Evaluating the effect of acute diesel exhaust particle exposure on P-glycoprotein efflux transporter in the blood-brain barrier co-cultured with microglia

Air Pollution-Induced Neurotoxicity: The Relationship Between Air Pollution, Epigenetic Changes, and Neurological Disorders

Air pollution is a major global health threat, responsible for over 8 million deaths in 2021, including 700,000 fatalities among children under the age of five. It is currently the second leading risk factor for mortality worldwide. Key pollutants, such as particulate matter (PM2.5, PM10), ozone, sulfur dioxide, nitrogen oxides, and carbon monoxide, have significant adverse effects on human health, contributing to respiratory and cardiovascular diseases, as well as neurodevelopmental and neurodegenerative disorders. Among these, particulate matter poses the most significant threat due to its highly complex mixture of organic and inorganic compounds with diverse sizes, compositions, and origins. Additionally, it can penetrate deeply into tissues and cross the blood-brain barrier, causing neurotoxicity which contributes to the development of neurodegenerative diseases. Although the link between air pollution and neurological disorders is well documented, the precise mechanisms and their sequence remain unclear. Beyond causing oxidative stress, inflammation, and excitotoxicity, studies suggest that air pollution induces epigenetic changes. These epigenetic alterations may affect the expression of genes involved in stress responses, neuroprotection, and synaptic plasticity. Understanding the relationship between neurological disorders and epigenetic changes induced by specific air pollutants could aid in the early detection and monitoring of central nervous system diseases.

Modulation of miR-466d-3p on Wnt signaling pathway in response to DEPs-induced blood-brain barrier disruption

BACKGROUND

Diesel exhaust particles (DEPs), a predominant component of ambient particulate matter (PM), are classified as ultrafine particles with the capacity to penetrate the cerebral blood-brain barrier (BBB). This penetration is implicated in the pathogenesis of central nervous system (CNS) disorders. The integrity of the BBB is inextricably linked to cerebrovascular homeostasis and the development of neurodegenerative disease, highlighting the importance of studying the effects and mechanisms of DEPs on BBB function damage.

METHODS AND RESULTS

Utilizing mouse cerebral microvascular endothelial cells (bEnd.3 cells) as an in vitro model of the BBB, we explored the detrimental effects of DEPs exposure on BBB permeability and integrity, with particular focus on inflammation, cell apoptosis, and miRNA expression profiles. Our findings revealed that exposure to DEPs at varying concentrations for 48 h resulted in the inhibition of bEND.3 cell proliferation, induction of cell apoptosis, and an upregulation in the secretion of inflammatory cytokines/chemokines and adhesion molecules. The BBB integrity was further compromised, as evidenced by a decrease in trans-epithelial electrical resistance(TEER), a reduction in cytoskeletal F-actin, and diminished tight junction (TJ) protein expression. Microarray analysis revealed that 23 miRNAs were upregulated and 11 were downregulated in response to a 50 μg/mL DEPs treatment, with miR-466d-3p being notably differentially expressed. Wnt3 was identified as a target of miR-466d-3p, with the Wnt signaling pathway being significantly enriched. We validated that miR-466d-3p expression was downregulated, and the protein expression levels of Wnt/β-catenin and Wnt/PCP signaling components were elevated. The modulation of the Wnt signaling pathway by miR-466d-3p was demonstrated by the transfection of miR-466d-3p mimic, which resulted in a downregulation of Wnt3 and β-catenin protein expression, and the mRNA level of Daam1, as well as an enhancement of TJ proteins ZO-1 and Claudin-5 expression.

CONCLUSIONS

Our study further confirmed that DEPs can induce the disruption of BBB integrity through inflammatory processes. We identified alterations in the expression profile of microRNAs (miRNAs) in endothelial cells, with miR-466d-3p emerging as a key regulator of tight junction (TJ) proteins, essential for maintaining BBB integrity. Additionally, our findings primarily demonstrated that the Wnt/ β-catenin and Wnt/PCP signaling pathway can be activated by DEPs and are regulated by miR-466d-3p. Under the combined effects of Wnt/PCP and inflammation, there is an ultimate increase in BBB hyperpermeability.

In vitro neurotoxicity of particles from diesel and biodiesel fueled engines following direct and simulated inhalation exposure

Combustion-derived particulate matter (PM) is a major source of air pollution. Efforts to reduce diesel engine emission include the application of biodiesel. However, while urban PM exposure has been linked to adverse brain effects, little is known about the direct effects of PM from regular fossil diesel (PMDEP) and biodiesel (PMBIO) on neuronal function. Furthermore, it is unknown to what extent the PM-induced effects in the lung (e.g., inflammation) affect the brain. This in vitro study investigates direct and indirect toxicity of PMDEP and PMBIO on the lung and brain and compared it with effects of clean carbon particles (CP). PM were generated using a common rail diesel engine. CP was sampled from a spark generator. First, effects of 48 h exposure to PM and CP (1.2-3.9 µg/cm2) were assessed in an in vitro lung model (air-liquid interface co-culture of Calu-3 and THP1 cells) by measuring cell viability, cytotoxicity, barrier function, inflammation, and oxidative and cell stress. None of the exposures caused clear adverse effects and only minor changes in gene expression were observed. Next, the basal medium was collected for subsequent simulated inhalation exposure of rat primary cortical cells. Neuronal activity, recorded using microelectrode arrays (MEA), was increased after acute (0.5 h) simulated inhalation exposure. In contrast, direct exposure to PMDEP and PMBIO (1-100 µg/mL; 1.2-119 µg/cm2) reduced neuronal activity after 24 h with lowest observed effect levels of respectively 10 µg/mL and 30 µg/mL, indicating higher neurotoxic potency of PMDEP, whereas neuronal activity remained unaffected following CP exposure. These findings indicate that combustion-derived PM potently inhibit neuronal function following direct exposure, while the lung serves as a protective barrier. Furthermore, PMDEP exhibit a higher direct neurotoxic potency than PMBIO, and the data suggest that the neurotoxic effects is caused by adsorbed chemicals rather than the pure carbon core.