Expression of Non-steroidal Anti-inflammatory Drug-activated Gene-1 in Human Nasal Mucosa and Cultured Nasal Epithelial Cells: A Preliminary Investigation

Abstract

Objective - Non-steroidal anti-inflammatory drug-activated gene-1 (NAG-1) is a recently discovered transforming growth factor-beta superfamily cytokine. The localization and functions of NAG-1 have not been thoroughly studied. The aims of this study were to investigate its expression and localization in human nasal mucosa and also the change in NAG-1 expression as a function of muscociliary and squamous differentiation.Materials and Methods - Anterior and middle portions of human inferior turbinate were used and immunohistochemical studies were performed using NAG-1 antibody. Passage-2 normal human nasal epithelial (NHNE) cell culture was performed for 14 days using the air-liquid interface method and the cells were dividied into retinoic acid (RA)-sufficient and -deficient groups. Each group of cells was stained with hematoxylin-eosin to study the degree of differentiation. Western blot analysis for NAG-1 expresion was performed in each group after 0, 7 and 14 days.Results - NAG-1 expression in mucociliated epithelium was noted in ciliated cells and serous acini, but was not found in goblet cells or mucous acini. In squamous epithelium, NAG-1 expression was weaker than that in mucociliated epithelium. In RA-sufficient culture, NHNE cells were differentiated into ciliated epithelium, but in RA-deficient culture, keratinizing squamous epithelium was noted. Western blot analysis showed that NAG-1 expression was significantly higher in RA-sufficient than -deficient culture (three-fold difference) and this expression was time-dependent.Conclusions - NAG-1 may be involved in differentiation and apoptotic processes of nasal epithelial cells. However, it is still unclear whether NAG-1 is an inducer or a byproduct of differentiation or apoptosis. The role of NAG-1 protein remains to be solved.