One mechanism leading to neurodegeneration in Alzheimer's disease (AD) is amyloid-beta (Abeta) peptide neurotoxicity. The presence of apoptotic bodies in the brain of AD patients and the ability of Abeta to elicit apoptosis and cell death in cultured CNS neurons suggest that the aberrant induction of apoptosis by Abeta peptides may be an important cause in removing the irreplaceable neurons in AD. However, the mechanism by which Abeta causes apoptosis and cell death neurons remains largely unknown. Since ceramide, a lipid second messenger, produced by the degradation of sphingomyelin is an important inducer of apoptosis and cell death in various cell types including neuronal cells, we decided to investigate whether Abeta induces the production of ceramide in neuronal cells. Interestingly, we have found that Abeta induces the production of ceramide by more than 10 fold within 24 h in rat pheochromocytoma (PC 12) cells. Furthermore, PP2, a specific inhibitor of Src tyrosine kinases, but not PP3, a negative control of PP2, inhibits Abeta-mediated induction of ceramide production. Taken together, these observations suggest that src tyrosine kinase(s) may play an important role in Abeta-induced production of ceramide in neuronal cells and that ceramide may participate in the pathogenesis of AD. To establish this hypothesis, we have proposed three simple specific aims. Since ceramide produced from the degradation of sphingomyelin by sphingomyelinases (neutral, NSMase; acidic, ASMase), Specific aim I will investigate whether Abeta induces the activation of sphingomyelinases (N-SMase and/or A-SMase) neuronal cells.
Specific aim II has been designed to investigate whether Src is involved in Abeta-mediated degradation of sphingomyelin to ceramide in neuronal cells.
Specific aim III has been devoted to analyze the levels of ceramide and sphingomyelin in postmortem brains of AD and non-demented controls. Results obtained from this pilot proposal will significantly enhance our understanding about the cause of neuronal loss in AD and will provide promising therapeutic strategies for AD patients.
