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Title: Brain iron trafficking in health and disease : a systems approach
Author: Tjendana Tjhin, Vindy
ISNI:       0000 0004 8498 0332
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2019
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The study in this thesis sets to explore the techniques to study the iron trafficking into the brain, and more closely in the substantia nigra par compacta (SNpc) region, and also, the altered iron loading mechanism, with particular application in disorders where specific compartments show elevated iron concentration, such as Parkinson's disease (PD). Iron is essential for numerous biochemical reactions in the brain, but excess iron may produce reactive oxygen species that can induce cell death. The increase in iron concentration in this area has been shown repeatedly over the years, and it has been accepted as one of the main characteristics of PD. Another main characteristic of PD is the loss of neuromelanin containing dopaminergic (DA) neurone in the SNpc. Neuromelanin binds to and stores iron. The disappearance of neuromelanin in the SNpc is another indication that iron is involved in the progression of PD. The detail of iron involvement in PD, however, is still unknown. Attempts have been made in this thesis to create tools to answer some of the questions by image analysis to examine post-mortem human brain tissue; and building a novel computational model of iron transport into the brain. Synchrotron-based experiments, scanning transmission X-ray microscopy (STXM) and synchrotron X-ray fluorescence (SXRF), on post-mortem tissue are described in this thesis to investigate the spatial distribution and relative concentration of iron in the DA neurone and the redox state of the iron. These methods do not require dyes or fixing of the sample, thus allowing the native chemistry of the tissue samples to be better preserved. The investigation of the chemical state of iron using STXM method is of interest because it shows the region-specific toxicity state of the iron in the tissue and the neuromelanin. SXRF mapping can produce a high-resolution map of iron distribution in the tissue, and also calculate the relative concentration of iron in the DA neurone compared to the extracellular concentration. SXRF mapping and processing are described in detail in this thesis to inform how SXRF could be an excellent tool to study the involvement of iron in the PD. SXRF maps from experiments performed before this project are analysed and presented here. The iron absorption spectra from STXM mapping of 200 nm resin-embedded tissues revealed the presence of redox-active iron in the PD case but not in the control. This result supports the hypothesis that the cell death in PD is induced by oxidative stress. Carbon Kedge examination of the neuromelanin in the tissue reveals a feature in the energy spectrum that is possibly unique to neuromelanin. However, further study needs to be done to confirm this finding. The result of such a study would allow label-free direct analysis of the chemical state of iron in the neuromelanin and to determine if the state changes in PD. Two computational models were built to create in silico representations of (1) iron transport into the interstitial fluid of the brain, and (2) iron transport into the DA neurones, using the modelling software COPASI. Model 1, the barrier systems model, was based on an existing well-developed concept from Drs Mitchell and Collingwood, and the original work in this thesis arose from testing and refining the model. Model 2, the DA neurone model, is completely original work, and designed so that it can be integrated with the barrier systems model in the longer term. The models are comprised from nonlinear ordinary differential equations which are used to characterise the kinetics of each chemical species incorporated. Model parameters values for compartmental volumes, and initial concentrations and rate constants for each species, were derived from experimental results from the literature. The simulations show that the regulatory activity of the brain barrier systems protects the brain against excessive iron loading, and a sensing mechanism may be required to prevent low brain iron concentration. Metabolic control analysis identified TfR as the key regulatory factor of iron concentration in the dopaminergic neurones and also the brain barrier systems. These new models are, to the best of our knowledge, the most comprehensive computational models of brain iron transport that have been developed to date. It is intended that they will provide in silico resources to explore the dysregulation of iron transport in PD and related disorders. The synchrotron-based mapping techniques and computational modelling presented in this thesis are excellent tools to study the implication of iron in PD. The SXRF mapping has the potential to produce a cell-specific concentration of iron as an input to the computational model, and the STXM mapping has the potential to reveal the basic knowledge for building the models, such as the compartmentalisation of the iron deposits in the neuromelanin. The synchrotron-based analyses produce results that are useful in the building of the computational model, and the computational models reveal the dynamic processes involved that cannot be observed from post-mortem analysis, so they are both critical. In combination, they offer a new approach to study unresolved questions in the field.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council ; University Hospitals Coventry and Warwickshire NHS Trust ; University of Warwick
Qualification Name: Thesis (D.Eng.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry ; QP Physiology ; RC Internal medicine