Caractérisation de modèles pouvant modifier le métabolisme énergétique mitochondrial : syndrome de Leigh et haplogroupes mitochondriaux

Abstract : The mitochondrion is an intracellular organelle responsible for the cellular energy production, by synthesizing ATP through the oxidative phosphorylation (OXPHOS). One of the characteristics of this organelle is that it has its own DNA (mtDNA) encoding for subunits of OXPHOS complexes. Any alterations of mitochondrial energy metabolism cause mitochondrial pathologies whose severity is generally inversely proportional to the age of onset. Some scientific studies are looking at the mechanisms of occurrence and development of these diseases in order to better understand them and to be able to offer therapies. However, there is no tool that can transform mtDNA in a targeted way by mutation or DNA rearrangement. Moreover, there are still few animal models of mitochondrial pathology that would allow integrative studies on the one hand, and on the other hand, to try out possible therapeutic molecules. In this thesis, we studied two types of models involving the modification of mitochondrial metabolism either by chemical treatment or by the use of mutations found in individuals. In a first part, we were interested in the realization of mouse model with a large number of characteristics of the Leigh syndrome, a progressive neurological disease characterized by neuropathological lesions associating a damage of the brain stem and the basal ganglia. For this study, we have used the 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP) neurotoxin, known for its toxicity to dopamine neurons and also as an inhibitor of mitochondrial respiratory chain. We analyzed the activity of the OXPHOS complexes I to IV on brain tissues (cerebelum, cortex, striatum and substancia nigra) and peripheral tissues (heart, liver, muscle and kidney) from treated and untreated mice. Inhibition of complexes III and/or IV in the liver, cortex, striatum and cerebellum was found. These results, combined with an increased neurodegeneration found in a previous study, are all characteristics of Leigh Syndrome. Mice treated with MPTP seem to be a good model for this mitochondrial pathology. In the second project, we looked at the effect of mtDNA haplogroups (haplotypes grouping) on mitochondrial metabolism. Although, haplogroups are defined by neutral mutations of mtDNA (polymorphism), several studies have shown associations between haplogroups and some pathologies suggesting that haplogroups are able to have a protective effect or being a risk factor in the pathology development. Recently, our laboratory has confirmed that some haplogroups may not be neutral and have the ability to influence the mitochondrial energy metabolism functioning. Therefore, my research project consisted of setting up a model to study these cellular and molecular mechanisms. We looked for haplogroups of interest in the population in order to elaborate a cellular collection where each cell line has a particular haplogroup but with a common nuclear genetic background in all the cell lines. This collection was obtained by cybride constructions. We characterized these cybrides biochemically by analyzing the activity of each complex, determining kinetic parameters (KM and Vmax) and titration specific respiratory chain inhibitors. Concomitantly, we defined cell parameters via growth curves. All these results were integrated into a computer model specifically developed in our laboratory to model mitochondrial processes. This project gives us some evidence of the mtDNA haplogroups' influence on mitochondrial metabolism and to propose a modulated vision of mitochondrial pathologies for their study and their diagnosis, highlighting the notion of personalized medicine. As each haplogroup modulates in the different way the mitochondrial metabolism, each individual could have a personal response to the same mutation or pathology. In future, the mtDNA genetics background should be taken into account to find new strategies or new targets for the therapies of mitochondrial diseases.
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Barbara da Costa. Caractérisation de modèles pouvant modifier le métabolisme énergétique mitochondrial : syndrome de Leigh et haplogroupes mitochondriaux. Anthropologie biologique. Université Paul Sabatier - Toulouse III, 2017. Français. ⟨NNT : 2017TOU30325⟩. ⟨tel-01990554⟩

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