| Due to the wide applications and lack of toxicity assessments in the early development of conventional pollutants,such as Polychlorinated biphenyls(PCBs)and DTTs,they have induced severe environmental contamination.Although most countries have already prohibited the produce and use of these compouds,they still could be detected in soil,water,animals and even human beings.To date,the toxicities of these pollutants and their underlying mechanisms have been fully investigated,however,few studies have been discussed their potential toxic effects on systemic iron metabolism.Moreover,in addition to the conventional pollutants,various manufactured nanomaterials have been rapidly developed and applied,due to their unique nano-properties.To avoid the similar issue of conventional pollutants,the potential toxicity of nanomaterials to the environment should be thoroughly evaluated in the initial stage of applications.Thus,in the present study,the adverse effects,as well as the underlying molecular mechanisms of a typical nanopartical silver nanoparticals,conventional pollutant PCBs,environmental endocrine disruptor 17?-estradiol and chiral pesticides fipronil were fully investigated.PCBs,with 209 congeners,are a large family of persistent organic pollutants.PCBs elicit a wide range of toxicities,such as neurotoxicity,hepatoxicity,oncogenicity and endocrine disruption effects.However,the understanding of potential disruption of systematic iron metabolism by PCBs is still limited.The balance of iron homeostasis is rigorously dependent on the hepcidin–ferroportin(FPN)axis,and hepcidin is the central governor in guiding dietary iron absorption and iron egress from macrophages.Hepcidin is secreted by hepatocytes,and binds to FPN to conduct its degradation.Dysregulation of hepcidin gives rise to disordered iron homeostasis,associated with diverse diseases including anemia and ?-thalassemia.Our previous study demonstrated that there is an estrogen response element(ERE)within the promoter of hepcidin gene,and its expression is subjected to the regulation by estrogen.In the current study,we demonstrated that both PCB153 and PCB126 greatly suppressed hepcidin expression in HepG2 cells,with a greater repression in cells upon PCB126 treatment.Further studies uncovered that both PCB153 and PCB126 harbored estrogenic activity,and the estrogenic activity of PCB126 was stronger than that of PCB153 in HepG2 cells.Mechanistic investigation revealed that PCBs suppressed hepcidin transcription through a functional ERE within the hepcidin promoter,analogous to the action of 17?-estradiol.Moreover,hepatic hepcidin was down-regulated in wild type mice upon PCB126 administration,coupled with elevated serum iron content as well as reduced hepatic and splenic iron mass.These changes were not replicated in hepcidin-deficient mice upon PCB administration.Additionally,hepatocytes were observed with severe accumulation of lipid droplets in livers from mice challenged by PCB126,irrespective of the presence of hepcidin.To summarize,our results deciphered a suppressive role of PCBs in restraining the expression of hepcidin through mimicking estrogenic activity,and revealed a novel property of PCBs in disrupting systemic iron metabolism.This study also unearthed a PCB-mediated tie that links estrogen-like activity,iron effects and lipid homeostasis.17?-Estradiol(E2),similar to the endocrine effects of PCBs,exhibited the strongest estrogenic activity among all the endorine disrupting chemicals.Due to its estrogenic interference effect,E2 exerts various toxicities including reproductive toxicity and carcinogenesis in sexual hormone-dependent organs.Moreover,serum iron storage is conversely related with the estrogen level in the female bodies,and women in post-menopause are possibly subjected to iron retention.However,the potential effects of estrogen on iron metabolism,especially via FPN signaling,are not clearly understood.Here,FPN mRNA transcription in all selected estrogen receptor positive(ER+)cells was significantly reduced upon E2 treatment;and this inhibitory effect could be attenuated by ER antagonist tamoxifen.Likewise,in murine bone marrow-derived macrophages(BMDMs),FPN reduction with elevated intracellular iron(reflected by increased ferritin)was observed in response to E2;however,ferritin level barely responded to E2 in FPN-null BMDMs.The observation of inhibition of FPN mRNA expression was not replicated in ER-cells upon E2.A functional estrogen response element(ERE)was identified within the promoter of FPN,and this ERE was responsible for the suppressive effect of E2 on FPN expression.Moreover,ovariectomized(OVX)and sham-operated(SHAM)mice were used to further confirm the in vitro finding.The expression of hepatic FPN was induced in OVX mice,compared to that in the SHAM mice.Taken together,our results demonstrated that estrogen is involved in regulating FPN expression through a functional ERE on its promoter,providing additional insights into a vital role of estrogen in iron metabolism.Apart from the traditional contaminants mentioned above,the potential toxicities induced by multiple emerging industrial materials have been increasingly concerned.Among the newly applied materials,silver nanoparticles(nanosilver,AgNPs)are one of the most used products and have been shown to induce toxicity in vitro and in vivo;however,the molecular bases underlying the detrimental effects have not been thoroughly understood.Although there are numerous studies on its genotoxicity,only a few studies have investigated the epigenetic changes,even less on the changes of histone modifications by AgNPs.In the current study,we probed the AgNP-induced alterations to histone methylation that could be responsible for globin reduction in erythroid cells.AgNP treatment caused a significant reduction of global methylation level for histone 3(H3)in erythroid MEL cells at sublethal concentrations,devoid of oxidative stress.The ChIP-PCR analyses demonstrated that methylation of H3 at lysine(Lys)4(H3K4)and Lys 79(H3K79)on the ?-globin locus was greatly reduced.The reduction in methylation could be attributed to decreased histone methylatransferase DOT-1L and MLL levels as well as the direct binding between AgNPs to H3/H4 that provide steric hindrance to prevent methylation as predicted by the all-atom molecular dynamics simulations.This direct interaction was further proved by AgNP-mediated pull-down assay and immunoprecipitation assay.These changes,together with decreased RNA polymerase II activity and chromatin binding at this locus,resulted in decreased hemoglobin production.By contrast,Ag ion-treated cells showed no alterations in histone methylation level.Taken together,these results showed a novel finding in which AgNPs could alter the methylation status of histone.Our study therefore opens a new avenue to study the biological effects of AgNPs at sublethal concentrations from the perspective of epigenetic mechanisms.Except for the histone methylation,DNA methylation also play an important role in biological process.Our previous study has found that fipronil exerted significant enantioselective toxicity in the development of zebrafish embryos,as S-enantiomer was more toxic than R-enantiomer.However,the underlying mechanism responsible for the enantioselective developmental toxicity was still unclear.Thus,we carried out the Methylated DNA immunoprecipitation-sequencing(MeDIP-Seq)and discovered that S-fipronil could induced more obvious differentially DNA methylation than R-fipronil during the development of zebrafish embryos.Moreover,we demonstrated that a majority of hyper-methylated genes in S-fipronil-treated group involved in the developmental associated signal pathways via Gene Ontology and KEGG analyses,which indicated that those genes might be responsible for the enantioselective developmental toxicity incurred by fipronil.Our study thus provides an inspiration to investigated the enantioselective effect of chiral pesticides from the perspective of epigenetic alterations. |
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