Aniridia-related keratopathy : structural changes, signaling pathways and clinical aspects

Aniridia is a congenital autosomal dominant, bilateral, panocular condition, caused by haploinsufficiency of the Pax6 transcription factor. Aniridia-related keratopathy (ARK) significantly affects vision and quality of life in these patients. ARK is a chronic progressive keratopathy comprising limbal stem cell deficiency associated with impaired epithelial cell adhesion, corneal conjunctivalization, epithelial erosions and corneal vascular pannus that typically only appear after childhood. The aims were i) to evaluate the structural changes and ii) cell signaling pathways, including the Notch1, Sonic Hedgehog (SHH), mTOR and Wnt/beta-catenin cell signaling pathways in naïve and surgically treated corneas of aniridia cases with advanced ARK and comparing with normal human adult and fetal corneas and iii) to develop a corneal cell culture model of aniridia. Naïve ARK corneas removed at the time of the first transplantation and ARK corneal buttons removed after a failed keratolimbal allograft and failed centered and decentered transplantations were included. These were compared with normal human adult and fetal (10-11 and 20 weeks) corneas. Sections were studied with immunofluorescence using antibodies against extracellular matrix components in the stroma and in the epithelial basement membrane (collagen I and IV, collagen receptor a11 integrin and laminin a3 chain), markers of fibrosis, wound healing and vascularization (fibronectin, tenascin-C, vimentin, a-SMA and caveolin-1), cell division (Ki-67) and macrophages (CD68); antibodies against Pax6 and keratin 13; and antibodies against elements of the Notch1 (Notch1; Dlk1; Numb), Wnt/beta-catenin (Wnt5a; Wnt7a; beta- catenin), Sonic Hedgehog (Gli1; Hes1) and mTOR (mTOR1; rpS6) signaling pathways. An in vitro cell culture model of mutant PAX6 corneal cells, obtained with CRISPR was created to study the same signaling pathways with Western blot and RT-qPCR. All ARK corneas and transplanted corneal buttons presented similar histopathological changes with irregular epithelium and disruption or absence of epithelial basal membrane. There was a loss of the orderly pattern of collagen lamellae and absence of collagen I in all ARK corneas. Vascularization was revealed in the pannus of all ARK corneas and the changes observed in decentered and centered transplants were analogous. Furthermore, ARK corneas presented analogous signaling pathways changes in the subepithelial pannus and epithelium, with decreased detection of Notch1 signaling pathway and increased presence of the Notch1 inhibitors Numb and Dlk1. Increased detection of Wnt/beta-catenin (enhanced presence of Wnt5a, Wnt7a and beta-catenin), SHH (detection of GLI1 and HES1) and mTOR (identification of mTOR and rpS6) signaling pathways were found in the subepithelial pannus and epithelium of all ARK corneas, when compared to normal controls. In the mutant PAX6 corneal cells, the signaling pathway changes encountered were similar to those found in the ARK patients. The cell signaling pathway dissimilarities encountered in ARK corneas were similar to the pattern found in human fetal corneas with the exception of Notch1. The analogous pathological features of all ARK cases and the similarity in pathway alterations found in all ARK corneas irrespective of being naïve or previously submitted to distinct surgical procedures involving transplantation of limbal stem cells or not, and mutant PAX6 corneal cells, advocates an important role for host specific factors in the pathophysiology of ARK. Moreover, the similar pattern found between fetal human corneas and ARK corneas indicates a less differentiated host milieu in ARK. The present results provide the basis for further studies investigating the possibility of modulating these pathways in order to delay or avoid ARK