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Oxidant-induced apoptosis in human retinal pigment epithelial cells: dependence on extracellular redox state
Shunai Jiang1, Siobhan E Moriarty-Craige, Michael Orr
1Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, USA.
Purpose:
To test whether variation in extracellular cysteine (Cys) redox potential (E(h)) over the physiologic range occurring in human plasma affects oxidant-induced apoptosis in cultured human retinal pigment epithelial (hRPE) cells.
Methods:
The hRPE cells were incubated in culture medium with E(h) established over the range of -16 mV (most oxidized) to -158 mV (most reduced) by adding different concentrations of Cys and cystine (CySS) with constant total Cys equivalents. Apoptosis was induced with tert-butylhydroperoxide (tBH).
Results:
The hRPE cells were sensitized to tBH-induced apoptosis in the more oxidized extracellular conditions (E(h) > -55 mV) compared with the reduced conditions (E(h) < -89 mV). Loss of mitochondrial membrane potential (Deltapsi(m)), release of cytochrome c, and activation of caspase 3 after tBH treatments all increased under the more oxidized conditions. However, the extracellular redox state did not affect expression of Fas or FasL in hRPE cells.
Conclusions:
The hRPE cells that are exposed to a more oxidized extracellular redox environment have increased susceptibility to oxidant-induced apoptosis through the intrinsic mitochondrial pathway, which could contribute to an age-related decline in cell populations in the retina and thereby provide a potential mechanism for the degenerative changes that are associated with age-related macular degeneration (ARMD).
