Department of Neuropathology, Charité - Universitätsmedizin, Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health (BIH), Berlin, Germany.
Oxford University Hospitals Foundation Trust, Neuropathology & Ocular Pathology Department, John Radcliffe Hospital, Oxford, OX3 9DU, UK.
Brain Pathol. 2020 Mar;30(2):261-271. doi: 10.1111/bpa.12772. Epub 2019 Aug 27.
Diffuse myofiber necrosis in the context of inflammatory myopathy is the hallmark of immune-mediated necrotizing myopathy (IMNM). We have previously shown that skeletal muscle fibers of IMNM patients may display nonrimmed vacuoles and sarcoplasmic irregularities. The dysfunctional chaperone activity has been linked to the defective assembly of skeletal muscle proteins and their degradation via lysosomes, autophagy and the proteasomal machinery. This study was undertaken to highlight a chaperone-assisted selective autophagy (CASA) pathway, functionally involved in protein homeostasis, cell stress and the immune response in skeletal muscle of IMNM patients. Skeletal muscle biopsies from 54 IMNM patients were analyzed by immunostaining, as well as by qPCR. Eight biopsies of sIBM patients served as pathological controls, and eight biopsies of nondisease control subjects were included. Alteration of autophagy was detectable in all IMNM biopsy samples highlighted via a diffuse sarcoplasmic staining pattern by p62 and LC3 independent of vacuoles. This pattern was at variance with the coarse focal staining pattern mostly confined to rimmed vacuoles in sIBM. Colocalization of p62 with the chaperone proteins HSP70 and αB-crystalline points to the specific targeting of misfolded proteins to the CASA machinery. Bcl2-associated athanogene 3 (BAG3) positivity of these fibers emphasizes the selectivity of autophagy processes and these fibers also express MHC class I sarcolemma. Expression of genes involved in autophagy and endoplasmic reticulum (ER) stress pathways studied here is significantly upregulated in IMNM. We highlight that vacuoles without sarcolemmal features may arise in IMNM muscle biopsies, and they must not be confounded with sIBM-specific vacuoles. Further, we show the activation of selective autophagy and emphasize the role of chaperones in this context. CASA occurs in IMNM muscle, and specific molecular pathways of autophagy differ from the ones in sIBM, with p62 as a unique identifier of this process.
在炎症性肌病的背景下，弥漫性肌纤维坏死是免疫介导的坏死性肌病（IMNM）的标志。我们之前已经表明，IMNM 患者的骨骼肌纤维可能会显示出非 rimmed 空泡和肌浆不规则。功能失调的伴侣蛋白活性与骨骼肌蛋白的缺陷组装及其通过溶酶体、自噬和蛋白酶体机制降解有关。本研究旨在强调一种伴侣蛋白辅助的选择性自噬（CASA）途径，该途径在 IMNM 患者的骨骼肌中参与蛋白质动态平衡、细胞应激和免疫反应。通过免疫染色和 qPCR 分析了 54 名 IMNM 患者的骨骼肌活检。8 份 sIBM 患者的活检作为病理对照，8 份非疾病对照受试者的活检作为对照。通过 p62 和 LC3 检测到所有 IMNM 活检样本中自噬的改变，这些改变表现为弥漫性肌浆染色模式，与 sIBM 中主要局限于 rimmed 空泡的粗糙点状染色模式不同。p62 与伴侣蛋白 HSP70 和 αB-晶状体的共定位表明，错误折叠的蛋白质被特异性靶向 CASA 机制。这些纤维中 Bcl2 相关的athanogene 3（BAG3）阳性强调了自噬过程的选择性，这些纤维还表达 MHC Ⅰ类肌膜。研究中涉及自噬和内质网（ER）应激途径的基因表达在 IMNM 中显著上调。我们强调，在 IMNM 肌肉活检中可能会出现没有肌膜特征的空泡，并且不能与 sIBM 特异性空泡混淆。此外，我们还显示了选择性自噬的激活，并强调了伴侣蛋白在这种情况下的作用。CASA 发生在 IMNM 肌肉中，自噬的特定分子途径与 sIBM 中的不同，p62 是该过程的唯一标识符。
