Background: The complex genetics underlying human cardiac disease is evidenced by its heterogenous manifestation, multigenic basis, and sporadic occurrence. These features have hampered disease modeling and mechanistic understanding. Here, we show that 2 structural cardiac diseases, left ventricular noncompaction (LVNC) and bicuspid aortic valve, can be caused by a set of inherited heterozygous gene mutations affecting the NOTCH ligand regulator MIB1 (MINDBOMB1) and cosegregating genes. Methods: We used CRISPR-Cas9 gene editing to generate mice harboring a nonsense or a missense MIB1 mutation that are both found in LVNC families. We also generated mice separately carrying these MIB1 mutations plus 5 additional cosegregating variants in the ASXL3, APCDD1, TMX3, CEP192, and BCL7A genes identified in these LVNC families by whole exome sequencing. Histological, developmental, and functional analyses of these mouse models were carried out by echocardiography and cardiac magnetic resonance imaging, together with gene expression profiling by RNA sequencing of both selected engineered mouse models and human induced pluripotent stem cell-derived cardiomyocytes. Potential biochemical interactions were assayed in vitro by coimmunoprecipitation and Western blot. Results: Mice homozygous for the MIB1 nonsense mutation did not survive, and the mutation caused LVNC only in heteroallelic combination with a conditional allele inactivated in the myocardium. The heterozygous MIB1 missense allele leads to bicuspid aortic valve in a NOTCH-sensitized genetic background. These data suggest that development of LVNC is influenced by genetic modifiers present in affected families, whereas valve defects are highly sensitive to NOTCH haploinsufficiency. Whole exome sequencing of LVNC families revealed single-nucleotide gene variants of ASXL3, APCDD1, TMX3, CEP192, and BCL7A cosegregating with the MIB1 mutations and LVNC. In experiments with mice harboring the orthologous variants on the corresponding Mib1 backgrounds, triple heterozygous Mib1 Apcdd1 Asxl3 mice showed LVNC, whereas quadruple heterozygous Mib1 Cep192 Tmx3;Bcl7a mice developed bicuspid aortic valve and other valve-associated defects. Biochemical analysis suggested interactions between CEP192, BCL7A, and NOTCH. Gene expression profiling of mutant mouse hearts and human induced pluripotent stem cell-derived cardiomyocytes revealed increased cardiomyocyte proliferation and defective morphological and metabolic maturation. Conclusions: These findings reveal a shared genetic substrate underlying LVNC and bicuspid aortic valve in which MIB1-NOTCH variants plays a crucial role in heterozygous combination with cosegregating genetic modifiers.

Transthyretin (TTR) amyloid cardiomyopathy (ATTR-CM) is a life-threatening disease caused by the abnormal production of misfolded TTR protein by liver cells, which is then released systemically. Its amyloid deposition in the heart is linked to cardiac toxicity and progression toward heart failure. A human induced pluripotent stem cell (iPSC) line was generated from peripheral blood mononuclear cells (PBMCs) from a patient suffering familial transthyretin amyloid cardio-myopathy carrying a c.128G>A (p.Ser43Asn) mutation in the TTR gene. This iPSC line offers a useful resource to study the disease pathophysiology and a cell-based model for therapeutic discovery.

Biofabrication of human tissues has seen a meteoric growth triggered by recent technical advancements such as human induced pluripotent stem cells (hiPSCs) and additive manufacturing. However, generation of cardiac tissue is still hampered by lack of adequate mechanical properties and crucially by the often unpredictable post-fabrication evolution of biological components. In this study we employ melt electrowriting (MEW) and hiPSC-derived cardiac cells to generate fibre-reinforced human cardiac minitissues. These are thoroughly characterized in order to build computational models and simulations able to predict their post-fabrication evolution. Our results show that MEW-based human minitissues display advanced maturation 28 post-generation, with a significant increase in the expression of cardiac genes such as MYL2, GJA5, SCN5A and the MYH7/MYH6 and MYL2/MYL7 ratios. Human iPSC-cardiomyocytes are significantly more aligned within the MEW-based 3D tissues, as compared to conventional 2D controls, and also display greater expression of C x43. These are also correlated with a more mature functionality in the form of faster conduction velocity. We used these data to develop simulations capable of accurately reproducing the experimental performance. In-depth gauging of the structural disposition (cellular alignment) and intercellular connectivity (C x43) allowed us to develop an improved computational model able to predict the relationship between cardiac cell alignment and functional performance. This study lays down the path for advancing in the development of in silico tools to predict cardiac biofabricated tissue evolution after generation, and maps the route towards more accurate and biomimetic tissue manufacture.

Adeno-associated viruses (AAV) have become one of the most promising tools for gene transfer in clinics. Among all the serotypes, AAV9 has been described as the most efficient for cardiac transduction. In order to achieve optimal therapeutic delivery in heart disease, we have explored AAV9 transduction efficiency in an infarcted heart using different routes of administration and promoters, including a cardiac-specific one. AAV9 vectors carrying luciferase or green fluorescence protein under the control of the ubiquitous elongation-factor-1-alpha or the cardiac-specific troponin-T (TnT) promoters were administered by intramyocardial or intravenous injection, either in healthy or myocardial-infarcted mice. The transduction efficacy and specificity, the time-course expression, and the safety of each vector were tested. High transgene expression levels were found in the heart, but not in the liver, of mice receiving AAV-TnT, which was significantly higher after intramyocardial injection regardless of ischemia-induction. On the contrary, high hepatic transgene expression levels were detected with the elongation-factor-1-alpha-promoter, independently of the administration route and heart damage. Moreover, tissue-specific green fluorescence protein expression was found in cardiomyocytes with the TnT vector, whereas minimal cardiac expression was detected with the ubiquitous one. Interestingly, we found that myocardial infarction greatly increased the transcriptional activity of AAV genomes. Our findings show that the use of cardiac promoters allows for specific and stable cardiac gene expression, which is optimal and robust when intramyocardially injected. Furthermore, our data indicate that the pathological status of the tissue can alter the transcriptional activity of AAV genomes, an aspect that should be carefully evaluated for clinical applications.

We generated a rat iPSC line called ATCi-rSD95 from transgenic Sprague-Dawley GFP fetal fibroblasts. Established ATCi-rSD95 cells present a normal karyotype, silencing of the transgenes and express pluripotency-associated markers. Additionally, ATCi-rSD95 cells are able to form teratoma with differentiated cells derived from the three germ-layers that maintain the GFP expression.

We generated two rat embryonic stem cell (ESC) lines: ATCe-SD7.8 from Sprague-Dawley strain and ATCe-WK1 from Wistar Kyoto strain. Cells were marked with enhanced green fluorescent protein (eGFP) by transduction with a lentiviral vector. Cells present a normal karyotype and express pluripotency-associated markers. Pluripotency was tested in vivo with the teratoma formation assay. Cells maintain eGFP expression upon differentiation to the three-germ layers. These cells can be a useful tool for cell therapy studies and chimera generation as they can be easily tracked by eGFP expression.

Mef2c Anterior Heart Field (AHF) enhancer is activated during embryonic heart development and it is expressed in multipotent cardiovascular progenitors (CVP) giving rise to endothelial and myocardial components of the outflow tract, right ventricle and ventricular septum. Here we have generated iPSC from transgenic Mef2c-AHF-Cre x Ai6(RCLZsGreen) mice. These iPSC will provide a novel tool to investigate the AHF-CVP and their cell progeny. (C) 2016 The Authors. Published by Elsevier B.V.

Stem cell-derived cardiomyocytes (CMs) are often electrophysiologically immature and heterogeneous, which represents a major barrier to their in vitro and in vivo application. Therefore, the purpose of this study was to examine whether Neuregulin-1 beta (NRG-1 beta) treatment could enhance in vitro generation of mature "working-type" CMs from induced pluripotent stem (iPS) cells and assess the regenerative effects of these CMs on cardiac tissue after acute myocardial infarction (AMI). With that purpose, adult mouse fibroblast-derived iPS from alpha-MHC-GFP mice were derived and differentiated into CMs through NRG-1 beta and/or dimethyl sulfoxide (DMSO) treatment. Cardiac specification and maturation of the iPS was analyzed by gene expression array, quantitative real-time polymerase chain reaction, immunofluorescence, electron microscopy, and patch-clamp techniques. In vivo, the iPS-derived CMs or culture medium control were injected into the peri-infarct region of hearts after coronary artery ligation, and functional and histology changes were assessed from 1 to 8 weeks post-transplantation. On differentiation, the iPS displayed early and robust in vitro cardiogenesis, expressing cardiac-specific genes and proteins. More importantly, electrophysiological studies demonstrated that a more mature ventricular-like cardiac phenotype was achieved when cells were treated with NRG-1 beta and DMSO compared with DMSO alone. Furthermore, in vivo studies demonstrated that iPS-derived CMs were able to engraft and electromechanically couple to heart tissue, ultimately preserving cardiac function and inducing adequate heart tissue remodeling. In conclusion, we have demonstrated that combined treatment with NRG-1 beta and DMSO leads to efficient differentiation of iPS into ventricular-like cardiac cells with a higher degree of maturation, which are capable of preserving cardiac function and tissue viability when transplanted into a mouse model of AMI.

Substrate stiffness, biochemical composition, and matrix topography deeply influence cell behavior, guiding motility, proliferation, and differentiation responses. The aim of this work was to determine the effect that the stiffness and protein composition of the underlying substrate has on the differentiation of induced pluripotent stem (iPS) cells and the potential synergy with specific soluble cues. With that purpose, murine iPS-derived embryoid bodies (iPS-EBs) were seeded on fibronectin- or collagen I-coated polyacrylamide (pAA) gels of tunable stiffness (0.6, 14, and 50 kPa) in the presence of basal medium; tissue culture polystyrene plates were employed as control. Specification of iPS cells toward the three germ layers was analyzed, detecting an increase of tissue-specific gene markers in the pAA matrices. Interestingly, soft matrix (0.6 kPa) coated with fibronectin favored differentiation toward cardiac and neural lineages and, in the case of neural differentiation, the effect was potentiated by the addition of specific soluble factors. The generation of mature astrocytes, neural cells, and cardiomyocytes was further proven by immunofluorescence and transmission electron microscopy. In summary, this work emphasizes the importance of using biomimetic matrices to accomplish a more specific and mature differentiation of stem cells for future therapeutic applications.

Infarcted hearts are macroscopically stiffer than healthy organs. Nevertheless, although cell behavior is mediated by the physical features of the cell niche, the intrinsic micromechanical properties of healthy and infarcted heart extracellular matrix (ECM) remain poorly characterized. Using atomic force microscopy, we studied ECM micromechanics of different histological regions of the left ventricle wall of healthy and infarcted mice. Hearts excised from healthy (n = 8) and infarcted mice (n = 8) were decellularized with sodium dodecyl sulfate and cut into 12 gm thick slices. Healthy ventricular ECM revealed marked mechanical heterogeneity across histological regions of the ventricular wall with the effective Young's modulus ranging from 30.2 +/- 2.8 to 74.5 +/- 8.7 kPa in collagen- and elastin-rich regions of the myocardium, respectively. Infarcted ECM showed a predominant collagen composition and was 3-fold stiffer than collagen-rich regions of the healthy myocardium. ECM of both healthy and infarcted hearts exhibited a solid-like viscoelastic behavior that conforms to two power-law rheology. Knowledge of intrinsic micromechanical properties of the ECM at the length scale at which cells sense their environment will provide further insight into the cell-scaffold interplay in healthy and infarcted hearts.