title: Altered nuclear dynamics in MDX myofibers.
abstract: Duchenne muscular dystrophy (DMD) is a genetic disorder in which the absence of dystrophin leads to progressive muscle degeneration and weakness. Although the genetic basis is known, the pathophysiology of dystrophic skeletal muscle remains unclear. We examined nuclear movement in wild-type (WT) and muscular dystrophy mouse model for DMD (MDX) (dystrophin-null) mouse myofibers. We also examined expression of proteins in the linkers of nucleoskeleton and cytoskeleton (LINC) complex, as well as nuclear transcriptional activity via histone H3 acetylation and polyadenylate-binding nuclear protein-1. Because movement of nuclei is not only LINC dependent but also microtubule dependent, we analyzed microtubule density and organization in WT and MDX myofibers, including the application of a unique 3D tool to assess microtubule core structure. Nuclei in MDX myofibers were more mobile than in WT myofibers for both distance traveled and velocity. MDX muscle shows reduced expression and labeling intensity of nesprin-1, a LINC protein that attaches the nucleus to the microtubule and actin cytoskeleton. MDX nuclei also showed altered transcriptional activity. Previous studies established that microtubule structure at the cortex is disrupted in MDX myofibers; our analyses extend these findings by showing that microtubule structure in the core is also disrupted. In addition, we studied malformed MDX myofibers to better understand the role of altered myofiber morphology vs. microtubule architecture in the underlying susceptibility to injury seen in dystrophic muscles. We incorporated morphological and microtubule architectural concepts into a simplified finite element mathematical model of myofiber mechanics, which suggests a greater contribution of myofiber morphology than microtubule structure to muscle biomechanical performance.NEW & NOTEWORTHYMicrotubules provide the means for nuclear movement but show altered organization in the muscular dystrophy mouse model (MDX) (dystrophin-null) muscle. Here, MDX myofibers show increased nuclear movement, altered transcriptional activity, and altered linkers of nucleoskeleton and cytoskeleton complex expression compared with healthy myofibers. Microtubule architecture was incorporated in finite element modeling of passive stretch, revealing a role of fiber malformation, commonly found in MDX muscle. The results suggest that alterations in microtubule architecture in MDX muscle affect nuclear movement, which is essential for muscle function.
authors.affiliation: Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Shama R
authors.initials: SR
authors.lastname: Iyer
authors.affiliation: Departments of Orthopaedic Surgery and Bioengineering, University of California San Diego, La Jolla, California.
authors.forename: Sameer B
authors.initials: SB
authors.lastname: Shah
authors.affiliation: Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Ana P
authors.initials: AP
authors.lastname: Valencia
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Martin F
authors.initials: MF
authors.lastname: Schneider
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Erick O
authors.initials: EO
authors.lastname: Hernández-Ochoa
authors.affiliation: Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Stains
authors.affiliation: Department of Biomedical Engineering and Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia; and.
authors.forename: Silvia S
authors.initials: SS
authors.lastname: Blemker
authors.affiliation: Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, Maryland; rlovering@som.umaryland.edu.|Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Richard M
authors.identifier: http://orcid.org/0000-0002-9899-5071
authors.initials: RM
authors.lastname: Lovering
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism* / Q000473:pathology*; D002478:Cells, Cultured; D003198:Computer Simulation; D005260:Female; D020342:Finite Element Analysis; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018101:Mice, Inbred mdx; D008954:Models, Biological; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000473:pathology*; D009136:Muscular Dystrophies / Q000473:pathology* / Q000503:physiopathology*
keywords: bifurcated fibers; cytoskeleton; muscular dystrophy