Activation of the calpain/cdk5/p25 pathway in the girus cinguli in Parkinson's disease.

The mechanisms involved in neuronal loss in Parkinson's disease (PD) are not known, although recent studies performed in PD experimental models suggest that cdk5/p25 plays a predominant role. In the present study, we examined the gyrus cinguli of cases with PD and compared them with age-matched controls, and we demonstrated an activation of the calpain/cdk5 pathway. We found an increase in the p25/p35 immunoreactivity ratio and in the expression of transcription factor E2F-1. Our results implicate the cdk5/p25 pathway and re-entry into the cell cycle in the process of neuronal loss in patients with PD.