Induction of indoleamine 2,3-dioxygenase by interferon-gamma in human lens epithelial cells: apoptosis through the formation of 3-hydroxykynurenine.
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.
Mailankot
Maneesh
M
Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, United States.
Nagaraj
Ram H
RH
D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D004847:Epithelial Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology*; D007737:Kynurenine / Q000031:analogs & derivatives* / Q000378:metabolism; D007908:Lens, Crystalline / Q000166:cytology*
D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; C005045:3-hydroxykynurenine; D007737:Kynurenine; D007371:Interferon-gamma