSC-derived cardiomyocytes. Chemical screening and computational approaches indicated that most of these miRNAs (67) target different components of the Hippo pathway and that their activity depends on the nuclear translocation of the Hippo transcriptional effector YAP. 53 of the 67 miRNAs are present in human iPSC cardiomyocytes, yet anti-miRNA screening revealed that none are individually essential for basal proliferation of hiPSC cardiomyocytes despite the importance of YAP for proliferation. We propose a model in which multiple endogenous miRNAs redundantly suppress Hippo signaling to sustain the cell cycle of immature cardiomyocytes.

Notch and interacting signalling pathways in cardiac development, disease, and regeneration

Cardiogenesis is a complex developmental process involving multiple overlapping stages of cell fate specification, proliferation, differentiation, and morphogenesis. Precise spatiotemporal coordination between the different cardiogenic processes is ensured by intercellular signalling crosstalk and tissue-tissue interactions. Notch is an intercellular signalling pathway crucial for cell fate decisions during multicellular organismal development and is aptly positioned to coordinate the complex signalling crosstalk required for progressive cell lineage restriction during cardiogenesis. In this Review, we describe the role of Notch signalling and the crosstalk with other signalling pathways during the differentiation and patterning of the different cardiac tissues and in cardiac valve and ventricular chamber development. We examine how perturbation of Notch signalling activity is linked to congenital heart diseases affecting the neonate and adult, and discuss studies that shed light on the role of Notch signalling in heart regeneration and repair after injury.

Epigenetics and Mechanobiology in Heart Development and Congenital Heart Disease

: Congenital heart disease (CHD) is the most common birth defect worldwide and the number one killer of live-born infants in the United States. Heart development occurs early in embryogenesis and involves complex interactions between multiple cell populations, limiting the understanding and consequent treatment of CHD. Furthermore, genome sequencing has largely failed to predict or yield therapeutics for CHD. In addition to the underlying genome, epigenetics and mechanobiology both drive heart development. A growing body of evidence implicates the aberrant regulation of these two extra-genomic systems in the pathogenesis of CHD. In this review, we describe the stages of human heart development and the heart defects known to manifest at each stage. Next, we discuss the distinct and overlapping roles of epigenetics and mechanobiology in normal development and in the pathogenesis of CHD. Finally, we highlight recent advances in the identification of novel epigenetic biomarkers and environmental risk factors that may be useful for improved diagnosis and further elucidation of CHD etiology.

Reversible Notch1 acetylation tunes proliferative signalling in cardiomyocytes

Aims

The Notch signalling pathway regulates the balance between proliferation and differentiation in several tissues, including the heart. Our previous work has demonstrated that the proliferative potential of neonatal cardiomyocytes relies on Notch1 activity. A deep investigation on the biochemical regulation of the Notch signalling in cardiomyocytes is the focus of the current research.

Methods and results

We show that the Notch1 intracellular domain is acetylated in proliferating neonatal rat cardiomyocytes and that acetylation tightly controls the amplitude and duration of Notch signalling. We found that acetylation extends the half-life of the protein, and enhanced its transcriptional activity, therefore counteracting apoptosis and sustaining cardiomyocyte proliferation. Sirt1 acted as a negative modulator of Notch1 signalling; its overexpression in cardiomyocytes reverted Notch acetylation and dampened its stability. A constitutively acetylated fusion protein between Notch1 and the acetyltransferase domain of p300 promoted cardiomyocyte proliferation, which was remarkably sustained over time. Viral vector-mediated expression of this protein enhanced heart regeneration after apical resection in neonatal mice.

Conclusion

These results identify the reversible acetylation of Notch1 as a novel mechanism to modulate its signalling in the heart and tune the proliferative potential of cardiomyocytes.

Molecular discoveries and treatment strategies by direct reprogramming in cardiac regeneration

Cardiac tissue has minimal endogenous regenerative capacity in response to injury. Treatment options are limited following tissue damage after events such as myocardial infarction. Current strategies are aimed primarily at injury prevention, but attention has been increasingly targeted toward the development of regenerative therapies. This review focuses on recent developments in the field of cardiac fibroblast reprogramming into induced cardiomyocytes. Early efforts to produce cardiac regeneration centered around induced pluripotent stem cells, but clinical translation has proved elusive. Currently, techniques are being developed to directly transdifferentiate cardiac fibroblasts into induced cardiomyocytes. Viral vector-driven expression of a combination of transcription factors including Gata4, Mef2c, and Tbx5 induced cardiomyocyte development in mice. Subsequent combinational modifications have extended these results to human cell lines and increased efficacy. The miRNAs including combinations of miR-1, miR-133, miR-208, and miR-499 can improve or independently drive regeneration of cardiomyocytes. Similar results could be obtained by combinations of small molecules with or without transcription factor or miRNA expression. The local tissue environment greatly impacts favorability for reprogramming. Modulation of signaling pathways, especially those mediated by VEGF and TGF-β, enhance differentiation to cardiomyocytes. Current reprogramming strategies are not ready for clinical application, but recent breakthroughs promise regenerative cardiac therapies in the near future.

ALMS1 and Alström syndrome: a recessive form of metabolic, neurosensory and cardiac deficits

Alström syndrome (AS) is characterised by metabolic deficits, retinal dystrophy, sensorineural hearing loss, dilated cardiomyopathy and multi-organ fibrosis. Elucidating the function of the mutated gene, ALMS1, is critical for the development of specific treatments and may uncover pathways relevant to a range of other disorders including common forms of obesity and type 2 diabetes. Interest in ALMS1 is heightened by the recent discovery of its involvement in neonatal cardiomyocyte cell cycle arrest, a process with potential relevance to regenerative medicine. ALMS1 encodes a ~ 0.5 megadalton protein that localises to the base of centrioles. Some studies have suggested a role for this protein in maintaining centriole-nucleated sensory organelles termed primary cilia, and AS is now considered to belong to the growing class of human genetic disorders linked to ciliary dysfunction (ciliopathies). However, mechanistic details are lacking, and recent studies have implicated ALMS1 in several processes including endosomal trafficking, actin organisation, maintenance of centrosome cohesion and transcription. In line with a more complex picture, multiple isoforms of the protein likely exist and non-centrosomal sites of localisation have been reported. This review outlines the evidence for both ciliary and extra-ciliary functions of ALMS1.

Loss of embryonic neural crest derived cardiomyocytes causes adult onset hypertrophic cardiomyopathy in zebrafish

Neural crest cells migrate to the embryonic heart and transform into a small number of cardiomyocytes, but their functions in the developing and adult heart are unknown. Here, we show that neural crest derived cardiomyocytes (NC-Cms) in the zebrafish ventricle express Notch ligand jag2b, are adjacent to Notch responding cells, and persist throughout life. Genetic ablation of NC-Cms during embryogenesis results in diminished jag2b, altered Notch signaling and aberrant trabeculation patterns, but is not detrimental to early heart function or survival to adulthood. However, embryonic NC-Cm ablation results in adult fish that show severe hypertrophic cardiomyopathy (HCM), altered cardiomyocyte size, diminished adult heart capacity and heart failure in cardiac stress tests. Adult jag2b mutants have similar cardiomyopathy. Thus, we identify a cardiomyocyte population and genetic pathway that are required to prevent adult onset HCM and provide a zebrafish model of adult-onset HCM and heart failure.

A conserved HH-Gli1-Mycn network regulates heart regeneration from newt to human

The mammalian heart has a limited regenerative capacity and typically progresses to heart failure following injury. Here, we defined a hedgehog (HH)-Gli1-Mycn network for cardiomyocyte proliferation and heart regeneration from amphibians to mammals. Using a genome-wide screen, we verified that HH signaling was essential for heart regeneration in the injured newt. Next, pharmacological and genetic loss- and gain-of-function of HH signaling demonstrated the essential requirement for HH signaling in the neonatal, adolescent, and adult mouse heart regeneration, and in the proliferation of hiPSC-derived cardiomyocytes. Fate-mapping and molecular biological studies revealed that HH signaling, via a HH-Gli1-Mycn network, contributed to heart regeneration by inducing proliferation of pre-existing cardiomyocytes and not by de novo cardiomyogenesis. Further, Mycn mRNA transfection experiments recapitulated the effects of HH signaling and promoted adult cardiomyocyte proliferation. These studies defined an evolutionarily conserved function of HH signaling that may serve as a platform for human regenerative therapies.

Due to the limited proliferation capacity of adult mammalian cardiomyocytes, the human heart has negligible regenerative capacity after injury. Here the authors show that a Hedgehog-Gli1-Mycn signaling cascade regulates cardiomyocyte proliferation and cardiac regeneration from amphibians to mammals.

Notch pathway activation enhances cardiosphere in vitro expansion

Cardiospheres (CSps) are self‐assembling clusters of a heterogeneous population of poorly differentiated cells outgrowing from in vitro cultured cardiac explants. Scanty information is available on the molecular pathways regulating CSp growth and their differentiation potential towards cardiac and vascular lineages. Here we report that Notch1 stimulates a massive increase in both CSp number and size, inducing a peculiar gene expression programme leading to a cardiovascular molecular signature. These effects were further enhanced using Adeno‐Associated Virus (AAV)‐based gene transfer of activated Notch1‐intracellular domain (N1‐ICD) or soluble‐Jagged1 (sJ1) ligand to CSp‐forming cells. A peculiar effect was exploited by selected pro‐proliferating miRNAs: hsa‐miR‐590‐3p induced a cardiovascular gene expression programme, while hsa‐miR‐199a‐3p acted as the most potent stimulus for the activation of the Notch pathway, thus showing that, unlike in adult cardiomyocytes, these miRNAs involve Notch signalling activation in CSps. Our results identify Notch1 as a crucial regulator of CSp growth and differentiation along the vascular lineage, raising the attracting possibility that forced activation of this pathway might be exploited to promote in vitro CSp expansion as a tool for toxicology screening and cell‐free therapeutic strategies.

Notch3 is involved in adipogenesis of human adipose-derived stromal/stem cells

Human adipose-derived stromal/stem cells (hASCs) have tremendous therapeutic potential and the ability to offer insight into human development and disease. Here we subject human ASCs to siRNA-mediated knockdown of Notch3 cultured under both self-renewing and adipogenic differentiation conditions. Self-renewal was monitored by assessing viability and proliferation rates through staining and alamarBlue assays, respectively. Adipogenesis was measured through Oil-Red O staining, western blot, and quantitative real-time RT-PCR that determined expression levels of multipotency and adipogenic markers over time. Notch3 was expressed in self-renewing hASCs but knockdown, as validated by qRT-PCR and western blot, showed no impact on cell viability, as measured through live-dead staining, or cell proliferation rates, as measured through alamarBlue assays. However, although Notch3 expression was observed to increase during adipogenesis, in the absence of Notch3 there was a significant increase in hASC adipogenesis as demonstrated through an increased number of lipid vesicles, and increased expression of adipogenic markers ppar-γ, adiponectin, fabp4, and plin2. Although Notch3 is only one of four Notch receptors expressed on the surface of hASCs, this receptor appears important for proper regulation of adipogenic differentiation, possibly serving as a negative regulator to prevent inappropriate adipogenesis or promote other lineage commitments of ASCs.

Neonatal Apex Resection Triggers Cardiomyocyte Proliferation, Neovascularization and Functional Recovery Despite Local Fibrosis

So far, opposing outcomes have been reported following neonatal apex resection in mice, questioning the validity of this injury model to investigate regenerative mechanisms. We performed a systematic evaluation, up to 180 days after surgery, of the pathophysiological events activated upon apex resection. In response to cardiac injury, we observed increased cardiomyocyte proliferation in remote and apex regions, neovascularization, and local fibrosis. In adulthood, resected hearts remain consistently shorter and display permanent fibrotic tissue deposition in the center of the resection plane, indicating limited apex regrowth. However, thickening of the left ventricle wall, explained by an upsurge in cardiomyocyte proliferation during the initial response to injury, compensated cardiomyocyte loss and supported normal systolic function. Thus, apex resection triggers both regenerative and reparative mechanisms, endorsing this injury model for studies aimed at promoting cardiomyocyte proliferation and/or downplaying fibrosis.

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Apex resection triggers fibrosis, neovascularization, and cardiomyocyte proliferation

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Permanent fibrotic deposition is confined to the apex

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Injured hearts display morphometric alterations but regain functional competence

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Cardiomyocyte proliferation is sufficient to compensate tissue loss by resection

Polydatin Protects Diabetic Heart against Ischemia-Reperfusion Injury via Notch1/Hes1-Mediated Activation of Pten/Akt Signaling

Diabetes exacerbates oxidative/nitrative stress during myocardial ischemia-reperfusion (MI/R) injury. Recent studies highlighted the cardioprotective actions of polydatin. However, its effect on diabetic MI/R injury and the underlying mechanisms remain unknown. This work was undertaken to evaluate the effect of polydatin on diabetic MI/R injury with a focus on Notch1/Hes1 signaling and myocardial oxidative/nitrative stress. Streptozotocin- (STZ-) induced diabetic rats were administered with polydatin (20 mg/kg/d) in the absence or presence of DAPT (a γ-secretase inhibitor) or LY294002 (a PI3K/Akt inhibitor) and then subjected to MI/R injury. Polydatin administration preserved cardiac function and reduced myocardial infarct size. Moreover, polydatin ameliorated myocardial oxidative/nitrative stress damage as evidenced by decreased myocardial superoxide generation, malondialdehyde, gp91^phox expression, iNOS expression, NO metabolite level, and nitrotyrosine content and increased eNOS phosphorylation. However, these effects were blocked by DAPT administration. DAPT also inhibited the stimulatory effect of polydatin on the Notch1/Hes1-Pten/Akt signaling pathway in a diabetic myocardium. Additionally, LY294002 not only abolished polydatin's antiapoptotic effect but also reversed its inhibitory effect on myocardial oxidative/nitrative stress. Polydatin effectively reduced MI/R injury and improved left ventricular functional recovery under diabetic condition by ameliorating oxidative/nitrative stress damage. Importantly, Notch1/Hes1-mediated activation of Pten/Akt signaling played a crucial role in this process.

Integrated molecular, biochemical, and physiological assessment unravels key extraction method mediated influences on rat neonatal cardiomyocytes

Neonatal cardiomyocytes are instrumental for disease modeling, but the effects of different cell extraction methods on basic cell biological processes remain poorly understood. We assessed the influence of two popular methods to extract rat neonatal cardiomyocytes, Pre-plating (PP), and Percoll (PC) on cell structure, metabolism, and function. Cardiomyocytes obtained from PP showed higher gene expression for troponins, titin, and potassium and sodium channels compared to PC. Also, PP cells displayed higher levels of troponin I protein. Cells obtained from PC displayed higher lactate dehydrogenase activity and lactate production than PP cells, indicating higher anaerobic metabolism after 8 days of culture. In contrast, reactive oxygen species levels were higher in PP cells as indicated by ethidium and hydroxyethidium production. Consistent with these data, protein nitration was higher in PP cells, as well as nitrite accumulation in cell medium. Moreover, PP cells showed higher global intracellular calcium under basal and 1 mM isoprenaline conditions. In a calcium-transient assessment under electrical stimulation (0.5 Hz), PP cells displayed higher calcium amplitude than cardiomyocytes obtained from PC and using a traction force microscope technique we observed that PP cardiomyocytes showed the highest relaxation. Collectively, we demonstrated that extraction methods influence parameters related to cell structure, metabolism, and function. Overall, PP derived cells are more active and mature than PC cells, displaying higher contractile function and generating more reactive oxygen species. On the other hand, PC derived cells display higher anaerobic metabolism, despite comparable high yields from both protocols.

Mechanisms of Cardiomyocyte Proliferation and Differentiation in Development and Regeneration

PURPOSE OF REVIEW

Congenital heart disease is the most common birth defect and acquired heart disease is the leading cause of death in adults. Understanding the mechanisms that drive cardiomyocyte proliferation and differentiation has the potential to advance the understanding and potentially the treatment of different cardiac pathologies, ranging from myopathies and heart failure to myocardial infarction. This review focuses on studies aimed at elucidating signal transduction pathways and molecular mechanisms that promote proliferation, differentiation, and regeneration of differentiated heart muscle cells, cardiomyocytes.

RECENT FINDINGS

There is now significant evidence that demonstrates cardiomyocytes continue to proliferate into adulthood. Potential regulators have been identified, including cell cycle regulators, extracellular ligands such as neuregulin, epigenetic targets, reactive oxygen species, and microRNA. The necessary steps should involve validating and applying the new knowledge about cardiomyocyte regeneration towards the development of therapeutic targets for patients. This will be facilitated by the application of standardized pre-clinical models to study cardiomyocyte regeneration.

MIB2 variants altering NOTCH signalling result in left ventricle hypertrabeculation/non-compaction and are associated with Ménétrier-like gastropathy

We performed whole exome sequencing in individuals from a family with autosomal dominant gastropathy resembling Ménétrier disease, a premalignant gastric disorder with epithelial hyperplasia and enhanced EGFR signalling. Ménétrier disease is believed to be an acquired disorder, but its aetiology is unknown. In affected members, we found a missense p.V742G variant in MIB2, a gene regulating NOTCH signalling that has not been previously linked to human diseases. The variant segregated with the disease in the pedigree, affected a highly conserved amino acid residue, and was predicted to be deleterious although it was found with a low frequency in control individuals. The purified protein carrying the p.V742G variant showed reduced ubiquitination activity in vitro and white blood cells from affected individuals exhibited significant reductions of HES1 and NOTCH3 expression reflecting alteration of NOTCH signalling. Because mutations of MIB1, the homolog of MIB2, have been found in patients with left ventricle non-compaction (LVNC), we investigated members of our family with Ménétrier-like disease for this cardiac abnormality. Asymptomatic left ventricular hypertrabeculation, the mildest end of the LVNC spectrum, was detected in two members carrying the MIB2 variant. Finally, we identified an additional MIB2 variant (p.V984L) affecting protein stability in an unrelated isolated case with LVNC. Expression of both MIB2 variants affected NOTCH signalling, proliferation and apoptosis in primary rat cardiomyocytes.In conclusion, we report the first example of left ventricular hypertrabeculation/LVNC with germline MIB2 variants resulting in altered NOTCH signalling that might be associated with a gastropathy clinically overlapping with Ménétrier disease.

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.

In Vivo Functional Selection Identifies Cardiotrophin-1 as a Cardiac Engraftment Factor for Mesenchymal Stromal Cells

BACKGROUND

Transplantation of cells into the infarcted heart has significant potential to improve myocardial recovery; however, low efficacy of cell engraftment still limits therapeutic benefit. Here, we describe a method for the unbiased, in vivo selection of cytokines that improve mesenchymal stromal cell engraftment into the heart both in normal conditions and after myocardial infarction.

METHODS

An arrayed library of 80 secreted factors, including most of the currently known interleukins and chemokines, were individually cloned into adeno-associated viral vectors. Pools from this library were then used for the batch transduction of bone marrow-derived mesenchymal stromal cells ex vivo, followed by intramyocardial cell administration in normal and infarcted mice. Three weeks after injection, vector genomes were recovered from the few persisting cells and identified by sequencing DNA barcodes uniquely labeling each of the tested cytokines.

RESULTS

The most effective molecule identified by this competitive engraftment screening was cardiotrophin-1, a member of the interleukin-6 family. Intracardiac injection of mesenchymal stromal cells transiently preconditioned with cardiotrophin-1 preserved cardiac function and reduced infarct size, parallel to the persistence of the transplanted cells in the healing hearts for at least 2 months after injection. Engraftment of cardiotrophin-1-treated mesenchymal stromal cells was consequent to signal transducer and activator of transcription 3-mediated activation of the focal adhesion kinase and its associated focal adhesion complex and the consequent acquisition of adhesive properties by the cells.

CONCLUSIONS

These results support the feasibility of selecting molecules in vivo for their functional properties with adeno-associated viral vector libraries and identify cardiotrophin-1 as a powerful cytokine promoting cell engraftment and thus improving cell therapy of the infarcted myocardium.