Neutrophil association and degradation of normal and acute-phase high-density lipoprotein 3.
The interaction of normal and acute-phase high-density lipoproteins of the subclass 3 (N-HDL3 and AP-HDL3) with human neutrophils and the accompanying degradation of HDL3 apolipoproteins have been studied in vitro. The chemical composition of normal and acute-phase HDL3 was similar except that serum amyloid A protein (apo-SAA) was a major apolipoprotein in AP-HDL3 (approx. 30% of total apolipoproteins). 125I-labelled AP-HDL3 was degraded 5-10 times faster than 125I-labelled N-HDL3 during incubation with neutrophils or neutrophil-conditioned medium. Apo-SAA, like apolipoprotein A-II (apo-A-II), was more susceptible than apolipoprotein A-I (apo-A-I) to the action of proteases released from the cells. The amounts of cell-associated AP-HDL3 apolipoproteins at saturation were up to 2.8 times greater than N-HDL3 apolipoproteins; while apo-A-I was the major cell-associated apolipoprotein when N-HDL3 was bound, apo-SAA constituted 80% of the apolipoproteins bound in the case of AP-HDL3. The associated intact apo-SAA was mostly surface-bound as it was accessible to the action of exogenous trypsin. alpha 1-Antitrypsin-resistant (alpha 1-AT-resistant) cellular degradation of AP-HDL3 apolipoproteins also occurred; experiments in which pulse-chase labelling was performed or lysosomotropic agents were used indicated that insignificant intracellular degradation occurred which points to the involvement of cell-surface proteases in this degradation.
D000209:Acute-Phase Proteins / Q000097:blood*; D001053:Apolipoproteins / Q000378:metabolism; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008055:Lipids / Q000032:analysis; D008075:Lipoproteins, HDL / Q000097:blood*; D053440:Lipoproteins, HDL3; D009504:Neutrophils / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D011506:Proteins / Q000032:analysis
D000209:Acute-Phase Proteins; D001053:Apolipoproteins; D008055:Lipids; D008075:Lipoproteins, HDL; D053440:Lipoproteins, HDL3; D011506:Proteins; D010447:Peptide Hydrolases