Lipopolysaccharide induces autophagy by targeting the AMPK-mTOR pathway in Human Nasal Epithelial Cells

Chronic rhinosinusitis (CRS) is a well-known disease encountered in the department of otorhinolaryngology, yet little is known about its pathogenesis. Autophagy, a lysosome-dependent degradation process, has been reported to be involved in the process of many chronic inflammatory diseases. Here we tried to evaluate the function of autophagy in CRS as well as explore the related mechanisms. We first stained light chain 3B (LC3B) with immunohistochemistry in uncinate tissues (UT) from patients with and without CRS and found that its expression was up-regulated in CRS patients. Then, Human Nasal Epithelial Cells (HNEpC) were treated with lipopolysaccharide (LPS), one of the most common pathogenic elements in CRS, and we found that autophagy was induced in a dose- and time-dependent manner. This is supported by a rise in the expression of light chain 3B-II (LC3B-II), accumulation of GFP-LC3 vesicles, as well as decreased p62 expression. Furthermore, we found that LPS promoted AMPK phosphorylation and inactived mTOR, while AMPK inhibition by compound C significantly attenuated LPS-induced autophagy. Besides, treatment of HNEpC with LPS increased the amount of Toll-like receptor 4 (TLR4) while inhibiting TLR4 by Polymyxin B (PMB) declined autophagy caused by LPS. Taken together, our study first demonstrated that LPS caused autophagy in HNEpC, and this process was AMPK-mTOR dependent. These data suggested the relationship between LPS and autophagy in the pathogenesis of CRS.