Mitochondrial DNA variants as genetic risk factors for Parkinson disease.

BACKGROUND AND PURPOSE: Investigation of the relationship between mitochondrial DNA (mtDNA) variants and Parkinson disease (PD) remains an issue awaiting more supportive evidence. Moreover, an affirming cellular model study is also lacking. METHODS: The index mtDNA variants and their defining mitochondrial haplogroup were determined in 725 PD patients and 744 non-PD controls. Full-length mtDNA sequences were also conducted in 110 cases harboring various haplogroups. Cybrid cellular models, composed by fusion of mitochondria-depleted rho-zero cells and donor mitochondria, were used for a rotenone-induced PD simulation study. RESULTS: Multivariate logistic regression analysis revealed that subjects harboring the mitochondrial haplogroup B5 have resistance against PD (odds ratio 0.50, 95% confidence interval 0.32-0.78; P = 0.002). Furthermore, a composite mtDNA variant group consisting of A10398G and G8584A at the coding region was found to have resistance against PD (odds ratio 0.50, 95% confidence interval 0.33-0.78; P = 0.001). In cellular studies, B4 and B5 cybrids were selected according to their higher resistance to rotenone, in comparison with cybrids harboring other haplogroups. The B5 cybrid, containing G8584A/A10398G variants, showed more resistance to rotenone than the B4 cybrid not harboring these variants. This is supported by findings of low reactive oxygen species generation and a low apoptosis rate in the B5 cybrid, whereas a higher expression of autophagy was observed in the B4 cybrid particularly under medium dosage and longer treatment time with rotenone. CONCLUSIONS: Our studies, offering positive results from clinical investigations and cybrid experiments, provide data supporting the role of variant mtDNA in the risk of PD.

Expression of high-mobility group box protein 1 in diabetic foot atherogenesis.

The role of high mobility group box 1 (HMGB1) has been demonstrated in stroke and coronary artery disease but not in peripheral arterial occlusive disease (PAOD). The pathogenesis of HMGB1 in acute and chronic vascular injury is also not well understood. We hypothesized that HMGB1 induces inflammatory markers in diabetic PAOD patients. We studied 36 diabetic patients, including 29 patients with PAOD, who had undergone amputation for diabetic foot and 7 nondiabetic patients who had undergone amputation after traumatic injury. Expression of HMGB1 and inflammatory markers were quantified using immunohistochemical staining. Mitochondrial DNA copy number was quantified using real-time polymerase chain reaction. Compared with that in the traumatic amputation group, HMGB1 expression in vessels was significantly higher in the diabetes and diabetic PAOD groups. In all subjects, arterial stenosis grade was positively correlated with the expression levels of HMGB1, 8-hydroxyguanosine, malondialdehyde, vascular cell adhesion molecule 1, and inflammatory markers CD3, and CD68 in both the intima and the media of vessels. Furthermore, HMGB1 expression level was positively correlated with 8-hydroxyguanosine, vascular cell adhesion molecule 1, nuclear factor-kB, CD3, and CD68 expression. Within the PAOD subgroup, subjects with HMGB1 expression had higher expression of the autophagy marker LC3A/B and higher mitochondrial DNA copy number. HMGB1 may be an inflammatory mediator with roles in oxidative damage and proinflammatory and inflammatory processes in diabetic atherogenesis. Moreover, it may have dual effects by compensating for increased mitochondrial DNA copy number and increased autophagy marker expression.

Role of mitochondrial DNA variants and copy number in diabetic atherogenesis.

Hyperglycemia-induced reactive oxygen species production can cause diabetes and its complications, including atherosclerosis. The role of mitochondrial DNA variants and mitochondrial copy number in the pathogenesis of diabetic atherogenesis is not well understood. We examined 36 diabetic patients who had undergone amputation for diabetic foot and seven non-diabetic patients who had undergone amputation after traumatic injury. Mitochondrial DNA was extracted and used for sequencing. Single nucleotide polymorphisms (SNPs) relative to the Cambridge reference sequence were analyzed. Mitochondrial DNA copy number was quantified by real-time PCR. Twenty-one novel variants were detected in 29 diabetic patients with arterial stenosis; six of the variants were heteroplasmic, and most occurred in highly evolutionarily conserved residues. These variants were more prevalent in patients with arterial stenosis than in those without stenosis. The novel variants included four in complex I (ND1: C3477A/C, A3523A/G; ND5: C13028A/C, C13060A/C), one in complex IV (COX1: T6090A/T), and one in rRNA (12srRNA: G857G/T). Compared with non-diabetic patients, the diabetic patients had significantly less mitochondrial DNA. Furthermore, among diabetic patients with arterial stenosis, there was a significant positive correlation between mitochondrial DNA copy number and the number of total SNPs. In conclusion, we identified six novel heteroplasmic mitochondrial DNA variants among diabetic patients with arterial stenosis, and we found that diabetic atherogenesis is associated with decreased amounts of mitochondrial DNA.

Association between a common mitochondrial DNA D-loop polycytosine variant and alteration of mitochondrial copy number in human peripheral blood cells.

BACKGROUND: A T-to-C transition at mitochondrial DNA (mtDNA) nucleotide position 16189 can generate a variable length polycytosine tract (poly-C). This tract variance has been associated with disease. A suggested pathogenesis is that it interferes with the replication process of mtDNA, which in turn decreases the mtDNA copy number and generates disease. METHODS: In this study, 837 healthy adults' blood samples were collected and determined for their mtDNA D-loop sequence. The mtDNA copy number in the leucocytes and serum levels of oxidative thiobarbituric acid reactive substance (TBARS) and antioxidative thiols were measured. All subjects were then categorised into three groups: wild type or variant mtDNA with presence of an interrupted/uninterrupted poly-C at 16180-16195 segment. RESULTS: A step-wise multiple linear regression analysis identified factors affecting expression of mtDNA copy number including TBARS, thiols, age, body mass index and the mtDNA poly-C variant. Subjects harbouring a variant uninterrupted poly-C showed lowest mean (SD) mtDNA copy number (330 (178)), whereas an increased copy number was noted in subjects harbouring variant, interrupted poly-C (420 (273)) in comparison with wild type (358 (215)). The difference between the three groups and between the uninterrupted poly-C and the composite data from the interrupted poly-C and wild type remained consistent after adjustment for TBARS, thiols, age and body mass index (p=0.001 and p=0.011, respectively). A trend for decreased mtDNA copy number in association with increased number of continuous cytosine within the 16180-16195 segment was noted (p(trend)<0.006). CONCLUSIONS: Our results substantiate a previous suggestion that the mtDNA 16189 variant can cause alteration of mtDNA copy number in human blood cells.