Mechanism Of Cr³⁺ And Cr⁶⁺ Exposure On Glucose Metabolism Pathways In The Development Of Epinephelus Coioides

Chromium is not only a trace element required by human and animal,but also of the heavy metal pollutants,which has severely affected the ecological environment of aquaculture.Epinephelus coioides is one of the important farmed fishes in the South China Sea.Its embryos formation were not only a complex biological stage sensitive to environmental pollutants,but also a key stage for incubation of its survival rate.In this study,typical environmental pollutants Cr³⁺and Cr⁶⁺were exposed to embryos at concentrations of 0,0.2,0.6,1,5,10,and 20 mg L-1 for 30 hours.The bioaccumulation,glycolysis,gluconeogenesis and PI3K-AKT-GSK3 pathway,and then correlate the bioaccumulation amount with genes in the glucose metabolism pathway to assess its impact on embryo development.The experimental results were as follows:Firstly,the bioaccumulation of grouper embryos in the morula stage,the blastula stage,the late gastrula,the brain vesicle stage and the heart beating stage under Cr³⁺and Cr⁶⁺exposure had no linear relationship with the embryonic development stage.However,with the increasing concentration of Cr³⁺and Cr⁶⁺,the bioaccumulation also increased,and the bioaccumulation under the exposure of Cr⁶⁺was as large as under the exposure of Cr³⁺（P<0.05）.In contrast,the bioaccumulation of grouper eggs exposed to Cr⁶⁺in the morula stage,the blastula stage,the late gastrula,the brain vesicle stage,and the heart beating stage were respectively exposed to Cr³⁺exposure（2.7-20.2）,（6.4-20.1）,（2.6-50.4）,（3.0-47.3）,and（2.4-20.4）times（P<0.05）.The uptake rates of grouper embryos exposed to Cr⁶⁺in the morula stage,the blastula stage,the late gastrula,brain vesicle stage,and heart beating stage were respectively（15.5）,（10.2）,（21.9）,（15.5）and（7.6）times（P<0.05）.Secondly,in the glycolytic pathway,we found that the mRNA expression of PFK gene was higher under Cr⁶⁺exposure than under Cr³⁺exposure,especially under low concentration(0.2-1 mg L^-1)of Cr⁶⁺exposure（P<0.05）.The PK genes,compared with the control group,the mRNA expression levels of the PK genes in grouper embryos exposed to Cr³⁺and Cr⁶⁺were significantly increased.However,the mRNA expression of PK genes of grouper embryos exposed to Cr³⁺and Cr⁶⁺was significance different（P<0.05）.Thirdly,in the gluconeogenesis pathway,the expression levels of G6P and PCK genes in fish eggs exposed to Cr³⁺and Cr⁶⁺were significantly increased compared to the control group（P<0.05）.However,the expression of the G6P gene mRNA under high exposure to Cr³⁺(10-20 mg L^-1)were greater than the expression of the G6P gene mRNA under high exposure(10-20 mg L^-1),the mRNA expression of the G6P gene under Cr⁶⁺exposure was higher at the low concentration(0.2-1 mg L^-1)（P<0.05）.In the PCK gene,the expression of the PCK gene mRNA was significantly increased at low concentrations(0.2-0.6 mg L^-1)of Cr⁶⁺during the blastula stage,late gastrula stage,brain vesicle stage,and heart beating stage.During the morula stage under Cr³⁺and Cr⁶⁺exposure,the expression of PCK gene mRNA was significantly inhibited（P<0.05）.Finally in the PI3K-AKT-GSK3 pathway,we found that the mRNA expression of the PI3K gene was exposed to Cr³⁺and Cr⁶⁺compared to the control group.(5 mg L^-1)concentration,the late gastrula(0.2-10 mg L^-1)and brain vesicle stage(0.2 and 5 mg L^-1)concentrations increased significantly（P<0.05）.During heart beating stage,compared with the control group,the expression of PI3K mRNA was significantly suppressed under Cr³⁺and Cr⁶⁺exposure（P<0.05）.Compared with the control group,the expression level of AKT gene mRNA was almost inhibited（in the morula stage and blastula stage）and the difference was not significant（at the late gastrula stage,the brain vesicle stage and the heart beating stage compared with the control group）.The expression of AKT gene was significantly increased only at the end of the late gastrula stage with 0.2 mg L^-1 Cr⁶⁺exposure,20 mg L^-1 Cr³⁺exposure and 0.6 mg L^-1Cr³⁺exposure during heart beating stage（P<0.05）.Compared with the control group,the mRNA expression of the downstream GSK3 gene was exposed to Cr³⁺and Cr⁶⁺.The brain vesicle stage increased significantly（P<0.05）.Its expression was significantly suppressed during the beating period of the heart（P<0.05）.