Mutation in EGFP domain of LDL receptor-related protein 6 impairs cellular LDL clearance.
Mutation in EGFP domain of LDL receptor-related protein 6 impairs cellular LDL clearance.
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DOI：
10.1161/circresaha.108.183863
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发表时间：
2008-11-21
影响因子：
20.1
通讯作者：
Mani A
中科院分区：
文献类型：
--
作者：
Liu W;Mani S;Davis NR;Sarrafzadegan N;Kavathas PB;Mani A
LDL受体相关蛋白6（LRP 6 R611 C）的EGFP结构域突变与高胆固醇血症和早发性动脉粥样硬化相关，但其致病机制尚不清楚。在来自LRP 6 +/−小鼠和LRP 6 R611 C突变携带者的细胞中检查胆固醇摄取。LRP 6 +/−小鼠的脾B细胞的LRP 6表达和LDL摄取显著低于野生型（WT）同窝小鼠。尽管在LRP 6 R611 C突变携带者和未受影响的家族成员的淋巴母细胞（LCL）中发现了相似的总LRP 6水平，但突变细胞中的LDL摄取显著较低。突变型和野生型受体在中性pH值下对apoB表现出相似的亲和力。LRP 6与LDL共定位，并与NPC 1（一种LDL转运的内吞调节因子）共免疫沉淀。然而，LRP 6在突变细胞中的细胞定位从细胞表面转移到晚期内体/溶酶体。与WT受体相比，LRP 6 R611 C的质膜表达水平较低，并且在富含LDL的培养基中下降的程度更大。进一步的检查显示，在酸性pH下，与WT受体相比，apoB从LRP 6 R611 C解离的功效较低。这些研究将LRP 6鉴定为LDL内吞作用的受体，并暗示R611 C突变导致LRP 6膜表达降低和LDL清除降低。基于我们的研究结果，我们得出结论，在酸性pH下，LDL突变体受体的亲和力增加导致其在晚期内体中的解离受损，这损害了它们向质膜的再循环。
Mutation in the EGFP domain of LDL receptor-related protein 6 (LRP6R611C) is associated with hypercholesterolemia and early-onset atherosclerosis, but the mechanism by which it causes disease is not known. Cholesterol uptake was examined in cells from LRP6 +/− mice and LRP6R611C mutation carriers. Splenic B cells of LRP6 +/− mice have significantly lower LRP6 expression and LDL uptake than those of the wildtype (WT) littermates. Although similar levels of total LRP6 were found in lymphoblastoid cells (LCLs) of LRP6R611C mutation carriers and those of the unaffected family member, LDL uptake was significantly lower in the mutant cells. Mutant and wildtype receptors show similar affinities for apoB at neutral pH. LRP6 colocalized with LDL and was coimmunoprecipitated with NPC1, an endocytic regulator of LDL trafficking. However, the cellular localization of LRP6 in the mutant cells shifted from cell surface to late endosomes/lysosomes. Plasma membrane expression levels of LRP6R611C was lower compared to WT receptor and declined to a greater extent in LDL-rich medium. Further examinations revealed lower efficacy of apoB dissociation from LRP6R611C compared to WT receptor at an acidic pH. These studies identify LRP6 as a receptor for LDL endocytosis and imply that R611C mutation results in reduced LRP6 membrane expression and decreased LDL clearance. Based on our findings, we conclude that the increased affinity of the mutant receptor for LDL in acidic pH leads to their impaired dissociation in late endosomes.which compromises their recycling to the plasma membrane.