Effects Of Persistent Organic Pollutant PCBs On Lipid Metabolism In Male And Female Zebrafish

Polychlorinated biphenyls(PCBs)are persistent organic pollutants that are widely distributed in aquatic environments.Because of its stable physical and chemical properties,long half-life,and accumulation with the food chain,it is not easy to degrade,so PCBs can cause a variety of adverse effects on aquatic organisms,mammals and even humans,including neurotoxicity,reproductive toxicity and Immunotoxicity,etc.Since PCBs can also cause endocrine disorders in animals,they are also classified as environmental endocrine disruptors(EDC).Studies in mammals have shown that many EDCs can cause obesity by disrupting fat metabolism and promoting fat accumulation;they can also lead to obesity by regulating hormone levels that control appetite and satiety.However,the effect of EDC on lipid metabolism in fish that survives in the water environment remains poorly studied.In this paper,zebrafish was used as a research model to explore the possible negative effects of high and low concentrations of PCBs exposure on lipid metabolism in male and female fish.In addition,it’s the first time to discuss the interaction between different fat levels in feed and PCBs exposure on zebrafish lipid metabolism.All these provide a new reference for a deeper understanding of the ecotoxicological effects of polychlorinated biphenyls on aquatic animals,and provide new ideas for understanding the mechanism of fish fatty liver production in aquaculture.The main results and conclusions of this study are as follows:(1).Effects of Different Concentrations of PCBs on Lipid Metabolism in Male and Female ZebrafishIn this experiment,we used the concentrations of 0.2μg/L,2μg/L and 20μg/L PCB1254 to expose male and female zebrafish for 6 weeks.The results showed that PCB exposure had no significant effect on the weight gain and survival rate of each group,but the high PCB concentration of 20 μg/L caused the male body weight to be significantly lower than that of the control group,and the PCB concentration was 0.2 μg/L and 2 μg/L.Group,this may be due to the toxic effects of PCB.In terms of fat accumulation in the tissues,the visceral weight of female zebrafish was higher than that of males and in the male group of 2μg/L was significantly higher than the group of 0.2μg/L PCB;total lipids in the whole fish also appeared similar phenomenon,before the PCB concentration is 2μg/L,the body fat content of male fish increases with the PCB concentration,but in the female does not have this phenomenon;From the paraffin section of the liver we can see that when the PCB concentration is 2μg/L the fat accumulation in fish liver is the most whatever the male and female zebrafish.The above results show that: PCB concentration of 2μg / L can cause fat accumulation in the liver of male and female zebrafish,and there are gender differences in the effect of PCB on lipid metabolism of male and female zebrafish.Two-way ANOVA showed that gender significantly affected terminal body weight,visceral weight,and total body lipid,but PCB had no significant effect on these three indicators,suggesting that PCB effects on females may be overshadowed by gender differences.From the molecular indicators related to lipid metabolism in the liver and adipose tissue,the expression of genes involved in fat synthesis,catabolism,and transport in the liver of males increased with increasing concentrations of PCBs,specifically in DGAT-1a.PPARγ,CPT-1a,PPARα and FABP.In females,on the contrary,except for the highest expression level of DGAT-1a in the PCB concentration of 20 μg/L,the remaining genes have a tendency to decrease as the PCB concentration increases.Two-way ANOVA showed that PCB had a significant effect on DGAT-1a,PPARγ,FAS,CPT-1a,PPARα,FABP,and VTG;gender factors were DGAT-1a,PPARγ,SREBP,CPT-1a,LPL,PPARα,FABP,VTG and ER have significant effects;PCB and gender interactions can have a significant effect on most genes except SREBP and ER.The expression of male fish in adipose tissue was similar to that of liver,but in females the expression of DGAT-1a,DGAT2,ATGL and FABP increased as the concentration of PCB increased.In terms of dose,the highest expression level of most genes in male fish appeared in PCB concentration 2μg/L group,while the highest value of partial gene expression in female fish appeared in PCB concentration 20μg/L.The results of the two-way ANOVA also showed that gender and PCB have a significant impact on almost all genes.These results show that: 1)The response of male and female zebrafish to PCB is different.2)PCB has a greater influence on male than female.The relevant indicators of oxidative stress indicate that the PCB did not cause oxidative stress on zebrafish.Studies of genes associated with stress and apoptosis have shown that the expression of HSP70,CAS3,BCL2,and BAX increases as the concentration of PCB increases in males,but not in females.This suggest that PCBs have a greater effect on stress and apoptosis in males than females.Males are more sensitive than females.Overall,low-dose PCB(0.2μg/L and 2μg/L)exposures had significantly more fat accumulation in zebrafish than high doses(20μg/L),which may have caused a sub-toxic effect.The effect of fat accumulation at 2 μg/L was more pronounced,and fat accumulation increased with increasing concentrations at low and medium doses but decreased at high doses.This shows that the mechanism of low-medium dose PCB and high-dose may have different effects on lipid metabolism.In terms of the sensitivity of lipid metabolism to PCBs in different sexes,we found that males are more sensitive than females,which may be related to different fat accumulation in the male and female body.It may also be that the estrogens in the male and female fish are different,resulting in different sensitivity to environmental estrogens.These results provide new insights into the complex interactions between persistent organic pollutants and lipid metabolism,and also contribute to a more systematic assessment of environmental pollutants in the future.(2).Effects of Diets with Different Fat Levels on Lipid Metabolism of PCB-exposed Male and Female ZebrafishThe previous part of the work determined the concentrations of PCBs that cause lipid metabolism disorders in zebrafish.In this experiment we used this concentration,and then fed low-fat and normal-fat diets respectively for 6 weeks.To test the interaction of different fat levels feed and PCB on zebrafish lipid metabolism.From the results of growth and fat accumulation in tissue: PCB had no effect on the weight gain rate of male and female fish.The content of triglyceride in liver was significantly higher in the female low-fat group than in the control group,and the visceral weight appeared consistent.The fat content of the whole fish showed a significant higher in the male normal lipid group than in the control group,but there was no significant difference in the other groups.The paraffin section of the liver also showed that the normal fat in the male PCB has the effect of promoting fat accumulation,but has little effect on the female fish.From the molecular indicators of liver and adipose tissue,in the normal lipid group of male fish,the expression of CPT-1a,HAD,and PPARα genes related to lipolysis was down-regulated in the effect of PCBs,and little change was observed in the low-fat groups.Interestingly,the opposite was shown in females.PCBs in the low-fat and normal-lipid groups significantly increased the expression of CPT-1a,HAD,PPARα,and ATGL.A similar trend was also observed in the expression of genes related to fat synthesis.The PCBs in the normal fat group of male fish significantly decreased the expression levels of DGAT-1a,DGAT-1b,FAS,and SREBP,but did not affect the low-fat groups.The PCB in the group had a significant effect on the expression of DGAT-1a,DGAT-1b,and FAS,but had little effect on the normal lipid group.However,in the normal fat group of male the expression of genes associated with fat transport,FABP and LPL was significantly under the influence of PCB,whereas in females,they are significantly decreased;in the group of low fat,PCBs significantly reduced the expression of LPL in male zebrafish,and significantly increased the expression of FABP in the female zebrafish.In summary,the results show that: 1)PCBs are more sensitive to males than females;2)In males,PCBs have a more pronounced effect on the normal lipid group,whereas in females PCB have a more significantly effect on the low-fat group;3)The mechanism of lipid metabolism of PCB is different for male and female zebrafish.In male fish,PCB mainly promotes the transport of fat,so that the fat in the liver accumulates,and PCB in females can accelerate lipid metabolism.The data in adipose tissue indicate that the expression of genes related to fat synthesis,catabolism and transport in low fat and normal lipids is up-regulated in male zebrafish.This is similar to the results in female livers.This similarity may be related to the different fat content in tissues.PCBs in the normal fat group of females caused down-regulation of genes related to fat synthesis,decomposition,and transport.In the same tissues,the differences in the expression of lipid metabolism-related genes in males and females may be due to different responses of the sex to the PCB.From the results of oxidative stress,the levels of MDA and SOD in both male and female fishes increased with the increase of dietary lipid content,but there was no significant difference between the PCB exposure group and the control group.The activity of GSH decreased with the increase of dietary lipid content,and the PCB exposure group had a tendency to decrease compared with the control group,and there was a significant difference in the male normal lipid group.These data indicate that PCBs do not cause oxidative stress in low-fat and normal-fat fed male and female zebrafish.In summary of all the work in this paper,the lipid metabolism interference effect of low concentration PCB is stronger than that of high concentration PCB.In the male fish,the normal lipid group was more significantly affected by PCB,and it was able to accumulate fat in the liver,but there was no significant effect in the low-fat group.In the female fish,the opposite results were shown.In the low-fat group,the effect of PCB on lipid metabolism was more sensitive,and the expression of genes associated with fat synthesis increased significantly,but there was no significant difference in the normal lipid group.This shows again that gender plays an important role in lipid metabolism,and the effect of PCBs about mechanism of lipid metabolism in female and male fish is different.The results of this study provide important references for understanding the mechanism of fish fat deposition in natural and aquaculture waters,and provide new ideas and evidence for elucidating the mechanism of fatty liver in farmed fish.