The regulation of tau-dependent neurodegeneration by Brain Selective/SAD kinases
Lyn-Adams, Ceri Louise (2011) The regulation of tau-dependent neurodegeneration by Brain Selective/SAD kinases. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2533308~S1
Brain-selective kinases (BRSK1 and BRSK2) are serine/threonine kinase members of the AMPK-related family of protein kinases, the majority of which are regulated by the upstream kinase LKB1 whilst AMPK itself is regulated by CaMKK. The BRSKs are highly expressed in brain and have been implicated in neuronal polarization and the regulation of neurotransmitter release. They have also been shown to be involved in the basal phosphorylation of tau at the Alzheimer‟s disease (AD) related residue, serine 262, and are highly expressed in areas of the brain affected by AD, namely the hippocampus and the cortex. I have utilised the model organism Drosophila melanogaster to investigate interactions between transgenically expressed human tau, human BRSKs and upstream regulators Selective over-expression of 0N4R human tau in the Drosophila eye resulted in a disruption of eye morphology. In contrast, over-expression of human wild type BRSK2 (B-WT) had no obvious effect on the eye. However, co-expression of both tau and B-WT resulted in a neurodegenerative phenotype more severe than tau alone. This enhancement of phenotype was not observed when BRSK2 was expressed that either lacked the activating phosphorylation site (non-phosphorylatable, B-NP) or that is unable to bind ATP (kinase dead, B-KD). Co-expression of human tau and BWT significantly elevated tau phosphorylation at S262, suggesting that S262 is a key residue for tau-induced toxic phenotypes and the BRSK/tau interaction I observe. In support of this, no phenotype was observed in flies expressing the S262A variant of human tau with or without B-WT. To establish the upstream kinases responsible for activating human BRSK2 in Drosophila I removed endogenous Drosophila LKB1 by RNAi. This prevented the enhanced degeneration of the eye caused by tau/B-WT co-expression, demonstrating that LKB1 is a key upstream regulator of BRSK2. I also found that down regulation of the Drosophila CaMKK homologue, CG17698, by the same method, ameliorated B-WT induced eye degeneration implicating a calcium-dependent pathway in the regulation of BRSK. Over-expression of human CaMKKα in the CG17698 RNAi background prevented the rescue seen with CG17698 RNAi. Over-expression of cac1, a calcium channel subunit, in the presence of B-WT and human tau exacerbated the B-WT induced eye phenotype in a B-WT dependent manner, supporting the hypothesis that the human tau and B-WT interaction can be regulated in a calcium-dependent manner. Expression of total BRSK2, LKB1 and CaMKK were not altered in human postmortem AD brain tissue when compared to control. However, with the exception of LKB1, due to limited reagents and time constraints I was unable to investigate the proportion of phosphorylated (and thus active) to total kinase. This study defines a novel Ca2+ -dependent regulatory pathway to tau, which may contribute to AD and other tauopathies.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||Q Science > QP Physiology|
|Library of Congress Subject Headings (LCSH):||Protein kinases, Nervous system -- Degeneration, Drosophila melanogaster -- Physiology|
|Institution:||University of Warwick|
|Theses Department:||School of Life Sciences|
|Supervisor(s)/Advisor:||Frenguelli, Bruno ; Moffat, Kevin ; Sutherland, Calum|
|Sponsors:||Alzheimer's Research UK|
|Extent:||316 leaves : ill., charts|
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