New mtDNA Association Model, MutPred Variant Load, Suggests Individuals With Multiple Mildly Deleterious mtDNA Variants Are More Likely to Suffer From Atherosclerosis

The etiology of common complex diseases is multifactorial, involving both genetic, and environmental factors. A role for mitochondrial dysfunction and mitochondrial DNA (mtDNA) variation has been suggested in the pathogenesis of common complex traits. The aim of this study was to investigate a potential role of mtDNA variants in the development of obesity, diabetes, and atherosclerosis in the Polish population. Whole mtDNA sequences from 415 Polish individuals representing three disease cohorts and a control group were obtained using high-throughput sequencing. Two approaches for the assessment of mtDNA variation were applied, traditional mitochondrial haplogroup association analysis and the mutational or variant load model using the MutPred pathogenicity prediction algorithm for amino acid substitutions in humans. We present a possible association between mildly deleterious mtDNA variant load and atherosclerosis that might be due to having more than one likely mildly deleterious non-synonymous substitution. Moreover, it seems largely dependent upon a few common haplogroup associated variants with MutPred score above 0.5.

Investigation of whole mitochondrial genome variation in normal tension glaucoma

Glaucoma is one of the leading causes of visual impairment and blindness worldwide. However, the cause of retinal ganglion cell loss and damage of the optic nerve in its pathogenesis is largely unknown. The high energy demands of these cells may reflect their strong dependence on mitochondrial function and thus sensitivity to mitochondrial defects. To address this issue, we studied whole mitochondrial genome variation in normal tension glaucoma patients and control individuals from the Polish population using next generation sequencing. Our findings indicate that few features of mitochondrial DNA variation are different for glaucoma patients and control subjects. New insights into normal tension glaucoma development are discussed. We provide also a comprehensive approach for mitochondrial DNA analysis and variant evaluation.

Sex, death and the (nerve) cell

Men and women not only look different, but they have different risks of multiple diseases like migraine, neurodegenerative disorders or numerous cancers. Even the nerve cells may die in different ways and exhibit different sensitivity to pro-apoptotic factors. Some of the differences can be explained by the action of sex hormones, but the experiments on four core genotype mouse model, in which XX and XY mice can be of either sex showed that not all differences are due to hormones. An example of a disease with no simple explanation of sex bias is Leber hereditary optic neuropathy, a mitochondrial disease with about 4:1 male to female ratio. The apoptotic death of retinal ganglion cells forming an optic disc is a proposed mechanism of the disease pathophysiology. The mechanisms causing different sensitivity of the nerve cells of male and female subjects may be responsible for the gender bias in LHON and merit further studies.

Sex, death and the (nerve) cell

Men and women not only look different, but they have different risks of multiple diseases like migraine, neurodegenerative disorders or numerous cancers. Even the nerve cells may die in different ways and exhibit different sensitivity to pro-apoptotic factors. Some of the differences can be explained by the action of sex hormones, but the experiments on four core genotype mouse model, in which XX and XY mice can be of either sex showed that not all differences are due to hormones. An example of a disease with no simple explanation of sex bias is Leber hereditary optic neuropathy, a mitochondrial disease with about 4:1 male to female ratio. The apoptotic death of retinal ganglion cells forming an optic disc is a proposed mechanism of the disease pathophysiology. The mechanisms causing different sensitivity of the nerve cells of male and female subjects may be responsible for the gender bias in LHON and merit further studies.

Mitochondrial genotype in vulvar carcinoma - cuckoo in the nest

Vulvar squamous cell carcinoma (VSCC) is a rare female genital neoplasm. Although numerous molecular changes have been reported in VSCC, biomarkers of clinical relevance are still lacking. On the other hand, there is emerging evidence on the use of mtDNA as a diagnostic tool in oncology. In order to investigate mtDNA status in VSCC patients, haplogroup distribution analysis and D-loop sequencing were performed. The results were compared with available data for the general Polish population, cancer free-centenarians as well as patients with endometrial and head and neck cancer. The obtained data were also compared with the current status of mitochondrial databases. Significant differences in haplogroup distribution between VSCC cohort, general Polish population and cancer-free centenarians cohort were found. Moreover, a correlation between the VSCC patients haplogroup and HPV status was observed. Finally, a specific pattern of mtDNA polymorphisms was found in VSCC. Our results suggest that the mitochondrial genetic background may influence the risk of VSCC occurrence as well as susceptibility to HPV infection.

A family with 3460G>A and 11778G>A mutations and haplogroup analysis of Polish Leber hereditary optic neuropathy patients

Three mutations in mitochondrial DNA complex I genes are responsible for over 90% of Leber hereditary optic neuropathy (LHON) cases in Europe. A family with two LHON mutations--practically homoplasmic 11778G>A and varying levels of 3460G>A--was found during analysis of Polish patients. DNA and visual acuity was analyzed in four affected brothers and their unaffected sister and mother as well as in their step brother. Four male patients experienced vision loss around the age of 20 while for their step brother the onset was late--at the age of 33. No additional neurological symptoms were observed and both women were completely asymptomatic. The mutation occurred in a haplogroup H background, the most common one in both the Polish population and among patients. Double LHON mutations are extremely rare, and this particular combination has not been previously described in the literature.

G8363A mitochondrial DNA mutation is not a rare cause of Leigh syndrome - clinical, biochemical and pathological study of an affected child

Leigh syndrome (LS), or subacute necrotizing encephalomyelopathy, having relatively homogeneous clinical symptomatology and pattern of neuropathological changes, shows remarkable heterogeneity in biochemical and molecular background. G8363A mitochondrial DNA mutation typical for MERRF syndrome and progressive cardiomyopathy may also be associated with LS. Clinical, biochemical and pathological findings in a boy aged 28 months who died with classical COX-deficientLSassociatedwithmtG8363Aisdescribedindetail.Hyperlactataemia,LCHAD-like organic acids profile and respiratory alkalosis(pH7.47,pCO2 4.9 mmHg, HCO3 3.0 mmol/l) were observed. Spectrophotometric assay showed deficit of respiratory chain complexes IVand I. Skeletal muscle biopsy revealed mosaic cytochrome oxidase deficit,lipid accumulation and ultrastructural abnormalities of mitochondria. Postmortem examination confirmed the presence of typical LS central nervous system lesions as well as hypertrophy of the left ventricle of the heart.

CONCLUSION

mtG8363A "MERRF-like" mutation should be included in the differential diagnosis of classical LS in infants. This case is in agreement with our hypothesis that hyperventilation plays a substantial role in progression of central nervous system damage.

Mitochondrial DNA in polish centenarians

Mitochondrial haplogroups can differ in frequency of occurrence in those who are 100 years old and in the rest of the population. These differences are not universally observed; moreover, they are population-specific. We analyzed the haplogroups in 97 Polish 100-year-olds and compared them with those of more than 145 people who served as controls. No statistically significant differences were observed. In additions, we checked D-loop sequences in 31 controls and in some of the centenarians. Statistically significant differences were found for sites 73 and 152 in the D-loop.

Investigation of a pathogenic mtDNA microdeletion reveals a translation-dependent deadenylation decay pathway in human mitochondria

Human mtDNA is transcribed from both strands, producing polycistronic RNA species that are immediately processed. Discrete RNA units are matured by the addition of nucleotides at their 3' termini: -CCA trinucleotide is added to mt-tRNAs, whilst mt-rRNAs and mt-mRNAs are oligo- or polyadenylated, respectively. The cis-acting elements, enzymes and indeed the mechanisms involved in these processes are still largely uncharacterized. Further, the function of polyadenylation in promoting stability, translation or decay of human mt-mRNA is unclear. A microdeletion has been identified in a patient presenting with mtDNA disease. Loss of these two residues removes the termination codon for MTATP6 and sets MTCO3 immediately in frame. Accurate processing at this site still occurs, but there is a markedly decreased steady-state level of RNA14, the ATPase 8- and 6-encoding bi-cistronic mRNA unit, establishing that an mtDNA mutation can cause dysregulation of mRNA stability. Analysis of the polyadenylation profile of the processed RNA14 at steady state revealed substantial abnormalities. The majority of mutated RNA14 terminated with short poly (A) extensions and a second, partially truncated population, was also present. Initial maturation of mutated RNA14 was unaffected, but deadenylation occurred rapidly. Inhibition of mitochondrial protein synthesis showed that the deadenylation was dependent on translation. Finally, deadenylation was shown to enhance mRNA decay, explaining the decrease in steady-state RNA14. An hypothesis is presented to describe how an mtDNA mutation that results in the loss of a termination codon causes enhanced mt-mRNA decay by translation-dependent deadenylation.