Characterisation of mitochondria by electron microscopy

Abstract

Mitochondria have varied morphology depending on the tissue, cell type, and location within the cell. Brain and skeletal muscle are among the most metabolically active tissues and are particularly vulnerable to mitochondrial defects. In particular, alteration to mitochondrial dynamics and morphology have been demonstrated in several pathological conditions, including mitochondrial disease and ageing. This thesis, therefore, will be separated into two parts. The first part aimed to advance the characterisation of the mitochondrial morphology and function link in skeletal muscle of mitochondrial disease patients. I optimised cytochrome c oxidase electron microscopy (COXEM) technique to investigate mitochondrial morphology and COX activity using mouse muscle by serial block-face EM (SBF-SEM). This technique was then used to investigate the link between mitochondrial morphology and COX deficiency in human skeletal muscle affected by mitochondrial disease. Using the optimised COX-EM technique I discovered three mitochondrial COX activity populations within muscle fibres. I also showed that COX deficient fibres exhibited fragmented and spherical mitochondria compared to those fibres with normal COX activity. The second part aimed to understand better the cellular and network-level changes in memoryrelated areas during ageing within the hippocampal region of mouse brain. I used SBF-SEM to map and define mitochondrial morphology in the specific region (CA1 and DG region) of the young and old mouse hippocampus. I showed that mitochondrial morphology differs between sub-cellular location with major morphological differences between axonal and dendritic mitochondria. My studies also showed that the DG may be more vulnerable to the effects of ageing In conclusion, this work advances our understanding of mitochondrial morphology in human muscle and ageing mouse hippocampus.