Induction of Indoleamine 2,3-dioxygenase by Interferon-Gamma in Human Lens Epithelial Cells: Apoptosis Through the Formation of 3-hydroxykynurenine

Int J Biochem Cell Biol. 2010 Sep;42(9):1446-54. doi: 10.1016/j.biocel.2010.04.014. Epub 2010 May 6.

Abstract

Interferon-gamma (IFN-gamma) is known to cause apoptosis of lens epithelial cells and cataract formation, but the molecular mechanisms underlying these effects are unknown. IFN-gamma induces the expression of indoleamine 2,3-dioxygenase (IDO) and thereby enhances the production of kynurenines from l-tryptophan. The present study was designed to investigate the role of IDO and kynurenines in the IFN-gamma-mediated apoptosis of lens epithelial cells and to determine the signaling pathways involved. IFN-gamma stimulated the synthesis of IDO and activated the JAK-STAT1 signaling pathway in human lens epithelial cells (HLE-B3) in a dose-dependent manner. Meanwhile, fludarabine, an inhibitor of STAT1 activation, blocked IFN-gamma-mediated IDO expression. N-Formylkynurenine, kynurenine (Kyn) and 3-hydroxykynurenine (3OHKyn) were detected in cells, with 3OHKyn concentrations being higher than those of the other kynurenines. The intracellular production of kynurenines was completely blocked by 1-methyl-DL-tryptophan (MT), an inhibitor of IDO. Kyn- and 3OHKyn-modified proteins were detected in IFN-gamma-treated cells. The induction of IDO by IFN-gamma in HLE-B3 cells caused increases in intracellular ROS, cytosolic cytochrome c and caspase-3 activity, along with a decrease in protein-free thiol content. These changes were accompanied by apoptosis. At equimolar concentrations, 3OHKyn caused higher levels of apoptosis than the other kynurenines in HLE-B3 cells. MT and a kynurenine 3-hydroxylase inhibitor (Ro61-8048) effectively inhibited IFN-gamma-mediated apoptosis in HLE-B3 cells. Our results show that the induction of IDO by IFN-gamma is JAK-STAT1 pathway-dependent and that this induction causes 3OHKyn-mediated apoptosis in HLE-B3 cells. These data suggest that IDO-mediated kynurenine formation could play a role in cataract formation related to chronic inflammation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects*
  • Blotting, Western
  • Cell Line
  • Chromatography, High Pressure Liquid
  • Electrophoresis, Polyacrylamide Gel
  • Enzyme Activation / drug effects
  • Epithelial Cells / cytology*
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism*
  • Humans
  • Immunohistochemistry
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / metabolism*
  • Interferon-gamma / pharmacology*
  • Kynurenine / analogs & derivatives*
  • Kynurenine / metabolism
  • Lens, Crystalline / cytology*

Substances

  • Indoleamine-Pyrrole 2,3,-Dioxygenase
  • 3-hydroxykynurenine
  • Kynurenine
  • Interferon-gamma