Atherosclerosis, a multifaceted disease, is the result of metabolic aberration(s) in the arterial wall aggravated by physiological stressors set up by life style risk factors. The hallmark feature of early atherosclerosis is accumulation of esterified cholesterol in foam cells originating from either monocytes migrating into the arterial wall or from constituent smooth muscle cells. Genetic factors governing susceptibility to atherosclerosis are believed to reside at least in part at the level of the arterial wall, and the long-term goals of this laboratory are: 1) to determine the mechanism(s) responsible for pathogenic accumulation of cholesteryl esters within arterial smooth muscle cells; and, 2) to describe genetic factors controlling these mechanisms. Use of the atherosclerosis-susceptible White Carneau and -resistant Show Racer pigeon model system is advantageous for these goals since: foam cells are formed from smooth muscle cells in the naturally-occurring disease; genetic susceptibility/resistance resides in the arterial wall; and, life-style risk factors are not involved. Once this """"""""simplest-case"""""""" scenario for atherogenesis -- i.e. metabolic abnormality in vascular smooth muscle cells -- is understood, other components of the pathogenic process (eg., lipoproteins, endothelial damage, monocyte infiltration, etc.) can be more completely evaluated. Early differences in glycosaminoglycan (chondroitin-6-sulfate) accumulation and intracellular distribution of B-glucuronidase (greater localization in endoplasmic reticulum) precede cholesteryl ester accretion in lesion-prone areas of susceptible aortas. In the endoplasmic reticulum, B-glucuronidase is bound to the protein egasyn, an esterase which occurs both bound and free in this organelle. Egasyn possesses much greater lipase (cholesteryl esterase?) activity when free, and its activity may be regulated by the amount of B-glucuronidase present in the endoplasmic reticulum. Thus, the specific aims are: 1) to describe changes in cholesterol metabolism produced by chondroitin-6-sulfate (C-6-S) added to cultured aorta smooth muscle cells from atherosclerosis-susceptible and atherosclerosis-resistant pigeons; and, 2) to define alterations in B-glucuronidase/egasyn distribution produced by C-6-S in the same system. Radioactively labeled metabolites (acetate, cholesterol) will be added to cultures in the presence or absence of C-6-S and the appearance and/or disappearance of cholesteryl esters in cells from both breeds monitored as a function of time. Cells will also be analyzed for the total B-glucuronidase activity and for the proportion of bound and unbound egasyn as a function of treatment with C-6-S.
