Trichostatin A enhances differentiation of human induced pluripotent stem cells to cardiogenic cells for cardiac tissue engineering

Microencapsulation-based cell therapies

Mapping a new therapeutic route can be fraught with challenges, but recent developments in the preparation and properties of small particles combined with significant improvements to tried and tested techniques offer refined cell targeting with tremendous translational potential. Regenerating new cells through the use of compounds that regulate epigenetic pathways represents an attractive approach that is gaining increased attention for the treatment of several diseases including Type 1 Diabetes and cardiomyopathy. However, cells that have been regenerated using epigenetic agents will still encounter immunological barriers as well as limitations associated with their longevity and potency during transplantation. Strategies aimed at protecting these epigenetically regenerated cells from the host immune response include microencapsulation. Microencapsulation can provide new solutions for the treatment of many diseases. In particular, it offers an advantageous method of administering therapeutic materials and molecules that cannot be substituted by pharmacological substances. Promising clinical findings have shown the potential beneficial use of microencapsulation for islet transplantation as well as for cardiac, hepatic, and neuronal repair. For the treatment of diseases such as type I diabetes that requires insulin release regulated by the patient's metabolic needs, microencapsulation may be the most effective therapeutic strategy. However, new materials need to be developed, so that transplanted encapsulated cells are able to survive for longer periods in the host. In this article, we discuss microencapsulation strategies and chart recent progress in nanomedicine that offers new potential for this area in the future.

Human iPSC-Cardiomyocytes as an Experimental Model to Study Epigenetic Modifiers of Electrophysiology

The epigenetic landscape and the responses to pharmacological epigenetic regulators in each human are unique. Classes of epigenetic writers and erasers, such as histone acetyltransferases, HATs, and histone deacetylases, HDACs, control DNA acetylation/deacetylation and chromatin accessibility, thus exerting transcriptional control in a tissue- and person-specific manner. Rapid development of novel pharmacological agents in clinical testing-HDAC inhibitors (HDACi)-targets these master regulators as common means of therapeutic intervention in cancer and immune diseases. The action of these epigenetic modulators is much less explored for cardiac tissue, yet all new drugs need to be tested for cardiotoxicity. To advance our understanding of chromatin regulation in the heart, and specifically how modulation of DNA acetylation state may affect functional electrophysiological responses, human-induced pluripotent stem-cell-derived cardiomyocyte (hiPSC-CM) technology can be leveraged as a scalable, high-throughput platform with ability to provide patient-specific insights. This review covers relevant background on the known roles of HATs and HDACs in the heart, the current state of HDACi development, applications, and any adverse cardiac events; it also summarizes relevant differential gene expression data for the adult human heart vs. hiPSC-CMs along with initial transcriptional and functional results from using this new experimental platform to yield insights on epigenetic control of the heart. We focus on the multitude of methodologies and workflows needed to quantify responses to HDACis in hiPSC-CMs. This overview can help highlight the power and the limitations of hiPSC-CMs as a scalable experimental model in capturing epigenetic responses relevant to the human heart.

4-phenylbutyrate exerts stage-specific effects on cardiac differentiation via HDAC inhibition

4-phenylbutyrate (4-PBA), a terminal aromatic substituted fatty acid, is used widely to specifically attenuate endoplasmic reticulum (ER) stress and inhibit histone deacetylases (HDACs). In this study, we investigated the effect of 4-PBA on cardiac differentiation of mouse embryonic stem (ES) cells. Herein, we found that 4-PBA regulated cardiac differentiation in a stage-specific manner just like trichostatin A (TSA), a well-known HDAC inhibitor. 4-PBA and TSA favored the early-stage differentiation, but inhibited the late-stage cardiac differentiation via acetylation. Mechanistic studies suggested that HDACs exhibited a temporal expression profiling during cardiomyogenesis. Hdac1 expression underwent a decrease at the early stage, while was upregulated at the late stage of cardiac induction. During the early stage of cardiac differentiation, acetylation favored the induction of Isl1 and Nkx2.5, two transcription factors of cardiac progenitors. During the late stage, histone acetylation induced by 4-PBA or TSA interrupted the gene silence of Oct4, a key determinant of self-renewal and pluripotency. Thereby, 4-PBA and TSA at the late stage hindered the exit from pluripotency, and attenuated the expression of cardiac-specific contractile proteins. Overexpression of HDAC1 and p300 exerted different effects at the distinct stages of cardiac induction. Collectively, our study shows that timely manipulation of HDACs exhibits distinct effects on cardiac differentiation. And the context-dependent effects of HDAC inhibitors depend on cell differentiation states marked by the temporal expression of pluripotency-associated genes.

Cardiac Differentiation of Mesenchymal Stem Cells: Impact of Biological and Chemical Inducers

Cardiovascular disorders (CVDs) are the leading cause of global death, widely occurs due to irreparable loss of the functional cardiomyocytes. Stem cell-based therapeutic approaches, particularly the use of Mesenchymal Stem Cells (MSCs) is an emerging strategy to regenerate myocardium and thereby improving the cardiac function after myocardial infarction (MI). Most of the current approaches often employ the use of various biological and chemical factors as cues to trigger and modulate the differentiation of MSCs into the cardiac lineage. However, the recent advanced methods of using specific epigenetic modifiers and exosomes to manipulate the epigenome and molecular pathways of MSCs to modify the cardiac gene expression yield better profiled cardiomyocyte like cells in vitro. Hitherto, the role of cardiac specific inducers triggering cardiac differentiation at the cellular and molecular level is not well understood. Therefore, the current review highlights the impact and recent trends in employing biological and chemical inducers on cardiac differentiation of MSCs. Thereby, deciphering the interactions between the cellular microenvironment and the cardiac inducers will help us to understand cardiomyogenesis of MSCs. Additionally, the review also provides an insight on skeptical roles of the cell free biological factors and extracellular scaffold assisted mode for manipulation of native and transplanted stem cells towards translational cardiac research.

Culture Variabilities of Human iPSC-Derived Cerebral Organoids Are a Major Issue for the Modelling of Phenotypes Observed in Alzheimer's Disease

Apolipoprotein E (APOE) is the most important susceptibility gene for late onset of Alzheimer's disease (AD), with the presence of APOE-ε4 associated with increased risk of developing AD. Here, we reprogrammed human fibroblasts from individuals with different APOE-ε genotypes into induced pluripotent stem cells (iPSCs), and generated isogenic lines with different APOE profiles. Following characterisation of the newly established iPSC lines, we used an unguided/unpatterning differentiation method to generate six-month-old cerebral organoids from all iPSC lines to assess the suitability of this in vitro system to measure APOE, β amyloid, and Tau phosphorylation levels. We identified variabilities in the organoids' cell composition between cell lines, and between batches of differentiation for each cell line. We observed more homogenous cerebral organoids, and similar levels of APOE, β amyloid, and Tau when using the CRISPR-edited APOE isogenic lines, with the exception of one site of Tau phosphorylation which was higher in the APOE-ε4/ε4 organoids. These data describe that pathological hallmarks of AD are observed in cerebral organoids, and that their variation is mainly independent of the APOE-ε status of the cells, but associated with the high variability of cerebral organoid differentiation. It demonstrates that the cell-line-to-cell-line and batch-to-batch variabilities need to be considered when using cerebral organoids.

Interactivity of biochemical and physical stimuli during epigenetic conditioning and cardiomyocytic differentiation of stem and progenitor cells derived from adult hearts

Mixed populations of cardiosphere-derived stem and progenitor cells containing proliferative and cardiomyogenically committed cells were obtained from adult rat hearts. The cells were cultured in either static 2D monolayers or dynamic 3D scaffold systems with fluid flow. Cardiomyocyte lineage commitment in terms of GATA4 and Nkx2.5 expression was significantly enhanced in the dynamic 3D cultures compared with static 2D conditions. Treatment of the cells with 5-azacytidine (5-aza) produced different responses in the two culture systems, as activity of this chemical epigenetic conditioning agent depended on the cell attachment and hydrodynamic conditions provided during culture. Cell growth was unaffected by 5-aza in the static 2D cultures but was significantly reduced under dynamic 3D conditions relative to untreated controls. Myogenic differentiation measured as Mef2c expression was markedly upregulated by 5-aza in the dynamic 3D cultures but downregulated in the static 2D cultures. The ability of the physical environment to modulate the cellular cardiomyogenic response to 5-aza underscores the interactivity of biochemical and physical stimuli applied for cell differentiation. Accordingly, observations about the efficacy of 5-aza as a cardiomyocyte induction agent may not be applicable across different culture systems. Overall, use of dynamic 3D rather than static 2D culture was more beneficial for cardio-specific myogenesis than 5-aza treatment, which generated a more ambiguous differentiation response.

A Tissue Engineering Chamber for Continuous Pulsatile Electrical Stimulation of Vascularized Cardiac Tissues In Vivo

Background: Cardiomyocytes derived from pluripotent stem cells are immature. Maturation of cardiomyocytes is a multifactorial dynamic process that involves various factors in vivo that cannot be fully recapitulated in vitro. Here, we report a novel tissue engineering chamber with an integrated electrical stimulator and electrodes that will allow wireless electrical stimulation of cardiac tissue in vivo. Materials and Methods: Immunocompromised rats were implanted with tissue engineering chambers containing the stimulator and electrodes, and control chambers (chambers with electrical stimulator but without the electrodes) in the contralateral limb. Each chamber contained cardiomyocytes derived from human induced pluripotent stem cells (iPSCs). After 7 days of chamber implantation, the electrical stimulators were activated for 4 h per day, for 21 consecutive days. Results: At 4 weeks postimplantation, cardiomyocytes derived from human iPSCs survived, were assembled into compact cardiac tissue, and were perfused and vascularized by the host neovessels. Conclusion: This proof-of-principle study demonstrates the biocompatibility of the tissue engineering chamber with integrated electrical stimulator and electrodes. This could be utilized to study the influence of continuous electrical stimulation on vascularized cardiac or other tissues in vivo.

Mitochondrial Fusion by M1 Promotes Embryoid Body Cardiac Differentiation of Human Pluripotent Stem Cells

Human induced pluripotent stem cells (iPSCs) can be differentiated in vitro into bona fide cardiomyocytes for disease modelling and personalized medicine. Mitochondrial morphology and metabolism change dramatically as iPSCs differentiate into mesodermal cardiac lineages. Inhibiting mitochondrial fission has been shown to promote cardiac differentiation of iPSCs. However, the effect of hydrazone M1, a small molecule that promotes mitochondrial fusion, on cardiac mesodermal commitment of human iPSCs is unknown. Here, we demonstrate that treatment with M1 promoted mitochondrial fusion in human iPSCs. Treatment of iPSCs with M1 during embryoid body formation significantly increased the percentage of beating embryoid bodies and expression of cardiac-specific genes. The pro-fusion and pro-cardiogenic effects of M1 were not associated with changes in expression of the α and β subunits of adenosine triphosphate (ATP) synthase. Our findings demonstrate for the first time that hydrazone M1 is capable of promoting cardiac differentiation of human iPSCs, highlighting the important role of mitochondrial dynamics in cardiac mesoderm lineage specification and cardiac development. M1 and other mitochondrial fusion promoters emerge as promising molecular targets to generate lineages of the heart from human iPSCs for patient-specific regenerative medicine.

The effect of sodium valproate on differentiation of human adipose-derived stem cells into cardiomyocyte-like cells in two-dimensional culture and fibrin scaffold conditions

Differentiation of mesenchymal stem cells (MSCs) into cardiomyocytes is a complex phenomenon, and attempts to find an effective inducing agent are still ongoing. We studied the effect of fibrin scaffold and sodium valproate (VPA, as a histone deacetylase inhibitor) on the differentiation of human adipose-derived stem cells (hADSCs) into cardiomyocyte-like cells. The cells were cultured in culture flask (2D) and in fibrin scaffold (3D), fabricated of human plasma fibrinogen, with and without VPA (1 mM). QRT-PCR, Western blot, and immunochemistry assays were used to evaluate the expression of cardiac markers at gene and protein levels. High levels of CD44, CD90, CD73, and CD105 were expressed on the surface of hADSCs. Treated encapsulated hADSCs (3D) presented significantly higher mRNA expression of HAND1 (1.54-fold), HAND2 (1.59-fold), cTnI (1.76-fold), MLC2v (1.4-fold), Cx43 (1.38-fold), βMHC (1.34-fold), GATA4 (1.48-fold), and NKX2.5 (1.66-fold) in comparison to 2D conditions at four weeks after induction. The protein expressions of NKX2.5 (0.78 vs 0.65), cTnI (1.04 vs 0.81), and Cx43 (1.11 vs 1.08) were observed in the differentiated cells both in 3D and 2D groups, while control cells were absolutely negative for these proteins. The frequency of cTnI and Cx43-positive cells was significantly higher in 3D (24.2 ± 15 and 12 ± 3%) than 2D conditions (19.8 ± 3 and 10 ± 2%). Overall, the results showed that VPA can increase cardiomyogenesis in hADSCs and that fibrin scaffold enhances the inductive effect of VPA. Results of this study may improve cell-based protocols for implementation of more successful cardiac repair strategies.

Epigenetics, cardiovascular disease, and cellular reprogramming

Under the seeming disorder of "junk" sequences the last decade has seen developments in our understanding of non-coding RNA's (ncRNAs). It's a complex revised order and nowhere is this more relevant than in the developing heart whereby old rules have been set aside to make room for new ones. The development of the mammalian heart has been studied at the genetic and cellular level for several decades because these areas were considered ideal control points. As such, detailed mechanisms governing cell lineages are well described. Emerging evidence suggests a complex new order regulated by epigenetic mechanisms mark cardiac cell lineage. Indeed, molecular cardiologists are in the process of shedding light on the roles played by ncRNAs, nucleic acid methylation and histone/chromatin modifications in specific pathologies of the heart. The aim of this article is to discuss some of the recent advances in the field of cardiovascular epigenetics that are related to direct cell reprogramming and repair. As such, we explore ncRNAs as nodes regulating signaling networks and attempt to make sense of regulatory disorder by reinforcing the importance of epigenetic components in the developmental program.

Bmi-1 high-expressing cells enrich cardiac stem/progenitor cells and respond to heart injury

Bmi‐1 gene is well recognized as an oncogene, but has been recently demonstrated to play a role in the self‐renewal of tissue‐specific stem cells. By using Bmi‐1^GFP/+ mice, we investigated the role of Bmi‐1 in cardiac stem/progenitor cells and myocardial repair. RT‐PCR and flow cytometry analysis indicated that the expression of Bmi‐1 was significantly higher in cardiac side population than the main population from CD45⁻Ter119⁻CD31⁻ heart cells. More Sca‐1⁺ cardiac stem/progenitor cells were found in Bmi‐1 GFP^hi subpopulation, and these Bmi‐1 GFP^hi heart cells showed the potential of differentiation into SMM⁺ smooth muscle‐like cells and TnT⁺ cardiomyocyte‐like cells in vitro. The silencing of Bmi‐1 significantly inhibited the proliferation and differentiation of heart cells. Otherwise, myocardial infarction induced a significantly increase (2.7‐folds) of Bmi‐1 GFP^hi population, mainly within the infarction and border zones. These preliminary data suggest that Bmi‐1^hi heart cells are enriched in cardiac stem/progenitor cells and may play a role in myocardial repair.

The impact of in vitro cell culture duration on the maturation of human cardiomyocytes derived from induced pluripotent stem cells of myogenic origin

Ischemic heart disease, also known as coronary artery disease (CAD), poses a challenge for regenerative medicine. iPSC technology might lead to a breakthrough due to the possibility of directed cell differentiation delivering a new powerful source of human autologous cardiomyocytes. One of the factors supporting proper cell maturation is in vitro culture duration. In this study, primary human skeletal muscle myoblasts were selected as a myogenic cell type reservoir for genetic iPSC reprogramming. Skeletal muscle myoblasts have similar ontogeny embryogenetic pathways (myoblasts vs. cardiomyocytes), and thus, a greater chance of myocardial development might be expected, with maintenance of acquired myogenic cardiac cell characteristics, from the differentiation process when iPSCs of myoblastoid origin are obtained. Analyses of cell morphological and structural changes, gene expression (cardiac markers), and functional tests (intracellular calcium transients) performed at two in vitro culture time points spanning the early stages of cardiac development (day 20 versus 40 of cell in vitro culture) confirmed the ability of the obtained myogenic cells to acquire adult features of differentiated cardiomyocytes. Prolonged 40-day iPSC-derived cardiomyocytes (iPSC-CMs) revealed progressive cellular hypertrophy; a better-developed contractile apparatus; expression of marker genes similar to human myocardial ventricular cells, including a statistically significant CX43 increase, an MHC isoform switch, and a troponin I isoform transition; more efficient intercellular calcium handling; and a stronger response to β-adrenergic stimulation.

Mitochondrial fission protein Drp1 inhibition promotes cardiac mesodermal differentiation of human pluripotent stem cells

Human induced pluripotent stem cells (iPSCs) are a valuable tool for studying the cardiac developmental process in vitro, and cardiomyocytes derived from iPSCs are a putative cell source for personalized medicine. Changes in mitochondrial morphology have been shown to occur during cellular reprogramming and pluripotent stem cell differentiation. However, the relationships between mitochondrial dynamics and cardiac mesoderm commitment of iPSCs remain unclear. Here we demonstrate that changes in mitochondrial morphology from a small granular fragmented phenotype in pluripotent stem cells to a filamentous reticular elongated network in differentiated cardiomyocytes are required for cardiac mesodermal differentiation. Genetic and pharmacological inhibition of the mitochondrial fission protein, Drp1, by either small interfering RNA or Mdivi-1, respectively, increased cardiac mesoderm gene expression in iPSCs. Treatment of iPSCs with Mdivi-1 during embryoid body formation significantly increased the percentage of beating embryoid bodies and expression of cardiac-specific genes. Furthermore, Drp1 gene silencing was accompanied by increased mitochondrial respiration and decreased aerobic glycolysis. Our findings demonstrate that shifting the balance of mitochondrial morphology toward fusion by inhibition of Drp1 promoted cardiac differentiation of human iPSCs with a metabolic shift from glycolysis towards oxidative phosphorylation. These findings suggest that Drp1 may represent a new molecular target for future development of strategies to promote the differentiation of human iPSCs into cardiac lineages for patient-specific cardiac regenerative medicine.

Differentiation of human adipose-derived stem cells into cardiomyocyte-like cells in fibrin scaffold by a histone deacetylase inhibitor

Background

Human adipose-derived stem cells (hADSCs) are capable of differentiating into many cells such as cardiac cells. Different types of inducers are used for cardiac cell differentiation, but this question still remains to be investigated, which one is the best. The aim of this paper was to investigate the effect of combination of fibrin scaffold and trichostatin A (TSA), for differentiation of hADSCs into cardiomyocyte-like cells.

Methods

After approval of characteristics of hADSCs and fibrin scaffold, hADSCs were cultured in fibrin scaffold with 10 µM TSA for 72 h and kept in standard conditions for 4 weeks. QRT-PCR and immunostaining assay were performed for evaluating the expression pattern of special cardiac genes and proteins.

Results

In particular, our study showed that fibrin scaffold alongside TSA enhanced expression of the selected genes and proteins.

Conclusions

We concluded that the TSA alone or with fibrin scaffold can lead to the generation of cardiac like cells in a short period of time.

Friedreich's ataxia induced pluripotent stem cell-derived cardiomyocytes display electrophysiological abnormalities and calcium handling deficiency

We sought to identify the impacts of Friedreich's ataxia (FRDA) on cardiomyocytes. FRDA is an autosomal recessive degenerative condition with neuronal and non-neuronal manifestations, the latter including progressive cardiomyopathy of the left ventricle, the leading cause of death in FRDA. Little is known about the cellular pathogenesis of FRDA in cardiomyocytes. Induced pluripotent stem cells (iPSCs) were derived from three FRDA individuals with characterized GAA repeats. The cells were differentiated into cardiomyocytes to assess phenotypes. FRDA iPSC- cardiomyocytes retained low levels of FRATAXIN (FXN) mRNA and protein. Electrophysiology revealed an increased variation of FRDA- cardiomyocyte beating rates which was prevented by addition of nifedipine, suggestive of a calcium handling deficiency. Finally, calcium imaging was performed and we identified small amplitude, diastolic and systolic calcium transients confirming a deficiency in calcium handling. We defined a robust FRDA cardiac-specific electrophysiological profile in patient-derived iPSCs which could be used for high throughput compound screening. This cell-specific signature will contribute to the identification and screening of novel treatments for this life-threatening disease.

Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber

In reconstructive surgery, there is a clinical need for an alternative to the current methods of autologous reconstruction which are complex, costly and trade one defect for another. Tissue engineering holds the promise to address this increasing demand. However, most tissue engineering strategies fail to generate stable and functional tissue substitutes because of poor vascularization. This paper focuses on an in vivo tissue engineering chamber model of intrinsic vascularization where a perfused artery and a vein either as an arteriovenous loop or a flow-through pedicle configuration is directed inside a protected hollow chamber. In this chamber-based system angiogenic sprouting occurs from the arteriovenous vessels and this system attracts ischemic and inflammatory driven endogenous cell migration which gradually fills the chamber space with fibro-vascular tissue. Exogenous cell/matrix implantation at the time of chamber construction enhances cell survival and determines specificity of the engineered tissues which develop. Our studies have shown that this chamber model can successfully generate different tissues such as fat, cardiac muscle, liver and others. However, modifications and refinements are required to ensure target tissue formation is consistent and reproducible. This article describes a standardized protocol for the fabrication of two different vascularized tissue engineering chamber models in vivo.

Using human pluripotent stem cells to study Friedreich ataxia cardiomyopathy

Friedreich ataxia (FRDA) is the most common of the inherited ataxias. It is an autosomal recessive disease characterised by degeneration of peripheral sensory neurons, regions of the central nervous system and cardiomyopathy. FRDA is usually due to homozygosity for trinucleotide GAA repeat expansions found within first intron of the FRATAXIN (FXN) gene, which results in reduced levels of the mitochondrial protein FXN. Reduced FXN protein results in mitochondrial dysfunction and iron accumulation leading to increased oxidative stress and cell death in the nervous system and heart. Yet the precise functions of FXN and the underlying mechanisms leading to disease pathology remain elusive. This is particularly true of the cardiac aspect of FRDA, which remains largely uncharacterized at the cellular level. Here, we summarise current knowledge on experimental models in which to study FRDA cardiomyopathy, with a particular focus on the use of human pluripotent stem cells as a disease model.

Three Dimensional Collagen Scaffold Promotes Intrinsic Vascularisation for Tissue Engineering Applications

Here, we describe a porous 3-dimensional collagen scaffold material that supports capillary formation in vitro, and promotes vascularization when implanted in vivo. Collagen scaffolds were synthesized from type I bovine collagen and have a uniform pore size of 80 μm. In vitro, scaffolds seeded with primary human microvascular endothelial cells suspended in human fibrin gel formed CD31 positive capillary-like structures with clear lumens. In vivo, after subcutaneous implantation in mice, cell-free collagen scaffolds were vascularized by host neovessels, whilst a gradual degradation of the scaffold material occurred over 8 weeks. Collagen scaffolds, impregnated with human fibrinogen gel, were implanted subcutaneously inside a chamber enclosing the femoral vessels in rats. Angiogenic sprouts from the femoral vessels invaded throughout the scaffolds and these degraded completely after 4 weeks. Vascular volume of the resulting constructs was greater than the vascular volume of constructs from chambers implanted with fibrinogen gel alone (42.7±5.0 μL in collagen scaffold vs 22.5±2.3 μL in fibrinogen gel alone; p<0.05, n = 7). In the same model, collagen scaffolds seeded with human adipose-derived stem cells (ASCs) produced greater increases in vascular volume than did cell-free collagen scaffolds (42.9±4.0 μL in collagen scaffold with human ASCs vs 25.7±1.9 μL in collagen scaffold alone; p<0.05, n = 4). In summary, these collagen scaffolds are biocompatible and could be used to grow more robust vascularized tissue engineering grafts with improved the survival of implanted cells. Such scaffolds could also be used as an assay model for studies on angiogenesis, 3-dimensional cell culture, and delivery of growth factors and cells in vivo.

Techniques for the induction of human pluripotent stem cell differentiation towards cardiomyocytes

The derivation of pluripotent stem cells from human embryos and the generation of induced pluripotent stem cells (iPSCs) from somatic cells opened a new chapter in studies on the regeneration of the post-infarction heart and regenerative medicine as a whole. Thus, protocols for obtaining iPSCs were enthusiastically adopted and widely used for further experiments on cardiac differentiation. iPSC-mediated cardiomyocytes (iPSC-CMs) under in vitro culture conditions are generated by simulating natural cardiomyogenesis and involve the wingless-type mouse mammary tumour virus integration site family (WNT), transforming growth factor beta (TGF-β) and fibroblast growth factor (FGF) signalling pathways. New strategies have been proposed to take advantage of small chemical molecules, organic compounds and even electric or mechanical stimulation. There are three main approaches to support cardiac commitment in vitro: embryoid bodis (EBs), monolayer in vitro cultures and inductive co-cultures with visceral endoderm-like (END2) cells. In EB technique initial uniform size of pluripotent stem cell (PSC) colonies has a pivotal significance. Hence, some methods were designed to support cells aggregation. Another well-suited procedure is based on culturing cells in monolayer conditions in order to improve accessibility of growth factors and nutrients. Other distinct tactics are using visceral endoderm-like cells to culture them with PSCs due to secretion of procardiac cytokines. Finally, the appropriate purification of the obtained cardiomyocytes is required prior to their administration to a patient under the prospective cellular therapy strategy. This goal can be achieved using non-genetic methods, such as the application of surface markers and fluorescent dyes. Copyright © 2016 John Wiley & Sons, Ltd.

Electrical Stimulation Promotes Cardiac Differentiation of Human Induced Pluripotent Stem Cells

Background. Human induced pluripotent stem cells (iPSCs) are an attractive source of cardiomyocytes for cardiac repair and regeneration. In this study, we aim to determine whether acute electrical stimulation of human iPSCs can promote their differentiation to cardiomyocytes. Methods. Human iPSCs were differentiated to cardiac cells by forming embryoid bodies (EBs) for 5 days. EBs were then subjected to brief electrical stimulation and plated down for 14 days. Results. In iPS(Foreskin)-2 cell line, brief electrical stimulation at 65 mV/mm or 200 mV/mm for 5 min significantly increased the percentage of beating EBs present by day 14 after plating. Acute electrical stimulation also significantly increased the cardiac gene expression of ACTC1, TNNT2, MYH7, and MYL7. However, the cardiogenic effect of electrical stimulation was not reproducible in another iPS cell line, CERA007c6. Beating EBs from control and electrically stimulated groups expressed various cardiac-specific transcription factors and contractile muscle markers. Beating EBs were also shown to cycle calcium and were responsive to the chronotropic agents, isoproterenol and carbamylcholine, in a concentration-dependent manner. Conclusions. Our results demonstrate that brief electrical stimulation can promote cardiac differentiation of human iPS cells. The cardiogenic effect of brief electrical stimulation is dependent on the cell line used.

Dual gene expression in embryoid bodies derived from human induced pluripotent stem cells using episomal vectors

Transcription factors are essential for the differentiation of human induced pluripotent stem cells (iPS) into specialized cell types. Embryoid body (EB) formation promotes the differentiation of iPS cells. We sought to establish an efficient method of transfection and rotary culture to generate EBs that stably express two genes. The pMetLuc2-Reporter vector was transfected using FuGENE HD (FuGENE), Lipofectamine LTX (LTX), X-tremeGENE, or TransIT-2020 transfection reagents. The media was analyzed using a Metridia luciferase (MetLuc) assay. Transfections were performed on cells adherent to plates/dishes (adherent method) or suspended in the media (suspension method). The 201B7 cells transfected with episomal vectors were selected using G418 (200 μg/mL) or hygromycin B (300 μg/mL). Rotary culture was performed at 2.5 or 9.9 rpm. Efficiency of EB formation was compared among plates and dishes. Cell density was compared at 1.6×10(3),×10(4), and×10(5) cells/mL. The suspended method of transfection using the FuGENE HD reagent was the most efficient. The expression of pEBMulti/Met-Hyg was detected 11 days posttransfection. Double transformants were selected 6 days posttransfection with pEBNK/EGFP-Neo and pEBNK/Cherry-Hyg. Both EGFP and CherryPicker were expressed in all of the surviving cells. EBs were formed most efficiently from cells cultured at a density of 1.6×10(5) cells/mL in six-well plates or 6 cm dishes. The selected cells formed EBs. FuGENE-mediated transfection of plasmids using the suspension method was effective in transforming iPS cells. Furthermore, the episomal vectors enabled us to perform a stable double transfection of EB-forming iPS cells.

Cardiac Repair With a Novel Population of Mesenchymal Stem Cells Resident in the Human Heart

Cardiac resident stem cells (CRSCs) hold much promise to treat heart disease but this remains a controversial field. Here, we describe a novel population of CRSCs, which are positive for W8B2 antigen and were obtained from adult human atrial appendages. W8B2(+) CRSCs exhibit a spindle-shaped morphology, are clonogenic and capable of self-renewal. W8B2(+) CRSCs show high expression of mesenchymal but not hematopoietic nor endothelial markers. W8B2(+) CRSCs expressed GATA4, HAND2, and TBX5, but not C-KIT, SCA-1, NKX2.5, PDGFRα, ISL1, or WT1. W8B2(+) CRSCs can differentiate into cardiovascular lineages and secrete a range of cytokines implicated in angiogenesis, chemotaxis, inflammation, extracellular matrix remodeling, cell growth, and survival. In vitro, conditioned medium collected from W8B2(+) CRSCs displayed prosurvival, proangiogenic, and promigratory effects on endothelial cells, superior to that of other adult stem cells tested, and additionally promoted survival and proliferation of neonatal rat cardiomyocytes. Intramyocardial transplantation of human W8B2(+) CRSCs into immunocompromised rats 1 week after myocardial infarction markedly improved cardiac function (∼40% improvement in ejection fraction) and reduced fibrotic scar tissue 4 weeks after infarction. Hearts treated with W8B2(+) CRSCs showed less adverse remodeling of the left ventricle, a greater number of proliferating cardiomyocytes (Ki67(+) cTnT(+) cells) in the remote region, higher myocardial vascular density, and greater infiltration of CD163(+) cells (a marker for M2 macrophages) into the border zone and scar regions. In summary, W8B2(+) CRSCs are distinct from currently known CRSCs found in human hearts, and as such may be an ideal cell source to repair myocardial damage after infarction.

Bioengineering and Stem Cell Technology in the Treatment of Congenital Heart Disease

Congenital heart disease places a significant burden on the individual, family and community despite significant advances in our understanding of aetiology and treatment. Early research in ischaemic heart disease has paved the way for stem cell technology and bioengineering, which promises to improve both structural and functional aspects of disease. Stem cell therapy has demonstrated significant improvements in cardiac function in adults with ischaemic heart disease. This finding, together with promising case studies in the paediatric setting, demonstrates the potential for this treatment in congenital heart disease. Furthermore, induced pluripotent stems cell technology, provides a unique opportunity to address aetiological, as well as therapeutic, aspects of disease.

Cardiac disease modeling using induced pluripotent stem cell-derived human cardiomyocytes

Causative mutations and variants associated with cardiac diseases have been found in genes encoding cardiac ion channels, accessory proteins, cytoskeletal components, junctional proteins, and signaling molecules. In most cases the functional evaluation of the genetic alteration has been carried out by expressing the mutated proteins in in-vitro heterologous systems. While these studies have provided a wealth of functional details that have greatly enhanced the understanding of the pathological mechanisms, it has always been clear that heterologous expression of the mutant protein bears the intrinsic limitation of the lack of a proper intracellular environment and the lack of pathological remodeling. The results obtained from the application of the next generation sequencing technique to patients suffering from cardiac diseases have identified several loci, mostly in non-coding DNA regions, which still await functional analysis. The isolation and culture of human embryonic stem cells has initially provided a constant source of cells from which cardiomyocytes (CMs) can be obtained by differentiation. Furthermore, the possibility to reprogram cellular fate to a pluripotent state, has opened this process to the study of genetic diseases. Thus induced pluripotent stem cells (iPSCs) represent a completely new cellular model that overcomes the limitations of heterologous studies. Importantly, due to the possibility to keep spontaneously beating CMs in culture for several months, during which they show a certain degree of maturation/aging, this approach will also provide a system in which to address the effect of long-term expression of the mutated proteins or any other DNA mutation, in terms of electrophysiological remodeling. Moreover, since iPSC preserve the entire patients’ genetic context, the system will help the physicians in identifying the most appropriate pharmacological intervention to correct the functional alteration. This article summarizes the current knowledge of cardiac genetic diseases modelled with iPSC.

Biomimetic 3D Tissue Models for Advanced High-Throughput Drug Screening

Most current drug screening assays used to identify new drug candidates are 2D cell-based systems, even though such in vitro assays do not adequately re-create the in vivo complexity of 3D tissues. Inadequate representation of the human tissue environment during a preclinical test can result in inaccurate predictions of compound effects on overall tissue functionality. Screening for compound efficacy by focusing on a single pathway or protein target, coupled with difficulties in maintaining long-term 2D monolayers, can serve to exacerbate these issues when using such simplistic model systems for physiological drug screening applications. Numerous studies have shown that cell responses to drugs in 3D culture are improved from those in 2D, with respect to modeling in vivo tissue functionality, which highlights the advantages of using 3D-based models for preclinical drug screens. In this review, we discuss the development of microengineered 3D tissue models that accurately mimic the physiological properties of native tissue samples and highlight the advantages of using such 3D microtissue models over conventional cell-based assays for future drug screening applications. We also discuss biomimetic 3D environments, based on engineered tissues as potential preclinical models for the development of more predictive drug screening assays for specific disease models.

Vascularisation to improve translational potential of tissue engineering systems for cardiac repair

Cardiac tissue engineering is developing as an alternative approach to heart transplantation for treating heart failure. Shortage of organ donors and complications arising after orthotopic transplant remain major challenges to the modern field of heart transplantation. Engineering functional myocardium de novo requires an abundant source of cardiomyocytes, a biocompatible scaffold material and a functional vasculature to sustain the high metabolism of the construct. Progress has been made on several fronts, with cardiac cell biology, stem cells and biomaterials research particularly promising for cardiac tissue engineering, however currently employed strategies for vascularisation have lagged behind and limit the volume of tissue formed. Over ten years we have developed an in vivo tissue engineering model to construct vascularised tissue from various cell and tissue sources, including cardiac tissue. In this article we review the progress made with this approach and others, together with their potential to support a volume of engineered tissue for cardiac tissue engineering where contractile mass impacts directly on functional outcomes in translation to the clinic. It is clear that a scaled-up cardiac tissue engineering solution required for clinical treatment of heart failure will include a robust vascular supply for successful translation. This article is part of a directed issue entitled: Regenerative Medicine: the challenge of translation.

SCL/TAL1-mediated transcriptional network enhances megakaryocytic specification of human embryonic stem cells

Human embryonic stem cells (hESCs) are a unique in vitro model for studying human developmental biology and represent a potential source for cell replacement strategies. Platelets can be generated from cord blood progenitors and hESCs; however, the molecular mechanisms and determinants controlling the in vitro megakaryocytic specification of hESCs remain elusive. We have recently shown that stem cell leukemia (SCL) overexpression accelerates the emergence of hemato-endothelial progenitors from hESCs and promotes their subsequent differentiation into blood cells with higher clonogenic potential. Given that SCL participates in megakaryocytic commitment, we hypothesized that it may potentiate megakaryopoiesis from hESCs. We show that ectopic SCL expression enhances the emergence of megakaryocytic precursors, mature megakaryocytes (MKs), and platelets in vitro. SCL-overexpressing MKs and platelets respond to different activating stimuli similar to their control counterparts. Gene expression profiling of megakaryocytic precursors shows that SCL overexpression renders a megakaryopoietic molecular signature. Connectivity Map analysis reveals that trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA), both histone deacetylase (HDAC) inhibitors, functionally mimic SCL-induced effects. Finally, we confirm that both TSA and SAHA treatment promote the emergence of CD34(+) progenitors, whereas valproic acid, another HDAC inhibitor, potentiates MK and platelet production. We demonstrate that SCL and HDAC inhibitors are megakaryopoiesis regulators in hESCs.

Histone deacetylase inhibitor induces the expression of select epithelial genes in mouse utricle sensory epithelia-derived progenitor cells

Mouse utricle sensory epithelial cell-derived progenitor cells (MUCs), which have hair cell progenitor and mesenchymal features via epithelial-to-mesenchymal transition (EMT) as previously described, provide a potential approach for hair cell regeneration via cell transplantation. In this study, we treated MUCs with trichostatin A (TSA) to determine whether histone deacetylase inhibitor is able to stimulate the expression of epithelial genes in MUCs, an essential step for guiding mesenchymal-like MUCs to become sensory epithelial cells. After 72 h of TSA treatment, MUCs acquired epithelial-like features, which were indicated by increased expression of epithelial markers such as Cdh1, Krt18, and Dsp. Additionally, TSA decreased the expression of mesenchymal markers, including Zeb1, Zeb2, Snai1, and Snai2, and prosensory genes Lfng, Six1, and Dlx5. Moreover, the expression of the hair cell genes Atoh1 and Myo6 was increased in TSA-treated MUCs. We also observed significantly decreased expression of Hdac2 and Hdac3 in TSA-treated MUCs. However, no remarkable change was detected in protein expression using immunofluorescence, indicating that TSA-induced HDAC inhibition may contribute to the initial stage of the mesenchymal-to-epithelial phenotypic change. In the future, more work is needed to induce hair cell regeneration using inner ear tissue-derived progenitors to achieve an entire mesenchymal-to-epithelial transition.

Cell and gene therapy for Friedreich ataxia: progress to date

Neurodegenerative disorders such as Friedreich ataxia (FRDA) present significant challenges in developing effective therapeutic intervention. Current treatments aim to manage symptoms and thus improve quality of life, but none can cure, nor are proven to slow, the neurodegeneration inherent to this disease. The primary clinical features of FRDA include progressive ataxia and shortened life span, with complications of cardiomyopathy being the major cause of death. FRDA is most commonly caused by an expanded GAA trinucleotide repeat in the first intron of FXN that leads to reduced levels of frataxin, a mitochondrial protein important for iron metabolism. The GAA expansion in FRDA does not alter the coding sequence of FXN. It results in reduced production of structurally normal frataxin, and hence any increase in protein level is expected to be therapeutically beneficial. Recently, there has been increased interest in developing novel therapeutic applications like cell and/or gene therapies, and these cutting-edge applications could provide effective treatment options for FRDA. Importantly, since individuals with FRDA produce frataxin at low levels, increased expression should not elicit an immune response. Here we review the advances to date and highlight the future potential for cell and gene therapy to treat this debilitating disease.

Efficient generation of integration-free human induced pluripotent stem cells from keratinocytes by simple transfection of episomal vectors

Keratinocytes represent an easily accessible cell source for derivation of human induced pluripotent stem (hiPS) cells, reportedly achieving higher reprogramming efficiency than fibroblasts. However, most studies utilized a retroviral or lentiviral method for reprogramming of keratinocytes, which introduces undesirable transgene integrations into the host genome. Moreover, current protocols of generating integration-free hiPS cells from keratinocytes are mostly inefficient. In this paper, we describe a more efficient, simple-to-use, and cost-effective method for generating integration-free hiPS cells from keratinocytes. Our improved method using lipid-mediated transfection achieved a reprogramming efficiency of ∼0.14% on average. Keratinocyte-derived hiPS cells showed no integration of episomal vectors, expressed stem cell-specific markers and possessed potentials to differentiate into all three germ layers by in vitro embryoid body formation as well as in vivo teratoma formation. To our knowledge, this represents the most efficient method to generate integration-free hiPS cells from keratinocytes.

The Power and the Promise of Cell Reprogramming: Personalized Autologous Body Organ and Cell Transplantation

Reprogramming somatic cells to induced pluripotent stem cells (iPSCs) or direct reprogramming to desired cell types are powerful and new in vitro methods for the study of human disease, cell replacement therapy, and drug development. Both methods to reprogram cells are unconstrained by the ethical and social questions raised by embryonic stem cells. iPSC technology promises to enable personalized autologous cell therapy and has the potential to revolutionize cell replacement therapy and regenerative medicine. Potential applications of iPSC technology are rapidly increasing in ambition from discrete cell replacement applications to the iPSC assisted bioengineering of body organs for personalized autologous body organ transplant. Recent work has demonstrated that the generation of organs from iPSCs is a future possibility. The development of embryonic-like organ structures bioengineered from iPSCs has been achieved, such as an early brain structure (cerebral organoids), bone, optic vesicle-like structures (eye), cardiac muscle tissue (heart), primitive pancreas islet cells, a tooth-like structure (teeth), and functional liver buds (liver). Thus, iPSC technology offers, in the future, the powerful and unique possibility to make body organs for transplantation removing the need for organ donation and immune suppressing drugs. Whilst it is clear that iPSCs are rapidly becoming the lead cell type for research into cell replacement therapy and body organ transplantation strategies in humans, it is not known whether (1) such transplants will stimulate host immune responses; and (2) whether this technology will be capable of the bioengineering of a complete and fully functional human organ. This review will not focus on reprogramming to iPSCs, of which a plethora of reviews can be found, but instead focus on the latest developments in direct reprogramming of cells, the bioengineering of body organs from iPSCs, and an analysis of the immune response induced by iPSC-derived cells and tissues.

Human pluripotent stem cell-derived cardiomyocytes as research and therapeutic tools

Human pluripotent stem cells (hPSCs), namely, embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), with their ability of indefinite self-renewal and capability to differentiate into cell types derivatives of all three germ layers, represent a powerful research tool in developmental biology, for drug screening, disease modelling, and potentially cell replacement therapy. Efficient differentiation protocols that would result in the cell type of our interest are needed for maximal exploitation of these cells. In the present work, we aim at focusing on the protocols for differentiation of hPSCs into functional cardiomyocytes in vitro as well as achievements in the heart disease modelling and drug testing on the patient-specific iPSC-derived cardiomyocytes (iPSC-CMs).

Inhibition of stearoyl-coA desaturase selectively eliminates tumorigenic Nanog-positive cells: improving the safety of iPS cell transplantation to myocardium

Induced pluripotent stem cells (iPS) can differentiate into cardiomyocytes (CM) and represent a promising form of cellular therapy for heart regeneration. However, residual undifferentiated iPS derivates (iPSD), which are not fully eliminated by cell differentiation or purification protocols, may form tumors after transplantation, thus compromising therapeutic application. Inhibition of stearoyl-coA desaturase (SCD) has recently been reported to eliminate undifferentiated human embryonic stem cells, which share many features with iPSD. Here, we tested the effects of PluriSin#1, a small-molecule inhibitor of SCD, on iPS-derived CM. We found that plurisin#1 treatment significantly decreased the mRNA and protein level of Nanog, a marker for both cell pluripotency and tumor progression; importantly, we provide evidence that PluriSin#1 treatment at 20 µM for 1 day significantly induces the apoptosis of Nanog-positive iPSD. In addition, PluriSin#1 treatment at 20 µM for 4 days diminished Nanog-positive stem cells in cultured iPSD while not increasing apoptosis of iPS-derived CM. To investigate whether PluriSin#1 treatment prevents tumorigenicity of iPSD after cell transplantation, we intramyocardially injected PluriSin#1- or DMSO-treated iPSD in a mouse model of myocardial infarction (MI). DMSO-treated iPSD readily formed Nanog-expressing tumors 2 weeks after injection, which was prevented by treatment with PluriSin#1. Moreover, treatment with PluriSin#1 did not change the expression of cTnI, α-MHC, or MLC-2v, markers of cardiac differentiation (P>0.05, n = 4). Importantly, pluriSin#1-treated iPS-derived CM exhibited the ability to engraft and survive in the infarcted myocardium. We conclude that inhibition of SCD holds the potential to enhance the safety of therapeutic application of iPS cells for heart regeneration.

Cardiac regeneration and diabetes

The prevalence of diabetes continues to increase world-wide and is a leading cause of morbidity, mortality, and rapidly rising health care costs. Although strict glucose control combined with good pharmacological and non-pharmacologic interventions can increase diabetic patient life span, the frequency and mortality of myocardial ischemia and infarction remain drastically increased in diabetic patients. Therefore, more effective therapeutic approaches are urgently needed. Over the past 15 years, cellular repair of the injured adult heart has become the focus of a rapidly expanding broad spectrum of pre-clinical and clinical research. Recent clinical trials have achieved favorable initial endpoints with improvements in cardiac function and clinical symptoms following cellular therapy. Due to the increased risk of cardiac disease, cardiac regeneration may be one strategy to treat patients with diabetic cardiomyopathy and/or myocardial infarction. However, pre-clinical studies suggest that the diabetic myocardium may not be a favorable environment for the transplantation and survival of stem cells due to altered kinetics in cellular homing, survival, and in situ remodeling. Therefore, unique conditions in the diabetic myocardium will require novel solutions in order to increase the efficiency of cellular repair following ischemia and/or infarction. This review briefly summarizes some of the recent advances in cardiac regeneration in non-diabetic conditions and then provides an overview of some of the issues related to diabetes that must be addressed in the coming years.

Enhancing Human Cardiomyocyte Differentiation from Induced Pluripotent Stem Cells with Trichostatin A

Human induced pluripotent stem (iPS) cells are a promising source of autologous cardiomyocytes to repair and regenerate myocardium for treatment of heart disease. In this study, we describe a method for enhanced cardiomyocyte production from human iPS cells by treating embryoid bodies with a histone deacetylase inhibitor, trichostatin A (TSA), together with activin A and bone morphogenetic protein (BMP)-4. The resulting cardiomyocytes expressed cardiac-specific transcription factors and contractile proteins at both gene and protein levels. Functionally, the contractile embryoid bodies (EBs) displayed calcium cycling and were responsive to the chronotropic agents isoprenaline (0.1 μM) and carbachol (1 μM). The cardiomyocytes derived from human iPS cells may be used to engineer functional cardiac muscle tissue for studying pathophysiology of cardiac disease, for drug discovery test beds, and potentially for generation of cardiac grafts to surgically replace damaged myocardium.