Date of Award
Doctor of Philosophy
Field of Study
Biochemistry and Molecular Biology
Graduate School of Biomedical Sciences
Peter Gargalovic, Identification and Characterization of Caveolins in Mouse Macrophages. Doctor of Philosophy (Biochemistry and Molecular Biology), December 2002, 206 pp., 3 tables, 41 illustrations, references, 296 titles. The understanding of the mechanisms which control macrophage-lipid management, and their accumulation in atherosclerotic lesions, is of significant importance. Caveolins are proteins associated with cholesterol-rich membrane domains and are intimately linked to the regulation of lipid metabolism and transport. The expression and function of caveolin proteins in three macrophage cell types: thioglycollate-elicited mouse peritoneal macrophages, resident mouse peritoneal macrophages and the J774 macrophage cell line. Data in this work establish that the primary macrophages express caveolin-1 and -2, while J774 cells express only caveolin-2. Immunofluorescence microscopy studies indicate that caveolins in primary macrophages do not colocalize, with caveolin-1 being present on the cell surface and cavelon-2 in the Golgi compartment. Analysis of macrophages also showed that caveolin-1, but not caveolin-2, is present in detergent insoluble lipid raft membranes. While caveolin expression in macrophages is not regulated by sterols, both caveolin isoforms can be secreted from cholesterol-loaded macrophages in the presence of high-density lipoprotein (HDL). Secreted caveolins are part of the complex that has a density similar to HDL, which suggests their association with HDL and potentially a role in HDL-mediated reverse cholesterol transport. The examination of caveolin expression in macrophages shows that caveolin-1, but not caveolin-2 expression is highly upregulated by agents that induce apoptosis in these cells. Induction of caveolin-1 expression precedes DNA fragmentation, is independent of caspase activation, and correlates with the exposure of phosphatidylserine on the cell surface. Importantly, immunofluorescence analysis determined that caveolin-1 in lipid rafts colocalizes extensively with phosphatidylserine present on the surface of apoptotic cells. This study thus identifies caveolin-1 as a specific and early marker of the macrophage apoptotic phenotype. Findings here strongly implicate the involvement of caveolin-1 and lipid rafts in the changes of plasma membrane lipid composition as well as involvement in efficient clearance of apoptotic cells by a phosphatidylserine-mediated mechanism.
"Identification and Characterization of Caveolins in Mouse Macrophages" Fort Worth, Tx: University of North Texas Health Science Center;
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