Mitochondrial DNA Variation of Leber's Hereditary Optic Neuropathy in Western Siberia

Our data first represent the variety of Leber's hereditary optic neuropathy (LHON) mutations in Western Siberia. LHON is a disorder caused by pathogenic mutations in mitochondrial DNA (mtDNA), inherited maternally and presents mainly in young adults, predominantly males. Clinically, LHON manifests itself as painless central vision loss, resulting in early onset of disability. The epidemiology of LHON has not been fully investigated yet. In this study, we report 44 genetically unrelated families with LHON manifestation. We performed whole mtDNA genome sequencing and provided genealogical and molecular genetic data on mutations and haplogroup background of LHON patients. Known "primary" pathogenic mtDNA mutations (MITOMAP) were found in 32 families: m.11778G>A represents 53.10% (17/32), m.3460G>A-21.90% (7/32), m.14484T>C-18.75% (6/32), and rare m.10663T>C and m.3635G>A represent 6.25% (2/32). We describe potentially pathogenic m.4659G>A in one subject without known pathogenic mutations, and potentially pathogenic m.6261G>A, m.8412T>C, m.8551T>C, m.9444C>T, m.9921G>A, and m.15077G>A in families with known pathogenic mutations confirmed. We suppose these mutations could contribute to the pathogenesis of optic neuropathy development. Our results indicate that haplogroup affiliation and mutational spectrum of the Western Siberian LHON cohort substantially deviate from those of European populations.

Genetic evidence of broad spreading of Lymantria dispar in the West Siberian Plain

Gypsy moth Lymantria dispar L. 1758 (Lepidoptera: Erebidae) is one of the most dangerous forest pests of the Holarctic region. Outbreaks of gypsy moth populations lead to significant defoliation of local forests. Within the vast territory of the West Siberian Plain, we noted the outbreak front movement in the north-east direction with a speed 100-200 km per year. The reason for the outbreak's movement is still unclear because L. dispar females are characterised by limited flight ability, which is not enough to support that movement per se. Herein, we analysed the mtDNA divergence pattern among L. dispar populations collected from the vast territory of the West Siberian Plain to determine the boundaries of populations and reveal the effect of the outbreak's front movement on mtDNA patterns of populations. The 590-bp region of the cytochrome oxidase subunit I gene of the mitochondrial genome was sequenced for 220 specimens that were collected from 18 localities along a transect line (~ 1400 km). Our results clearly show that the gypsy moth populations of the vast Siberian territory are not subdivided. This result can be explained by extensive genetic exchange among local populations. Taking into account that the flight ability of L. dispar females is rather limited, we suggest that spreading occurs through ballooning of early instar larvae. This hypothesis was confirmed by the coincidence of the outbreaks' movement direction with that of the dominant winds, complemented by the observation of ballooned larvae far from a forest edge.

From Normal to Obesity and Back: The Associations between Mitochondrial DNA Copy Number, Gender, and Body Mass Index

Mitochondrial DNA (mtDNA) encodes core subunits of oxidative phosphorylation complexes and, as a result of intricate regulatory crosstalk between nuclear and mitochondrial genomes, the total number of mtDNA copies fits the requirements of each cell type. Deviations from the physiological number of mtDNA copies are expected to be deleterious and might cause some inherited diseases and normal ageing. We studied 46 obese patients with type 2 diabetes (T2DM) one year after a laparoscopic sleeve gastrectomy (LSG) and Roux-en-Y gastric bypass (RYGB). The results were compared with normal-weight patients without T2DM (control group 1) (body mass index (BMI) = 22.5 ± 3.01 kg/m²) and patients with obesity without T2DM (control group 2) (BMI = 36 ± 3.45 kg/m²). We detected an increase of mtDNA copy number in the cells of the buffy coat obtained from peripheral blood, sampled one year after bariatric surgery. We also found that average mtDNA copy number as well as its dynamics (before and after the surgery) are gender-specific. To the best of our knowledge, this is the first evidence for the restoration of mtDNA copy number in obese patients after LSG and RYGB.

The relationship between the mtDNA copy number in insulin-dependent tissues and markers of endothelial dysfunction and inflammation in obese patients

Background

Mitochondria play a central role in the regulation of energy metabolism, and the biogenesis of mitochondria is enhanced by the action of nitric oxide (NO), which is the key signaling molecule in the regulation of vascular homeostasis. A disturbance in the regulation of energy metabolism can be a key reason for the formation of insulin resistance and type 2 diabetes mellitus. Moreover, mitochondrial dysfunction leads to oxidative stress, which increases the production of proinflammatory cytokines. In this regard, the aim of this study was to identify the relationship of the copy number of mtDNA in adipose tissue from different locations (subcutaneous adipose tissue (SAT), mesentery (Mes), greater omentum (GO)), liver biopsy samples and mononuclear blood cells (MNCs) with endothelial dysfunction markers (eNOS, ET-1, iCAM-1, vCAM-1, VEGF) and inflammatory mediators (TNF-α, IL-6, IL-8, CRP, leptin) in obese patients (body mass index (BMI) > 35 kg/m²) with and without type 2 diabetes.

Methods

The study included 88 obese patients (BMI > 35 kg/m2) treated at the Kaliningrad Region Hospital. The control group consisted of 20 healthy donors. To measure mtDNA copy number we used droplet digital PCR. The concentrations of molecules (TNF-α, IL-6, IL-8, VEGF, eNOS, ET-1, iCAM-1, vCAM-1, VEGF) were measured in plasma using the following sandwich enzyme-linked immunosorbent assays (ELISAs). Quantitative determination of leptin was evaluated by flow-fluorimetry on a «Bio-Plex Protein Assay System». Statistical analysis and graphs were obtained in R Statistical Software (version 3.3.1).

Results

The systemic character of chronic subclinical inflammation in obesity is established, and an increase in the level of endothelial dysfunction molecules was observed in the blood plasma. The levels of TNF-a, IL-6, and IL-8 were positively correlated with increases in BMI, serum glucose and cholesterol levels.

Conclusions

The copy number of mtDNA in various fat stores was higher in obese patients with type 2 diabetes than in obese patients without diabetes or in the control subjects and was related to the levels of leptin and proinflammatory cytokines.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0486-7) contains supplementary material, which is available to authorized users.

Interrelation of chemerin and TNF-α with mtDNA copy number in adipose tissues and blood cells in obese patients with and without type 2 diabetes

BACKGROUND

Inflammatory response plays a key role in the development of insulin resistance (IR) in obesity. Oxidative stress triggers the replication of the mitochondrial genome and division of the organelle. The purpose of this study was to identify the relationship of chemerin and TNF-α with mitochondrial DNA (mtDNA) copy number in subcutaneous adipose tissue (SAT) and visceral adipose tissue (mesentery of the small intestine (Mes), greater omentum (GO) and blood mononuclear cells (MNCs)) in patients with obesity with/without type 2 diabetes mellitus (T2DM).

METHODS

The study included 142 obese patients and 34 healthy donors. The samples used for the study were peripheral venous blood (MNCs) and ATs (SAT, Mes and GO). The measurement of mtDNA copy number was done by droplet digital PCR. Quantitative determination of insulin, adiponectin, TNF-α and chemerin in serum/plasma was performed by flow-through fluorometry and commercial ELISA kit. Statistical analysis and graphs were obtained in R Statistical Software (version 3.3.1).

RESULTS

The increase in body mass index (BMI) was accompanied by an increase in TNF-α production, an increase in mtDNA copy number in SAT and a decrease in mtDNA copy number in MNCs. The negative association between plasma chemerin and mtDNA copy number in the Mes, as well as between mtDNA copy number and chemerin expression in the Mes, in the group with BMI > 40 kg/m2 without T2DM demonstrates the protective effect of chemerin against the development of IR via the regulation of mtDNA copy number in adipose tissues.

CONCLUSIONS

We thus speculated the existence of a compensatory mechanism in which leads to the increased number of mtDNA copies under the influence of proinflammatory factors. Based on the obtained data, we propose that reducing mtDNA copy number in cases of morbid obesity without T2DM has a positive effect on carbohydrate metabolism, which may help maintain glucose levels within reference values. Obesity, type 2 diabetes, mtDNA, cytokines, TNF-a, chemerin.

Future of human mitochondrial DNA editing technologies

ATP and other metabolites, which are necessary for the development, maintenance, and functioning of bodily cells are all synthesized in the mitochondria. Multiple copies of the genome, present within the mitochondria, together with its maternal inheritance, determine the clinical manifestation and spreading of mutations in mitochondrial DNA (mtDNA). The main obstacle in the way of thorough understanding of mitochondrial biology and the development of gene therapy methods for mitochondrial diseases is the absence of systems that allow to directly change mtDNA sequence. Here, we discuss existing methods of manipulating the level of mtDNA heteroplasmy, as well as the latest systems, that could be used in the future as tools for human mitochondrial genome editing.