Reversing increased neuronal nitric oxide synthase in Alzheimer’s disease prevents aberrant glutamatergic calcium responses

Abstract

Abstract Background Nitrosative stress is a feature of Alzheimer’s disease, however the underlying mechanisms driving nitrosative stress and the impact of nitric oxide on neuronal function in Alzheimer’s disease is still largely unknown. Methods We analysed neuronal nitric oxide synthase (nNOS) protein levels in post mortem tissue and induced pluripotent stem cell (iPSC) derived neurons from Alzheimer’s patients and controls by immunohistochemistry and western blots. Furthermore, we assessed the impact of modulating nNOS function or nitric oxide levels on neuronal glutamatergic signalling using calcium imaging. Results We show that nNOS protein levels are increased in early and severely affected brain regions of late-onset Alzheimer’s disease post mortem tissue, but not late and mildly affected regions, or cognitively normal individuals. The increased nNOS phenotype was also present in iPSC-derived neurons from Alzheimer’s disease patients compared to controls, along with increased levels of nitrite, a stable marker of nitric oxide. We observed a divergent functional impact of nitric oxide that included strengthening the calcium response in control neurons, while dysregulating calcium signaling and altering the amplitude and kinetics of the calcium responses to glutamate in the Alzheimer’s disease neurons. Pharmacological modulation of nitric oxide levels or production prevented aberrant calcium signaling in Alzheimer’s disease neurons. Conclusions Together these data identify increases in nNOS protein in Alzheimer’s disease. Functional data suggest nitric oxide modulation of glutamatergic calcium signaling is neuroprotective under non-pathogenic conditions, with increased nNOS and nitric oxide contributing to pathogenic signaling changes during Alzheimer’s disease.