Effects On Gene Expression Profiling And Enzyme Activities Of Antioxidant Enzymes Induced By Hexavalent Chromium In Rare Minnow Larvae

The aquatic environmental pollution of heavy metals such as hexavalent chromium (Cr6+)is increasingly serious in recent years. Rare minnow (Gobiocypris rarus) an unique smallcyprinidae fish in China, has been widely used as an experimental animal for aquatic toxicitystudies. In order to explore the mechanism underlying antioxidant to oxidative stress inresponse to Cr6+. Full-length cDNA sequences of cat, Cu/Zn sod and gpx1were isolated andcharacterized from the rare minnow using homology cloning and RACE methods. The keygenes’ transcripts of Keap1-Nrf2system, ubiquition proteasome pathway and metallothioneinway upon Cr6+exposure were detected by qRT-PCR. The activities of the main antioxidativeenzymes, the contents of GSH, MDA, the total protein and the total carbonyl upon Cr6+exposure were also detected. The main results are as follows.1) The full-length cDNA sequences of G.rarus cat, Cu/Zn sod and gpx1are2130,850and917bp, encoding525,191and154amine acids, respectively. Multiple alignment andphylogenetic tree analysis indicated that G. rarus cat, Cu/Zn-sod, gpx1shared the highestamino acid identities with counterparts of other three cyprinidae species.2) One-month old rare minnow juveniles were exposed to0.1mg/L Cr6+, with exposureduration of four weeks and subsequent one week of depuration in clean water. Gr-cattranscript was extremely significantly decreased and Gr-Cu/Zn sod transcript was extremelysignificantly increased under4-week Cr6+exposure at0.1mg/L, respectively. Two-week Cr6+exposure caused extremely significant increase of Gr-mt1and Gr-uba52transcripts. Theanalysis revealed. Transcripts of Gr-gstp and Gr-Cu/Zn sod were significantly negativelycorrelated with transcript of Gr-Nrf2, while Gr-gr showed extremely significant positivecorrelation with Gr-Nrf2.3) The enzyme activities of CAT, GR, GST and SOD were increased in the1-week Cr6+exposure. GST, GPx and GR activity had the same change trend with the change of GSHconten.In summary, the increased ROS induced by Cr6+exposure caused significant regulationon antioxidant enzymes in transcript and enzyme activity levels in G. rarus. Keap1-Nrf2pathway could invole in the regulation.