title: T(3) stimulates resting metabolism and UCP-2 and UCP-3 mRNA but not nonphosphorylating mitochondrial respiration in mice.
abstract: The molecular basis for variations in resting metabolic rate (RMR) within a species is unknown. One possibility is that variations in RMR occur because of variations in uncoupling protein 2 (UCP-2) and uncoupling protein 3 (UCP-3) expression, resulting in mitochondrial proton leak differences. We tested the hypothesis that UCP-2 and -3 mRNAs positively correlate with RMR and proton leak. We treated thyroidectomized and sham-operated mice with triiodothyronine (T(3)) or vehicle and measured RMR, liver, and skeletal muscle mitochondrial nonphosphorylating respiration and UCP-2 and -3 mRNAs. T(3) stimulated RMR and liver UCP-2 and gastrocnemius UCP-2 and -3 expression. Mitochondrial respiration was not affected by T(3) and did not correlate with UCP-2 and -3 mRNAs. Gastrocnemius UCP-2 and -3 expression did correlate with RMR. We conclude 1) T(3) did not influence intrinsic mitochondrial properties such as membrane structure and composition, and 2) variations in UCP-2 and -3 expression may partly explain variations in RMR. One possible explanation for these data is that T(3) stimulates the leak in vivo but not in vitro because a posttranslational regulator of UCP-2 and -3 is not retained in the mitochondrial fraction.
authors.affiliation: Section of Neurobiology, Physiology, and Behavior, Division of Biological Sciences, School of Medicine, University of California, Davis, California 95616, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Jekabsons
authors.forename: F M
authors.initials: FM
authors.lastname: Gregoire
authors.forename: N A
authors.initials: NA
authors.lastname: Schonfeld-Warden
authors.forename: C H
authors.initials: CH
authors.lastname: Warden
authors.forename: B A
authors.initials: BA
authors.lastname: Horwitz
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology*; D007473:Ion Channels; D008297:Male; D026901:Membrane Transport Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D008930:Mitochondria, Liver / Q000378:metabolism; D008931:Mitochondria, Muscle / Q000378:metabolism; D024101:Mitochondrial Proteins; D018482:Muscle, Skeletal / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D012146:Rest; D013965:Thyroidectomy; D014284:Triiodothyronine / Q000494:pharmacology / Q000502:physiology*; D000071246:Uncoupling Protein 2; D000071247:Uncoupling Protein 3
chemical_list: D002352:Carrier Proteins; D007473:Ion Channels; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D012333:RNA, Messenger; C000604390:Ucp2 protein, mouse; C000604393:Ucp3 protein, mouse; D000071246:Uncoupling Protein 2; D000071247:Uncoupling Protein 3; D014284:Triiodothyronine