Department of Biology, Molecular Biology and Heart Institutes, San Diego State University, San Diego, CA, USA.
Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
Hum Mol Genet. 2019 Feb 1;28(3):351-371. doi: 10.1093/hmg/ddy332.
Laminopathies are diseases caused by dominant mutations in the human LMNA gene encoding A-type lamins. Lamins are intermediate filaments that line the inner nuclear membrane, provide structural support for the nucleus and regulate gene expression. Drosophila melanogaster models of skeletal muscle laminopathies were developed to investigate the pathological defects caused by mutant lamins and identify potential therapeutic targets. Human disease-causing LMNA mutations were modeled in Drosophila Lamin C (LamC) and expressed in indirect flight muscle (IFM). IFM-specific expression of mutant, but not wild-type LamC, caused held-up wings indicative of myofibrillar defects. Analyses of the muscles revealed cytoplasmic aggregates of nuclear envelope (NE) proteins, nuclear and mitochondrial dysmorphology, myofibrillar disorganization and up-regulation of the autophagy cargo receptor p62. We hypothesized that the cytoplasmic aggregates of NE proteins trigger signaling pathways that alter cellular homeostasis, causing muscle dysfunction. In support of this hypothesis, transcriptomics data from human muscle biopsy tissue revealed misregulation of the AMP-activated protein kinase (AMPK)/4E-binding protein 1 (4E-BP1)/autophagy/proteostatic pathways. Ribosomal protein S6K (S6K) messenger RNA (mRNA) levels were increased and AMPKα and mRNAs encoding downstream targets were decreased in muscles expressing mutant LMNA relative controls. The Drosophila laminopathy models were used to determine if altering the levels of these factors modulated muscle pathology. Muscle-specific over-expression of AMPKα and down-stream targets 4E-BP, Forkhead box transcription factors O (Foxo) and Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α), as well as inhibition of S6K, suppressed the held-up wing phenotype, myofibrillar defects and LamC aggregation. These findings provide novel insights on mutant LMNA-based disease mechanisms and identify potential targets for drug therapy.
核纤层病是由编码 A 型核纤层蛋白的人类 LMNA 基因突变引起的疾病。核纤层蛋白是位于核内膜的中间丝，为核提供结构支持并调节基因表达。开发了骨骼肌核纤层病的果蝇模型，以研究突变核纤层蛋白引起的病理缺陷，并确定潜在的治疗靶点。在果蝇的 Lamin C（LamC）中模拟了人类致病性的 LMNA 突变，并在间接飞行肌（IFM）中表达。突变型但非野生型 LamC 的 IFM 特异性表达导致翅膀抬起，表明肌原纤维缺陷。对肌肉的分析显示核膜（NE）蛋白的细胞质聚集、核和线粒体形态异常、肌原纤维紊乱以及自噬货物受体 p62 的上调。我们假设 NE 蛋白的细胞质聚集触发改变细胞内稳态的信号通路，导致肌肉功能障碍。支持这一假设的是，来自人类肌肉活检组织的转录组学数据显示 AMP 激活的蛋白激酶（AMPK）/4E 结合蛋白 1（4E-BP1）/自噬/蛋白质稳态途径的失调。在表达突变型 LMNA 的肌肉中，核糖体蛋白 S6K（S6K）信使 RNA（mRNA）水平升高，而 AMPKα 和编码下游靶标的 mRNAs 减少。使用果蝇核纤层病模型来确定是否改变这些因素的水平可以调节肌肉病理学。肌肉特异性过表达 AMPKα 和下游靶标 4E-BP、叉头框转录因子 O（Foxo）和过氧化物酶体增殖物激活受体 γ 共激活因子 1-α（PGC1α），以及抑制 S6K，均可抑制翅膀抬起表型、肌原纤维缺陷和 LamC 聚集。这些发现为基于突变型 LMNA 的疾病机制提供了新的见解，并确定了药物治疗的潜在靶点。
