Transforming Growth Factor-β Signaling Pathway Activation in Keratoconus

PURPOSE: To assess the presence of transforming growth factor-beta (TGF beta) pathway markers in the epithelium of keratoconus patient corneas. DESIGN: Retrospective, comparative case series of laboratory specimens. METHODS: Immunohistochemistry results for TGF beta 2, total TGF beta, mothers against decacentaplegic homolog (Smad) 2, and phosphorylated Smad2 was performed on formalin-fixed, paraffin-embedded sections of keratoconus patient corneas and normal corneas from human autopsy eyes. Keratoconus patient corneas were divided in two groups, depending on their severity based on keratometer readings and pachymetry. Autopsy controls were age-matched with the keratoconus cases. Immunohistochemistry signal quantification was performed using automated software. Real-time reverse-transcriptase polymerase chain reaction was performed on total ribonucleic acid of epithelium of keratoconus patient corneas and autopsy control corneas. RESULTS: Immunohistochemistry quantification showed a significant increase in mean signal in the group of severe keratoconus cases compared with normal corneas for TGF beta 2 and phosphorylated Smad2 (P <.05). Immunohistochemistry analysis using antibodies against total TGF beta and Smad2 did not show any significant increase in the keratoconus cases versus the autopsy controls. Reverse-transcriptase polymerase chain reaction exhibited elevated messenger ribonucleic acid levels of Smad2 and TGF beta 2 in severe keratoconus corneal epithelium. CONCLUSIONS: This work shows increased TGF beta pathway markers in severe keratoconus cases and provides the rationale for investigating TGF beta signaling further in the pathophysiology of keratoconus. (Am J Ophthalmol 2011;151:752-759. (C) 2011 by Elsevier Inc. All rights reserved.)