Study On The Molecular Mechanism Of Inflammatory Injury Induced By Environmental Estrogen 4-octylphenol In Common Carp(Cyprinus Carpio) Gills

4-octylphenol（4-OP）is a toxic estrogenic environmental pollutant,which is accumulated in organisms through various ways,threatening aquatic animal and human health.Common carp（Cyprinus carpio）is a kind of economic freshwater fish widely reared in China.As the respiratory and immune organ of fish,gill is also one of the organs directly contacted with environmental pollutants in water.However,the toxic effect and mechanism of 4-OP in common carp are stll unclear.Thus,in this study,a 4-OP poisoning model of common carp was successfully established.81 common carp were randomly divided into the control group,the solvent control group,and the4-OP group（4-OP concentration was 17μg/L）,the length and weight of common carp were recorded,and then blood and gill tissues were collected on day 60.The serum biochemical parameters of common carp were detected using an automatic biochemical analyzer.Taking gill as the target organ,the content of 4-OP in common carp gills was tested by liquid chromatography-tandem mass spectrometry;morphological changes were observed by hematoxylin-eosin staining and transmission electron microscopy;ATPase activity,oxidative stress indicators,and inflammatory indicators were determined using kits;after transcriptomics sequencing,the expression of complement-related,immune-related,and inflammation-related genes were detected by q RT-PCR.To investigate the toxic effect of 4-OP on common carp and the molecular mechanism of gill inflammatory injury caused by 4-OP.The main results are as follows:（1）4-OP exposure inhibited the growth of common carp;increased serum ALT,AST,ALP,and LDH activities,as well as GLU and CHO contents,decreased TP,ALB,GLO,and CA contents.The above results confirmed that 4-OP exposure induced tissue damage and immunity decreased in common carp,which had a negative impact on the health of common carp.（2）The 4-OP content in common carp gills of the 4-OP group was several times higher than the environmental concentration,indicating that 4-OP was enriched in common carp gills,and gill was a target organ attacked by 4-OP.（3）4-OP exposure caused gill filament damage,lamellar swelling and inflammatory hyperplasia,as well as a variety of cell swelling and disruption on gill slices.Morphological changes confirmed that 4-OP exposure caused common carp gill inflammatory injury.（4）4-OP exposure elevated the activity of ATPase(Na⁺K⁺-ATPase,Ca²⁺-ATPase,Mg²⁺-ATPase,and Ca²⁺Mg²⁺-ATPase);inhibited antioxidant system（CAT,GSH-Px,GST,T-SOD,and T-AOC activites and GSH content）and promoted oxidation system（H₂O₂and MDA contents）.The above results indicated that 4-OP exposure induced energy metabolism disorder and oxidative stress in common carp gills.（5）Compared with the control group,1605 genes were differentially expressed due to 4-OP exposure,including 898 up-regulated genes and 707 down-regulated genes.KEGG and GO enrichment analyses showed that differentially expressed genes were mainly involved in biological pathways and functions such as complement activation,immune response,and inflammatory response.（6）4-OP exposure up-regulated complement-related genes（C3,C3a,C3a R,C5,C5a,and C5a R1）and triggered C3a/C3a R axis and C5a/C5a R1 axis;down-regulated Th1 cytokines（TNF-βand IFN-γ）and Treg cytokines（TGF-βand IL-10）,up-regulated Th2 cytokines（IL-4 and IL-6）and Th17 cytokines（IL-17 and IL-21）,and induced the imbalances of Th1/Th2 and Treg/Th17 cells;increased NO content and i NOS activity,up-regulated pro-inflammatory factors（TLR7,NF-κB,CXCL8,COX-2,NOS2b,TNF-α,and PGE2）,down-regulated anti-inflammatory factor（IκBα）,and mediated inflammatory response via TLR7/IκBα/NF-κB pathway.The above results confirmed that4-OP exposure caused complement activation,immunosuppression,and inflammatory response in common carp gills.In conclusion,4-OP had a negative effect on the health of common carp.Energy metabolism disorder,oxidative stress,complement activation,immunosuppression,and inflammatory response were involved in the poisoning mechanism of 4-OP-caused inflammatory injury in common carp gills.The findings of this study will provide pioneering information and theoretical support for the toxic effect and mechanism of 4-OP,and provide theoretical reference for scientific assessment of estrogenic environmental pollution risk.