Autophagy Reduces the Degradation and Promotes Membrane Localization of Occludin to Enhance the Intestinal Epithelial Tight Junction Barrier against Paracellular Macromolecule Flux

Abstract

Background and aim Functional loss of the gut epithelium's paracellular tight junction (TJ) barrier and defective autophagy are factors potentiating inflammatory bowel disease (IBD). Previously, we showed the role of autophagy in enhancing the intestinal TJ barrier via pore-forming claudin-2 degradation. How autophagy regulates the TJ barrier forming proteins remain unknown. Here, we investigated the role of autophagy in the regulation of occludin, a principal TJ component involved in TJ barrier enhancement. Results Autophagy induction using pharmacological activators and nutrient starvation increased total occludin levels in intestinal epithelial cells, mouse colonocytes, and human colonoids. Autophagy induction enriched membrane occludin levels and reduced paracellular permeability of macromolecules. Autophagy-mediated TJ barrier enhancement was contingent on the presence of occludin as OCLN-/- nullified its TJ barrier enhancing effect against macromolecular flux. Autophagy inhibited the constitutive degradation of occludin by preventing its caveolar endocytosis from the membrane and protected against inflammation-induced TJ barrier loss. Autophagy enhanced the phosphorylation of ERK-1/2 and inhibition of these kinases in Caco-2 cells and human colonic mucosa prevented the macromolecular barrier-enhancing effects of autophagy. In-vivo, autophagy induction by rapamycin enhanced occludin levels in WT mouse intestines and protected against LPS and TNF-α-induced TJ barrier loss. Disruption of autophagy with acute Atg7 knockout in adult mice decreased intestinal occludin levels, increasing baseline colonic TJ permeability and exacerbating the effect of experimental colitis. Conclusion Our data suggest a novel role of autophagy in promoting the intestinal TJ barrier by increasing occludin levels in an ERK1/2 MAPK-dependent mechanism.

Metabolic Role of Autophagy in the Pathogenesis and Development of NAFLD

“…Disruption of the intestinal TJ barrier leads to the permeation of pro-inflammatory molecules from the gut lumen into the circulating system, which is considered a risk factor for NAFLD development [ 88 ]. Autophagy strengthens the intestinal TJ barrier through two distinct mechanisms: by targeting pore-forming claudin-2 protein degradation and/or inhibiting the degradation of occludin by preventing its caveolar endocytosis from the membrane [ 89 , 90 ]. Autophagy also protects against LPS- and TNFα-induced intestinal injury in vivo as rapamycin significantly attenuated LPS- and TNFα-induced increases in intestinal permeability [ 90 ].…”

“…Autophagy strengthens the intestinal TJ barrier through two distinct mechanisms: by targeting pore-forming claudin-2 protein degradation and/or inhibiting the degradation of occludin by preventing its caveolar endocytosis from the membrane [ 89 , 90 ]. Autophagy also protects against LPS- and TNFα-induced intestinal injury in vivo as rapamycin significantly attenuated LPS- and TNFα-induced increases in intestinal permeability [ 90 ]. Emerging evidence supports that the gut microbiota may contribute to liver diseases through multiple mechanisms influenced by bacterial composition [ 91 ].…”

Gastrodia elata polysaccharide alleviates Parkinson's disease via inhibiting apoptotic and inflammatory signaling pathways and modulating the gut microbiota

“…Occludin, a tight junction protein, is essential for the maintenance and regulation of intestinal barrier function and is commonly used to evaluate the integrity of the intestinal barrier. 52 In mice with MPTP-induced gut microbiota dysbiosis, the fluorescence intensity of occludin decreased compared with the control group (Fig. 9A and B, p < 0.05), suggesting the possibility of intestinal barrier damage.…”

Untargeted metabolomics revealed the regulatory effect of Maillard reaction products of ovalbumin with different degrees on the metabolism of colitis mice

“…One of the main features of intestinal barrier dysfunction is the disruption of the tight junction structure, which leads to a loose arrangement of cells and increased intestinal permeability. 27 Once intestinal permeability increases, harmful antigens enter the lamina propria of the intestine, which triggers the secretion of pro-inflammatory cytokines by immune cells such as dendritic cells. 28 In addition, the occurrence of inflammatory reactions is usually accompanied by oxidative stress, leading to an increase in ROS.…”