Functional Mutation Analysis Provides Evidence for a Role of REEP1 in Lipid Droplet Biology
Functional Mutation Analysis Provides Evidence for a Role of REEP1 in Lipid Droplet Biology
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DOI：
10.1002/humu.22521
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发表时间：
2014-04-01
期刊：
影响因子：
3.9
通讯作者：
Beetz, Christian
中科院分区：
文献类型：
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作者：
Falk, Julia;Rohde, Magdalena;Beetz, Christian
遗传性轴突病通常由内质网（ER）中的蛋白质突变引起。然而，许多ER功能中哪些与病理相关仍有待确定。REEP 1是遗传性痉挛性截瘫（HSP）和遗传性运动神经病（HMN）中突变的ER蛋白。我们发现，在REEP 1的N-末端的HSP相关的错义变体废除ER靶向，而另外两个中心变体要么是罕见的良性SNP，要么通过不同的机制赋予致病性。错误靶向的变体在脂滴（LD）处积累。N-末端标记，N-末端的缺失，和一个小REEP 1亚型的表达具有相同的效果。我们还证实了在atlastins和REEP 1共同过表达时LD大小的增加。当单独表达时，野生型REEP 1、LD靶向HSP变体和非LD靶向HMN变体都不能再现这种效应。我们的结论是，REEP 1的N末端对于正确靶向和/或保留在ER中是必要的。该蛋白质也与LD相关的潜力证实了与阿司他丁对LD大小的协同作用。有趣的是，LD大小也在seipin敲低后改变，seipin的突变也引起HSP和HMN。因此，LD的调节可能是长期轴突维持的关键ER功能。
Hereditary axonopathies are frequently caused by mutations in proteins that reside in the endoplasmic reticulum (ER). Which of the many ER functions are pathologically relevant, however, remains to be determined. REEP1 is an ER protein mutated in hereditary spastic paraplegia (HSP) and hereditary motor neuropathy (HMN). We found that HSP-associated missense variants at the N-terminus of REEP1 abolish ER targeting, whereas two more central variants are either rare benign SNPs or confer pathogenicity via a different mechanism. The mis-targeted variants accumulate at lipid droplets (LDs). N-terminal tagging, deletion of the N-terminus, and expression of a minor REEP1 isoform had the same effect. We also confirmed an increase in LD size upon cooverexpression of atlastins and REEP1. Neither wild-type REEP1, LD-targeted HSP variants, nor a non-LD-targeted HMN variant reproduced this effect when expressed alone. We conclude that the N-terminus of REEP1 is necessary for proper targeting to and/or retention in the ER. The protein's potential to also associate with LDs corroborates a synergistic effect with atlastins on LD size. Interestingly, LD size is also altered upon knockdown of seipin, mutations of which also cause HSP and HMN. Regulation of LDs may thus be an ER function critical for long-term axonal maintenance.