Prenatal NO₂ exposure and cardiac developmental dysfunction: CD4⁺ T cell imbalance drives cardiac fibrosis through placenta-heart axis immune transmission.

Epidemiological studies show maternal nitrogen dioxide (NO2) exposure associates with congenital heart disease (CHD) risk, but subtypes and mechanisms unclear. Here, we first conducted a systematic review and meta-analysis, which confirmed that prenatal NO₂ exposure significantly increased the risk of coarctation of the aorta (COA) (OR = 1.15, 95% CI: 1.04-1.26). Using a mouse model of prenatal NO₂ exposure, we demonstrated that prenatal NO2 exposure adversely affected fetal cardiac structure and function at embryonic day 18.5, characterized by ventricular dilation, myocardial wall thinning, systolic dysfunction, and cardiac fibrosis predominantly localized to the outflow tract and major vascular roots. Transcriptional profiling of fetal hearts revealed significant enrichment of T cell differentiation pathways, including Th1, Th2, and Th17 cell differentiation. Immunofluorescence analysis further confirmed the imbalance of CD4⁺ T cell subsets, specifically reduced Th1/Th2 and Th17/Treg ratios (key mediators of the above fibrotic phenotype). Importantly, placental proteomics showed activated immune responses and upregulated pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-17) in fetal circulation, disrupting fetal cardiac CD4+ T-cell homeostasis and inducing fibrosis. Together, these findings identify a "maternal-placental-fetal cardiac immune regulation axis" as critical in NO₂-induced CHD, offering a comprehensive framework for policymakers and clinicians to mitigate CHD burden in polluted areas.