The Molecular Mechanism Of Nano-Selenium Antagonized Cadmium-Induced Neurotoxicity In Cerebrum Of Chicken

Cadmium（Cd）as a ubiquitous toxic heavy metal has potential ecotoxicological effects on humans and animals.Due to the widespread application of Cd in industrial,agricultural,and medical products,the risk of Cd contamination in the environment increases,causing damaging effects to human beings and in a variety of organs and tissues of animals,including chicken,resulting in hepatotoxicity,nephrotoxicity,and testicular toxicity.However,the molecular mechanism of Cd-induced neurotoxicity in the chicken brain is unclear.In recent years,due to the high safety margin of Nano-selenium（Nano-Se）and the use of low dosage,it has been widely used in the treatment and prevention of heavy metal toxicity.However,the role of Nano-Se in protecting Cd-induced brain injury is unclear.In order to reveal the toxic effect of Cd on chicken brain,and explore the protective effect of Nano-Se against Cd-induced neurotoxicity in chicken brain,a total of 160 one-day-old Hy-Line white variety chicks（20 chicks/group）were selected and randomly divided into eight（8）groups:control group,Cd 35 group,Cd 70 group,Cd 140 group,NS1 group,NS2 group,NS1+Cd group,and NS2+Cd group;control group,Cd 35 group,Cd 70group,and Cd 140 group were fed with basic feed containing 0 mg/kg Cd Cl₂,35 mg/kg Cd Cl₂,70mg/kg Cd Cl₂,and 140 mg/kg Cd Cl₂,respectively for 90 days,while NS1,NS2,NS1+Cd,and NS2+Cd groups were fed with basic feed containing 0.3 mg/kg Nano-Se,0.6 mg/kg Nano-Se,0.3mg/kg Nano-Se+140 mg/kg Cd Cl₂,and 0.6 mg/kg Nano-Se+140 mg/kg Cd Cl₂,respectively and reared for 90 days.The pathological changes of the brain tissue,the levels of related metals and their transporters,oxidative stress parameters,the expression levels of MTF1 and its target genes,selenoproteins levels,the levels of HSR-related stress proteins,endoplasmic reticulum（ER）stress,levels of autophagy and apoptosis-related markers,and mitochondrial damage were detected.The findings are as follows:（1）Cd exposure induced swelling,decrease in the number of neurons in brain tissue,loss of axons and dendrites,degeneration of cytoplasmic vacuoles,widening of capillary diameter,swelling of endoplasmic reticulum and mitochondria,and formation of autophagosomes.Nano-Se intervention restored neuronal morphology,endoplasmic reticulum,and mitochondrial structure,and thereby reduced neuronal damage.（2）Cd exposure induced an imbalance of redox homeostasis in brain tissue,increased levels of MDA and H₂O₂,and decreased GPX,CAT,T-SOD activity and T-AOC levels,leading to oxidative stress.Nano-Se intervention relieved oxidative stress state in brain tissue,decreased MDA and H₂O₂ levels,and increased GPX,CAT,T-SOD activity and T-AOC levels.（3）Cd exposure induced up-regulation of metal transporters（DMT1,ZIP8,and ZIP10）in brain tissue,and down-regulation of transcription factor MTF1 and its downstream targets（MT1,MT2,FPN1,ATOX1,and XIAP）,resulting in increased brain Cd accumulation The expression of DMT1,ZIP8,ZIP10,ZNT3,ZNT5 and ZNT6 decreased in brain tissue after the Nano-Se intervention,activated the expression of transcription factor MTF1 and its downstream targets（MT1 and MT2）,and reduced the accumulation of Cd in brain tissue,thereby alleviating the brain damage in chickens.（4）Cd exposure induced abnormal expression of 6 transcription factors and 24 selenoproteins related to selenoprotein synthesis in brain tissue,especially SEPSECS,SPS1-1,GPx1,GPx2,GPx3,GPx4,Sel W,Sel K,Sel T,Sep P1,Sep P2,Dio1 and Dio3,suggesting that several selenoproteins may be potential targets of Cd exposure-induced brain damage in chickens.The expressions of SEPSECS,SPS1-1,GPx1,GPx2,GPx3,GPx4,Sel W,Sel K,Sel T,Sep P1,Sep P2,Dio1 and Dio3 in brain tissue increased after the Nano-Se intervention,and the expressions of Sel M,Dio2,Txn Rd2,Txn Rd3,Sel I,Sel N,and Sel H were decreased after the Nano-Se intervention in brain tissue,and thereby the selenoprotein expressions were restored to mediate the homeostasis imbalance.（5）Cd exposure increased the expression of heat shock proteins（HSP60,HSP70,and HSP90）in brain tissue,and activated the heat shock response（HSR）response.The expression of heat shock transcription factors（HSF1and HSF3）and heat shock proteins（HSP60,HSP70,and HSP90）in brain tissue decreased after Nano-Se intervention,which could regulate the process of Cd-triggered heat shock response and alleviate the Cd-induced toxicity in chicken brain tissue.（6）Cd exposure increased the expression of GRP78,PERK,and e IF-2αin brain tissue,triggered endoplasmic reticulum stress,activated mitophagy-related indicators（Mfn2 and PINK1）,and promoted the formation of autophagosomes.Nano-Se intervention regulates the protein expressions of GRP78,e IF2α,PERK,Mfn2 and PINK1,and alleviates Cd-induced endoplasmic reticulum stress and mitochondrial morphological,and structural damages.（7）Cd exposure up-regulated the expression of Beclin1,LC3B,p62,pro-inflammatory factor TNF-αin brain tissue,inhibited the expression of anti-inflammatory factor IL-10,and induced autophagy and inflammatory response in chicken brain tissue.Nano-Se intervention reduced Cd-induced inflammation and autophagy in brain tissue by reducing Beclin1,P62,TNF-αand LC3B expression and up-regulating IL-10 expression.（8）Cd exposure induced a decrease in the level of connexin 43（Cx43）protein in chicken brain tissue,which was phosphorylated and involved in the formation of autophagosomes.Nano-Se intervention restores the expression level of the gap junction protein Cx43 and modulates Cd-induced brain damage.Cd exposure increased GFAP in astrocytes,but decreased after Nano-Se intervention.Cx43 may be a potential target of Nano-Se antagonized Cd-induced astrocyte neurotoxicity.（9）Cd exposure induced neuronal apoptosis in chicken brain and activated the caspase-dependent apoptosis signaling pathway,indicating that Cd exposure induced neuronal apoptosis.Nano-Se alleviated Cd-induced neuronal apoptosis by inhibiting Cd-mediated activation of the caspase-1/8 pathway.In conclusion,Cd exposure can lead to the imbalance of metal homeostasis,damage to the tissue morphology and organelles of chicken brain,abnormal expression of MTF1-related factors,selenoproteins,heat-shock transcription-related factors,and heat-shock proteins,triggering ER stress,autophagy,neuroinflammatory responses,and apoptosis.Nano-Se intervention attenuates Cd-induced oxidative stress,metal homeostasis imbalance,tissue structure damage,ER stress,autophagy,and apoptosis.This study elucidated the antagonistic effects of Nano-Se on Cd exposure on the brain of chicken,and provided a theoretical basis for the molecular mechanism of Nano-Se to alleviate Cd-induced neurotoxicity in chicken.