Purpose: To study the cellular distribution of extracellular matrix metalloproteinase inducer (EMMPRIN; CD147) in the human eye and the corneal and retinal pigment epithelium cell lines and its possible existence as a soluble protein in ocular fluids.
Methods: Immunohistochemistry was performed on human eyes and for cell cultures. Different EMMPRIN isoforms were analyzed by Western blotting in ocular fluids.
Results: EMMPRIN immunostaining could be detected in the corneal and conjunctival epithelium, the endothelium, and in the stromal keratocytes, the retinal pigment epithelium, several retinal layers and nerve fibers in the optic nerve head. Both cell lines deposit EMMPRIN on the cell membranes. Soluble EMMPRIN could also be detected in the tear fluid, aqueous humor, and vitreous samples in the form of multiple immunoreactive species.
Conclusions: EMMPRIN is specifically expressed in the human eye only by certain tissue structures, thus suggesting specialized functions. The protein also exists naturally in soluble forms in ocular fluids representing presumably monomeric and multimeric forms, a notion that confirm and further extends its previously known role mainly as a transmembrane protein. These findings suggest that EMMPRIN can regulate not only cell surface functions in the human eye but also certain peri- and extracellular functions.