Background: Nasal polyposis is characterised by persistent inflammation of the upper airways. Autophagy has been implicated in many chronic inflammatory diseases. Whether autophagy plays a role in nasal polyp (NP) inflammation is completely unknown and deserves investigation.
Methods: LC3 and COX-2 expression, the common autophagy and inflammation indicators, respectively, was analysed by immunoblotting in fresh tissues of NP and control nasal mucosa (NM). Primary cultures of NP-derived fibroblasts (NPDFs) and NMDFs were established for in vitro studies. Autophagy was induced by amino acid starvation and LC3 ectopic overexpression or inhibited by 3-methyladenine in the fibroblasts. Inflammation was induced by IL1-β and TNF-α. LC3 and COX-2 expression was confirmed in NP specimens by immunohistochemistry.
Results: LC3 expression was decreased while COX-2 expression was significantly increased in fresh NP tissues compared with the NM control. In NMDFs and NPDFs, autophagy induction by starvation and LC3 overexpression downregulated COX-2 expression. Conversely, autophagy inhibition by 3-methyladenine enhanced COX-2 expression. However, IL1-β and TNF-α had no effect on autophagy. Immunohistochemical studies on the NP specimens showed that most displayed low LC3 expression, whereas COX-2 was highly expressed in >50% of the specimens. Examination of two consecutive NP sections from the same tissue blocks revealed a negative correlation between LC3 and COX-2 expression.
Conclusion: Autophagy is deficient in NP tissues and COX-2 is negatively regulated by autophagy in NP-derived fibroblasts. Since COX-2 is essential for the production of pro-inflammatory mediators, this study might help interpret persistent mucosal inflammation in NP. Attenuation of inflammation by restoring autophagy might be a therapeutic strategy for treating NP.