Redox regulation of neuroinflammatory pathways contributes to damage in Alzheimer's disease brain

The mechanism(s) whereby redox stress mediates aberrant immune signaling in age-related neurological disorders remains largely unknown. Normally, the innate immune system mounts a robust response to infectious stimuli. However, unintentional activation by host-derived factors, such as aggregated proteins associated with neurodegenerative disorders or by cytoplasmic genomic or mitochondrial DNA, can elicit aberrant immune responses. One such immune response is represented by the cytosolic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. Using redox chemical biology and mass spectrometry approaches, we identified S -nitrosylation of STING cysteine 148 as a novel posttranslational redox modification underlying aberrant type 1 interferon signaling in Alzheimer's disease (AD). Critically, we observed S -nitrosylated STING (SNO-STING) in postmortem human AD brains, in hiPSC-derived microglia (hiMG) exposed to amyloid-β (Aβ)/α-synuclein (αSyn) aggregates, and in 5xFAD transgenic mice. Mechanistically, our findings reveal that STING S -nitrosylation is critical in initiating signaling cascades by promoting the formation of disulfide-bonded STING oligomers. This leads to neuroinflammation early in the course of disease in vivo in 5xFAD mice with consequent synaptic loss. Collectively, our research supports the role of SNO-STING in neuroinflammation associated with AD, and points to a novel druggable cysteine residue in STING to prevent this S -nitrosylation reaction with its inherent inflammatory response.

S -Nitrosylation of STING triggers activation of cGAS-STING signaling in Alzheimer's disease brain and subserves a novel link between excessive nitrosative stress and dysregulated innate immunity, thus contributing to disease progression.