Role Of Hexavalent Chromium-induced Endoplasmic Reticulum Stress And Ferroptosis In Myocardial Injury In Ducks

Hexavalent chromium is one of the most important environmental pollutants causing intoxication in livestock,and ducks,as an important economic animal in the region,are extremely sensitive to heavy metal toxicity.To investigate the role of endoplasmic reticulum stress（ERS）mediated by the Nrf2 pathway and ferroptosis in myocardial injury induced by hexavalent chromium exposure in ducks,48 healthy 7-day-old Tianfu ducks were divided into four groups:Control（0 mg/kg）,LCr（9.28 mg/kg）,MCr（46.4 mg/kg）and HCr（232 mg/kg）.Potassium dichromate（K₂Cr₂O₇）was used as a source of hexavalent chromium[Cr（VI）].On day 49 of the experiment,12 ducks were randomly selected from each group and myocardial samples were collected.ICP-MS,bioreagent kits,tissue sectioning and transmission electron microscopy,real-time quantitative PCR（RT-q PCR）,protein blotting（Western blotting,WB）,immunofluorescence and immunohistochemistry were applied.Trace element Cr levels,oxidative stress levels,tissue damage,ultrastructural changes and expression of the Nrf2 pathway,ERS and transcription and translation of ferroptosis-related genes in myocardial tissues were measured.Results:1.Cr levels and creatine kinase（CK）activity were significantly increased in the hexavalent chromium-treated group compared to the control group（P<0.01）.2.HE staining of myocardial tissue in the HCr group showed loosened myocardial cell arrangement,enlarged gaps and damaged myofibres.Transmission electron microscopy showed that the endoplasmic reticulum was ruptured,mitochondrial membranes were damaged and cristae were disorganised in the HCr group.2.Compared with the control group,myocardial ferrous ion(Fe²⁺)content increased in the hexavalent chromium-treated group（P<0.01）;GSH-Px and CAT activity decreased significantly（P<0.05）,and T-SOD activity showed a decreasing trend but the difference was not significant（P>0.05）;H2O2 and MDA content increased significantly（P<0.01）.3,compared to the control group,m RNA of Nrf2,HO-1,GRP78,PERK,ATF4,ATF4,DDIT3,CHAC1,IRE1,XBP1,ATF6,COX-2,ACLS4,TFR1 and NCOA4 increased in the hexavalent chromium-treated group,and m RNA of GRP78,PERK,ATF4,CHOP,IRE1,ATF6,COX-2,ACLS4,NCOA4 protein expression（P<0.05 or P<0.01）;m RNA inhibition of Keap1,GPX4,FTH1,x CT and protein expression of GPX4,FTH1,x CT（P<0.05 or P<0.01）.4,Compared with the control group,in the hexavalent chromium-treated group,ATF4immunofluorescence intensity increased,GPX4 decreased and COX-2immunohistochemical brown staining deepened.In summary,hexavalent chromium was able to elicit oxidative stress,activate the Nrf2signalling pathway,cause endoplasmic reticulum stress and ferroptosis in duck myocardium.Therefore,Nrf2-mediated antioxidant defence responses induced by hexavalent chromium in duck myocardium may be related to the activation of crosstalk between ferroptosis and endoplasmic reticulum stress.Hexavalent chromium may exacerbate myocardial damage in ducks.