Inhibition of neuroinflammatory nitric oxide signaling suppresses glycation and prevents neuronal dysfunction in mouse prion disease

Julie-Myrtille Bourgognon,Jereme G Spiers,Sue W Robinson,Hannah Scheiblich,Paul Glynn,Catharine Ortori,Sophie J Bradley,Andrew B Tobin,Joern R Steinert

doi:10.1073/pnas.2009579118

Abstract

Several neurodegenerative diseases associated with protein misfolding (Alzheimer's and Parkinson's disease) exhibit oxidative and nitrergic stress following initiation of neuroinflammatory pathways. Associated nitric oxide (NO)-mediated posttranslational modifications impact upon protein functions that can exacerbate pathology. Nonenzymatic and irreversible glycation signaling has been implicated as an underlying pathway that promotes protein misfolding, but the direct interactions between both pathways are poorly understood. Here we investigated the therapeutic potential of pharmacologically suppressing neuroinflammatory NO signaling during early disease progression of prion-infected mice. Mice were injected daily with an NO synthase (NOS) inhibitor at early disease stages, hippocampal gene and protein expression levels of oxidative and nitrergic stress markers were analyzed, and electrophysiological characterization of pyramidal CA1 neurons was performed. Increased neuroinflammatory signaling was observed in mice between 6 and 10 wk postinoculation (w.p.i.) with scrapie prion protein. Their hippocampi were characterized by enhanced nitrergic stress associated with a decline in neuronal function by 9 w.p.i. Daily in vivo administration of the NOS inhibitor L-NAME between 6 and 9 w.p.i. at 20 mg/kg prevented the functional degeneration of hippocampal neurons in prion-diseased mice. We further found that this intervention in diseased mice reduced 3-nitrotyrosination of triose-phosphate isomerase, an enzyme involved in the formation of disease-associated glycation. Furthermore, L-NAME application led to a reduced expression of the receptor for advanced glycation end-products and the diminished accumulation of hippocampal prion misfolding. Our data suggest that suppressing neuroinflammatory NO signaling slows functional neurodegeneration and reduces nitrergic and glycation-associated cellular stress.

Highlights

Diseases associated with old age, including Alzheimer’s disease (AD) and other forms of dementia, are increasing in prevalence, and symptomatic treatments exist, no cure to prevent the disease progression has yet been described
We examined the contributions of neuroinflammatory and oxidative stress-related signaling in prion-infected mice (RML) at a time point prior to onset of reported disease symptoms, as well as advanced disease stages
Together with the enhanced levels of nitrergic stress associated with augmented expression levels of iNOS mRNA (Fig. 1), we found total amounts of 3-nitrotyrosinated proteins to be greater than fivefold elevated in prion-infected mice compared to normal brain homogenate (NBH) controls at 9 w.p.i. (P = 0.0005, control NBH vs. Rocky Mountain Laboratory (RML), one-way analysis of variance (ANOVA); Fig. 4B)

Summary

Introduction

Diseases associated with old age, including Alzheimer’s disease (AD) and other forms of dementia, are increasing in prevalence, and symptomatic treatments exist, no cure to prevent the disease progression has yet been described. We confirmed that pharmacological suppression of nitrergic activity reduces the formation of advanced glycation end-products, diminishes prion protein misfolding, and averts neuronal dysfunction This intervention could present an approach to diminish the detrimental neuroinflammatory effects seen in neurodegeneration and highlights nitrergic stress and glycation signaling as putative targets for disease-modifying treatments. RAGE activation results in the stimulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase [33], an enzyme that produces superoxide radicals It induces the production of cytokines via NF-κB expression, followed by upregulation of inflammatory pathways [32]. AGEformation and RAGE expression are increased in brains from Creutzfeldt Jakob disease (CJD) patients and are associated with enhanced oxidative and nitrergic stress [34, 35] suggesting the possibility that AGE-mediated modifications might, in part, play a role in the accumulation of the aberrant prion protein. We further found that blocking NO signaling prevented nitrotyrosination of TPI and RAGE upregulation

Methods

Results

Conclusion