Doxycycline-regulated co-expression of GDNF and TH in PC12 cells.

Current gene therapy models for Parkinson's disease (PD) have adapted two treatment strategies. One is to restore dopamine (DA) production by delivering the genes of DA-synthesizing enzymes such as tyrosine hydroxylase (TH) to the striatum to relieve motor symptoms of PD. Another is to block or slow down progressive degenerative changes by delivering neurotrophic factors such as glial cell line-derived neurotrophic factor (GDNF) to protect the remained neurons. To test the assumption that the combination of the two strategies may have a compound or synergistic effect, we had constructed tetracycline-inducible (tet-off) AAV vector carrying GDNF and TH. After co-transfection of PC12 cells with this vector and the inducer plasmid, the expression of GDNF and TH protected these cells from 1-methyl-4-phenyl-pyridinium-induced injury, and significantly increased the content of dopamine in GDNF/TH-expressing cells compared with the control. Furthermore, mRNA expression of GDNF and TH could be effectively and reversibly regulated by doxycycline (Dox) and the function of GDNF and TH could be repressed by Dox. These results suggest that the tet-off AAV vector carrying GDNF and TH may be a useful tool for gene therapy in the treatment of PD.