NADPH Oxidase 2 in Parkinson's Disease Pathogenesis

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ABSTRACT Reductive-oxidative (redox) imbalance in nigrostriatal neurons has been indicated as an important cause of nigrostriatal degeneration in familial and idiopathic Parkinson disease (PD). While it is generally assumed that the oxidative damage seen in PD derives from dysfunctional mitochondrial electron transport chain, there is growing consensus that NADPH oxidase isoform 2 (NOX2) may be important and, in some cellular systems, the two appear intimately related in a redox regulatory pathway recently termed “ROS-induced ROS production” (RIRP). However, the relevance of NOX2 in PD pathogenesis remains underexplored. Additionally, the in-situ detection of NOX2 activity state has been difficult to assess. Using a novel histological proximity ligation (PL) assay to detect NOX2 activation state with excellent cellular resolution, our preliminary findings address the relevance of NOX2 activity, in idiopathic PD and in PD animal models of parkinsonism. Our preliminary studies reveal that NOX2 can be activated by mitochondrially-derived ROS in a RIRP manner, which serves to greatly amplify ROS production. The resultant NOX2 activity is necessary and sufficient to both activate wildtype LRRK2 and to cause accumulation and oxidative post-translational modifications of α-synuclein (4-HNE-α-syn and NO-α-syn). The NOX2-activated LRRK2 kinase activity leads to endo-lysosomal and autophagic defects and decreased degradation of toxic species of α-synuclein, such as pSer129-α-synuclein. In this way, NOX2 activity both drives the formation and inhibits the disposal of toxic forms of α-synuclein. In turn, as shown in previous work, these forms of α-synuclein bind to mitochondrial TOM20, blocking protein import and leading to mitochondrial functional alterations and relative increased ROS production. Thus, there appears to be a feedforward cycle, in which NOX2 plays an essential amplification role in PD pathogenesis. However, other NOXs, including isoforms 1 and 4 – also highly expressed in brain - might contribute somehow to this pathogenic process. In this context, the current proposal is designed to further explore and define the exclusive role of NOX2 in PD. Positive outcomes demonstrating the relevance of NOX2 in PD pathogenesis and the efficacy of NOX2-directed therapies using antisense oligonucleotides (ASOs), will reveal potential therapeutic strategies for neuroprotection and ameliorate the PD-related movement disorder. As such, this project has compelling practical significance for PD therapeutics.