Ethics of mitochondrial therapy for deafness

Mitochondrial therapy may provide the relief to many families with inherited mitochondrial diseases. However, it also has the potential for use in non-fatal disorders such as inherited mitochondrial deafness, providing an option for correction of the deafness using assisted reproductive technology. In this paper we discuss the potential for use in correcting mitochondrial deafness and consider some of the issues for the deaf community.

Rapid isolation and purification of mitochondria for transplantation by tissue dissociation and differential filtration

Previously described mitochondrial isolation methods using differential centrifugation and/or Ficoll gradient centrifugation require 60 to 100 min to complete. We describe a method for the rapid isolation of mitochondria from mammalian biopsies using a commercial tissue dissociator and differential filtration. In this protocol, manual homogenization is replaced with the tissue dissociator's standardized homogenization cycle. This allows for uniform and consistent homogenization of tissue that is not easily achieved with manual homogenization. Following tissue dissociation, the homogenate is filtered through nylon mesh filters, which eliminate repetitive centrifugation steps. As a result, mitochondrial isolation can be performed in less than 30 min. This isolation protocol yields approximately 2 x 10(10) viable and respiration competent mitochondria from 0.18 ± 0.04 g (wet weight) tissue sample.

The commercialization of human eggs in mitochondrial replacement research

After the development of induced pluripotent stem cells (IPSCs) in 2007, the pressure to commercialize women's eggs for stem cell research could have been expected to lessen. However, the pressure to harvest human eggs in large quantities for research has not diminished; rather, it has taken different directions, for example in germline mitochondrial research. Yet there has been little acknowledgement of these technologies' need for human eggs, the possible risks to women and the ethical issues concerning potential exploitation. Rather, there has been a renewed campaign to legalize payment for eggs in research, although the actual scientific advances are at best modest. This article shows why a market in women's eggs is ethically problematic in terms of the doctor's duty to do no harm and the limitations of 'informed' consent.

Ethical considerations, safety precautions and parenthood in legalising mitochondrial donation

This article outlines some of the main ethical considerations specifically relating to legalisation of mitochondrial donation. Safety requirements, were the technique to be legalised, are then discussed, followed by an exploration of parenthood in the context of mitochondrial donation. It is concluded that there are no ethical objections specifically relating to the legalisation of mitochondrial donation, but that various safety precautions must be established prior to its use, including the availability of relevant medical information about the mitochondrial donors to any resultant children. It is also found that introduction of this technique would not necessitate modifications to current British legal definitions of parenthood. However, it is clear that societal attitudes in this area are changing, and it is recommended that this opportunity be taken to review concepts of parenthood, particularly the number of parents a child may have at one time.

Oocyte Mitochondria: Strategies to Improve Embrbryogenesis

Mitochondria play a central role to provide ATP for fertilization and preimplantation embryo development in the ooplasm. The mitochondrial dysfunction of oocyte has been proposed as one of the causes of high levels of developmental retardation and arrest that occur in preimplantation embryos generated using Assisted Reproductive Technology. Cytoplasmic transfer (CT) from a donor to a recipient oocyte has been applied to infertility due to dysfunctional ooplasm, with resulting pregnancies and births. However, neither the efficacy nor safety of this procedure has been appropriately investigated. In order to improve embryogenesis, we observed the mitochondrial distribution in ooplasma under the several conditions using mitochondrial GFP-transgenic mice (mtGFP-tg mice) in which the mitochondria are visualized by GFP. In this report, we will present our research about the mitochondrial distribution in ooplasm during early embryogenesis and the fate of injected donor mitochondria after CT using mtGFP-tg mice. The mitochondria in ooplasm from the germinal vesicle stage to the morula stage were accumulated in the perinuclear region. The mitochondria of the mtGFP-tg mouse oocyte transferred into the wild type mouse embryo could be observed until the blastocysts stage, suggesting that the mtGFP-tg mice oocyte is very useful for visual observation of the mitochondrial distribution in the oocyte, and that the aberrant early developmental competences due to the oocyte mitochondrial dysfunction may be overcome by transferring the "normal" mitochondria.

Role of the mitochondrial genome in assisted reproductive technologies and embryonic stem cell-based therapeutic cloning

Mitochondria play a pivotal role in cellular metabolism and are important determinants of embryonic development. Mitochondrial function and biogenesis rely on an intricate coordination of regulation and expression of nuclear and mitochondrial genes. For example, several nucleus-derived transcription factors, such as mitochondrial transcription factor A, are required for mitochondrial DNA replication. Mitochondrial inheritance is strictly maternal while paternally-derived mitochondria are selectively eliminated during early embryonic cell divisions. However, there are reports from animals as well as human patients that paternal mitochondria can occasionally escape elimination, which in some cases has led to severe pathologies. The resulting existence of different mitochondrial genomes within the same cell has been termed mitochondrial heteroplasmy. The increasing use of invasive techniques in assisted reproduction in humans has raised concerns that one of the outcomes of such techniques is an increase in the incidence of mitochondrial heteroplasmy. Indeed, there is evidence that heteroplasmy is a direct consequence of ooplasm transfer, a technique that was used to 'rescue' oocytes from older women by injecting ooplasm from young oocytes. Mitochondria from donor and recipient were found in varying proportions in resulting children. Heteroplasmy is also a byproduct of nuclear transfer, as has been shown in studies on cloned sheep, cattle and monkeys. As therapeutic cloning will depend on nuclear transfer into oocytes and the subsequent generation of embryonic stem cells from resulting blastocysts, the prospect of mitochondrial heteroplasmy and its potential problems necessitate further studies in this area.

Mitochondria transfer can enhance the murine embryo development

PURPOSE

To evaluate the effect of mitochondrial transfer on embryonic development.

MATERIALS AND METHODS

Mitochondria concentrates were collected from murine hepatocytes and fertilized murine zygotes from young and older mice in the 2PN stage were subjected to mitochondrial transfer and cultured in vitro to evaluate the embryonic development.

RESULTS

After extended in vitro culture, 37.65% and 20.91% embryos from the young mice developed to the blastocyst stage in the injected and control groups respectively, which is statistically significant. There was no difference in terms of hatching rates (1.76% and 1.82% respectively). Zygotes from the older mice (>20 weeks old) that received mitochondrial transfer also had a better developmental outcome than the control group (54.35% and 18.92% developed to morula stage, 43.48% and 8.11% developed to the blastocyst stage respectively), which is statistically significant.

CONCLUSIONS

Our results for the murine model provide direct scientific evidence that mitochondrial transfer improves embryonic development. However, potential risks such as mitochondrial heteroplasmy, nuclear-mitochondrial interaction and epigenetic aspects all deserve further evaluation before mitochondrial transfer is applied clinically.

Effects of Granulosa Cell Mitochondria Transfer on the Early Development of Bovine Embryos In Vitro

The objective of this study was to determine the effect of exogenous mitochondria obtained from granulosa cells on the development of bovine embryos in vitro. We classified cumulus oocyte complexes (COCs) as good (G)- and poor (P)-quality oocytes based on cytoplasmic appearance and cumulus characteristics, and assessed mtDNA copy numbers in the G and P oocytes with real-time polymerase chain reaction (PCR). The mitochondria were isolated by fractionation and suspended in mitochondria injection buffer (MIB). Part one of the experiment consisted of the following treatments: (1) G-oocytes + sperm, (2) P-oocytes + mitochondria + MIB + sperm, (3) P-oocytes + MIB + sperm, and (4) P-oocytes + sperm. In part 2, oocytes were parthenogenetically activated. The treatments were: (1) G-oocytes, (2) P-oocytes + mitochondria + MIB, (3) P-oocytes + MIB, and (4) P-oocytes alone. The results indicated a significant difference in mtDNA copy number between G (361 113 +/- 147 114) and P (198 293 +/- 174 178) oocytes (p < 0.01). The rates of morula, blastocyst, and hatched blastocysts derived from P-oocytes + mitochondria were similar to those of G-oocytes, but significantly higher than P-oocytes without exogenous mitochondria in both the ICSI and parthenogenetic activation experiments. We found no difference in blastomere numbers between G-oocytes and P-oocytes + mitochondria in either experiment, but blastomere numbers in these two groups were significantly higher than in P-oocyte groups without exogenous mitochondria. These data suggest that mtDNA content is very important for early embryo development. Furthermore, the transfer of mitochondria from the same breed may improve embryo quality during preimplantation development.

How to prevent 'half-bastard' progeny? or An alternative for three-parent babies: two-parent babies through transplantation of sperm mitochondria

Body development and activity depend on the level of internal energy generation. Therefore, unaffected, optimally active mitochondria are indispensable in a healthy and vital body. A mutation in the DNA of the semi-autonomous mitochondria (mtDNA) may cause an inheritable insufficiency that is due to decreased energy generation needed for adequate development. Sperm mitochondria will not enter the egg cell during fusion of male and female gametocytes. Since women with mutated mtDNA will increasingly know and realize the effect of such mutation in their own body, they will more often ask for treatment to stop the effect of such inconvenient mutation in their progeny. Thus far, solutions for this problem were thought to be: (i) nucleus transplantation just after fertilization into a nucleus-free egg cell of a second healthy woman and later (ii) transplantation of healthy mitochondria from a second woman into the egg cell before fertilization. Although both transplantations create babies with three, instead of two-parents that have contributed to the genetic content, in case of the newer mitochondria transplantation technique the part of the second woman is somewhat more reduced, but still clearly present. Thus, assisted-reproduction techniques that mix egg cell mitochondria from two women may create not only 'three-parents' babies, but also fears for 'three-parents' babies, since this handling may create non-scientific problems, especially regarding emotional, ethical, religious and juridical aspects of life. Transplantation of healthy sperm mitochondria of the partner into the egg cell with insufficient mitochondria is thought to be the best solution for this problem, since it may create a 'two-parents' instead of a 'three-parents' baby. This only implies that at the moment of (successful) transplantation the biological dogma is broken that mitochondria are maternally inherited: the mitochondria of the maternal line of the woman will have been substituted by the mitochondria of the maternal line of the man.

Assaying the probabilities of obtaining maternally inherited heteroplasmy as the basis for modeling OXPHOS diseases in animals

Gross alterations in cell energy metabolism underlie manifestations of hereditary OXPHOS (oxidative phosphorylation) diseases, many of which depend on proportion of mutant mitochondrial DNA (mtDNA) in tissues. An animal model of OXPHOS disease with maternal inheritance of mitochondrial heteroplasmy might help understanding the peculiarities of abnormal mtDNA distribution and its effect on pre- and postnatal development. Previously we obtained mice that carry human mtDNA in some tissues. It co-existed with murine mtDNA (heteroplasmy) and was transmitted maternally to the progeny of animals developed from zygotes injected with human mitochondria. To analyze the probability of obtaining heteroplasmic mice we increased the number of experiments with early embryos and obtained more specimens from F1. About 33% of zygotes injected with human mtDNA developed into post-implantation embryos (7th-13th days). Lower amount of such developed into neonate mice (ca. 21%). Among post-implantation embryos and in generations F0 and F1 percentages of human mtDNA-carriers were ca. 14-16%. Such percentages are sufficient for modeling maternally inherited heteroplasmy in small animal groups. More data are needed to understand the regularities of anomalous mtDNA distribution among cells and tissues and whether heart and muscles frequently carrying human mtDNA in our experiments are particularly susceptible to heteroplasmy.

Mitochondria directly influence fertilisation outcome in the pig

The mitochondrion is explicitly involved in cytoplasmic regulation and is the cell’s major generator of ATP. Our aim was to determine whether mitochondria alone could influence fertilisation outcome.In vitro, oocyte competence can be assessed through the presence of glucose-6-phosphate dehydrogenase (G6PD) as indicated by the dye, brilliant cresyl blue (BCB). Using porcinein vitrofertilisation (IVF), we have assessed oocyte maturation, cytoplasmic volume, fertilisation outcome, mitochondrial number as determined by mtDNA copy number, and whether mitochondria are uniformly distributed between blastomeres of each embryo. After staining with BCB, we observed a significant difference in cytoplasmic volume between BCB positive (BCB+) and BCB negative (BCB−) oocytes. There was also a significant difference in mtDNA copy number between fertilised and unfertilised oocytes and unequal mitochondrial segregation between blastomeres during early cleavage stages. Furthermore, we have supplemented BCB−oocytes with mitochondria from maternal relatives and observed a significant difference in fertilisation outcomes following both IVF and intracytoplasmic sperm injection (ICSI) between supplemented, sham-injected and non-treated BCB−oocytes. We have therefore demonstrated a relationship between oocyte maturity, cytoplasmic volume, and fertilisation outcome and mitochondrial content. These data suggest that mitochondrial number is important for fertilisation outcome and embryonic development. Furthermore, a mitochondrial pre-fertilisation threshold may ensure that, as mitochondria are diluted out during post-fertilisation cleavage, there are sufficient copies of mtDNA per blastomere to allow transmission of mtDNA to each cell of the post-implantation embryo after the initiation of mtDNA replication during the early postimplantation stages.