Inflammation-induced Occludin Downregulation Limits Epithelial Apoptosis by Suppressing Caspase-3 Expression.

Abstract

BACKGROUND & AIMS:

Epithelial tight junctions are compromised in gastrointestinal disease. Processes that contribute to the resulting barrier loss include endocytic occludin removal from the tight junction and reduced occludin expression. Nevertheless, the relatively-normal basal phenotype of occludin knockout (KO) mice has been taken as evidence that occludin does not contribute to gastrointestinal barrier function. We asked whether stress could unmask occludin functions within intestinal epithelia.

METHODS:

Wildtype (WT), universal and intestinal epithelial-specific occludin KO, and villin-EGFP-occludin transgenic mice as well as WT and occludin knockdown (KD) Caco-2BBe cell monolayers were challenged with DSS, TNBS, staurosporine, 5-FU, or TNF. Occludin and caspase-3 expression were assessed in patient biopsies.

RESULTS:

Intestinal epithelial occludin loss limited severity of DSS- and TNBS-induced colitis due to epithelial resistance to apoptosis; activation of both intrinsic and extrinsic apoptotic pathways was blocked in occludin KO epithelia. Promoter analysis revealed that occludin enhances CASP3 transcription and, conversely, that occludin downregulation reduces caspase-3 expression. Analysis of biopsies from Crohn's disease and ulcerative colitis patients and normal controls demonstrated that disease-associated occludin downregulation was accompanied by and correlated with reduced caspase-3 expression. In vitro, cytokine-induced occludin downregulation resulted in reduced caspase-3 expression and resistance to intrinsic and extrinsic pathway apoptosis, demonstrating an overall protective effect of inflammation-induced occludin loss.

CONCLUSIONS:

The tight junction protein occludin regulates apoptosis by enhancing caspase-3 transcription. These data suggest that reduced epithelial caspase-3 expression downstream of occludin downregulation is a previously-unappreciated anti-apoptotic process that contributes to mucosal homeostasis in inflammatory conditions.

• Authors: Wei-Ting Kuo, Le Shen, Li Zuo, Nitesh Shashikanth, Ma Lora Drizella M Ong, Licheng Wu, Juanmin Zha, Karen L Edelblum, Yitang Wang, Yingmin Wang, Steven P Nilsen, Jerrold R Turner
• Journal: Gastroenterology (Gastroenterology) Vol. 157 Issue 5 Pg. 1323-1337 (11 2019) ISSN: 1528-0012 [Electronic] United States
• PMID: 31401143 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2019 AGA Institute. Published by Elsevier Inc. All rights reserved.

Chemical References

• OCLN protein, human
• Occludin
• Ocln protein, mouse
• Tjp1 protein, mouse
• Zonula Occludens-1 Protein
• Trinitrobenzenesulfonic Acid
• Dextran Sulfate
• CASP3 protein, human
• Casp3 protein, mouse
• Caspase 3

Topics

• Animals
• Apoptosis
• Caco-2 Cells
• Case-Control Studies
• Caspase 3 (deficiency, genetics, metabolism)
• Colitis (chemically induced, enzymology, genetics, pathology)
• Colitis, Ulcerative (enzymology, pathology)
• Colon (enzymology, pathology)
• Crohn Disease (enzymology, pathology)
• Dextran Sulfate
• Disease Models, Animal
• Epithelial Cells (enzymology, pathology)
• Humans
• Intestinal Mucosa (enzymology, pathology)
• Mice, Inbred C57BL
• Mice, Knockout
• Occludin (deficiency, genetics, metabolism)
• Signal Transduction
• Trinitrobenzenesulfonic Acid
• Zonula Occludens-1 Protein (genetics, metabolism)