Vascular endothelial cells (ECs) form a flattened "epithelium" that lines blood vessels. Like epithelial cells, ECs are polarized, exhibiting two major plasma membrane domains (apical or luminal and basolateral or abluminal). However, little is known about the distribution of proteins between these two domains. We know that ICAM-1 and VCAM-1 are expressed on ECs' luminal domain because they regulate the interactions of ECs with blood leukocytes, and that beta 1 and beta 3 integrins are expressed on ECs' abluminal domain because they regulate adhesive interactions of ECs' with its basement membrane. We do not know whether ICAM-1 or VCAM-1 also are expressed on ECs' abluminal domain, or whether beta 1 and beta 3 integrins also are expressed on ECs' luminal domain. Moreover, with the exception of VCAM-1, we have little detained information on the effects of elevations of lipoprotein levels on the expression and distribution of these surface proteins. We do know that soon after the onset of hypercholesterolemia in experimental animals there are profound changes in the structure of arterial endothelium and in associated subendothelial structures. Dr. Nicolae Simionescu and his colleagues at the Institute for Cellular Biology and Pathology in Romania have observed that within days after the onset of hypercholesterolemia in rabbits and hamsters there is deposition of lipid and of apolipoprotein fragments in the subendothelial space, an increase in the secretory apparatus of ECs, hypertrophy and proliferation of the subendothelial basement membrane, and migration of monocytes from the blood into the subendothelial space. My colleagues and I have been exploring the cellular and molecular mechanisms that regulate leukocyte movement across endothelia. We have developed cell culture systems that closely mimic the barrier properties of endothelia in vivo. Dr. Simionescu and I now wish to explore in detail the effects of elevated levels of normal and modified lipoproteins on the structure and function of ECs and their underlying basement membrane, and the mechanisms by which normal and modified lipoproteins promote monocyte emigration and localization to the subendothelium. It is evident to both groups that specific fundamental information is required for further progress, that both in vivo and in vitro systems are needed to obtain this information, and that our laboratories will progress at a significantly faster rate by sharing observations, experimental technologies, and resources. For these reasons we are submitting this application for FIRCA support. Our SPECIFIC AIMS are: (1) Determine whether VCAM-1, ICAM-1, beta 1, and beta 3 integrins are distributed randomly or in a polar (e.g. apical vs basolateral membranes) fashion on the surfaces of normal endothelial cells, and whether the expression and/or distribution of these proteins is altered in endothelia exposed to hypercholesterolemic conditions. (2) Identify the effects of hypercholesterolemia on the formation and structure of basal lamina and extracellular matrix components by endothelial cells during the prelesional phase of atherogenesis. (3) Study the molecular mechanisms of monocyte migration and subendothelial homing, and determine the effect(s) of hypercholesterolemia on these processes.