Increases of Mitochondrial Mass and Mitochondrial Genome in Association with Enhanced Oxidative Stress in Human Cells Harboring 4,977 BP‐Deleted Mitochondrial DNA

Abstract

In order to investigate the effect of aging-and disease-associated deletion of mtDNA on cellular functions, we used cytoplasm fusion to construct a series of the cybrids harboring varying proportions of mtDNA with 4,977 bp deletion from skin fibroblasts of a patient with chronic progressive external ophthalmoplegia. The cybrids were grown in the Dulbecco's modified Eagle medium supplemented with 5% fetal bovine serum, 100 g/ml pyruvate and 50 g/ml uridine. The population doubling time was longer for the cybrids containing higher proportions of 4,977 bp-deleted mtDNA. In addition, we found that the respiratory function was decreased with the increase of mtDNA with 4,977 bp deletion in the cybrids. Since impairment of the respiratory system of mitochondria increases the electron leak of the respiratory chain, we further determined the oxidative stress in these cybrids. The results showed that the specific contents of 8-hydroxy 2-deoxyguanosine and lipid peroxides of the cybrids harboring > 65% of the 4,977 bp-deleted mtDNA were significantly increased as compared with those of the cybrids containing undetectable mutant mtDNA. On the other hand, we found that the mitochondrial mass and the relative content of the mitochondrial genome in the cybrids harboring 4,977 bpdeleted mtDNA were higher than those of the cybrids containing only wild type mtDNA. The relative content of mtDNA was increased 17% and 30%, respectively, in the cybrids harboring 17% and 56% of mtDNA with 4,977 bp deletion. Moreover, both mitochondrial mass and mtDNA content were concurrently increased by treatment of the cybrids with 180 M of hydrogen peroxide. Taken these findings together, we conclude that increase of mitochondrial mass and mtDNA are the molecular events associated with enhanced oxidative stress in human cells with impaired respiratory function caused by mtDNA deletion.

Increased Mitochondrial DNA Content in Saliva Associated with Head and Neck Cancer

“…Mitochondrial alterations have long been suspected as contributes to carcinogenesis (16). Previous studies showed that the increased mtDNA in human cells harboring 4,977 bp deleted mtDNA in response to oxidative stress (17). In addition, mitochondrial genomic mutations have been found in HNSC (11).…”

Mitochondrial DNA deletions inhibit proteasomal activity and stimulate an autophagic transcript

“…Thus, the very strong inhibition of many subunits of the ubiquitin-proteasome system is likely a consequence of misfolded and damaged mitochondrial proteins specified by the mtDNA deletions. Also, recent studies have demonstrated that mtDNA deletions increase ROS production, which would seem to compound the misfolding/damage problem [31]. To test these ideas, we measured oxidative damage to proteins by the Oxyblot method, and observed a >300% increase in oxidized proteins.…”

Impact of Nucleoside Reverse Transcriptase Inhibitors on Mitochondria in Human Immunodeficiency Virus Type 1-Infected Children Receiving Highly Active Antiretroviral Therapy

“…Because ZDV has been reported to cause significant mitochondrial toxicity in different in vitro models (23), this may reflect a compensatory response to mitochondrial dysfunction caused by a different pathway. Importantly, an increase in mtDNA does not necessarily mean an increase in mitochondrial function; several studies have shown inhibition of the respiratory function by NRTIs independently through mtDNA polymerase ␥ (29), oxidative stress (26), and increases in mtDNA levels and mitochondrial mass by oxidative stress (27,51). In addition, treatment with NRTIs, including 3TC, abacavir, emtricitabine, and tenofovir, which are known to be less toxic to mitochondria, have been shown to result in increases in mtDNA levels in HepG2 cells (20), human skeletal muscle cells (2), and lymphoblasts (40).…”