title: Cold temperature blocks thyroid hormone-induced changes in lipid and energy metabolism in the liver of Lithobates catesbeianus tadpoles.
abstract: BACKGROUND
  Exposure of the American bullfrog Lithobates catesbeianus tadpoles to low temperature affects many biological processes including lipid metabolism and the thyroid hormone (TH) signaling pathway, resulting in arrest of TH-induced metamorphosis. To clarify what molecular events occur in this phenomenon, we investigated the glycerophospholipid and fatty acid (FA) compositions, the activities of mitochondrial enzymes and the transcript levels of related genes in the liver of control (26 °C) and cold-treated (4 °C) tadpoles with or without 5 nM 3,3',5-triiodothyronine (T3).
  
  
  RESULTS
  Exposure to T3 decreased the tail height and polyunsaturation of FAs in the glycerophospholipids, and increased plasma glucose levels and transcript levels of primary TH-response genes including TH receptor, and some energy metabolic (cox4, srebp1 and fas) and FA chain elongase genes (elovl3 and elovl5). However, these T3-induced responses were abolished at 4 °C. Exposure to cold temperature enhanced plasma glucose, triglyceride and free FA levels, monounsaturation of FAs, mitochondrial enzymes activities (cytochrome c oxidase and carnitine palmitoyltransferase; U/g liver), with the upregulation of the genes involved in glycogenolysis (pygl), gluconeogenesis (pck1 and g6pc2), FA β-oxidation (acadl), and cholesterol uptake and synthesis (hmgcr, srebp2 and ldlr1), glycerophospholipids synthesis (pcyt1, pcyt2, pemt, and pparg), and FA monounsaturation (scd1) and chain elongation (elovl1 and elovl2). T3 had little effect on the cold-induced changes.
  
  
  CONCLUSIONS
  Our study demonstrated that exposures to T3 and cold temperature exert different effects on lipid metabolism, resulting in changes in the FA composition in glycerophospholipids, and suggests that a cold-induced signal may block TH-signaling pathway around primary TH-response genes.
authors.affiliation: Department of Biological Science, Graduate School of Science, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8529 Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Department of Biological Science, Graduate School of Science, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8529 Japan.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Awai
authors.affiliation: Department of Biological Science, Graduate School of Science, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8529 Japan ; Green Biology Research Division, Research Institute of Green Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8529 Japan.
authors.forename: Akinori
authors.initials: A
authors.lastname: Ishihara
authors.affiliation: Department of Biological Science, Graduate School of Science, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8529 Japan ; Green Biology Research Division, Research Institute of Green Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8529 Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Yamauchi
keywords: Cold exposure; Desaturase; Fatty acid; Glycerophospholipid; Lithobates catesbeianus; Tadpole; Thyroid hormone