The presence and suggested role of mesothelial proteins in the human corneal endothelium

Abstract

Abstract Purpose To determine whether proteins that are characteristic of the human mesothelial cell phenotype are expressed in human corneal endothelium. Methods Cadaverous human corneo‐scleral discs and pathological corneal specimens (melted and rejected corneas) were used. The detection of mesothelin, proteinase inhibitor‐9 (PI‐9), calretinin and HBME‐1 protein (a membrane protein of mesothelial cells) was performed on cryosections and corneal endothelial imprints using indirect immunofluorescent or enzymatic immuncytochemistry. The staining intensity was assessed using fluorescent or light microscopy, and the percentage of positive cells was calculated. Semi‐quantitative RT PCR of PI‐9, mesothelin and calretinin was performed using mRNA isolated from endothelial imprints. Results A strong signal for mesothelin was present in the corneal epithelium, while less intensive staining was visible in the endothelium. These results were confirmed using qRT‐PCR. Immunostaining for PI‐9 was observed in almost all corneal epithelial cells and in approximately 50% of the endothelial cells. An increased number of PI‐9‐positive cells was detected in stromal infiltrates of most melted corneal explants, while almost no positivity was observed in rejected explants. Calretinin was detected in the corneal epithelium and less intensively in the corneal endothelium, where both cytoplasmic and nuclear localisation were demonstrated. HBME‐1 antibody strongly stained the corneal endothelium and stromal keratocytes. Conclusion The proteins expressed constitutively in mesothelial cells (PI‐9, mesothelin, calretinin and HBME‐1 protein) are present in adult human corneal endothelium, confirming that this layer expresses markers typical of mesothelial cells.