Physiology - Research Publications

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    Metabolic remodeling of dystrophic skeletal muscle reveals biological roles for dystrophin and utrophin in adaptation and plasticity
    Hardee, JP ; Martins, KJB ; Miotto, PM ; Ryall, JG ; Gehrig, SM ; Reljic, B ; Naim, T ; Chung, JD ; Trieu, J ; Swiderski, K ; Philp, AM ; Philp, A ; Watt, MJ ; Stroud, DA ; Koopman, R ; Steinberg, GR ; Lynch, GS (ELSEVIER, 2021-01-12)
    OBJECTIVES: Preferential damage to fast, glycolytic myofibers is common in many muscle-wasting diseases, including Duchenne muscular dystrophy (DMD). Promoting an oxidative phenotype could protect muscles from damage and ameliorate the dystrophic pathology with therapeutic relevance, but developing efficacious strategies requires understanding currently unknown biological roles for dystrophin and utrophin in dystrophic muscle adaptation and plasticity. METHODS: Combining whole transcriptome RNA sequencing and mitochondrial proteomics with assessments of metabolic and contractile function, we investigated the roles of dystrophin and utrophin in fast-to-slow muscle remodeling with low-frequency electrical stimulation (LFS, 10 Hz, 12 h/d, 7 d/wk, 28 d) in mdx (dystrophin null) and dko (dystrophin/utrophin null) mice, two established preclinical models of DMD. RESULTS: Novel biological roles in adaptation were demonstrated by impaired transcriptional activation of estrogen-related receptor alpha-responsive genes supporting oxidative phosphorylation in dystrophic muscles. Further, utrophin expression in dystrophic muscles was required for LFS-induced remodeling of mitochondrial respiratory chain complexes, enhanced fiber respiration, and conferred protection from eccentric contraction-mediated damage. CONCLUSIONS: These findings reveal novel roles for dystrophin and utrophin during LFS-induced metabolic remodeling of dystrophic muscle and highlight the therapeutic potential of LFS to ameliorate the dystrophic pathology and protect from contraction-induced injury with important implications for DMD and related muscle disorders.
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    First person – Savant Thakur
    Lynch, GS (The Company of Biologists, 2020-01-01)
    ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Biology Open. Savant Thakur is first author on ‘HSP70 drives myoblast fusion during C2C12 myogenic differentiation’, published in BiO. Savant was a Ph.D. student in the lab of Professor Gordon S. Lynch at the Centre for Muscle Research, Department of Physiology, The University of Melbourne, working towards understanding the mechanisms of defective muscle repair in muscle diseases and wasting disorders. Sadly, Savant passed away on June 16, 2019 and so one of his supervisors, Professor Lynch, spoke to BiO about Savant's work and character.
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    Spatiotemporal Mapping Reveals Regional Gastrointestinal Dysfunction in mdx Dystrophic Mice Ameliorated by Oral L-arginine Supplementation
    Swiderski, K ; Bindon, R ; Trieu, J ; Naim, T ; Schokman, S ; Swaminathan, M ; Leembruggen, AJL ; Hill-Yardin, EL ; Koopman, R ; Bornstein, JC ; Lynch, GS (KOREAN SOC NEUROGASTROENTEROLOGY & MOTILITY, 2020-01-01)
    BACKGROUND/AIMS: Patients with Duchenne muscular dystrophy exhibit significant, ongoing impairments in gastrointestinal (GI) function likely resulting from dysregulated nitric oxide production. Compounds increasing neuronal nitric oxide synthase expression and/or activity could improve GI dysfunction and enhance quality of life for dystrophic patients. We used video imaging and spatiotemporal mapping to identify GI dysfunction in mdx dystrophic mice and determine whether dietary intervention to enhance nitric oxide could alleviate aberrant colonic activity in muscular dystrophy. METHODS: Four-week-old male C57BL/10 and mdx mice received a specialized diet either with no supplementation (control) or supplemented (1 g/kg/day) with L-alanine, L-arginine, or L-citrulline for 8 weeks. At the conclusion of treatment, mice were sacrificed by cervical dislocation and colon motility examined by spatiotemporal (ST) mapping ex vivo. RESULTS: ST mapping identified increased contraction number in the mid and distal colon of mdx mice on control and L-alanine supplemented diets relative to C57BL/10 mice (P < 0.05). Administration of either L-arginine or L-citrulline attenuated contraction number in distal colons of mdx mice relative to C57BL/10 mice. CONCLUSIONS: GI dysfunction in Duchenne muscular dystrophy has been sadly neglected as an issue affecting quality of life. ST mapping identified regional GI dysfunction in the mdx dystrophic mouse. Dietary interventions to increase nitric oxide signaling in the GI tract reduced the number of colonic contractions and alleviated colonic constriction at rest. These findings in mdx mice reveal that L-arginine can improve colonic motility and has potential therapeutic relevance for alleviating GI discomfort, improving clinical care, and enhancing quality of life in Duchenne muscular dystrophy.
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    HSP70 drives myoblast fusion during C2C12 myogenic differentiation
    Thakur, SS ; Swiderski, K ; Chhen, VL ; James, JL ; Cranna, NJ ; Islam, AMT ; Ryall, JG ; Lynch, GS (COMPANY BIOLOGISTS LTD, 2020-07-01)
    In response to injury, skeletal muscle stem cells (MuSCs) undergo myogenesis where they become activated, proliferate rapidly, differentiate and undergo fusion to form multinucleated myotubes. Dramatic changes in cell size, shape, metabolism and motility occur during myogenesis, which cause cellular stress and alter proteostasis. The molecular chaperone heat shock protein 70 (HSP70) maintains proteostasis by regulating protein biosynthesis and folding, facilitating transport of polypeptides across intracellular membranes and preventing stress-induced protein unfolding/aggregation. Although HSP70 overexpression can exert beneficial effects in skeletal muscle diseases and enhance skeletal muscle repair after injury, its effect on myogenesis has not been investigated. Plasmid-mediated overexpression of HSP70 did not affect the rate of C2C12 proliferation or differentiation, but the median number of myonuclei per myotube and median myotube width in differentiated C2C12 myotubes were increased with HSP70 overexpression. These findings reveal that increased HSP70 expression can promote myoblast fusion, identifying a mechanism for its therapeutic potential to enhance muscle repair after injury.This article has an associated First Person interview with the first author of the paper.