Triple transduction with adeno-associated virus vectors expressing tyrosine hydroxylase, aromatic-L-amino-acid decarboxylase, and GTP cyclohydrolase I for gene therapy of Parkinson's disease

Parkinson's disease (PD), a neurological disease suited to gene therapy, is biochemically characterized by a severe decrease in the dopamine content o f the striatum, One current strategy for gene therapy of PD involves local production of dopamine in the striatum achieved by inducing the expression of enzymes involved in the biosynthetic pathway for dopamine. We previously showed that the coexpression of tyrosine hydroxylase (TH) and aromatic-L-a mino-acid decarboxylase (AADC), using two separate adeno-associated virus ( AAV) vectors, resulted in more effective dopamine production and more remar kable behavioral recovery in 6-hydroxydopamine-lesioned parkinsonian rats, compared with the expression of TH alone. Not only levels of TH and AADC bu t also levels of tetrahydrobiopterin (BH4), a cofactor of TH, and GTP cyclo hydrolase I (GCH), a rate-limiting enzymes for BH4 biosynthesis, are reduce d in parkinsonian striatum, In the present study, we investigated whether t ransduction with separate AAV vectors expressing TH, AADC, and GCH was effe ctive for gene therapy of PD, In vitro experiments showed that triple trans duction with AAV-TH, AAV-AADC, and AAV-GCH resulted in greater dopamine pro duction than double transduction with AAV-TH and AAV-AADC in 293 cells. Fur thermore, triple transduction enhanced BH4 and dopamine production in dener vated striatum of parkinsonian rats and improved the rotational behavior of the rats more efficiently than did double transduction. Behavioral recover y persisted for at least 12 months after stereotaxic intrastriatal injectio n. These results suggest that GCH, in addition to TH and AADC, is important for effective gene therapy of PD.