title: ADrosophilamodel of dominant inclusion body myopathy type 3 shows diminished myosin kinetics that reduce muscle power and yield myofibrillar defects.
abstract: Individuals with inclusion body myopathy type 3 (IBM3) display congenital joint contractures with early-onset muscle weakness that becomes more severe in adulthood. The disease arises from an autosomal dominant point mutation causing an E706K substitution in myosin heavy chain type IIa. We have previously expressed the corresponding myosin mutation (E701K) in homozygousDrosophilaindirect flight muscles and recapitulated the myofibrillar degeneration and inclusion bodies observed in the human disease. We have also found that purified E701K myosin has dramatically reduced actin-sliding velocity and ATPase levels. Since IBM3 is a dominant condition, we now examine the disease state in heterozygoteDrosophilain order to gain a mechanistic understanding of E701K pathogenicity. Myosin ATPase activities in heterozygotes suggest that approximately equimolar levels of myosin accumulate from each allele.In vitroactin sliding velocity rates for myosin isolated from the heterozygotes were lower than the control, but higher than for the pure mutant isoform. Although sarcomeric ultrastructure was nearly wild type in young adults, mechanical analysis of skinned indirect flight muscle fibers revealed a 59% decrease in maximum oscillatory power generation and an approximately 20% reduction in the frequency at which maximum power was produced. Rate constant analyses suggest a decrease in the rate of myosin attachment to actin, with myosin spending decreased time in the strongly bound state. These mechanical alterations result in a one-third decrease in wing beat frequency and marginal flight ability. With aging, muscle ultrastructure and function progressively declined. Aged myofibrils showed Z-line streaming, consistent with the human heterozygote phenotype. Based upon the mechanical studies, we hypothesize that the mutation decreases the probability of the power stroke occurring and/or alters the degree of movement of the myosin lever arm, resulting in decreasedin vitromotility, reduced muscle power output and focal myofibrillar disorganization similar to that seen in individuals with IBM3.
authors.affiliation: Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, CA 92182-4614, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Suggs
authors.affiliation: Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, CA 92182-4614, USA.
authors.forename: Girish C
authors.initials: GC
authors.lastname: Melkani
authors.affiliation: Department of Biological Sciences and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY 12180-3590, USA.
authors.forename: Bernadette M
authors.initials: BM
authors.lastname: Glasheen
authors.affiliation: Department of Biological Sciences and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY 12180-3590, USA.
authors.forename: Mia M
authors.initials: MM
authors.lastname: Detor
authors.affiliation: Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, CA 92182-4614, USA.
authors.forename: Anju
authors.initials: A
authors.lastname: Melkani
authors.affiliation: Department of Biological Sciences and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY 12180-3590, USA.
authors.forename: Nathan P
authors.initials: NP
authors.lastname: Marsan
authors.affiliation: Department of Biological Sciences and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY 12180-3590, USA swankd@rpi.edu sbernstein@mail.sdsu.edu.
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Swank
authors.affiliation: Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, CA 92182-4614, USA swankd@rpi.edu sbernstein@mail.sdsu.edu.
authors.forename: Sanford I
authors.identifier: 0000-0001-7094-5390
authors.initials: SI
authors.lastname: Bernstein
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000375:Aging / Q000473:pathology; D000818:Animals; D001696:Biomechanical Phenomena; D003286:Contracture / Q000378:metabolism* / Q000473:pathology*; D004195:Disease Models, Animal; D004331:Drosophila melanogaster / Q000378:metabolism*; D055119:Elastic Modulus; D005426:Flight, Animal / Q000502:physiology; D006579:Heterozygote; D006720:Homozygote; D007700:Kinetics; D009043:Motor Activity; D018482:Muscle, Skeletal / Q000473:pathology / Q000503:physiopathology*; D050505:Mutant Proteins / Q000378:metabolism; D009210:Myofibrils / Q000473:pathology* / Q000648:ultrastructure; D009218:Myosins / Q000378:metabolism*; D018979:Myositis, Inclusion Body / Q000151:congenital* / Q000378:metabolism / Q000473:pathology; D009886:Ophthalmoplegia / Q000378:metabolism* / Q000473:pathology*; D014921:Wings, Animal / Q000502:physiology
chemical_list: D050505:Mutant Proteins; D000251:Adenosine Triphosphatases; D009218:Myosins
keywords: Drosophila melanogaster; Inclusion body myopathy type 3; Muscle mechanics; Myofibril; Myosin heavy chain