Altered Signaling Pathways in Aniridia-Related Keratopathy

Abstract

PURPOSE. To study the Notch1, Wnt/beta-catenin, sonic hedgehog (SHH), and mammalian target of rapamycin (mTOR) cell signaling pathways in naïve and surgically treated corneas of aniridia cases with advanced aniridia-related keratopathy (ARK). METHODS.Two naïve corneal buttons from patients with advanced ARK submitted to penetrating keratoplasty for the first time, one corneal button from an ARK patient that had undergone a keratolimbal allograft (KLAL), two corneal buttons from ARK patients who had previously undergone centered or decentered transplantation, and two adult healthy control corneas were processed for immunohistochemistry in this descriptive study. Antibodies specific against elements of the Notch1 (Notch1; Dlk1; Numb), Wnt/beta-catenin (Wnt5a; Wnt7a; beta-catenin), SHH (glioma-associated oncogene homolog [Gli1]; Hes1), and mTOR (mTOR1; ribosomal protein S6 [rpS6]) signaling pathways were used as well as antibodies against PAX6 and keratin 13 (Krt13). RESULTS.All ARK corneas presented signs of conjunctivalization and analogous signaling pathway changes in the subepithelial pannus and epithelium, with decreased detection of the Notch1 signaling pathway and an increased presence of the Notch1 inhibitors Numb and Dlk1. Increased detections 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 with normal controls. CONCLUSIONS.The similarity in pathway alterations found in all ARK corneas, irrespective of limbal stem cell transplantation, further supports the discussion on the role of host-specific factors and limbal stem cell deficiency in ARK.

Aniridia-related Keratopathy Relevant Cell Signaling Pathways in Human Fetal Corneas

“…This cell signaling pathway has a very diverse 32 and its presence is enhanced in the epithelium and pannus of corneas with advanced ARK. 7 In the present study we showed that in fetal corneas at 10-11 wg and 20 wg, Wnt5a, and Wnt7a were abundantly identified in the corneal epithelial cells and stroma, whereas their presence was practically limited to the epithelium in normal adult corneas, as assessed by immunostaining. Upregulation of this signaling pathway in fetal corneas (as shown by both immunolabelling and gene expression analysis), was similar to what has been described in other ocular tissues during eye development.…”

“…19 We have previously shown that Dlk1 activation is increased in ARK corneal epithelial cells and stroma. 7 Numb, another important negative regulator of Notch1, is also upregulated in ARK corneas. 7 Determination of limbal stem cell fate is regulated by the Notch1 and Wnt/β-catenin signaling pathways and are essential during normal tissue development and regeneration.…”

“…7 Numb, another important negative regulator of Notch1, is also upregulated in ARK corneas. 7 Determination of limbal stem cell fate is regulated by the Notch1 and Wnt/β-catenin signaling pathways and are essential during normal tissue development and regeneration. 16,20 The extracellular ligands Wnt5a and Wnt7a stimulate the Wnt/β-catenin signaling cascade, which leads to proliferation of corneal limbal stem cells 21 , and is increased in ARK corneas.…”

“…9,12 Notch1, Wnt/β-catenin, SHH, and mTOR cell signaling pathways are essential for eye development, regulate both cell proliferation and homeostasis in mammals and are altered in ARK corneas. 7,[13][14][15][16] The Notch1 signaling pathway coordinates corneal epithelial repair, vertical migration and regulation of basal corneal epithelial cells. 35 In the central corneal epithelium, these processes depend on transient amplifying cells (TAC), which have high migratory and proliferative capacity.…”

“…16,20 The extracellular ligands Wnt5a and Wnt7a stimulate the Wnt/β-catenin signaling cascade, which leads to proliferation of corneal limbal stem cells 21 , and is increased in ARK corneas. 7 β catenin is important for the regulation of epithelial differentiation and stratification. 22 The SHH pathway regulates maintenance of cell polarity, cell differentiation and proliferation and leads to activation of the glioma-associated oncogene homolog (Gli1) transcription factor that controls cell growth and survival.…”