bluuebunny/crossref_metadata_2025 huggingface dataset:
Extended β-globin locus control region elements promote consistent therapeutic expression of a γ-globin lentiviral vector in murine β-thalassemia
Authors: Hanawa Hideki , Hargrove Phillip W. , Kepes Steven , Srivastava Deo K. , Nienhuis Arthur W. , Persons Derek A.
Published: June 2004

Since increased fetal hemoglobin diminishes the severity of β-thalassemia and sickle cell anemia, a strategy using autologous, stem cell–targeted gene transfer of a γ-globin gene may be therapeutically useful. We previously found that a γ-globin lentiviral vector utilizing the β-globin promoter and elements from the β-globin locus control region (LCR) totaling 1.7 kb could correct murine β-thalassemia. However, therapeutic consistency was compromised by chromosomal position effects on vector expression. In contrast, we show here that the majority of animals that received transplants of β-thalassemic stem cells transduced with a new vector containing 3.2 kb of LCR sequences expressed high levels of fetal hemoglobin (17%-33%), with an average vector copy number of 1.3. This led to a mean 26 g/L (2.6 g/dL) increase in hemoglobin concentration and enhanced amelioration of other hematologic parameters. Analysis of clonal erythroid cells of secondary spleen colonies from mice that underwent transplantation demonstrated an increased resistance of the larger LCR vector to stable and variegating position effects. This trend was also observed for vector insertion sites located inside genes, where vector expression was often compromised, in contrast to intergenic sites, where higher levels of expression were observed. These data emphasize the importance of overcoming detrimental position effects for consistent therapeutic globin vector expression.
Positive air pressure transient propagation in building drainage and vent systems
Authors: Swaffield JA , Jack LB , Campbell DP , Gormley M
Published: June 2004

A major objective of drainage research over the past 100 years has been a reduction in the complexity of building drainage vent systems associated with the retention of appliance trap seals. Further simplification requires that the system operation is recognized as time dependent, where changes in water flow conditions result in the propagation of air pressure transients. Negative pressure transients that reduce trap seal levels by induced siphonage are well understood. More problematic is the propagation of positive air pressure transients, generated by stack or branch surcharge. The paper identifies the sources of positive air pressure transient propagation and demonstrates that such transients may be described by the St Venant equations of unsteady flow. Solutions are provided based on the proven finite difference methods and the method of characteristics and an understanding of the boundary conditions that represent the constituent components of a building drainage and vent system.
Study of heat and moisture transport for concrete sandwich panel wall construction
Authors: Lü XS , Lu T , Penttala V , Lehtinen T
Published: June 2004

This paper presents a mathematical model for simulation of transient heat and moisture transfer in concrete sandwich panel wall constructions with variable outdoor temperature and humidity as boundary conditions. The objective is to evaluate the possibility of diminishing moisture content in constructions in order to reduce deterioration risks. Some control strategies involving installation of heating cables in the air gap are proposed and investigated. Simulations demonstrate that the moisture condition of the construction can be improved by using the control regulation developed in this paper. This study improves the understanding of the heat and moisture transport properties of concrete sandwich panels and provides useful information on the decision making in solving the construction's moisture problems.
Achieving quality through statistical prediction for building services systems
Authors: Loy HM , John GA , Clements-Croome DJ , Fairey V , Neale K
Published: June 2004

The application of prediction theories has been widely practised for many years in many industries such as manufacturing, defence and aerospace. Although these theories are not new, their application has not been widely used within the building services industry. Collectively, the building services industry should take a deeper look at these approaches in comparison with the traditional deterministic approaches currently being practised. By extending the application into this industry, this paper seeks to provide the industry with an overview of how simplified stochastic modelling coupled with availability and reliability predictions using historical data compiled from various sources could enhance the quality of building services systems.
A performance indicator for vibration isolation of building services equipment
Authors: Mak CM , Tse CP
Published: June 2004

There is an increasing concern about the sound emitted into the indoor environment due to the vibration of rooftop building services equipment. Force transmissibility or isolation efficiency is a performance indicator of vibration isolators for building services equipment. In the derivation of the force transmissibility, floor structure is usually assumed to be rigid and immovable. The floor structural dynamic characteristics are therefore neglected. It is used in situations for a single contact point or symmetrical arrangement of symmetrical contact points. In the most common situation where a machine with four symmetrical contact points is placed asymmetrically on a floor, dynamic forces transmitted to the floor through each contact point are different. A force transmissibility vector, which comprises these different dynamic forces transmitted to the floor, is introduced. Measurements of the floor mobility have been conducted in several sites. The effect of floor mobility on force transmissibility vector particularly at disturbing frequencies near the resonant frequencies of the floor is also discussed.
A modelling method for conjugate heat transfer and fluid flow in building spaces
Authors: Potter SE , Underwood CP
Published: June 2004

Computational fluid dynamics (CFD) has been used extensively for the prediction of air movement in buildings. In many cases buoyancy forces generated at heated surfaces that dissipate their energy by an interactive process of convection, radiation and conduction dominate air movement. In this work a new method for calculating conjugate fluxes at surfaces involving coupled short-wave and long-wave radiation, convection and conduction is developed as part of the CFD eld problem. The method is based on translating surface radiant exchanges into local volumetric fluxes. Results for a test room with a heated surface compared with data generated within the framework of IEA Annex 20 show that the method produces better results than might be expected from conventional models that use simplified radiant treatments.
The control of pre-cooled natural ventilation
Authors: Chenvidyakarn T , Woods A
Published: June 2004

This paper investigates the control of the natural ventilation of an auditorium or other occupied open-plan space, which vents into a cold exterior through its upper opening, and into which fresh pre-cooled air is drawn through its lower opening. The occupants located at an intermediate level between the upper and lower openings act as an internal source of heat, providing upward buoyancy which drives the ventilation and draws fresh air through the pre-cooling system. These conditions produce a steady state displacement ventilation regime in which the room becomes stratified into two layers, with the transition zone dividing the upper layer of warm air from the lower layer of pre-cooled air across the occupied level. A quantitative model is developed to describe this ventilation process and to investigate the sensitivity of the system. The model is successfully tested with laboratory experiments and shows that with pre-cooled natural ventilation, both ventilation rate and the temperature in the region above and below the heat source may be controlled by the pre-cooling. The paper discusses how such pre-cooling may be manipulated to bring about ventilation and thermal comfort in the ventilated space with a view to maximizing the seasonal range for which natural ventilation is possible.
A robust sequencing control strategy for air-handling units
Authors: Xu Xinhua , Wang Shengwei , Shi Wen-zhong
Published: June 2004

The controllers of air-handling units (AHU) should exploit split-range sequencing control strategies to determine the most economic way to use the AHU components to maintain the outlet air temperature at the set point. The control instability during the transition regions between different control modes as well as the problems in tuning the control loop(s) involving processes of different dynamic parameters are among the major diffculties when utilizing AHU sequencing control strategies in applications. A three PIs split-range sequencing control strategy with ‘freezing’ and gain scheduling schemes (SRFG) is developed addressing these problems. ‘Freezing’ means that the PI output is xed at zero or one together with its integral term. SRFG is evaluated in various simulation tests and by comparing with conventional three PIs split-range sequencing control strategies. Test results demonstrate that SRFG strategy allows stable and robust AHU control.
Pollen productivity estimates for the reconstruction of past vegetation cover in the cultural landscape of southern Sweden
Authors: Broström Anna , Sugita Shinya , Gaillard Marie-José
Published: June 2004

Pollen productivity estimates (PPE) are one of the critical parameters for a quantitative recon struction of past vegetation from fossil pollen records. Modern pollen and vegetation data were collected in traditional landscapes of southern Sweden to derive PPE for the most characteristic plant taxa. The 42 selected sites are assumed to be good analogues of historical to prehistorical grasslands. A sampling method of vegetation, designed to produce plant abundance data in different distance classes, allowed the use of distance-weighted plant abundance around the surface pollen sites. PPE for 11 herb taxa and Juniperus communis were estimated by extended R-value (ERV) models, using the distance-weighted plant abundance and surface pollen data. Results using three ERV submodels, data sets from open and semi-open landscapes, and two distance-weighting methods are generally consistent. The herb taxa analysed have higher PPE than Poaceae except Cyperaceae and Compositae (sub-family) Cichorioideae. Calluna vulgaris, Rumex acetosa type, Juniperus communis and Plantago lanceolata have the highest PPE. Most of the common tree taxa in the region produce 6–8 times as much pollen per unit area as Poaceae. The present set of PPE covers most of the common herb taxa of northwest Europe and will be useful for simu lating pollen dispersal and deposition in heterogeneous landscapes of open and forested vegetation, which will help in future research project design and in the interpretation of fossil data.
Post-traumatic acute renal failure: its pathophysiological basis and treatment
Authors: Ievins FA
Published: June 2004

Acute post-traumatic renal failure is one of the most serious complications that can affect polytrauma patients, with a high morbidity and mortality. The kidney is vulnerable to developing acute renal failure by virtue of the arrangement of its blood supply and the high metabolic demands involved in the production of urine. While several intrinsic mechanisms exist to protect the kidney, these may be swamped following polytrauma. In particular haemorrhage and hypotension can lead to early renal failure; and the massive release of cytokines occurring in the systemic inflammatory response syndrome can lead to renal failure as part of the multiorgan failure syndrome. Early initiation of a renal protection protocol, followed by early conversion to renal replacement therapy if failure develops, reduces both morbidity and mortality. Continuous veno-venous haemofiltration mimics normal production of a glomerular filtrate and forms the basis of renal replacement strategies. It has several potential complications, but modern computerized systems have minimized these.
Medical emergencies in trauma
Authors: Nathani Naz , Perkins Gavin D , Thickett David R
Published: June 2004

Increasing elderly population means an increasing proportion of elderly trauma patients. This group commonly have associated chronic medical disorders which can influence the presentation and outcome of trauma. The common medical causes of trauma include falls, syncope, obstructive sleep apnoea and diabetes mellitus. Comorbid medical conditions mean poor physiological reserve and therefore the importance of timely medical intervention by early identification of a deteriorating patient. Modified Early Warning Score (MEWS) is one such tool which can help early idenfication of a deteriorating patient. Elderly trauma patients frequently develop medical complications while in the hospital and the trauma surgeon should be alert to this and initiate appropriate early management. The Acute Life-threatening Events Recognition and Treatment (ALERTTM) course assessment algorithm (Figure 1) helps in this by providing a system for the comprehensive review of a critically ill patient. Trauma in elderly calls for a multidisciplinary approach and close cooperation between the elderly care physician and the trauma surgeon.
The role of external fixation in trauma
Authors: Pacheco Ricardo J. , Saleh Michael
Published: June 2004

External fixation is a method of immobilization that uses percutaneous pins placed in bone and linked with external connectors to maintain the fracture segments in a desired spatial relationship. It is a valuable clinical treatment option, providing surgeons with the ability to affect the spatial relationship of tissues, both statically and dynamically, via minimally invasive techniques. The ease and speed of application, adjustability of the frame, and minimization of blood loss with preservation of blood supply at the cutaneous and osseous levels are advantages of the external fixation technique. Care of the trauma patient remains one of the major applications for external fixation. Open fractures with severe soft tissue injuries and/or massive contamination are ideally suited to this technique. External fixation is also a versatile salvage technique for the complications arising from extremity trauma. The management of residual fracture deformity, bone loss, infections, and complex post-traumatic arthritis are often facilitated by external fixation.
Cycling: the risks
Authors: Hamilton Richard J , Stott JR Rollin
Published: June 2004

On average, 140 cyclists are killed each year on Britain’s roads and a further 22 785 injured. About a third of those injured are children. This review examines the nature and circumstances of cycling injuries and contrasts them with the risks associated with other modes of transport. It looks at the effectiveness of cycle helmet use and suggests other measures to best reduce cycling injuries.
Myocardial contusion
Authors: Ranasinghe AM , Lewis ME , Graham TR
Published: June 2004

Myocardial contusion can be a difficult diagnosis to make. There is currently no gold standard of investigation that allows its accurate diagnosis in the clinical setting. Trauma surgeons need to have a high degree of clinical suspicion when dealing with patients who have received blunt thoracic injuries in order that the diagnosis of myocardial contusion may be made. In this article we discuss the diagnosis, potential complications and investigation of patients with suspected myocardial contusion and also present a fl ow diagram for the possible management of patients with trauma who may have suspected myocardial contusion.
Learning about Cardiac Calcium Signaling from Genetic Engineering
Authors: MORAD MARTIN , CHAU MY
Published: June 2004

Abstract: Genetic engineering has already provided critical data on the Ca‐induced Ca2+ release (CICR) hypothesis issues and promises even greater future insights. The two approaches employed thus far are (1) the construction of transgenic animal models with deletion or overexpression of Ca2+ signaling proteins, and (2) direct structure‐function studies of these proteins in artificial systems. In our laboratory both approaches have provided some insight into molecular modulation of CICR and the pathophysiology arising from the deletion or overactivity of these proteins. Probing the cytoplasmic segments of the carboxyl c‐terminal tail of Ca2+ channel, we identified two calcium sensing and calmodulin binding domains (LA and K) that have been implicated in Ca2+‐induced inactivation of Ca2+ channels. Introducing these peptides into atrial myocytes, where a large fraction of Ca2+ release sites are unassociated with the dihydropyridine receptors (DHPRs) (no t‐tubules), suggests that LA, but not K motif, increases the sensitivity of RyRs to Ca2+, is responsible for the higher frequency of Ca2+ sparks in the peripheral sites, and provides for the voltage dependence of CICR. Genetic overexpression or deletion of the primary proteins of the Ca2+ signaling cascade also provides supportive evidence for the Ca2+ current (ICa)‐gated CICR mechanism, generates some novel and unexpected cardiac phenotypes in transgenic mice, and suggests that Ca2+ signaling defects can trigger compensatory molecular mechanisms that underlie the observed cardiac phenotype and pathophysiology.
Modeling the Actions of β‐Adrenergic Signaling on Excitation—Contraction Coupling Processes
Authors: GREENSTEIN JOSEPH L. , TANSKANEN ANTTI J. , WINSLOW RAIMOND L.
Published: June 2004

Abstract: Activation of the β‐adrenergic (β‐AR) signaling pathway enhances cardiac function through protein kinase A (PKA)—mediated phosphorylation of target proteins involved in the process of excitation—contraction (EC) coupling. Experimental studies of the effects of β‐AR stimulation on EC coupling have yielded complex results, including increased, decreased, or unchanged EC coupling gain. In this study, we extend a previously developed model of the canine ventricular myocyte describing local control of sarcoplasmic reticulum (SR) calcium (Ca2+) release to include the effects of β‐AR stimulation. Incorporation of phosphorylation‐dependent effects on model membrane currents and Ca2+‐cycling proteins yields changes of action potential (AP) and Ca2+ transients in agreement with those measured experimentally in response to the nonspecific β‐AR agonist isoproterenol (ISO). The model reproduces experimentally observed alterations in EC coupling gain in response to β‐AR agonists and predicts the specific roles of L‐type Ca2+ channel (LCC) and SR Ca2+ release channel phosphorylation in altering the amplitude and shape of the EC coupling gain function. The model also indicates that factors that promote mode 2 gating of LCCs, such as β‐AR stimulation or activation of the Ca2+/calmodulin‐dependent protein kinase II (CaMKII), may increase the probability of occurrence of early after‐depolarizations (EADs), due to the random, long‐duration opening of LCC gating in mode 2.
Integrated Ca2+ Management in Cardiac Myocytes
Authors: SHANNON THOMAS R. , BERS DONALD M.
Published: June 2004

Abstract: Cardiac myocyte excitation—contraction coupling is complex. There are many systems involved that interact to form varied, but well‐tuned, effects that are essential to contractile regulation. Nearly all of these systems are Ca‐dependent, and Ca homeostasis within the myocyte is carefully controlled. Contractile activation results from Ca entry via Ca current, and Ca release from the sarcoplasmic reticulum (SR). Ca extrusion from the cytosol is controlled by Ca transport by (1) the Na—Ca exchanger, (2) the SR Ca‐pump (which is balanced by a Ca leak out of the SR), and (3) slower systems (including Ca transport by mitochondria and the sarcolemmal Ca‐pump). These systems interact to regulate the amount of Ca within the cell at rest, most of which is stored within the SR. The amount of Ca released from the SR depends nonlinearly upon SR [Ca], specifically the free SR [Ca] ([Ca]SR). The relationship is particularly steep at high [Ca]SR, where spontaneous release can take place, resulting in electrical arrhythmias. In many models of heart failure, SR [Ca] is reduced, which may cause decreased Ca release and contractile dysfunction. In summary, the varied processes responsible for Ca regulation within the myocyte are critical to normal heart function, and disruption of the normal operation of these proteins can cause widely varied pathological effects, in large part due to dysfunctional Ca handling.
Molecular and Integrated Biology of Thin Filament Protein Phosphorylation in Heart Muscle
Authors: SUMANDEA MARIUS P. , BURKART EILEEN M. , KOBAYASHI TOMOYOSHI , DE TOMBE PIETER P. , SOLARO R JOHN
Published: June 2004

Abstract: An increasing body of evidence points to posttranslational modifications of the thin filament regulatory proteins, cardiac troponin T (cTnT) and cardiac troponin I (cTnI) by protein kinase C (PKC) phosphorylation as important in both long‐ and short‐term regulation of cardiac function and potentially implicated in the transition between compensated hypertrophy and decompensation. The main sites for PKC‐dependent phosphorylation on cTnI are Ser43, Ser45, and Thr144 and on cTnT are Thr197, Ser201, Thr206, and Thr287 (mouse sequence). We analyzed the function of each phosphorylation residue using a phosphorylation mimic approach introducing glutamates (E) at PKC phosphorylation sites and then measuring the isometric tension of fiber bundles exchanged with these mutants. We also directly phosphorylated cTnI and cTnT by PKC, incorporated the phosphorylated troponins in the myofilament lattice, and determined the isometric tension at varying Ca2+ concentrations. We followed the experimental data with computational analysis prediction of helical content of cTnI and cTnT peptides that undergo phosphorylation. Here we summarize our recent data on the specific functional role of PKC phosphorylation sites of cTnI and cTnT.
The Adaptive Intracellular Control of Cardiac Muscle Function
Authors: LANDESBERG AMIR , LEVY CARMIT , YANIV YAEL , SIDEMAN SAMUEL
Published: June 2004

Abstract: This study explores the mechanisms dominating the regulation of the biochemical energy consumption and the mechanical output of the actin‐myosin motor units, the crossbridges (Xbs), in the cardiac sarcomere. Our analytical model, which couples Xbs cycling dynamics with the kinetics of the free Ca2+ binding to troponin‐C (Tn‐C), includes two feedback mechanisms: (1) a cooperativity mechanism, whereby the amount of force generating Xbs determines the affinity of calcium binding to the regulatory protein and the force‐length relationship (FLR); and (2) a mechanical (negative) feedback, whereby the filament shortening velocity affects the rate of Xb turnover from the force‐ to the nonforce‐generating state, allows the analytical solution for the muscle force‐velocity relationship (FVR), and the linear relation between energy consumption and the generated mechanical energy. Our experimental and analytical studies of the force response to large‐amplitude sarcomere length (SL) oscillations at various frequencies and constant [Ca2+] in the isolated tetanized rat trabeculae reveal that the generated force depends on the history of contraction and establishes the validity of these two feedbacks. The cooperativity mechanism generates counterclockwise (CCW) hystereses, where the muscle generates external work; while at higher frequencies the mechanical feedback produces clockwise (CW) hystereses, where the muscle behaves as a damper. The cooperativity provides the adaptive control of the cardiac response to short‐term changes in the load by modulating Xb recruitment. The cardiac efficiency, defined as the ratio of the generated mechanical energy (i.e., external work and pseudo‐potential energy) to the sarcomere energy consumption, is determined by the mechanical feedback, reflecting an inherent property of the single Xb. The efficiency is thus independent of the number of strong Xbs and is constant and load independent.
Genetics of Cardiac Arrhythmias and Sudden Cardiac Death
Authors: PRIORI SILVIA G. , NAPOLITANO CARLO
Published: June 2004

Abstract: This presentation deals with the molecular substrates of the inherited diseases leading to genetically determined cardiac arrhythmias and sudden death. In the first part of this article the current knowledge concerning the molecular basis of cardiac arrhythmias will be summarized. Second, we will discuss the most recent evidence showing that the picture of the molecular bases of cardiac arrhythmias is becoming progressively more complex. Thanks to the contribution of molecular genetics, the genetic bases, pathogenesis, and genotype‐phenotype correlation of diseases—such as the long QT syndrome, the Brugada syndrome, progressive cardiac conduction defect (Lenegre disease), catecholaminergic polymorphic ventricular tachycardia, and Andersen syndrome—have been progressively unveiled and shown to have an extremely high degree of genetic heterogeneity. The evidence supporting this concept is outlined, with particular emphasis on the growing complexity of the molecular pathways that may lead to arrhythmias and sudden death, in terms of the relationships between genetic defect(s) and genotype(s), as well as gene‐to‐gene interactions. The current knowledge is reviewed, focusing on the evidence that a single clinical phenotype may be caused by different genetic substrates and, conversely, a single gene may cause very different phenotypes acting through different pathways.
Pacemaker Channels
Authors: BARUSCOTTI MIRKO , DIFRANCESCO DARIO
Published: June 2004

Abstract: The pacemaker “funny” current (If) has been the object of detailed investigations since its original description in sinoatrial node myocytes in the late 1970s; its role in underlying generation of spontaneous activity and autonomic modulation of cardiac rate has been amply demonstrated. In the late 1990s four isoforms of the hyperpolarization‐activated, cyclic nucleotide‐gated (HCN) channels, the molecular components of native pacemaker channels, were cloned, and structure‐function relation studies provided a molecular interpretation of several features of the native channels. Its role in pacemaking makes If a natural target of heart rate modulating agents; several heart rate reducing molecules are known today that exert their action by specific inhibition of f‐channels. Experiments aimed at determining the role of If relative to other proposed pacemaker mechanisms such as SR Ca2+ transients confirm that the If‐mediated rate control is a key process in pacemaker generation and autonomic control.
Ventricular Fibrillation: New Insights into Mechanisms
Authors: WEISS JAMES N. , CHEN PENG‐SHENG , WU TSU‐JUEY , SIEGERMAN CARIN , GARFINKEL ALAN
Published: June 2004

Abstract: Device therapy with implantable cardioverter‐defibrillators is currently the only proven effective therapy against sudden cardiac death due to ventricular fibrillation. However, the expanded clinical indications for device therapy come at a staggering cost to an already overburdened health care system. Given these statistics, it is both highly desirable and economically imperative to develop alternative therapies. New insights into the mechanisms of ventricular fibrillation, particularly the role of dynamic factors causing wave instability, are providing a promising avenue for developing novel therapies to prevent sudden cardiac death.
Mechanical Induction of Arrhythmias during Ventricular Repolarization: Modeling Cellular Mechanisms and Their Interaction in Two Dimensions
Authors: GARNY ALAN , KOHL PETER
Published: June 2004

Abstract: Nonpenetrating mechanical stimulation of the precordial chest is particularly likely to instantaneously induce sustained rhythm disturbances if timed to coincide with ventricular repolarization. A number of possible mechanisms have been proposed, including mechanoelectric feedback acting via stretch‐activated ion channels. The cellular effects of such channel activation have been studied and mathematically modeled in great detail. In this study, we investigate their dynamic interaction with the trailing wave of action potential repolarization in a two‐dimensional model of ventricular tissue. The model identifies how stretch activation of cation‐nonselective ion channels causes ectopic excitation in fully repolarized tissue and functional block of conduction at the intersection of the mechanical stimulus and the repolarization wave end, which may give rise to both trigger and sustaining mechanisms of ventricular arrhythmia. Simulation of stretch activation of K+‐selective ion channels alone is insufficient in causing instantaneous arrhythmia, although it may, via action potential shortening, contribute to its sustenance.
Cardiac Ryanodine Receptor Function and Regulation in Heart Disease
Authors: LEHNART STEPHAN E. , WEHRENS XANDER H. T. , KUSHNIR ALEXANDER , MARKS ANDREW R.
Published: June 2004

Abstract: The cardiac ryanodine receptor (RyR2) located on the sarcoplasmic reticulum (SR) controls intracellular Ca2+ release and muscle contraction in the heart. Ca2+ release via RyR2 is regulated by several physiological mediators. Protein kinase (PKA) phosphorylation dissociates the stabilizing FKBP12.6 subunit (calstabin2) from the RyR2 complex, resulting in increased contractility and cardiac output. Congestive heart failure is associated with elevated plasma catecholamine levels, and chronic stimulation of β‐adrenergic receptors leads to PKA hyperphosphorylation of RyR2 in failing hearts. PKA hyperphosphorylation results in calstabin2‐depleted RyR2 that displays altered channel gating and may cause aberrant SR Ca2+ release, depletion of SR Ca2+ stores, and reduced myocardial contractility in heart failure. Calstabin2‐depleted RyR2 may also trigger cardiac arrhythmias that cause sudden cardiac death. In patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), RyR2 missense mutations cause reduced calstabin2 binding to RyR2. Increased RyR2 phosphorylation and pathologically increased calstabin2 dissociation during exercise results in aberrant diastolic calcium release, which may trigger ventricular arrhythmias and sudden cardiac death. In conclusion, heart failure and exercise‐induced sudden cardiac death have been linked to defects in RyR2‐calstabin2 regulation, and this may represent a novel target for the prevention and treatment of these forms of heart disease.
Modulation of the Cardiomyocyte Cell Cycle in Genetically Altered Animals
Authors: FIELD LOREN J.
Published: June 2004

Abstract: Many forms of cardiovascular disease are associated with cardiomyocyte loss via apoptosis and/or necrosis. Although there is currently debate regarding the level at which adult cardiomyocytes can reenter the cell cycle and proliferate, it is clear that the intrinsic regenerative growth capacity is insufficient to reverse the progression to failure in badly injured hearts. The ability to reactivate cardiomyocyte proliferation in damaged hearts might permit regenerative growth, provided that the nascent cells are able to participate in a functional syncytium with the surviving myocardium. In this review, techniques commonly used to monitor cardiomyocyte cell cycle activity in normal and injured hearts are discussed. In addition, several genetic models are described wherein the expression of fundamental cell cycle regulatory proteins has been altered in cardiomyocytes.
Development of the Building Plan of the Heart
Authors: MOORMAN ANTOON F. M. , SOUFAN ALEXANDRE T. , HAGOORT JACO , DE BOER PIET A. J. , CHRISTOFFELS VINCENT M.
Published: June 2004

Abstract: In this communication we discuss the formation of the synchronously contracting chambered heart from a peristaltically contracting linear heart tube. It is proposed that members of the T‐box family of transcription factors play a crucial role in the formation of the building plan of the formed heart. Tbx5 may confer venoarterial polarity to the heart tube, whereas Tbx2 initially and Tbx3 in later developmental stages prevent the cardiac inflow tract, atrioventricular region, outflow tract, as well as the cardiac inner curvatures from chamber differentiation. With the exception of the outflow tract that becomes incorporated into the ventricles, these regions contribute to the cardiac conduction system.
Cardiac Muscle Plasticity in Adult and Embryo by Heart‐Derived Progenitor Cells
Authors: OH HIDEMASA , CHI XUAN , BRADFUTE STEVEN B. , MISHINA YUJI , POCIUS JENNIFER , MICHAEL LLOYD H. , BEHRINGER RICHARD R. , SCHWARTZ ROBERT J. , ENTMAN MARK L. , SCHNEIDER MICHAEL D.
Published: June 2004

Abstract: The evidence of cardiomyocyte proliferation in damaged heart implied cardiac regeneration might occur by resident or extra cardiac stem cells. However, the specification and origin of these cells remain unknown. Here, we report using fluorescence‐activated cell sorting that cardiac progenitor cells resided in adult heart and colocalized with small capillary vessels, within the stem cell antigen (Sca‐1) population expressing high telomerase activity. Notably, hematopoietic stem cells capable of efflux Hoechst 33342, termed side population cells, also were identified within the heart‐derived cells. The cardiac progenitor cells (CD45−/CD34−) express neither cardiac muscle nor endothelial cell markers at an undifferentiated stage. The exposure of 5‐azacytidine induced cardiac differentiation, which depends, in part, on Bmpr1a, a type IA receptor for bone morphogenetic protein (BMP). The capability of adult Sca1+ cells to adopt a cardiac muscle in embryogenesis was substantiated by blastocyst injection, using progenitors from the adult hearts of transgenic mice that harbor a bacterial artificial chromosome expressing GFP via the Nkx‐2.5 locus. Intravenously injected progenitors, shortly after ischemic/reperfusion, homed and functionally differentiated 3.5% of total left ventricle in the host myocardium. Differentiation included both fusion‐independent and fusion‐associated components, proved by the Cre/loxP donor/recipient system. Our studies suggest that endogenous cardiac progenitors reside in the adult heart, regenerate cardiomyocytes functionally, and integrate into the existing heart circuitry.
Linking Gene Expression to Function: Metabolic Flexibility in the Normal and Diseased Heart
Authors: TAEGTMEYER HEINRICH , GOLFMAN LEONARD , SHARMA SAUMYA , RAZEGHI PETER , VAN ARSDALL MELISSA
Published: June 2004

Abstract: Metabolism transfers energy from substrates to ATP. As a “metabolic omnivore,” the normal heart adapts to changes in the environment by switching from one substrate to another. We propose that this flexibility is lost in the maladapted, diseased heart. Both adaptation and maladaptation are the results of metabolic signals that regulate transcription of key cardiac regulatory genes. We propose that metabolic remodeling precedes, initiates, and sustains functional and structural remodeling. The process of metabolic remodeling then becomes a target for pharmacological intervention restoring metabolic flexibility and normal contractile function of the heart.
Molecular and Cellular Aspects of Troponin Cardiomyopathies
Authors: GOMES ALDRIN V. , POTTER JAMES D.
Published: June 2004

Abstract: Advances in molecular genetics have led to the identification of mutations in each troponin subunit that cause different human cardiomyopathies. Mutations in the genes for cardiac troponin T (CTnT), troponin I (CTnI), and troponin C (CTnC) cause familial hypertrophic cardiomyopathy (FHC) and are associated with varying prognosis and mild‐to‐moderate hypertrophy. Mutations in CTnT and CTnC can also cause dilated cardiomyopathy (DCM), whereas mutations in CTnI can cause restrictive cardiomyopathy (RCM). All together, 60 mutations have so far been found in troponin subunits associated with cardiomyopathy. Recently, multiple cardiomyopathic phenotypes (either HCM or RCM), arising from a single nucleotide mutation in the same codon of CTnI, R145, have been documented. Although the clinical phenotypes of the cardiomyopathies vary, two common features are present in most cardiomyopathy patients: altered Ca2+ sensitivity of force development and impaired energy metabolism. Here, we present the analyses of how these troponin mutations affect the in vitro contractile protein function and the hypotheses derived to explain the development of these disease states.
Genetic Factors in Cardiac Hypertrophy
Authors: DORN GERALD W. , HAHN HARVEY S.
Published: June 2004

Abstract: Cardiac hypertrophy is an adaptive response to any cardiac insult or stress that increases hemodynamic load. Cardiac hypertrophy can exist in a state of compensation or progress to a decompensated state (i.e., heart failure) over time. It has been established through transgenic overexpression and gene ablation studies that multiple signaling pathways are involved in the induction of hypertrophy as well as its decompensation. This article reviews the role of Gaq in the development of pressure overload hypertrophy and discusses the relationships between Gαq and β‐adrenergic receptors, RGS proteins, and the proapoptotic factor, Nix/Bnip3L.
“Energenetics” of Heart Failure
Authors: VAN BILSEN MARC
Published: June 2004

Abstract: It has been postulated that the failing heart suffers from chronic energy starvation, and that the derangements in cardiac energy production contribute to the inevitable transition from compensated hypertrophy to decompensated heart failure. Although the existence of metabolic alterations is hardly disputed anymore, the molecular mechanisms driving this “metabolic remodeling” process and its significance for the development of cardiac failure are still open to discussion. Next to changes in mitochondrial function, the hypertrophied heart is characterized by a marked change in substrate preference away from fatty acids toward glucose. Several lines of evidence suggest that these metabolic adaptations are brought about, at least in part, by alterations in the rate of transcription of genes encoding for proteins involved in substrate transport and metabolism. Here, we present an overview of the principal metabolic changes and discuss the various mechanisms that are likely to play a role, with special emphasis on gene regulatory mechanisms. In addition, the significance of these changes for the etiology of heart failure is discussed.
Regulation of Cell Size and Contractile Function by AKT in Cardiomyocytes
Authors: LATRONICO MICHAEL V. G. , COSTINEAN STEFAN , LAVITRANO MARIA LUISA , PESCHLE CESARE , CONDORELLI GIANLUIGI
Published: June 2004

Abstract: AKT is a serine‐threonine kinase involved in several different cellular functions, including the control of cell size and the regulation of survival and metabolism. Many studies have demonstrated that AKT also plays a critical role in the homeostasis of the cardiomyocyte. In these cells, AKT is activated by upstream molecules such as β‐adrenergic receptor, insulin‐like growth factor‐1 or insulin receptor, through PI3Kα; whereas its activation is inhibited by the PTEN molecule. Downstream targets of AKT in the cardiomyocyte include glycogen‐synthase kinase‐3β and S6 kinase. Major effects of AKT activation in the cardiomyocyte are increase in cell size, prevention of apoptosis, and regulation of glucose metabolism. Interestingly, the AKT‐dependent hypertrophic pathway is distinct from that activated by MAPKs. In fact, overexpression of AKT does not lead to MAPK activation. Our group has shown, moreover, that AKT exerts a positive effect on both inotropism and relaxation. In fact, mice overexpressing the E40K mutant of AKT in the heart showed improved cardiac function. Thus, AKT increases both cell size through the S6 kinase pathway and inotropism through the functional regulation of critical Ca2+‐handling proteins. Therefore, AKT is a critical mediator of physiological hypertrophy.
From Genetics to Cellular Function Using Computational Biology
Authors: RUDY YORAM
Published: June 2004

Abstract: This article illustrates how computational biology (computer modeling) can be used to link genetic mutations to their cellular phenotypes. Examples are provided from ion channel defects that are associated with hereditary cardiac arrhythmias—that is, the long QT and Brugada syndromes. State‐specific Markov models of wild‐type and mutant channels are formulated and introduced into a computer model of the ventricular cardiac cell. Simulations are conducted to study the rate‐dependent alterations in action potential properties caused by the mutations. Results provide insights into the cellular mechanisms of QT‐interval prolongation on the ECG in the long QT syndrome and of ST‐segment elevation in the right precordial leads in the Brugada syndrome.
Genetically Engineered Stem Cell Therapy for Tissue Regeneration
Authors: ALESSANDRI GIULIO , EMANUELI COSTANZA , MADEDDU PAOLO
Published: June 2004

Abstract: Therapeutic angiogenesis/vasculogenesis represents a new approach to treat patients with ischemic disease not curable with conventional treatment. This review focuses on the rationale and preliminary results of combining stem cell and gene therapy for regenerative medicine. Under disease conditions, impaired neovascularization results from diminished vascular growth factor production and primary dysfunction of endothelial cells and their progenitors. Advances in our ability to genetically manipulate cells ex vivo has provided the technological platform to implement stem cell biology and circumvent the potential hazard of direct gene transfer. Ex vivo engineered endothelial progenitor cells have been used for the treatment of peripheral limb ischemia. The approach eliminates the drawback of immune response against viral vectors and makes feasible repeating the therapeutic procedure in case of injury recurrence. The strategy of using stem cells as vectors for curative agents proved to be of value for the treatment of pulmonary hypertension and thrombosis. Transplantation of neural stem cells genetically modified to secrete nerve growth factor was able to ameliorate the death of striatal projection neurons caused by transient focal ischemia in the adult rat. By a similar approach, engineered neural stem cells might be used for treating neurodegenerative disorders. Therefore, genetic manipulation of stem cells opens new avenues for regenerative medicine.
Potential Applications of Human Embryonic Stem Cell‐Derived Cardiomyocytes
Authors: CASPI OREN , GEPSTEIN LIOR
Published: June 2004

Abstract: The recent establishment of the human embryonic stem cell lines and the demonstration of their ability to differentiate in vitro to cardiomyocytes brings a unique promise to both basic and clinical research. The present report describes the characteristics of the human embryonic stem cell lines and focuses on the structural and functional properties of their cardiomyocyte derivatives. In addition, the possible signals and cues involved in the commitment and early differentiation of cardiomyocytes will be discussed. Finally, the potential applications of this unique differentiating system in several research and clinical areas are discussed, with special emphasis on the steps required to fully harness their potential for myocardial regeneration strategies.
Controlling the Cellular Organization of Tissue‐Engineered Cardiac Constructs
Authors: GONEN‐WADMANY MAYA , GEPSTEIN LIOR , SELIKTAR DROR
Published: June 2004

Abstract: There are currently no effective treatments to restore the cardiac muscle lost because of ischemia for the millions of people who suffer heart attacks annually. Cell therapy procedures have emerged as novel therapeutic strategies for treatment of heart failure after myocardial infarction but have been hampered by the lack of adequate cell sources of cardiomyocytes and by the inability to integrate cell grafts into cardiac muscle. A cardiac patch composed of organized and functional cardiomyocytes could drastically enhance the efficacy of this important clinical approach. Here, we report our ongoing efforts to develop a bioartificial cardiac muscle capable of synchronized multidirectional contraction within a three‐dimensional hydrogel scaffold. Neonatal rat cardiomyocytes, smooth muscle cells, and reconstituted polymeric collagen enriched with growth factors and hormones are used. A bioreactor system is used to impart precise strains onto the developing tissue constructs in vitro. The results demonstrate that cell‐mediated collagen compaction is significantly enhanced by strain preconditioning, resulting in a more favorable cellular organization. Furthermore, the results demonstrate that strain stimulation guides cellular orientation in the direction of applied strain (i.e., in the circumferential direction). Hence, we demonstrate the importance of mechanical preconditioning as a means of promoting the in vitro development of engineered cardiac muscle for use with myocardial regeneration therapies.
Myocardial Tissue Engineering: Creating a Muscle Patch for a Wounded Heart
Authors: LEOR JONATHAN , COHEN SMADAR
Published: June 2004

Abstract: Cardiac tissue engineering promises to revolutionize the treatment of patients with end‐stage heart failure and provide new solutions to the serious problem of heart donor shortage. By its broad definition, tissue engineering involves the construction of tissue equivalents from donor cells seeded within three‐dimensional polymeric scaffolds, then culturing and implanting of the cell‐seeded scaffolds to induce and direct the growth of new, healthy tissue. Here, we present an up‐to‐date summary of research studies in cardiac tissue engineering, with an emphasis on the critical design principles.
Models of Dilated Cardiomyopathy in Small Animals and Novel Positive Inotropic Therapies
Authors: HOSHIJIMA MASAHIKO
Published: June 2004

Abstract: Several randomized clinical trials of vesnarinone and milrinone in patients with heart failure left disappointing results in the 1990s. Thereafter, use of positive inotropic agents has been avoided. Exceptions are the use of digitalis glycosides to treat mild‐moderate heart failure and the intravenous administration of catecholamines and phosphodiesterase inhibitors in patients with acute and/or refractory heart failure. It is not, however, exactly known whether chronic enhancement of cardiac contractility indeed has harmful effects, besides increased risk of arrhythmia and mortality. We investigated the potential chronic benefit of positive inotropic modification to treat progressive cardiomyopathy and associated heart failure using a genetic complementation strategy of muscle lim‐protein and phospholamban (PLN) double mutagenesis in the mouse and found clear evidence of positive effects. Subsequent somatic modification of PLN function via gene transfer with recombinant adeno‐associated virus vectors in small animal models of dilated cardiomyopathy further supported the chronic benefit of enhanced cardiac function achieved in an β‐adrenergic stimulus‐independent manner. This study examines current small animal models of dilated cardiomyopathy and recent multiple attempts to use these models as novel gene‐based inotropic therapies.
Gene Therapy for Cardiac Arrhythmias
Authors: DONAHUE J KEVIN
Published: June 2004

Abstract: Myocardial gene transfer has shown tremendous potential to investigate pathophysiology and potential therapies for cardiac diseases. In the field of cardiac arrhythmias, there is a tremendous need for new therapeutic options. The current work reviews the need for new therapies for cardiac arrhythmias, the use of gene transfer to evaluate cellular electrophysiology, the application of in vivo gene transfer to treatment of common arrhythmias, and the current problems in the field of cardiac gene therapy. Arrhythmia gene therapy is a field in its infancy, and future human applications are dependent on solutions to the problems discussed here.