The Neurotoxicity Effect And Molecular Mechanism In Response To Atmospheric PM_2.5 Inhalation

Air pollution is a major environmental health threat worldwide.Atmospheric particulate matter,especially fine particulate matter(PM_2.5,aerodynamic diameter?2.5 ?m)is a key indicator of the current air quality situation in China,and is an important contributor to the health effects of air pollution.PM_2.5 originates from different sources and contains multiple chemical components.Epidemiological and experimental investigations have demostrated that PM_2.5 air pollutants not only cause damage to the cardiopulmonary system but are also associated with neuropathological dysfunction through variety of actions.Air pollution represents a diverse mixture of substances including particulate matter and gaseous pollutants.The toxic effects are closely related to the type of pollutants,the level of different pollutants and the interaction between pollutants.The current evidence mainly focuses on the adverse effects of a single air pollutant,ignoring the cognitive risk to the co-existence of these pollutants in the actual air pollution environment.Therefore,we proposed the research to discusse the key components of PM_2.5 which play a key role in health injury and elucidate the related biological effects.Then,we clarify the molecular mechanism of neurotoxicity induced by PM_2.5 from the functional alterations and genetic/epigenetic levels,and further analyze the toxic effects of air pollutants co-exposure.1.As one of the toxicant constituents in PM_2.5,metal can bring significant health risks to a population;however,the exposure to PM_2.5 bound metals and their biological impacts are not fully understood.In this study,we first collected the PM_2.5 samples from winter of Taiyuan,a typical coal-fired city in northern China.The contents of six metals?Zn,Pb,Mn,As,Cu,and Cd?in the samples were determined by inductively coupled plasma-mass spectrometry?ICP-MS?,and the EF value was calculated to quantitatively evaluate the levels and sources of metal pollution.Then,C57BL/6 mice with different ages?4 weeks,4 months,10 months old?received oropharyngeal aspiration of PM_2.5 at 3 mg/kg every other day for 4 weeks.The metabolic distribution of six metals and the contents of triglyceride?TG?and total cholesterol?TCHO?in the whole blood,lung,heart and cerebral cortex were investigated following PM_2.5 inhalation of mice at different developmental windows.The results indicate that Zn,Pb and Cd may originate from anthropogenic sources,such as coal burning.In contrast,Mn,Cu and As may be originating from the natural environment,such as ore,soil parent material and parent rocks.The fine particles mainly deposited in the lung,while the PM_2.5 bound metals could reach and gather in secondary off-target tissues?lung,liver,heart and brain?with a developmental window-dependent property.Furthermore,the elevation of triglycerides and cholesterol levels at sensitive developmental windows?the young and elderly stages?occurred.Correlation analysis of heavy metal and lipid in different organs indicated that Pb,Cd,Mn and As were significantly associated with TCHO in the heart,lung,brain and liver,respectively.These findings provide further experimental evidence that PM_2.5 produced adverse biological effects are associated with internal exposure and the effects of specific compositions,and the sensitivity of the process is related to developmental windows.2.PM_2.5 is one of the leading environmental risk factors for the global burden of disease.Whereas increasing evidence has linked the adverse roles of PM_2.5 with cardiovascular and respiratory diseases,limited but growing emerging evidence suggests that PM_2.5 exposure can affect the nervous system,especially neuroinflammation,synaptic dysfunction and cognitive deterioration.However,the molecular mechanisms underlying the synaptic and cognitive deficits elicited by PM_2.5 inhalation are largely unknown.In the present study,C57BL/6 mice received oropharyngeal aspiration of PM_2.5?1 and 5 mg/kg bw?every other day for 4 weeks.The expression of inflammatory cytokines were measured by enzyme-linked immunosorbent assay?ELISA?following PM_2.5 exposure and the results indicated that PM_2.5 exposure increased the release of interleukin 1??IL-1??and tumor necrosis factor-??TNF-??in the lung,blood and brain,suggesting that PM_2.5 exposure induced systemic inflammation.Additionally,our results showed PM_2.5 exposure deteriorated functional synaptic integrity and spatial learning and memory through electrophysiological recordings,western-blot?WB?and morris water maze?MWM?assays.Activation of ?-site amyloid precursor protein cleaving enzyme 1?BACE1?was detected to play an important role in this process but not amyloid beta?A??accumulation,and BACE1 inhibition rescued synaptic and cognitive impairment in animals following PM_2.5 inhalation.Furthermore,microRNAs?miRNAs?microarray analysis,quantitative real-time polymerase chain reaction?q RT-PCR?verification and dual-luciferase reporter gene study indicated that mi R-574-5p expression was downregulated in a dose-dependent manner following PM_2.5 inhalation,and miR-574-5p can reverse BACE1 expression and synaptic plasticity and cognitive impairment by binding to BACE1 3'URT region.To test this prediction,we overexpressed miR-574-5p by stereotaxically injecting LV-miR-574-5p lentiviral constructs into the hippocampal area.Overexpression of miR-574-5p in the hippocampal region decreased BACE1 expression,restored synaptic function,and improved spatial memory and learning following PM_2.5 exposure.In addition,our study further revealed that PM_2.5 stimulates neuronal inflammatory cytokines to activate NF-?B,and the binding of NF-?B to the miR-574-5p promoter region is an important regulatory step in the initiation of the BACE1 signaling pathway through miR-574-5p.Taken together,our findings provide a novel epigenetic mechanism underlying impaired synaptic and cognitive function following PM_2.5 exposure,suggesting that miR-574-5p is a potential intervention target for prevention and treatment of PM_2.5-induced neurological disorders.3.Air pollution is a serious environmental health problem that has been previously associated with neuropathological disorders.However,current experimental evidence mainly focuses on the adverse effects of a single air pollutant,ignoring the biological responses to the co-existence of these pollutants.In the present study,we co-exposed C57BL/6 mice to PM_2.5,SO₂ and NO₂ at various concentrations(0.5 mg/m3 SO₂ and 0.2 mg/m3 NO₂ via dynamic inhalation simultaneously?6 h/d,28 d?followed by oropharyngeal aspiration of 1 mg/kg PM_2.5 every other day during these exposures;or 3.5 mg/m3 SO₂,2 mg/m3 NO₂ and 3 mg/kg PM_2.5).We explored differences in the profiles of plasma miRNAs in mice after co-exposure,and the mi Randa,miRDB,miRWalk and Targetscan software were used to predict the target genes of miRNAs with significant changes.The following gene ontology?GO?and pathway of target genes were also analyzed.Spatial learning and memory were assessed with the Morris water maze test and histopathological abnormalities were observed by hematoxylin-eosin?HE?staining.Then we used western blot and transmission electron microscopy?TEM?to detect apoptosis-related protein expression and mitochondrial dysfunction,respectively.The results showed that the levels of plasma miRNAs were altered following PM_2.5,SO₂ and NO₂ co-exposure,and bioinformatics analysis showed that differentially expressed miRNAs were associated with central nervous system injury.Air pollutants co-exposure impaired spatial learning and memory and caused abnormal expression of apoptosis-related genes?p53,bax and bcl-2?.Additionally,these alterations were related to morphological changes in mitochondria,a reduction of ATP,the elevation of mitochondrial fission proteins and the downregulation of fusion proteins.These findings provide a basis for the understanding neuropathological dysfunction in response to co-exposure to ambient air pollutants.In this study,we first established the PM_2.5 exposure-biotoxicity evaluation model based on the heavy metal components to evaluate the susceptibility of PM_2.5 exposure to different developmental windows.Additionally,our results provide a novel miRNAs epigenetic mechanism responsible for PM_2.5 exposure-caused synaptic and cognitive impairments to indicate early detection and risk assessment of effects.Then,we investigate the effects of PM_2.5,SO₂ and NO₂ on the neurological function and its molecular mechanism,which provide the new ideas for pollution control and health protection in polluted areas.