Abstract
Cardiovascular development is directed or modulated by genetic and epigenetic factors. The latter include blood flow-related shear stress and blood pressure-related circumferential strain. This review focuses on shear stress and its effects on endothelial cells lining the inner surfaces of the heart and blood vessels. Flow characteristics of the embryonic blood, like velocity, viscosity and periodicity, are taken into account to describe the responses of endothelial cells to shear stress and the sensors for this friction force. The primary cilium, which is an integral part of the shear sensor, connects to the cytoskeletal microtubules and transmits information about the level and direction of blood flow into the endothelial cell. When the heart remodels from a more or less straight into a c-shaped tube the sharp curvature, in combination with the small vessel dimensions and high relative viscosity, directs the highest shear stress to the inner curvature of this pump. This proves to be an important epigenetic modulator of cardiac morphogenesis because when shear stress is experimentally altered inner curvature remodeling is affected which leads to the development of congenital cardiovascular anomalies. The best of both worlds, mechanics and biology, are used here to describe early cardiogenesis.
Highlights
The heart develops as a primary heart tube from the splanchnic mesoderm as an endocardial vessel surrounded by a double layer of cardiomyocytes, in the midline of the embryo
Endothelial and endocardial cells require a sensor for shear stress in order to respond to changes in blood flow
This results in a rise in intracellular Ca2+ and activation of the Nodal signaling program on the left side of the organizing center, which forms the basis of asymmetric development
Summary
The heart develops as a primary heart tube from the splanchnic mesoderm as an endocardial vessel surrounded by a double layer of cardiomyocytes, in the midline of the embryo. Upon initiation of this primary tube, cardiac looping commences with a rightward shift of the outflow part of the heart. In this “c-looping” phase, the original dorsal side of the heart tube becomes the inner curvature[1,2]. TheScientificWorldJOURNAL (2008) 8, 212–222 the embryonic vasculature to the vessels that develop in the yolk sac, blood flow through the heart is low and highly irregular. Upon connection to the extraembryonic vasculature, blood flow becomes regular and laminar by nature (see below). This review will focus on the role of blood flow on heart looping and inner curvature remodeling
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