Induction Of Oxidative Stress And The Transcription Of Genes Related To Apoptosis In Rare Minnow(gobiocypris Rarus) With Aroclor1254 Exposure

Polychlorinated biphenyls(PCBs) are a group of environmental contaminants widely dispersed in aquatic system. They are damage to the growth, development and reproduction of aquatic animals, and threaten the human health through food chain’s bioaccumulation. Aroclor1254 is a kind of highly chlorinated PCB mixture.Oxidative stress has become an important subject in aquatictoxicology. However,knowledge on the responses toAroclor 1254 in fish is still scarce.In order to study the effect of Aroclor 1254 on the mRNA expressions of antioxidant genes in rare minnow(Gobiocypris rarus) larvaeand elucidate the potential mechanism underlying themodulation from the level of transcription, in present study, G. rarus larvae were exposed to the Aroclor 1254 at four concentrations(5, 50, 500 and 5000μg/L) for 7 d. The mRNA expressions of Cu/Zn-sod,Mnsod, Cat, Gpx1, Gclc, Nrf2 and NF-κB, and the content of H2O2 and protein thiol were examined.Oxidative stress-induced apoptosis is thought to contribute to abnormaldevelopment during larval stage. A number of studies havefocused on apoptosis induced by environmental chemicals. Although evidence aboutoxidative stress-induced apoptosis is increasing, it is still insufficient to elucidate the complex mechanism.In order to study the effect of Aroclor1254 on the mRNA expressions of apoptosis related genes and elucidate the potential mechanism of apoptosis induced by Aroclor1254 in G. rarus larvae from the level of transcription, in present study, G. rarus larvae were exposed to the Aroclor 1254 at four concentrations(5, 50, 500 and 5000μg/L) for 7 d.The mRNA expressions of p53, Trx1, JNK,puma,Casp8, Casp9, Bcl2 and Baxa were examined.Previousresearchs showed that mitochondrial respiratory chain damage can lead to ROS generation. In order to study the effect of Aroclor 1254 onthe activity of mitochondrial antioxidant enzyme, and the mRNA expressions of mitochondrial antioxidant genes and respiratory chain related genes,in the present study, female adultG. rarus were exposed to Aroclor 1254 at 1, 10, 100 and 1000 μg/L for 14 d. The m RNA expressions of NDI, Cytb,CoxI, Cls, Cu/Znsod, Mnsod, Trx1 and Trx2, the content of H2O2, GSH and MDA, and theactivity of Cu/Zn-sod and Mn-sod were examined.The main results of the present study are as follows.1. H2O2 was significantly inducedby 500 and 5000 μg/L Aroclor 1254 exposure suggests that Aroclor 1254 has induced oxidative stress in G. rarus larvae.Protein thiolcontent was significantly decreased in whole body upon 5000 μg/L Aroclor1254 exposure suggests thatprotein thiolshave been oxidized by Aroclor1254-induced ROS. With middle and high concentration Aroclor 1254 exposure for 7 d, the expression of antioxidant genes such asCu/Zn-sod, Mn-sod, Cat, Gpx1 and Gclc were up-regulated in G.rarus larvae.Meanwhile,the expression of Nrf2 and NF-κB were significantly up-regulated bymiddle and high concentration Aroclor 1254. Taken together, from change of their transcription level, we proposed that Nrf2 and NF-κB might be involved in the potential mechanism underlying the antioxidant gene expression induction in G. rarus larvae by Aroclor 1254.2. The responses of Casp8 and Casp9 genes to 500 and 5000 μg/L Aroclor 1254 successfully demonstratethe possible activation of extrinsic and intrinsicapoptotic pathways induced by Aroclor1254 in exposed fish.p53 and Pumaplay an important role in DNA damage-induced apoptosis. The mRNA expression of p53 and Puma were up-regulated by Aroclor 1254 exposure suggests that the DNA damage might be involved in triggeringapoptosis.A decrease in the ratio of Bcl2 and Baxa mRNA expressions suggests that the mitochondrial membrane integritycould be disrupted by Aroclor1254.The up-regulation of Trx1 and JNKmRNA expressions suggests thatJNK-mediatedapoptotic pathway could be involved in waterborne Aroclor1254-induced apoptosis.3. The up-regulation of Mn-sodand Trx2 expression andthe increase of Mn-sod activity suggest that14-day Aroclor 1254 exposure has induced mitochondrial oxidative stress in the live of G. rarus.The mRNA expression of Mn-sod is more sensitive than Cu/Zn-sod to 10μg/LAroclor 1254. The content of MDA was significantly increased by 1000 μg/L Aroclor1254 suggests thatAroclor 1254 has induced lipid peroxidationin the live of G. rarus. The up-regulation of Clswith100 and 1000 μg/L Aroclor 1254 exposure suggests that mitochondrial cardiolipin might be oxidated by Aroclor 1254 in the live of G. rarus.The transcription of mitochondrial respiratory chain genes(NDI, Cytb and CoxI)had no apparent change upon Aroclor1254 exposurein the live of G. rarus.