Copyright@ Sabah Nisar, Sheema Hashem | Biomed J Sci & Tech Res | BJSTR. MS.ID.003637. 16048 Mini Review ISSN: 2574 -1241 Claudins and Intestinal Barrier Function; The Positive Side Sabah Nisar # , Sheema Hashem # and Ajaz A Bhat* Translational Medicine, Qatar *Corresponding author: Ajaz A Bhat, Translational Medicine, Research Branch, Sidra Medicine, Qatar # Both authors contributed equally DOI: 10.26717/BJSTR.2019.21.003637 Introduction Background The intestinal barrier is a thick lining of the gut that is composed of different types of epithelial cells. These epithelial cells act as selective barriers between internal and external cellular environments that allows control of pathogens and other foreign substances. Epithelial cells also control selective movement of ions and solutes. Underneath the epithelial layer, there is a thin layer of connective tissue known as the lamina propria which separates the innermost epithelial cells from the smooth muscle tissue called muscularis mucosa [1]. The epithelial barrier is composed of Tight Junctions (TJ) and adherens junctions, collectively known as Apical Junctional Complex (AJC). AJC is a multifunctional apparatus that plays an important role in cell polarization and tissue differentiation [2] and regulates the structure and function of the cell [3]. Most importantly, the AJC provides strong adhesion between adjacent cells. Other intercellular junctions that reside below the AJC are desmosomes and gap junctions. These intercellular junctions mediate intercellular adhesion and allow cross talk between adjacent epithelial cells [4,5]. The immune cells such as exudate macrophages, eosinophils, neutrophils, eosinophils, and T- cells, help in eliminating antigens and potential pathogens that are resistant to the effector mechanisms of the resident cells of the local immune system and aid in the orchestration of local immune response in the intestinal mucosa [6]. A dense layer of mucus layer that covers the intestinal epithelium prevents the translocation of pathogenic microorganisms and gut microbiota in the underlying intestinal tissues [7,8]. and the absence of mucin, a glycoprotein in the mucus layer can lead to intestinal inflammation that predispose an Individual to Various Gastrointestinal (GI) diseases and promote the development of colorectal cancer [9]. Claudins along with occludins are large family of transmembrane proteins that are important components of the TJs. As TJs are the vital components of the epithelial barrier, they are under a constant threat from pro-inflammatory mediators and pathogenic bacteria and viruses [10]. Different claudins perform different Received: September 22, 2019 Published: September 30, 2019 Citation: Sabah Nisar, Sheema Hashem, Ajaz A Bhat. Claudins and Intestinal Barrier Function; The Positive Side. Biomed J Sci & Tech Res 21(4)-2019. BJSTR. MS.ID.003637. ARTICLE INFO Abstract Epithelial cell polarity is defined, in part, by Apical Junctional Complex (AJC) that separates the plasma membrane into the apical domain and the basolateral domain. Tight junctions are integral to AJC and form the border between the apical and basolateral cell surface domains in polarized epithelia and support the maintenance of cell polarity. Tight junctions also play an important role in cell signaling mechanisms essential for cell proliferation, migration, differentiation and survival. The claudins, which constitute a family of at least 24 members, are the main structural components of the tight junctions, expressed in a tissue-specific manner and their composition determines the ion selectivity of the paracellular pathway. Any alteration or disruption in claudins leads to disorder of epithelial cell polarity and defects in junction formation or maintenance which in turn results in various pathophysiological conditions like inflammation and cancer. This mini review discusses the positive relationship between claudins and intestinal barrier function under normal physiological conditions and how the dysregulation/mislocalization of claudins can affect the intestinal permeability under pathological conditions.