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  • Identification of Thymosin β4 as an effector of Hand1-mediated vascular development.

    12 December 2017

    The bHLH transcription factor Hand1 (Heart and neural crest-derived transcript-1) has a fundamental role in cardiovascular development; however, the molecular mechanisms have not been elucidated. In this paper we identify Thymosin β4 (Tβ4/Tmsb4x), which encodes an actin monomer-binding protein implicated in cell migration and angiogenesis, as a direct target of Hand1. We demonstrate that Hand1 binds an upstream regulatory region proximal to the promoter of Tβ4 at consensus Thing1 and E-Box sites and identify both activation and repression of Tβ4 by Hand1, through direct binding within either non-canonical or canonical E-boxes, providing new insight into gene regulation by bHLH transcription factors. Hand1-mediated activation of Tβ4 is essential for yolk sac vasculogenesis and embryonic survival, and administration of synthetic TB4 partially rescues yolk sac capillary plexus formation in Hand1-null embryos. Thus, we identify an in vivo downstream target of Hand1 and reveal impaired yolk sac vasculogenesis as a primary cause of early embryonic lethality following loss of this critical bHLH factor.

  • Amniotic fluid stem cells are cardioprotective following acute myocardial infarction.

    12 December 2017

    In recent years, various types of stem cells have been characterized and their potential for cardiac regeneration has been investigated. We have previously described the isolation of broadly multipotent cells from amniotic fluid, defined as amniotic fluid stem (AFS) cells. The aim of this study was to investigate the therapeutic potential of human AFS cells (hAFS) in a model of acute myocardial infarction. Wistar rats underwent 30 min of ischemia by ligation of the left anterior descending coronary artery, followed by administration of hAFS cells and 2 h of reperfusion. Infarct size was assessed by 2,3,5-triphenyltetrazolium chloride staining and planimetry. hAFS cells were also analyzed by enzyme-linked immunosorbent assay to detect secretion of putative paracrine factors, such as the actin monomer-binding protein thymosin β4 (Tβ4). The systemic injection of hAFS cells and their conditioned medium (hAFS-CM) was cardioprotective, improving myocardial cell survival and decreasing the infarct size from 53.9%±2.3% (control animals receiving phosphate-buffered saline injection) to 40.0%±3.0% (hAFS cells) and 39.7%±2.5% (hAFS-CM, P<0.01). In addition, hAFS cells were demonstrated to secrete Tβ4, previously shown to be both cardioprotective and proangiogenic. Our results suggest that AFS cells have therapeutic potential in the setting of acute myocardial infarction, which may be mediated through paracrine effectors such as Tβ4. Therefore, AFS cells might represent a novel source for cell therapy and cell transplantation strategies in repair following ischemic heart disease, with a possible paracrine mechanism of action and a potential molecular candidate for acute cardioprotection.

  • Thymosin beta4 facilitates epicardial neovascularization of the injured adult heart.

    12 December 2017

    Ischemic heart disease complicated by coronary artery occlusion causes myocardial infarction (MI), which is the major cause of morbidity and mortality in humans (http://www.who.int/cardiovascular_diseases/resources/atlas/en/index.html). After MI the human heart has an impaired capacity to regenerate and, despite the high prevalence of cardiovascular disease worldwide, there is currently only limited insight into how to stimulate repair of the injured adult heart from its component parts. Efficient cardiac regeneration requires the replacement of lost cardiomyocytes, formation of new coronary blood vessels, and appropriate modulation of inflammation to prevent maladaptive remodeling, fibrosis/scarring, and consequent cardiac dysfunction. Here we show that thymosin beta4 (Tbeta4) promotes new vasculature in both the intact and injured mammalian heart. We demonstrate that limited EPDC-derived endothelial-restricted neovascularization constitutes suboptimal "endogenous repair," following injury, which is significantly augmented by Tbeta4 to increase and stabilize the vascular plexus via collateral vessel growth. As such, we identify Tbeta4 as a facilitator of cardiac neovascularization and highlight adult EPDCs as resident progenitors which, when instructed by Tbeta4, have the capacity to sustain the myocardium after ischemic damage.

  • The role of photon scattering in voltage-calcium fluorescent recordings of ventricular fibrillation

    20 November 2017

    Recent optical mapping studies of cardiac tissue suggest that membrane voltage (V m ) and intracellular calcium concentrations (Ca) become dissociated during ventricular fibrillation (VF), generating a proarrhythmic substrate. However, experimental methods used in these studies may accentuate measured dissociation due to differences in fluorescent emission wavelengths of optical voltage/calcium (V opt /Ca opt ) signals. Here, we simulate dual voltage-calcium optical mapping experiments using a monodomain-Luo-Rudy ventricular-tissue model coupled to a photon-diffusion model. Dissociation of both electrical, V m /Ca, and optical, V opt /Ca opt , signals is quantified by calculating mutual information (MI) for VF and rapid pacing protocols. We find that photon scattering decreases MI of V opt /Ca opt signals by 23% compared to unscattered V m /Ca signals during VF. Scattering effects are amplified by increasing wavelength separation between fluorescent voltage/calcium signals and respective measurement-location misalignment. In contrast, photon scattering does not affect MI during rapid pacing, but high calcium dye affinity can decrease MI by attenuating alternans in Ca opt but not in V opt . We conclude that some dissociation exists between voltage and calcium at the cellular level during VF, but MI differences are amplified by current optical mapping methods. © 2011 Biophysical Society.

  • Minimum Information about a Cardiac Electrophysiology Experiment (MICEE): Standardised reporting for model reproducibility, interoperability, and data sharing

    12 December 2017

    Cardiac experimental electrophysiology is in need of a well-defined Minimum Information Standard for recording, annotating, and reporting experimental data. As a step towards establishing this, we present a draft standard, called Minimum Information about a Cardiac Electrophysiology Experiment (MICEE). The ultimate goal is to develop a useful tool for cardiac electrophysiologists which facilitates and improves dissemination of the minimum information necessary for reproduction of cardiac electrophysiology research, allowing for easier comparison and utilisation of findings by others. It is hoped that this will enhance the integration of individual results into experimental, computational, and conceptual models. In its present form, this draft is intended for assessment and development by the research community. We invite the reader to join this effort, and, if deemed productive, implement the Minimum Information about a Cardiac Electrophysiology Experiment standard in their own work. © 2011 Elsevier Ltd.

  • An investigation into the role of the optical detection set-up in the recording of cardiac optical mapping signals: A Monte Carlo simulation study

    12 December 2017

    Photon scattering is known to distort the fluorescence signals recorded from optically mapped cardiac tissue. However, the contribution of the parameters which define the optical detection set-up has not been assessed. In this study, Monte Carlo (MC) simulations of photon scattering within ventricular tissue are combined with a detailed model of a tandem-lens optical detection apparatus to characterise (i) the spatial origin upon emission of photons recorded in voltage-sensitive fluorescence measurements of cardiac electrical activity (using the fluorescent dye di-4-ANEPPS) and how this affects signal distortion, and (ii) the role the detector characteristics could play in modulating signal distortion during uniform illumination and photon emission from tissue depth. Results show that, for the particular excitation/emission wavelengths considered (488 nm and 669 nm, respectively), the dimensions of the scattering volume during uniform illumination extend around 3 times further in the surface recording plane than in depth. As a result, fluorescence recordings during electrical propagation are more distorted when transmembrane potential levels differ predominantly in the surface plane than in depth. In addition, MC simulation results show that the spatial accuracy of the fluorescence signal is significantly limited due to photon scattering, with only a small fraction of the recorded signal intensity originating from tissue beneath the pixel (approximately 11% for a 0.25×0.25 mm pixel). Increasing pixel size increases this fraction, however, it also results in an increase in the scattering volume dimensions, thus reducing the spatial resolution of the optical system, and increasing signal distortion. MC simulations also demonstrate that photon scattering in cardiac tissue limits the ability of optical detection system tuning in accurately locating fluorescent emission from depth. Specifically, our results prove that the focal plane depth that yields maximum signal intensity provides an underestimation of the emission depth. In conclusion, our study demonstrates the potential of MC simulations of photon scattering in guiding the design of optical mapping set-ups to optimise performance under diverse experimental conditions. © 2008 Elsevier B.V. All rights reserved.

  • Resetting and annihilating reentrant waves in a ring of cardiac tissue: Theory and experiment

    27 October 2017

    Theory predicts that a stimulus delivered to an excitation wave circulating on a ring of excitable media will either have no effect, or it will reset or annihilate the excitation depending on the phase and magnitude of the stimulus. We summarize the basis for these theoretical predictions and demonstrate these phenomena in an experimental system consisting of a tissue culture of embryonic chick heart cells cultured in the shape of a ring.

  • Robbins Group

    23 October 2017

    Human physiology: Effects of hypoxia and exercise on respiratory, cardiovascular and metabolic function

  • Smart Group

    10 July 2016

    Development, maintenance and regeneration of the cardiovascular system

  • Srinivas Group

    10 July 2016

    Patterning and morphogenesis of the early mammalian embryo

  • Stein Group

    16 September 2013

    Visuomotor control in movement disorders and developmental dyslexia

  • Swietach Group

    10 July 2016

    SURVIVING METABOLISM: acid handling and signalling

  • Szele Group

    10 July 2016

    We study postnatal and adult mammalian brain stem cells to uncover fundamental developmental mechanisms and disease pathogenesis.

  • Taylor Group

    10 July 2016

    Axon Growth and Guidance in the Developing and Regenerating Central Nervous System

  • Tyler Group

    10 July 2016

    Development and Application of Cardiac Magnetic Resonance Imaging and Spectroscopy

  • Urban Group

    16 September 2013

  • Waddell Group

    10 July 2016

    Memory, motivation and individuality