Peter Vennemann

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

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., in the cardiac outflow tract and atrioventricular canal, are characterized by high expression of Krüppel‐like factor 2 (Klf2) and by transforming growth factor‐beta (Tgfβ)‐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 Tgfβ‐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, Tgfβ ligands, and their downstream signaling targets. Results show that, in embryonic EC, shear stress activates Tgfβ/Alk5 signaling and that induction of Klf2 is an Alk5 dependent process. Developmental Dynamics 240:1670–1680, 2011.

The Endothelin-1 Pathway and the Development of Cardiovascular Defects in the Haemodynamically Challenged Chicken Embryo

Background/Aims: Ligating the right lateral vitelline vein of chicken embryos (venous clip) results in cardiovascular malformations. These abnormalities are similar to malformations observed in knockout mice studies of components of the endothelin-1 (ET-1)/endothelin-converting enzyme-1/endothelin-A receptor pathway. In previous studies we demonstrated that cardiac ET-1 expression is decreased 3 h after clipping, and ventricular diastolic filling is disturbed after 2 days. Therefore, we hypothesise that ET-1-related processes are involved in the development of functional and morphological cardiovascular defects after venous clip. Methods: In this study, ET-1 and endothelin receptor antagonists (BQ-123, BQ-788 and PD145065) were infused into the HH18 embryonic circulation. Immediate haemodynamic effects on the embryonic heart and extra-embryonic vitelline veins were examined by Doppler and micro-particle image velocimetry. Ventricular diastolic filling characteristics were studied at HH24, followed by cardiovascular morphologic investigation (HH35). Results: ET-1 and its receptor antagonists induced haemodynamic effects at HH18. At HH24, a reduced diastolic ventricular passive filling component was demonstrated, which was compensated by an increased active filling component. Thinner ventricular myocardium was shown in 42% of experimental embryos. Conclusion: We conclude that cardiovascular malformations after venous clipping arise from a combination of haemodynamic changes and altered gene expression patterns and levels, including those of the endothelin pathway.

Measurement of shear stress on endothelium in a flow chamber and its gene expression response

The purpose of this study is to develop a new method for discriminate emboli from micro-bubbles in blood flow in vivo. An artificial valve or a left ventricular assist device embedded generates a lot of micro-bubbles besides emboli in blood flow. The existing ultrasound method cannot discriminate emboli from micro-bubbles. We paid attention to a difference in the motion between the micro-bubble and the embolus when irradiated by ultrasound. We made a simulation experiment in vitro by using elasto-flexible polymeric gel particles as a model of emboli which were suspended in a model plasma solution together with air micro-bubbles. The change in the velocity of the model emboli and micro-bubbles was measured by both an ultrasound Doppler velocimeter (USD) and a laser Doppler velocimeter (LDV). As a result, it was found that air micro-bubbles were made to move by ultrasound irradiation while model emboli was not made to move. In order to confirm this phenomenon, we made several careful experiments in which ultrasound was irradiated from upstream, downstream and laterally, the motion of the two was observed and measured. We concluded that this phenomenon was because of much difference in the acoustic impedance and the mass of the model embolus and the air bubble, and that by using the difference in velocity waveform of emboli and air microbubble on ultrasound irradiation we can discriminate the former from the latter on blood flow in vivo.