Güttsches Anne-Katrin, Brady Stefen, Krause Kathryn, Maerkens Alexandra, Uszkoreit Julian, Eisenacher Martin, Schreiner Anja, Galozzi Sara, Mertens-Rill Janine, Tegenthoff Martin, Holton Janice L, Harms Matthew B, Lloyd Thomas E, Vorgerd Matthias, Weihl Conrad C, Marcus Katrin, Kley Rudolf A
Department of Neurology, Heimer Institute for Muscle Research, University Hospital Bergmannsheil, Ruhr-University Bochum, Bochum, Germany.
Department of Neurology, Southmead Hospital, Bristol, United Kingdom.
Ann Neurol. 2017 Feb;81(2):227-239. doi: 10.1002/ana.24847. Epub 2017 Jan 27.
Sporadic inclusion body myositis (sIBM) pathogenesis is unknown; however, rimmed vacuoles (RVs) are a constant feature. We propose to identify proteins that accumulate within RVs.
RVs and intact myofibers were laser microdissected from skeletal muscle of 18 sIBM patients and analyzed by a sensitive mass spectrometry approach using label-free spectral count-based relative protein quantification. Whole exome sequencing was performed on 62 sIBM patients. Immunofluorescence was performed on patient and mouse skeletal muscle.
A total of 213 proteins were enriched by >1.5 -fold in RVs compared to controls and included proteins previously reported to accumulate in sIBM tissue or when mutated cause myopathies with RVs. Proteins associated with protein folding and autophagy were the largest group represented. One autophagic adaptor protein not previously identified in sIBM was FYCO1. Rare missense coding FYCO1 variants were present in 11.3% of sIBM patients compared with 2.6% of controls (p = 0.003). FYCO1 colocalized at RVs with autophagic proteins such as MAP1LC3 and SQSTM1 in sIBM and other RV myopathies. One FYCO1 variant protein had reduced colocalization with MAP1LC3 when expressed in mouse muscle.
This study used an unbiased proteomic approach to identify RV proteins in sIBM that included a novel protein involved in sIBM pathogenesis. FYCO1 accumulates at RVs, and rare missense variants in FYCO1 are overrepresented in sIBM patients. These FYCO1 variants may impair autophagic function, leading to RV formation in sIBM patient muscle. FYCO1 functionally connects autophagic and endocytic pathways, supporting the hypothesis that impaired endolysosomal degradation underlies the pathogenesis of sIBM. Ann Neurol 2017;81:227-239.
散发性包涵体肌炎（sIBM）的发病机制尚不清楚；然而，镶边空泡（RVs）是其一个持续存在的特征。我们旨在鉴定在RVs内积聚的蛋白质。
从18例sIBM患者的骨骼肌中激光显微切割出RVs和完整的肌纤维，并采用基于无标记光谱计数的相对蛋白质定量的灵敏质谱方法进行分析。对62例sIBM患者进行了全外显子组测序。对患者和小鼠的骨骼肌进行了免疫荧光检测。
与对照组相比，共有213种蛋白质在RVs中富集超过1.5倍，其中包括先前报道在sIBM组织中积聚或突变时导致伴有RVs的肌病的蛋白质。与蛋白质折叠和自噬相关的蛋白质是占比最大的类别。一种先前未在sIBM中鉴定出的自噬衔接蛋白是FYCO1。11.3%的sIBM患者存在罕见的编码FYCO1的错义变体，而对照组为2.6%（p = 0.003）。在sIBM和其他伴有RVs的肌病中，FYCO1与自噬蛋白如MAP1LC3和SQSTM1在RVs处共定位。一种FYCO1变体蛋白在小鼠肌肉中表达时与MAP1LC3的共定位减少。
本研究采用无偏倚蛋白质组学方法鉴定sIBM中的RV蛋白，其中包括一种参与sIBM发病机制的新蛋白。FYCO1在RVs处积聚，sIBM患者中FYCO1的罕见错义变体比例过高。这些FYCO1变体可能损害自噬功能，导致sIBM患者肌肉中形成RVs。FYCO1在功能上连接自噬和内吞途径，支持内溶酶体降解受损是sIBM发病机制基础的假说。《神经病学纪事》2017年；81:227 - 239。
