Biomedical subjects

M E Vazquez-Memije

Publications and source records attributed to M E Vazquez-Memije.

4 recordsLinked to original sources

PubMed2000

Rearrangements of human mitochondrial DNA (mtDNA): new insights into the regulation of mtDNA copy number and gene expression.

Mitochondria from patients with Kearns-Sayre syndrome harboring large-scale rearrangements of human mitochondrial DNA (mtDNA; both partial deletions and a partial duplication) were introduced into human cells lacking endogenous mtDNA. Cytoplasmic hybrids containing 100% wild-type mtDNA, 100% mtDNA with partial duplications, and 100% mtDNA with partial deletions were isolated and characterized. The cell lines with 100% deleted mtDNAs exhibited a complete impairment of respiratory chain function and oxidative phosphorylation. In contrast, there were no detectable respiratory chain or protein synthesis defects in the cell lines with 100% duplicated mtDNAs. Unexpectedly, the mass of mtDNA was identical in all cell lines, despite the fact that different lines contained mtDNAs of vastly different sizes and with different numbers of replication origins, suggesting that mtDNA copy number may be regulated by tightly controlled mitochondrial dNTP pools. In addition, quantitation of mtDNA-encoded RNAs and polypeptides in these lines provided evidence that mtDNA gene copy number affects gene expression, which, in turn, is regulated at both the post-transcriptional and translational levels.

Cell Division↗

PubMed1999

Oligomycin induces a decrease in the cellular content of a pathogenic mutation in the human mitochondrial ATPase 6 gene.

A T --> G mutation at position 8993 in human mitochondrial DNA is associated with the syndrome neuropathy, ataxia, and retinitis pigmentosa and with a maternally inherited form of Leigh's syndrome. The mutation substitutes an arginine for a leucine at amino acid position 156 in ATPase 6, a component of the F0 portion of the mitochondrial ATP synthase complex. Fibroblasts harboring high levels of the T8993G mutation have decreased ATP synthesis activity, but do not display any growth defect under standard culture conditions. Combining the notions that cells with respiratory chain defects grow poorly in medium containing galactose as the major carbon source, and that resistance to oligomycin, a mitochondrial inhibitor, is associated with mutations in the ATPase 6 gene in the same transmembrane domain where the T8993G amino acid substitution is located, we created selective culture conditions using galactose and oligomycin that elicited a pathological phenotype in T8993G cells and that allowed for the rapid selection of wild-type over T8993G mutant cells. We then generated cytoplasmic hybrid clones containing heteroplasmic levels of the T8993G mutation, and showed that selection in galactose-oligomycin caused a significant increase in the fraction of wild-type molecules (from 16 to 28%) in these cells.

Adenosine Triphosphatases↗

PubMed1996

Comparative biochemical studies in fibroblasts from patients with different forms of Leigh syndrome.

We have compared respiratory chain enzyme activities, ATP synthesis, and ATP hydrolysis in cultured fibroblast mitochondria from patients with Leigh syndrome (LS) due to: (i) cytochrome oxidase (COX) deficiency (#6); (ii) pyruvate dehydrogenase complex (PDHC) deficiency (#4); and (iii) maternally inherited LS (MILS) with the T8993G mutation in the ATPase 6 gene of mtDNA (#5). Enzyme activities were normal in patients with MILS and variably decreased in those with COX and PDHC deficiency. ATP hydrolysis was normal or mildly decreased in all three groups. In contrast, ATP synthesis was decreased in all patients but more markedly in those with MILS, and especially with pyruvate/malate as substrate. These studies show that impaired ATP production is the common feature of all three forms of LS, but it is both more severe and more specific in MILS, consistent with the genetic defect.

Adenosine Triphosphatases↗

PubMed1996

Clinical heterogeneity associated with the mitochondrial DNA T8993C point mutation.

The mitochondrial DNA (mtDNA) point mutation T8993G has been associated with maternally inherited Leigh syndrome (MILS) when very abundant (> 95%). MILS patients are usually severely affected and die in early infancy. In 1993, a novel T8993C point mutation was described in a juvenile form of Leigh syndrome (LS) characterized by a less aggressive clinical course. We describe four unrelated T8993C patients who had diverse, relatively mild, clinical manifestations. Polymerase chain reaction-restriction fragment length polymphorphism analysis showed that the heteroplasmic T8993C point mutation was very abundant in several tissues from all four patients (94.2 +/- 1.5%) but was less copious in blood from 20 maternal relatives. ATP production in mitochondria isolated from skin fibroblasts in three patients was normal, whereas in one patient it was decreased to 20-35% of controls. These findings suggest that the T8993C mutation is less severe than the more common T8993G mutation.

Adenosine Triphosphate↗