Phosphorylation based Models of Neurodegenerative Diseases

• Main Author: Koss, David John
• Published: University of Aberdeen 2008
• Subjects: 616.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485668

Aberrant protein phosphorylation is a hallmark of neurodegenerative diseases, such as Alzheimer's disease (AD) and tauopathies. Pathological phosphorylation is commonly observed as intracellular tau containing deposits correlating with neuronal death. Tau is a cytoskeletal protein, key to the stabilisation of the microtubules (MT), important ,for structural integrity and protein trafficking. Tau's ability to promote MTs is regulated by protein phosphorylation by kinases/phosphatases. In spontaneous AD, the activity/expression of kinases are enhanced w$ilst phosphatases are decreased. Alterations in phosphorylation have significant regulatory effects on neuronal signalling which may lead to deficits in neuronal signalling prior to neuronal death. Using cultured rat hippocampal neurons and pharmacological inhibitors of serine/threonine (Okadaic acid and Cantharidin) and tyrosine (Sodium orthovanadate) phosphatases, the consequences of increased phosphorylation for neuronal signalling were investigated. Using Fura-2 Ca2+ imaging, serine/threonine phosphatase inhibition was determined to exert bidirectional modulation on neuronal excitability. Low level short duration inhibition enhanced, whilst str9nger or more prolonged inhibition suppressed Ca2 + responses towards stimulation. Suppression of excitability was coincident with' a reduction in receptor expression and an increase in cytoskeletal phosphorylation. The data mimic changes in signalling utilising alternative means of modelling AD, suggesting that common ' phosphorylation cascades may be active within these models and in the disease process. Acute inhibition of tyrosine phosphatases evoked a prolonged Ca2 + response dependent on the activation of trans-plasma membrane Ca2+ channels. Prolonged inhibition of tyrosine phosphatases enhanced neuronal excitability. A novel sponge toxin polymeric 1,3-alkylpyridinium salts was employed as an agent for inducing tau over-expression in cultured neurons and further Ca2 + imaging studies conducted. Modulation on excitability was observed to be dependent on the level oftau expression. Overall, this thesis furthers the understanding of phospho-regulation of neuronal signalling ~oth physiologically, and pathologically and provides preliminary data for novel roles of tau in neuronal signalling regulation.