Optic nerve alterations in P27(Kip1) knockout mice.

PURPOSE. To study the morphologic characteristics of the optic nerve (ON) by using an experimental model of knockout mice for the expression of the P27 Kip1 gene, mainly involved in cell cycle arrest, apoptosis control, and retinoblastoma protein phosphorylation. METHODS. Eyeballs with the retrobulbar ON attached were obtained from 26-week-old mice. By using morphologic and morphometric techniques, light and electron transmission microscopy, the ON characteristics were determined in two groups of mice: 1) wild type mice as the control group (n=15), 2) homozygous knockout mice (-/-) for the P27 Kip1 gene as the knockout group (n=15). Glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP) were studied using Western blot and immunoblotting approaches. RESULTS. The ON cross-sectional area was significantly larger in the P27 Kip1 knockout mice group than in the control group (p<0.001). The axon sizes in knockout animals were much larger than in wild-type mice (p<0.001). Higher number of axons forming the ON, intra-axonal degeneration, myelin sheath, and axoplasm density alterations were found in P27 Kip1 knockout mice when compared with control group (p<0.001). Analysis of lysates of optic nerves by Western blot showed less expression of myelin basic protein and GFAP in P27 Kip1 knockout mice as compared to wild type mice (p<0.005, p<0.01, respectively). CONCLUSIONS. The morphologic and morphometric results suggest that homozygous P27 Kip1 knockout mice had hypertrophic, hyperplastic, and dystrophic ON.