Rupture of atherosclerotic plaques is the underlying cause for the majority of acute strokes and myocardial infarctions. Rupture of the plaque occurs when the stress in the plaque exceeds the... Show moreRupture of atherosclerotic plaques is the underlying cause for the majority of acute strokes and myocardial infarctions. Rupture of the plaque occurs when the stress in the plaque exceeds the strength of the material locally. Biomechanical stress analyses are commonly based on pressurized geometries, in most cases measured by in-vivo MRI. The geometry is therefore not stress-free. The aim of this study is to identify the effect of neglecting the initial stress state on the plaque stress distribution. Fifty 2D histological sections (7 patients, 9 diseased coronary artery segments), perfusion fixed at 100 mmHg, were segmented and finite element models were created. The Backward Incremental method was applied to determine the initial stress state and the zero-pressure state. Peak plaque and cap stresses were compared with and without initial stress. The effect of initial stress on the peak stress was related to the minimum cap thickness, maximum necrotic core thickness, and necrotic core angle. When accounting for initial stress, the general relations between geometrical features and peak cap stress remain intact. However, on a patient-specific basis, accounting for initial stress has a different effect on the absolute cap stress for each plaque. Incorporating initial stress may therefore improve the accuracy of future stress based rupture risk analyses for atherosclerotic plaques. (C) 2011 Elsevier Ltd. All rights reserved. Show less
BACKGROUND Hyperpolarization-activated cyclic nucleotidegated channel 4 (HCN4) in the mouse is expressed in the developing cardiac conduction system (CCS). In the sinoatrial node (SAN), HCN4 is the... Show moreBACKGROUND Hyperpolarization-activated cyclic nucleotidegated channel 4 (HCN4) in the mouse is expressed in the developing cardiac conduction system (CCS). In the sinoatrial node (SAN), HCN4 is the predominant isoform responsible for the funny current. To date, no data are available on HCN4 expression during chicken CCS development. OBJECTIVE The purpose of this study was to provide the full-length sequence of Hcn4 and describe its expression pattern during development in relation to the CCS in the chicken embryo. METHODS Hcn4 RNA expression was studied by in situ hybridization in sequential chick developmental stages (HH11-HH35) and immunohistochemical staining was conducted for the myocardial protein cardiac troponin I and the cardiac transcription factor Nkx2.5. RESULTS We obtained the full-length sequence of Hcn4 in chick. Hcn4 expression was observed early in development in the primary heart tube. At later stages, expression became restricted to transitional zones flanked by working myocardium, comprising the sinus venosus myocardium where the SAN develops, the atrioventricular canal myocardium, the primary fold (a myocardial zone between the developing ventricles), and the developing outflow tract. Further in development, Hcn4 expression was restricted to the SAN, the atrioventricular node, the common bundle, the bundle branches, and the internodal and atrioventricular ring myocardium. CONCLUSION We have identified Hcn4 as a marker of the developing CCS in the chick. The primary heart tube expresses Hcn4, which is later restricted to the transitional zones and eventually the elements of the mature CCS. Furthermore, we hypothesize that expression patterns during development may delineate potential arrhythmogenic sites in the adult heart. Show less
Endothelial cells (EC) translate biomechanical forces into functional and phenotypic responses that play important roles in cardiac development. Specifically, EC in areas of high shear stress, i.e.... Show moreEndothelial cells (EC) translate biomechanical forces into functional and phenotypic responses that play important roles in cardiac development. Specifically, EC in areas of high shear stress, i.e., in the cardiac outflow tract and atrioventricular canal, are characterized by high expression of Kruppel-like factor 2 (Klf2) and by transforming growth factor-beta (Tgf beta)-driven endothelial-to-mesenchymal transition. Extraembryonic venous obstruction (venous clip model) results in congenital heart malformations, and venous clip-induced alterations in shear stress-related gene expression are suggestive for an increase in cardiac shear stress. Here, we study the effects of shear stress on Klf2 expression and Tgf beta-associated signaling in embryonic EC in vivo using the venous clip model and in vitro by subjecting cultured EC to fluid flow. Cellular responses were assessed by analysis of Klf2, Tgf beta ligands, and their downstream signaling targets. Results show that, in embryonic EC, shear stress activates Tgf beta/Alk5 signaling and that induction of Klf2 is an Alk5 dependent process. Developmental Dynamics 240: 1670-1680, 2011. (C) 2011 Wiley-Liss, Inc. Show less
Egorova, A.D.; Heiden, K. van der; Pas, S. van de; Vennemann, P.; Poelma, C.; DeRuiter, M.C.; ... ; Hierck, B.P. 2011
Rationale: Primary cilia are cellular protrusions that serve as mechanosensors for fluid flow. In endothelial cells (ECs), they function by transducing local blood flow information into functional... Show moreRationale: Primary cilia are cellular protrusions that serve as mechanosensors for fluid flow. In endothelial cells (ECs), they function by transducing local blood flow information into functional responses, such as nitric oxide production and initiation of gene expression. Cilia are present on ECs in areas of low or disturbed flow and absent in areas of high flow. In the embryonic heart, high-flow regime applies to the endocardial cushion area, and the absence of cilia here coincides with the process of endothelial-to-mesenchymal transition (EndoMT). Objective: In this study, we investigated the role of the primary cilium in defining the responses of ECs to fluid shear stress and in EndoMT. Methods and Results: Nonciliated mouse embryonic ECs with a mutation in Tg737/Ift88 were used to compare the response to fluid shear stress to that of ciliated ECs. In vitro, nonciliated ECs undergo shear-induced EndoMT, which is accompanied by downregulation of Klf4. This Tgf beta/Alk5-dependent transformation is prevented by blocking Tgf beta signaling, overexpression of Klf4, or rescue of the primary cilium. In the hearts of Tg737(orpk/orpk) embryos, Tgf beta/Alk5 signaling was activated in areas in which ECs would normally be ciliated but now lack cilia because of the mutation. In these areas, ECs show increased Smad2 phosphorylation and expression of alpha-smooth muscle actin. Conclusions: This study demonstrates the central role of primary cilia in rendering ECs prone to shear-induced activation of Tgf beta/Alk5 signaling and EndoMT and thereby provides a functional link between primary cilia and flow-related endothelial performance. (Circ Res. 2011;108:1093-1101.) Show less
Methods and Results: Expression of RhoA, myocardial markers cTnI and Nkx2.5, transcription factors Isl-1 and Tbx18, and cation channel HCN4 were examined in sequential stages in chick embryos.... Show moreMethods and Results: Expression of RhoA, myocardial markers cTnI and Nkx2.5, transcription factors Isl-1 and Tbx18, and cation channel HCN4 were examined in sequential stages in chick embryos. Electrical activation patterns were studied using microelectrodes and optical mapping. Embryonic sinus venosus myocardium is cTnI and HCN4 positive, Nkx2.5 negative, complemented by distinct patterns of Isl-1 and Tbx18. During development, initial myocardium-wide expression of RhoA becomes restricted to right-sided sinus venosus myocardium, comprising the SAN. Electrophysiological measurements revealed initial capacity of both atria to show electrical activity that in time shifts to a right-sided dominance, coinciding with persistence of RhoA, Tbx18, and HCN4 and absence of Nkx2.5 expression in the definitive SAN. Conclusion: Results show an initially bilateral electrical potential of sinus venosus myocardium evolving into a right-sided activation pattern during development, and suggest a role for RhoA in conduction system development. We hypothesize an initial sinus venosus-wide capacity to generate pacemaker signals, becoming confined to the definitive SAN. Lack of differentiation toward a chamber phenotype would explain ectopic pacemaker foci. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1284-1292, November 2010). Show less
Technical advances that have made it possible to perform physiological measurements on very small organisms, including those in embryonic and larval stages, have resulted in the formation of the... Show moreTechnical advances that have made it possible to perform physiological measurements on very small organisms, including those in embryonic and larval stages, have resulted in the formation of the discipline of developmental physiology. The transparency and size of developing organisms in some areas permit insights into physiological processes that cannot be obtained with opaque, adult organisms. On the other hand, it is widely accepted that without eggs, there are no chickens, so physiological adaptations during early life are just as important to species survival as those manifested by adults. Physiological adaptations of early developmental stages, however, are not always the same as patterns known in adults; they often follow their own rules. The adaptability of early developmental stages demonstrates that development is not stereotyped and a phenotype is not just the result of genetic information and the expression of a certain series of genes. Environmental factors influence phenotype production, and this in turn results in flexibility and plasticity in physiological processes. This article comprises exemplary studies presented at the Fourth International Conference in Africa for Comparative Physiology and Biochemistry (Maasai Mara, Kenya, 2008). It includes a brief introduction into technical advances, discusses the developing cardiovascular system of various vertebrates, and demonstrates the flexibility and plasticity of early developmental stages. Fluid forces, oxygen availability, ionic homeostasis, and the chemical environment (including, e. g., hormone concentrations or cholesterol levels) all contribute to the shaping and performance of the cardiovascular system. Show less
Development of the epicardium Epithelial-mesenchymal transition into EPDCs Derivatives of EPDCs Potential role of EPDCs in cardiomyopathy and valve disease Potential of EPDCs as adult stem cells... Show moreDevelopment of the epicardium Epithelial-mesenchymal transition into EPDCs Derivatives of EPDCs Potential role of EPDCs in cardiomyopathy and valve disease Potential of EPDCs as adult stem cells Reactivation of endogenous epicardium after ischemia The proepicardial-derived epicardium covers the myocardium and after a process of epithelial-mesenchymal transition (EMT) forms epicardium-derived cells (EPDCs). These cells migrate into the myocardium and show an essential role in the induction of the ventricular compact myocardium and the differentiation of the Purkinje fibres. EPDCs are furthermore the source of the interstitial fibroblast, the coronary smooth muscle cell and the adventitial fibroblast. The possible differentiation into cardiomyocytes, endothelial cells and the recently described telocyte and other cells in the cardiac stem cell niche needs further investigation. Surgically or genetically disturbed epicardial and EPDC differentiation leads to a spectrum of abnormalities varying from thin undifferentiated myocardium, which can be embryonic lethal, to a diminished coronary vascular bed with even absent main coronary arteries. The embryonic potential of EPDCs has been translated to both structural and functional congenital malformations and adult cardiac disease, like development of Ebstein's malformation, arrhythmia and cardiomyopathies. Furthermore, the use of adult EPDCs as a stem cell source has been explored, showing in an animal model of myocardial ischemia the recapitulation of the embryonic program with improved function, angiogenesis and less adverse remodeling. Combining EPDCs and adult cardiomyocyte progenitor cells synergistically improved these results. The contribution of injected EPDCs was instructive rather than constructive. The finding of reactivation of the endogenous epicardium in ischemia with re-expression of developmental genes and renewed EMT marks the onset of a novel therapeutic focus. Show less
Winter, E.M.; Hogers, B.; Graaf, L.M. van der; Gittenberger-de Groot, A.C.; Poelmann, R.E.; Weerd, L. van der 2010
Recently, debate has arisen about the usefulness of cell tracking using iron oxide-labeled cells. Two important issues in determining the usefulness of cell tracking with MRI are generally... Show moreRecently, debate has arisen about the usefulness of cell tracking using iron oxide-labeled cells. Two important issues in determining the usefulness of cell tracking with MRI are generally overlooked; first, the effect of graft rejection in immunocompetent models, and second, the necessity for careful histological confirmation of the fate of the labeled cells in the presence of iron oxide. Therefore, both iron oxide-labeled living as well as dead epicardium-derived cells (EPDCs) were investigated in ischemic myocardium of immunodeficient non-obese diabetic (NOD)/acid: non-obese diabetic severe combined immunodeficient (NOD/scid) mice with 9.4T MRI until 6 weeks after surgery, at which time immunohistochemical analysis was performed. In both groups, voids on MRI scans were observed that did not change in number, size, or localization over time. Based on MRI, no distinction could be made between living and dead injected cells. Prussian blue staining confirmed that the hypointense spots on MRI corresponded to iron-loaded cells. However, in the dead-EPDC recipients, all iron-positive cells appeared to be macrophages, while the living-EPDC recipients also contained engrafted iron-loaded EPDCs. Iron labeling is inadequate for determining the fate of transplanted cells in the immunodeficient host, since dead cells produce an MRI signal indistinguishable from incorporated living cells. Magn Reson Med 63:817-821, 2010. (C) 2010 Wiley-Liss, Inc. Show less
Poelma, C.; Heiden, K. van der; Hierck, B.P.; Poelmann, R.E.; Westerweel, J. 2010
In order to study the role of blood-tissue interaction in the developing chicken embryo heart, detailed information about the haemodynamic forces is needed. In this study, we present the first in... Show moreIn order to study the role of blood-tissue interaction in the developing chicken embryo heart, detailed information about the haemodynamic forces is needed. In this study, we present the first in vivo measurements of the three-dimensional distribution of wall shear stress (WSS) in the outflow tract (OFT) of an embryonic chicken heart. The data are obtained in a two-step process: first, the three-dimensional flow fields are measured during the cardiac cycle using scanning microscopic particle image velocimetry; second, the location of the wall and the WSS are determined by post-processing flow velocity data (finding velocity gradients at locations where the flow approaches zero). The results are a three-dimensional reconstruction of the geometry, with a spatial resolution of 15-20 mu m, and provides detailed information about the WSS in the OFT. The most significant error is the location of the wall, which results in an estimate of the uncertainty in the WSS values of 20 per cent. Show less
