Increased levels of catalase and cathepsin V/L2 but decreased TIMP-1 in keratoconus corneas: evidence that oxidative stress plays a role in this disorder

Invest Ophthalmol Vis Sci. 2005 Mar;46(3):823-32. doi: 10.1167/iovs.04-0549.


Purpose: The mRNA levels of antioxidant enzymes, matrix metalloproteinases, cathepsin V/L2, and tissue inhibitor of matrix metalloproteinases (TIMPs) were determined in keratoconus and normal corneas. Protein levels or enzyme activities were analyzed when RNA levels were different.

Methods: A total of 25 physiologic (normal) and 32 keratoconus corneas were studied. mRNAs were analyzed by semiquantitative reverse transcription-polymerase chain reaction and Southern blot analysis. Proteins were assessed by immunohistochemistry and/or Western blot analysis. Catalase activity was measured in corneal extracts. Antioxidant enzymes examined were catalase, superoxide dismutase (SOD)-1, SOD3, glutathione reductase, glutathione S-transferase and aldehyde dehydrogenase 3A1. Degradative enzymes examined were cathepsin V/L2 and matrix metalloproteinase (MMP)-1, -2, -7, -9, and -14. Tissue inhibitor of matrix metalloproteinase (TIMP)-1, -2, and -3 were also examined.

Results: Keratoconus corneas exhibited a 2.2-fold increase of catalase mRNA level (P < 0.01) and 1.8-fold of enzyme activity (P < 0.03); a 1.5-fold increase of cathepsin V/L2 mRNA (P < 0.03) and abnormal protein distribution; and a 1.8-fold decrease of TIMP-1 mRNA (P < 0.05) and 2.8-fold decrease of protein (P < 0.0001) compared with normal (physiologic) corneas. RNA levels for other antioxidant and degradative enzymes were similar between normal and keratoconus corneas.

Conclusions: Keratoconus corneas have elevated levels of cathepsins V/L2, -B, and -G, which can stimulate hydrogen peroxide production, which, in turn, can upregulate catalase, an antioxidant enzyme. In addition, decreased TIMP-1 and increased cathepsin V/L2 levels may play a role in the matrix degradation that is a hallmark of keratoconus corneas. The findings support the hypothesis that keratoconus corneas undergo oxidative stress and tissue degradation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aldehyde Dehydrogenase / genetics
  • Aldehyde Dehydrogenase / metabolism
  • Blotting, Western
  • Catalase / genetics
  • Catalase / metabolism*
  • Cathepsins / genetics
  • Cathepsins / metabolism*
  • Cornea / enzymology*
  • Cysteine Endopeptidases / genetics
  • Cysteine Endopeptidases / metabolism*
  • Fluorescent Antibody Technique, Indirect
  • Gene Expression Regulation, Enzymologic / physiology
  • Glutathione Reductase / genetics
  • Glutathione Reductase / metabolism
  • Glutathione Transferase / genetics
  • Glutathione Transferase / metabolism
  • Humans
  • Keratoconus / enzymology*
  • Keratoconus / genetics
  • Matrix Metalloproteinases / genetics
  • Matrix Metalloproteinases / metabolism
  • Oxidative Stress / physiology*
  • RNA, Messenger / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Superoxide Dismutase / genetics
  • Superoxide Dismutase / metabolism
  • Tissue Inhibitor of Metalloproteinase-1 / genetics
  • Tissue Inhibitor of Metalloproteinase-1 / metabolism*


  • RNA, Messenger
  • Tissue Inhibitor of Metalloproteinase-1
  • Catalase
  • Superoxide Dismutase
  • Aldehyde Dehydrogenase
  • Glutathione Reductase
  • Glutathione Transferase
  • Cathepsins
  • Cysteine Endopeptidases
  • CTSV protein, human
  • Matrix Metalloproteinases