The IL-10 Promoter Function Is Inhibited By TGF Beta (TGF-b) And Partially Rescued By Statin Co-treatment

Abstract

IL-10 is an anti-inflammatory cytokine expressed mainly in blood cells. Both elevated and decreased levels of IL-10 were reported to be present in the bronchoalveolar lavage fluid (BALF) of asthmatic patients. Compared to wild type animals, IL-10 knockout mice exhibit attenuated lung inflammation after allergen sensitization and challenge. We showed that transgene overexpression of TGF-b from the airway epithelium of mice resulted in lung remodeling and airflow obstruction, and correlated with decreased IL-10 levels in BALF. Administration of lovastatin augmented IL-10 amounts in BALF and prevented development of airway remodeling in these transgenic mice. Thus, we hypothesize that TGF-b exposure inhibits IL-10 expression in human airway epithelial cells (HAEC), and lovastatin co-treatment prevents the inhibition of IL-10 promoter function induced by TGF-b. To test this hypothesis, we transfected HAEC with reporter plasmids in which luciferase is driven by either 1538, 938, 688, 336, 158 or 78 bp of the mouse IL-10 5' regulatory region. Transfected cells were treated with none or TGF-b (2.5ng/mL) +/-lovastatin (10 uM) in 1% FBS-containing medium for 24 hrs. We found robust promoter function in HAEC from constructs harboring sequences upstream of -336 bp. Stimulation with TGF-b significantly reduced promoter activity more than half. DNA sequences between -158 and -78 bp were responsive to TGF-b administration. The inhibitory effect of TGF-b was partially blocked by lovastatin; bp -938 to -688 were required for the lovastatin effect. Analysis of a Smad-dependent promoter function showed that the enhancing activity of lovastatin is independent of Smad protein. Modulation of IL-10 promoter was specific because neither the viral MSV promoter nor the promoter-less vector elicit the same response to TGF-b or lovastatin in HAEC. To our knowledge, this the first report that the IL-10 promoter is active in resident cells of the lung; that IL-10 promoter function is inhibited by TGF-b stimulation, and that lovastatin antagonizes the suppressing effect of TGF-b. We conclude that augmentation of IL-10 expression is a plausible mechanism by which lovastatin decreases airway remodeling, and we propose that IL10 activation may be beneficial for treating asthma. This abstract is funded by: K01HL092588, NIH-CTSA UL1RR024999, RHAMC, R34AI080962 Am J Respir Crit Care Med