Deficiency of the HDL receptor, SR-BI, in humans

描述(申请人提供)：大多数流行病学研究表明，高密度脂蛋白胆固醇(HDL)水平与心血管疾病(CVD)呈负相关。然而，一部分高密度脂蛋白血症(HA)和高密度脂蛋白胆固醇(HB)升高的患者患心血管疾病的风险增加。这种增加心血管疾病风险的表型(HA/HB)类似于在高密度脂蛋白受体，清道夫受体，B类，I型(SR-BI)基因敲除小鼠中所描述的。在人类中，SR-BI基因的多态与高密度脂蛋白和低密度脂蛋白胆固醇水平以及体重指数有关，但到目前为止，还没有关于该受体功能缺陷的报道。我们已经确认了第一例SR-BI缺乏症的成年女性杂合子；这是基于在先证者的巨噬细胞中发现显著降低的SR-BI RNA和蛋白质以及SR-BI功能降低，以及编码功能性细胞外环的基因区域内的一个新的剪接变体。我们还发现，先证者的母亲、姐妹和一名患有HA/HB的无关成年女性的巨噬细胞培养的SR-BI RNA表达降低。我们假设SR-BI基因的突变/多态与SR-BI功能降低密切相关，并与HA/HB和动脉粥样硬化风险增加相关。这项建议的目的是1)彻底表征40名HA/HB成人受试者的脂蛋白和高密度脂蛋白胆固醇酯的部分清除；2)评估从HA/HB和对照受试者分离的单核细胞来源的巨噬细胞中SR-BI的表达和功能。考虑到从这些供体获取肝组织的局限性，SR-BI表达和功能的人巨噬细胞模型有望作为肝脏SR-BI的替代物。SR-BI基因敲除小鼠将被用于将巨噬细胞SR-BI表达和功能的变化与肝脏SR-BI功能相关联，并证实我们在人类SR-BI缺陷巨噬细胞中的发现；以及3)在HA/HB和对照受试者中鉴定SR-BI基因的多态和/或突变。COS-7细胞的瞬时转基因实验也将验证SR-BI变异体的重要性。这项工作将为SR-BI在人类血脂异常和动脉粥样硬化中的作用提供新的见解，并挑战理想的高密度脂蛋白胆固醇水平总是具有心脏保护作用的概念。

DESCRIPTION (provided by applicant): Most epidemiological studies have shown that high density lipoprotein cholesterol (HDL) levels are inversely correlated to cardiovascular disease (CVD). Nonetheless, a subset of patients with elevated HDL (hyperalphalipoproteinemia, HA) and elevated LDL cholesterol (hyperbetalipoproteinemia, HB) levels are at increased risk for CVD. This phenotype (HA/HB) with increased risk for CVD is similar to that described in the HDL receptor, scavenger receptor, class B, type I (SR-BI) knockout mouse. In humans, polymorphisms of the SR-BI gene have been associated with HDL and LDL cholesterol levels and body mass index, but to date, no functional defects in the receptor have been reported. We have identified the first case of an adult female heterozygote for SR-BI deficiency; this was based on finding markedly lower SR-BI RNA and protein and decreased SR-BI function in the proband's macrophages, and a novel splice variant within the region of the gene that encodes the functional extracellular loop. We also found decreased SR-BI RNA expression in macrophages cultured from the proband's mother, sister, and an unrelated adult female with HA/HB. We hypothesize that mutations/polymorphisms in the SR-BI gene strongly correlate with decreased SR-BI function and are associated with HA/HB and increased risk for atherosclerosis. The aims of this proposal are 1) to thoroughly characterize the lipoproteins and the fractional clearance of HDL-cholesteryl ester in a cohort of 40 adult subjects with HA/HB; 2) to assess SR-BI expression and function in monocyte-derived macrophages isolated from HA/HB and control subjects. The human macrophage model for SR-BI expression and function is expected to act as a surrogate for hepatic SR-BI, given the limitations in obtaining liver tissue from these donors. SR-BI knockout mice will be used to correlate changes in macrophage SR-BI expression and function with hepatic SR-BI function and to corroborate our findings in human SR-BI deficient macrophages; and 3) to identify polymorphisms and/or mutations of the SR-BI gene in HA/HB and control subjects. Transient transfection experiments with COS-7 cells will also verify the significance of SR-BI variants. This work will provide new insights into the role of SR-BI in human dyslipidemia and atherosclerosis and challenge the concept that desirable HDL cholesterol levels are always cardioprotective.