Abstract
Purpose: :
The effects of oxygen concentration on the proliferation and survival of corneal epithelial cells were investigated.
Methods: :
Simian virus 40 (SV40)–transformed human corneal epithelial (HCE) cells were cultured under various concentrations (1, 21, or 60%) of oxygen gas. Cell proliferation was evaluated by counting of cell number and by measurement of the incorporation of bromodeoxyuridine (BrdU). Progression of the cell cycle was examined by immunoblot analysis of the abundance of cyclins A, B1, D1, and E. Cell viability was determined by measurement of the release of lactate dehydrogenase (LDH), and apoptotic cells were detected by flow cytometric analysis of the binding of annexin V to phosphatidylserine exposed at the cell surface.
Results: :
Cells grown under the normoxic (21% oxygen) or hypoxic (1% oxygen) conditions increased in number exponentially during culture for 48 hours. Those grown under the hyperoxic condition (60% oxygen), however, increased in number during only the first 24 hours of culture. The incorporation of BrdU by HCE cells after culture for 48 hours was significantly reduced for those maintained under 60% oxygen compared with those maintained under 21% oxygen but did not differ between those cultured under 21 or 1% oxygen. No differences in the expression of cyclins A, B1, or D1 were apparent among cells cultured under the three different oxygen conditions. However, the expression of cyclin E was reduced in cells cultured under 60% O2 compared with those cultured under normoxic or hypoxic conditions. Both the release of LDH and the binding of annexin V to the cell surface were increased for cells exposed to hyperoxia compared with those incubated under 1 or 21% oxygen.
Conclusions: :
Exposure of HCE cells to hyperoxia resulted in inhibition of cell proliferation and induced cell death by apoptosis. In contrast, cells exposed to hypoxia did not manifest differences in proliferation or apoptosis compared with those cultured under the normoxic condition.
Keywords: cornea: epithelium • proliferation • apoptosis/cell death