title: The nuclear receptor, Nor-1, markedly increases type II oxidative muscle fibers and resistance to fatigue.
abstract: Nuclear hormone receptors (NR) have been implicated as regulators of lipid and carbohydrate metabolism. The orphan NR4A subgroup has emerged as regulators of metabolic function. Targeted silencing of neuron-derived orphan receptor 1 (Nor-1)/NR4A3 in skeletal muscle cells suggested that this NR was necessary for oxidative metabolism in vitro. To investigate the in vivo role of Nor-1, we have developed a mouse model with preferential expression of activated Nor-1 in skeletal muscle. In skeletal muscle, this resulted in a marked increase in: 1) myoglobin expression, 2) mitochondrial DNA and density, 3) oxidative enzyme staining, and 4) genes/proteins encoding subunits of electron transport chain complexes. This was associated with significantly increased type IIA and IIX myosin heavy chain mRNA and proteins and decreased type IIB myosin heavy chain mRNA and protein. The contractile protein/fiber type remodeling driving the acquisition of the oxidative type II phenotype was associated with 1) the significantly increased expression of myocyte-specific enhancer factor 2C, and phospho-histone deacetylase 5, and 2) predominantly cytoplasmic HDAC5 staining in the Tg-Nor-1 mice. Moreover, the Nor-1 transgenic line displayed significant improvements in glucose tolerance, oxygen consumption, and running endurance (in the absence of increased insulin sensitivity), consistent with increased oxidative capacity of skeletal muscle. We conclude that skeletal muscle fiber type is not only regulated by exercise-sensitive calcineurin-induced signaling cascade but also by NR signaling pathways that operate at the nexus that coordinates muscle performance and metabolic capacity in this major mass tissue.
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Pearen
authors.forename: Natalie A
authors.initials: NA
authors.lastname: Eriksson
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Fitzsimmons
authors.forename: Joel M
authors.initials: JM
authors.lastname: Goode
authors.forename: Nick
authors.initials: N
authors.lastname: Martel
authors.forename: Sofianos
authors.initials: S
authors.lastname: Andrikopoulos
authors.forename: George E O
authors.initials: GE
authors.lastname: Muscat
mesh_terms: D000818:Animals; D001786:Blood Glucose; D050259:Genes, Mitochondrial; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008928:Mitochondria / Q000378:metabolism; D018656:Muscle Fibers, Fast-Twitch / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D009211:Myoglobin / Q000235:genetics / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D057106:Nuclear Receptor Subfamily 4, Group A, Member 3 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010084:Oxidation-Reduction; D010766:Phosphorylation; D010807:Physical Endurance / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D013385:Succinate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D001786:Blood Glucose; D009211:Myoglobin; D057106:Nuclear Receptor Subfamily 4, Group A, Member 3; D020033:Protein Isoforms; D009243:NAD; D013385:Succinate Dehydrogenase; C498618:Hdac5 protein, mouse; D006655:Histone Deacetylases; D018995:Myosin Heavy Chains