Expression of Lubricin mRNA and protein in human ocular surface tissues

Purpose Friction is an inherent potential source of wounding for ocular surface tissues during the blink and bulbus movements and is identified as a major contributor to ocular surface disease of the dry eye type. The expression of lubricin, a boundary lubricant in articulating joints that protects against frictional forces, cell adhesion and protein deposition, was investigated at the ocular surface. Methods Human corneal, conjunctival and control cartilage tissues were fixed with 4% paraformaldehyde, embedded in paraffin, sectioned serially, exposed to antigen retrieval buffers, and stained for lubricin by immunohistochemistry (IHC) with a rabbit polyclonal anti‐human lubricin antibody. Several negative and positive controls were performed. Respective fresh tissues were analysed by reverse transcriptase polymerase chain reaction (RT‐PCR) in order to verify the presence of the mRNA. Results The mRNA for lubricin was found in human corneal and conjunctival cell lines and in complete ocular surface tissues similar to cartilage. The mRNA is translated and expressed into lubricin protein and protein staining was observed along the complete corneal and conjunctival epithelial surface, most strongly expressed in the corneal epithelium . The specificity of staining was verified in several positive and negative controls including use of irrelevant antibodies and preincubation of the anti‐lubricin antibody with a pure peptide, which had served to generate the antibody. Conclusion These findings verify that lubricin is synthesized and expressed by epithelial cells of the human cornea and conjunctiva and conceivably serves protective functions against frictional forces at the human ocular surface similar to the joint.