Epithelial tight junction (TJ) is the primary component of intestinal mucosal barrier function that prevents diffusion of toxins, allergens and pathogens from the gut lumen into mucosa and eventually to systemic circulation. Disruption of TJs and permeability to injurious factors is associated with many gastrointestinal (GI) diseases, including radiation-induced GI syndrome (RIGS). Therefore, understanding the structure and regulation of TJs is essential to our understanding of the pathogenesis of many GI diseases and design of therapeutic strategies in treatment of the diseases. Occludin is one of the transmembrane proteins of TJs, the expression and distribution of which is altered in many GI diseases. The precise function of occludin is unclear. Out studies so far have identified a phosphorylation hotspot in the C-terminal domain of occludin, which we named as ?Occludin Regulatory Motif (ORM)?. Our preliminary studies show that ORM may be required for regulation of TJ integrity by interacting with specific proteins, such as MAP7, especially during radiation-induced injury. Our preliminary data also show that probiotic, Lactobacillus casei (L. casei) attenuates radiation-induced barrier dysfunction by a mechanism involving epidermal growth factor receptor (EGFR) tyrosine kinase activity. On the basis of above information it is hypothesized that: a) ?Occludin Regulatory Motif (ORM)? plays a role in regulation of tight junction dynamics in the intestinal epithelium, b) occludin- MAP7 interaction, mediated by oxidative stress and JNK2-cSrc signaling, plays a role in radiation- induced TJ disruption in the intestinal epithelium and c) oligopeptide factor produced by Lactobacillus plantarum attenuates radiation-induced tight junction disruption by an EGF receptor-dependent mechanism. Using both mouse models and Caco-2 cell monolayers we will determine that: 1) ORM is required for regulation of occludin mobility and tight junction dynamics, 2) Regulatory proteins interact with ORM by a phosphorylation-dependent mechanism, 3) ORM-MAP7 interaction regulates TJ dynamics by a phosphorylation-dependent mechanism, 4) ORM-MAP7 interaction is involved in radiation-induced TJ disruption and barrier dysfunction, 5) Oxidative stress and JNK2-cSrc signaling mediate radiation-induced alteration of ORM-MAP7 interaction and TJ disruption, 6) L. plantarum soluble factor attenuates radiation-induced tight junction disruption by suppressing oxidative stress, JNK2-cSrc signaling and occludin-MAP7 interaction, 7) EGF receptor transactivation is involved in L. plantarum-mediated TJ protection from radiation, and 8) Oligopeptide factor in L. plantarum is responsible for epithelial protection from radiation injury. Out come of these studies will open a new mechanism in epithelial tight junction regulation and therapeutic strategies for treatment of RIGS.

Public Health Relevance

On the basis of our recent publications and our preliminary data we hypothesized that occludin and its regulatory motif play a crucial role in regulation of tight junction in the intestinal epithelium under physiologic and pathophysiologic conditions. We propose to conduct studies to establish that regulatory region of occludin interacts with specific proteins such as MAP7 by a phosphorylation-dependent mechanism, and this interaction is required for occludin dynamics and TJ regulation. We plan to conduct studies to demonstrate that such occludin-regulated process is involved in radiation-induced intestinal mucosal barrier dysfunction, and this can be prevented by Lactobacillus plantarum soluble factor.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
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Clinical, Integrative and Molecular Gastroenterology Study Section (CIMG)
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Greenwel, Patricia
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University of Tennessee Health Science Center
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Meena, Avtar S; Shukla, Pradeep K; Sheth, Parimal et al. (2018) EGF receptor plays a role in the mechanism of glutamine-mediated prevention of alcohol-induced gut barrier dysfunction and liver injury. J Nutr Biochem 64:128-143
Shukla, Pradeep K; Meena, Avtar S; Rao, Vaishnavi et al. (2018) Human Defensin-5 Blocks Ethanol and Colitis-Induced Dysbiosis, Tight Junction Disruption and Inflammation in Mouse Intestine. Sci Rep 8:16241
Shukla, Pradeep K; Meena, Avtar S; Manda, Bhargavi et al. (2018) Lactobacillus plantarum prevents and mitigates alcohol-induced disruption of colonic epithelial tight junctions, endotoxemia, and liver damage by an EGF receptor-dependent mechanism. FASEB J :fj201800351R
Manda, Bhargavi; Mir, Hina; Gangwar, Ruchika et al. (2018) Phosphorylation hotspot in the C-terminal domain of occludin regulates the dynamics of epithelial junctional complexes. J Cell Sci 131:
Sahay, Peeyush; Shukla, Pradeep K; Ghimire, Hemendra M et al. (2017) Quantitative analysis of nanoscale intranuclear structural alterations in hippocampal cells in chronic alcoholism via transmission electron microscopy imaging. Phys Biol 14:026001
Gangwar, Ruchika; Meena, Avtar S; Shukla, Pradeep K et al. (2017) Calcium-mediated oxidative stress: a common mechanism in tight junction disruption by different types of cellular stress. Biochem J 474:731-749
Chaudhry, Kamaljit K; Shukla, Pradeep K; Mir, Hina et al. (2016) Glutamine supplementation attenuates ethanol-induced disruption of apical junctional complexes in colonic epithelium and ameliorates gut barrier dysfunction and fatty liver in mice. J Nutr Biochem 27:16-26
Samak, Geetha; Gangwar, Ruchika; Meena, Avtar S et al. (2016) Calcium Channels and Oxidative Stress Mediate a Synergistic Disruption of Tight Junctions by Ethanol and Acetaldehyde in Caco-2 Cell Monolayers. Sci Rep 6:38899
Shukla, Pradeep K; Chaudhry, Kamaljit K; Mir, Hina et al. (2016) Chronic ethanol feeding promotes azoxymethane and dextran sulfate sodium-induced colonic tumorigenesis potentially by enhancing mucosal inflammation. BMC Cancer 16:189
Mir, Hina; Meena, Avtar S; Chaudhry, Kamaljit K et al. (2016) Occludin deficiency promotes ethanol-induced disruption of colonic epithelial junctions, gut barrier dysfunction and liver damage in mice. Biochim Biophys Acta 1860:765-74

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