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  • Title: Characterization of alpha 2-macroglobulin receptor low density lipoprotein receptor-related protein (alpha 2 MR/LRP) in White Carneau pigeon peritoneal macrophages: its role in lipoprotein metabolism.
    Author: Seo T, Wang HC, Feldman SR, St Clair RW.
    Journal: Biochim Biophys Acta; 1997 Jan 21; 1344(2):171-88. PubMed ID: 9030194.
    Abstract:
    White Carneau pigeons develop atherosclerosis naturally, and at an accelerated rate with cholesterol feeding. Macrophages play a central role in the pathogenesis of atherosclerosis in pigeons, as they do in man. The purpose of this study was to determine whether pigeon macrophages express the alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2 MR/LRP) and whether this receptor would recognize beta-VLDL, the major cholesterol-transporting lipoprotein in cholesterol-fed pigeons. The binding of 125I-methylamine-treated alpha 2M (125I-alpha 2 M+) at 4 degrees C was saturable (> 10 nM), specific, Ca2+ dependent, was competed for by the receptor-associated protein (RAP), and had a Kd of binding of 1-5.6 nM, similar to mouse peritoneal macrophages studied simultaneously. At 37 degrees C the bound 125I-alpha 2 M+ was rapidly internalized and degraded in lysosomes. The binding of alpha 2 M+ was not down-regulated with cholesterol loading, as is the LDL receptor on pigeon macrophages. At 4 degrees C there was no competition for binding of 125I-alpha 2 M+ by either pigeon or rabbit beta-VLDL, nor was binding of 125I-pigeon or rabbit beta-VLDL competed for by alpha 2 M+. Stimulation of cholesterol esterification by rabbit or pigeon beta-VLDL was unaffected by RAP, lactoferrin, or alpha 2 M+. Metabolism of 125I-pigeon or rabbit beta-VLDL was not competed by RAP, lactoferrin, or alpha 2 M+ even in the presence of lipoprotein lipase. Pigeon macrophages, and a 500 kDa membrane protein isolated from them, were recognized by several antihuman alpha 2 MR/LRP monoclonal antibodies. The 500 kDa membrane protein also bound 45Ca. These data suggest considerable sequence homology with the human alpha 2 MR/LRP. This is the first study to characterize a functional alpha 2 MR/LRP on peritoneal macrophages from an avian species. There was no evidence, however, that the alpha 2 MR/LRP mediates uptake of beta-VLDL by pigeon macrophages.
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