Apolipoprotein J expression in human ocular surface epithelium.

PURPOSE Apolipoprotein J (apoJ) expression has been detected in various mouse mucosal epithelial cells, as well as in the human ciliary body, retina, vitreous humor, and aqueous humor. The purpose of this study was to determine the expression and localization pattern of apoJ mRNA transcripts and protein in the human ocular surface epithelium. METHODS The expression of apoJ mRNA in corneal and conjunctival epithelial cells was investigated by reverse-transcriptase polymerase chain reaction (RT-PCR). mRNA localization in the corneal epithelium and protein localization in corneal and conjunctival epithelia were analyzed by in situ hybridization and immunohistochemistry, respectively. RESULTS The RT-PCR studies demonstrated the expression of apoJ mRNA transcripts in corneal and conjunctival epithelial cells. In situ hybridization analysis revealed that apoJ mRNA signals were detected in all layers of the corneal epithelium, most prominently in the basal cells. Immunohistochemical analysis revealed positive immunostaining for apoJ in the apical cell layers of corneal and conjunctival epithelia. CONCLUSIONS ApoJ is synthesized by and localized in the ocular surface epithelium. This suggests a role for this protein at the tear-ocular surface interface.