Claudin
Family of tetraspan transmembrane proteins forming the sealing strand of epithelial tight junctions; determines paracellular permeability selectivity.
For laboratory and research use only — not for human consumption.
Claudins are a family of 27 tetraspan transmembrane proteins (23-27 kDa) that form the principal sealing element of epithelial and endothelial tight junctions, determining tissue-specific paracellular permeability characteristics. Distinct claudin subtypes assemble into homomeric and heteromeric strands with different pore properties: claudin-1 and -3 form near-impermeable barriers in skin epidermis; claudin-2 and -15 form cation-selective pores relevant to intestinal water and ion transport; claudin-4 and -8 form anion-restricting barriers. In the intestinal epithelium, claudin expression is regulated by pro-inflammatory cytokines (IL-13 upregulates claudin-2; TNF-α downregulates claudin-1) and modulated by zonulin, EGF signalling, and myosin light chain kinase. Loss or redistribution of tight-junction claudins underlies the 'leaky gut' phenotype in coeliac disease, inflammatory bowel disease, and NSAID enteropathy. In peptide research, claudin-4 and occludin preservation is documented for BPC-157 in NSAID-enteropathy models; larazotide indirectly stabilises claudin architecture by blocking zonulin-driven tight-junction disassembly; KPV supports tight-junction protein expression through NF-κB pathway suppression. Immunofluorescence localisation is the standard readout.