Tight junction transmembrane protein claudin subtype expression and distribution in human corneal and conjunctival epithelium.

The combination of the tight junction transmembrane protein claudin subtypes is one of the most important determinants of variations in the tightness of individual paired tight junction strands. The barrier function of corneal epithelium is much stronger than that of conjunctival epithelium. In this study, the expression and cellular distribution of claudin species in in vivo human corneal and conjunctival epithelium were investigated. Reverse transcription-polymerase chain reaction was used to reveal the claudin mRNA. Immunohistochemistry was used to determine the tissue distribution of tight junction-related proteins and MUC5AC. Transcripts for claudin-1, -2, -3, -4, -7, -9, and -14 were identified in human corneal epithelium. Transcripts for claudin-1, -2, -4, -7, -9, -10, and -14 were identified in human conjunctival epithelium. By immunohistochemistry, claudin-1, -4, and -7 were found to be localized at the membrane of human corneal and conjunctival epithelial cells. In human conjunctival epithelium, claudin-10 staining was observed at several, but not all, apical epithelial cell-to-goblet cell junctions. Claudin-1, -4, and -7 are expressed in corneal and conjunctival epithelia. Claudin-10 is prominent at several junctions between apical epithelial cells and goblet cells in conjunctival epithelium. Except for claudin-10 expression in conjunctival epithelium, the claudin subtype expressions of corneal and conjunctival epithelia are similar. Therefore, there must be a difference between these two epithelial types with regard to the specific ratio of claudin subtypes expressed or their phosphorylation status. The distribution of goblet cells in conjunctival epithelium also influences the difference in barrier function.