Increased Ventricular Preload Is Compensated by Myocyte Proliferation in Normal and Hypoplastic Fetal Chick Left Ventricle

Abstract

Abstract-Hemodynamics influence cardiac development, and alterations in blood flow may lead to impaired cardiac growth and malformations. The developing myocardium adapts to augmented workload by increasing cell number (hyperplasia). The aim of this study was to determine the influence of alterations in ventricular preload on fetal myocyte proliferation by manipulation of intracardiac shunting at the atrial level. We hypothesized that partial clipping of the right atrial appendage would increase the blood flow to the left ventricle and, in turn, lead to an increase in chamber volume and myocardial mass based on myocyte proliferation. Using an ex ovo culture setup, we performed partial right atrial clipping on embryonic day 8 chick embryos. Ultrasound imaging was performed before and after the surgery to assess the changes in left ventricular volume. Sampling after 24 hours was preceded by 2 hour of pulse-labeling with 5-bromodeoxyuridine. Ultrasound imaging showed that partial right atrial clipping led to a significant increase in left ventricular end-diastolic volume, demonstrating increased blood flow and preload. Anti-5-bromodeoxyuridine immunolabeling revealed a significant increase in myocyte proliferation in the left ventricle and atrium. No significant changes were found in the right heart structures. Increased left ventricular myocyte proliferation and myocardial mass after right atrial clipping was also observed in embryos with experimental left ventricular hypoplasia. These results demonstrate the ability of fetal myocardium to respond to increased preload by myocyte hyperplasia and support the rationale for prenatal surgical interventions in certain cases of congenital heart disease such as hypoplastic left heart syndrome. (Circ Res. 2007;100:1363-1370.)Key Words: chick embryo Ⅲ hemodynamics Ⅲ fetal surgery Ⅲ hypoplastic left heart syndrome H ypoplastic left heart syndrome (HLHS) refers to a group of congenital cardiac anomalies characterized by underdevelopment of the left side of the heart. The anatomic abnormalities include underdevelopment of the left atrium and ventricle and hypoplastic or atretic mitral and aortic valves, and the right ventricle, rather than the left, forms the apex of the heart. 1,2 HLHS affects more than 2000 infants a year in the United States alone and accounts for approximately 25% of cardiac deaths within the first year of life. 3

Abnormal Myocardial and Coronary Vasculature Development in Experimental Hypoxia

“…Expressing the proliferative index in cells per volume of tissue results in less time-consuming cell counting and validation by counting in one group (ED6) also the total number of cell nuclei showed that the values were within the range of 15%-50% of positive myocytes, comparable with our previous studies in the embryonic chick (Sedmera et al, 2002a;deAlmeida et al, 2007). Apoptosis is a rare event in the developing ventricular myocardium and is considered a morphogenetic mechanism used for elimination of no longer needed subpopulations of myocytes in the AV region, outflow tract, and conduction system (Cheng et al, 2002;Sugishita et al, 2004).…”

Computational hemodynamic optimization predicts dominant aortic arch selection is driven by embryonic outflow tract orientation in the chick embryo

“…Extensive studies using the chick embryo model have shown that epigenetic perturbations in blood flow can also lead to altered cardiovascular morphogenesis and congenital defects, implicating hemodynamics as a major environmental, epigenetic factor (deAlmeida et al 2007;Gessner 1966;Hogers et al 1999;Lucitti et al 2005;Reckova et al 2003;Sedmera et al 1999;Tobita et al 2005). This relationship has been validated for the global growth of the aortic arches by several studies, where changes in aortic arch perfusion by occlusion of a vitelline vein (Hogers et al 1999;Rychter and Lemez 1965), left atrial ligation (Hu et al 2009), manipulation of the outflow tract (Gessner 1966), or ligation of individual aortic arches (Rychter 1962) generated abnormal arch growth and defects in arch derivatives.…”

Tgfβ/Alk5 signaling is required for shear stress induced klf2 expression in embryonic endothelial cells

“…Shear stress modulates endothelial structure and function and results in an accurate regulation of endothelial gene expression in vitro (Dekker et al, 2002) and in vivo (Groenendijk et al, 2004;Dekker et al, 2005). Several animal models show that congenital malformations can result from disturbed blood flow (Hogers et al, 1997;Sedmera et al, 1999;Tobita et al, 2002;Hove et al, 2003;Dealmeida et al, 2007;Butcher et al, 2007). The large and rapid changes in volume and geometry of cardiac compartments during development are translated into local changes in shear stress and concomitant gene expression patterns of, e.g., Krü ppel like factor 2 (KLF2) (Groenendijk et al, 2004).…”