Low Hemodynamic Loading Alters Heart Morphogensis in E8.5 to E9.5 Mouse Embryos

Hemodynamic loading, the force exerted on the cardiovascular walls as blood circulates, has been shown to alter heart morphology in chick and zebrafish embryos, but has yet to be shown to singly influence mouse heart development. Defects of heart morphology found in model organisms with physically altered hemodynamics resemble the aberrations seen in human congenital heart disease and are therefore crucial to understand in a mammalian model. In the present study, hemodynamic loading was altered by lowering the hematocrit of early stage mouse embryos. This was accomplished by injecting acrylamide and TEMED into the blood islands of cultured embryos to create a gel matrix which prevented blood cells from entering the circulatory system and thus created a low-hemodynamic loading environment inside the embryo’s cardiovascular system. The treatment was allowed to take affect for twenty-four hours in static culture, followed by visualization using immunostaining and optical projection tomography. The embryos with lowered hemodynamic loading displayed a decrease in heart volume size and compact myocardial thickness, less defined trabeculation, and inhibition of cardiac looping. Furthermore, the results showed an unexpected outcome, whereby acrylamide-only injections of the blood islands also resulted in some morphometric heart abnormalities (trabeculation and looping). The results from this study suggest this could be due to a slight reduction in red blood cell development, indicating a continuum by which hemodynamic loading affects heart morphogenesis