Function of ceramide in neurodegenerative disease



 DESCRIPTION (provided by applicant): Alzheimer's disease (AD) is characterized by progressive neurodegeneration and build-up of Aβ peptides, amyloid plaques, and neurofibrillary tau tangles. Current strategies to prevent Aβ formation or secretion are not successful. Preventing Aβ build-up while enhancing Aβ uptake and clearance is an alternative approach to minimize the effect of Aβ peptides. A critical barrier to progress in the development of novel drugs that prevent Aβ build-up and improve clearance is the lack of a thorough understanding of how Aβ amyloid plaques are nucleated and proliferate instead of Aβ being taken up and cleared by glial cells. Our goal is to interrupt amyloid plaque nucleation and propagation to enhance Aβ clearance and delay the onset and reduce neurodegeneration in AD. Our central hypothesis is that ceramide-enriched exosomes secreted by astrocytes form complexes with Aβ (Aβ/Exos) that function as "seeds" to catalyze nucleation and propagation of neurotoxic plaques instead of facilitating Aβ transport and clearance by microglia. Secretion, aggregation, and neurotoxicity of Aβ/Exos is enhanced by elevation of ceramide levels, in particular by neutral sphingomyelinase 2 (nSMase2), an enzyme generating ceramide when activated by Aβ. Drug (e.g., nSMase2 inhibitor)-induced reduction of ceramide will prevent Aβ/Exo build-up/spreading and protect neurons, which is a novel treatment option for AD. Our objectives are to 1) test key regulatory factors that control secretion of exosomes and their association with Aβ; 2) test a novel molecular mechanism by which Aβ/Exos induce plaque formation, tau hyperphosphorylation, and neuronal cell death; 3) test pharmacological drugs that prevent exosome secretion, Aβ/Exo-induced plaque formation, tau hyperphosphorylation, and neuronal cell death in vitro and in vivo; and 4) test if Aβ/Exos in serum and cerebrospinal fluid from AD model mice and AD patients can be used as a novel diagnostic tool for monitoring plaque and tangle build-up, and treatment success. Our expected outcomes include 1) determining an exosome composition that induces association with Aβ, plaque nucleation and propagation, tau hyperphosphorylation, and neuronal cell death; 2) identifying ceramide- modulating drugs that prevent Aβ/Exo-induced plaque formation, tau hyperphosphorylation, and neuronal cell death; and 3) defining a level of Aβ/Exos in serum that indicates severity of AD and success of treatment. The impact of this project on public health will include knowledge needed for the development of new strategies and treatments that could delay and reduce the onset of progressive neurodegeneration in AD. We will test by which mechanism ceramide promotes association and aggregation of Aβ42 (Aim 1), how Aβ42/Exos induce plaque formation and neurodegeneration (Aim 2), and which treatment prevents exosome-induced amyloid aggregation, plaque formation, and AD pathology (Aim 3).