Differential expression of selected mitochondrial genes in hibernating little brown bats, Myotis lucifugus.
High rates of non-shivering thermogenesis by brown adipose tissue accompanied by additional shivering thermogenesis in skeletal muscle provide the powerful reheating of body organs that allows hibernating mammals to return from their state of cold torpor back to euthermic function. Previous studies have suggested that changes to brown adipose mitochondria occur during hibernation and are partially responsible for its capacity for non-shivering thermogenesis. The current study shows that selected mitochondrial enzyme activities are elevated and selected genes and proteins are induced during torpor in brown adipose tissue of the little brown bat, Myotis lucifugus. Cytochrome oxidase activity in brown adipose tissue was more than 3-fold higher during torpor than in euthermic animals. Transcript levels of mitochondria-encoded genes, coxII and nad4, were also 3-4-fold higher during torpor, as evidenced by northern blotting. By contrast, transcripts of these genes were unchanged in skeletal muscle during torpor. Protein levels of carnitine palmitoyl transferase-1beta, an enzyme embedded in the outer membrane of the mitochondria that is the rate-limiting step enzyme in beta-oxidation, were also elevated by 2-fold during torpor in brown adipose but were unchanged in skeletal muscle. Cloning and sequencing of a 624 bp segment of cpt-1beta revealed a number of amino acid substitutions in the bat protein as compared to CPT-1beta from other mammals; these may be beneficial for enzyme function at low body temperatures during torpor. This study provides further evidence for a key role of mitochondria in hibernation.
Eddy
Sean F
SF
Institute of Biochemistry and Department of Chemistry Carleton University, Ottawa, Ont., Canada K1S 5B6. eddy@biochem.bumc.bu.edu
Morin
Pier
P
Storey
Kenneth B
KB
D002001:Adipose Tissue, Brown / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D001831:Body Temperature / Q000235:genetics / Q000502:physiology; D002334:Carnitine O-Palmitoyltransferase / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D002685:Chiroptera / Q000235:genetics* / Q000502:physiology; D003080:Cold Temperature; D042967:Electron Transport Complex I / Q000235:genetics / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology*; D050259:Genes, Mitochondrial / Q000235:genetics*; D006605:Hibernation / Q000235:genetics* / Q000502:physiology; D008928:Mitochondria / Q000502:physiology; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D022722:Thermogenesis / Q000235:genetics / Q000502:physiology
D003576:Electron Transport Complex IV; D002334:Carnitine O-Palmitoyltransferase; D042967:Electron Transport Complex I