Tauroursodeoxycholic acid prevents amyloid-β peptide-induced neuronal death via a phosphatidylinositol 3-kinase-dependent signaling pathway

Tauroursodeoxycholic acid (TUDCA), an endogenous bile acid, modulates cell death by interrupting classic pathways of apoptosis. Amyloid-beta (Abeta) peptide has been implicated in the pathogenesis of Alzheimer's disease, where a significant loss of neuronal cells is thought to occur by apoptosis. In this study, we explored the cell death pathway and signaling mechanisms involved in Abeta-induced toxicity and further investigated the anti-apoptotic effect(s) of TUDCA. Our data show significant induction of apoptosis in isolated cortical neurons incubated with Abeta peptide. Apoptosis was associated with translocation of pro-apoptotic Bax to the mitochondria, followed by cytochrome c release, caspase activation, and DNA and nuclear fragmentation. In addition, there was almost immediate but weak activation of the serine/threonine protein kinase Akt. Inhibition of the phosphatidylinositide 3'-OH kinase (PI3K) pathway with wortmannin did not markedly affect Abeta-induced cell death, suggesting that this signaling pathway is not crucial for Abeta-mediated toxicity. Notably, co-incubation with TUDCA significantly modulated each of the Abeta-induced apoptotic events. Moreover, wortmannin decreased TUDCA protection against Abeta-induced apoptosis, reduced Akt phosphorylation, and increased Bax translocation to mitochondria. Together, these findings indicate that Abeta-induced apoptosis of cortical neurons proceeds through a Bax mitochondrial pathway. Further, the PI3K signaling cascade plays a role in regulating the anti-apoptotic effects of TUDCA.