title: Abnormal distribution of heterogeneous nuclear ribonucleoproteins in sporadic inclusion body myositis.
abstract: Previous histopathologic studies of sporadic inclusion body myositis (sIBM) identified sarcoplasmic aggregation and myonuclear depletion of the predominantly nuclear heterogeneous nuclear ribonucleoprotein (hnRNP) TDP-43 in sIBM myofibers. Here, we examined sIBM muscle for abnormalities in two other hnRNPs hnRNPA1 and hnRNPA2B1, mutations in which cause multisystem proteinopathy associated with rimmed-vacuolar myopathies. Muscle biopsy specimens from 13 patients with sIBM and 13 patients without sIBM (dermatomyositis N=3, polymyositis N=3, muscular dystrophy N=3, motor neuron disease N=2, non-neuromuscular disease N=2) underwent immunohistochemistry for hnRNPA1, hnRNPA2B1, and TDP-43. Muscle transcriptional microarray data from 27 patients with sIBM and 12 patients without neuromuscular disease was analyzed. Depletion of hnRNPA1 and hnRNPA2B1 was present in 15% and 7% of sIBM myonuclei, respectively, compared with 1% and 0% of myonuclei in non-sIBM muscle. Sarcoplasmic aggregates of hnRNPA1 and hnRNPA2B1 distinct from TDP-43 aggregates were also found in sIBM. hnRNPA1 and hnRNPA2B1, as well as other hnRNPs, gene expression was unaltered in sIBM compared to normal muscle. Along with TDP-43, other hnRNPs, including hnRNPA1 and hnRNPA2B1, are depleted from sIBM myonuclei at the protein but not transcript level. The depletion of multiple hnRNPs from sIBM myonuclei together with their sarcoplasmic aggregation suggests that one aspect of sIBM pathophysiology may involve abnormal RNA metabolism that includes hyperassembly of ribonucleoprotein granules mediated by prion-like domains in hnRNPs, evolving into pathological aggregates.
authors.affiliation: Brigham and Women's Hospital, Department of Neurology, Harvard Medical School, Boston, MA, USA.
authors.forename: Jack L
authors.initials: JL
authors.lastname: Pinkus
authors.affiliation: Brigham and Women's Hospital, Department of Neurology, Harvard Medical School, Boston, MA, USA.
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Amato
authors.affiliation: Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: J Paul
authors.initials: JP
authors.lastname: Taylor
authors.affiliation: Brigham and Women's Hospital, Department of Neurology, Harvard Medical School, Boston, MA, USA; Children's Hospital Informatics Program, Harvard-MIT Division of Health Sciences and Technology, Boston, MA, USA. Electronic address: sagreenberg@partners.org.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Greenberg
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D046228:Microarray Analysis; D018482:Muscle, Skeletal / Q000378:metabolism; D009132:Muscles / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism; D018979:Myositis, Inclusion Body / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D012261:Ribonucleoproteins; C439768:hnRNP A2; C000619656:hnRNPA1 protein, human
keywords: Inclusion body myositis