PM_2.5-induced Liver Injury In Mice And Its Related Molecular Mechanism

With the rapid development of economy and technology,the intensity of exploitation and utilization of natural resources and the degree of disturbance to ecological environment are increasing.Pollutants emitted into the air by human activities during production and consumption have caused serious atmospheric environmental pollution,which can affect human health,and restrict the sustainable development of human society and the natural environment.Particulate matter?PM?is one of the major air pollutants and the primary pollutant that affects air quality in many regions of the world.PM_2.5 has attracted worldwide attention due to its long residence time in the air,long transmission distance,high content of toxic and harmful components.Furthermore,considering that PM_2.5 can penetrate the air-blood barrier into the blood circulation,it may cause damage to human health.According to the World Health Organization report,in 2017,92% of the world's population lived in areas where PM_2.5 concentrations exceeded WHO guidelines and caused 2.94 million deaths.China is one of the countries with the most serious PM_2.5 pollution in the world.In 2017,about 852,000 people died due to PM_2.5 exposure and is the fourth largest risk factor for death in China.Based on this,it is necessary to conduct extensive researches on the toxicological effects of PM_2.5,its underlying mechanism of action and related scientific issues.A large amount of scientific evidence indicates that exposure to PM_2.5 has toxic effects on human health,including adverse effects on the respiratory system,cardiovascular system,nervous system and reproductive development.In addition,PM_2.5 exposure has been reported to be related to kidney,liver,olfactory and influenza diseases.The liver is the largest digestive gland and metabolic activity center of the human body,whose blood content and blood flow are rich.After penetrating the air-blood barrier and entering the blood circulation,PM_2.5 will inevitably affect the liver.However,the study on PM_2.5 exposure and liver injury is seriously ignored.In this study,the toxic effect of PM_2.5 exposure on liver and susceptible population were discussed,the possible molecular mechanism of affecting liver lipid metabolism was analyzed,and the key components of PM_2.5 leading to liver toxicity were preliminarily identified.1)In this study,we examined the liver damage of mice at different ages after PM_2.5 treatment,and analyzed its effect on liver lipid metabolism.4-week-old,4-month-old,and 10-month-old C57BL/6 mice were exposed to PM_2.5?3 mg/kg,poisoned every other day?for four weeks.The body weight and liver weight of 10-month-old mice were significantly reduced compared to the control group.Electron microscopy revealed a slight accumulation of lipids in the liver tissue of 4-week and 10-month-old mice.The m RNA expressions of Cyp1a1?product reactive oxygen species?and Sod1?antioxidant enzyme?were tested by RT-PCR.The results showed that Cyp1a1 expression was significantly up-regulated and Sod1 expression was significantly down-regulated in 4-week-old and 10-month-old mice.The gene expression of lipid synthesis-related enzymes in the liver of 10-month-old mice was significantly up-regulated,and the gene expression of lipid transport and catabolism-related enzymes was down-regulated,but the fold change was small.Most genes of lipid metabolism-related enzymes in mice of other age groups did not change significantly.Similar results were confirmed by Western blot analysis.In addition,the concentrations of HDL and LDL in liver tissue were determined by enzyme-linked immunosorbent assay.The concentration of HDL did not change significantly.The concentration of LDL was significantly increased in the liver of 10-month-old mice.These results indicate that PM_2.5 exposure can induce oxidative stress,disturb liver lipid metabolism and slightly increase liver lipid accumulation,and 10-month-old mice are more susceptible than other age groups.2)Most studies that have investigated liver damage from PM_2.5 exposure were mainly focused on only one aspect or on specific metabolic pathways.Considering PM_2.5 is a mixture containing a variety of chemical components,whether it has multiple effects on the liver needs further study.To this end,we selected 10-month-old mice that were more susceptible and used a combination of transcriptomics and metabolomics techniques to analyze the effects of PM_2.5 on the liver.Transcriptome analysis revealed that there were 1081 differentially expressed genes?DEGs?in the liver of mice treated with PM_2.5,of which 452 DEGs were significantly up-regulated and 629 DEGs were significantly down-regulated.KEGG enrichment analysis of differentially expressed genes showed that DEGs were enriched in 253 pathways,of which 19 pathways were significantly enriched.Liver lipid metabolism was the biological process most affected by PM_2.5 exposure.There were four significantly enriched KEGG pathways,including steroid biosynthesis,primary bile acid biosynthesis,steroid hormone biosynthesis,and linoleic acid metabolism.Metabolomic analysis showed that biodegradation and metabolism of exogenous chemicals are the second type of body processes that were significantly affected by PM_2.5 exposure,including cytochrome P450 metabolism of exogenous substances,drug metabolism-cytochrome P450,and drug metabolism-other enzymes.Two immune related pathways,namely hematopoietic cell line,complement and coagulation cascade,were also enriched.In addition,chemical carcinogenic and AGE-RAGE signaling pathway in diabetic complications were also significantly affected by PM_2.5 exposure.In addition,metabolomics analysis screened a total of 45 significantly changed metabolites,mainly focused on the increased lipids and the decreased amino acids and their metabolites.The changes of lipid metabolites showed that PM_2.5 promoted the hydrolysis of lipid and the conversion of cholesterol to bile acids.The decreased amino acids weakened the citric acid cycle and affected the expression of functional proteins.These metabolic results suggested that PM_2.5 exposure promoted the development of nonalcoholic fatty liver disease.3)The components of PM_2.5 are significantly different due to the different emission sources and weather conditions.Studies have shown that the toxicity of particulate matter depends on the combination of all components and their interactions.It is necessary to study the differences among the hepatic toxicological effects induced by PM_2.5 collected from different cities.According to the results of omics studies,liver lipid metabolism is the biological process that most affected by PM_2.5.Therefore,we collected PM_2.5 samples from 4 cities in different regions of China and analyzed the content of main toxic components.Firstly,10-year-old mice were exposed to PM_2.5 collected from different cities in groups.Four weeks later,the expression of lipid metabolism-related genes were tested by RT-PCR.The content of PAHs in PM_2.5 collected from Taiyuan accounts for 0.26% of the total particulate matter,which is about 10 times than the content of other cities.The proportion of metal in PM_2.5 from the four cities was relatively similar.The sulfate content of PM_2.5 from Guangzhou was higher than that in other cities,and the nitrate content in the air of southern cities was higher than that of northern cities.The results of PCR analysis showed that PM_2.5 exposure promoted lipid synthesis and catabolism,with the Hangzhou group being the least affected,and there was no significant difference between the remaining urban groups.In addition,liver lipid metabolism was affected by the combination of PM_2.5 components,but preliminary analysis suggested that nitrate and polycyclic aromatic hydrocarbons may be the more critical components.In this study,we analyzed the liver damage caused by PM_2.5 in mice of different age groups,and found that elderly mice were more sensitive.The molecular process and mechanism of PM_2.5-induced liver injury in elderly mice were studied using transcriptomics and metabolomics methods,and lipid metabolism was found to be the most affected biological process.Finally,the key components affecting liver lipid metabolism were preliminarily identified,by analyzing the main toxic components of PM_2.5 form different cities and their effect on liver lipid metabolism in aged mice.The present study provides new evidence of PM_2.5 on liver injury and can be used as reference information for further research on PM_2.5 induced liver toxicological effects and health protection.