title: Myopathic lamin mutations cause reductive stress and activate the nrf2/keap-1 pathway.
abstract: Mutations in the human LMNA gene cause muscular dystrophy by mechanisms that are incompletely understood. The LMNA gene encodes A-type lamins, intermediate filaments that form a network underlying the inner nuclear membrane, providing structural support for the nucleus and organizing the genome. To better understand the pathogenesis caused by mutant lamins, we performed a structural and functional analysis on LMNA missense mutations identified in muscular dystrophy patients. These mutations perturb the tertiary structure of the conserved A-type lamin Ig-fold domain. To identify the effects of these structural perturbations on lamin function, we modeled these mutations in Drosophila Lamin C and expressed the mutant lamins in muscle. We found that the structural perturbations had minimal dominant effects on nuclear stiffness, suggesting that the muscle pathology was not accompanied by major structural disruption of the peripheral nuclear lamina. However, subtle alterations in the lamina network and subnuclear reorganization of lamins remain possible. Affected muscles had cytoplasmic aggregation of lamins and additional nuclear envelope proteins. Transcription profiling revealed upregulation of many Nrf2 target genes. Nrf2 is normally sequestered in the cytoplasm by Keap-1. Under oxidative stress Nrf2 dissociates from Keap-1, translocates into the nucleus, and activates gene expression. Unexpectedly, biochemical analyses revealed high levels of reducing agents, indicative of reductive stress. The accumulation of cytoplasmic lamin aggregates correlated with elevated levels of the autophagy adaptor p62/SQSTM1, which also binds Keap-1, abrogating Nrf2 cytoplasmic sequestration, allowing Nrf2 nuclear translocation and target gene activation. Elevated p62/SQSTM1 and nuclear enrichment of Nrf2 were identified in muscle biopsies from the corresponding muscular dystrophy patients, validating the disease relevance of our Drosophila model. Thus, novel connections were made between mutant lamins and the Nrf2 signaling pathway, suggesting new avenues of therapeutic intervention that include regulation of protein folding and metabolism, as well as maintenance of redox homoeostasis.
authors.affiliation: Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: George
authors.initials: G
authors.lastname: Dialynas
authors.affiliation: Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Om K
authors.initials: OK
authors.lastname: Shrestha
authors.affiliation: Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Ponce
authors.affiliation: Weill Institute for Cell and Molecular Biology, Department of Biomedical Engineering, Cornell University, Ithaca, New York, United States of America.
authors.forename: Monika
authors.initials: M
authors.lastname: Zwerger
authors.affiliation: Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Dylan A
authors.initials: DA
authors.lastname: Thiemann
authors.affiliation: Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Grant H
authors.initials: GH
authors.lastname: Young
authors.affiliation: Department of Pathology, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Moore
authors.affiliation: Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America; NMR Facility, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Liping
authors.initials: L
authors.lastname: Yu
authors.affiliation: Weill Institute for Cell and Molecular Biology, Department of Biomedical Engineering, Cornell University, Ithaca, New York, United States of America.
authors.forename: Jan
authors.initials: J
authors.lastname: Lammerding
authors.affiliation: Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America; Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Lori L
authors.initials: LL
authors.lastname: Wallrath
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002467:Cell Nucleus; D004330:Drosophila / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006706:Homeostasis; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D000072019:Kelch-Like ECH-Associated Protein 1; D034904:Lamin Type A / Q000235:genetics* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D009136:Muscular Dystrophies / Q000235:genetics*; D009154:Mutation; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D034881:Nuclear Lamina / Q000235:genetics / Q000378:metabolism; D018384:Oxidative Stress; D011487:Protein Conformation; D017510:Protein Folding; D000071456:Sequestosome-1 Protein; D015398:Signal Transduction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D047908:Intracellular Signaling Peptides and Proteins; C431364:KEAP1 protein, human; D000072019:Kelch-Like ECH-Associated Protein 1; C494847:LMNA protein, human; D034904:Lamin Type A; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; C440308:lamin C