Hepatic Expression of Cu/Zn-Superoxide Dismutase Transcripts in Response to Acute Metal Exposure and Heat Stress in Hemibarbus mylodon (Teleostei: Cypriniformes)

Abstract

Hemibarbus mylodon (Cypriniformes) is an endemic freshwater fish species in the Korean peninsula, for which urgent conservation efforts are needed. To understand their stress responses in relation to metal toxicity and thermal elevation, we performed a real-time RT-PCR-based expression assay of hepatic copper/zinc-superoxide dismutase (Cu/Zn-SOD), a key antioxidant enzyme, in response to experimental heavy metal exposure or heat treatment. The transcription of hepatic Cu/Zn-SOD was differentially modulated by acute exposure to Cu, cadmium (Cd), or Zn. Exposure to each metal at <TEX>$5{\mu}M$</TEX> for 24 h revealed that Cu stimulated the mRNA expression of Cu/Zn-SOD to a greater extent than the other two heavy metals. The elevation in Cu/Zn-SOD transcripts in response to Cu exposure was dose-dependent (0.5 to <TEX>$5{\mu}M$</TEX>). Time course analysis of Cu/Zn-SOD expression in response to Cd exposure (<TEX>$5{\mu}M$</TEX>) revealed a transient pattern up to day 7. Exposure to thermal stress (an increase from 22 to <TEX>$30^{\circ}C$</TEX> at a rate of <TEX>$1^{\circ}C/h$</TEX> followed by <TEX>$30^{\circ}C$</TEX> for 18 h) did not significantly alter SOD transcription, although heat shock protein 90 kDa (HSP90) transcription was positively correlated with an increase in temperature.