Influence of Air Pollution Exposure on the microRNA Content of Neuronal Extracellular Vesicles in Subjects Affected by Major Depressive Disorder

Major depressive disorder (MDD) has been recently linked to air pollution exposure; nevertheless, the biological mechanisms underlying this association remain underinvestigated. Air pollution might modulate the microRNA (miRNA) content of neuron-derived extracellular vesicles (NdEVs), potentially mirroring brain epigenetic alterations. In the present study, we investigated the relationship between air pollution, NdEV miRNAs, and MDD severity in a population of 200 patients with depression. After signing informed consent, participants compiled questionnaires about demographics, lifestyle and clinical history, and donated a blood sample. MDD severity was assessed by five scales. Particulate matter ≤2.5 μm (PM_2.5) and nitrogen dioxide (NO₂) exposure was assigned based on participants' residential address. Plasma NdEVs were obtained by L1CAM immunocapture. NdEV miRNAs were queried by RT-qPCR (microarray) following a two-stage approach. Associations between air pollutants, NdEV miRNAs, and MDD severity were assessed by multivariable regression models. The regulatory function of NdEV miRNAs was investigated by gene target and pathway analysis. As a result, exposure to NO₂ was associated with decreased levels of miR-191 and miR-24, while PM_2.5 was negatively associated with miR-191, miR-223, miR-24, miR-320, miR-451, miR-572, and miR-638. Decreased miR-126, miR-19b, miR-320, miR-451, miR-572, and miR-638 were associated with higher MDD severity scores. Target genes at the interface between air pollution exposure and MDD severity were mainly involved in inflammation and cell cycle regulation. These findings suggest that air pollutants might modulate MDD severity by triggering NdEV miRNA alterations. Longitudinal studies are needed to evaluate whether NdEV miRNAs might serve as novel biomarkers for MDD prognosis.