Mitochondrial Diseases (MD) are disorders of function in cellular oxidative phosphorylation caused by diverse nuclear DNA and mtDNA mutations and seen in 1/5,000 births. The purpose of this study was to examine relationships across medical indices, biochemical measures, and neurobehavioral functioning in children with MD. Findings from Western Blot, Native Gels, High Resolution Respirometry, and the Nijmegen diagnostic criteria were assessed in relation to children’s processing speed and attention, based on the prediction that impaired functioning of proteins, complexes, and cellular respiration, that are critical in ATP production, will impact neurodevelopment and related neuropsychological processes in children with MD. Twenty-five children (ages 4-13) were administered subtests from the DAS-II and NEPSY-II. Results from multiple regression analyses suggest that processing speed and attention deficits may be markers of abnormal protein expression that interferes with the production of ATP in the oxidative phosphorylation process; implications for future research are presented.

Genetic variation has a powerful impact on human metabolism and disease. Traditionally, this relationship has either been studied at a high level using top-down descriptive studies of patients with genetically defined inborn errors of metabolism, or else from the bottom up, with molecular biology and biochemical studies of single proteins. Recent advances in genetic sequencing, metabolic profiling technology, and structural biology are rapidly enabling the integration of these approaches towards a more complete description of human metabolism.

The human mitochondrial DNA polymerase (Pol γ) catalyzes mitochondrial DNA synthesis, and thus is essential for the integrity of the organelle. Mutations of Pol γ have been implicated in more than 150 human diseases. Reduced Pol γ activity caused by inhibition of anti-HIV drugs targeted to HIV reverse transcriptase confers major drug toxicity. To illustrate the structural basis for mtDNA replication and facilitate rational design of antiviral drugs, I have determined the crystal structure of human Pol γ holoenzyme. The structure reveals heterotrimer architecture of Pol γ holoenzyme with a monomeric catalytic subunit Pol γA, and a dimeric processivity factor Pol γB. While the polymerase and exonuclease domains in Pol γA present high structural homology with the other members of the DNA Pol I family, the spacer between the two functional domains shows a unique fold, and constitutes the subunit interface. The structure suggests a novel mechanism for Pol γ’s high processivity of DNA replication. Furthermore, the structure reveals dissimilarity in the active sites between Pol γ and HIV RT, thereby indicating an exploitable space for design of less toxic anti-HIV drugs. Interestingly, the structure shows an asymmetric subunit interaction, that is, one monomer of dimeric Pol γB primarily participates in interactions with Pol γA. To understand the roles of each Pol γB monomer, I generated a monomeric human Pol γB variant by disrupting the dimeric interface of the subunit. Comparative studies of this variant and dimeric wild-type Pol γB reveal that each monomer in the dimeric Pol γB makes a distinct contribution to processivity: one monomer (proximal to Pol γA) increases DNA binding affinity whereas the other monomer (distal to Pol γA) enhances the rate of polymerization. The pol γ holoenzyme structure also gives a rationale to establish the genotypic-phenotypic relationship of many disease-implicated mutations, especially for those located outside of the conserved pol or exo domains. Using the structure as a guide, I characterized a substitution of Pol γA residue R232 that is located at the subunit interface but far from either active sites. Kinetic analyses reveal that the mutation has no effect on intrinsic Pol γA activity, but shows functional defects in the holoenzyme, including decreased polymerase activity and increased exonuclease activity, as well as reduced discrimination between mismatched and corrected base pair. Results provide a molecular rationale for the Pol γA-R232 substitution mediated mitochondrial diseases. / text

No description available.

Submitted by Caroline Periotto (carol@ufscar.br) on 2016-09-12T14:10:40Z No. of bitstreams: 1 DissCHM.pdf: 2847929 bytes, checksum: db6163924f9983d42120de5673f3df0a (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-13T14:25:07Z (GMT) No. of bitstreams: 1 DissCHM.pdf: 2847929 bytes, checksum: db6163924f9983d42120de5673f3df0a (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-13T14:25:18Z (GMT) No. of bitstreams: 1 DissCHM.pdf: 2847929 bytes, checksum: db6163924f9983d42120de5673f3df0a (MD5) / Made available in DSpace on 2016-09-13T14:25:25Z (GMT). No. of bitstreams: 1 DissCHM.pdf: 2847929 bytes, checksum: db6163924f9983d42120de5673f3df0a (MD5) Previous issue date: 2015-11-30 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Mitochondrial dysfunctions caused by mutations in the mitochondrial DNA (mtDNA) represent an important group of human pathologies. However, it is not possible to predict with accuracy the risk of a woman with mutant mtDNA to transmit her pathology to her descendants. This is mainly due to out limited understanding of the molecular basis of mitochondrial inheritance. Since development of a technology that enabled derivation of induced pluripotent stem cells (iPSCs) from in vitro culture of somatic cells, iPSCs have become an interesting model to study mitochondrial inheritance. Derivation of iPSCs from patients with pathogenic mtDNA mutations has revealed that the mutant load decreases through in vitro culture of iPSCs, suggesting the existence of a specific mechanism that eliminates mutant mtDNA in the germ line. Thus, the aim of this work was to use iPSCs derived from patients with mitochondrial disorders to investigate the existence of a mechanism that eliminates mtDNA molecules with pathogenic mutations. In this way, we used heteroplasmic fibroblasts harboring a point mutation A3243G in mtDNA causing mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS); heteroplasmic fibroblasts harboring a deletion in mtDNA causing Kearn-Sayre Syndrome (KSS) and homoplasmic fibroblasts containing only wild-type mtDNA (Control). The KSS lineage derivation resulted in iPSCs with low levels of mutant mtDNA (<0,1%), and the elimination of mutant molecules during the culture. The MELAS derivation resulted in iPSCs with high levels of mutant mtDNA (> 98%), and indication of mutant molecules elimination as well. However, unexpectedly, there was no reduction of mtDNA content in iPSCs compared to fibroblasts in all lineages. On contrary, mtDNA copy number increased in MELAS and KSS iPSCs, perhaps due to the high levels of mutations in the cells. No effect of Rapamycin (mitophagy inductor) treatment was detected on the yield of colony formation in MELAS iPSCs. Additionally, Rapamycin did not affect the mutation levels in MELAS iPSCS compared to untreated iPSCs. Finally, gene expression analysis of MELAS iPSCs provided evidences of an autophagic mechanism directed towards the mitochondrion. / Disfunções mitocondriais causadas por mutações no DNA mitocondrial (mtDNA) representam um importante grupo de patologias humanas. No entanto, não é possível predizer com acurácia o risco de uma mulher acometida por uma mutação no mtDNA transmitir a patologia para seus descendentes. Isso se deve, em parte, ao desconhecimento dos mecanismos moleculares que controlam a herança mitocondrial. Com o desenvolvimento de metodologias que possibilitam a derivação de células pluripotentes induzidas (iPSCs) a partir de células somáticas cultivadas in vitro, as iPSCs se tornaram um interessante modelo para o estudo da herança mitocondrial. A derivação de iPSCs de pacientes com mutações patogênicas no mtDNA tem revelado que a porcentagem de moléculas mutantes diminui ao longo do cultivo, sugerindo a existência na linhagem germinativa de mecanismos específicos para eliminação de mtDNAs mutantes. Portanto, o presente trabalho investigou em iPSCs derivadas de pacientes com desordens mitocondriais a existência de um mecanismo celular que elimina as moléculas de mtDNA com mutações patogênicas. Para tanto, foram utilizados fibroblastos heteroplásmicos portadores da mutação pontual A3243G no mtDNA causadora de encefalomiopatia mitocondrial, acidose lática e episódios tipo acidente vascular cerebral (MELAS); fibroblastos heteroplásmicos portadores de uma deleção de 4,9 kb no mtDNA causadora da Síndrome de Kearns-Sayre (KSS) e fibroblastos Controle, contendo apenas mtDNA selvagem. A derivação de linhagens portadoras de KSS resultou em iPSCs com baixos níveis de mtDNA mutante (< 0,1%), e na eliminação de moléculas mutantes ao longo do cultivo. A derivação de linhagens portadoras de MELAS resultou em iPSCs com alta taxa de mutação (> 98%), também com indícios de diminuição da quantidade de moléculas mutantes ao longo do cultivo. No entanto, ao contrário do esperado, não houve diminuição da quantidade de cópias de mtDNA nas iPSCs em relação aos fibroblastos em todas as linhagens (Controle, KSS e MELAS), sendo que as iPSCs de MELAS e KSS apresentaram um aumento significativo na quantidade de cópias de mtDNA, provavelmente devido a efeitos causados pela mutação no mtDNA. Ao analisar o efeito do tratamento com Rapamicina (indutor de mitofagia) durante a derivação de MELAS não observamos aumento na eficiência de formação de colônias, além de o tratamento não afetar a quantidade de mtDNA mutante, resultando em iPSCs com níveis de mutação similares aos encontrados nas iPSC MELAS não tratadas com o rapamicina. Por fim, resultados de expressão gênica das iPSCs do grupo MELAS revelaram indícios de mecanismos autofágicos direcionados a mitocôndria provavelmente devido ao efeitos causados pela a alta taxa da mutação. / 2013/13869-5

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23034号 / 理博第4711号 / 新制||理||1675(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 杉山 弘, 教授 深井 周也, 教授 秋山 芳展 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

No description available.

No description available.

No description available.

Eight carriers of the A3243G mutation of mitochondrial DNA without stroke-like episodes were monitored for up to 7 years in clinical and metabolic studies, by magnetic resonance imaging (MRI) and positron emission tomography (PET). None developed mitochondrial encephalopathy (MELAS), but 2 developed diabetes mellitus, 1 terminal kidney failure and 2 cardiomyopathy. One patient improved markedly under ubiquinone. Electroencephalography showed progressive slowing in 2 cases, but electrophysiological tests and MRI were otherwise noncontributary. PET showed widespread cortical and basal ganglion metabolic deficits in 6 cases. We conclude that internal medical complications are more common than MELAS in adult carriers of the mutation. PET findings, firstly reported in such patients, suggest that chronic subclinical encephalopathy is very frequent, and PET may play a role in monitoring in the future. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.