Wilding Brendan R, McGrath Meagan J, Bonne Gisèle, Mitchell Christina A
Department of Biochemistry & Molecular Biology, Faculty of Medicine, Nursing & Health Sciences, Monash University, Clayton, VIC 3800, Australia.
Inserm, U974, Paris, F-75013, France Université Pierre et Marie Curie-Paris 6, UM 76, CNRS, UMR7215, Institut de Myologie, IFR14, Paris, F-75013, France AP-HP, Groupe Hospitalier Pitié-Salpêtrière, U.F. Cardiogénétique et Myogénétique Moléculaire, Service de Biochimie Métabolique, Paris, F-75013, France.
J Cell Sci. 2014 May 15;127(Pt 10):2269-81. doi: 10.1242/jcs.140905. Epub 2014 Mar 14.
FHL1 mutations cause several clinically heterogeneous myopathies, including reducing body myopathy (RBM), scapuloperoneal myopathy (SPM) and X-linked myopathy with postural muscle atrophy (XMPMA). The molecular mechanisms underlying the pathogenesis of FHL1 myopathies are unknown. Protein aggregates, designated 'reducing bodies', that contain mutant FHL1 are detected in RBM muscle but not in several other FHL1 myopathies. Here, RBM, SPM and XMPMA FHL1 mutants were expressed in C2C12 cells and showed equivalent protein expression to wild-type FHL1. These mutants formed aggregates that were positive for the reducing body stain Menadione-NBT, analogous to RBM muscle aggregates. However, hypertrophic cardiomyopathy (HCM) and Emery-Dreifuss muscular dystrophy (EDMD) FHL1 mutants generally exhibited reduced expression. Wild-type FHL1 promotes myoblast differentiation; however, RBM, SPM and XMPMA mutations impaired differentiation, consistent with a loss of normal FHL1 function. Furthermore, SPM and XMPMA FHL1 mutants retarded myotube formation relative to vector control, consistent with a dominant-negative or toxic function. Mutant FHL1 myotube formation was partially rescued by expression of a constitutively active FHL1-binding partner, NFATc1. This is the first study to show that FHL1 mutations identified in several clinically distinct myopathies lead to similar protein aggregation and impair myotube formation, suggesting a common pathogenic mechanism despite heterogeneous clinical features.
FHL1基因突变会导致多种临床异质性肌病，包括消瘦性肌病（RBM）、肩胛腓骨肌病（SPM）和伴有姿势性肌肉萎缩的X连锁肌病（XMPMA）。FHL1肌病发病机制的分子机制尚不清楚。在RBM肌肉中可检测到含有突变型FHL1的蛋白聚集体，即“消瘦体”，但在其他几种FHL1肌病中未检测到。在此，RBM、SPM和XMPMA的FHL1突变体在C2C12细胞中表达，且与野生型FHL1表现出相当的蛋白表达。这些突变体形成了对甲萘醌-NBT还原体染色呈阳性的聚集体，类似于RBM肌肉聚集体。然而，肥厚型心肌病（HCM）和埃默里-德赖富斯肌营养不良症（EDMD）的FHL1突变体通常表现出表达降低。野生型FHL1促进成肌细胞分化；然而，RBM、SPM和XMPMA突变损害了分化，这与正常FHL1功能丧失一致。此外，相对于载体对照，SPM和XMPMA的FHL1突变体延缓了肌管形成，这与显性负性或毒性功能一致。通过组成型活性FHL1结合伴侣NFATc1的表达，部分挽救了突变型FHL1的肌管形成。这是第一项表明在几种临床不同的肌病中鉴定出的FHL1突变会导致相似的蛋白聚集并损害肌管形成的研究，提示尽管临床特征异质性，但存在共同的致病机制。
