Peripheral Tumor Necrosis Factor-Alpha (TNF-α) Modulates Amyloid Pathology by Regulating Blood-Derived Immune Cells and Glial Response in the Brain of AD/TNF Transgenic Mice

Increasing evidence has suggested that systemic inflammation along with local brain inflammation can play a significant role in Alzheimer's disease (AD) pathogenesis. Identifying key molecules that regulate the crosstalk between the immune and the CNS can provide potential therapeutic targets. TNF- alpha is a proinflammatory cytokine implicated in the pathogenesis of systemic inflammatory and neurodegenerative diseases, such as rheumatoid arthritis (RA) and AD. Recent studies have reported that anti-TNF-alpha therapy or RA itself can modulate AD pathology, although the underlying mechanism is unclear. To investigate the role of peripheral TNF-alpha as a mediator of RA in the pathogenesis of AD, we generated double-transgenic 5XFAD/Tg197 AD/TNF mice that develop amyloid deposits and inflammatory arthritis induced by human TNF-alpha (huTNF-alpha) expression. We found that 5XFAD/Tg197 mice display decreased amyloid deposition, compromised neuronal integrity, and robust brain inflammation characterized by extensive gliosis and elevated blood-derived immune cell populations, including phagocytic macrophages and microglia. To evaluate the contribution of peripheral huTNF-alpha in the observed brain phenotype, we treated 5XFAD/Tg197 mice systemically with infliximab, an anti-huTNF-alpha antibody that does not penetrate the blood-brain barrier and prevents arthritis. Peripheral inhibition of huTNF-alpha increases amyloid deposition, rescues neuronal impairment, and suppresses gliosis and recruitment of blood-derivedimmunecells, without affecting brain huTNF-alpha levels. Our data report, for the first time, a distinctive role for peripheral TNF-alpha in the modulation of the amyloid phenotype in mice by regulating blood-derived and local brain inflammatory cell populations involved in beta-amyloid clearance.