title: Altered Tnnt3 characterizes selective weakness of fast fibers in mice overexpressing FSHD region gene 1 (FRG1).
abstract: Facioscapulohumeral muscular dystrophy (FSHD), a common hereditary myopathy, is characterized by atrophy and weakness of selective muscle groups. FSHD is considered an autosomal dominant disease with incomplete penetrance and unpredictable variability of clinical expression within families. Mice overexpressing FRG1 (FSHD region gene 1), a candidate gene for this disease, develop a progressive myopathy with features of the human disorder. Here, we show that in FRG1-overexpressing mice, fast muscles, which are the most affected by the dystrophic process, display anomalous fast skeletal troponin T (fTnT) isoform, resulting from the aberrant splicing of the Tnnt3 mRNA that precedes the appearance of dystrophic signs. We determine that muscles of FRG1 mice develop less strength due to impaired contractile properties of fast-twitch fibers associated with an anomalous MyHC-actin ratio and a reduced sensitivity to Ca(2+). We demonstrate that the decrease of Ca(2+) sensitivity of fast-twitch fibers depends on the anomalous troponin complex and can be rescued by the substitution with the wild-type proteins. Finally, we find that the presence of aberrant splicing isoforms of TNNT3 characterizes dystrophic muscles in FSHD patients. Collectively, our results suggest that anomalous TNNT3 profile correlates with the muscle impairment in both humans and mice. On the basis of these results, we propose that aberrant fTnT represents a biological marker of muscle phenotype severity and disease progression.
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy;
authors.forename: Valentina
authors.initials: V
authors.lastname: Sancisi
authors.forename: Elena
authors.initials: E
authors.lastname: Germinario
authors.forename: Alessandra
authors.initials: A
authors.lastname: Esposito
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Morini
authors.forename: Samantha
authors.initials: S
authors.lastname: Peron
authors.forename: Maurizio
authors.initials: M
authors.lastname: Moggio
authors.forename: Giuliano
authors.initials: G
authors.lastname: Tomelleri
authors.forename: Daniela
authors.initials: D
authors.lastname: Danieli-Betto
authors.forename: Rossella
authors.initials: R
authors.lastname: Tupler
mesh_terms: D017398:Alternative Splicing / Q000502:physiology; D000818:Animals; D015415:Biomarkers; D005786:Gene Expression Regulation / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D008840:Microfilament Proteins; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018908:Muscle Weakness / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins; D020107:Troponin T / Q000235:genetics / Q000378:metabolism*
chemical_list: D015415:Biomarkers; C484440:Frg1 protein, mouse; D008840:Microfilament Proteins; D011506:Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D020107:Troponin T
keywords: FRG1; aberrant splicing; muscle weakness; muscular dystrophy; troponin T