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Scavenger Receptor Class B Type I-mediated Reverse Cholesterol Transport Is Inhibited by Advanced Glycation End Products

2001; Elsevier BV; Volume: 276; Issue: 16 Linguagem: Inglês

10.1074/jbc.m011613200

1083-351X

Nobutaka Ohgami, Ryoji Nagai, Akira Miyazaki, Mamoru Ikemoto, Hiroyuki Arai, Seikoh Horiuchi, Hitoshi Nakayama,

Natural Antidiabetic Agents Studies

Cellular interactions of advanced glycation end products (AGE) are mediated by AGE receptors. We demonstrated previously that class A scavenger receptor types I and II (SR-A) and CD36, a member of class B scavenger receptor family, serve as the AGE receptors. In this study, we investigated whether scavenger receptor class B type I (SR-BI), another receptor belonging to class B scavenger receptor family, was also an AGE receptor. We used Chinese hamster ovary (CHO) cells overexpressed hamster SR-BI (CHO-SR-BI cells). 125I-AGE-bovine serum albumin (AGE-BSA) was endocytosed in a dose-dependent fashion and underwent lysosomal degradation by CHO-SR-BI cells. 125I-AGE-BSA exhibited saturable binding to CHO-SR-BI cells (Kd= 8.3 μg/ml). Endocytic uptake of 125I-AGE-BSA by CHO-SR-BI cells was completely inhibited by oxidized low density lipoprotein (LDL) and acetylated LDL, whereas LDL exerted only a weak inhibitory effect (<20%). Cross-competition experiments showed that AGE-BSA had no effect on HDL binding to these cells and vice versa. Interestingly, however, SR-BI-mediated selective uptake of HDL-CE was completely inhibited by AGE-BSA in a dose-dependent manner (IC50 <10 μg/ml). Furthermore, AGE-BSA partially inhibited (by <30%) the selective uptake of HDL-CE in human hepatocarcinoma HepG2 cells (IC50 <30 μg/ml). In addition, [3H]cholesterol efflux from CHO-SR-BI cells to HDL was significantly inhibited by AGE-BSA in a dose-dependent manner (IC50 <30 μg/ml). Our results indicate that AGE proteins, as ligands for SR-BI, effectively inhibit both SR-BI-mediated selective uptake of HDL-CE and cholesterol efflux from peripheral cells to HDL, suggesting that AGE proteins might modulate SR-BI-mediated cholesterol metabolism in vivo. Cellular interactions of advanced glycation end products (AGE) are mediated by AGE receptors. We demonstrated previously that class A scavenger receptor types I and II (SR-A) and CD36, a member of class B scavenger receptor family, serve as the AGE receptors. In this study, we investigated whether scavenger receptor class B type I (SR-BI), another receptor belonging to class B scavenger receptor family, was also an AGE receptor. We used Chinese hamster ovary (CHO) cells overexpressed hamster SR-BI (CHO-SR-BI cells). 125I-AGE-bovine serum albumin (AGE-BSA) was endocytosed in a dose-dependent fashion and underwent lysosomal degradation by CHO-SR-BI cells. 125I-AGE-BSA exhibited saturable binding to CHO-SR-BI cells (Kd= 8.3 μg/ml). Endocytic uptake of 125I-AGE-BSA by CHO-SR-BI cells was completely inhibited by oxidized low density lipoprotein (LDL) and acetylated LDL, whereas LDL exerted only a weak inhibitory effect (<20%). Cross-competition experiments showed that AGE-BSA had no effect on HDL binding to these cells and vice versa. Interestingly, however, SR-BI-mediated selective uptake of HDL-CE was completely inhibited by AGE-BSA in a dose-dependent manner (IC50 <10 μg/ml). Furthermore, AGE-BSA partially inhibited (by <30%) the selective uptake of HDL-CE in human hepatocarcinoma HepG2 cells (IC50 <30 μg/ml). In addition, [3H]cholesterol efflux from CHO-SR-BI cells to HDL was significantly inhibited by AGE-BSA in a dose-dependent manner (IC50 62%) replaced by unlabeled Ox-LDL and acetyl-LDL and by unlabeled AGE-BSA, whereas unlabeled LDL and HDL had a slightly weaker effect (<20%) (Fig.4 A). Non-glycated BSA, a negative control, had no effect on this process (Fig. 4 A). Parallel experiments demonstrated that cellular binding of125I-HDL to CHO-SR-BI cells was effectively (60%) replaced by unlabeled HDL, whereas AGE-BSA had little effect ( 85%) replaced by unlabeled Ox-LDL and acetyl-LDL and by unlabeled AGE-BSA, whereas the effect of unlabeled LDL and HDL was almost negligible ( 85%) by the presence of unlabeled Ox-LDL, acetyl-LDL, and unlabeled AGE-BSA, whereas unlabeled LDL and HDL also exerted a much weaker effect (<25%) (Fig. 5 B). The results of endocytic experiments are consistent with those of the binding experiments (Fig.