The Mechanisms Of Low-Dose Gestational BPA Exposure On Glucose/Lipid Metabolism In Adult Offspring Mice

Background:Nowadays,a rapid rise in incidence of metabolic disease has become a serious public health issue in the society.Finding the cause and effective intervention measures are the important scientific issues in public health field.Substantial researches have showed that several exogenous chemicals that severely interfere with endocrine and metabolic functions were closely related to the occurrence of metabolic diseases.Bisphenol A(BPA)is a common synthetic chemical used extensively in numerous consumer products,and human exposure to BPA is ubiquitous.Thus,it can be detected in human blood plasma,urine and breast milk.Studies have confirmed that BPA is a typical endocrine disrupting chemicals(EDCs),which plays an estrogen-like substance in the body and may be associated with early onset of secondary sexual characteristics in children,such as early menstruation in girls and breast development in boys.Many experts of public health suspect that metabolic related diseases such as obesity and hepatic steatosis in children and adults may be related to early exposure to BPA.Prenatal exposure to environmental contaminants,especially EDCs,even at low levels of exposure,can result in serious adverse consequences for health of offspring.Some studies have shown that exposure to BPA in a series of signal regulatory molecules related to glucose and lipid metabolism in the liver of offspring,leading to the disorder of glucose and lipid metabolism in offspring during pregnancy may cause changes.However,there are still many questions about its patterns,characteristics,and mechanisms,which affect research on effective measure for people’s preventive intervention.Aiming at the above scientific problems,this study established an animal model of prenatal exposure to BPA in mice,in order to determine the dose-effect relationship and gender differences between BPA exposure during pregnancy and glycolipid metabolism in mice,biochemical,pathological,enzymatic,signal regulatory and reactive oxygen species indexes related to glycolipid metabolism were measured.The key transcriptional factors,effector factors,influencing factors and the mechanism of mutual regulation that cause damage were mainly studied.Objective:1.To observe the abnormal index of glucose and lipid metabolism and its effect relationship in adult offspring mice,we established the model of BPA exposure in mice during pregnancy.2.To study the important role of PPARγ(peroxisome proliferator activated receptor γ)and HNF1b(hepatocyte nuclear factor 1b)in the metabolic disorders of glucose and lipid metabolism in offspring induced by BPA exposure during pregnancy.3.To further investigate the role of ROS(reactive oxygen species)in BPA-induced glucose and lipid metabolism disorders and the regulation relationship between ROS and HNF1b.4.Verification of that HNF1b/PPARγ signal is a new and different signal pathway with the estrogen signal in regulating BPA-induced glucose and lipid metabolism disorder.Methods:Establishing BPA-exposed models at different doses during pregnancy in mice:control group,1 g/kg/d BPA group,10 g/kg/d BPA group,100 g/kg/d BPA group,and1000 g/kg/d BPA group.Intragastric administration of BPA at different concentrations were performed on mice during the embryonic period from 7.5(embryonic day 7.5,E7.5)to 16.5 days(E16.5).Mice were raised normally until the 14 th week after birth,relevant indexes were determined after sacrifice.The optimal dose was selected from the above experiments.The offspring mice were randomly divided into 6 groups: control group,HFD(high fat diet)group,BPA group,BPA + HFD group,BPA + Rh1(Ginsenoside Rh1)group and BPA + NAC(N-Acetyl-L-cysteine)group.The relevant indexes were measured and the high-throughput genetic analysis were performed at the 14 th week of newborn mice.Establishing BPA-exposed model in L02 cells.Lipid accumulation was also induced by treating L02 cells with palmitic acid(PA).Lentiviral transfection was used to construct PPARγ silencing and HNF1b-overexpressed L02 cell models.The related indexes of glucose and lipid metabolism after BPA exposure were detected.Results1.Low-dose group(1 μg/kg/d BPA)showed significantly higher degree of liver damage in adult male mice offspring than those in other three higher groups(mice exposed to 10,100,and 1000 μg/kg/d during pregnancy).BPA exposure during pregnancy significantly increased liver mass and triglyceride(TG)and aggravated HFD-induced lipid metabolism disorder in adult offspring.Perinatal BPA exposure resulted in glucose metabolism disorder and increased insulin resistance(IR).The results showed a significant low-dose effect and gender differences.2.It was found that PPARγ level was significantly increased while HNF1b was significantly decreased.Inhibiting the expression level of PPARγ significantly reduced the disorder of glucose and lipid metabolism induced by BPA.Overexpression of HNF1b can significantly decreased BPA-induced lipid accumulation.3.Prenatal BPA exposure induced accumulation of ROS in offspring mice.Removal of ROS can decrease the expression of HNF1b and greatly alleviate the lipid accumulation in liver.In addition,BPA exposure resulted in increased mitochondrial ROS(mt ROS).Removal of mt ROS can alleviate the lipid accumulation in liver.HNF1b overexpression could significantly reduced oxidative damage caused by too much mt ROS.4.In the liver of male offspring exposed to BPA during pregnancy,the expression levels of a series of regulatory molecules related to estrogen were significantly increased.HNF1b/PPARγ signal is not affected by estrogen signal in the disorder of glucose and lipid metabolism induced by BPA.Conclusion:1.The toxic effects of low dose of BPA(1 μg/kg/d BPA)are most pronounced on glucose and lipid metabolism disorder of male offspring.HFD has a synergistic effect to enhance BPA-induced glucose and lipid metabolism disorder.2.HNF1b directly regulates the transcription level of PPARγ.HNF1b/PPARγ signal plays an important role in low-dose BPA-induced glucose and lipid metabolism disorders during pregnancy.3.The increase of mt ROS caused by oxidative damage to mitochondria is an important reason for the increase level of BPA-induced ROS.And there is a regulatory relationship between ROS and HNF1b.4.HNF1b/PPARγ signal and estrogen signal affect BPA-induced glucose and lipid metabolism disorder through different pathways,and they have a synergistic effect on glucose and lipid metabolism.