Expressions of cyclin dependent kinase inhibitors p21 and p27 in rabbit retina and their association with proliferation

The imbalance of cell cycle regulation results in proliferative vitreoretinopathy (PVR). Studing the effects of cyclin dependent kinase (CDK) and CDK inhibitor (CKI) on the cell cycle regulation of retinal pigment epithelial (RPE) cells and fibroblasts in PVR formation is of important significance.

This study was to investigate the expressing trend of p21, p27 and CDK inhibitors in retinas of different ages of rabbits and explore the relationship between p21 or p27 and cell growth.

Nine clean New Zealand rabbits were assigned to 10-week group, 20-week group and 30-week group according to the age and 3 rabbits for each.The eyeballs were enucleated binocularly after the animals were sacrificed and retinas were isolated.Real-time PCR and Western blot were employed to detect the expressions of p21 and p27 mRNA and their proteins in retinas of the rabbits.The use and care of the animals followed the Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Committee.

The relative expressing levels of p21 mRNA were 1.631±0.063, 1.506±0.012 and 1.585±0.015, and those of p27 mRNA were 1.581±0.048, 1.470±0.012 and 1.490±0.013 in the 10-week group, 20-week group and 30-week group, respectively, showing significant differences among the groups (p21 mRNA: F=9.311, P=0.014; p27 mRNA: F=12.360, P=0.007), and the p21 and p27 mRNA expressing levels were significantly higher in the 10-week group and 30-week group than those in the 20-week group (all at P<0.05). The expressing levels of p21 protein were 0.675±0.061, 0.089±0.001 and 0.200±0.007, and those of p27 protein were 0.928±0.019, 0.183±0.005 and 0.576±0.089 in the 10-week group, 20-week group and 30-week group, respectively, with remarkable differences among the groups (p21: F=228.905, P<0.001; p27: F=148.957, P<0.001), and the expressions were significantly raised in the 10-week group and 30-week group in comparison with the 20-week group (all at P<0.01). Significantly positive correlations were found in the expressing levels of p21 and p27 both in transcriptional and protein levels (mRNA: r=0.906, P<0.01; protein: r=0.913, P<0.01).

The expressions of p21 and p27 up-regulate in the retinas of developing stage of rabbits but gradually reduce with adultness.However, p21 and p27 levels appear to be increasingly raised with aging of the rabbits.It is implied that p21 and p27 play a balancing role in the process of cycle regulation in retina cells.