[Effects of induced deletion of repeats in binding domain of the VLDL receptor on its ligand-binding capacity].

The ligand-binding domain of the very low-density lipoprotein receptor (VLDL-R) contains eight cysteine-rich repeat sequences that have been postulated as ligand-binding sites. This is obviously different from that of low-density lipoprotein receptor (LDL-R) that includes seven similar repeats. To make clear the contribution of these repeats to ligand-binding and to explore the reason of both receptors' ligand-binding characteristic, the VLDL-R recombinants lacking different repeat(s) were constructed by oligonucleotide-directed mutagenesis and transfected into ldl-A7 cell. Ligand-binding results showed that repeat 1 and repeat 2 were the most important in binding with apoE-rich lipoprotein(VLDL and beta-VLDL). Repeat 3 and repeat 6 also important for binding VLDL. The results also showed that VLDL-R lacking LBR7 retained partly LDL-R ligand-binding properties. It suggests that LBR7 in VLDL-R may responsible for both receptors' ligand-binding properties differences.

Oxidative Modification of Very Low Density Lipoprotein by Arterial Wall Cells.

Modification of VLDL by arterial wall cells was observed. After incubating VLDL (200 &mgr;g protein/ml) with bovine aortic endothelial cells (EC), rabbit aortic smooth muscle cells (SMC) or mouse peritoneal macrophages (Mpsi)for 24 hours, the TBARS in VLDL increased strikingly to 7.80+/-O.75, 1O.6+/-O.90 and 11.4+/-O.70 nmol/mg-protein respectively, much higher than those of their controls (5.1O+/-0.60, 7.20+/-0.89, 5.30+/-O.54 nmol/mg-protein). The cell-modified VLDL migrated faster than the controls on agarose electrophoregram and the SDS-PAGE of the apolipoproteins showed that apo B(100) of VLDL was degraded to fragments without distinct bands, while apo E was essentially kept intact. Phosphatidylcholine was hydrolyzed to lysophosphatidylcholine during the modification process. These changes were inhibited by BHT, indicating that the modification of VLDL was an oxidative process. The result suggests that since VLDL could be oxidatively modified by arterial wall cells including EC, SMC, Mpsi in vitro, suggesting the oxidative modification of VLDL may occur in vivo and play an important role in atherogenesis.