Study On The Differences In Lipid Distribution And Mechanisms Induced By PFOA And PFOS Exposure In Mice

Per-and polyfluoroalkyl substances(PFAS)are a class of man-made compounds with hydrophobic and oleophobic properties,highly surfactant activity and thermal stability.The distribution and metabolic balance of lipids in organisms are essential for its maintenance of normal life activities.Due to their structural similarity to fatty acids,PFAS can interfere with lipid transport and metabolic processes in organisms,causing abnormal energy metabolism and even inducing metabolic diseases.Previous studies have shown that PFAS with different structures have distinct toxicity,but the differences of lipid distribution caused by PFAS and its molecular mechanism need to be further explored.To address the above questions,the most typical PFAS-perfluorooctanoic acid(PFOA)and perfluorooctanoic acid(PFOS)were studied in this thesis,the molecular pathways that might be affected by them in response to the differences in lipid droplets(LDs)distribution in hepatocytes were further explored.Finally,several PFAS with different carbon chain lengths and structures were selected for exposure experiments to explore the structure-effect relationships between PFAS structures and the distribution and contents of nuclear lipid droplets(n LDs)and cytoplasmic lipid droplets(c LDs)in mouse hepatocytes.The main studies are as follows:(1)Effects of PFOA and PFOS on lipid content and distribution in mice.Different doses of PFOA and PFOS both altered the lipid content and distribution in mice.At the ending of the experiment,a decrease in lipid content was observed in all PFOA-treated group;while an increase was observed in the low and medium dose PFOS-treated group,only the high dose of PFOS decreased the lipid content.PFOA altered a variety of metabolic indicators and increased energy expenditure in mice.All treated mouse showed different extent of hepatomegaly and abnormal lipid accumulation,and more hepatic lipids were accumulated in PFOS-exposed mice than PFOA-treated individuals.This section demonstrated the different effects of PFOA and PFOS on lipid content and distribution in mice,which resulted in their distinct toxic effects.(2)The mechanism of the different distribution of LDs in mouse hepatocytes caused by PFOS and PFOA was investigated.Combining the abnormal distribution of LDs in mouse hepatocytes affected by PFOS and PFOA,the content of LDs in the nucleus was detected by flow cytometry,demonstrating that PFOA induces abnormal accumulation of n LDs.The effects of PFOA and PFOS on LDs generation and transport pathways related to lipid exchange between cytoplasm and nucleus were analyzed with proteomics techniques,and both were found to affect the levels of fatty acid metabolism pathway,cytochrome P450 pathway-related proteins.PFOA also significantly affected aerobic respiration and mitochondrial ATP synthesis coupled proton transport pathway.PFOS significantly affected the glutathione derivative biosynthetic process,cholesterol metabolism and triglyceride metabolism process.It was verified that PFOA can affect the expression levels of key proteins MTP,Ces1 d,and Seipin in the molecular pathways related to the formation and aggregation of n LDs in hepatocytes,resulting in the abnormal accumulation of n LDs in mouse hepatocytes based on molecular biology and protein technology.In this section,we compared and analyzed the underlying molecular mechanism of the difference of lipid distribution in hepatocytes caused by PFOS and PFOA,and further explained the reason of the difference of toxicity between PFOS and PFOA.(3)Exploring the structure-effect relationship of different structural PFAS affecting lipid accumulation and distribution in the liver.The accumulation of liver triglyceride and the accumulation of n LDs in hepatocytes of mice exposed to PFAS were analyzed.The distribution and content of LDs in the nucleus and cytoplasm of mouse hepatocytes exhibited a significant structure-effect relationship with the structure of PFAS,the target proteins/genes for n LDs formation in hepatocytes were influenced by PFAS and closely related to its structure.This part of the study initially explored the pattern of lipid metabolism disorders in organisms caused by different structures of PFAS,which may provide some scientific basis for predicting the toxic effects of novel PFAS alternatives.In this thesis,we systematically investigated the effects of PFOA and PFOS on lipid distribution,especially the abnormal distribution of LDs in hepatocytes by using a combination of metabolic rate monitoring,histopathology,molecular biology and proteomics,and initially identified the molecular targets of PFOA that may affect the abnormal accumulation of n LDs in mouse hepatocytes,and found that the structure of PFAS has a significant relationship with the distribution of LDs in mouse hepatocytes.The abnormal accumulation of LDs is closely related to a variety of metabolic diseases,and the results of this study are beneficial to the analysis of the human health effects of PFAS and to the development of PFAS alternatives with high biosafety.