Regulation of Peroxisome Proliferator-Activated Receptor-γ Expression in Human Eosinophils by Estradiol

Abstract

Background: Peroxisome proliferator-activated receptor-γ (PPARγ) is a nuclear receptor that regulates not only adipogenesis but also immune reaction. We previously demonstrated that human eosinophils expressed functional PPARγ, although the modulator of PPARγ expression is less well understood. Because clinical studies have shown that the efficacy of PPARγ agonists as insulin sensitizers is stronger in women than in men, we investigated whether sex hormones caused any changes in eosinophil PPARγ expression levels. Methods: First, purified human peripheral blood eosinophils were cultured with 17β-estradiol for 24 h, followed by PPARγ measurement using a flow cytometer. Next, eosinophil PPARγ expression and serum estradiol were studied in 10 healthy women during the menstrual and follicular phases to identify the physiological significance of estradiol. Eosinophil PPARγ expression was also compared in 22 men, 21 non-pregnant women, and 15 pregnant women. Results: We observed that PPARγ protein expression in eosinophils was significantly enhanced by 10^–6M 17β-estradiol. Although serum estradiol concentration was increased during the follicular phase, PPARγ expression levels were not affected by the menstrual cycle. In addition, no significant differences in PPARγ expression were observed in terms of sex and pregnancy. Conclusions: These findings suggest that estradiol potentially upregulates eosinophil PPARγ expression in vitro, although some other mechanisms might be involved in its regulation in vivo.