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

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.