The Toxicological Effect And Molecular Mechanism Of PM_2.5 And SO₂ On Neurodegeneration

Industrial production,coal combustion and transportation brought serious atmospheric particulate matter pollution.Epidemiological studies have shown that particulate matter not only increases the incidence of cardiopulmonary disease but also relates to the development of neurodegenerative diseases.Considering that PM_2.5 is highly heterogeneous with regional disparity and seasonal variation,it is necessary to explore whether PM_2.5exposure induced neuronal injuries in a season-dependent matter.Air pollutant is a complex mixture of particulate and gaseous components in the atmospheric environment.Understanding the health risks of these pollutants requires an evaluation of their combined effects rather than predictions of single chemical toxicity.However,few studies have examined the potential impact of these pollutants on neurodegeneration,especially at no observed effect concentration（NOEC）.We proposed the topic research,to investigate the toxicological effect and possible molecular mechanism of co-exposure to particulate matter(PM_2.5)and sulfur dioxide（SO₂）from coal combustion emission.In this study,firstly,the mouse primary cultured cortical neurons were treated with different seasonal PM_2.5 at the same concentration.Applying immunoblotting analysis,we detected the protein levels of phosphorylated extracellular signal-regulated kinase 1/2（p-ERK1/2）and phosphorylated cAMP-response element binding protein（p-CREB）;we also determined their downstream apoptosis-related proteins（bax,bcl-2 and cleaved caspase-3）,and synaptic-related proteins（PSD-95 and NR2B）expression level.Then we verified neuronal apoptosis by TUNEL staining.These results showed that PM_2.5 exposure can inhibit phosphorylation of ERK1/2 and CREB,thereby induce bax and bcl-2,and activate caspase-3;decrease the level of PSD-95 and NR2B expression,inducing neuronal apoptosis and synaptic plasticity injuries.The effects were season-dependent and significant after PM_2.5exposure collected from spring and winter in primary cultured cortical neurons.Therefore,we analyzed the correlation be-tween the chemical composition of PM_2.5 and the biological markers,re-vealed that PAHs is one of the main component of PM_2.5 seasonally induced neurodegenerative injury.To investigate PM_2.5 and SO₂ derivatives / SO₂-induced neurodegenerative injury,the primary cortical neurons and animal models were used in present study.The NOECs of PM_2.5 or SO₂ derivatives were determined by MTT assay and nonlinear curve optimal fitting model;the effects of neuronal apoptosis and synaptic degeneration were observed by TUNEL staining and immunoblotting at low concentration of PM_2.5 and SO₂;the mechanism of microRNA was verified by dual luciferase reporter gene assay.The results showed that PM_2.5 and SO₂ co-exposure synergistically induced neuronal apoptosis（increased caspase-3 activation and TNNEL staning）and synaptic injury（decreased PSD-95 and NR2 B expression）in vitro;and lead to neurodegeneration in vitro and in vivo（tau and phosphorylated tau）.In addition,mmu-mi R-337-5p which is homologous to a human miRNA that targets microtubule associated protein tau（Mapt）,was involved in the combined effect and contributed to synergistic neurodegeneration.This study suggested that PM_2.5 in coal-burning areas is associated with neurodegenerative injury and the synergistic effect with SO₂ may decrease the threshold of effect in spring / winter seasons.This study also established new molecular markers for the implementation of the prevention of neurodegenerative diseases,early diagnosis and clinical treatment in contaminated areas.