Background and Objectives: Nonsteroidal anti-inflammatory drug-activated gene-1 (NAG-1) is a recently discovered TGF-beta superfamily cytokine. But localization and functions of NAG-1 have not been thoroughly studied. So, we wanted to investigate its expression and localization in human nasal mucosa and also wanted to investigate the change of NAG-1 expression as a function of mucociliary and squamous differentiation.
Materials and Method: Anterior and middle portion of human inferior turbinate were used and immunohistochemistry with NAG-1 antibody was done. Passage-2 normal human nasal epithelial cell culture using air-liquid interface method was performed for 14 days and the cells were divided as retinoic acid (RA)-sufficient and RA-deficient group. Hematoxylin and eosin staining was done on each group to study the degree of differentiation. Western blot analysis for NAG-1 expression was performed on each group on 0, 7, and 14 days.
Results: NAG-1 expression of mucociliated epithelium was noted in ciliated cells and serous acini, but was not found in goblet cells and mucous acini. In the squamous epithelium, its expression was weaker than in the mucociliated epithelium. In the RA-sufficient culture, NHNE cells were differentiated into ciliated epithelium, but in the RA-deficient culture, keratinizing squamous epithelium was noted. In the Western blot analysis, NAG-1 expression was significantly higher in the RA-sufficient culture than in the RA-deficient culture and this expression was time-dependent.
Conclusion: NAG-1 may be related to differentiation and apoptotic process 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.
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