Hansen G H, Niels-Christiansen L-L, Immerdal L, Danielsen E M
Department of Medical Biochemistry and Genetics, Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark.
Gut. 2003 Oct;52(10):1424-31. doi: 10.1136/gut.52.10.1424.
Scavenger receptor class B type I (SR-BI) is known to mediate cellular uptake of cholesterol from high density lipoprotein particles and is particularly abundant in liver and steroidogenic tissues. In addition, SR-BI expression in the enterocyte brush border has also been reported but its role in the small intestine remains unclear.
To gain insight into the possible function of pig SR-BI during uptake of dietary fat, its localisation in enterocytes was studied in the fasting state and during fat absorption by immunogold electron microscopy and subcellular fractionation.
In the fasting state, SR-BI was mainly localised in the microvillar membrane and in apical invaginations/pits between adjacent microvilli. In addition, a subapical compartment and small cytoplasmic lipid droplets were distinctly labelled. During lipid absorption, the receptor was found in clathrin positive apical coated pits and vesicles. In addition, cytoplasmic lipid droplets that greatly increased in size and number were strongly labelled by the SR-BI antibody whereas apolipoprotein A-1 positive chylomicrons were largely devoid of the receptor.
During absorption of dietary fat, SR-BI is endocytosed from the enterocyte brush border and accumulates in cytoplasmic lipid droplets. Internalisation of the receptor occurs mainly by clathrin coated pits rather than by a caveolae/lipid raft based mechanism.
已知I型清道夫受体B类（SR-BI）介导细胞从高密度脂蛋白颗粒摄取胆固醇，且在肝脏和类固醇生成组织中含量特别丰富。此外，也有报道称SR-BI在肠上皮细胞刷状缘表达，但其在小肠中的作用仍不清楚。
为深入了解猪SR-BI在膳食脂肪摄取过程中的可能功能，通过免疫金电子显微镜和亚细胞分级分离技术，研究其在空腹状态和脂肪吸收过程中在肠上皮细胞中的定位。
在空腹状态下，SR-BI主要定位于微绒毛膜以及相邻微绒毛之间的顶端内陷/小窝。此外，顶端下区室和小的细胞质脂滴也有明显标记。在脂质吸收过程中，该受体存在于网格蛋白阳性的顶端被膜小窝和小泡中。此外，SR-BI抗体强烈标记了大小和数量大幅增加 的细胞质脂滴，而载脂蛋白A-1阳性乳糜微粒大多缺乏该受体。
在膳食脂肪吸收过程中，SR-BI从肠上皮细胞刷状缘内吞并积聚在细胞质脂滴中。该受体的内化主要通过网格蛋白被膜小窝而非小窝/脂筏依赖机制发生。
