The roles of the extracellular signal-regulated kinase (ERK) pathway in the expression of cyclin D1 and p27(KIP1), the phosphorylation of p27(KIP1), and proliferation activity were examined after retinal detachment.

Normal eyes and eyes at 15 min, 2 and 4 days after retinal detachment in C57Bl6 mice were examined by immunohistochemistry using anti-phosphorylated (p) ERK1/2, anti-cyclin D1, anti-p27(KIP1), anti-p27(KIP1) phosphorylated at serine 10 (S10-phospho-p27), and anti-proliferating cell nuclear antigen (PCNA) antibodies with or without treatment with a specific ERK inhibitor, PD98059. Mouse Müller cells were isolated and examined for alteration of p27(KIP1) and cyclin D1 after exposure of basic fibroblast growth factor (bFGF) with and without treatment of PD98059 using Western blotting.

In the normal retina, nuclear immunoreactivity for p27(KIP1), but not S10-phospho-p27 or pERK1/2, was observed in the middle sublayer of the inner nuclear layer (INL), where Müller glial cells are situated. At 15 min after the retinal detachment, p27(KIP1), S10-phospho-p27 and pERK1/2-positive nuclei were noted in the INL, whereas immunoreactivity for pERK1/2 or S10-phospho-p27 was not observed after treatment with PD98095. Cyclin D1 was induced in the INL 2 days after the retinal detachment, and the induction was inhibited by PD98059. At 4 days after the detachment, p27(KIP1) immunoreactivity was not observed, and cyclin D1 and PCNA were expressed. The disappearance of p27(KIP1) was suppressed, whereas expression of cyclin D1 and PCNA was not observed in mice treated with PD98059. Exposure of bFGF relatively decreased the expression level of p27(KIP1) and increased the level of cyclin D1 in mouse Müller cells, compared with control level. Induction of cyclin D1 and decrease in p27(KIP1) were inhibited with treatment of PD98059.

Phosphorylation of ERK and expression of p27(KIP1) and cyclin D1 are involved in the proliferation of Müller cells after retinal detachment.