Purpose: To determine if human corneal and conjunctival epithelial synthesize MUC1 mucin, a membrane-spanning mucin present in a variety of simple epithelia.
Methods: Reverse transcription-polymerase chain reaction (RT-PCR) was carried out to examine the expression of MUC1 mRNA by epithelial cells, using total cellular RNA prepared from cultured corneal epithelial cells and conjunctival epithelial cells stripped from the ocular surface with nitrocellulose filter paper. Northern blot analysis was performed to examine the transcription of MUC1 gene in cultured corneal epithelial cells. In situ hybridization histochemistry was performed to determine distribution of MUC1 mRNA in ocular surface epithelium. Human milk fat globule antibody (HMFG-1) and monoclonal antibody 139H2, which are specific for MUC1 core protein, were used in immunoblot analysis, immunohistochemistry, or both, to determine the presence and distribution of MUC1.
Results: MUC1 mRNA was detected in cultured corneal and ex vivo conjunctival epithelial cells by RT-PCR. Northern blot analysis showed production of two different sizes of transcripts in the cultured corneal epithelium. Expression of MUC1 mRNA was observed in all layers of corneal epithelium. By immunoblot analysis, HMFG-1 binding (> 200 kd) was detected in human cultured corneal epithelium, and its binding was enhanced by neuraminidase pretreatment. Immunohistochemically, HMFG-1 binding was observed along the apical membranes of corneal epithelium after neuraminidase pretreatment. In the conjunctiva, HMFG-1 and 139H2 binding were detected in the basal region and sporadically on the apical surface, but not in the goblet cells.
Conclusions: The stratified epithelia of the cornea and conjunctiva synthesize MUC1 mucin. This transmembrane mucin may have a role in tear film spread and may prevent adhesion of foreign debris, cells, or pathogens to the ocular surface.