Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, USA.
Robarts Research Institute, Western University, London, Ontario, Canada; Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.
J Lipid Res. 2021;62:100045. doi: 10.1016/j.jlr.2021.100045. Epub 2021 Feb 9.
HDL and its primary receptor, scavenger receptor class B type I (SR-BI), work together to promote the clearance of excess plasma cholesterol, thereby protecting against atherosclerosis. Human variants of SR-BI have been identified in patients with high HDL-cholesterol levels, and at least one variant has been linked to cardiovascular disease. Therefore, while often regarded as beneficial, very high levels of HDL-cholesterol may result from impaired cholesterol clearance through SR-BI and contribute to cardiovascular risk. In this study, we characterized the function of a rare human variant of SR-BI, resulting in the substitution of arginine-174 with cysteine (R174C), which was previously identified in a heterozygous individual with high levels of HDL-cholesterol. We hypothesized that the R174C-SR-BI variant has impaired cholesterol transport functions, which were assessed in COS-7 cells after transient transfection with full-length WT or R174C-SR-BI. Although R174C-SR-BI was expressed at levels comparable to the WT receptor, HDL binding, cholesteryl hexadecyl ether uptake, free cholesterol efflux, and modulation of membrane cholesterol were disrupted in the presence of R174C-SR-BI. We further examined the role of salt bridges as a potential mechanism for R174C-SR-BI dysfunction. If translatable, this human variant could lead to increased plasma HDL-cholesterol levels, impaired cholesterol clearance, and increased cardiovascular disease risk.
高密度脂蛋白（HDL）及其主要受体——清道夫受体 B 型 I 类（SR-BI）协同作用，促进过量血浆胆固醇的清除，从而预防动脉粥样硬化。在高 HDL-胆固醇水平的患者中已经鉴定出人源 SR-BI 的变体，至少有一种变体与心血管疾病相关。因此，尽管 HDL-胆固醇通常被认为是有益的，但非常高的 HDL-胆固醇水平可能是由于通过 SR-BI 清除胆固醇受损而导致的，并增加心血管风险。在这项研究中，我们对先前在一个 HDL-胆固醇水平升高的杂合个体中鉴定出的 SR-BI 稀有人类变体 R174C 进行了功能表征，该变体导致精氨酸 174 被半胱氨酸取代（R174C）。我们假设 R174C-SR-BI 变体的胆固醇转运功能受损，在瞬时转染全长 WT 或 R174C-SR-BI 后，在 COS-7 细胞中进行了评估。尽管 R174C-SR-BI 的表达水平与 WT 受体相当，但在存在 R174C-SR-BI 的情况下，HDL 结合、胆甾醇十六烷基醚摄取、游离胆固醇流出和膜胆固醇调节均受到破坏。我们进一步研究了盐桥作为 R174C-SR-BI 功能障碍的潜在机制的作用。如果可翻译，这种人类变体可能导致血浆 HDL-胆固醇水平升高、胆固醇清除受损和心血管疾病风险增加。
