Expression of phosphorylated cell cycle related proteins in developing and aging rat hippocampus

AIM: To observe the expression of phosphorylated cell cycle related proteins cyclin-dependent kinase (CDK) and the retinoblastoma protein (Rb) in the developing and aging rat hippocampus. METHODS: The immunofluorescent staining for anti-phospho- CDK2, anti-phospho- CDC2, anti-phospho-Rb and anti-NeuN antibodies was used to determine their expressions and distributions in Wistar rat hippocampus at different ages. The expressions of phosphorylated cell cycle related proteins were also assessed by Western blotting analysis. RESULTS: (1) The number of neurons of CA1 area in hippocampus decreased during the period from 1 day to 15 months. (2) The positive expressions of phospho- CDK2 and phospho-Rb increased with aging. (3) No apparent change in the expression of phospho- CDC2 in the hippocampus of all the five groups was observed. CONCLUSION: The expressions of phospho-CDK2 and phospho-Rb suggest that differentiated neuron can re-enter the cell cycle and more neurons enter the cell cycle in the aged rat brain. Re-entering the cell cycle of differential neurons probably results in apoptosis.