Neutralization of TRAIL death pathway protects human neurional cell line from β-amyloid toxicity

Here we report that a novel member of the TNF-alpha family, TNF-related apoptosis-inducing ligand (TRAIL), contributes substantially to amyloid-induced neurotoxicity in human SH-SY5Y neuronal cell line. Involvement of TRAIL in the amyloid-induced cell death is supported by cDNA array, Northern blot, and Western blot data, demonstrating increased TRAIL expression after treatment of the cells with a neurotoxic fragment of amyloid protein (PAP). TRAIL was also found to be released in the culture media after betaAP treatment with a time-course overlapping to contents of the intracellular protein. Contribution of TRAIL to betaAP neurotoxicity is demonstrated by data showing that TRAIL-neutralizing monoclonal antibody protects neuronal SH-SY5Y cells from betaAP neurotoxicity. Moreover, exposure of neuronal SH-SY5Y cells to TRAIL leads to cell death, indicating that this substance per se is endowed with neurotoxic properties. We also found that, similarly to betaAP and TRAIL, activation of the death-domain adaptor protein FADD results in neuronal cell death. Lack of FADD function, by overexpression of its dominant negative, rescued cells from either TRAIL- or betaAP-induced neurotoxicity, supporting the hypothesis that these three molecules share common intracellular pathways. Finally, we found that betaAP strongly activated caspase-8, and the cell-permeable, selective caspase-8 inhibitor z-IETD-FMK prevents both betaAP- and TRAIL-induced neurotoxicity. In view of TRAIL's potency in inducing neuronal death, and its role as mediator of betaAP, it is plausible to hypothesize that TRAIL can be regarded as a molecule that provides substantial contribution to betaAP-dependent cell death, which takes part in the progression of the neurode-generative process and related chronic inflammatory response.