title: Dystrophin-deficient dogs with reduced myostatin have unequal muscle growth and greater joint contractures.
abstract: BACKGROUND
  Myostatin (Mstn) is a negative regulator of muscle growth whose inhibition promotes muscle growth and regeneration. Dystrophin-deficient mdx mice in which myostatin is knocked out or inhibited postnatally have a less severe phenotype with greater total mass and strength and less fibrosis and fatty replacement of muscles than mdx mice with wild-type myostatin expression. Dogs with golden retriever muscular dystrophy (GRMD) have previously been noted to have increased muscle mass and reduced fibrosis after systemic postnatal myostatin inhibition. Based partly on these results, myostatin inhibitors are in development for use in human muscular dystrophies. However, persisting concerns regarding the effects of long-term and profound myostatin inhibition will not be easily or imminently answered in clinical trials.
  
  
  METHODS
  To address these concerns, we developed a canine (GRippet) model by crossbreeding dystrophin-deficient GRMD dogs with Mstn-heterozygous (Mstn (+/-)) whippets. A total of four GRippets (dystrophic and Mstn (+/-)), three GRMD (dystrophic and Mstn wild-type) dogs, and three non-dystrophic controls from two litters were evaluated.
  
  
  RESULTS
  Myostatin messenger ribonucleic acid (mRNA) and protein levels were downregulated in both GRMD and GRippet dogs. GRippets had more severe postural changes and larger (more restricted) maximal joint flexion angles, apparently due to further exaggeration of disproportionate effects on muscle size. Flexors such as the cranial sartorius were more hypertrophied on magnetic resonance imaging (MRI) in the GRippets, while extensors, including the quadriceps femoris, underwent greater atrophy. Myostatin protein levels negatively correlated with relative cranial sartorius muscle cross-sectional area on MRI, supporting a role in disproportionate muscle size. Activin receptor type IIB (ActRIIB) expression was higher in dystrophic versus control dogs, consistent with physiologic feedback between myostatin and ActRIIB. However, there was no differential expression between GRMD and GRippet dogs. Satellite cell exhaustion was not observed in GRippets up to 3 years of age.
  
  
  CONCLUSIONS
  Partial myostatin loss may exaggerate selective muscle hypertrophy or atrophy/hypoplasia in GRMD dogs and worsen contractures. While muscle imbalance is not a feature of myostatin inhibition in mdx mice, findings in a larger animal model could translate to human experience with myostatin inhibitors.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA ; Department of Neurology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA ; Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843-4458 USA.
authors.forename: Joe N
authors.identifier: 0000-0002-5594-1882
authors.initials: JN
authors.lastname: Kornegay
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Bogan
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA.
authors.forename: Janet R
authors.initials: JR
authors.lastname: Bogan
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Dow
authors.affiliation: Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA.
authors.forename: Jiahui
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Neurology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Fan
authors.affiliation: The Hugo W. Moser Research Institute at Kennedy Krieger Institute and Departments of Neurology and Neuroscience, Johns Hopkins School of Medicine, Baltimore, MD 21205 USA.
authors.forename: Naili
authors.initials: N
authors.lastname: Liu
authors.affiliation: The Hugo W. Moser Research Institute at Kennedy Krieger Institute and Departments of Neurology and Neuroscience, Johns Hopkins School of Medicine, Baltimore, MD 21205 USA.
authors.forename: Leigh C
authors.initials: LC
authors.lastname: Warsing
authors.affiliation: Department of Human Nutrition, Foods and Exercise, Virginia Tech University, Blacksburg, VA 24061 USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Grange
authors.affiliation: Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA.
authors.forename: Mihye
authors.initials: M
authors.lastname: Ahn
authors.affiliation: Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843-4458 USA.
authors.forename: Cynthia J
authors.initials: CJ
authors.lastname: Balog-Alvarez
authors.affiliation: Department of Pathology, The Ohio State University, Columbus, OH 43210 USA.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Cotten
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA.
authors.forename: Monte S
authors.initials: MS
authors.lastname: Willis
authors.affiliation: Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843-4458 USA.
authors.forename: Candice
authors.initials: C
authors.lastname: Brinkmeyer-Langford
authors.affiliation: Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA.
authors.forename: Hongtu
authors.initials: H
authors.lastname: Zhu
authors.affiliation: Rare Disease Research Unit, Pfizer, Inc., Cambridge Park Drive, Cambridge, MA USA.
authors.forename: Joe
authors.initials: J
authors.lastname: Palandra
authors.affiliation: Rare Disease Research Unit, Pfizer, Inc., Cambridge Park Drive, Cambridge, MA USA.
authors.forename: Carl A
authors.initials: CA
authors.lastname: Morris
authors.affiliation: Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA ; Department of Computer Science, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 USA.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Styner
authors.affiliation: The Hugo W. Moser Research Institute at Kennedy Krieger Institute and Departments of Neurology and Neuroscience, Johns Hopkins School of Medicine, Baltimore, MD 21205 USA.
authors.forename: Kathryn R
authors.initials: KR
authors.lastname: Wagner
mesh_terms: D030301:Activin Receptors, Type II / Q000378:metabolism; D000818:Animals; D030801:Animals, Genetically Modified; D001696:Biomechanical Phenomena; D003286:Contracture / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D004285:Dogs; D016189:Dystrophin / Q000172:deficiency* / Q000235:genetics; D005684:Gait; D020022:Genetic Predisposition to Disease; D006824:Hybridization, Genetic; D007596:Joints / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D008279:Magnetic Resonance Imaging; D053580:Muscle Strength; D009137:Muscular Dystrophy, Animal / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D055435:Myostatin / Q000172:deficiency* / Q000235:genetics; D051763:PAX7 Transcription Factor / Q000378:metabolism; D010641:Phenotype; D011187:Posture; D052097:Quadriceps Muscle / Q000254:growth & development / Q000378:metabolism* / Q000473:pathology; D032496:Satellite Cells, Skeletal Muscle / Q000378:metabolism / Q000473:pathology
chemical_list: D016189:Dystrophin; D055435:Myostatin; D051763:PAX7 Transcription Factor; D030301:Activin Receptors, Type II; C425584:activin receptor type II-B
keywords: Contractures; Dogs; Golden retriever muscular dystrophy (GRMD); Muscle hypertrophy; Muscular dystrophy; Myostatin inhibition; Whippets