Collagen type XII is undetectable in keratoconus Bowman's layer.

Abstract

Corneal biomechanical failure is the hallmark of keratoconus (KC); however, the cause of this failure remains elusive. Collagen type XII (<i>COL12A1</i>), which localises to Bowman's layer (BL), is thought to function in stress-bearing areas, such as BL. Given the putative protective role of <i>COL12A1</i> in biomechanical stability, this study aims to characterise <i>COL12A1</i> expression in all corneal layers involved in KC. TaqMan quantitative PCR was performed on 31 corneal epithelium samples of progressive KC and myopic control eyes. Tissue microarrays were constructed using full-thickness corneas from 61 KC cases during keratoplasty and 18 non-KC autopsy eyes and stained with an antibody specific to COL12A1. Additionally, <i>COL12A1</i> was knocked out in vitro in immortalised HEK293 cells. <i>COL12A1</i> expression was reduced at transcript levels in KC epithelium compared with controls (ratio: 0.58, p<0.03). Immunohistochemical studies demonstrated that COL12A1 protein expression in BL was undetectable, with reduced expression in KC epithelium, basement membrane and stroma. The apparent absence of COL12A1 in KC BL, together with the functional importance that <i>COL12A1</i> is thought to have in stress bearing areas, suggests that <i>COL12A1</i> may play a role in the pathogenesis of KC. Further studies are necessary to investigate the mechanisms that lead to <i>COL12A1</i> dysregulation in KC.