Genetic Deletion of Tumor Necrosis Factor-α Attenuates Amyloid-β Production and Decreases Amyloid Plaque Formation and Glial Response in the 5XFAD Model of Alzheimer's Disease.

Abstract

Increasing evidence suggests that neuroinflammation comprises a major characteristic of Alzheimer's disease (AD). Tumor necrosis factor-α (TNF-α) is a pleiotropic pro-inflammatory cytokine implicated in neurodegenerative diseases including AD, and has been proposed as a potent therapeutic target for AD. Although a number of studies focusing on pharmacological or genetic manipulation of TNF-α and its receptors in AD mice have provided significant knowledge regarding the role of TNF-α signaling pathway in the pathogenesis of AD, the consequences of TNF-α genetic deletion have not been thoroughly examined. Here, we focused on the effect of TNF-α deficiency on the amyloid phenotype of 5XFAD mice. Our analysis revealed that amyloid deposition, amyloid-β (Aβ) levels, and AβPP-carboxyterminal fragments are significantly reduced in the brains of 5XFAD/TNF-α-/- mice compared to the 5XFAD/TNF-α+/+. We found decreased protein levels of β- and α-secretases in the 5XFAD/TNF-α-/- brains, suggesting for an effect of TNF-α on AβPP processing and Aβ generation. We also show for the first time that TNF-α affects PS1in vivo, as 5XFAD mice lacking TNF-α expression display reduced PS1-carboxyterminal fragments implying for diminished PS1 activity. Moreover, TNF-α deficiency decreases microglial and astrocytic activation and significantly restricts the phagocytic activity of macrophages against Aβ, supporting for reduced responsiveness of phagocytes toward Aβ. Overall, our results reveal that TNF-α genetic deletion in 5XFAD mice attenuates amyloid plaque formation by lowering Aβ generation through the reduction of functionally active PS1 and β-secretase rather than promoting Aβ clearance by phagocytic cells. Our data further suggest TNF-α inhibition as a therapeutic approach for AD.