Objective: LIPA (lysosomal acid lipase) mediates cholesteryl ester hydrolysis, and patients with rare loss-of-function mutations develop hypercholesterolemia and severe disease. Genome-wide association studies of coronary artery disease have identified several tightly linked, common intronic risk variants in LIPA which unexpectedly associate with increased mRNA expression. However, an exonic variant (rs1051338 resulting in T16P) in linkage with intronic variants lies in the signal peptide region and putatively disrupts trafficking. We sought to functionally investigate the net impact of this locus on LIPA and whether rs1051338 could disrupt LIPA processing and function to explain coronary artery disease risk. Approach and Results: In monocytes isolated from a large cohort of healthy individuals, we demonstrate both exonic and intronic risk variants are associated with increased LIPA enzyme activity coincident with the increased transcript levels. To functionally isolate the impact of rs1051338, we studied several in vitro overexpression systems and consistently observed no differences in LIPA expression, processing, activity, or secretion. Further, we characterized a second common exonic coding variant (rs1051339), which is predicted to alter LIPA signal peptide cleavage similarly to rs1051338, yet is not linked to intronic variants. rs1051339 also does not impact LIPA function in vitro and confers no coronary artery disease risk. Conclusions: Our findings show that common LIPA exonic variants in the signal peptide are of minimal functional significance and suggest coronary artery disease risk is instead associated with increased LIPA function linked to intronic variants. Understanding the mechanisms and cell-specific contexts of LIPA function in the plaque is necessary to understand its association with cardiovascular risk.

中文翻译：

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与冠状动脉疾病相关的 LIPA（溶酶体酸性脂肪酶）变体的功能特征

客观的：LIPA（溶酶体酸性脂肪酶）介导胆固醇酯水解，患有罕见功能丧失突变的患者会出现高胆固醇血症和严重疾病。冠状动脉疾病的全基因组关联研究已经确定了几种紧密相关的、常见的内含子风险变异利帕这与 mRNA 表达的增加出乎意料地相关。然而，与内含子变体连锁的外显子变体（rs1051338 导致 T16P）位于信号肽区域，并可能破坏运输。我们试图从功能上研究该位点对 LIPA 的净影响，以及 rs1051338 是否会破坏 LIPA 处理和功能以解释冠状动脉疾病风险。 方法和结果：在从一大群健康个体中分离出的单核细胞中，我们证明外显子和内含子风险变异都与 LIPA 酶活性增加相关，同时转录水平增加。为了在功能上分离 rs1051338 的影响，我们研究了几种体外过表达系统，并一致观察到 LIPA 表达、加工、活性或分泌没有差异。此外，我们还描述了第二种常见的外显子编码变体 (rs1051339)，预计它会与 rs1051338 类似地改变 LIPA 信号肽切割，但与内含子变体无关。rs1051339 也不影响体外 LIPA 功能，并且不会带来冠状动脉疾病风险。 结论：我们的研究结果表明，信号肽中常见的 LIPA 外显子变异的功能意义很小，表明冠状动脉疾病风险与内含子变异相关的 LIPA 功能增强有关。了解斑块中 LIPA 功能的机制和细胞特异性背景对于了解其与心血管风险的关联是必要的。