Control of dopamine-secretion by Tet-Off system in an in vivo model of parkinsonian rat.

We established a PC12 cell line (PC12TH Tet-Off) in which human tyrosine hydroxylase (TH) expression can be negatively controlled by Doxycycline (Dox). First, dopamine (DA)-secretion from PC12TH Tet-Off cells was controlled by Dox-administration in a dose-responsive manner ranging from 0 to 100 ng/ml for 70 days in vitro. Furthermore, Parkinson's disease model of rats receiving encapsulated PC12TH Tet-Off cells displayed a significant decrease of dopamine concentration in the cerebrospinal fluid (CSF) and increase of the number of apomorphine-induced rotations by Dox-administration, as compared to transplanted rats without Dox-administration, although the significant decrease of the reduction ratio of DA concentration in the CSF with Dox-administration was recognized over time. At 2 months post-implantation, concentration of dopamine in the implanted striatum and from the retrieved capsules demonstrated that the control of DA-secretion could be partially achieved for 2 months in vivo. Our results support both the value of cell therapy using Tet-Off system and the technique of encapsulation might be a feasible option for Parkinson's disease especially in resolving the problem of dopamine oversupply in the future, although a more efficient way to control DA-secretion with quicker regulation and much titration of dose should be explored before clinical application.