Longitudinal CSF proteomics identifies NPTX2 as a prognostic biomarker of Alzheimer's disease.

INTRODUCTION: Biomarkers that reflect pathologic processes affecting neuronal function during preclinical and early stages of Alzheimer's disease (AD) are needed to aid drug development. METHODS: A targeted, stable isotope, quantitative mass spectrometry-based investigation of longitudinal changes in concentrations of previously identified candidate biomarkers was performed in cerebrospinal fluid (CSF) of Alzheimer's Disease Neuroimaging Initiative participants who were classified as cognitively normal (CN; n = 76) or with mild cognitive impairment (MCI; n = 111) at baseline. RESULTS: Of the candidate biomarkers, the CSF concentration of neuronal pentraxin 2 (NPTX2), a protein involved in synaptic function, exhibited rates of change that were significantly different between three comparison groups (i.e., CN vs. MCI participants; AD pathology positive vs. negative defined by phosphorylated tau181/amyloid beta1-42 ratio; and clinical progressors vs. non-progressors). The rate of change of NPTX2 also significantly correlated with declining cognition. DISCUSSION: CSF NPTX2 concentration is a strong prognostic biomarker candidate of accelerated cognitive decline with potential use as a therapeutic target.

Intersecting pathways to neurodegeneration in Parkinson's disease: effects of the pesticide rotenone on DJ-1, alpha-synuclein, and the ubiquitin-proteasome system.

Sporadic Parkinson's disease (PD) is most likely caused by a combination of environmental exposures and genetic susceptibilities, although there are rare monogenic forms of the disease. Mitochondrial impairment at complex I, oxidative stress, alpha-synuclein aggregation, and dysfunctional protein degradation, have been implicated in PD pathogenesis, but how they are related to each other is unclear. To further evaluated PD pathogenesis here, we used in vivo and in vitro models of chronic low-grade complex I inhibition with the pesticide rotenone. Chronic rotenone exposure in vivo caused oxidative modification of DJ-1, accumulation of alpha-synuclein, and proteasomal impairment. Interestingly, the effects become more regionally restricted such that systemic complex I inhibition eventually results in highly selective degeneration of the nigrostriatal pathway. DJ-1 modifications, alpha-synuclein accumulation, and proteasomal dysfunction were also seen in vitro and these effects could be prevented with alpha-tocopherol. Thus, chronic exposure to a pesticide and mitochondrial toxin brings into play three systems, DJ-1, alpha-synuclein, and the ubiquitin-proteasome system, and implies that mitochondrial dysfunction and oxidative stress link environmental and genetic forms of the disease.

Effects of DJ-1 mutations and polymorphisms on protein stability and subcellular localization.

Mutations in the DJ-1 gene are associated with recessive, early onset Parkinson's disease (PD). We reported previously that one of the point mutations, L166P, destabilizes the protein and thus produces an effective knockout of the gene. Here, we have expanded this analysis to include a series of mutations and polymorphisms identified throughout the gene. The M26I point mutation was also unstable, although the effect was not as dramatic as with L166P. Protein levels were rescued in part, but not completely, by proteasome inhibition. Other variants, such as R98Q, were generally stable. We noted that M26I and L166P are both in helical regions near the dimer interface. However, M26I retains the ability to dimerize. We also examined the subcellular localization of DJ-1 and found that most mutations were similar to the wild-type (wt) protein in that a few cells showed mitochondrial staining. However, in all cases, the proportion of cells with mitochondrial DJ-1 staining was increased in oxidative conditions, suggesting that oxidation promotes the mitochondrial localization of DJ-1.

The Parkinson's disease protein DJ-1 is neuroprotective due to cysteine-sulfinic acid-driven mitochondrial localization.

Loss-of-function DJ-1 mutations can cause early-onset Parkinson's disease. The function of DJ-1 is unknown, but an acidic isoform accumulates after oxidative stress, leading to the suggestion that DJ-1 is protective under these conditions. We addressed whether this represents a posttranslational modification at cysteine residues by systematically mutating cysteine residues in human DJ-1. WT or C53A DJ-1 was readily oxidized in cultured cells, generating a pI 5.8 isoform, but an artificial C106A mutant was not. We observed a cysteine-sulfinic acid at C106 in crystalline DJ-1 but no modification of C53 or C46. Oxidation of DJ-1 was promoted by the crystallization procedure. In addition, oxidation-induced mitochondrial relocalization of DJ-1 and protection against cell death were abrogated in C106A but not C53A or C46A. We suggest that DJ-1 protects against neuronal death, and that this is signaled by acidification of the key cysteine residue, C106.