The Parkinson's Disease-Related Protein DJ-1 Protects Dopaminergic Neurons in vivo and Cultured Cells from Alpha-Synuclein and 6-Hydroxydopamine Toxicity

Background: Dopaminergic degeneration is a major finding in brains of patients with Parkinson's disease (PD), together with Lewy bodies, intraneuronal inclusions mainly composed of the fibrillogenic protein ??-synuclein (??-syn). The familial-PD-related protein DJ-1 was reported to reduce dopaminergic degeneration triggered by ??-syn or by the dopaminergic-selective neurotoxin 6-hydroxydopamine (6-OHDA). Objective: The aim was to further investigate the role of DJ-1 in dopaminergic degeneration and to see whether a cell-permeable recombinant form of DJ-1 (TAT-DJ-1) could restore dopamine depletion in vivo, thus representing an innovative therapeutic approach. Methods: We developed in vitro (PC12/TetOn cells and mouse primary mesencephalic neurons) and in vivo models [including DJ-1 knockout (-/-) mice] to investigate DJ-1 in dopaminergic degeneration. Results: We found that in PC12/TetOn cells overexpressing ??-syn with the familial-PD linked mutation A30P, DJ-1 silencing increased ??-syn (A30P) toxicity. Primary mesencephalic neurons from DJ-1 (-/-) mice were more vulnerable to a cell-permeable form of ??-syn (TAT-??-syn) and to 6-OHDA. Intrastriatally administered TAT-DJ-1 reduced 6-OHDA toxicity in vivo in C57BL/6 mice. Finally, when we injected TAT-??-syn (A30P) in the striatum of DJ-1 (-/-) animals, dopamine was depleted more than in the control strain. Conclusion: DJ-1 appears to have a protective role against dopaminergic degeneration triggered by ??-syn or 6-OHDA, reinforcing the possible therapeutic importance of this protein in PD.