Therapeutic treatments of mtDNA diseases at the earliest stages of human development

Comparing four laboratory three-parent techniques to construct human aged non-surrounded nucleolus germinal vesicle oocytes: A case-control study

Background

The three-parent assisted reproductive technique may increase oocyte competence.

Objective

In this case-control study, the suitability of germinal vesicle transfer (GVT), synchronous ooplasmic transfer (sOT), asynchronous ooplasmic transfer using cryopreserved MII oocyte (caOT), and asynchronous ooplasmic transfer using waste MII oocyte (waOT) for maturation of the human-aged non-surrounded nucleolus germinal vesicle-stage (NSN-GV) oocyte were investigated.

Materials and Methods

NSN-GV oocytes were subjected to four methods: group A (GVT), B (sOT), C (caOT) D (waOT), and E (Control). The fusion rates, MI, MII, ICSI observations and cleavage at 2-cell, 4-cell, and 8-cell stages were compared in the groups.

Results

In GVT, none of the oocytes fused. In sOT, all oocytes fused, 20 achieved the MI, 14 progressed to MII, 8 fertilized, 6 cleaved and 5, 4, and 3 achieved the 2-cells, 4-cells and 8-cells, respectively. In caOT, all oocytes fused and achieved the MI, 8 progressed to MII and fertilized, 6 cleaved and 6, 5, and 5 achieved the 2-cells, 4-cells, and 8-cells respectively. In waOT, all oocytes fused, 5 and 3 progressed to MI and MII, respectively, but only one fertilized, cleaved and reached a 4-cells stage. In group E, 6 and 2 oocytes progressed to MI and MII, respectively, and only one fertilized but arrested at the zygote stage. caOT had the highest survival rate when compared to sOT (p = 0.04), waOT (p = 0.002), and control (p = 0.001).

Conclusion

The caOT method was beneficial over sOT, waOT, and GVT in supplementing the developmental capacity of human-aged NSN-GV oocytes.

Tri-parent Baby Technology and Preservation of Lineage: An Analysis from the Perspective of Maqasid al-Shari'ah Based Islamic Bioethics

Tri-parent baby technology is an assisted reproductive treatment which aims to minimize or eliminate maternal inheritance of mutated mitochondrial DNA (mtDNA). The technology became popular following the move by the United Kingdom in granting license to a group of researchers from the Newcastle Fertility Centre, Newcastle University to conduct research on the symptoms of defective mtDNA. This technology differs from other assisted reproductive technology because it involves the use of gamete components retrieved from three different individuals. Indirectly, it affects the preservation of lineage which is important from an Islamic point of view. This paper aims to analyze and discuss the implications of the tri-parent technology on preservation of lineage from the perspective of Maqasid al-Shari'ah based the Islamic bioethics. The analysis shows that there are a few violations of the preservation of lineage, hence the tri-parent baby technology should not be permitted.

A genome-wide association study of mitochondrial DNA copy number in two population-based cohorts

BACKGROUND

Mitochondrial DNA copy number (mtDNA CN) exhibits interindividual and intercellular variation, but few genome-wide association studies (GWAS) of directly assayed mtDNA CN exist. We undertook a GWAS of qPCR-assayed mtDNA CN in the Avon Longitudinal Study of Parents and Children (ALSPAC) and the UK Blood Service (UKBS) cohort. After validating and harmonising data, 5461 ALSPAC mothers (16-43 years at mtDNA CN assay) and 1338 UKBS females (17-69 years) were included in a meta-analysis. Sensitivity analyses restricted to females with white cell-extracted DNA and adjusted for estimated or assayed cell proportions. Associations were also explored in ALSPAC children and UKBS males.

RESULTS

A neutrophil-associated locus approached genome-wide significance (rs709591 [MED24], β (change in SD units of mtDNA CN per allele) [SE] - 0.084 [0.016], p = 1.54e-07) in the main meta-analysis of adult females. This association was concordant in magnitude and direction in UKBS males and ALSPAC neonates. SNPs in and around ABHD8 were associated with mtDNA CN in ALSPAC neonates (rs10424198, β [SE] 0.262 [0.034], p = 1.40e-14), but not other study groups. In a meta-analysis of unrelated individuals (N = 11,253), we replicated a published association in TFAM (β [SE] 0.046 [0.017], p = 0.006), with an effect size much smaller than that observed in the replication analysis of a previous in silico GWAS.

CONCLUSIONS

In a hypothesis-generating GWAS, we confirm an association between TFAM and mtDNA CN and present putative loci requiring replication in much larger samples. We discuss the limitations of our work, in terms of measurement error and cellular heterogeneity, and highlight the need for larger studies to better understand nuclear genomic control of mtDNA copy number.

Next generation sequencing in family with MNGIE syndrome associated to optic atrophy: Novel homozygous POLG mutation in the C-terminal sub-domain leading to mtDNA depletion

INTRODUCTION

Mitochondrial diseases are a group of disorders caused mainly by the impairment of the mitochondrial oxidative phosphorylation process, due to mutations either in the mitochondrial or nuclear genome. Among them, the mitochondrial neuro-gastrointestinal encephalo-myopathy (MNGIE) syndrome affects adolescents or young adults, and is mostly caused by TYMP mutations encoding a cytosolic thymidine phosphorylase (TP).

PATIENTS AND METHODS

The present study reports the molecular investigation by next-generation re-sequencing of 281 nuclear genes, encoding mitochondrial proteins, of consanguineous family including two individuals with MNGIE syndrome associated to optic atrophy. Bioinformatic analysis was also performed in addition to mtDNA deletion screening and mtDNA copy number quantification in blood of the two patients which were carried out by solf clipping program and qPCR respectively.

RESULTS

Next-generation re-sequencing revealed a novel homozygous c.2391G > T POLG mutation (p.M797I) co-occurring with the hypomorphic c.1311A > G OPA1 variant (p.I437M). Analysis of the mitochondrial genome in the two patients disclosed mtDNA depletion in blood, but no deletion. Bio-informatics investigations supported the pathogenicity of the novel POLG mutation that is located in the C-terminal subdomain and might change POLG 3D structure, stability and function.

CONCLUSION

The novel homozygous p.M797I POLG mutation is responsible for MNGIE combined to optic atrophy and mtDNA depletion in the two patients.

Mitochondria and reproduction: possibilities for testing and treatment

Mitochondria, known as the energy factories in all cells, are key regulators of multiple vital cellular processes and affect all aspects of mammalian reproduction, being essential for oocyte maturation, fertilization and embryonic development. Mitochondrial dysfunction is consequently implicated in disease as well as age-related infertility. Since mitochondria are inherited exclusively from the mother, the female gamete is central to reproductive outcome and therapeutic interventions, such as mitochondrial replacement therapy (MRT), and development of new diagnostic tools. The primary purpose of MRT is to improve oocyte quality, embryogenesis and fetal development by correcting the imbalance between mutant and wild-type mitochondrial DNA (mtDNA) in the oocyte or zygote, either by replacing mutant mtDNA or supplementing with wild-type counterparts from heterologous or autologous sources. However, the efficacy and safety of these new technologies have not yet been tested in clinical trials, and various concerns exist. Nonetheless, the perspectives for such procedures are intriguing and include two distinct patient populations that could potentially benefit from the clinical implementation of MRT; 1) patients with mtDNA-disease transmission risk; 2) patients undergoing IVF with recurrent poor embryo outcomes due to advanced maternal age. In this review, we outline the intrinsic roles of mitochondria during oogenesis and early embryogenesis in relation to disease and infertility, and discuss the progress in MRT with the developments in reproductive technologies and the related concerns. In addition, we assess the use of mtDNA as a potential biomarker for embryo viability in assisted reproduction.

The role of mitochondria in the female germline: Implications to fertility and inheritance of mitochondrial diseases

Mitochondria play a fundamental role during development of the female germline. They are fragmented, round, and small. Despite these characteristics suggesting that they are inactive, there is accumulating evidence that mitochondrial dysfunctions are a major cause of infertility and generation of aneuploidies in humans. In addition, mitochondria and their own genomes (mitochondrial DNA-mtDNA) may become damaged with time, which might be one reason why aging leads to infertility. As a result, mitochondria have been proposed as an important target for evaluating oocyte and embryo quality, and developing treatments for female infertility. On the other hand, mutations in mtDNA may cause mitochondrial dysfunctions, leading to severe diseases that affect 1 in 4,300 people. Moreover, very low levels of mutated mtDNA seem to be present in every person worldwide. These may increase with time and associate with late-onset degenerative diseases such as Parkinson disease, Alzheimer disease, and common cancers. Mutations in mtDNA are transmitted down the maternal lineage, following a poorly understood pattern of inheritance. Recent findings have indicated existence in the female germline of a purifying filter against deleterious mtDNA variants. Although the underlying mechanism of this filter is largely unknown, it has been suggested to rely on autophagic degradation of dysfunctional mitochondria or selective replication/transmission of non-deleterious variants. Thus, understanding the mechanisms regulating mitochondrial inheritance is important both to improve diagnosis and develop therapeutic tools for preventing transmission of mtDNA-encoded diseases.

Mitochondrial Replacement Techniques: Divergence in Global Policy

In 2015, the UK became the first country permitting the clinical application of mitochondrial replacement techniques (MRT). Here, we explore how MRT have led to diverging international policy. In response, we recommend focused regulatory efforts coupled with United Nations (UN) leadership to build international consensus on the future of MRT.

Experimental strategies towards increasing intracellular mitochondrial activity in oocytes: A systematic review

PURPOSE

The mitochondrial complement is critical in sustaining the earliest stages of life. To improve the Assisted Reproductive Technology (ART), current methods of interest were evaluated for increasing the activity and copy number of mitochondria in the oocyte cell.

METHODS

This covered the researches from 1966 to September 2015.

RESULTS

The results provided ten methods that can be studied individually or simultaneously.

CONCLUSION

Though the use of these techniques generated great concern about heteroplasmy observation in humans, it seems that with study on these suggested methods there is real hope for effective treatments of old oocyte or oocytes containing mitochondrial problems in the near future.

Mitochondrial DNA triplication and punctual mutations in patients with mitochondrial neuromuscular disorders

Mitochondrial diseases are a heterogeneous group of disorders caused by the impairment of the mitochondrial oxidative phosphorylation system which have been associated with various mutations of the mitochondrial DNA (mtDNA) and nuclear gene mutations. The clinical phenotypes are very diverse and the spectrum is still expanding. As brain and muscle are highly dependent on OXPHOS, consequently, neurological disorders and myopathy are common features of mtDNA mutations. Mutations in mtDNA can be classified into three categories: large-scale rearrangements, point mutations in tRNA or rRNA genes and point mutations in protein coding genes. In the present report, we screened mitochondrial genes of complex I, III, IV and V in 2 patients with mitochondrial neuromuscular disorders. The results showed the presence the pathogenic heteroplasmic m.9157G>A variation (A211T) in the MT-ATP6 gene in the first patient. We also reported the first case of triplication of 9 bp in the mitochondrial NC7 region in Africa and Tunisia, in association with the novel m.14924T>C in the MT-CYB gene in the second patient with mitochondrial neuromuscular disorder.

Social and ethical issues in mitochondrial donation

INTRODUCTION OR BACKGROUND

The UK is at the forefront of mitochondrial science and is currently the only country in the world to legalize germ-line technologies involving mitochondrial donation. However, concerns have been raised about genetic modification and the 'slippery slope' to designer babies.

SOURCES OF DATA

This review uses academic articles, newspaper reports and public documents.

AREAS OF AGREEMENT

Mitochondrial donation offers women with mitochondrial disease an opportunity to have healthy, genetically related children.

AREAS OF CONTROVERSY

Key areas of disagreement include safety, the creation of three-parent babies, impact on identity, implications for society, definitions of genetic modification and reproductive choice.

GROWING POINTS

The UK government legalized the techniques in March 2015. Scientific and medical communities across the world followed the developments with interest.

AREAS TIMELY FOR DEVELOPING RESEARCH

It is expected that the first cohort of 'three parent' babies will be born in the UK in 2016. Their health and progress will be closely monitored.

The impact of mitochondrial function/dysfunction on IVF and new treatment possibilities for infertility

Mitochondria play vital roles in oocyte functions and they are critical indicators of oocyte quality which is important for fertilization and development into viable offspring. Quality-compromised oocytes are correlated with infertility, developmental disorders, reduced blastocyst cell number and embryo loss in which mitochondrial dysfunctions play a significant role. Increasingly, women affected by metabolic disorders such as diabetes or obesity and oocyte aging are seeking treatment in IVF clinics to overcome the effects of adverse metabolic conditions on mitochondrial functions and new treatments have become available to restore oocyte quality. The past decade has seen enormous advances in potential therapies to restore oocyte quality and includes dietary components and transfer of mitochondria from cells with mitochondrial integrity into mitochondria-impaired oocytes. New technologies have opened up new possibilities for therapeutic advances which will increase the success rates for IVF of oocytes from women with compromised oocyte quality.

Phylogenetic analysis of mitochondrial DNA in a patient with Kearns-Sayre syndrome containing a novel 7629-bp deletion

Mitochondrial DNA mutations have been associated with different illnesses in humans, such as Kearns-Sayre syndrome (KSS), which is related to deletions of different sizes and positions among patients. Here, we report a Mexican patient with typical features of KSS containing a novel deletion of 7629 bp in size with 85% heteroplasmy, which has not been previously reported. Sequence analysis revealed 3-bp perfect short direct repeats flanking the deletion region, in addition to 7-bp imperfect direct repeats within 9-10 bp. Furthermore, sequencing, alignment and phylogenetic analysis of the hypervariable region revealed that the patient may belong to a founder Native American haplogroup C4c.

Manipulation of mtDNA heteroplasmy in all striated muscles of newborn mice by AAV9-mediated delivery of a mitochondria-targeted restriction endonuclease

Mitochondrial diseases are frequently caused by heteroplasmic mtDNA mutations. Because these mutations express themselves only at high relative ratios, any approach able to manipulate mtDNA heteroplasmy can potentially be curative. In this study we developed a system to manipulate mtDNA heteroplasmy in all skeletal muscles from neonate mice. We selected muscle because it is one of the most clinically affected tissues in mitochondrial disorders. A mitochondria targeted restriction endonuclease (mito-ApaLI) expressed from AAV9 particles was delivered either by intraperitoneal or intravenous injection in neonate mice harboring two mtDNA haplotypes, only one of which was susceptible to ApaLI digestion. A single injection was able to elicit a predictable and marked change in mtDNA heteroplasmy in all striated muscles analyzed, including heart. No health problems or reduction in mtDNA levels were observed in treated mice, suggesting that this approach could have clinical applications for mitochondrial myopathies.

Mitochondrial function in the human oocyte and embryo and their role in developmental competence

The role of mitochondria as a nexus of developmental regulation in mammalian oogenesis and early embryogenesis is emerging from basic research in model species and from clinical studies in infertility treatments that require in vitro fertilization and embryo culture. Here, mitochondrial bioenergetic activities and roles in calcium homeostasis, regulation of cytoplasmic redox state, and signal transduction are discussed with respect to outcome in general, and as possible etiologies of chromosomal defects, maturation and fertilization failure in human oocytes, and as causative factors in early human embryo demise. At present, the ability of mitochondria to balance ATP supply and demand is considered the most critical factor with respect to fertilization competence for the oocyte and developmental competence for the embryo. mtDNA copy number, the timing of mtDNA replication during oocyte maturation, and the numerical size of the mitochondrial complement in the oocyte are evaluated with respect to their relative contribution to the establishment of developmental competence. Rather than net cytoplasmic bioenergetic capacity, the notion of functional compartmentalization of mitochondria is presented as a means by which ATP may be differentially supplied and localized within the cytoplasm by virtue of stage-specific changes in mitochondrial density and potential (ΔΨm). Abnormal patterns of calcium release and sequestration detected at fertilization in the human appear to have coincident effects on levels of mitochondrial ATP generation. These aberrations are not uncommon in oocytes obtained after ovarian hyperstimulation for in vitro fertilization. The possibility that defects in mitochondrial calcium regulation or bioenergetic homeostasis could have negative downstream development consequences, including imprinting disorders, is discussed in the context of signaling pathways and cytoplasmic redox state.