Polymorphisms of mitochondrial DNA control region are associated to endometriosis

New insights on mitochondrial heteroplasmy observed in ovarian diseases

BACKGROUND

The reportedly high mutation rate of mitochondrial DNA (mtDNA) may be attributed to the absence of histone protection and complete repair mechanisms. Mitochondrial heteroplasmy refers to the coexistence of wild-type and mutant mtDNA. Most healthy individuals carry a low point mutation load (<1 %) in their mtDNA, typically without any discernible phenotypic effects. However, as it exceeds a certain threshold, it may cause the onset of various diseases. Since the ovary is a highly energy-intensive organ, it relies heavily on mitochondrial function. Mitochondrial heteroplasmy can potentially contribute to a variety of significant ovarian disorders.

AIM OF REVIEW

In this review, we have elucidated the close relationship between mtDNA heteroplasmy and ovarian diseases, and summarized novel avenues and strategies for the potential treatment of these ovarian diseases.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Mitochondrial heteroplasmy can potentially contribute to a variety of significant ovarian disorders, including polycystic ovary syndrome, premature ovarian insufficiency, and endometriosis. Current strategies related to mitochondrial heteroplasmy are untargeted and have low bioavailability. Nanoparticle delivery systems loaded with mitochondrial modulators, mitochondrial replacement/transplantation therapy, and mitochondria-targeted gene editing therapy may offer promising paths towards potentially more effective treatments for these diseases, despite ongoing challenges.

Mitochondrial DNA Polymorphism in HV1 and HV2 Regions and 12S rDNA in Perimenopausal Hypertensive Women

Estrogens enhance cellular mitochondrial activity. The diminution of female hormones during menopause may have an effect on the mitochondrial genome and the expression of mitochondrial proteins. Hence, oxidative stress and the pro-inflammatory state contribute to the formation of systemic illnesses including arterial hypertension (AH). This study aimed to determine the types and frequency of mutations in the mitochondrial DNA (mtDNA) nucleotide sequence in the hypervariable regions 1 and 2 (HV1 and HV2) and the 12S RNA coding sequence of the D-loop in postmenopausal women with hypertension. In our study, 100 women were investigated, 53 of whom were postmenopausal and 47 of whom were premenopausal (53.9 ± 3.7 years vs. 47.7 ± 4.2 years, respectively). Of those studied, 35 premenopausal and 40 postmenopausal women were diagnosed with AH. A medical checkup with 24 h monitoring of blood pressure (RR) and heart rate was undertaken (HR). The polymorphism of the D-loop and 12S rDNA region of mtDNA was examined. Changes in the nucleotide sequence of mtDNA were observed in 23% of the group of 100 women. The changes were identified in 91.3% of HV1 and HV2 regions, 60.9% of HV1 segments, 47.5% of HV2 regions, and 43.5% of 12S rDNA regions. The frequency of nucleotide sequence alterations in mtDNA was substantially higher in postmenopausal women (34%) than in premenopausal women (10.6%), p = 0.016. A higher frequency of changes in HV1 + HV2 sections in postmenopausal women (30.2%) compared to the premenopausal group (10.6%) was detected, p = 0.011. Only postmenopausal women were found to have modifications to the HV2 segment and the 12S rDNA region. After menopause, polymorphism in the mtDNA region was substantially more frequent in women with arterial hypertension than before menopause (p = 0.030; 37.5% vs. 11.5%). Comparable findings were observed in the HV2 and HV1 regions of the AH group (35% vs. 11.5%), p = 0.015, in the HV1 segment (25% vs. 11.5%), p = 0.529, and in the HV2 segment, 12S rDNA (25% vs. 0%). More than 80% of all changes in nucleotide sequence were homoplasmic. The mtDNA polymorphisms of the nucleotide sequence in the HV1 and HV2 regions, the HV2 region alone, and the 12S RNA coding sequence were associated with estrogen deficiency and a more severe course of arterial hypertension, accompanied by symptoms of adrenergic stimulation.

Insight of the mitochondrial genomes of the Orang Asli and Malays: The heterogeneity and the disease-associated variants

Orang Asli are the oldest inhabitants in Peninsular Malaysia that forms as a national minority while the Malays are the majority. The study aimed to screen the mitochondrial genomes of the Orang Asli and the Malays to discover the disease-associated variants. A total of 99 Orang Asli from six tribes (Bateq, Cheq Wong, Orang Kanaq, Kensiu, Lanoh, and Semai) were recruited. Mitochondrial genome sequencing was conducted using a next-generation sequencing platform. Furthermore, we retrieved mitochondrial DNA sequences from the Malays for comparison. The clinical significance, pathogenicity prediction and frequency of variants were determined using online tools. Variants associated with mitochondrial diseases were detected in the 2 populations. A high frequency of variants associated with mitochondrial diseases, breast cancer, prostate cancer, and cervical cancer were detected in the Orang Asli and modern Malays. As medicine evolves to adopt prediction and prevention of diseases, this study highlights the need for intervention to adopt genomics medicine to strategise better healthcare management as a way forward for Precision Health.

Comparison of methods for isolation and quantification of circulating cell-free DNA from patients with endometriosis

RESEARCH QUESTION

Which is the optimal extraction method for isolating and quantifying circulating cell-free DNA (ccfDNA) from patients with endometriosis? Endometriosis is a common benign disease, associated with pain, infertility and reduced quality of life. Endometriosis is also a known risk factor for various cancers. Robust biomarkers for early detection and prediction of prognosis, however, are lacking. CcfDNA is an easy to obtain biomarker associated with prognosis of cancer patients and enables non-invasive analysis of somatic mutations. Recently, elevated levels of ccfDNA were detected in patients with endometriosis.

DESIGN

Two different ccfDNA extraction methods were compared: Maxwell RSC ccfDNA plasma kit (Maxwell) and QiAamp minElute ccfDNA mini kit (QIAamp). The ccfDNA and circulating mitochondrial DNA (mtDNA) quantities from 34 patients diagnosed with endometriosis were analysed. Fluorometric measurement and quantitative reverse transcription polymerase chain reaction (qRT-PCR) of short and long ALU and mtDNA fragments were used to quantiy ccfDNA.

RESULTS

The yield of ccfDNA isolated with the Maxwell method was significantly higher compared with the QIAamp method (P < 0.0001). Integrity of ccfDNA was significantly higher in the QIAamp isolate (P < 0.0001). Recovered mtDNA was not significantly different between both extraction methods used.

CONCLUSIONS

The choice of extraction method can significantly influence the ccfDNA output and integrity. Both methods, however, enabled isolation of sufficient ccfDNA for further downstream applications. With this approach, isolation of ccfDNA could enable the non-invasive detection and analysis of somatic mutation within endometriosis tissue.

Association between mitochondrial DNA D-loop region polymorphisms and endometriosis in a Chinese population

OBJECTIVE

To investigate the correlation between endometriosis and mitochondrial DNA (mtDNA) D-loop single nucleotide polymorphisms (SNPs) and haplotype, as well as the predictive power of certain SNPs in reproductive outcomes in a Chinese Han population.

METHODS

A case-control study was conducted in which 125 endometriosis patients and 124 controls were recruited from an academic fertility center. The entire 1124-bp D-loop region of mtDNA of whole blood samples from all subjects was amplified, sequenced, and compared with the revised Cambridge Reference Sequence (rCRS) to identify SNPs and haplotypes. The association between D-loop SNPs and embryo quality and clinical outcome following in vitro fertilization (IVF) was also assessed.

RESULTS

A total of 321 polymorphisms were identified by sequencing, allowing comparison of the D-loop between endometriosis patients and controls. The frequency of the AC523-524 del, T16172C, and C16290T variants were significantly higher, while the frequency of polymorphisms T195C, 573XCins, 16036Gins, 16049Gins, T16140C, A16183C, T16189C, and 16193Cins were lower, in the endometriosis group compared with the control group (p < 0.05). Within the endometriosis group, the high-quality blastocyst rate in the 16,290T subgroup was significantly lower than that in the 16290C subgroup (p < 0.05). In the control group, 16519C carriers showed a lower rate of high-quality blastocyst development compared with 16519T (p < 0.05). In endometriosis patients clinical pregnancy rate was significantly lower in the 150T subgroup compared with the 150C subgroup (p < 0.05).

DISCUSSION

Data confirms a correlation between D-loop polymorphisms and endometriosis. The polymorphisms AC523-524 del, T16172C, and C16290T are associated with increased risk of endometriosis, while T195C, 573XCins, 16036Gins, 16049Gins, T16140C, A16183C, T16189C, and 16193Cins are associated with decreased risk of endometriosis. In addition, C16290T and T16519C can be associated with poor quality blastocyst development in population with and without endometriosis, respectively and C150T can be a predictor of poor IVF outcome.

Mitochondrial and Nuclear Mitochondrial Variants in Allergic Diseases

The mitochondrial genome encodes core catalytic peptides that affect major metabolic processes within a cell. Here, we investigated the association between mitochondrial DNA (mtDNA) variants and allergic diseases, including atopic dermatitis (AD) and asthma, alongside heteroplasmy within the mtDNA in subjects with allergic sensitization. We collected genotype data from 973 subjects with allergic sensitization, consisting of 632 children with AD, 498 children with asthma, and 481 healthy controls by extracting DNA from their blood samples. Fisher's exact test was used to investigate mtDNA and nuclear DNA variants related to mitochondrial function (MT-nDNA) to identify their association with allergic diseases. Among the 69 mtDNA variants, rs28357671 located on the MT-ND6 gene displayed statistically significant associations with allergic diseases (Bonferroni-corrected P < 7.25E-4), while 6, 4, and 2 genes were associated with allergic sensitization, AD, and asthma, respectively (P < 0.0002), including NLRX1, OCA2, and CHCHD3 among the MT-nDNA genes. Heteroplasmy of mitochondrial DNA associated with allergic sensitization was evaluated in a separate cohort of patients consisting of 59 subjects with allergic sensitization and 52 controls. Heteroplasmy was verified when a patient carried both alleles of a mitochondrial single-nucleotide polymorphism (SNP) when clustered. One of the 134 mitochondrial SNPs showed heteroplasmy at a level of 0.4313 when clustering was applied. The probe sequence located at mitochondrial position 16217 and within the D-loop, which acts as a major control site for mtDNA expression. This is the first study to evaluate the association between mitochondrial DNA variants and allergic diseases. A harmonized effect of genes related to mitochondrial function may contribute to the risk of allergic diseases.

Associations of Mitochondrial Deoxyribonucleic Acid Polymorphisms With Behçet's Disease in the Korean Population

Objectives

This study aims to examine the possible associations of mitochondrial single nucleotide polymorphisms (SNPs) and Behçet's disease (BD) in a larger patient group.

Patients and methods

Whole blood or buffy coat was collected from 98 BD patients (31 males, 67 females; mean age 48±2.8 years; range 20 to 60 years) from four university hospitals located in the Chung-Cheong district of the Republic of Korea, and 196 age- and sex-matched healthy controls (HCs) (62 males, 134 females; mean age 46.91±12.90 years; range 20 to 68 years) from Konyang University Hospital. Twenty targeted mitochondrial deoxyribonucleic acids (DNAs) were genotyped and compared using the revised Cambridge Reference Sequence. Chi square and Fisher's exact tests were used to analyze association of mitochondrial DNA SNPs with BD susceptibility and its clinical characteristics.

Results

There were no differences for m.248A>G, m.304C>A, m.709G>A, m.3010G>A, m.3970C>T, m.4883C>T, m.5178C>A, m.6392T>C, m.6962G>A, m.10310G>A, m.10609T>C, m.12406G>A, m.12882C>T, m.13928G>C, m.14668C>T, m.16129G>A, and m16304T> between patient and HC groups. However, m.16182A>C and m.16183A>C were more frequently observed in the patient group than the HC group (22 [22.4%] vs. 24 [12.2%], p=0.061 and 32 [32.7%] vs. 42 [21.4%], p=0.092) but without statistical significance. m.4883C>T and m.5178C>A were associated with posterior location of oral ulcers (p=0.025 for each) and m.16183A>C was associated with deep oral ulcers (p=0.001), while m.16189T>C was associated with deep oral ulcers and thrombosis (p=0.042, 0.048, respectively).

Conclusion

m.16182A>C and m.16183A>C may be associated with BD in the Korean population.