Expression and Distribution Pattern of Retinoic Acid Receptors in the Nasal Mucosa

Retinoids are naturally occurring vitamin A derivatives that regulate cellular processes and metabolism. In particular, retinoids play a key role in cellular proliferation by binding to retinoic acid receptors (RAR)-alpha, beta, and gamma. Considering the functional role of nasal mucosa where active cell regeneration occurs, RAR may play a role in tissue remodeling of the human nasal mucosa.

In this study, we investigated the expression and distribution pattern of RAR using reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry (IHC) and Western blot in normal ethmoid mucosa (NE), chronic rhinosinusitis (IE) and polyp (P).

IE and P samples showed higher expression levels of RAR in RT-PCR and Western blot than NE samples. RAR reactivity was also observed in the NE group, which indicates that cell regeneration also occurs in normal condition. Through IHC, we found the localization of RAR. RAR-α was distributed in the epithelial cells, submucosal glands, and endothelial cells. RAR-β was located in the basal epithelium, while RAR-γ was present in goblet cells and submucosal glands. The staining intensity of RAR-α, β and γ was higher than that in the NE group. Especially in the P group, RARs were abundantly distributed in the stalks of polyps.

The stalk region contains a lot of collagen and fibroblasts to support polyp formation, and the greater amount of RAR in the stalk suggested that RARs may be associated with angiogenesis and cell proliferation. Accordingly, elevated RAR levels in chronic rhinosinusitis could indicate that RARs play a critical role in cell regeneration, angiogenesis and immunomodulation under inflammatory conditions in the human nasal mucosa.