title: alpha-Skeletal muscle actin nemaline myopathy mutants cause cell death in cultured muscle cells.
abstract: Nemaline myopathy is a neuromuscular disorder, characterized by muscle weakness and hypotonia and is, in 20% of the cases, caused by mutations in the gene encoding alpha-skeletal muscle actin, ACTA1. It is a heterogeneous disease with various clinical phenotypes and severities. In patients the ultrastructure of muscle cells is often disturbed by nemaline rods and it is thought this is the cause for muscle weakness. To search for possible defects during muscle cell differentiation we expressed alpha-actin mutants in myoblasts and allowed these cells to differentiate into myotubes. Surprisingly, we observed two striking new phenotypes in differentiating myoblasts: rounding up of cells and bleb formation, two features reminiscent of apoptosis. Indeed expression of these mutants induced cell death with apoptotic features in muscle cell culture, using AIF and endonuclease G, in a caspase-independent but calpain-dependent pathway. This is the first report on a common cellular defect induced by NM causing actin mutants, independent of their biochemical phenotypes or rod and aggregate formation capacity. These data suggest that lack of type II fibers or atrophy observed in nemaline myopathy patients may be also due to an increased number of dying muscle cells.
authors.affiliation: Department of Biochemistry, Ghent University, A. Baertsoenkaai 3, B-9000, Gent, Belgium.
authors.forename: Drieke
authors.initials: D
authors.lastname: Vandamme
authors.forename: Ellen
authors.initials: E
authors.lastname: Lambert
authors.forename: Davy
authors.initials: D
authors.lastname: Waterschoot
authors.forename: Christian
authors.initials: C
authors.lastname: Cognard
authors.forename: Joël
authors.initials: J
authors.lastname: Vandekerckhove
authors.forename: Christophe
authors.initials: C
authors.lastname: Ampe
authors.forename: Bruno
authors.initials: B
authors.lastname: Constantin
authors.forename: Heidi
authors.initials: H
authors.lastname: Rommelaere
mesh_terms: D000199:Actins / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D002154:Calpain / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004706:Endodeoxyribonucleases / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006801:Humans; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics*; D032446:Myoblasts / Q000378:metabolism*; D017696:Myopathies, Nemaline / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D010641:Phenotype; D011487:Protein Conformation; D051381:Rats
chemical_list: C494829:AIFM1 protein, human; D000199:Actins; D051033:Apoptosis Inducing Factor; D004706:Endodeoxyribonucleases; C052391:endonuclease G; D002154:Calpain; D020169:Caspases