Morris Gavin E, Braund Peter S, Moore Jasbir S, Samani Nilesh J, Codd Veryan, Webb Tom R
From the Department of Cardiovascular Sciences, University of Leicester and National Institute for Health Research Leicester Cardiovascular Biomedical Research Unit, Glenfield Hospital, United Kingdom.
Arterioscler Thromb Vasc Biol. 2017 Jun;37(6):1050-1057. doi: 10.1161/ATVBAHA.116.308734. Epub 2017 Mar 9.
Genome-wide association studies have linked variants at chromosome 10q23 with increased coronary artery disease risk. The disease-associated variants fall in , which encodes lysosomal acid lipase (LAL), the enzyme responsible for lysosomal cholesteryl ester hydrolysis. Loss-of-function mutations in result in accelerated atherosclerosis. Surprisingly, the coronary artery disease variants are associated with increased expression in some cell types. In this study, we address this apparent contradiction.
We investigated a coding variant rs1051338, which is in high linkage disequilibrium (=0.89) with the genome-wide association study lead-associated variant rs2246833 and causes a nonsynonymous threonine to proline change within the signal peptide of LAL. Transfection of allele-specific expression constructs showed that the risk allele results in reduced lysosomal LAL protein (=0.004) and activity (=0.005). Investigation of LAL localization and turnover showed the risk LAL protein is degraded more quickly. This mechanism was confirmed in disease-relevant macrophages from individuals homozygous for either the nonrisk or risk allele. There was no difference in LAL protein or activity in whole macrophage extracts; however, we found reduced LAL protein (=0.02) and activity (=0.026) with the risk genotype in lysosomal extracts, suggesting that the risk genotype affects lysosomal LAL activity. Inhibition of the proteasome resulted in equal amounts of lysosomal LAL protein in risk and nonrisk macrophages.
Our findings show that the coronary artery disease-associated coding variant rs1051338 causes reduced lysosomal LAL protein and activity because of increased LAL degradation, providing a plausible causal mechanism of increased coronary artery disease risk.
全基因组关联研究已将10号染色体q23处的变异与冠状动脉疾病风险增加联系起来。与疾病相关的变异位于 ，该基因编码溶酶体酸性脂肪酶（LAL），这是一种负责溶酶体胆固醇酯水解的酶。 功能丧失突变会导致动脉粥样硬化加速。令人惊讶的是，冠状动脉疾病变异在某些细胞类型中与 表达增加有关。在本研究中，我们解决了这一明显的矛盾。
我们研究了一个编码变异rs1051338，它与全基因组关联研究的主要相关变异rs2246833处于高度连锁不平衡状态（ = 0.89），并导致LAL信号肽内的苏氨酸变为脯氨酸的非同义变化。等位基因特异性表达构建体的转染表明，风险等位基因导致溶酶体LAL蛋白减少（ = 0.004）和活性降低（ = 0.005）。对LAL定位和周转的研究表明，携带风险等位基因的LAL蛋白降解更快。在非风险或风险等位基因纯合个体的疾病相关巨噬细胞中证实了这一机制。全巨噬细胞提取物中的LAL蛋白或活性没有差异；然而，我们发现溶酶体提取物中携带风险基因型的LAL蛋白（ = 0.02）和活性（ = 0.026）降低，这表明风险基因型影响溶酶体LAL活性。蛋白酶体的抑制导致风险和非风险巨噬细胞中溶酶体LAL蛋白含量相等。
我们的研究结果表明，与冠状动脉疾病相关的编码变异rs1051338由于LAL降解增加导致溶酶体LAL蛋白和活性降低，为冠状动脉疾病风险增加提供了一个合理的因果机制。
