Preventing the transmission of mitochondrial DNA disorders: selecting the good guys or kicking out the bad guys

Mechanisms of mitochondrial dysfunction in ovarian aging and potential interventions

Mitochondria plays an essential role in regulating cellular metabolic homeostasis, proliferation/differentiation, and cell death. Mitochondrial dysfunction is implicated in many age-related pathologies. Evidence supports that the dysfunction of mitochondria and the decline of mitochondrial DNA copy number negatively affect ovarian aging. However, the mechanism of ovarian aging is still unclear. Treatment methods, including antioxidant applications, mitochondrial transplantation, emerging biomaterials, and advanced technologies, are being used to improve mitochondrial function and restore oocyte quality. This article reviews key evidence and research updates on mitochondrial damage in the pathogenesis of ovarian aging, emphasizing that mitochondrial damage may accelerate and lead to cellular senescence and ovarian aging, as well as exploring potential methods for using mitochondrial mechanisms to slow down aging and improve oocyte quality.

Mitochondrial Transfer as a Novel Therapeutic Approach in Disease Diagnosis and Treatment

Mitochondrial dysfunction is a hallmark of numerous diseases, including neurodegenerative disorders, metabolic disorders, and cancer. Mitochondrial transfer, the transfer of mitochondria from one cell to another, has recently emerged as a potential therapeutic approach for restoring mitochondrial function in diseased cells. In this review, we summarize the current understanding of mitochondrial transfer, including its mechanisms, potential therapeutic applications, and impact on cell death pathways. We also discuss the future directions and challenges in the field of mitochondrial transfer as a novel therapeutic approach in disease diagnosis and treatment.

Mitochondrial Dysfunction and Oxidative Stress Caused by Cryopreservation in Reproductive Cells

Mitochondria, fundamental organelles in cell metabolism, and ATP synthesis are responsible for generating reactive oxygen species (ROS), calcium homeostasis, and cell death. Mitochondria produce most ROS, and when levels exceed the antioxidant defenses, oxidative stress (OS) is generated. These changes may eventually impair the electron transport chain, resulting in decreased ATP synthesis, increased ROS production, altered mitochondrial membrane permeability, and disruption of calcium homeostasis. Mitochondria play a key role in the gamete competence to facilitate normal embryo development. However, iatrogenic factors in assisted reproductive technologies (ART) may affect their functional competence, leading to an abnormal reproductive outcome. Cryopreservation, a fundamental technology in ART, may compromise mitochondrial function leading to elevated intracellular OS that decreases sperm and oocytes' competence and the dynamics of fertilization and embryo development. This article aims to review the role played by mitochondria and ROS in sperm and oocyte function and the close, biunivocal relationships between mitochondrial damage and ROS generation during cryopreservation of gametes and gonadal tissues in different species. Based on current literature, we propose tentative hypothesis of mechanisms involved in cryopreservation-associated mitochondrial dysfunction in gametes, and discuss the role played by antioxidants and other agents to retain the competence of cryopreserved reproductive cells and tissues.

Mitochondrial DNA Replacement Techniques to Prevent Human Mitochondrial Diseases

Background: Mitochondrial DNA (mtDNA) diseases are a group of maternally inherited genetic disorders caused by a lack of energy production. Currently, mtDNA diseases have a poor prognosis and no known cure. The chance to have unaffected offspring with a genetic link is important for the affected families, and mitochondrial replacement techniques (MRTs) allow them to do so. MRTs consist of transferring the nuclear DNA from an oocyte with pathogenic mtDNA to an enucleated donor oocyte without pathogenic mtDNA. This paper aims to determine the efficacy, associated risks, and main ethical and legal issues related to MRTs. Methods: A bibliographic review was performed on the MEDLINE and Web of Science databases, along with searches for related clinical trials and news. Results: A total of 48 publications were included for review. Five MRT procedures were identified and their efficacy was compared. Three main risks associated with MRTs were discussed, and the ethical views and legal position of MRTs were reviewed. Conclusions: MRTs are an effective approach to minimizing the risk of transmitting mtDNA diseases, but they do not remove it entirely. Global legal regulation of MRTs is required.

Inverted pyramid of prenatal care - is it enough? Should it be - extended inverted pyramid of prenatal care?

In recent years, the idea of the inverted pyramid of prenatal care and monitoring has emerged, for the purpose of prediction and prevention, early detection and treatment of health disorders of the fetus. Is this enough? If we analyze the period behind us, progress has been made in the field of detection of multiple pregnancies, dating of pregnancy and prenatal detection of chromosomal and structural fetal disorders, as well as a small amount of progress in terms of prediction and prevention of preeclampsia. If these disorders are the consequence of the disturbed or dysfunctional placentation, they are rooted at the time of implantation. This means that the changes that lead to the dysfunctional implantation should be sought in the pre-implantation period, in relation between the embryo and the endometrium. An extended inverted pyramid is necessary to find better results in perinatal medicine. This means that the interventions should be focused on the preconception and peri-implantation periods. The therapy should be on the subcellular and genetic level by applying the latest biotechnological procedures. It is possible that the time is approaching when the listed disorders of a pregnancy will be the indications for the application of a non stimulated in-vitro fertilization (IVF) (without ovary stimulating medication) with the use of new biotechnological achievements.

Mitochondrial Replacement Techniques : Examining Collective Representation in Emerging Technologies Governance

In this article, I draw on research carried out in Europe, primarily in Germany, on patients' and scientists' perspectives on mitochondrial replacement techniques (MRTs) in order to explore some of the complexities related to collective representation in health governance, which includes the translation of emerging technologies into clinical use. Focusing on observations, document analyses, and interviews with eight mitochondrial disease patient organization leaders, this contribution extends our understanding of the logic and meanings behind the ways in which patient participation and collective representation in health governance initiatives take shape. My findings highlight the ways in which a commitment to a global mitochondrial disease patient community and a sense of patient solidarity influence expressions of support with regard to legalizing mitochondrial replacement techniques. My analyses illustrate how normative practices and expectations of participatory governance potentially foreclose opportunities for sustained collective patient engagement with the complex ethical, social, and political dimensions of emerging technologies and may silence diverse and potentially dissenting embodied and lived responses to the prospects of particular technological developments.

Genetic manipulation for inherited neurodegenerative diseases: myth or reality?

Rare genetic diseases affect about 7% of the general population and over 7000 distinct clinical syndromes have been described with the majority being due to single gene defects. This review will provide a critical overview of genetic strategies that are being pioneered to halt or reverse disease progression in inherited neurodegenerative diseases. This field of research covers a vast area and only the most promising treatment paradigms will be discussed with a particular focus on inherited eye diseases, which have paved the way for innovative gene therapy paradigms, and mitochondrial diseases, which are currently generating a lot of debate centred on the bioethics of germline manipulation.

Evolutionary defined role of the mitochondrial DNA in fertility, disease and ageing

BACKGROUND

The endosymbiosis of an alpha-proteobacterium and a eubacterium a billion years ago paved the way for multicellularity and enabled eukaryotes to flourish. The selective advantage for the host was the acquired ability to generate large amounts of intracellular hydrogen-dependent adenosine triphosphate. The price was increased reactive oxygen species (ROS) inside the eukaryotic cell, causing high mutation rates of the mitochondrial DNA (mtDNA). According to the Muller's ratchet theory, this accumulation of mutations in asexually transmitted mtDNA would ultimately lead to reduced reproductive fitness and eventually extinction. However, mitochondria have persisted over the course of evolution, initially due to a rapid, extreme evolutionary reduction of the mtDNA content. After the phylogenetic divergence of eukaryotes into animals, fungi and plants, differences in evolution of the mtDNA occurred with different adaptations for coping with the mutation burden within these clades. As a result, mitochondrial evolutionary mechanisms have had a profound effect on human adaptation, fertility, healthy reproduction, mtDNA disease manifestation and transmission and ageing. An understanding of these mechanisms might elucidate novel approaches for treatment and prevention of mtDNA disease.

METHODS

The scientific literature was investigated to determine how mtDNA evolved in animals, plants and fungi. Furthermore, the different mechanisms of mtDNA inheritance and of balancing Muller's ratchet in these species were summarized together with the consequences of these mechanisms for human health and reproduction.

RESULTS

Animal, plant and fungal mtDNA have evolved differently. Animals have compact genomes, little recombination, a stable number of genes and a high mtDNA copy number, whereas plants have larger genomes with variable gene counts, a low mtDNA copy number and many recombination events. Fungal mtDNA is somewhere in between. In plants, the mtDNA mutation rate is kept low by effective ROS defence and efficient recombination-mediated mtDNA repair. In animal mtDNA, these mechanisms are not or less well-developed and the detrimental mutagenesis events are controlled by a high mtDNA copy number in combination with a genetic bottleneck and purifying selection during transmission. The mtDNA mutation rates in animals are higher than in plants, which allow mobile animals to adapt more rapidly to various environmental conditions in terms of energy production, whereas static plants do not have this need. Although at the level of the species, these mechanisms have been extremely successful, they can have adverse effects for the individual, resulting, in humans, in severe or unpredictably segregating mtDNA diseases, as well as fertility problems and unhealthy ageing.

CONCLUSIONS

Understanding the forces and processes that underlie mtDNA evolution among different species increases our knowledge on the detrimental consequences that individuals can have from these evolutionary end-points. Alternative outcomes in animals, fungi and plants will lead to a better understanding of the inheritance of mtDNA disorders and mtDNA-related fertility problems. These will allow the development of options to ameliorate, cure and/or prevent mtDNA diseases and mtDNA-related fertility problems.

A leap of faith? An interview study with professionals on the use of mitochondrial replacement to avoid transfer of mitochondrial diseases

STUDY QUESTION

What are the opinions of professionals in the field of genetics, reproductive science and metabolic diseases on the development of mitochondrial replacement technologies to be used in the context of medically assisted reproduction?

SUMMARY ANSWER

Although concerns regarding safety remain, interviewees supported the development of nuclear transfer techniques to help women who are at risk of transferring a mitochondrial DNA disease to their offspring conceive a genetically related child.

WHAT IS KNOWN ALREADY

Technological developments in the field of nuclear transfer have sparked new interest in the debate on the acceptability of the use of donor oocytes to prevent the transmission of mitochondrial diseases. For example, in the UK, extensive public consultations have been done to investigate whether such techniques would allow the passing of a law that involves making changes to a human oocyte or embryo before transfer to a woman's body. Until now, continental European countries seem to await the outcome of the British debate before themselves considering the arguments for and against this technology.

STUDY DESIGN, SIZE, AND DURATION

We interviewed 12 professionals from Belgium and The Netherlands.

PARTICIPANTS/MATERIALS, SETTING, AND METHODS

We conducted 12 interviews with fertility specialists, scientists, clinical geneticists, a pediatrician specialized in metabolic diseases and a specialist in metabolic diseases. The profiles of the interviewees varied but all had experience with mitochondrial diseases, either in treating patients or in providing counseling to patients or to prospective parents. The interviews were conducted face-to-face and took 30-45 min. The language of the interviews was Dutch. We analyzed the transcript of these interviews using QSR NVIVO 10 software to extract themes and categories.

MAIN RESULTS AND THE ROLE OF CHANCE

This study has shown that, although amongst the professionals we interviewed there was support for the development and deployment of nuclear transfer, this support does not necessarily correspond to uniform opinions about the importance of having a genetically own child or the contribution of mitochondrial DNA to essential characteristics of an individual.

LIMITATIONS, REASONS FOR CAUTION

In translating the quotes from Dutch to English some of the linguistic nuances may have been lost. We only interviewed 12 individuals, in two countries, whose view may not be representative of existing values and opinions that may be held by professionals worldwide on this matter. To further explore the issue at hand, a subsequent investigation of the opinions of people affected by mitochondrial diseases and of the general public is necessary.

WIDER IMPLICATIONS OF THE FINDINGS

With this study we have demonstrated there is in principle support for the nuclear transfer technique from Dutch and Belgian professionals. Further research, both scientific and ethical, is needed to define the modalities of its possible introduction in the fertility clinic.

STUDY FUNDING/COMPETING INTERESTS

This research was funded by GROW, School for Oncology and Developmental Biology, The Netherlands. The authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Präimplantationsdiagnostik

Für Paare mit hohem Risiko der Nachkommen für eine monogen-erbliche oder chromosomal-bedingte Erkrankung kann die Präimplantationsdiagnostik (PID) heute eine Option einer verantwortlichen Familienplanung sein. Voraussetzung für eine PID ist die Befruchtung von Eizellen im Reagenzglas (In-vitro-Fertilisation, IVF). Die Behandlungsergebnisse entsprechen weitgehend denen einer normalen Kinderwunschbehandlung mit intrazytoplasmatischer Spermieninjektion (ICSI) ohne PID. Die Grenzen und Chancen, aber auch der hohe Aufwand, sind frühzeitig und ergebnisoffen in einer interdisziplinären Beratung zu thematisieren, um dem Paar eine informierte Entscheidung und Abwägung der PID gegenüber anderen Alternativen im Rahmen der Familienplanung zu ermöglichen.

In diesem Beitrag werden der aktuelle internationale Kenntnisstand zur PID, einschließlich ihrer verschiedenen Anwendungsbereiche, sowie mögliche zukünftige Entwicklungen vorgestellt. Breiten Raum nimmt der rechtliche Rahmen für die eng begrenzte Durchführung einer PID in Deutschland ein, der durch den Deutschen Bundestag mit der Verabschiedung des Gesetzes zur Regelung der Präimplantationsdiagnostik (Präimplantationsdiagnostikgesetz, PräimpG) 2011 und der nachfolgenden Rechtsverordnung 2012 definiert wurde. Abschließend wird der derzeitige Stand der Umsetzung in Deutschland skizziert und eine nationale Koordination und Vernetzung der PID-Zentren angeregt, um zeitnah unter optimaler Nutzung der Ressourcen und Erfahrungen für ein möglichst breites Spektrum an seltenen Erkrankungen eine qualitätsgesicherte PID in Deutschland anbieten zu können.

Manipulating mitochondrial genomes in the clinic: playing by different rules

Recently, several publications have surfaced describing methods to manipulate mitochondrial genomes in tissues and embryos. With them, a somewhat sensationalistic uproar about the generation of children with 'three parents' has dominated the discussion in the lay media. It is important that society understands the singularities of mitochondrial genetics to judge these procedures in a rational light, so that this ongoing discussion does not preclude the helping of patients and families harboring mutated mitochondrial genomes.

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.

The wobbly evidence base of reproductive medicine

In assisted reproduction, there is strong evidence for some things done, but no or only very weak evidence for others. There are several reasons for this. Most assisted reproduction procedures have small signal-to-noise ratios. This means that their treatment effect is sometimes only little better than the spontaneous conception rate, or the conception rate with traditional treatment. Hence, large trials are required. These demand complex multicentre logistics. The latter require substantial funding and funding for reproductive medicine in most countries is notoriously difficult to obtain (as opposed, for example, to oncology research or cardiovascular research). Apart from these funding issues, the creation of embryos specifically for research is only allowed in a limited number of European countries, thus tempting clinicians to skip preclinical studies altogether and go directly for clinical application in their patients, raising an ethical issue. Introducing new treatments into the clinic without proper evidence, however, is perhaps even more of an ethical issue. Subfertile couples are very vulnerable and should not be exploited.