Inhibition of autophagic degradation process contributes to claudin-2 expression increase and epithelial tight junction dysfunction in TNF-α treated cell monolayers

Abstract

Tight junction dysfunction plays a vital role in some chronic inflammatory diseases. Pro-inflammatory cytokines, especially tumor necrosis factor alpha (TNF-α), act as important factors in intestinal epithelial tight junction dysfunction during inflammatory conditions. Autophagy has also been shown to be crucial in tight junction function and claudin-2 expression, but whether autophagy has an effect on the change of claudin-2 expression and tight junction function induced by TNF-α is still unknown. To answer this question, we examined the expression of claudin-2 protein, transepithelial electrical resistance (TER), and permeability of cell monolayers, autophagy flux change, and lysosomal pH after TNF-α with or without PP242 treatment. Our study showed that claudin-2 expression, intestinal permeability, microtubule-associated protein 1 light chain 3B II (LC3B-II) and sequestosome 1 (P62) expression largely increased while TER values decreased in TNF-α treated cell monolayers. Further research using 3-methyladenine (3-MA), bafilomycin A1, and ad-mCherry-GFP-LC3B adenovirus demonstrated that LC3B-II increase induced by TNF-α was attributed to the inhibition of autophagic degradation. Moreover, both qualitative and quantitative method confirmed the increase of lysosomal pH, and mammalian target of rapamycin (mTOR) inhibitor PP242 treatment relieved this elevation. Moreover, PP242 treatment also alleviated the change of autophagy flux, TER, and claudin-2 expression induced by TNF-α. Therefore, we conclude that increase of claudin-2 levels and intestinal epithelial tight junction dysfunction are partly caused by the inhibition of autophagic degradation in TNF-α treated cell monolayers.