The Role of TNF Signaling In Regulating Beta-Amyloid Burden in the 3xtgad Mouse Model of Alzheimer's Disease

Microglial activation and overproduction of inflammatory mediators in the CNS have been implicated in Alzheimer's Disease (AD), but the precise nature of the key molecular mediators of neurotoxicity that directly contribute to neurodegeneration or loss of specific neuronal populations is less clear. The pro-inflammatory cytokine Tumor Necrosis Factor (TNF) has been implicated in AD by its elevated presence in serum and post-mortem brains of patients with AD. To test the hypothesis that TNF-dependent neuroinflammation and neurotoxicity contributes to the increased microglial burden and exacerbated pathology observed in the hippocampus and cortex of 3xTgAD mice (transgenic mouse expressing human familial AD mutations in APP, PS1, and a familial frontotemporal dementia mutation in tau) after chronic systemic LPS exposure, we inhibited TNF signaling with novel engineered dominant negative TNF inhibitors (DN-TNF) selective for soluble TNF (solTNF) or lentiviral-derived DN-TNF to achieve long-term inhibition of TNF activity and halt or delay the early stages of amyloid-associated neuropathology. In vitro, cells infected with lenti-pro-DN-TNF-IRES-GFP produce sufficient levels of DN-TNF protein to block nuclear translocation of p65 in response to stimulation by TNF. Infection with lenti-DN-TNF also blocks solTNF-induced activation of primary microglia. Results from in vivo studies indicate that short-term pharmacological inhibition as well as long-term lentiviral-driven inhibition of soluble TNF signaling decreases the accumulation of intraneuronal full length APP in hippocampus and cortex induced by chronic systemic inflammation. To our knowledge, this is the first study that selectively inhibits soluble TNF signaling in an acute manner using a pharmacologic agent, thereby directly linking endogenous TNF activity in vivo to accumulation of APP in a model of Alzheimer's disease. Targeted inhibition of soluble TNF in the central nervous system may represent a new therapeutic approach to slow the appearance of amyloid pathology, cognitive deficits, and possibly the progressive loss of neurons in AD.