Research Progress on the Role of Mitochondrial DNA in the Pathogenesis of Chronic Liver Disease / 中华肝脏病杂志

Mitochondrial DNA is the mitochondria's own genetic material located within the mitochondrial matrix and is involved in cellular metabolism and energy supply. Mitochondrial DNA damage exacerbates oxidative stress by increasing the release of reactive oxygen species, while mitochondrial DNA release also triggers apoptosis and activates immune inflammatory responses through damage-related molecular patterns. Mitochondrial autophagy regulates mitochondrial DNA damage and release through a negative feedback mechanism to maintain intracellular homeostasis. Recent studies have shown that the occurrence and development of chronic liver disease are closely related to mitochondrial DNA-mediated immune inflammatory responses and oxidative stress.

Depletion of Mitochondrial DNA Stabilizes C1qTNF-Related Protein 6 mRNA in Muscle Cells

Mutation and reduction of mitochondrial DNA (mtDNA) have been suggested as factors in the pathogenesis of several metabolic diseases. Recently, we demonstrated that C1qTNF-related protein-6 (CTRP6) is involved in fatty acid metabolism in muscle cells. In this study, we showed that expression of CTRP6 was up-regulated in mtDNA-depleted C2C12 cells, which displayed a marked decrease in cellular mtDNA and ATP content. Replacement of mtDNA normalized the expression level of CTRP6 similar to that in normal C2C12 cells, indicating that CTRP6 expression was up-regulated by mtDNA depletion. However, CTRP6 promoter activity remained unchanged in mtDNA-depleted cells. We also found that mtDNA depletion inhibited decay of CTRP6 mRNA. Taken together, mtDNA depletion induces an increase in CTRP6 expression by increasing mRNA stability.

Síndrome de Kearns-Sayre / Kearns-Sayre syndrome

A síndrome de Kearns-Sayre é uma patologia rara, que acarreta piora da qualidade de vida; caracteriza-se por oftalmoplegia externa progressiva, fraqueza muscular e distúrbios na condução cardíaca. A entidade integra um grupo de desordens do metabolismo mitocondrial, denominadas miopatias mitocondriais ou citopatias mitocondriais.

Kearns-Sayres syndrome is a rare pathology which leads to a worse quality of life of the individual; it is characterized by progressive external ophthalmoplegia, muscular weakness, and cardiac conduction defects. The disease belongs to a group of mitochondrial metabolic disorders, named mitochondrial myopathies of mitochondrial cytopathies.

Depletion of mitochondrial DNA up-regulates the expression of MDR1 gene via an increase in mRNA stability

The mutation and reduction of mitochondrial DNA (mtDNA) have been suggested as factors in the carcinogenesis. However, whether the depletion of mtDNA induces multidrug resistance in cancer cells has not been fully investigated. To elucidate the association of cellular mtDNA content and drug resistance, we generated HCT-8 colon cancer cells which revealed a marked decrease in cellular mtDNA and ATP content, concomitant with a lack of mRNAs encoded by mtDNA. The mtDNA-depleted cells showed a decreased sensitivity and accumulation of anti-cancer drugs, suggesting that mtDNA depletion could develop multidrug resistance (MDR) phenotype in HCT-8 cells. We found that the expression level of MDR1 mRNA and its translated product P-glycoprotein was increased in the mtDNA- depleted cells, indicating that the decrease of sensitivity and accumulation of anti-cancer drug in the mtDNA-depleted cells might be due to a substantial increase in the expression of P-glycoprotein. Furthermore, increased expression of MDR1 mRNA and P-glycoprotein was due to an increase of mRNA stability rather than transcriptional activation. Taken together, these results indicate that mtDNA depletion can induce an increased P-glycoprotein expression via an increase of mRNA stability and suggest that the mtDNA depletion in cancer cells plays an important role in the induction of MDR phenotype.

Age-dependent mitochondrial DNA 4977bp depletion in human skeletal muscle / 法医学杂志

OBJECTIVE@#To explore depletion of human mitochondrial DNA 4977-bp and its relation with aging.@*METHODS@#Total DNA (nuclear and mtDNA) was extracted from 100mg muscle tissue. UV light illumination of ethidium bromide-stained PCR products was used to study the depletion of mtDNA (wild-type or mutant).@*RESULTS@#The proportions of mtDNA depletion in human skeletal muscle could be determined. The frequency of mtDNA 4977-bp depletion in different age groups (0-9, 10-19, 20-29, 30-39, 40-49, 50-59, 60-69, 70-79, 80-89, 90-99) was: 0%, 0%, 0.003%, 0.011%, 0.015%, 0.033%, 0.038%, 0.062%, 0.069%, and 0.091%, respectively.@*CONCLUSION@#Our findings suggest that the frequency of the mtDNA4977 depletion in human skeletal muscle increases with age. It might be useful for human age estimation.

Mitochondrial DNA damage associated with lipid peroxidation of the mitochondrial membrane induced by Fe2+-citrate

Desequilíbrio/acúmulo de ferro tem sido implicado em injúria oxidativa associada a diversas doenças degenerativas tais como, hemocromatose hereditária, b-talassemia e ataxia de Friedreich. As mitocôndrias são particularmente sensíveis a estresse oxidativo induzido por ferro - um carregamento alto de ferro em mitocôndrias isoladas pode causar uma extensiva peroxidação lipídica e a permeabilização de membrana. Nesse estudo, nós detectamos e caracterizamos danos do DNA mitocondrial em mitocôndrias isoladas de fígado de rato, expostas ao complexo Fe2+-citrato, um dos complexos de baixo peso molecular. A intensa fragmentação do DNA foi induzida após a incubação das mitocôndrias com o complexo de ferro. A detecção de finais 3' de fosfoglicolato nas quebras de fitas de DNA mitocondrial pelo ensaio 32P-postlabeling sugere um envolvimento de radicais hidroxila na fragmentação do DNA induzido por complexo Fe2+-citrato. Os níveis elevados de 8-oxo-7,8-diidro-2'-desoxiguanosina também sugerem que o estresse oxidativo induzido por Fe2+-citrato causa danos no DNA mitocondrial. Em conclusão, nossos resultados mostram que a peroxidação lipídica mediada por ferro esteve associada com severos danos do DNA mitocondrial derivados de ataque direto das espécies reativas de oxigênio.

Increase in mitochondrial DNA quantity and impairment of oxidative phosphorylation in bovine fibroblast cells treated with ethidium bromide for 15 passages in culture

Bovine fetal fibroblast cells were treated with ethidium bromide at a low concentration for 15 passages in culture to determine its effect on mitochondrial DNA copy number and on cell metabolism. Mitochondrial membrane potential and lactate production were estimated in order to characterize cell metabolism. In addition, mitochondrial DNA ND5 in proportion to a nuclear gene (luteinizing hormone receptor) was determined at the 1st, 2nd, 3rd, 10th, and 15th passages using semi-quantitative PCR amplification. Treated cells showed a lower mitochondrial membrane potential and higher levels of lactate production compared with control cells. However, the mitochondrial DNA/nuclear DNA ratio was higher in treated cells compared with control cells at the 10th and 15th passages. This ratio changed between the 3rd and 10th passages. Despite a clear impairment in mitochondrial function, ethidium bromide treatment did not lead to mitochondrial DNA depletion. It is possible that in response to a lower synthesis of ATP, due to an impairment in oxidative phosphorylation, treated cells develop a mechanism to resist the ethidium bromide effect on mtDNA replication, resulting in an increase in mitochondrial DNA copy number.

report of rapid and efficient methods for mitochondrial DNA purification from human platelets

Based on the similarity of prokaryotic DNA to that of mitochondrial DNA, a rapid and efficient method for DNA purification from mitochondrial extracts obtained from different sources, was carried out based on the modification method described by Marmur [1983] which resulted in a high degree of purity [A260/A280=2] In addition we have applied the same technique for the first time to purify the mitochondrial DNA of platelets