Real-world PM2.5 exposure triggers early testicular epigenetic responses in the absence of significant changes in measured reproductive endpoints.

BACKGROUND: Industrialization has led to widespread air pollution, among which particulate matter ≤ 2.5 μm (PM2.5) represents a significant environmental pollutant associated with various adverse health outcomes. Emerging evidence indicates that the male reproductive system is a sensitive target organ of PM2.5 toxicity; however, the temporal progression of early biological responses before measurable reproductive changes become apparent remains insufficiently investigated. METHODS: Here, male mice were exposed to real-world ambient PM2.5 in Hangzhou using a whole-body inhalation system for 4, 8, or 12 weeks, enabling longitudinal assessment of testicular responses across approximately one to three spermatogenic cycles. RESULTS: Despite the absence of significant changes in sperm quality, reproductive hormone levels, histopathology, or oxidative DNA damage, testicular global 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) showed significant time-dependent changes. Specifically, global 5mC decreased after 4 weeks of PM2.5 exposure but increased after 12 weeks compared to controls (P < 0.05). Within the PM2.5-exposed groups, 5mC levels were also higher at 12 weeks than at 4 weeks (P < 0.05). For 5hmC, the decrease observed at 4 weeks was not significant, whereas 5hmC levels increased significantly after 12 weeks compared to controls and with the 4-week PM2.5-exposed group (P < 0.05). CONCLUSIONS: These findings indicate that testicular epigenetic remodeling is an early and sensitive molecular response to real-world PM2.5 exposure, detected in the absence of significant changes in the reproductive endpoints assessed in this study.