Ohgami N, Nagai R, Ikemoto M, Arai H, Kuniyasu A, Horiuchi S, Nakayama H
Department of Biofunctional Chemistry, Faculty of Pharmaceutical Sciences, Kumamoto University, 5-1 Ohe-Honmachi, Kumamoto 862-0973, Japan.
J Biol Chem. 2001 Feb 2;276(5):3195-202. doi: 10.1074/jbc.M006545200. Epub 2000 Oct 16.
Interaction of advanced glycation end products (AGE) with AGE receptors induces several cellular phenomena potentially relating to diabetic complications. Five AGE receptors identified so far are RAGE (receptor for AGE), galectin-3, 80K-H, OST-48, and SRA (macrophage scavenger receptor class A types I and II). Since SRA is known to belong to the class A scavenger receptor family, and the scavenger receptor collectively represents a family of multiligand lipoprotein receptors, it is possible that CD36, although belonging to the class B scavenger receptor family, can recognize AGE proteins as ligands. This was tested at the cellular level in this study using Chinese hamster ovary (CHO) cells overexpressing human CD36 (CD36-CHO cells). Cellular expression of CD36 was confirmed by immunoblotting and immunofluorescent microscopy using anti-CD36 antibody. Upon incubation at 37 degrees C, (125)I-AGE-bovine serum albumin (AGE-BSA) and (125)I-oxidized low density lipoprotein (LDL), an authentic ligand for CD36, were endocytosed in a dose-dependent fashion and underwent lysosomal degradation by CD36-CHO cells, but not wild-type CHO cells. In binding experiments at 4 degrees C, (125)I-AGE-BSA exhibited specific and saturable binding to CD36-CHO cells (K(d) = 5.6 microg/ml). The endocytic uptake of (125)I-AGE-BSA by these cells was inhibited by 50% by oxidized LDL and by 60% by FA6-152, an anti-CD36 antibody inhibiting cellular binding of oxidized LDL. Our results indicate that CD36 expressed by these cells mediates the endocytic uptake and subsequent intracellular degradation of AGE proteins. Since CD36 is one of the major oxidized LDL receptors and is up-regulated in macrophage- and smooth muscle cell-derived foam cells in human atherosclerotic lesions, these results suggest that, like oxidized LDL, AGE proteins generated in situ are recognized by CD36, which might contribute to the pathogenesis of diabetic macrovascular complications.
晚期糖基化终末产物（AGE）与AGE受体的相互作用会引发几种可能与糖尿病并发症相关的细胞现象。目前已鉴定出的五种AGE受体分别是RAGE（AGE受体）、半乳糖凝集素-3、80K-H、OST-48和SRA（I型和II型A类巨噬细胞清道夫受体）。由于已知SRA属于A类清道夫受体家族，且清道夫受体共同构成了一个多配体脂蛋白受体家族，因此尽管CD36属于B类清道夫受体家族，但它有可能将AGE蛋白识别为配体。本研究在细胞水平上使用过表达人CD36的中国仓鼠卵巢（CHO）细胞（CD36-CHO细胞）对此进行了测试。使用抗CD36抗体通过免疫印迹和免疫荧光显微镜确认了CD36的细胞表达。在37℃孵育时，（125）I-AGE-牛血清白蛋白（AGE-BSA）和（125）I-氧化低密度脂蛋白（LDL，CD36的一种真实配体）以剂量依赖的方式被CD36-CHO细胞内吞，并经历溶酶体降解，但野生型CHO细胞则不会。在4℃的结合实验中，（125）I-AGE-BSA与CD36-CHO细胞表现出特异性和饱和性结合（K（d）=5.6μg/ml）。这些细胞对（125）I-AGE-BSA的内吞摄取被氧化LDL抑制了50%，被抑制氧化LDL细胞结合的抗CD36抗体FA6-152抑制了60%。我们的结果表明，这些细胞表达的CD36介导了AGE蛋白的内吞摄取和随后的细胞内降解。由于CD36是主要的氧化LDL受体之一，且在人类动脉粥样硬化病变中巨噬细胞和平滑肌细胞衍生的泡沫细胞中上调，这些结果表明，与氧化LDL一样，原位产生的AGE蛋白可被CD36识别，这可能有助于糖尿病大血管并发症的发病机制。
