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Alpha-actin mutations in congenital myopathies: identification of cell death as a new cellular Nemaline Myopathy phenotype and induction of similar cytoskeletal defects by mutants associated with different myopathies

Drieke Vandamme (UGent)
(2009)
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(UGent)
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Abstract
The most abundant protein in eukaryotes is the cytoskeletal protein actin, of which six isoforms exist. Mutations in α-skeletal muscle actin, main actin isoform in skeletal muscle, are associated with three congenital myopathies : nemaline myopathy (NM), the core myopathies (CCD) and congenital fibre type disproportion (CFTD), all heterogeneous diseases characterized by muscle weakness and hypotonia. Nemaline myopathy is characterized by nemaline rods in patient muscle. However, there is no correlation between severity and rod occurrence. Previous research biochemically characterized 19 actin mutants, and could reproduce rods in fibroblasts. There was no correlation between biochemical and cellular phenotype. Here we biochemically characterized new NM associated actin mutants and expressed them in fibroblasts, Sol8 myoblasts and differentiating Sol8 muscle cells. Some of the mutants behaved as WT in the biochemical analysis, but we could find a cellular defect for all mutants, i.e. the induction of rods or aggregates in fibroblasts and myoblasts, a reduced incorporation in fibroblast stress fibers shown by diffuse cytoplasmic myc-actin staining, cell membrane blebbing in muscle cells and formation of thickened actin fibers in myotubes. None of the NM causing actin mutants induce all of the cellular phenotypes, but some induce multiple defects. However, in a second set of mutants we observed a common phenotype: induction of a calpain involved, caspase independent cell death with apoptotic features, via release of endoG and AIF, indicating other processes than the rod formation could underlie the pathogenesis of NM, and that nemaline rods are secondary to this pathogenesis. CCD and CFTD are characterized by core lesions and a difference in fibre size respectively. Biochemical characterization of CCD and CFTD causing actin mutants showed they behave as WT actin. We expressed them in fibroblasts, myoblasts and differentiating myotubes and found for two of the CFTD causing mutants similar phenotypes as for NM mutants: induction of rods in fibroblasts and thickened fibers in myotubes. These results show that the molecular mechanisms behind NM, CCD and CFTD caused by actin mutations could be (partly) related. I hypothesize on a central role for Ca2+ homeostasis via Ca2+ sensitivity and Ca2+ signaling in this pathogenesis.
Keywords
muscle cytoskeleton, actin, cell death, congenital myopathy

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MLA
Vandamme, Drieke. Alpha-Actin Mutations in Congenital Myopathies: Identification of Cell Death as a New Cellular Nemaline Myopathy Phenotype and Induction of Similar Cytoskeletal Defects by Mutants Associated with Different Myopathies. Ghent University. Faculty of Medicine and Health Sciences, 2009.
APA
Vandamme, D. (2009). Alpha-actin mutations in congenital myopathies: identification of cell death as a new cellular Nemaline Myopathy phenotype and induction of similar cytoskeletal defects by mutants associated with different myopathies. Ghent University. Faculty of Medicine and Health Sciences, Ghent, Belgium.
Chicago author-date
Vandamme, Drieke. 2009. “Alpha-Actin Mutations in Congenital Myopathies: Identification of Cell Death as a New Cellular Nemaline Myopathy Phenotype and Induction of Similar Cytoskeletal Defects by Mutants Associated with Different Myopathies.” Ghent, Belgium: Ghent University. Faculty of Medicine and Health Sciences.
Chicago author-date (all authors)
Vandamme, Drieke. 2009. “Alpha-Actin Mutations in Congenital Myopathies: Identification of Cell Death as a New Cellular Nemaline Myopathy Phenotype and Induction of Similar Cytoskeletal Defects by Mutants Associated with Different Myopathies.” Ghent, Belgium: Ghent University. Faculty of Medicine and Health Sciences.
Vancouver
1.
Vandamme D. Alpha-actin mutations in congenital myopathies: identification of cell death as a new cellular Nemaline Myopathy phenotype and induction of similar cytoskeletal defects by mutants associated with different myopathies. [Ghent, Belgium]: Ghent University. Faculty of Medicine and Health Sciences; 2009.
IEEE
[1]
D. Vandamme, “Alpha-actin mutations in congenital myopathies: identification of cell death as a new cellular Nemaline Myopathy phenotype and induction of similar cytoskeletal defects by mutants associated with different myopathies,” Ghent University. Faculty of Medicine and Health Sciences, Ghent, Belgium, 2009.
@phdthesis{706648,
  abstract     = {{The most abundant protein in eukaryotes is the cytoskeletal protein actin, of which six isoforms exist. Mutations in α-skeletal muscle actin, main actin isoform in skeletal muscle, are associated with three congenital myopathies : nemaline myopathy (NM), the core myopathies (CCD) and congenital fibre type disproportion (CFTD), all heterogeneous diseases characterized by muscle weakness and hypotonia. 
Nemaline myopathy is characterized by nemaline rods in patient muscle. However, there is no correlation between severity and rod occurrence. Previous research biochemically characterized 19 actin mutants, and could reproduce rods in fibroblasts. There was no correlation between biochemical and cellular phenotype. Here we biochemically characterized new NM associated actin mutants and expressed them in fibroblasts, Sol8 myoblasts and differentiating Sol8 muscle cells. Some of the mutants behaved as WT in the biochemical analysis, but we could find a cellular defect for all mutants, i.e. the induction of rods or aggregates in fibroblasts and myoblasts, a reduced incorporation in fibroblast stress fibers shown by diffuse cytoplasmic myc-actin staining, cell membrane blebbing in muscle cells and formation of thickened actin fibers in myotubes. None of the NM causing actin mutants induce all of the cellular phenotypes, but some induce multiple defects. However, in a second set of mutants we observed a common phenotype: induction of a calpain involved, caspase independent cell death with apoptotic features, via release of endoG and AIF, indicating other processes than the rod formation could underlie the pathogenesis of NM, and that nemaline rods are secondary to this pathogenesis. 
CCD and CFTD are characterized by core lesions and a difference in fibre size respectively. Biochemical characterization of CCD and CFTD causing actin mutants showed they behave as WT actin. We expressed them in fibroblasts, myoblasts and differentiating myotubes and found for two of the CFTD causing mutants similar phenotypes as for NM mutants: induction of rods in fibroblasts and thickened fibers in myotubes. 
These results show that the molecular mechanisms behind NM, CCD and CFTD caused by actin mutations could be (partly) related. I hypothesize on a central role for Ca2+ homeostasis via Ca2+ sensitivity and Ca2+ signaling in this pathogenesis.}},
  author       = {{Vandamme, Drieke}},
  keywords     = {{muscle cytoskeleton,actin,cell death,congenital myopathy}},
  language     = {{eng}},
  pages        = {{160 + addenda}},
  publisher    = {{Ghent University. Faculty of Medicine and Health Sciences}},
  school       = {{Ghent University}},
  title        = {{Alpha-actin mutations in congenital myopathies: identification of cell death as a new cellular Nemaline Myopathy phenotype and induction of similar cytoskeletal defects by mutants associated with different myopathies}},
  url          = {{http://lib.ugent.be/fulltxt/RUG01/001/339/611/RUG01-001339611_2010_0001_AC.pdf}},
  year         = {{2009}},
}