CLDN2

CLDN2 (claudin-2) encodes a tight junction transmembrane protein that forms cation-selective and water-permeable paracellular channels in epithelial tissues, particularly within kidney proximal tubules and the gastrointestinal tract, where it regulates epithelial permeability and ion homeostasis^[1][2]. Mechanistically, CLDN2 functions as a pore-forming claudin that contributes to Na⁺, water, and Ca²⁺ transport, and its expression is controlled by multiple signaling pathways and transcriptional regulators that coordinate tight junction remodeling and epithelial barrier function^[1][3]. In disease settings, CLDN2 expression is frequently dysregulated in inflammation, fibrosis, and cancer, and altered CLDN2 abundance correlates with changes in paracellular permeability, epithelial barrier integrity, and cellular behaviors including proliferation and migration^[1][4]. In inflammatory bowel disease, CLDN2 is strongly expressed in inflamed crypt epithelium and is associated with disrupted barrier properties, supporting its use as an experimental marker of epithelial leakiness and inflammatory remodeling^[4]. Compared with barrier-forming claudin family members such as CLDN3 and CLDN4, CLDN2 primarily generates a selective paracellular channel rather than a sealing barrier, making it a functionally distinct isoform within tight junction complexes^[4][6]. Experimental studies using knockout, overexpression, and RNA interference approaches have demonstrated that CLDN2 directly regulates epithelial transport properties and intestinal calcium absorption, providing valuable models for investigating epithelial physiology and disease-associated barrier dysfunction^[1][3].