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    P. Kouklis Laboratory

    A) We study the properties of adherens junctions (AJs) molecules using mature endothelial cells as a model system, because of the dynamic character of their junctions. Endothelial barrier function is dependent on VE-cadherin, an endothelial specific cadherin. Regulation of endothelial barrier function is an important property of the endothelium required for migration of salutes and cells from blood to tissues. Cadherin proteins are involved in serious diseases like atherosclerosis, inflammation and thrombosis.
    We examine the role of VE-cadherin in signaling and in the actin cytoskeleton rearrangement during cell-cell disruption. We also investigate the topology of VE-cadherin in the plasma membrane and we come to conclusion that it depends on a specialized lipid microenvironment that includes the Phosphatidyl-Inositol-(4,5)phosphate (PIP2). We also examine the oligomerization states of VE-cadherin and we have interest in studying mechanisms involved in shedding of this molecule during inflammatory signaling.

    B) Cell-cell adhesion is a key morphogenetic process during differentiation. Adherens junctions specifically have a pivotal role in cell-cell adhesion and influence the formation of cell junctions. Disruption or alteration of the expression levels of the tissue-specific cadherin can cause dramatic alterations in formation of various tissues. We are interested to investigate the role of organized endothelium during differentiation of mesodermal or other cell lineages. For this purpose we chose to use a well-established in vitro system i.e. the differentiation of embryonic stem cells through embryoid bodies formation, that allows precise monitoring various types of progenitor cells in relationship to each other in a timely and spatially manner. It also allows the study of phenotypes in vitro that otherwise it would be difficult to analyze in a knock-out animal due to lethality. Embryoid bodies were created having impaired capacity to form endothelium by expressing a dominant negative mutant, which has been shown to be a disruptor of cell-cell adhesion in endothelial specific fashion. Disruption of endothelium is associated with loss of beating phenotype and decrease of cardiomyocyte differentiation, normally observed between D11-D17. This effect seems to be the result of a substantial impairment of cardiac progenitors’ differentiation. We are studying the interactions between endothelial and the progenitor cells.