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Here we propose a bio‐MEMS device designed to evaluate contractile force and conduction velocity of cell sheets in response to mechanical and electrical stimulation of the cell source as it grows to form a cellular sheet. Moreover, the design allows for the incorporation of patient‐specific data and cell sources. An optimized device would allow cell sheets to be cultured, characterized, and conditioned to be compatible with a specific patient's cardiac environment in vitro, before implantation. This design draws upon existing methods in the literature but makes an important advance by combining the mechanical and electrical stimulation into a single system for optimized cell sheet growth. The device has been designed to achieve cellular alignment, electrical stimulation, mechanical stimulation, conduction velocity readout, contraction force readout, and eventually cell sheet release. The platform is a set of comb electrical contacts consisting of three‐dimensional walls made of polydimethylsiloxane and coated with electrically conductive metals on the tops of the walls. Not only do the walls serve as a method for stimulating cells that are attached to the top, but their geometry is tailored such that they are flexible enough to be bent by the cells and used to measure force. The platform can be stretched via a linear actuator setup, allowing for simultaneous electrical and mechanical stimulation that can be derived from patient‐specific clinical data.

Changes in gene expression due to cell heterogeneity and response to stressors in specific microenvironments remains poorly understood. Current methodologies that seek to interrogate gene expression at a molecular level require sampling of cellular transcriptome and therefore lysis of the cell preventing serial analysis of cellular transcriptome. To address this area of unmet need, we have recently developed a new technology allowing transcriptomic analysis over time without cellular destruction. Our novel method, TRACE-seq (TRanscriptomic Analysis Captured in Extracellular vesicles using sequencing), is characterized by a cell-type specific transgene expression. It provides data on a representative part of the cell transcriptome inside extracellular vesicles. Thus, the transcriptome of cells expressing TRACE can be followed over time in a non-destructive manner, which is a powerful tool for many fields of fundamental and translational biology research.

Summary Defining the pathways that control cardiac development facilitates understanding the pathogenesis of congenital heart disease. Herein, we identify enrichment of a Cullin5 Ub ligase key subunit, Asb2, in myocardial progenitors and differentiated cardiomyocytes. Using two conditional murine knockouts, Nkx+/Cre.Asb2fl/fl and AHF-Cre.Asb2fl/fl, and tissue clarifying technique, we reveal Asb2 requirement for embryonic survival and complete heart looping. Deletion of Asb2 results in upregulation of its target Filamin A (Flna), and concurrent Flna deletion partially rescues embryonic lethality. Conditional AHF-Cre.Asb2 knockouts harboring one Flna allele have double outlet right ventricle (DORV), which is rescued by biallelic Flna excision. Transcriptomic and immunofluorescence analyses identify Tgfβ/Smad as downstream targets of Asb2/Flna. Finally, using CRISPR/Cas9 genome editing, we demonstrate Asb2 requirement for human cardiomyocyte differentiation suggesting a conserved mechanism between mice and humans. Collectively, our study provides deeper mechanistic understanding of the role of the ubiquitin proteasome system in cardiac development and suggests a previously unidentified murine model for DORV., Graphical Abstract, Highlights • Flna removal partially rescues embryonic lethality of Asb2-heart-specific knockout • AHF-Asb2 knockouts harboring one Flna allele have double outlet right ventricle • Asb2-Flna regulate TGFβ-Smad2 signaling in the heart • Conserved role of Asb2 in heart morphogenesis between mice and humans, Biological Sciences; Molecular Biology; Developmental Biology

Rationale: Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are a readily available, robustly reproducible, and physiologically appropriate human cell source for cardiac disease modeling, drug discovery, and toxicity screenings in vitro. However, unlike adult myocardial cells in vivo, hPSC-CMs cultured in vitro maintain an immature metabolic phenotype, where majority of ATP is produced through aerobic glycolysis instead of oxidative phosphorylation in the mitochondria. Little is known about the underlying signaling pathways controlling hPSC-CMs’ metabolic and functional maturation. Objective: To define the molecular pathways controlling cardiomyocytes’ metabolic pathway selections and improve cardiomyocyte metabolic and functional maturation. Methods and Results: We cultured hPSC-CMs in different media compositions including glucose-containing media, glucose-containing media supplemented with fatty acids, and glucose-free media with fatty acids as the primary carbon source. We found that cardiomyocytes cultured in the presence of glucose used primarily aerobic glycolysis and aberrantly upregulated HIF1α (hypoxia-inducible factor 1α) and its downstream target lactate dehydrogenase A. Conversely, glucose deprivation promoted oxidative phosphorylation and repressed HIF1α. Small molecule inhibition of HIF1α or lactate dehydrogenase A resulted in a switch from aerobic glycolysis to oxidative phosphorylation. Likewise, siRNA inhibition of HIF1α stimulated oxidative phosphorylation while inhibiting aerobic glycolysis. This metabolic shift was accompanied by an increase in mitochondrial content and cellular ATP levels. Furthermore, functional gene expressions, sarcomere length, and contractility were improved by HIF1α/lactate dehydrogenase A inhibition. Conclusions: We show that under standard culture conditions, the HIF1α-lactate dehydrogenase A axis is aberrantly upregulated in hPSC-CMs, preventing their metabolic maturation. Chemical or siRNA inhibition of this pathway results in an appropriate metabolic shift from aerobic glycolysis to oxidative phosphorylation. This in turn improves metabolic and functional maturation of hPSC-CMs. These findings provide key insight into molecular control of hPSC-CMs’ metabolism and may be used to generate more physiologically mature cardiomyocytes for drug screening, disease modeling, and therapeutic purposes.

The advent of human pluripotent stem cell (hPSC) biology has opened unprecedented opportunities for the use of tissue engineering to generate human cardiac tissue for in vitro study. Engineering cardiac constructs that recapitulate human development and disease requires faithful recreation of the cardiac niche in vitro. Here we discuss recent progress in translating the in vivo cardiac microenvironment into PSC models of the human heart. We review three key physiologic features required to recreate the cardiac niche and facilitate normal cardiac differentiation and maturation: the biochemical, biophysical, and bioelectrical signaling cues. Finally, we discuss key barriers that must be overcome to fulfill the promise of stem cell biology in preclinical applications and ultimately in clinical practice.

A fundamental goal in the biological sciences is to determine how individual cells with varied gene expression profiles and diverse functional characteristics contribute to development, physiology, and disease. Here, we report a novel strategy to assess gene expression and cell physiology in single living cells. Our approach utilizes fluorescently labeled mRNA-specific anti-sense RNA probes and dsRNA-binding protein to identify the expression of specific genes in real-time at single-cell resolution via FRET. We use this technology to identify distinct myocardial subpopulations expressing the structural proteins myosin heavy chain α and myosin light chain 2a in real-time during early differentiation of human pluripotent stem cells. We combine this live-cell gene expression analysis with detailed physiologic phenotyping to capture the functional evolution of these early myocardial subpopulations during lineage specification and diversification. This live-cell mRNA imaging approach will have wide ranging application wherever heterogeneity plays an important biological role.

Post-cardiac surgical sternal and epicardial adhesions increase the risk and complexity of cardiac re-operative surgeries, which represent a significant challenge for patients with the congenital cardiac disease. Bioresorbable membranes can serve as barriers to prevent postoperative adhesions. Herein, we fabricated a bioresorbable gelatin/polycaprolactone (GT/PCL) composite membrane via electrospinning. The membrane was characterized in terms of morphology, mechanical properties, and biocompatibility. We then evaluated its efficacy as a physical barrier to prevent cardiac operative adhesions in a rabbit model. Our results showed that the membrane had a nanofibrous structure and was sturdy enough to be handled for the surgical procedures. In vitro studies with rabbit cardiac fibroblasts demonstrated that the membrane was biocompatible and inhibited cell infiltration. Further application of the membrane in a rabbit cardiac adhesion model revealed that the membrane was resorbed gradually and effectively resisted the sternal and epicardial adhesions. Interestingly, six months after the operation, the GT/PCL membrane was completely resorbed with simultaneous ingrowth of host cells to form a natural barrier. Collectively, these results indicated that the GT/PCL membrane might be a suitable barrier to prevent sternal and epicardial adhesions and might be utilized as a novel pericardial substitute for cardiac surgery. STATEMENT OF SIGNIFICANCE: Electrospinning is a versatile method to prepare nanofibrous membranes for tissue engineering and regenerative medicine applications. However, with the micro-/nano-scale structure and high porosity, the electrospun membrane might be an excellent candidate as a barrier to prevent postoperative adhesion. Here we prepared an electropun GT/PCL nanofibrous membrane and applied it as a barrier to prevent sternal and epicardial adhesions. Our results showed that the membrane had sufficient mechanical strength, good biocompatibility, and effectively resisted the sternal and epicardial adhesions. What's more, the membrane was bioresorbable and allowed simultaneous ingrowth of host cells to form a natural barrier. We believe that the current will inspire more research on nanomaterials to prevent postoperative adhesion applications.

Background— Heart development is tightly regulated by signaling events acting on a defined number of progenitor and differentiated cardiac cells. Although loss of function of these signaling pathways leads to congenital malformation, the consequences of cardiac progenitor cell or embryonic cardiomyocyte loss are less clear. In this study, we tested the hypothesis that embryonic mouse hearts exhibit a robust mechanism for regeneration after extensive cell loss. Methods and Results— By combining a conditional cell ablation approach with a novel blastocyst complementation strategy, we generated murine embryos that exhibit a full spectrum of cardiac progenitor cell or cardiomyocyte ablation. Remarkably, ablation of up to 60% of cardiac progenitor cells at embryonic day 7.5 was well tolerated and permitted embryo survival. Ablation of embryonic cardiomyocytes to a similar degree (50% to 60%) at embryonic day 9.0 could be fully rescued by residual myocytes with no obvious adult cardiac functional deficit. In both ablation models, an increase in cardiomyocyte proliferation rate was detected and accounted for at least some of the rapid recovery of myocardial cellularity and heart size. Conclusion— Our study defines the threshold for cell loss in the embryonic mammalian heart and reveals a robust cardiomyocyte compensatory response that sustains normal fetal development.

Human pluripotent stem-cell derived cardiomyocytes (hPSC-CMs) hold great promise for applications in human disease modeling, drug discovery, cardiotoxicity screening, and, ultimately, regenerative medicine. The ability to study multiple parameters of hPSC-CM function, such as contractile and electrical activity, calcium cycling, and force generation, is therefore of paramount importance. hPSC-CMs cultured on stiff substrates like glass or polystyrene do not have the ability to shorten during contraction, making them less suitable for the study of hPSC-CM contractile function. Other approaches require highly specialized hardware and are difficult to reproduce. Here we describe a protocol for the preparation of hPSC-CMs on soft substrates that enable shortening, and subsequently the simultaneous quantitative analysis of their contractile and electrical activity, calcium cycling, and force generation at single-cell resolution. This protocol requires only affordable and readily available materials and works with standard imaging hardware. © 2017 by John Wiley & Sons, Inc.

Cardiac myocytes (CMs) obtained by differentiating embryonic stem cells (ES-CMs) have an immature phenotype and promoting the maturation of such PSC-derived cardiomyocytes remains a major limitation in the development of stem cell models of human cardiovascular disease. We cultured murine ES-CMs in a collagen gel (3D) at a low density, or on collagen-coated polystyrene (2D) and found that 3D culture results in dramatic improvement of the maturation rate and end-state gene expression of ES-CMs. There are two main differences between CMs cultured in 3D versus 2D; in 3D the mechanical stiffness of the environment is lower, enabling auxotonic instead of isometric contraction; and, in 3D the amount of cell-cell interaction is higher. To isolate the contributions, we first cultured ES-CMs on gels (2D substrates) that are softer than tissue culture plastic, enabling auxotonic contraction, while controlling for dimensionality and cell interaction. This indeed promoted a mature gene expression profile, while also enabling the maintenance of sarcomeres. Next, we determined that increased cell-cell interaction inhibits the mature gene expression of ES-CMs. Thus, auxotonic contraction is the likely mechanism for improved gene expression in sub-confluent 3D culture. However, 2D auxotonic contraction may offer a suitable compromise between obtaining enhanced gene expression and morphology. After 6 weeks of culture on gels, via Di-8-ANEPPs and WGA staining we also detected CMs forming a t-tubule network. Collectively these results demonstrate that 3D and 2D cultures that enable auxotonic contraction enhance aspects of the maturation of ES-CMs.

The immature phenotype of human pluripotent stem cell derived cardiomyocytes (hPSC-CMs) constrains their potential in cell therapy and drug testing. In this study, we report that shifting hPSC-CMs from glucose-containing to galactose- and fatty acid-containing medium promotes their fast maturation into adult-like CMs with higher oxidative metabolism, transcriptional signatures closer to those of adult ventricular tissue, higher myofibril density and alignment, improved calcium handling, enhanced contractility, and more physiological action potential kinetics. Integrated “-Omics” analyses showed that addition of galactose to culture medium improves total oxidative capacity of the cells and ameliorates fatty acid oxidation avoiding the lipotoxicity that results from cell exposure to high fatty acid levels. This study provides an important link between substrate utilization and functional maturation of hPSC-CMs facilitating the application of this promising cell type in clinical and preclinical applications., Scientific Reports, 7, ISSN:2045-2322

Acute myocardial infarction is a leading cause of cardiac dysfunction and heart failure. As a result, developing in vitro models of myocardial ischemia has been important for the elucidation of the mechanisms of hypoxic injury and the development of novel cardioprotective strategies. During acute ischemia, cardiac injury occurs in minutes to hours in vivo but in hours to days in vitro. This difference in response to ischemia is compounded by differences in cardiomyocytes’ (CMs) metabolism and substrate utilization under standard in vitro growth conditions. An important challenge in modeling ischemia has been to faithfully recapitulate the in vivo cellular response to hypoxic stress. To address this limitation, we have performed comprehensive phenotypic characterization of myocardial metabolism and contractile functions in vitro during normoxia and hypoxia under different metabolic conditions. We show that, unlike CMs in the adult heart, adult murine CMs and hPSC-CMs cultured in glucose as the primary energy source utilize aerobic glycolysis and not oxidative phosphorylation (OXPHOS) for ATP generation. In contrast, CMs cultured with fatty acids as the primary energy source are dependent on OXPHOS for ATP generation and contractile function. Consistent with these findings, only CMs cultured in fatty acid have an acute drop in ATP production and contractility in response to hypoxia. We then show that by modulating the transcriptional activity of hypoxia-inducible factor 1-alpha, its upstream regulator sirtuin, and its downstream target lactate dehydrogenase A, CMs cultured in glucose shift their metabolism from glycolysis to the more metabolically appropriate OXPHOS. Collectively, our results provide novel mechanistic insights into the key regulatory pathways that control hPSC-CMs’ energy metabolism and highlight the significance of comprehensive characterization of CMs’ metabolic and functional responses to ischemic stress in vitro. By creating in vitro models of ischemic injury that can faithfully recapitulate cellular responses of myocardial infarction, it is then possible to identify relevant therapeutic targets for the treatment the disease.

Three-dimensional (3D) cultures of human pluripotent stem cell derived cardiomyocytes (hPSC-CMs) hold great promise for drug discovery, providing a better approximation to the in vivo physiology over standard two-dimensional (2D) monolayer cultures. However, the transition of CM differentiation protocols from 2D to 3D cultures is not straightforward. In this work, we relied on the aggregation of hPSC-derived cardiac progenitors and their culture under agitated conditions to generate highly pure cardiomyocyte aggregates. Whole-transcriptome analysis and 13 C-metabolic flux analysis allowed to demonstrate at both molecular and fluxome levels that such 3D culture environment enhances metabolic maturation of hiPSC-CMs. When compared to 2D, 3D cultures of hiPSC-CMs displayed down-regulation of genes involved in glycolysis and lipid biosynthesis and increased expression of genes involved in OXPHOS. Accordingly, 3D cultures of hiPSC-CMs had lower fluxes through glycolysis and fatty acid synthesis and increased TCA-cycle activity. Importantly, we demonstrated that the 3D culture environment reproducibly improved both CM purity and metabolic maturation across different hPSC lines, thereby providing a robust strategy to derive enriched hPSC-CMs with metabolic features closer to that of adult CMs.

Background— Restrictive cardiomyopathy (RCM) is a rare cardiomyopathy characterized by impaired diastolic ventricular function resulting in a poor clinical prognosis. Rarely, heritable forms of RCM have been reported, and mutations underlying RCM have been identified in genes that govern the contractile function of the cardiomyocytes. Methods and Results— We evaluated 8 family members across 4 generations by history, physical examination, electrocardiography, and echocardiography. Affected individuals presented with a pleitropic syndrome of progressive RCM, atrioventricular septal defects, and a high prevalence of atrial fibrillation. Exome sequencing of 5 affected members identified a single novel missense variant in a highly conserved residue of FLNC (filamin C; p.V2297M). FLNC encodes filamin C—a protein that acts as both a scaffold for the assembly and organization of the central contractile unit of striated muscle and also as a mechanosensitive signaling molecule during cell migration and shear stress. Immunohistochemical analysis of FLNC localization in cardiac tissue from an affected family member revealed a diminished localization at the z disk, whereas traditional localization at the intercalated disk was preserved. Stem cell-derived cardiomyocytes mutated to carry the effect allele had diminished contractile activity when compared with controls. Conclusion— We have identified a novel variant in FLNC as pathogenic variant for familial RCM—a finding that further expands on the genetic basis of this rare and morbid cardiomyopathy.

Contains fulltext : 182343.pdf (Publisher’s version ) (Closed access) In response to heart failure (HF), the heart reacts by repressing adult genes and expressing fetal genes, thereby returning to a more fetal-like gene profile. To identify genes involved in this process, we carried out transcriptional analysis on murine hearts at different stages of development and on hearts from adult mice with HF. Our screen identified Oplah, encoding for 5-oxoprolinase, a member of the gamma-glutamyl cycle that functions by scavenging 5-oxoproline. OPLAH depletion occurred as a result of cardiac injury, leading to elevated 5-oxoproline and oxidative stress, whereas OPLAH overexpression improved cardiac function after ischemic injury. In HF patients, we observed elevated plasma 5-oxoproline, which was associated with a worse clinical outcome. Understanding and modulating fetal-like genes in the failing heart may lead to potential diagnostic, prognostic, and therapeutic options in HF.

The extracellular matrix (ECM) is the non-cellular component of all tissues consisting of many different bioactive macromolecules including proteins, proteoglycans, glycoproteins and gradients of growth factors. It is a highly complex and dynamic structure that is subject to constant remodeling in vivo. The ECM not only provides essential structural support for tissues and cell layers but also modulates molecular and biomechanical signaling cues.[1-4] ECM composition is tightly regulated during normal development and hemostasis and varies with tissue type as well as developmental stage. Hearts of different developmental stages have significant differences in ECM composition and elasticity.[5, 6] Dysregulation of the ECM has also been shown to result in human aortic and connective tissue diseases.[7] In addition, ECM has been shown to control cell behavior and function through its elasticity, topography, and dimensionality. In vitro, culture surface stiffness has been shown to directly control the lineage commitment of mesenchymal stem cells.[8, 9]

Rationale: Cardiogenesis is regulated by a complex interplay between transcription factors. However, little is known about how these interactions regulate the transition from mesodermal precursors to cardiac progenitor cells (CPCs). Objective: To identify novel regulators of mesodermal cardiac lineage commitment. Methods and Results: We performed a bioinformatic-based transcription factor binding site analysis on upstream promoter regions of genes that are enriched in embryonic stem cell–derived CPCs. From 32 candidate transcription factors screened, we found that Yin Yang 1 (YY1), a repressor of sarcomeric gene expression, is present in CPCs in vivo. Interestingly, we uncovered the ability of YY1 to transcriptionally activate Nkx2.5, a key marker of early cardiogenic commitment. YY1 regulates Nkx2.5 expression via a 2.1-kb cardiac-specific enhancer as demonstrated by in vitro luciferase-based assays, in vivo chromatin immunoprecipitation, and genome-wide sequencing analysis. Furthermore, the ability of YY1 to activate Nkx2.5 expression depends on its cooperative interaction with Gata4 at a nearby chromatin. Cardiac mesoderm–specific loss-of-function of YY1 resulted in early embryonic lethality. This was corroborated in vitro by embryonic stem cell–based assays in which we showed that the overexpression of YY1 enhanced the cardiogenic differentiation of embryonic stem cells into CPCs. Conclusions: These results demonstrate an essential and unexpected role for YY1 to promote cardiogenesis as a transcriptional activator of Nkx2.5 and other CPC-enriched genes.

In this essay the authors argue that chamber pressure dominates the biomechanics of the contraction cycle of the heart, while tissue stiffness dominates the relaxation cycle. This appears to be an under-recognized challenge in cardiac tissue engineering. Optimal approaches will involve constructing chambers or modulating the stiffness of the scaffold/substrate in synchrony with the beating cycle.

The promise of cardiac tissue engineering is in the ability to recapitulate in vitro the functional aspects of a healthy heart and disease pathology as well as to design replacement muscle for clinical therapy. Parts of this promise have been realized; others have not. In a meeting of scientists in this field, five central challenges or “big questions” were articulated that, if addressed, could substantially advance the current state of the art in modeling heart disease and realizing heart repair.

Summary The transcriptional regulator CITED2 is essential for heart development. Here, we investigated the role of CITED2 in the specification of cardiac cell fate from mouse embryonic stem cells (ESC). The overexpression of CITED2 in undifferentiated ESC was sufficient to promote cardiac cell emergence upon differentiation. Conversely, the depletion of Cited2 at the onset of differentiation resulted in a decline of ESC ability to generate cardiac cells. Moreover, loss of Cited2 expression impairs the expression of early mesoderm markers and cardiogenic transcription factors (Isl1, Gata4, Tbx5). The cardiogenic defects in Cited2-depleted cells were rescued by treatment with recombinant CITED2 protein. We showed that Cited2 expression is enriched in cardiac progenitors either derived from ESC or mouse embryonic hearts. Finally, we demonstrated that CITED2 and ISL1 proteins interact physically and cooperate to promote ESC differentiation toward cardiomyocytes. Collectively, our results show that Cited2 plays a pivotal role in cardiac commitment of ESC., Graphical Abstract, Highlights • Overexpression of CITED2 in ESC promotes cardiogenesis upon differentiation • Cited2 depletion reduces ESC ability to generate cardiac cells • Cited2 expression is enriched in cardiac progenitors • CITED2 and ISL1 cooperate to promote ESC differentiation toward cardiomyocytes, In this article, Bragança and colleagues show that the transcriptional regulator Cited2 is essential for cardiac commitment of mouse embryonic stem cells (ESC), and its depletion in ESC impairs the expression of early mesoderm markers and cardiogenic transcription factors. In addition, they demonstrate that CITED2 and ISL1 proteins interact and cooperate to promote ESC differentiation toward cardiomyocytes.

Cardiomyocytes derived from pluripotent stem cells can be applied in drug testing, disease modeling and cell-based therapy. However, without procardiogenic growth factors, the efficiency of cardiomyogenesis from pluripotent stem cells is usually low and the resulting cardiomyocyte population is heterogeneous. Here, we demonstrate that induced pluripotent stem cells (iPSCs) can be derived from murine ventricular myocytes (VMs), and consistent with other reports of iPSCs derived from various somatic cell types, VM-derived iPSCs (ViPSCs) exhibit a markedly higher propensity to spontaneously differentiate into beating cardiomyocytes as compared to genetically matched embryonic stem cells (ESCs) or iPSCs derived from tail-tip fibroblasts. Strikingly, the majority of ViPSC-derived cardiomyocytes display a ventricular phenotype. The enhanced ventricular myogenesis in ViPSCs is mediated via increased numbers of cardiovascular progenitors at early stages of differentiation. In order to investigate the mechanism of enhanced ventricular myogenesis from ViPSCs, we performed global gene expression and DNA methylation analysis, which revealed a distinct epigenetic signature that may be involved in specifying the VM fate in pluripotent stem cells.

The past few years have witnessed remarkable advances in stem cell biology and human genetics, and we have arrived at an era in which patient-specific cell and tissue models are now practical. The recent identification of cardiovascular progenitor cells, as well as the identification of genetic variants underlying congenital heart disorders and adult disease, opens the door to the development of human models of human cardiovascular disease. We review the current understanding of the contribution of progenitor cells to cardiogenesis and outline how pluripotent stem cells can be applied to the modeling of cardiovascular disorders of genetic origin. A key challenge will be to implement these models in an efficient manner to develop a molecular understanding of how genes lead to disease and to screen for genes and drugs that modify the disease process.

TJ was a pre-doctoral fellow of Fundacao para a Ciencia e Tecnologia (FCT; SFRH/BD/82280/2011), JFO (SFRH/BPD/46506/2008), JI (CEDOC/2015/36/iNOVA4Health/Multi/04462) and PNGP (SFRH/BPD/87114/2012) are FCT post-doctoral fellows. This work was supported by FCT grants (PTDC/SAU-ENB/121095/2010 and HMSP-ICT/0039/2013) to JA Belo. iNOVA4Health - UID/Multi/04462/2013, a program financially supported by Fundacao para a Ciencia e Tecnologia / Ministerio da Educacao e Ciencia, through national funds and co-funded by FEDER under the PT2020 Partnership Agreement is acknowledged. Understanding the molecular pathways regulating cardiogenesis is crucial for the early diagnosis of heart diseases and improvement of cardiovascular disease. During normal mammalian cardiac development, collagen and calcium-binding EGF domain-1 (Ccbe1) is expressed in the first and second heart field progenitors as well as in the proepicardium, but its role in early cardiac commitment remains unknown. Here we demonstrate that during mouse embryonic stem cell (ESC) differentiation Ccbe1 is upregulated upon emergence of Isl1- and Nkx2.5- positive cardiac progenitors. Ccbe1 is markedly enriched in Isl1-positive cardiac progenitors isolated from ESCs differentiating in vitro or embryonic hearts developing in vivo. Disruption of Ccbe1 activity by shRNA knockdown or blockade with a neutralizing antibody results in impaired differentiation of embryonic stem cells along the cardiac mesoderm lineage resulting in a decreased expression of mature cardiomyocyte markers. In addition, knockdown of Ccbe1 leads to smaller embryoid bodies. Collectively, our results show that CCBE1 is essential for the commitment of cardiac mesoderm and consequently, for the formation of cardiac myocytes in differentiating mouse ESCs. publishersversion published

Aims Atrial natriuretic peptide (ANP), secreted primarily by atrial cardiomyocytes, decreases blood pressure by raising cyclic 3’,5’-guanosine monophosphate (cGMP) levels and inducing vasorelaxation, natriuresis, and diuresis. Raising the level of ANP has been shown to be an effective treatment for hypertension. To advance the future development of an anti-microRNA (miR) approach to increasing expression of ANP, we investigated the regulation of NPPA expression by two miRs: miR-425 and miR-155. We examined whether miR-425 and miR-155 have an additive effect on the expression and function of ANP. Methods and results Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) were transfected with miR-425, miR-155, or a combination of the two miRs. Two days later, NPPA expression was measured using real time qPCR. Each of the miRs decreased NPPA expression over a wide range of concentrations, with a significant reduction at concentrations as low as 1 nM. The combination of miR-425 and miR-155 reduced NPPA expression to a greater extent than either miR-425 or miR-155 alone. An in vitro assay was developed to study the potential biological significance of the miR-induced decrease in NPPA expression. The cooperative effect of miR-425 and miR-155 on NPPA expression was associated with a significant decrease in cGMP levels. Conclusions These data demonstrate that miR-425 and miR-155 regulate NPPA expression in a cooperative manner. Targeting both miRNAs with anti-miRs (possibly at submaximal concentrations) might prove to be a more effective strategy to modulate ANP levels, and thus blood pressure, than targeting either miRNA alone.

A Fix to the Heart Regenerative cardiovascular medicine is a promising avenue for therapeutic application in advanced heart failure. Although clinical trials have suggested some limited benefits in cell transplantation therapy, robust cardiac muscle formation is lacking. Domian et al. (p. 426 ) examined the developmental processes in normal mature cardiac muscle. A two-color murine reporter system was used to isolate committed ventricular progenitors, which were then used to build functional force-generating cardiac tissue. Such combinations of tissue engineering and stem cell biology may eventually lead to cardiac regenerative therapy.

The generation and expansion of diverse cardiovascular cell lineages is a critical step during human cardiogenesis, with major implications for congenital heart disease. Unravelling the mechanisms for the diversification of human heart cell lineages has been hampered by the lack of genetic tools to purify early cardiac progenitors and define their developmental potential. Recent studies in the mouse embryo have identified a multipotent cardiac progenitor that contributes to all of the major cell types in the murine heart. In contrast to murine development, human cardiogenesis has a much longer onset of heart cell lineage diversification and expansion, suggesting divergent pathways. Here we identify a diverse set of human fetal ISL1(+) cardiovascular progenitors that give rise to the cardiomyocyte, smooth muscle and endothelial cell lineages. Using two independent transgenic and gene-targeting approaches in human embryonic stem cell lines, we show that purified ISL1(+) primordial progenitors are capable of self-renewal and expansion before differentiation into the three major cell types in the heart. These results lay the foundation for the generation of human model systems for cardiovascular disease and novel approaches for human regenerative cardiovascular medicine.

The heart is a complex organ system composed of a highly diverse set of muscle and nonmuscle cells. Understanding the pathways that drive the formation, migration, and assembly of these cells into the heart muscle tissue, the pacemaker and conduction system, and the coronary vasculature is a central problem in developmental biology. Efforts to unravel the biological complexity of in vivo cardiogenesis have identified a family of closely related multipotent cardiac progenitor cells. These progenitors must respond to non–cell-autonomous signaling cues to expand, differentiate, and ultimately integrate into the three-dimensional heart structures. Coupling tissue-engineering technologies with patient-specific cardiac progenitor biology holds great promise for the development of human cell models of human disease and may lay the foundation for novel approaches in regenerative cardiovascular medicine.

The heart is formed from cardiogenic progenitors expressing the transcription factors Nkx2-5 and Isl1 (refs 1 and 2). These multipotent progenitors give rise to cardiomyocyte, smooth muscle and endothelial cells, the major lineages of the mature heart. Here we identify a novel cardiogenic precursor marked by expression of the transcription factor Wt1 and located within the epicardium-an epithelial sheet overlying the heart. During normal murine heart development, a subset of these Wt1(+) precursors differentiated into fully functional cardiomyocytes. Wt1(+) proepicardial cells arose from progenitors that express Nkx2-5 and Isl1, suggesting that they share a developmental origin with multipotent Nkx2-5(+) and Isl1(+) progenitors. These results identify Wt1(+) epicardial cells as previously unrecognized cardiomyocyte progenitors, and lay the foundation for future efforts to harness the cardiogenic potential of these progenitors for cardiac regeneration and repair.

Atrial natriuretic peptide (ANP) has a central role in regulating blood pressure in humans. Recently, microRNA 425 (miR-425) was found to regulate ANP production by binding to the mRNA of NPPA, the gene encoding ANP. mRNAs typically contain multiple predicted microRNA (miRNA)-binding sites, and binding of different miRNAs may independently or coordinately regulate the expression of any given mRNA. We used a multifaceted screening strategy that integrates bioinformatics, next-generation sequencing data, human genetic association data, and cellular models to identify additional functional NPPA-targeting miRNAs. Two novel miRNAs, miR-155 and miR-105, were found to modulate ANP production in human cardiomyocytes and target genetic variants whose minor alleles are associated with higher human plasma ANP levels. Both miR-155 and miR-105 repressed NPPA mRNA in an allele-specific manner, with the minor allele of each respective variant conferring resistance to the miRNA either by disruption of miRNA base pairing or by creation of wobble base pairing. Moreover, miR-155 enhanced the repressive effects of miR-425 on ANP production in human cardiomyocytes. Our study combines computational, genomic, and cellular tools to identify novel miRNA regulators of ANP production that could be targeted to raise ANP levels, which may have applications for the treatment of hypertension or heart failure.

The extracellular matrix (ECM) impacts stem cell differentiation, but identifying formulations supportive of differentiation is challenging in 3D models. Prior efforts involving combinatorial ECM arrays seemed intuitively advantageous. We propose an alternative that suggests reducing sample size and technological burden can be beneficial and accessible when coupled to design of experiments approaches. We predict optimized ECM formulations could augment differentiation of cardiomyocytes derived in vitro. We employed native chemical ligation to polymerize 3D poly (ethylene glycol) hydrogels under mild conditions while entrapping various combinations of ECM and murine induced pluripotent stem cells. Systematic optimization for cardiomyocyte differentiation yielded a predicted solution of 61%, 24% and 15% of collagen type I, laminin-111 and fibronectin, respectively. This solution was confirmed by increased numbers of cardiac troponin T, α-myosin heavy chain and α-sarcomeric actinin-expressing cells relative to suboptimum solutions. Cardiomyocytes of composites exhibited connexin43 expression, appropriate contractile kinetics and intracellular calcium handling. Further, adding a modulator of adhesion, thrombospondin-1, abrogated cardiomyocyte differentiation. Thus, the integrated biomaterial platform statistically identified an ECM formulation best supportive of cardiomyocyte differentiation. In future, this formulation could be coupled with biochemical stimulation to improve functional maturation of cardiomyocytes derived in vitro or transplanted in vivo.

The cardiac natriuretic peptides (NPs), atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), have central roles in sodium and blood pressure regulation. Extracardiac factors (e.g., obesity and diabetes) influence NP production, potentially altering cardiovascular responses to volume and pressure stress.This study examined the effects of acute carbohydrate intake on the NP system in humans, and investigated underlying mechanisms.Normotensive subjects (N = 33) were given a high-carbohydrate shake. Venous blood was sampled to measure N-terminal (NT)-proANP and NT-proBNP levels. Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) and HepG2 cells were treated with glucose, and expression levels of NPs and micro ribonucleic acid 425 (miR-425), a negative regulator of ANP, were examined. The role of nuclear factor kappa B (NF-κB) in the glucose-mediated effects was investigated using a NF-κB inhibitor and expression plasmids encoding NF-κB subunits.We observed a 27% reduction in the levels of circulating NT-proANP (p 0.001, maximal at 6 h) after carbohydrate challenge, with no effect on NT-proBNP levels in our human subjects. Glucose treatment of hESC-CMs for 6 h and 24 h increased levels of the primary transcript of miR-425 (pri-miR-425) and mature miR-425. A corresponding decrease in NPPA messenger RNA levels was also observed at both time points. Overexpression of NF-κB subunits in H9c2 cardiomyocytes increased miR-425 levels, whereas inhibition of NF-κB abrogated the glucose-mediated increase in pri-miR-425 levels in HepG2 cells.Acute carbohydrate challenge is associated with a reduction in ANP production. The mechanism appears to involve a glucose-induced increase in the expression of miR-425, mediated by NF-κB signaling.

Introduction: The minor allele of a common variant (rs5068) in the 3’UTR of NPPA, the gene encoding atrial natriuretic peptide (ANP), is associated with increased plasma ANP levels, lower blood pressure, and reduced risk of hypertension. A microRNA (miR-425) expressed in the human heart binds to a sequence spanning rs5068 for the major but not the minor allele leading to reduced ANP biosynthesis. mRNAs typically contain multiple miR-binding sites, and binding of different miRs often coordinately regulates the function of any given mRNA. Hypothesis: We hypothesize that miRs, in addition to miR-425, target NPPA mRNA and that interference with miR-based silencing of NPPA mRNA using miR antagonists (antimiRs) could be used to increase ANP biosynthesis. Methods: Luciferase reporter assays were used to screen 10 miRs that are predicted in silico to interact with the NPPA 3’UTR. The expression levels of validated miRs in human atria were determined. Human cardiomyocyte progenitor cells (hCMPCs) or human embryonic stem cell (HUES 9)-derived cardiomyocytes (hESC-CMs) were transfected with antimiRs targeting the validated miRs, and the levels of NPPA mRNA were measured. Results: Of the 10 miRs predicted in silico to interact with the NPPA 3’UTR, we identified 3 miRs (miRs-103, -105, and -107) that reduced luciferase activity in cells containing a luciferase-NPPA 3’UTR construct (miR-103, p=0.034; miR-105, p=0.0009; and miR-107, p=0.021), but the miRs had no effect on luciferase activity in cells containing a luciferase construct in which the predicted miR-binding site in the NPPA 3’UTR was mutated. Using qRT-PCR, the three miRs were detected in human atria. Transfection of an antimiR directed against miR-103, miR-105, or miR-107 increased NPPA mRNA levels in hCMPCs (antimiR-103, p=0.024; antimiR-105, p=0.039; and antimiR-107, p=0.036). Similar results were observed in hESC-CMs. Conclusions: Our studies suggest that miRs-103, -105, and -107 regulate NPPA expression in human cardiomyocytes. AntimiRs directed against these miRs increased NPPA mRNA in human cardiomyocytes. AntimiR-based methods to increase ANP levels may represent a novel approach to the treatment of hypertension.

Introduction: A hallmark of Heart Failure (HF) is the re-emergence of the fetal gene program. The aim of this study was to identify novel genes associated with the fetal gene program in HF, by utilizing a mouse embryonic stem (mES) cell based micro-array. Methods/Results: The micro-array analysis was performed on mES cells, early and late mES-derived cardiac progenitors, and mouse neonatal right ventricular tissue. As expected, our screen effectively identified established fetal genes, including alpha smooth muscle actin. We further uncovered several novel genes behaving like fetal genes. The top 5 hits were validated in an in vivo pressure overload HF model. 5-oxoprolinase (OPLAH) was found to be the most significantly differentially expressed gene in the HF model. In a human organ panel, OPLAH gene expression was highest in cardiac tissue, and found to be expressed mainly in the cytosol of cardiomyocytes. Additionally OPLAH protein levels were reduced by 50-70% in both pressure overload and ischemia induced HF (p=0.001 and p=0.009, respectively). OPLAH is an ATP-hydrolyzing enzyme involved in the γ-Glutamyl cycle, responsible for the conversion of the metabolite 5-oxoproline into glutamate. To study OPLAH function we used siRNA and/or over-expression by means of viral transfection of neonatal rat ventricular myocytes. In vitro silencing of OPLAH resulted in an increased susceptibility towards oxidative stress induced apoptosis (40% increase in cleaved caspase-3 positive cells, p=0.02). Furthermore, exogenous administration of 5-oxoproline increased apoptosis in cardiomyocytes (40% increase in cleaved caspase-3 positive cells, p=0.04). Conclusions: We identified OPLAH as a novel enzyme associated with HF, behaving like fetal genes, which is involved in the innate protection against oxidative stress, by scavenging excess 5-oxoproline.

Controlled proliferation of cardiac myocytes remains a major limitation in cell biology and one of the main underlying hurdles for true modern regenerative medicine. Here we provide a technique to robustly expand early fetal-derived mouse ventricular cardiomyocytes on a platform usable for high-throughput molecular screening, tissue engineering or potentially useful for in vivo translational experiments. This method provides a small molecule-based approach to control proliferation or differentiation of early beating cardiac myocytes through modulation of the Wnt/β-catenin signaling pathway. Moreover isolation and expansion of fetal cardiomyocytes takes less than 3 weeks, yields a relatively pure (~70%) functional myogenic population and is highly reproducible.

Summary Stem cell-derived cardiomyocytes represent unique tools for cell- and tissue-based regenerative therapies, drug discovery and safety, and studies of fundamental heart-failure mechanisms. However, the degree to which stem cell-derived cardiomyocytes compare to mature cardiomyocytes is often debated. We reasoned that physiological metrics of engineered cardiac tissues offer a means of comparison. We built laminar myocardium engineered from cardiomyocytes that were differentiated from mouse embryonic stem cell-derived cardiac progenitors or harvested directly from neonatal mouse ventricles, and compared their anatomy and physiology in vitro. Tissues assembled from progenitor-derived myocytes and neonate myocytes demonstrated similar cytoskeletal architectures but different gap junction organization and electromechanical properties. Progenitor-derived myocardium had significantly less contractile stress and slower longitudinal conduction velocity than neonate-derived myocardium, indicating that the developmental state of the cardiomyocytes affects the electromechanical function of the resultant engineered tissue. These data suggest a need to establish performance metrics for future stem cell applications., Graphical Abstract, Highlights • Engineered myocardium was compared with progenitor-derived and neonatal myocytes • Progenitor-derived and neonatal myocytes had similar sarcomere and actin structure • Progenitor-derived tissue had significantly slower conduction velocity than neonate • Progenitor-derived tissue generated significantly less contractile stress than neonate, Parker and colleagues engineered myocardium from cardiomyocytes either differentiated from mouse embryonic stem cell-derived cardiac progenitors or harvested directly from neonatal mouse ventricles, and compared their anatomy and physiology in vitro. Results show the ability to build structurally similar tissues, but the progenitor-derived myocardium had significantly lower conduction velocity and contractile stress generation than the neonatal myocardium.

Advanced heart failure represents a major unmet clinical challenge, arising from the loss of viable and/or fully functional cardiac muscle cells. Despite optimum drug therapy, heart failure represents a leading cause of mortality and morbidity in the developed world. A major challenge in drug development is the identification of cellular assays that accurately recapitulate normal and diseased human myocardial physiology in vitro. Likewise, the major challenges in regenerative cardiac biology revolve around the identification and isolation of patient-specific cardiac progenitors in clinically relevant quantities. These cells have to then be assembled into functional tissue that resembles the native heart tissue architecture. Microcontact printing allows for the creation of precise micropatterned protein shapes that resemble structural organization of the heart, thus providing geometric cues to control cell adhesion spatially. Herein we describe our approach for the isolation of highly purified myocardial cells from pluripotent stem cells differentiating in vitro, the generation of cell growth surfaces micropatterned with extracellular matrix proteins, and the assembly of the stem cell-derived cardiac muscle cells into anisotropic myocardial tissue.

The Caulobacter cell cycle exhibits time-dependent expression of differentiation events. These include the morphological transition of a swarmer cell to a replication-competent stalked cell and the subsequent polarized distribution of specific gene products that results in an asymmetric predivisional cell. Cell division then yields a new swarmer cell and a stem-cell-like stalked cell. Two-component signal transduction proteins involved in cell cycle control and proteins required for cell division and flagellar biogenesis have been shown to be regulated temporally and spatially during the cell cycle. The mechanisms underlying this regulation include protein phosphorylation and proteolysis.

Induced pluripotent cells (iPSCs) were first generated by the laboratory of Takahashi and Yamanaka1 in 2006 by reprogramming somatic cells into pluripotent stem cells capable of differentiating into any cell type. In a landmark series of experiments, the Yamanaka laboratory transduced mouse fibroblasts with retroviruses coding 4 transcription factors, the so-called reprogramming factors, Oct4, Sox2, c-Myc, and Klf4. Germline transmission of murine iPS cells was reported in the following year.2,3 Shortly thereafter, human iPSCs were derived, opening new avenues for regenerative medicine with autologous patient-specific cells.4,5 Article see p 667 These early approaches of iPS cell production uniformly involved the introduction of reprogramming genes with retroviral or lentiviral vectors. Accordingly, the reprogramming genes irreversibly integrated into the host genome at multiple poorly defined sites. Interestingly, the expression of these genes was largely silenced after iPSC induction, thereby allowing differentiation in vitro and in vivo. Nonetheless, it was known right from the second round of mouse iPS articles in 20072,3 that there is low residual expression of transgenes in reprogrammed cells. Because of this concern, inducible expression systems were developed with reduced likelihood of aberrant reprogramming gene expression. In all of these early strategies, however, the integrated reprogramming vectors remained in the host genome and could in principle become reactivated over time. Indeed, the laboratory of Yamanaka demonstrated that tumors arise in mice generated from iPS cells, and that the c-myc transgene (a classical oncogene) is reactivated in the tumor …

Cardiac malformations and disease are the leading causes of death in the United States in live-born infants and adults, respectively. In both of these cases, a decrease in the number of functional cardiomyocytes often results in improper growth of heart tissue, wound healing complications, and poor tissue repair. The field of cardiac tissue engineering seeks to address these concerns by developing cardiac patches created from a variety of biomaterial scaffolds to be used in surgical repair of the heart. These scaffolds should be fully degradable biomaterial systems with tunable properties such that the materials can be altered to meet the needs of both in vitro culture (e.g., disease modeling) and in vivo application (e.g., cardiac patch). Current platforms do not utilize both structural anisotropy and proper cell-matrix contacts to promote functional cardiac phenotypes and thus there is still a need for critically sized scaffolds that mimic both the structural and adhesive properties of native tissue. To address this need, we have developed a silk-based scaffold platform containing cardiac tissue-derived extracellular matrix (cECM). These silk-cECM composite scaffolds have tunable architectures, degradation rates, and mechanical properties. Subcutaneous implantation in rats demonstrated that addition of the cECM to aligned silk scaffold led to 99% endogenous cell infiltration and promoted vascularization of a critically sized scaffold (10 mm × 5 mm × 2.5 mm) after 4 weeks in vivo. In vitro, silk-cECM scaffolds maintained the HL-1 atrial cardiomyocytes and human embryonic stem cell-derived cardiomyocytes and promoted a more functional phenotype in both cell types. This class of hybrid silk-cECM anisotropic scaffolds offers new opportunities for developing more physiologically relevant tissues for cardiac repair and disease modeling.

The master CtrA response regulator functions in Caulobacter to repress replication initiation in different phases of the cell cycle. Here, we identify an essential histidine kinase, CckA, that is responsible for CtrA activation by phosphorylation. Although CckA is present throughout the cell cycle, it moves to a cell pole in S phase, and upon cell division it disperses. Removal of the membrane-spanning region of CckA results in loss of polar localization and cell death. We propose that polar CckA functions to activate CtrA just after the initiation of DNA replication, thereby preventing premature reinitiations of chromosome replication. Thus, dynamic changes in cellular location of critical signal proteins provide a novel mechanism for the control of the prokaryote cell cycle.

Caulobacter crescentus divides asymmetrically generating two distinct cell types at each cell division: a stalked cell competent for DNA replication, and a swarmer cell that is unable to initiate DNA replication until it differentiates into a stalked cell later in the cell cycle. The CtrA protein, a member of the response regulator family of the two-component signal transduction system, controls multiple cell cycle processes in Caulobacter and is present in swarmer cells but absent from stalked cells. We report that CtrA binds five sites within the chromosome replication origin in vitro . These sites overlap an essential DnaA box and a promoter in the origin that is essential for replication initiation. Analysis of mutant alleles of ctrA and point mutations in one of the CtrA binding sites in the origin demonstrate that CtrA represses replication in vivo . CtrA-mediated repression at the origin thus restricts replication to the stalked cell type. Thus, the direct coupling of chromosome replication with the cell cycle is mediated by the ubiquitous two-component signaling proteins.

The global transcriptional regulator CtrA controls multiple events in the Caulobacter cell cycle, including the initiation of DNA replication, DNA methylation, cell division, and flagellar biogenesis. CtrA is a member of the response regulator family of two component signal transduction systems and is activated by phosphorylation. We report here that this phosphorylation signal enters the cell cycle at mid S phase. In addition, CtrA function is modulated by temporally and spatially controlled proteolysis. When an active CtrA protein is present at the wrong time in the cell cycle, owing to expression of a mutant CtrA derivative that is active in the absence of phosphorylation and is not turned over during the cell cycle, the G1-to-S transition is blocked and the cell cycle aborts. Thus, both phosphorylation and proteolysis are critical determinants of bacterial cell cycle control in a manner that is analogous to the control of the eukaryotic cell cycle.