title: Activation of antioxidant defenses in response to freezing in freeze-tolerant painted turtle hatchlings.
abstract: BACKGROUND
  Hatchlings of the painted turtle, Chrysemys picta marginata can endure long-term freezing of their extracellular body fluids. We hypothesized that freezing survival would include adaptive up-regulation of antioxidant defenses to deal with ischemia-reperfusion injuries associated with the freeze-thaw cycle. A number of antioxidant enzymes are under the control of the NF-E2 related factor 2 (Nrf2) transcription factor including members of the glutathione S-transferase (GST) and aldo-keto reductase (AKR) families.
  
  
  METHODS
  RT-PCR and Western immunoblotting were used to measure changes in transcript and protein levels in response to 5-h freezing exposure of hatchlings.
  
  
  RESULTS
  Transcript levels of Nrf2 increased in turtle brain, liver, and muscle by 1.5- to 2-fold, and protein levels increased in the brain and muscle by 1.6- to 2.3-fold in response to freezing. GSTs responded strongly to freezing in turtle brain with amounts of GSTP1, M1, K1, and A3 elevated by 1.5- to 2.4-fold. GSTM3 and T1 rose by 1.8- to 2.3-fold in gut, whereas reduced levels of GSTP1, M1, M3, and K1 were found in livers of frozen animals. Levels of the AKR1B4 isozyme rose 2.1-fold during freezing in brain.
  
  
  CONCLUSIONS
  Freezing triggered tissue-specific changes in the antioxidant defenses in C.pictamarginata organs.
  
  
  CONCLUSIONS
  These data indicate that activation of an antioxidant response is an important aspect of natural freeze tolerance in turtles.
authors.affiliation: Institute of Biochemistry and Department of Biology, Carleton University, Ottawa, Ontario, Canada K1S 5B6. krivoruchko@gmail.com
authors.forename: Anastasia
authors.initials: A
authors.lastname: Krivoruchko
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Storey
mesh_terms: D000064:Acclimatization; D000595:Amino Acid Sequence; D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D015153:Blotting, Western; D002645:Chickens / Q000235:genetics; D017931:DNA Primers; D004531:Eggs; D005260:Female; D005615:Freezing; D005784:Gene Amplification; D006801:Humans; D008969:Molecular Sequence Data; D051267:NF-E2-Related Factor 2 / Q000737:chemistry / Q000235:genetics*; D016133:Polymerase Chain Reaction; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D017386:Sequence Homology, Amino Acid; D014426:Turtles / Q000235:genetics / Q000502:physiology*; D014981:Xenopus / Q000235:genetics; D015027:Zebrafish / Q000235:genetics
chemical_list: D000975:Antioxidants; D017931:DNA Primers; D051267:NF-E2-Related Factor 2; D012313:RNA