Tubulin and tau protein changes in ischaemic brain injury: implications for vascular dementia and Alzheimer’s disease

Background:
Vascular abnormalities are associated with cognitive decline, ranging from mild cognitive impairment to fulminant dementia, including those in Alzheimer’s disease (AD) and vascular dementia (VaD). The overlap of these two most common causes of dementia has been further documented by the high prevalence of similar vascular risk factors underlying their cognitive impairment, the risk for AD increasing after a stroke or transient ischaemic attacks. Our previous work has demonstrated that one of the neuropathological hallmarks of AD, Aβ protein accumulation, although prominent in AD and present in other ageing-related dementias, has distinctive patterns of localization in VaD. Furthermore, VaD subjects over the age of 80 years have almost equal concentrations of soluble Aβ42 as AD subjects, suggesting that increasing age is a risk factor for development of AD-like neuropathology in VaD. Although this is known for total extractable Aβ, what befalls the microtubule associated tau protein or tubulin that may explain the metabolism of tau or tubulin proteins and the lack of characteristic neurofibrillary pathology in VaD?

We recently described neuronal cell volume changes in the dorsolateral prefrontal cortex (DLPFC), with the neuronal cell volume significantly decrease in people with dementia, including VaD, post-stroke dementia (PSD) and AD, and followed up these findings with a biochemical study to elicit the aetiology of these changes. The smaller neuronal volumes observed in the neocortical layers III and V in VaD subjects and PSD occurred in the absence of visible neuropathological changes in the same area, but there was loss of t-SNARE complex proteins (syntaxin and SNAP-25) and tubulin, but not tau protein. This suggests that the loss of tubulin in VaD maybe an early molecular intraneuronal change preceding the changes in other cytoskeletal proteins.

Hypothesis:
Reduced brain perfusion leads to cortical and white matter changes, which contribute to the degeneration of the neuronal cytoskeleton. Molecular changes in tubulin and tau proteins are related to the lack of neurofibrillary pathology in cerebral ischaemic injury. To test these hypotheses, we propose one main aim to address the questions below:

Aim:
Characterisation of protein changes in vascular and neurodegenerative pathologies. For this, we will determine: 1. Specific changes in α -and β-tubulin subunits in VaD compared to other causes of dementia ie AD. 2. Specific posttranslational tubulin changes characteristic for VaD. 3. How are tubulin changes related to total and phosphorylated tau in VaD? 4. How are these changes related to underlying neurofibrillary pathology (tangles, plaques and dystrophic neurites) and cognitive impairment in people with VaD.
Expected outcomes for dementia: Mapping the sequence of molecular events leading to dementia as a result of cerebral ischaemic injury, and modelling the disease process will help us understand the early neurobiological substrates of dementia in these subjects. The knowledge from this study has a potential to lead for novel pharmacological treatment to aid both prevention and cure of ischaemic VaD.

Experimental design and methods to investigate the problem
Sample recruitment: The brain tissue [grey and underlying white matter from frontal (BA9/46) and temporal (BA21/22) neocortical areas] will come from 33 controls, 27 Alzheimer disease, 15 Post-stroke no dementia, 23 PSD and 20 VaD subjects (total n=118). The study has an ethical approval for post mortem brain tissue research. Research plan: It includes biochemical analysis of brain homogenate and consists of a brain protein extraction and protein of analysis [quantitative measurements of α- (including acetylated and carboxyl-terminus polyglutamylated α-tubulin) and β- tubulin, as well as total and p- tau protein with ELISA assays), supported by a detailed correlative clinico-neurochemical analysis.

Learning outcomes: At the end of the PhD course, the student will: have a thorough knowledge of the literature and a comprehensive understanding of scientific methods and techniques applicable to their own research; be able to demonstrate originality in the application of knowledge, and a practical understanding of how research and enquiry are used to create and interpret knowledge in their field; has developed the ability to critically evaluate current research and research techniques and methodologies; has self-direction and originality in tackling and solving problems; be able to act autonomously in the planning and implementation of research; and has gained oral presentation and scientific writing skills.