Physical activity, black carbon exposure, and DNA methylation in the FOXP3 promoter

Abstract

Background: Physical activity is associated with improvement in lung function; however, pollution exposure during physical activity can lead to a transient reduction in lung function. This paradoxical relationship may be linked to altered T regulatory (Treg) cell activity, which increases with exercise and suppresses airway inflammation, but decreases in association with exposure to air pollution. To clarify these relationships, we investigated buccal cell DNA methylation of the forkhead box p3 (FOXP3) gene promoter, a proposed biomarker of Treg activity. We hypothesized that active urban children would have lower FOXP3 promoter methylation, associated with better lung function compared to non-active children. We also hypothesized that this relationship would be attenuated by high exposure to the air pollutant black carbon (BC).

Methods: We performed a cross-sectional study of 135 children ages 9-14 who live in New York City. Activity was measured across 6 days. BC exposure was assessed by personal monitors worn for two 24-h periods, followed by lung function assessment. Buccal swabs were collected for DNA methylation analysis of three regions (six CpG sites) in the FOXP3 promoter.

Results: In multivariable regression models, overall, there was no significant relationship between physical activity and FOXP3 promoter methylation (p > 0.05). However, in stratified analyses, among children with higher BC exposure (≥1200 ng/m³), physical activity was associated with 2.37% lower methylation in promoter 2 (CpGs -77, -65, and -58) (β_estimate = -2.37%, p < 0.01) but not among those with lower BC exposure (β_estimate = 0.54%, p > 0.05). Differences across strata were statistically significant (p_interaction = 0.04). Among all children, after controlling for BC concentration, promoter 2 methylation was associated with reduced FEV₁/FVC (β_estimate = -0.40%, p < 0.01) and reduced FEF_25-75% (β_estimate = -1.46%, p < 0.01).

Conclusions: Physical activity in urban children appeared associated with lower FOXP3 promoter methylation, a possible indicator of greater Treg function, under conditions of high BC exposure. Reduced FOXP3 promoter methylation was associated with higher lung function. These findings suggest that physical activity may induce immunologic benefits, particularly for urban children with greater risk of impaired lung function due to exposure to higher air pollution. FOXP3 promoter buccal cell methylation may function as a useful biomarker of that benefit.

Keywords: Air pollution; Biomarker; Buccal cells; Exercise; Lung function; Spirometry; Treg.

Fig. 1

Distribution of FOXP3 promoter methylation stratified by active vs. non-active children and by low vs. high black carbon (Kruskal-Wallis test). The short lines indicate individual observations, while the shaded areas indicated the distribution of the data for each respective group. The dotted lines indicate the mean percent methylation for all participants, and the thicker solid lines represent mean percent methylation for each respective group

Fig. 2

Non-active children with high BC on average have the highest FOXP3 promoter methylation (Kruskal-Wallis test). The short lines indicate individual observations, while the shaded areas indicated the distribution of the data for each respective group. The dotted lines indicate the mean percent methylation for all participants, and the thicker solid lines represent mean percent methylation for each respective group

Fig. 3

Lower FOXP3 promoter methylation is associated with higher FEV₁/FVC and FEF₂₅−_75%. The blue line represents the mean effect estimate, and the shaded gray area represents the 95% confidence interval (n = 135)