Glucocorticoid receptor expression on circulating leukocytes in healthy and asthmatic adolescents in response to exercise

BACKGROUND: Poor aerobic fitness is associated with worsening of asthma symptoms and fitness training may improve asthma control. The mechanism linking fitness with asthma is not known. We hypothesized that repeated bouts of exercise would lead to a downregulation of glucocorticoid receptor (GR) expression on circulating leukocytes reflecting a reduced responsiveness to stress. METHODS: In a prospective exercise training intervention of healthy and asthmatic adolescents, GR expression in leukocytes was measured using flow cytometry in response to a brief exercise challenge before and after the training intervention. PBMC gene expression of GR, GRβ, HSP70, and TGFβ1, 2 were determined using RT-PCR. RESULTS: Peak V̇O(2) increased by 14.6 ± 2.3% indicating an effective training (p<0.01). There was a significant difference in GR expression among leukocyte subtypes, with highest expression in eosinophils. Following the training intervention, there was a significant decrease in baseline GR expression (p<0.05) in leukocyte and monocyte subtypes in both healthy and asthmatic adolescents. CONCLUSIONS: This is the first study in adolescents to show that exercise training reduces GR expression on circulating leukocytes. We speculate that exercise training downregulates the stress response in general, manifested by decreased GR expression, and may explain why improving fitness improves asthma health.