Epigenetic Modifications Associated With Wildland-Urban Interface (WUI) Firefighting

Wildland-urban interface (WUI) firefighting involves exposure to burning vegetation, structures, and other human-made hazards, often without respiratory protection. Response activities can last for long periods of time, spanning multiple days or weeks. Epigenetic modifications, including microRNA (miRNA) expression and DNA methylation, are responsive to toxicant exposures and are part of the development of cancers and other diseases. Epigenetic modifications have not been studied in relation to WUI fires. Firefighters (n = 99) from southern California, including 79 firefighters who responded to at least one WUI fire, provided blood samples at baseline and approximately 10 months later. We quantified the relative abundance of 800 miRNAs in blood samples using the nCounter Human v3 miRNA expression panel and blood leukocyte DNA methylation throughout the genome via the Infinium EPIC array. We used linear mixed models to compare the expression of each miRNA across time and DNA methylation at each locus, adjusting for potential confounders. In the miRNA analysis among all firefighters, 65 miRNAs were significantly different at follow-up compared to baseline at a false discovery rate of 5%. Results were similar when restricted to firefighters with a recorded WUI fire exposure during the interim period, although only 50 were significant. Expression of miRNA hsa-miR-518c-3p, a tumor suppressor, was significantly associated with WUI fire response (fold change 0.77, 95% CI = [0.69, 0.87]). In the DNA methylation analysis, no statistically significant changes over time were identified. In summary, WUI fire exposures over a wildfire season altered miRNA expression but did not substantially impact DNA methylation.