Multi-cellularity in cardiac tissue engineering, how close are we to native heart tissue?

Tissue engineering is a complex field where the elements of biology and engineering are combined in an attempt to recapitulate the native environment of the body. Tissue engineering has shown one thing categorically; that the human body is extremely complex and it is truly a difficult task to generate this in the lab. There have been varied attempts at trying to generate a model for the heart with numerous cell types and different scaffolds or materials. The common underlying theme in these approaches is to combine together matrix material and different cell types to make something similar to heart tissue. Multi-cellularity is an essential aspect of the heart and therefore critical to any approach which would try to mimic such a complex tissue. The heart is made up of many cell types that combine to form complex structures like: deformable chambers, a tri-layered heart muscle, and vessels. Thus, in this review we will summarise how tissue engineering has progressed in modelling the heart and what gaps still exist in this dynamic field.

Generation of left ventricle-like cardiomyocytes with improved structural, functional, and metabolic maturity from human pluripotent stem cells.

Decreased left ventricle (LV) function caused by genetic mutations or injury often leads to debilitating and fatal cardiovascular disease. LV cardiomyocytes are, therefore, a potentially valuable therapeutical target. Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are neither homogeneous nor functionally mature, which reduces their utility. Here, we exploit cardiac development knowledge to instruct differentiation of hPSCs specifically toward LV cardiomyocytes. Correct mesoderm patterning and retinoic acid pathway blocking are essential to generate near-homogenous LV-specific hPSC-CMs (hPSC-LV-CMs). These cells transit via first heart field progenitors and display typical ventricular action potentials. Importantly, hPSC-LV-CMs exhibit increased metabolism, reduced proliferation, and improved cytoarchitecture and functional maturity compared with age-matched cardiomyocytes generated using the standard WNT-ON/WNT-OFF protocol. Similarly, engineered heart tissues made from hPSC-LV-CMs are better organized, produce higher force, and beat more slowly but can be paced to physiological levels. Together, we show that functionally matured hPSC-LV-CMs can be obtained rapidly without exposure to current maturation regimes.

In vivo grafting of large engineered heart tissue patches for cardiac repair.

Engineered heart tissue (EHT) strategies, by combining cells within a hydrogel matrix, may be a novel therapy for heart failure. EHTs restore cardiac function in rodent injury models, but more data are needed in clinically relevant settings. Accordingly, an upscaled EHT patch (2.5 cm × 1.5 cm × 1.5 mm) consisting of up to 20 million human induced pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) embedded in a fibrin-based hydrogel was developed. A rabbit myocardial infarction model was then established to test for feasibility and efficacy. Our data showed that hPSC-CMs in EHTs became more aligned over 28 days and had improved contraction kinetics and faster calcium transients. Blinded echocardiographic analysis revealed a significant improvement in function in infarcted hearts that received EHTs, along with reduction in infarct scar size by 35%. Vascularization from the host to the patch was observed at week 1 and stable to week 4, but electrical coupling between patch and host heart was not observed. In vivo telemetry recordings and ex vivo arrhythmia provocation protocols showed that the patch was not pro-arrhythmic. In summary, EHTs improved function and reduced scar size without causing arrhythmia, which may be due to the lack of electrical coupling between patch and host heart.

Epstein-Barr virus-encoded EBNA1 enhances RNA polymerase III-dependent EBER expression through induction of EBER-associated cellular transcription factors.

BACKGROUND: Epstein-Barr Virus (EBV)-encoded RNAs (EBERs) are non-polyadenylated RNA molecules transcribed from the EBV genome by RNA polymerase III (pol III). EBERs are the most abundant viral latent gene products, although the precise mechanisms by which EBV is able to achieve such high levels of EBER expression are not fully understood. Previously EBV has been demonstrated to induce transcription factors associated with EBER expression, including pol III transcription factors and ATF-2. We have recently demonstrated that EBV-encoded nuclear antigen-1 (EBNA1) induces cellular transcription factors, and given these findings, we investigated the role of EBNA1 in induction of EBER-associated transcription factors. RESULTS: Our data confirm that in epithelial cells EBNA1 can enhance cellular pol III transcription. Transient expression of EBNA1 in Ad/AH cells stably expressing the EBERs led to induction of both EBER1 and EBER2 and conversely, expression of a dominant negative EBNA1 led to reduced EBER expression in EBV-infected Ad/AH cells. EBNA1 can induce transcription factors used by EBER genes, including TFIIIC, ATF-2 and c-Myc. A variant chromatin precipitation procedure showed that EBNA1 is associated with the promoters of these genes but not with the promoters of pol III-transcribed genes, including the EBERs themselves. Using shRNA knock-down, we confirm the significance of both ATF-2 and c-Myc in EBER expression. Further, functional induction of a c-Myc fusion protein led to increased EBER expression, providing c-Myc binding sites upstream of EBER1 were intact. In vivo studies confirm elevated levels of the 102 kD subunit of TFIIIC in the tumour cells of EBV-positive nasopharyngeal carcinoma biopsies. CONCLUSIONS: Our findings reveal that EBNA1 is able to enhance EBER expression through induction of cellular transcription factors and add to the repertoire of EBNA1's transcription-regulatory properties.

Epstein-Barr virus-encoded EBNA1 inhibits the canonical NF-kappaB pathway in carcinoma cells by inhibiting IKK phosphorylation.

BACKGROUND: The Epstein-Barr virus (EBV)-encoded EBNA1 protein is expressed in all EBV-associated tumours, including undifferentiated nasopharyngeal carcinoma (NPC), where it is indispensable for viral replication, genome maintenance and viral gene expression. EBNA1's transcription factor-like functions also extend to influencing the expression of cellular genes involved in pathways commonly dysregulated during oncogenesis, including elevation of AP-1 activity in NPC cell lines resulting in enhancement of angiogenesis in vitro. In this study we sought to extend these observations by examining the role of EBNA1 upon another pathway commonly deregulated during carcinogenesis; namely NF-kappaB. RESULTS: In this report we demonstrate that EBNA1 inhibits the canonical NF-kappaB pathway in carcinoma lines by inhibiting the phosphorylation of IKKalpha/beta. In agreement with this observation we find a reduction in the phosphorylation of IkappaBalpha and reduced phosphorylation and nuclear translocation of p65, resulting in a reduction in the amount of p65 in nuclear NF-kappaB complexes. Similar effects were also found in carcinoma lines infected with recombinant EBV and in the EBV-positive NPC-derived cell line C666-1. Inhibition of NF-kappaB was dependent upon regions of EBNA1 essential for gene transactivation whilst the interaction with the deubiquitinating enzyme, USP7, was entirely dispensable. Furthermore, in agreement with EBNA1 inhibiting p65 NF-kappaB we demonstrate that p65 was exclusively cytoplasmic in 11 out of 11 NPC tumours studied. CONCLUSIONS: Inhibition of p65 NF-kappaB in murine and human epidermis results in tissue hyperplasia and the development of squamous cell carcinoma. In line with this, p65 knockout fibroblasts have a transformed phenotype. Inhibition of p65 NF-kappaB by EBNA1 may therefore contribute to the development of NPC by inducing tissue hyperplasia. Furthermore, inhibition of NF-kappaB is employed by viruses as an immune evasion strategy which is also closely linked to oncogenesis during persistent viral infection. Our findings therefore further implicate EBNA1 in playing an important role in the pathogenesis of NPC.

Natural Biomaterials for Cardiac Tissue Engineering: A Highly Biocompatible Solution.

Cardiovascular diseases (CVD) constitute a major fraction of the current major global diseases and lead to about 30% of the deaths, i.e., 17.9 million deaths per year. CVD include coronary artery disease (CAD), myocardial infarction (MI), arrhythmias, heart failure, heart valve diseases, congenital heart disease, and cardiomyopathy. Cardiac Tissue Engineering (CTE) aims to address these conditions, the overall goal being the efficient regeneration of diseased cardiac tissue using an ideal combination of biomaterials and cells. Various cells have thus far been utilized in pre-clinical studies for CTE. These include adult stem cell populations (mesenchymal stem cells) and pluripotent stem cells (including autologous human induced pluripotent stem cells or allogenic human embryonic stem cells) with the latter undergoing differentiation to form functional cardiac cells. The ideal biomaterial for cardiac tissue engineering needs to have suitable material properties with the ability to support efficient attachment, growth, and differentiation of the cardiac cells, leading to the formation of functional cardiac tissue. In this review, we have focused on the use of biomaterials of natural origin for CTE. Natural biomaterials are generally known to be highly biocompatible and in addition are sustainable in nature. We have focused on those that have been widely explored in CTE and describe the original work and the current state of art. These include fibrinogen (in the context of Engineered Heart Tissue, EHT), collagen, alginate, silk, and Polyhydroxyalkanoates (PHAs). Amongst these, fibrinogen, collagen, alginate, and silk are isolated from natural sources whereas PHAs are produced via bacterial fermentation. Overall, these biomaterials have proven to be highly promising, displaying robust biocompatibility and, when combined with cells, an ability to enhance post-MI cardiac function in pre-clinical models. As such, CTE has great potential for future clinical solutions and hence can lead to a considerable reduction in mortality rates due to CVD.

Epstein-Barr virus-encoded EBNA1 modulates the AP-1 transcription factor pathway in nasopharyngeal carcinoma cells and enhances angiogenesis in vitro.

The Epstein-Barr virus (EBV)-encoded EBNA1 protein is expressed in all virus-associated tumours, including nasopharyngeal carcinoma (NPC), where it plays an essential role in EBV genome maintenance, replication and transcription. Previous studies suggest that EBNA1 may have additional effects relevant to oncogenesis, including enhancement of cell survival, raising the possibility that EBNA1 may influence cellular gene expression. We have recently demonstrated by gene expression microarray profiling in an NPC cell model that EBNA1 influences the expression of a range of cellular genes, including those involved in transcription, translation and cell signalling. Here, we report for the first time that EBNA1 enhances activity of the AP-1 transcription factor in NPC cells and demonstrate that this is achieved by EBNA1 binding to the promoters of c-Jun and ATF2, enhancing their expression. In addition, we demonstrate elevated expression of the AP-1 targets interleukin 8, vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1alpha in response to EBNA1 expression, which enhances microtubule formation in an in vitro angiogenesis assay. Furthermore, we confirm elevation of VEGF and the phosphorylated isoforms of c-Jun and ATF2 in NPC biopsies. These findings implicate EBNA1 in the angiogenic process and suggest that this viral protein might directly contribute to the development and aggressively metastatic nature of NPC.

The estimation of carbon dioxide concentration in the presence of nitrous oxide, using a Lloyd-Haldane apparatus.

A method of gas analysis is described for estimating carbon dioxide in the presence of nitrous oxide, using a modified Lloyd-Haldane apparatus. Some of the sample, after scrubbing with soda-lime, bubbles through the potash and this eliminates the solubility effect of nitrous oxide by equilibrating the standard potash solution with nitrous oxide at the tension of the sample analysed and eliminating absorption of nitrous oxide from the burette. The results show close agreement with another apparatus and method based on different principles. The method is absolute, requiring neither empirical nor theoretical correction.

A paramagnetic method for measuring the carbon dioxide concentration of a gas.

A paramagnetic method of carbon dioxide analysis enables the simultaneous analysis of carbon dioxide and oxygen to be made at 2-min intervals. The method depends upon observing the change of oxygen concentration in a gas mixture before and after absorbing the carbon dioxide component. The carrier-gas in the experiments reported was nitrogen. The output of the paramagnetic meter was measured both by a digital voltmeter and by a chart recorded and the carbon dioxide concentrations calculated from these observations (Y1% and Y2% respectively) were compared with those obtained by Lloyd-Haldane (x%) gas analysis, for carbon dioxide concentration of 2-20% in a range of oxygen concentrations of about 9-90%. The agreement between paramagnetic and Lloyd-Haldane carbon dioxide analysis is shown in the following linear regression equations: Y1=0.996x-0.001 (r=0.9999+/-0.04 SEM of estimate; P less than 0.001); Y2=0.997x-0.006 (r=0.9999+/-0.06 SEM of estimate; P less than 0.001). Carbon dioxide in nitrogen was measured by the prior addition of an arbitrary concentration of oxygen, to a gas sample. The method is applicable to the measurement of carbon dioxide and oxygen, when the carrier-gas may have characteristics which preclude the use of katharometer, infra-red or Haldane analysis.

Hypoxia and pulmonary arterial pressure in the rabbit.

1. The effect of hypoxia on pulmonary arterial pressure was studied in young and adult rabbits.2. In isolated perfused lungs, hypoxia caused no rise in pulmonary arterial pressure in rabbits on the day of birth. The size of the hypoxic response increased progressively until 9-11 days of age, when the adult response of a 20% rise of pulmonary arterial pressure at constant flow was attained.3. The intact adult rabbit responded to hypoxia with a 14-30% rise in pulmonary arterial pressure, attributed to vasoconstriction and independent of frequency or tidal volume during positive pressure ventilation.

Cyanide stimulation of the systemic arterial chemoreceptors in foetal lambs.

1. In foetal lambs, delivered by Caesarean section under light chloralose anaesthesia, injection of sodium cyanide into the left atrium or ascending aorta caused a rise of arterial pressure and femoral vasoconstriction. The response to 0.77 mg/kg was barely present at 0.6 of term; by 0.8 of term there was a large response to one third of this dose.2. The cardiovascular response to cyanide injection into the left atrium or ascending aorta was diminished either by section of the vagi or by carotid denervation, and was abolished by cutting both sets of nerves.3. Injection of sodium cyanide into both common carotids simultaneously caused a substantial cardiovascular response and often a respiratory effort, abolished by carotid denervation, whereas injection into a single carotid rarely caused an effect.4. It is concluded that the carotid chemoreceptors in mature foetal lambs can be excited by a stimulus of sufficient intensity, even though they do not respond to moderate hypoxaemia.

Hypoxaemia and aortic chemoreceptor function in foetal lambs.

1. In foetal lambs the effect of raising and lowering arterial P(O2) (by varying the O(2) content of the maternal inspired gas mixture) was studied in order to determine whether the systemic arterial chemoreceptors regulated the circulation.2. From 0.7 of term relative hypoxaemia (e.g. reducing carotid P(O2) from 40 to 20 mm Hg) caused a rise of arterial pressure and femoral vaso-constriction. These changes were unaffected or even increased by bilateral section of the nerves from the carotid sinus and body. They were abolished by section of the vagi or aortic nerves.3. It is concluded that in foetal lambs during the last third of gestation the circulation is under reflex control by the aortic chemoreceptors.