title: FHL1 mutants that cause clinically distinct human myopathies form protein aggregates and impair myoblast differentiation.
abstract: 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.
authors.affiliation: Department of Biochemistry & Molecular Biology, Faculty of Medicine, Nursing & Health Sciences, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Brendan R
authors.initials: BR
authors.lastname: Wilding
authors.affiliation: Department of Biochemistry & Molecular Biology, Faculty of Medicine, Nursing & Health Sciences, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Meagan J
authors.initials: MJ
authors.lastname: McGrath
authors.affiliation: 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.
authors.forename: Gisèle
authors.initials: G
authors.lastname: Bonne
authors.affiliation: Department of Biochemistry & Molecular Biology, Faculty of Medicine, Nursing & Health Sciences, Monash University, Clayton, VIC 3800, Australia christina.mitchell@monash.edu.
authors.forename: Christina A
authors.initials: CA
authors.lastname: Mitchell
mesh_terms: D002454:Cell Differentiation / Q000502:physiology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism*; D060588:LIM Domain Proteins / Q000235:genetics* / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism*; D009135:Muscular Diseases / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009154:Mutation; D032446:Myoblasts / Q000378:metabolism* / Q000473:pathology*; D066329:Protein Aggregates
chemical_list: C101149:FHL1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; D009124:Muscle Proteins; D066329:Protein Aggregates
keywords: FHL1; Myopathy; RBM; SPM; XMPMA