Expression of tenascin-C splice variants in normal and bullous keratopathy human corneas.

PURPOSE To characterize the expression patterns of tenascin-C (TN-C) splice variants in normal corneas and in those affected by pseudophakic-aphakic bullous keratopathy (PBK-ABK). METHODS Alternatively spliced variants of TN-C mRNA from normal and age-matched human corneas with PBK-ABK were analyzed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot hybridization, using beta2-microglobulin as a housekeeping gene to normalize the samples. Normal and PBK-ABK corneas were studied by immunofluorescence and western blot analysis with antibodies to specific fibronectin type III-like (FN-III) repeats of TN-C. RESULTS Tenascin-C mRNA expression was detected in epithelial, stromal, and endothelial cells of normal and PBK-ABK central corneas, although the protein was seen only in diseased corneas. Assessed by RT-PCR, PBK-ABK corneas expressed approximately three times more total TN-C mRNA than did normal corneas. Four major TN-C mRNA variants (with no FN-III insertional repeats or with retained insertional repeats D, A1, or A1+D) and three minor variants (with retained repeats A1+A2, A1+A2+D, or A1+A2+B+D) were much more abundant in PBK-ABK than in normal corneas. Repeat A1 was more abundant in PBK-ABK TN-C protein than repeats A2, A3, B, or D. Major TN-C variants in PBK-ABK corneas were in the range of 190 kDa to 240 kDa. CONCLUSIONS Expression of TN-C mRNA and protein is higher in PBK-ABK corneas than in normal corneas. This increase mainly concerns relatively small TN-C splice variants that may affect corneal cell adhesion and migration and contribute to the exacerbation of PBK-ABK.