Modulation of keratin and connexin expression in limbal epithelium expanded on denuded amniotic membrane with and without a 3T3 fibroblast feeder layer.

PURPOSE Based on the knowledge that limbal epithelial stem cells (SCs) do not express keratin-3 (K3), connexin (Cx)43, and Cx50, a study was conducted to investigate amniotic membrane (AM) culturing conditions that promote limbal SC expansion. METHODS Human limbal epithelium was expanded on intact and epithelially denuded AM, with or without a 3T3 feeder layer, and subsequently transplanted to nude mice to induce epithelial stratification and differentiation. Immunostaining and Western blot analysis were used to determine protein expression of K3, Cx43, and Cx50. Expression of integrin-alpha3, -beta1, -alpha6, and -beta4 was investigated by immunostaining. RESULTS Protein levels of K3, Cx43, and Cx50 in limbal epithelium on intact AM was lower than those on denuded AM. Addition of 3T3 to denuded AM increased the level of Cx43 but decreased that of Cx50. After xenotransplantation, the basal layer of the resultant stratified epithelium on intact AM did not express K3, Cx43, and Cx50, whereas that on denuded AM expressed all three markers. The addition of 3T3 resulted in positive staining of Cx43 and K3 but negative staining of Cx50 in the basal epithelium. After stratification, integrin expression was detected at the basal epithelium-amniotic basement membrane interface in all three culture conditions. CONCLUSIONS Limbal cultures on intact AM retain a limbal epithelial phenotype, whereas those on denuded AM differentiate into a corneal phenotype. The addition of 3T3 slows but does not prevent corneal differentiation on denuded AM. Such a difference may involve integrin-mediated extracellular matrix interactions.