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D. M. Robertson, S. I. Ho, H. D. Cavanagh; Oxygen-Mediated Down-Regulation of Np63 in the Corneal Epithelium. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1518.
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All forms of contact lens wear inhibit renewal of the corneal epithelium with the degree of growth inhibition regulated in part by lens-oxygen transmission. The purpose of this study was to assess the relationship between reduced oxygen levels and the expression of a potential regulator for proliferation and differentiation, ΔNp63, in cultured corneal epithelium and in the rabbit contact lens model.
ΔNp63 levels were assessed in hTCEpi cells grown in serum-free culture after exposure to hypoxia (10% oxygen) or complete anoxia for 0, 8, 24 or 48 hours. An established rabbit contact lens model was used for in vivo experiments. Rabbits were fit in one eye with either a PMMA (Dk/t = 0) or a hyper Dk RGP (Menicon Z, Dk/t = 97) for 24 hours of lens wear, the contralateral eye was used as a control. All rabbits were treated according to the ARVO statement for the use of animals in ophthalmic and vision research. ΔNp63 expression was analyzed by western blot using a mouse monoclonal antibody directed against the N-terminus of p63.
In vitro, ΔNp63 levels were reduced to 69.3% normoxic levels (p=0.038) after 48 hours of continued culture; exposure to complete anoxia further reduced ΔNp63 to 50.7% normoxic levels (p=0.038). In vivo, compared to the non-lens wearing eye, 24 hour PMMA lens wear significantly decreased ΔNp63 expression in both the limbal and central corneal epithelium (p=0.029); by contrast, hyper Dk RGP lens wear did not significantly alter ΔNp63 expression in either compartment.
Reduced oxygen levels down-regulated ΔNp63 expression both in vitro and in vivo. The absence of any change in ΔNp63 expression following hyper DK lens wear in vivo further confirms that these changes are due to oxygen and not the mechanical presence of the rigid test lens. Alterations in the level of ΔNp63 in the corneal epithelium may account for the oxygen-dependent decrease in proliferation and differentiation previously reported with contact lens wear.
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