Friday, December 12, 2014

The Role of the NADPH Oxidase NOX2 in Prion Pathogenesis

The Role of the NADPH Oxidase NOX2 in Prion Pathogenesis
Silvia Sorce, Mario Nuvolone,  Annika Keller,  Jeppe Falsig,  Ahmet Varol, Petra Schwarz, Monika Bieri, Herbert Budka, Adriano Aguzzi mail
Published: December 11, 2014 •DOI: 10.1371/journal.ppat.1004531
Prion infections cause neurodegeneration, which often goes along with oxidative stress. However, the cellular source of reactive oxygen species (ROS) and their pathogenetic significance are unclear. Here we analyzed the contribution of NOX2, a prominent NADPH oxidase, to prion diseases. We found that NOX2 is markedly upregulated in microglia within affected brain regions of patients with Creutzfeldt-Jakob disease (CJD). Similarly, NOX2 expression was upregulated in prion-inoculated mouse brains and in murine cerebellar organotypic cultured slices (COCS). We then removed microglia from COCS using a ganciclovir-dependent lineage ablation strategy. NOX2 became undetectable in ganciclovir-treated COCS, confirming its microglial origin. Upon challenge with prions, NOX2-deficient mice showed delayed onset of motor deficits and a modest, but significant prolongation of survival. Dihydroethidium assays demonstrated a conspicuous ROS burst at the terminal stage of disease in wild-type mice, but not in NOX2-ablated mice. Interestingly, the improved motor performance in NOX2 deficient mice was already measurable at earlier stages of the disease, between 13 and 16 weeks post-inoculation. We conclude that NOX2 is a major source of ROS in prion diseases and can affect prion pathogenesis.
Author Summary
The deposition of misfolded, aggregated prion protein in the brain causes transmissible spongiform encephalopathies (TSE), a group of disorders including Creutzfeldt–Jakob disease and mad cow disease. TSE are characterized by neurodegeneration and progressive, lethal neurological dysfunction. Signs of oxidative damage are found in TSE, implying excessive production of reactive oxygen species (ROS), yet their source is unclear. Here, we analyzed the role of the NADPH oxidase enzyme, NOX2, in prion pathogenesis. NOX2 is a membrane-bound electrochemical pump that generates ROS. We found that NOX2 is upregulated in the brains of patients with Creutzfeldt-Jakob disease and of prion-infected mice. Interestingly, NOX2 ablation led to abrogation of ROS production in mice inoculated with prions, and was associated with a milder clinical course of the disease and increased life expectancy. We conclude that NOX2 is a relevant contributor to the excessive production of ROS. This study spawns the possibility that inhibiting NOX2 activation might help attenuate prion disease progression – a legitimate and important goal even if there is little reason to expect anti-NOX2 therapies to be curative.
Although NOX2 ablation does not ultimately prevent the development of prion disease, the results presented above show that NOX2 is a relevant constituent of the neurotoxic cascade in these diseases. Ablation or overexpression of superoxide dismutase, SOD1, activity can decrease or increase prion incubation time, respectively [7], [12]. Together with these previous findings, our data support the crucial impact of superoxide production in prion diseases. Moreover, they suggest that NOX2, expressed in microglial cells, is the major source of this superoxide production. The use of antioxidants as possible therapeutic approach for CNS diseases has been favored by promising results of rodent studies; however, disappointing and incongruous outcomes have been observed in clinical trials [50], [51]. Lack of specificity of antioxidant treatments could be one of the reasons that explain such a failure in clinical translation. Having identified NOX2 as a possible specific target may offer an opportunity to reduce the occurrence of oxidative stress insults in CJD patients. In particular, our data suggest that inhibition of NOX2 may attenuate, at least temporarily, the neurological dysfunctions associated with prion disease, thereby enhancing the quality of life – a legitimate and important goal even if the overall life expectancy may not be dramatically improved. ...
see full text above link at PLOS, and once again, many thanks to PLOS et al, and Scientist, for open access...tss

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