Disappearance of p27(KIP1) and Increase in Proliferation of the Lens Cells After Extraction of Most of the Fiber Cells of the Lens

Abstract

Purpose: Proliferation of the lens epithelial cells is involved in the fibrotic changes of lens capsules after cataract extraction. However, the mechanisms of the proliferation of the lens epithelial cells are largely unknown. The purpose of this study was to examine the correlation between the expression of p27(KIP1) and cell proliferation in the lens cells after the extraction of lens fiber cells. Methods: At embryonic days (E) 14 and 18, the C57Bl6 mice were anesthetized and the embryos were surgically removed. The eyes were dissected from these embryos and also from mice 12 weeks after birth. The 12-week-old mice were anesthetized, and then the lens fiber cells were extracted. Normal eyes at E14 and 18 and eyes fixed at 15 min and 48 hr after the extraction of the lens fiber cells were analyzed using immunohistochemistry with anti-p27(KIP1), p57(KIP2), and phosphorylated extracellular signal-regulated kinase (phospho-ERK) 1/2 antibodies, and cells in the S phase of the cell cycle were also examined using anti-bromodeoxyuridine (BrdU) antibody. Results: p27(KIP1) and p57(KIP2)-positive cells were present in the equatorial region of E14 mice. At E18, many lens fiber cells showed nuclear immunoreactivity for p27(KIP1), whereas a small number of cells were positive for p57(KIP2) in the equatorial region. At 12 weeks of age, all nuclei of the lens epithelial cells as well as lens fiber cells showed nuclear immunoreactivity for p27(KIP1). In contrast, p57(KIP2) and phospho-ERK1/2 were not expressed in the lens cells. At 15 min after the extraction of lens fiber cells, phospho-ERK1/2 as well as p27(KIP1) were detected in the lens cells. At 48 hr after the extraction of the lens fiber cells, a few p27(KIP1)-positive nuclei were observed in the equatorial region of the lens capsule. In contrast, many lens cells showed nuclear immunoreactivity for BrdU. Conclusions: These findings suggest that degradation of p27(KIP1) mediated by phosphorylation of ERK 1/2 is correlated with proliferation of the epithelial cells after the extraction of the lens fiber cells.