Investigating mitochondrial dysfunction in the nervous system

Abstract

Mitochondria play critical roles in the generation of cellular energy, apoptosis, calcium buffering, and mitochondrial dysfunction is strongly implicated in common neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. However, we still have a very poor understanding of the consequences of mitochondrial dysfunction in neurons in vivo. This thesis investigates mitochondrial dysfunction in patients with neurodegenerative disease and in a novel Drosophila model of neuronal mitochondrial dysfunction. I found that a single nucleotide polymorphism (SNP) in the gene mitochondrial transcription factor A (TFAM, SNP rs2306604 A>G) is associated with Parkinson’s disease dementia (PDD), but not with dementia with Lewy bodies (DLB). I have shown that mitochondrial DNA levels are significantly reduced in the frontal cortex of PDD patients, compared to controls. Furthermore, I have characterised the expression of TFAM and representative components of the mitochondrial electron transport (ETC) chain at the protein level in patients with Parkinson’s disease with and without dementia to determine whether rs2306604 A>G affects TFAM or ETC protein expression. In order to investigate mitochondrial dysfunction in a genetically tractable model system I have used a novel model of neuronal-specific mitochondrial dysfunction in Drosophila. I have used overexpression of TFAM, or expression of a mitochondrially-targeted restriction enzyme mitoXhoI, to cause mitochondrial dysfunction specifically in neurons. I have analysed the changes in mitochondrial DNA and mitochondrial gene expression in this model as well as characterising the behavioural and synaptic phenotypes. Using this model I performed microarray analysis to characterise the mitochondrial retrograde response in the Drosophila nervous system. This analysis revealed that neuronal mitochondrial dysfunction alters the expression of over 300 genes. I have validated the changes in expression of several of these genes in vivo. I have also characterised the involvement of the transcription factor hypoxia inducible factor alpha (HIFα) in the mitochondrial retrograde response in Drosophila. I found that HIFα regulates the expression of several retrograde response genes and that modulation of HIFα expression ameliorates some of the phenotypes associated with mitochondrial dysfunction.

Date of Award	2015
Original language	English
Awarding Institution	King's College London
Supervisor	Joseph Bateman (Supervisor) & Clive Ballard (Supervisor)