DISTINCT HUMAN MACROPHAGE RECEPTOR FOR ABNORMAL VLDL

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Elevated plasma triglycerides(TG) are a risk factor for atherothrombotic disease. Monocyte-macrophage(MM)-derived, lipid-filled "foam cells" are found in atherosclerotic lesions and, in certain hyperTG states, in bone marrow, skin, and spleen. Uptake of TG-rich lipoproteins(TGRLP) via a cell-surface, apoE-independent TGRLP receptor(R) distinct from previously described Rs that we identified in human MM may be involved in foam cell formation in humans. Unique sequence data from the purified human THP-1 R allowed production of R-specific, antipeptide antibodies that bind the native 200 and 235 kDa R forms and prove this R is unique. The goals of the proposed work are (1)to complete the molecular and functional characterization of this new and unique R and (2) to identify the R- binding domain(s) within the apoB of chylomicrons and HTG-VLDL and the effects of other TGRLP components on R binding. Molecular biological approaches will identify and sequence receptor complementary DNA clones to elucidate receptor primary structure, to characterize cellular mRNA, and to identify, localize, and characterize the genomic DNA to identify potential regulatory, tissue-specific elements and potential relationship to the atherogenic, small, dense LDL phenotype. The 35kDa R subunit will be isolated from the 235 kDa form by immunoaffinity purification of the 235 kDa form of the R followed by preparative SDS-PAGE for antibody production and microsequence analysis. R synthesis, cell itinerary, subunit interactions, and tissue distribution will be assessed with specific R antisera. Competitive and direct cell binding and ligand blotting studies with native and modified VLDL, model VLDL, and mapped monoclonal antibodies against apoB will pinpoint R binding determinants. These studies should provide basic cellular and molecular mechanisms pertinent to foam cell formation in humans.