Quantitative proteomic analysis of mitochondrial proteins: relevance to Lewy body formation and Parkinson's disease.

The mechanisms underlying Parkinson's disease (PD) and Lewy body (LB) formation, a pathological hallmark of PD, are incompletely understood; however, mitochondrial dysfunction is likely to be at least partially responsible. To study the processes that might be related to nigral neurodegeneration and LB formation, we employed nonbiased quantitative proteomics with isotope-coded affinity tag (ICAT) to compare the mitochondrial protein profiles in the substantia nigra (SN) between controls and mice treated chronically with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a potent mitochondrial toxicant, and an adjuvant, probenecid (prob), for 5 weeks, which produced selective nigrostriatal neurodegeneration with formation of LB-like cytoplasmic inclusions in the remaining nigral neurons. This method identified a total of more than 300 proteins; of these proteins, more than 100 displayed significant changes in relative abundance in the MPTP/prob-treated mice compared to the controls. We validated one of these proteins, DJ-1, whose mutation has been implicated in familial PD, with Western blot analysis, followed by immunohistochemical studies of its distribution in the SN in relation to cytoplasmic inclusions in mice, as well as in classical LBs in PD patients. The results demonstrated that DJ-1 was not only colocalized with alpha-synuclein in dopaminergic neurons but also to cytoplasmic inclusions in mice treated with MPTP/prob. In addition, DJ-1 was present in the halo but not in the core of classical LBs in patients with PD. Our findings suggested that DJ-1 might play an important role in mitochondrial dysfunction, as well as LB formation in PD.