The Molecular Mechanism of Amyloid β42 Peptide Toxicity: The Role of Sphingosine Kinase-1 and Mitochondrial Sirtuins.

Abstract

Our study focused on the relationship between amyloid β 1–42 (Aβ), sphingosine kinases (SphKs) and mitochondrial sirtuins in regulating cell fate. SphK1 is a key enzyme involved in maintaining sphingolipid rheostat in the brain. Deregulation of the sphingolipid metabolism may play a crucial role in the pathogenesis of Alzheimer’s disease (AD). Mitochondrial function and mitochondrial deacetylases, i.e. sirtuins (Sirt3,-4,-5), are also important for cell viability. In this study, we evaluated the interaction between Aβ1–42, SphKs and Sirts in cell survival/death, and we examined several compounds to indicate possible target(s) for a strategy protecting against cytotoxicity of Aβ1–42. PC12 cells were subjected to Aβ1–42 oligomers and SphK inhibitor SKI II for 24–96 h. Our data indicated that Aβ1–42 enhanced SphK1 expression and activity after 24 h, but down-regulated them after 96 h and had no effect on Sphk2. Aβ1–42 and SKI II induced free radical formation, disturbed the balance between pro- and anti-apoptotic proteins and evoked cell death. Simultaneously, up-regulation of anti-oxidative enzymes catalase and superoxide dismutase 2 was observed. Moreover, the total protein level of glycogen synthase kinase-3β was decreased. Aβ1–42 significantly increased the level of mitochondrial proteins: apoptosis-inducing factor AIF and Sirt3, -4, -5. By using several pharmacologically active compounds we showed that p53 protein plays a significant role at very early stages of Aβ1–42 toxicity. However, during prolonged exposure to Aβ1–42, the activation of caspases, MEK/ERK, and alterations in mitochondrial permeability transition pores were additional factors leading to cell death. Moreover, SphK product, sphingosine-1-phosphate (S1P), and Sirt activators and antioxidants, resveratrol and quercetin, significantly enhanced viability of cells subjected to Aβ1–42. Our data indicated that p53 protein and inhibition of SphKs may be early key events responsible for cell death evoked by Aβ1–42. We suggest that activation of S1P-dependent signalling and Sirts may offer a promising cytoprotective strategy.