P92	Interaction of mesenchymal stem cells with the endothelium.
1C.Steingen, 1K.Brixius, 1R.Schwinger, 2W.Bloch, 2A.Schmidt
1Clinic III for Inner Medicine, University of Cologne, Cologne, DE; 2German Sport University Cologne, Dept. for Molecular and Cellular Sport Medicine, Cologne, DE.

Adult pluripotent bone marrow derived mesenchymal stem cells are in the focus of scientific interest because of their ability to differentiate into mesenchymal tissues. Mesenchymal stem cells (MSCs) are already used in the field of tissue engineering and as a potential therapy for the regeneration of infarcted myocardial tissue. In the case of an intravascular application of MSCs, stem cells have to interact with endothelial cells and finally migrate across the endothelial barrier to leave the blood circulation. To date only a little is known about the underlying mechanisms. Our study focuses on the direct interaction of MSCs with the endothelium. For this purpose co-cultivation experiments have been performed. The experiments showed that a direct interaction between MSCs and the endothelium takes place within less than one hour. Integration of stem cells into the endothelium occurs with strong morphological changes of stem cells. Co-cultivation with different types of endothelial monolayer elucidates differences of the interaction depending on the segment of the vascular system. For this purpose HUVEC (human umbilical vein endothelial cells), HCAEC (human coronary artery endothelial cells) and magnet-associated cell sorting (MACS)-sorted endothelial cells from murine EBs (embryoid bodies) at days 5 and 7 were employed. The time course of integration in the endothelial monolayer and modification of shape of the MSCs is clearly depending on the type of endothelial cells and varies between 60 to 240 minutes. Additionally we focus on changes in the signal transduction which arise during co-cultivation by performing immunohistochemical staining. For example a distinct pattern of clustering and dissolution of β1 integrin and connexin 43 has been observed. Accomplished blockade experiments will help to identify cell adherence molecules involved in the interaction. In conclusion MSCs are able to integrate in endothelial monolayer and transmigrate across the endothelial barrier.

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