This study demonstrates a critical link between hypoxia-inducible factor (HIF) and claudin-1 (CLDN1). HIF1β-deficient intestinal epithelial cells develop abnormal tight junction (TJ) structure and have striking barrier defects. CLDN1 is an HIF target gene, and overexpression of CLDN1 in HIF1β-deficient cells restores TJ structure and function.

IL10 is a potent anti-inflammatory cytokine that inhibits the production of pro-inflammatory mediators. Signaling by IL10 occurs through the IL10 receptor (IL10R), which is expressed in numerous cell types, including intestinal epithelial cells (IEC), where it is associated with development and maintenance of barrier function. Guided by an unbiased metabolomics screen, we identified tryptophan (Trp) metabolism as a major modifying pathway in IFN-γ-dominant murine colitis. In parallel, we demonstrated that IFN-γ induction of IDO1, an enzyme that catalyzes the conversion of Trp to kynurenine (Kyn), induces IL10R1 expression. Based on these findings, we hypothesized that IL10R1 expression on IEC is regulated by Trp metabolites. Analysis of the promoter region of IL10R1 revealed a functional aryl hydrocarbon response element (AHRE), which is induced by Kyn in luciferase-based IL10R1 promoter assays. Additionally, this analysis confirmed that IL10R1 protein levels were increased in response to Kyn in IEC in vitro. Studies utilizing in vitro wounding assays revealed that Kyn accelerates IL10-dependent wound closure. Finally, reduction of murine DSS colitis through Kyn administration correlates with colonic IL10R1 expression. Together, these results provide evidence on the importance of IL10 signaling in intestinal epithelia and implicate AHR in the regulation of IL10R1 expression in the colon.

Barrier dysfunction has been implicated in the pathophysiology of eosinophilic esophagitis (EoE). TGF-β1, a potent pleiotropic molecule, is increased in EoE, however, no study has evaluated its influence on esophageal epithelial barrier. We hypothesized that TGF-β1 regulates barrier dysfunction in EoE. We aimed to determine the role of TGF-β1 in epithelial barrier in models of EoE. To examine the impact of TGF-β1 on esophageal barrier, immortalized human esophageal epithelial (EPC2-hTERT) cells were exposed to TGF-β1 during the 3-dimensional air liquid interface (3D-ALI) model in vitro. TGF-β1 exposure diminished EPC2-hTERT barrier function as measured by transepithelial electrical resistance (TEER) and 3kDa FITC dextran paracellular flux (FITC Flux) and H&E assessment revealed prominent cellular separation. In analysis of epithelial barrier molecules, TGF-β1 led to the specific reduction in expression of the tight-junction molecule, claudin-7 and this was prevented by TGF-β receptor I inhibitor. shRNA mediated claudin-7 knockdown diminished epithelial barrier function, while claudin-7 overexpression resulted in protection from TGF-β1-mediated barrier dysfunction. In analysis of pediatric EoE biopsies claudin-7 expression was decreased, altered localization was observed by immunofluorescence analysis and the TGF-β1 downstream transcription factor phosphorylated SMAD2/3 (pSMAD2/3) was increased. Our data suggest that TGF-β1 participates in esophageal epithelial barrier dysfunction through claudin-7 dysregulation.

The creatine/phosphocreatine pathway plays a conserved and central role in energy metabolism. Compartmentalization of specific creatine kinase enzymes permits buffering of local high energy phosphates in a thermodynamically favorable manner, enabling both rapid energy storage and energy transfer within the cell. Augmentation of this metabolic pathway by nutritional creatine supplementation has been shown to elicit beneficial effects in a number of diverse pathologies, particularly those that incur tissue ischemia, hypoxia or oxidative stress. In these settings, creatine and phosphocreatine prevent depletion of intracellular ATP and internal acidification, enhance post-ischemic recovery of protein synthesis and promote free radical scavenging and stabilization of cellular membranes. The creatine kinase energy system is itself further regulated by hypoxic signaling, highlighting the existence of endogenous mechanisms in mammals that can enhance creatine metabolism during oxygen deprivation to promote tissue resolution and homeostasis. Here, we review recent insights into the creatine kinase pathway, and provide rationale for dietary creatine supplementation in human ischemic and inflammatory pathologies.

(2019) Oral vitamin B 12 supplement is delivered to the distal gut, altering the corrinoid profile and selectively depleting Bacteroides in