The anti-oxidative role of ABCG2 in corneal epithelial cells.
OBJECTIVE
ABCG2 is a putative marker of progenitor cells, including the corneal epithelium. The authors investigated whether ABCG2 functions in the homeostasis of corneal epithelial cells using abcg2 knockout (KO) mice and corneal epithelial cell lines.


METHODS
abcg2 KO mice and a spontaneously immortalized murine corneal epithelial cell line (TKE2) were used for experiments. Flow cytometry was used to determine the presence of side population (SP) cells based on the ability of ABCG2 to efflux Hoechst 33342 dye. Expression of ABCG2 was also examined by RT-PCR. Cytotoxicity assay (IC(50)) and propidium iodide staining were performed in semiconfluent cells treated with hypoxia (1% O(2)) or with the pro-oxidant mitoxantrone.


RESULTS
abcg2 KO mice had a normal corneal epithelial phenotype; however, cultured abcg2 KO epithelial cells were prone to oxidative damage by mitoxantrone. TKE2 cells were resistant to mitoxantrone at low doses, but higher concentrations were toxic in a dose-dependent manner. Coculture with the ABCG2 inhibitors reserpine and Ko143 inhibited resistance to mitoxantrone, with a statistically higher cell death ratio. abcg2 KO cells were also significantly more sensitive to hypoxia than were wild-type control cells.


CONCLUSIONS
ABCG2 may protect corneal epithelial progenitor SP cells against oxidative stress induced by toxins and hypoxia.
Department of Ophthalmology, Keio University School of Medicine, Tokyo, Japan.
Miyuki
M
Kubota
Shigeto
S
Shimmura
Hideyuki
H
Miyashita
Motoko
M
Kawashima
Tetsuya
T
Kawakita
Kazuo
K
Tsubota
D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000818:Animals; D000975:Antioxidants / Q000502:physiology*; D002460:Cell Line; D002470:Cell Survival; D019573:Epithelium, Corneal / Q000187:drug effects / Q000378:metabolism*; D005434:Flow Cytometry; D000860:Hypoxia / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008942:Mitoxantrone / Q000633:toxicity; D018384:Oxidative Stress; D010641:Phenotype; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000378:metabolism
D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; C501412:Abcg2 protein, mouse; D000975:Antioxidants; D017382:Reactive Oxygen Species; D008942:Mitoxantrone