The induction of the TNFalpha death domain signaling pathway in Alzheimer's disease brain.

The tumor necrosis factor-alpha death domain pathway contributes to cellular degeneration in a variety of conditions. This study investigates the hypothesis that this death domain pathway is progressively induced in the brain during the progression of Alzheimer's disease (AD). AD cases had increased levels of proapoptotic markers including tumor necrosis factor-alpha (TNFalpha), TNF receptor type 1 (TNF-R1), TNF receptor-associated death domain (TRADD), and caspase-3, 2- to 10-fold higher (P < .01) than age-matched controls and 1 to 3 times higher than transitional cases. In striking contrast, potentially neuroprotective TNF receptor type 2 (TNF-R2), and Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE) inhibitor protein (FLIP) were decreased in AD as compared with age-matched control cases (P < .01). Overall, there was an elevation in proapoptotic elements, including a 5-fold increase in TNF-R1 and a 12-fold decrease in FLIP in AD brains. These changes may translate to increased degenerative potential because the downstream effector caspase-3 and product of the TNF pathway was also increased in parallel with enhanced TNF proapoptotic conditions. Our findings suggest that the TNF death receptor pathway and caspases are activated in the early stages of neuronal degeneration in AD.