Oxidant-induced apoptosis in human retinal pigment epithelial cells: dependence on extracellular redox state.
OBJECTIVE
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).
Jiang
Shunai
S
Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, USA.
Moriarty-Craige
Siobhan E
SE
Orr
Michael
M
Cai
Jiyang
J
Sternberg
Paul
P
Jones
Dean P
DP
D000328:Adult; D000368:Aged; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D003545:Cysteine / Q000494:pharmacology*; D003553:Cystine / Q000494:pharmacology*; D045304:Cytochromes c / Q000378:metabolism; D005110:Extracellular Space / Q000502:physiology*; D053222:Fas Ligand Protein; D006801:Humans; D020287:In Situ Nick-End Labeling; D008562:Membrane Glycoproteins / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects; D010084:Oxidation-Reduction; D010857:Pigment Epithelium of Eye / Q000378:metabolism / Q000473:pathology*; D019014:fas Receptor / Q000378:metabolism; D020122:tert-Butylhydroperoxide / Q000633:toxicity
C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D019014:fas Receptor; D003553:Cystine; D045304:Cytochromes c; D020122:tert-Butylhydroperoxide; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D003545:Cysteine