Cord-blood black carbon particle burden is associated with a C19MC small extracellular vesicle miRNA signature enriched for neurodevelopmental pathways

Background: Ambient air pollution, particularly black carbon (BC), is associated with adverse pregnancy outcomes, but the molecular pathways linking in utero particle exposure to fetal programming remain incompletely understood. We examined whether cord-blood BC particle burden relates to small extracellular vesicle (sEV)-associated microRNA (miRNA) profiles and enriched developmental pathways. Methods: Cord blood was collected from newborns in the Born in Bradford's Better Start (BiBBS) cohort. Plasma sEVs were isolated and miRNA was profiled by small RNA sequencing. BC particle load in whole cord blood was quantified by femtosecond pulsed-laser microscopy. After quality control and complete-case restriction, 68 newborns were included in the analysis. Candidate miRNAs were prioritised using elastic-net regression, and associations with log<inf>10</inf>-transformed BC particle burden were estimated using linear mixed-effects models with covariate adjustment and Benjamini---Hochberg false discovery rate (BH-FDR) control. Results: Five of the ten candidate miRNAs were associated with BC at BH-FDR =0.10: hsa-miR-25-3p and hsa-miR-433-3p (positive associations) and hsa-miR-518a-3p, hsa-miR-519a-3p/519b-3p, and hsa-miR-520g-3p/520h (negative associations). Three of the five negatively associated miRNAs belong to the placenta-specific chromosome 19 miRNA cluster (C19MC). All five signals were robust in 100 × 20% holdout resampling. Validated target pathway analysis revealed enrichment for developmental and specifically neurodevelopmental processes, including axon guidance and neurotrophin signaling. Conclusions: These findings link cord-blood BC particle burden to a placenta-linked C19MC miRNA signature in newborn sEVs and developmental pathway enrichment, providing molecular evidence consistent with particle-associated fetal programming at birth.