cyclin-d1 and Keratoconus

Keratoconus (KC) is a corneal dystrophy characterized by progressive ectasia that leads to severe visual impairment and remains one of the leading indications for corneal transplantation. The etiology is believed to be multifactorial and alterations have been documented in the biomechanical, biochemical and ultrastructural characteristics of the cornea. While the exact site of disease origin is still debated, changes in the corneal epithelium are believed to occur even before the disease is clinically manifested. In this study we investigate the possible role of β-catenin as mechanotransducer in KC corneal epithelium. The sheets of corneal epithelium removed from keratoconic eyes when they underwent collagen crosslinking as a therapeutic procedure were used for this study. The healthy corneal epithelium of patients undergoing Laser Refractive Surgery for the correction of their refractive error, served as controls. Immunoblotting and tissue immunofluorescence studies were performed on KC epithelium to analyse the expression and localization of β-catenin, E-cadherin, ZO1, α-catenin, Cyclin D1, α-actinin, RhoA, and Rac123. Co-immunoprecipitation of β-catenin followed by mass spectrometry of KC epithelium was performed to identify its interacting partners. This was further validated by using epithelial tissues grown on scaffolds of different stiffness. Histology data reported breaks in the Bowman's layer in KC patients. We hypothesize that these breaks expose the epithelium to the keratoconic corneal stroma, which, is known to have a decreased elastic modulus and that β-catenin acts as a mechanotransducer that induces structural changes such as loss of polarity (Syntaxin3) and barrier function (ZO1) through membrane delocalization. The results of our study strongly suggest that β-catenin could be a putative mechanotransducer in KC epithelium, thus supporting our hypothesis.

Topics: Actinin; Adolescent; Adult; alpha Catenin; beta Catenin; Cadherins; Cyclin D1; Epithelium, Corneal; Female; Humans; Immunoprecipitation; Keratoconus; Male; Mass Spectrometry; Mechanotransduction, Cellular; rhoA GTP-Binding Protein; Young Adult; Zonula Occludens-1 Protein

The precise role of a normal keratocyte in maintaining corneal structural integrity is unclear; it is generally considered to remain quiescent at the end of cell division. Given that integrins are essential for cell/extracellular matrix interactions, the authors tested the hypothesis that integrin expression by keratocytes is essential for corneal structure and function.. Using a tamoxifen-dependent cre recombinase expressed under the control of a fibroblast-specific promoter/enhancer, the authors conditionally deleted the integrin β1 (Itgb1) gene in mouse keratocytes during the postnatal matrix maturation phase of the cornea. The effects of this deletion were monitored histologically and by macroscopic observation of the cornea.. The resultant cornea shows an initial thinning of the stroma, reduced space between collagen fibrils, loss of epithelial layers and subsequent edema, thickening of Descemet's membrane, and degenerative changes in the endothelial cell layer, with eventual scarring. These pathologic changes have some similarities to human corneal disease keratoconus. The phenotype did not develop when Itgb1 was deleted after complete corneal maturation.. Loss of integrin β1 expression in keratocytes during the phase of stromal maturation results in corneal thinning and edema. Keratocyte-ECM interaction is essential for matrix maturation and thus in the maintenance of corneal structural integrity. This model has relevance in understanding corneal diseases such as keratoconus.

Topics: Animals; Cells, Cultured; Corneal Edema; Corneal Stroma; Cyclin D1; Endothelium, Corneal; Epithelium, Corneal; Extracellular Matrix; Female; Fibroblasts; Gene Deletion; Integrases; Integrin beta1; Keratoconus; Male; Mice; Mice, Knockout; Microscopy, Fluorescence; Polymerase Chain Reaction