title: Analysis of the ACTN3 heterozygous genotype suggests that α-actinin-3 controls sarcomeric composition and muscle function in a dose-dependent fashion.
abstract: A common null polymorphism (R577X) in ACTN3 causes α-actinin-3 deficiency in ∼ 18% of the global population. There is no associated disease phenotype, but α-actinin-3 deficiency is detrimental to sprint and power performance in both elite athletes and the general population. However, despite considerable investigation to date, the functional consequences of heterozygosity for ACTN3 are unclear. A subset of studies have shown an intermediate phenotype in 577RX individuals, suggesting dose-dependency of α-actinin-3, while others have shown no difference between 577RR and RX genotypes. Here, we investigate the effects of α-actinin-3 expression level by comparing the muscle phenotypes of Actn3(+/-) (HET) mice to Actn3(+/+) [wild-type (WT)] and Actn3(-/-) [knockout (KO)] littermates. We show reduction in α-actinin-3 mRNA and protein in HET muscle compared with WT, which is associated with dose-dependent up-regulation of α-actinin-2, z-band alternatively spliced PDZ-motif and myotilin at the Z-line, and an incremental shift towards oxidative metabolism. While there is no difference in force generation, HET mice have an intermediate endurance capacity compared with WT and KO. The R577X polymorphism is associated with changes in ACTN3 expression consistent with an additive model in the human genotype-tissue expression cohort, but does not influence any other muscle transcripts, including ACTN2. Overall, ACTN3 influences sarcomeric composition in a dose-dependent fashion in mouse skeletal muscle, which translates directly to function. Variance in fibre type between biopsies likely masks this phenomenon in human skeletal muscle, but we suggest that an additive model is the most appropriate for use in testing ACTN3 genotype associations.
authors.affiliation: Institute for Neuroscience and Muscle Research, The Children's Hospital Westmead, Sydney, NSW 2145, Australia, Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, NSW 2006, Australia.
authors.forename: Marshall W
authors.initials: MW
authors.lastname: Hogarth
authors.affiliation: Institute for Neuroscience and Muscle Research, The Children's Hospital Westmead, Sydney, NSW 2145, Australia, Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, NSW 2006, Australia, Murdoch Children's Research Institute, Melbourne, Vic 3052, Australia, Department of Paediatrics, University of Melbourne, Melbourne, Vic, Australia.
authors.forename: Fleur C
authors.initials: FC
authors.lastname: Garton
authors.affiliation: Institute for Neuroscience and Muscle Research, The Children's Hospital Westmead, Sydney, NSW 2145, Australia, Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, NSW 2006, Australia, Murdoch Children's Research Institute, Melbourne, Vic 3052, Australia, Department of Paediatrics, University of Melbourne, Melbourne, Vic, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Houweling
authors.affiliation: Analytic and Translational Genetics Unit, Massachusetts General Hospital, Boston, MA 02114, USA, Program in Medical and Population Genetics, Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA and.
authors.forename: Taru
authors.initials: T
authors.lastname: Tukiainen
authors.affiliation: Analytic and Translational Genetics Unit, Massachusetts General Hospital, Boston, MA 02114, USA, Program in Medical and Population Genetics, Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA and.
authors.forename: Monkol
authors.initials: M
authors.lastname: Lek
authors.affiliation: Analytic and Translational Genetics Unit, Massachusetts General Hospital, Boston, MA 02114, USA, Program in Medical and Population Genetics, Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA and.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Macarthur
authors.affiliation: Murdoch Children's Research Institute, Melbourne, Vic 3052, Australia, Department of Paediatrics, University of Melbourne, Melbourne, Vic, Australia.
authors.forename: Jane T
authors.initials: JT
authors.lastname: Seto
authors.affiliation: Institute for Neuroscience and Muscle Research, The Children's Hospital Westmead, Sydney, NSW 2145, Australia, Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, NSW 2006, Australia.
authors.forename: Kate G R
authors.initials: KG
authors.lastname: Quinlan
authors.affiliation: Institute for Neuroscience and Muscle Research, The Children's Hospital Westmead, Sydney, NSW 2145, Australia.
authors.forename: Nan
authors.initials: N
authors.lastname: Yang
authors.affiliation: School of Medical Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Stewart I
authors.initials: SI
authors.lastname: Head
authors.affiliation: Institute for Neuroscience and Muscle Research, The Children's Hospital Westmead, Sydney, NSW 2145, Australia, Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, NSW 2006, Australia, Murdoch Children's Research Institute, Melbourne, Vic 3052, Australia, Department of Paediatrics, University of Melbourne, Melbourne, Vic, Australia, kathryn.north@mcri.edu.au.
authors.forename: Kathryn N
authors.initials: KN
authors.lastname: North
mesh_terms: D000185:Actinin / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D018628:Gene Dosage; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008840:Microfilament Proteins; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D010805:Physical Conditioning, Animal; D010807:Physical Endurance / Q000235:genetics*; D011110:Polymorphism, Genetic; D012518:Sarcomeres / Q000378:metabolism
chemical_list: C498529:Actn2 protein, mouse; C525925:Actn3 protein, mouse; D008840:Microfilament Proteins; D009124:Muscle Proteins; C503771:Myot protein, mouse; D000185:Actinin