Single-step method for the determination of the amount of the common deletion in mitochondrial DNA

Age-associated mitochondrial DNA deletions are not evident chronically after experimental brain injury in the rat

The enduring cognitive and sensorimotor deficits that result from traumatic brain injury (TBI) are associated with metabolic stress and free radical cascades, which establish conditions that may promote mitochondrial DNA (mtDNA) deletion and oxidation, often observed as a consequence of normal aging. Without substantial mtDNA repair mechanisms, permanent alterations to essential mitochondrial enzymes could perpetuate post-injury pathologic cascades. To determine whether mitochondria from the injured cortex and hippocampus sustain mtDNA damage after TBI, we evaluated mtDNA deletion and oxidation following lateral fluid percussion TBI in the anesthetized adult Sprague-Dawley rat (4 months) compared with uninjured adult and aged rats (n = 4/group). The presence of the 4.8-KB common deletion in mtDNA was assessed by conventional PCR to generate products representing total, non-deleted wild-type, and deleted mtDNA in homogenized tissue and isolated mitochondria 3 and 14 days following TBI. Total and wild-type mtDNA amplification products were obtained from cortical and hippocampal tissue and mitochondria for all conditions. Although no mtDNA deletions were observed following experimental TBI, mtDNA deletion was detected in cortical tissue, but not isolated mitochondria, of naive, aged (24 months) Sprague-Dawley rats, suggesting that the isolation protocol may exclude mitochondria harboring mtDNA damage. Oxidative mtDNA damage in isolated mitochondria assayed by ELISA for 8-hydroxy-2'-deoxyguanosine (8-OHdG) from cortical (0.50 +/- 0.08 pg 8-OHdG/ micro g mitochondria) and hippocampal (0.35 +/- 0.02) regions were unaffected by TBI. However, mitochondrial protein yields from injured and aged brains were comparable and significantly lower than uninjured brain, suggesting that the underlying pathology between TBI and aging may be similar.

Mitochondrial DNA damage in lymphocytes: a role in immunosenescence?

An age-related increase of DNA damage/mutation has been previously reported in human lymphocytes. The high copy number and mutation rate make the mtDNA genome an ideal candidate for assessing damage and to act as a potential biomarker of ageing. In the present study, two assays were developed to evaluate the level of mtDNA(4977) and the accumulation of point mutations with age. A competitive polymerase chain reaction (PCR) methodology incorporating three primers was used to detect and quantify the levels of mtDNA(4977) and a novel heteroduplex reference strand conformational analysis (RSCA) technique was used to analyse the accumulation of point mutations. The assays were applied to an in vitro model of T cell ageing and ex vivo DNA samples from an elderly cohort of subjects and a younger control group. The mtDNA(4977) was detected in all the DNA samples examined but only a very low concentration was observed and no age-related increase or accumulation was observed. No accumulation of point mutations was identified using RSCA within the T cell clones as they were aged or the ex vivo lymphocytes from the elderly cohort. A higher level of variation was observed within the ex vivo DNA samples, verifying the high resolution of RSCA and its ability to identify different mtDNA species, although no correlation with age was observed. The low level of mtDNA damage observed with respect to the ex vivo lymphocyte DNA samples within this study may be due in part to the high turnover of blood cells/mtDNA, which may inhibit the accumulation of genetically abnormal mtDNA that may play a role in immunosenescence. A similar explanation may also apply to the in vitro model of T cell ageing if the vast majority of the cells are replicating rather than entering senescence.

Microsatellite instability, mitochondrial DNA large deletions, and mitochondrial DNA mutations in gastric carcinoma

Mitochondrial DNA (mtDNA) large deletions and mtDNA mutations have been demonstrated in various types of human cancer. The relationship between the occurrence of such alterations and the nuclear microsatellite instability (MSI) status of the neoplastic cells remains controversial. In an attempt to clarify the situation in gastric carcinoma, we studied, by PCR/SSCP and sequencing, five mitochondrial genes and two D-loop regions in 32 gastric carcinomas that had been previously screened for MSI and mitochondrial common deletion. MtDNA alterations were detected in 26 carcinomas (81%). All the mtDNA mutations, which occurred mainly in the D-loop and ND1 and ND5 genes, were transitions. D-loop alterations (insertions and/or deletions) were not significantly associated with mutations in the coding regions. There was a trend towards an inverse relationship between the occurrence of mitochondrial common deletion and mtDNA mutations. No significant relationship was observed between MSI status and mtDNA mutations, whereas the mitochondrial common deletion appeared to be almost exclusively restricted to MSI-negative tumors. The latter finding--almost no gastric carcinoma with MSI-positive phenotype has large deletions of mtDNA--needs to be confirmed in a larger series and in tumors from other organs.

Torsion-induced injury in rat testes does not affect mitochondrial respiration or the accumulation of mitochondrial mutations

Male rats were subjected to 1 h testicular torsion of the spermatic cord or 1 h torsion followed by detorsion and recovery up to 4 weeks. The extent of tissue damage was evaluated by a testicular biopsy score count and mitochondrial function. Torsion for 1 h followed by detorsion induced significant morphological damage, which became more severe with longer periods of recovery. This morphological damage could not be correlated with mitochondrial damage as assessed by measuring the 4834 bp mitochondrial DNA 'common deletion' using a quantitative competitive polymerase chain reaction (PCR) assay. Mitochondrial respiratory chain activity, as measured by mitochondrial oxygen consumption using an oxygen electrode, did not vary between the treated animals and the controls. We conclude that the common mitochondrial DNA deletion and oxygen consumption are not good indicators of testicular damage induced by torsion.