title: Myofibrillar disruption and RNA-binding protein aggregation in a mouse model of limb-girdle muscular dystrophy 1D.
abstract: Limb-girdle muscular dystrophy type 1D (LGMD1D) is caused by dominantly inherited missense mutations in DNAJB6, an Hsp40 co-chaperone. LGMD1D muscle has rimmed vacuoles and inclusion bodies containing DNAJB6, Z-disc proteins and TDP-43. DNAJB6 is expressed as two isoforms; DNAJB6a and DNAJB6b. Both isoforms contain LGMD1D mutant residues and are expressed in human muscle. To identify which mutant isoform confers disease pathogenesis and generate a mouse model of LGMD1D, we evaluated DNAJB6 expression and localization in skeletal muscle as well as generating DNAJB6 isoform specific expressing transgenic mice. DNAJB6a localized to myonuclei while DNAJB6b was sarcoplasmic. LGMD1D mutations in DNAJB6a or DNAJB6b did not alter this localization in mouse muscle. Transgenic mice expressing the LGMD1D mutant, F93L, in DNAJB6b under a muscle-specific promoter became weak, had early lethality and developed muscle pathology consistent with myopathy after 2 months; whereas mice expressing the same F93L mutation in DNAJB6a or overexpressing DNAJB6a or DNAJB6b wild-type transgenes remained unaffected after 1 year. DNAJB6b localized to the Z-disc and DNAJB6b-F93L expressing mouse muscle had myofibrillar disorganization and desmin inclusions. Consistent with DNAJB6 dysfunction, keratin 8/18, a DNAJB6 client also accumulated in DNAJB6b-F93L expressing mouse muscle. The RNA-binding proteins hnRNPA1 and hnRNPA2/B1 accumulated and co-localized with DNAJB6 at sarcoplasmic stress granules suggesting that these proteins maybe novel DNAJB6b clients. Similarly, hnRNPA1 and hnRNPA2/B1 formed sarcoplasmic aggregates in patients with LGMD1D. Our data support that LGMD1D mutations in DNAJB6 disrupt its sarcoplasmic function suggesting a role for DNAJB6b in Z-disc organization and stress granule kinetics.
authors.affiliation: Department of Neurology.
authors.forename: Rocio
authors.initials: R
authors.lastname: Bengoechea
authors.affiliation: Department of Neurology.
authors.forename: Sara K
authors.initials: SK
authors.lastname: Pittman
authors.affiliation: Department of Neurology.
authors.forename: Elizabeth P
authors.initials: EP
authors.lastname: Tuck
authors.affiliation: Department of Cell Biology and Physiology and and The Hope Center for Neurological Diseases, Washington University School of Medicine, St Louis, MO 63110, USA.
authors.forename: Heather L
authors.initials: HL
authors.lastname: True
authors.affiliation: Department of Neurology, The Hope Center for Neurological Diseases, Washington University School of Medicine, St Louis, MO 63110, USA weihlc@neuro.wustl.edu.
authors.forename: Conrad C
authors.initials: CC
authors.lastname: Weihl
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D050956:HSP40 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000378:metabolism*; D006801:Humans; D007633:Keratins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D049288:Muscular Dystrophies, Limb-Girdle / Q000378:metabolism* / Q000473:pathology; D009154:Mutation; D009210:Myofibrils / Q000378:metabolism* / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000378:metabolism
chemical_list: C485565:DNAJB6 protein, human; D050956:HSP40 Heat-Shock Proteins; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D018832:Molecular Chaperones; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D007633:Keratins