Up-Regulation of Claudin-6 in the Distal Lung Impacts Secondhand Smoke-Induced Inflammation

Abstract

It has long been understood that increased epithelial permeability contributes to inflammation observed in many respiratory diseases. Recently, evidence has revealed that environmental exposure to noxious material such as cigarette smoke reduces tight junction barrier integrity, thus enhancing inflammatory conditions. Claudin-6 (Cldn6) is a tetraspanin transmembrane protein found within the tight junctional complex and is implicated in maintaining lung epithelial barriers. To test the hypothesis that increased Cldn6 ameliorates inflammation at the respiratory barrier, we utilized the Tet-On inducible transgenic system to conditionally over-express Clnd6 in the distal lung. Cldn6 transgenic (TG) and control mice were continuously provided doxycycline from postnatal day (PN) 30 until euthanasia date at PN90. A subset of Cldn6 TG and control mice were also subjected to daily secondhand tobacco smoke (SHS) via a nose only inhalation system from PN30-90 and compared to room air (RA) controls. Animals were euthanized on PN90 and lungs were harvested for histological and molecular characterization. Bronchoalveolar lavage fluid (BALF) was procured for the assessment of inflammatory cells and molecules. Quantitative RT-PCR and immunoblotting revealed increased Cldn6 expression in TG vs. control animals and SHS decreased Cldn6 expression regardless of genetic up-regulation. Histological evaluations revealed no adverse pulmonary remodeling via Hematoxylin and Eosin (H&E) staining or any qualitative alterations in the abundance of type II pneumocytes or proximal non-ciliated epithelial cells via staining for cell specific propeptide of Surfactant Protein-C (proSP-C) or Club Cell Secretory Protein (CCSP), respectively. Immunoblotting and qRT-PCR confirmed the differential expression of Cldn6 and the pro-inflammatory cytokines TNF-α and IL-1β. As a general theme, inflammation induced by SHS exposure was influenced by the availability of Cldn6. These data reveal captivating information suggesting a role for Cldn6 in lungs exposed to tobacco smoke. Further research is critically necessary in order to fully explain roles for tight junctional components such as Cldn6 and other related molecules in lungs coping with exposure.

Knockdown of CLAUDIN-6 Inhibited Apoptosis and Induced Proliferation of Bovine Cumulus Cells

“…Generally, CLDN6 is a tetraspanin transmembrane protein located within the tight junctional complex [ 22 ], in the cell membrane of primary tumors, gastric cancer cells and mouse stem cells [ 23 , 24 ]. In mouse neonatal kidneys, CLDN6 was highly expressed and distributed on the membrane of proximal renal tubules, thick ascending ramus, distal convoluted tubules and collecting tubules [ 10 ].…”

CLDN6: From Traditional Barrier Function to Emerging Roles in Cancers

“…CLDN6 expression is inhibited by cigarette smoke and decreased oxygen tension via HIF-1α, culminating in barrier perturbation [21]. CLDN6 overexpression impacted secondhand tobacco smoke (SHS)-induced inflammation in the lung by reducing total bronchoalveolar lavage fluid (BALF) protein, cells, and secreted pro-inflammatory cytokines [40]. Similarly, CLDN6 decreases fine diesel particulate matter (DPM)-induced pulmonary inflammation in the same way [41].…”

CLDN6 inhibited cellular biological function of nonsmall cell lung cancer cells through suppressing aerobic glycolysis via the RIP1/ASK1/JNK axis

“…[7] Abnormal expression of CLDN6 disrupts the integrity of TJs via various mechanisms [8] and exerts an important role in the occurrence and development of tumors. [9][10][11] Furthermore, CLDN6 was reported to effectively improve lung inflammation [12,13] and regulates the development of chronic obstructive pulmonary disease. [14] Importantly, low CLDN6 expression was reported to be closely associated with the poor prognosis of NSCLC.…”