Histogenesis of the semilunar valves: an immunohistochemical analysis of tenascin and type-I collagen distribution in developing chick heart valves

Summary The development of the semilunar valves takes place in association with septation of the outflow tract in the embryonic heart. Although numerous studies have focused on this process, the causal mechanisms of valvular development remain obscure. This paper reports an immunohistochemical analysis of tenascin and type-I collagen distribution in developing chick heart valves. Tenascin is a glycoprotein that is present on some embryonic extracellular matrices. It plays several significant roles in tissue differentiation, cell growth, and tissue interactions; it is also important for the formation of specific zones of connective tissue that fulfill mechanical functions. Our results show that tenascin is present during valvular morphogenesis and histogenesis, and that its distribution is associated with zones specialized in bearing mechanical loads.     

Validation of numerical flow simulations against in vitro phantom measurements in different type B aortic dissection scenarios

An aortic dissection (AD) is a serious condition defined by the splitting of the arterial wall, thus generating a secondary lumen [the false lumen (FL)]. Its management, treatment and follow-up are clinical challenges due to the progressive aortic dilatation and potentially severe complications during follow-up. It is well known that the direction and rate of dilatation of the artery wall depend on haemodynamic parameters such as the local velocity profiles, intra-luminal pressures and resultant wall stresses. These factors act on the FL and true lumen, triggering remodelling and clinical worsening. In this study, we aimed to validate a computational fluid dynamic (CFD) tool for the haemodynamic characterisation of chronic (type B) ADs. We validated the numerical results, for several dissection geometries, with experimental data obtained from a previous in vitro study performed on idealised dissected physical models. We found a good correlation between CFD simulations and experimental measurements as long as the tear size was large enough so that the effect of the wall compliance was negligible.     

Effects of colchicine administration on the endothelial cells of the developing semilunar heart valves of the chick embryo

Summary Recent ultrastructural studies have revealed that differences exist in endothelial cell shape and cytoskeletal architecture between the arterial and ventricular faces of developing semilunar valves. In the present work we analyzed the morphologic response of the valvular endothelial cells of chick embryos to colchicine by light microscopy, scanning electron microscopy and transmission electron microscopy. The results show that colchicine administration during the stages of valve morphogenesis causes a very conspicuous disruption of the endothelial layer of the arterial face of the valves. The cells appear rounded and show massive surface blebbing. These alterations were not present in the endothelial cells on the ventricular face of the valves at the same stages. On the basis of these results we suggest that a difference in the degree of cell differentiation exists between the endothelial cells of the arterial and ventricular faces of the cusps and that this difference may have morphogenetic significance.     

Imaging analysis of collagen fiber networks in cusps of porcine aortic valves: effect of their local distribution and alignment on valve functionality

The cusps of native aortic valve (AV) are composed of collagen bundles embedded in soft tissue, creating a heterogenic tissue with asymmetric alignment in each cusp. This study compares native collagen fiber networks (CFNs) with a goal to better understand their influence on stress distribution and valve kinematics. Images of CFNs from five porcine tricuspid AVs are analyzed and fluid-structure interaction models are generated based on them. Although the valves had similar overall kinematics, the CFNs had distinctive influence on local mechanics. The regions with dilute CFN are more prone to damage since they are subjected to higher stress magnitudes.     

Structural reorganization of molecular sheets derived from cellulose II by molecular dynamics simulations

We investigated structural reorganization of two different kinds of molecular sheets derived from the cellulose II crystal using molecular dynamics (MD) simulations, in order to identify the initial structure of the cellulose crystal in the course of its regeneration process from solution. After a one-nanosecond simulation, the molecular sheet formed by van der Waals forces along the () crystal plane did not change its structure in an aqueous environment, while the other one formed by hydrogen bonds along the (1 1 0) crystal plane changed into a van der Waals-associated molecular sheet, such as the former. The two structures that were calculated showed substantial similarities such as the high occupancy of intramolecular hydrogen bonds between O3^H and O5 of over 0.75, few intermolecular hydrogen bonds, and the high occurrence of hydrogen bonding with water. The convergence of the two structures into one denotes that the van der Waals-associated molecular sheet can be the initial structure of the cellulose crystal formed in solution. The main chain conformations were almost the same as those in the cellulose II crystal except for a −16° shift of φ (dihedral angle of O5-C1-O1-C4) and the gauche-gauche conformation of the hydroxymethyl side group appears probably due to its hydrogen bonding with water. These results suggest that the van der Waals-associated molecular sheet becomes stable in an aqueous environment with its hydrophobic inside and hydrophilic periphery. Contrary to this, a benzene environment preferred a hydrogen-bonded molecular sheet, which is expected to be the initial structure formed in benzene.     

A versatile in vitro assay for investigating angiogenesis of the heart

Neovascularization in the heart is usually investigated with models of angiogenesis in vivo. Here we present a simple model that allows investigating heart angiogenesis in mice and rats in vitro. Small pieces of left ventricular myocardium were cultured in three-dimensional fibrin gels for 10 days. A single mouse heart allowed assessing 24 conditions, each tested in octuplicates. Rat recombinant VEGF164, human recombinant bFGF, and human recombinant PDGF-BB were used under normoxia (21% O2) and hypoxia (3% O2), and outgrowth of endothelial sprouts from heart pieces was quantified. In 4-week-old OF1 mice, endothelial sprouts formed spontaneously. In contrast, in 12-week-old adult mice, virtually no sprouts formed under normoxia. Under hypoxia, sprout formation increased substantially. Different growth factors induced formation of distinct patterns of sprouts and unorganized single cells. Sprouts were composed of endothelial cells with smooth muscle cells or pericytes interacting with them, as assessed by immunohistochemistry. Taken together, our model is suited for investigation of angiogenesis of the heart in vitro. It may allow performing extensive series of experiments in vitro including rapid screening of pharmacological compounds and assessment of mechanisms of heart angiogenesis in transgenic animals in an easy straightforward manner.