Cognitive Decline, Cerebral-Spleen Tryptophan Metabolism, Oxidative Stress, Cytokine Production, and Regulation of the Txnip Gene in 3xTg-AD Mice

Pathologic inflammation in response to injury, infection, or oxidative stress is a proposed mechanism relating cognitive decline to dementia. The kynurenine pathway and thioredoxin-interacting protein (TXNIP) activity regulate inflammation and neurotoxicity in Alzheimer disease (AD). We examined cognitive deficits, kynurenine pathway mediators, TXNIP, and oxidative damage in the cerebrum and spleen, as well as inflammatory cytokine production by stimulated splenocytes, from female 3xTg-AD mice in early and late stages of disease progression. We also characterized tissue-specific epigenetic regulation of Txnip gene expression in the cerebrum and spleen. Herein, we show that cognitive deficits in 7-month–old 3xTg-AD mice are associated with a stable increase in cerebrum and spleen tryptophan metabolites, with a concomitant increase in amyloid β 40 (Aβ 40 )/Aβ 42 and tau/hyperphosphorylated tau pathologies and a coordinated reduction in spleen proinflammatory cytokine production in 17-month–old mice. The enhanced cerebrum TXNIP expression is associated with increased histone acetylation, transcription factor (Aβ 42 or CTCF) binding, and Txnip promoter hypomethylation, whereas the attenuated spleen TXNIP expression is associated with increased histone methylation, reduced CTCF binding, and Txnip promoter hypermethylation. These results suggest a causal relationship among epigenomic state, TXNIP expression, cerebral-spleen tryptophan metabolism, inflammatory cytokine production, and cognitive decline; and they provide a potential mechanism for Txnip gene regulation in normal and pathologic conditions, suggesting TXNIP levels may be a useful predictive or diagnostic biomarker for Aβ 40 /Aβ 42 targeted AD therapies.