Retinoid receptors are expressed in mouse and human lungs

Retinoid receptors are members of nuclear receptor superfamily consisting of two distinct families: RARs (retinoic acid receptors) and RXRs (retinoid X receptors). Each family contains three receptor subtypes alpha, beta, and gamma. Retinoids transduce their effects through binding to retinoid receptors and inhibit transcription factors such as activator protein-1 and nuclear factor-kappa B (NF-kappa B) both of which regulate the transcription of several inflammatory genes. Considering the role of retinoid receptors in lung physiology, we need a precise understanding of their expression in normal and inflamed lungs. We used light and electron microscopic immunohistochemistry and Western blot to determine the expression of retinoid receptors in a murine model of endotoxin-induced (E. coli; 055:B5, 80 mu g intranasal) acute lung inflammation and normal human lungs. Western blot showed expression of all six retinoid receptor subtypes in normal and inflamed mouse lungs. Immunohistology localized differential expression of retinoid receptors in airway epithelium, alveolar/septal macrophages, vascular endothelium, and alveolar septum in mouse lungs. Intranasal LPS challenge in mice resulted in increased expression of RXR alpha in airway epithelium compared to control animals. All six retinoid receptor subtypes were expressed in normal human lungs. Immunoelectron microscopy further confirmed the localization of all the receptors in various lung cells including the nucleus of these cells. The basal and altered expression of retinoid receptors in normal and inflamed lungs, respectively, may suggest their roles in lung pathophysiology.