Accumulation Of Cadmium And Expression Changes Of MATE In Grass Carp Under Cadmium Stress And Purification

Grass carp（Ctenopharyngodon idellus）is one of the most productive and widely farmed economic fish in China.With the development of industry and agriculture in China,the pollution of the water environment has become increasingly serious,especially cadmium（Cd）pollution,which is seriously threatening grass carp culture and even people’s health.Therefore,it is important to understand the metabolic pathways of Cd in grass carp and find effective ways to reduce the concentration of Cd in the body.Multidrug and toxic compound extrusion family（MATE）is a class of multifunctional transporters that can discharge multiple metal ions from cells and effectively reduce the residual accumulation of toxic substances in the body.In this paper,exposure-purification experiment to grass carp was designed,including 4 days Cd challenge with mitochondria half-lethal concentration of 96 hours(96 h LC₅₀),and 10 days purified water purification.The dynamic changes of cadmium accumulation were detected in grass carp gill,hepatopancreas,kidney and muscle,and the relative expression levels of MATE3,MATE5 and MATE6 genes were determined.Moreover,the relationship between expression of MATE3,MATE5 and MATE6 mRNA and cadmium stress in different tissues was investigated in order to reveal the mechanism on cadmium excretion of MATE gene.Results in this paper will provide scientific basis and basic data for the study of fish MATE gene on the efflux of cadmium,and the detail are as follows:1.The 96 h LC₅₀0 of grass carp to cadmium was 6.30 mg/L by using Koushi method,and the exposure-purification experiment was carried out with 1/2 96 h LC_50。In the exposure experiment,the cadmium concentrations in gill,hepatopancreas,kidneys,and muscles all increased significantly,reaching peaks at 24 h,72 h,48 h,and 24 h after expoure,with the highest concentrations of 9.97 mg/kg and 7.63 mg/kg,7.30 mg/kg,and 0.40 mg/kg respectively.During the purification,the cadmium concentration of the gill and muscles was declined,while the cadmium concentration in the hepatopancreas and kidney incrased continuously.Statistical Package for Social Science（SPSS）showed a extremely significant positive correlation in the cadmium concentration between hepatopancreas and kidney（P<0.01）and significant positive correlation in the cadmium concentration between gill and muscles（P<0.05）.2、The relative expression of MATE3,MATE5,and MATE6 genes in grass carp gill,hepatopancreas,kidney,and muscle during the exposure-purification experiment were measured by real-time fluorescence quantification.In the exposure experiment,compared with the control group,the expression in MATE3 gene of grass carp gill was significantly increased at 96 hour after cadmium exposure（P<0.05）,but the expression was suppressed at other exposure time（P<0.05）.The expression of MATE3 in hepatopancreas only increased in response to 12 hours of cadmium exposure（P<0.05）,and then recoved.The level of MATE5mRNA expressions in grass carp hepatopancreas had a 2.70（P<0.05）、1.40、2.17（P<0.05）time increasement after exposure 6 h,12 h,24 h respectively,and then were back to normal.MATE6 mRNA in hepatopancreas was at a low texpression level（P<0.05）.The expression of MATE genes in kidney showed obvious increasement during cadmium exposure,and MATE3、MATE5、MATE6 mRNA reached the highest expression level at 6 h,12 h,6 h respectively（P<0.05）.The expression of MATE3 gene in muscles had no obvious changes in exposure time,while MATE5 was significantly increased at 24 h and 96 h（P<0.05）,and MATE6 was always under inhibitory expression（P<0.05）.In the purification test after cadmium exposure,compared with the control group,the expression of MATE3,MATE5,and MATE6 genes in grass carp showed a tendency of increased first but decreased afterwards,and reached the peak after 12 hours of purification（P<0.05）;The expression of MATE3,MATE5,MATE6 gene in hepatopancreas reached the highest point at 48 h（P<0.05）.The MATE3,MATE5,and MATE6 genes in the kidney reached the maximum value in 216hours after purification（P<0.05）,and MATE5 has been maintained at a high level（P<0.05）.The relative expression of MATE3,MATE5,MATE6 genes in muscle were under down-regultion（P<0.05）.3、The MATE3,MATE5,and MATE6 genes in grass carp gill showed high expression in the initial stage of purification,meanwhile the concentration of cadmium decreased to the lowest point.The growth rate of cadmium in hepatopancreas increases with the decreased expression of MATE5 while cadmium exposure.The expression of MATE3,MATE5,and MATE6 genes in grass carp hepatopancreas were induced by a high concentration of cadmium,then cadmium concentration was decrease in purification time.The MATE3,MATE5,and MATE6 expression in grass carp kidney were induced by cadmium accumulation,and the concentration of cadmium is in the dynamic equilibrium phenomenon at the later period of cadmium exposure.The large amount of cadmium accumulation also induced the MATE3,MATE5 genes exprssion,and the cadmium concentration were decrease after high expression.In summary,the gill,hepatopancreas,kidney,and muscle of grass carp can accumulate heavy metal cadmium,and the hepatopancreas and kidney are the main accumulative organs of cadmium.MATE3、MATE5、MATE6 could transport cadmium out of gill,hepatopancreas,kidney,and MATE5 is the main protein of the excretion of cadmium in the hepatopancreas and kidney.Further research is needed for the MATE transport mechanism.