Mitochondrial replacement techniques or therapies (MRTs) to improve embryo development and to prevent mitochondrial disease transmission

Human embryos derived from first polar body nuclear transfer exhibit comparatively abnormal morphokinetics during development

OBJECTIVE

Reconstructed oocytes after polar body genome transfer constitute a potential therapeutic option for patients with a history of embryo fragmentation and advanced maternal age. However, the rescue of genetic material from the first polar body (PB1) through introduction into the donor cytoplasm is not yet ready for clinical application.

METHODS

Eighty-five oocytes were obtained following in vitro maturation (IVM) and divided into two groups: PB1 nuclear transfer (PB1NT; n=54) and control (n=31). Following enucleation and PB1 genomic transfer, PB1 fusion was assessed. Subsequently, all fused oocytes underwent intracytoplasmic sperm injection (ICSI) and were cultured in an incubator under a time-lapse monitoring system to evaluate fertilization, embryonic morphokinetic parameters, and cleavage patterns.

RESULTS

Following enucleation and fusion, 77.14% of oocytes survived, and 92.59% of polar bodies (PBs) fused. However, the normal fertilization rate was lower in the PB1NT group than in the control group (56.41% vs. 92%, p=0.002). No significant differences were observed in embryo kinetics between the groups, but a significant difference was detected in embryo developmental arrest after the four-cell stage, along with abnormal cleavage division in the PB1NT group. This was followed by significant between-group differences in the implantation potential rate and euploidy status. Most embryos in the PB1NT group had at least one abnormal cleavage division (93.3%, p=0.001).

CONCLUSION

Fresh PB1NT oocytes successfully produced normal zygotes following PB fusion and ICSI in IVM oocytes. However, this was accompanied by low efficiency in developing into cleavage embryos, along with an increase in abnormal cleavage patterns.

Eight Strategies to Engineer Acceptance of Human Germline Modifications

Until recently, scientific consensus held firm that genetically manipulated embryos created through methods including Mitochondrial Replacement Therapy or human germline genome editing should not be used to initiate a pregnancy. In countries that have relevant laws pertaining to heritable human germline modifications, the vast majority prohibit or restrict this practice. In the last several years, scholars have observed a transformation of scientific and policy restrictions with insistent calls for creating a regulatory pathway. Multiple stakeholders highlight the role of social consensus and public engagement for governance of heritable human germline modifications. However, in the drive to gain public acceptance and lift restrictions, some proponents provide distorted or misleading narratives designed to influence public perception and incrementally shift the consensus. This article describes eight discrete strategies that proponents employ to influence framing, sway public opinion, and revise policymaking of human germline modifications in a manner that undermines honest engagement.

Reduction of mtDNA heteroplasmy in mitochondrial replacement therapy by inducing forced mitophagy

Mitochondrial replacement therapy (MRT) has been used to prevent maternal transmission of disease-causing mutations in mitochondrial DNA (mtDNA). However, because MRT requires nuclear transfer, it carries the risk of mtDNA carryover and hence of the reversion of mtDNA to pathogenic levels owing to selective replication and genetic drift. Here we show in HeLa cells, mouse embryos and human embryos that mtDNA heteroplasmy can be reduced by pre-labelling the mitochondrial outer membrane of a donor zygote via microinjection with an mRNA coding for a transmembrane peptide fused to an autophagy receptor, to induce the degradation of the labelled mitochondria via forced mitophagy. Forced mitophagy reduced mtDNA carryover in newly reconstructed embryos after MRT, and had negligible effects on the growth curve, reproduction, exercise capacity and other behavioural characteristics of the offspring mice. The induction of forced mitophagy to degrade undesired donor mtDNA may increase the clinical feasibility of MRT and could be extended to other nuclear transfer techniques.

Effects of various calcium transporters on mitochondrial Ca2+ changes and oocyte maturation

Ca2+ participates in many important cellular processes, but the underlying mechanisms are still poorly understood, especially during oocyte maturation. First, we confirmed that calcium in the culture medium was essential for oocyte maturation. Next, various inhibitors of Ca2+ channels were applied to investigate their roles in mitochondrial Ca2+ changes and oocyte maturation. Our results showed that Trmp7, Orai, T-type Ca2+ channels and Na+ /Ca2+ exchanger complex (NCLX) were important for oocyte maturation. Trmp7 inhibition delayed germinal vesicle breakdown. Orai and NCLX inhibition significantly weakened the distribution of mitochondrial Ca2+ around the nucleus compared to the Ctrl group. Interestingly, even T-type Ca2+ channels-specific inhibitor Mibefradil blocked germinal vesicle breakdown; mitochondrial Ca2+ surrounding the nucleus still was maintained at a high level without spindle formation. Two calcium transporter inhibitors, Thapsigargin and Ruthenium Red, which have been confirmed to inhibit oocyte activation, did not significantly affect oocyte maturation. Increasing the knowledge of calcium transport may provide a basis to build on for improving oocyte in vitro maturation in human assisted reproduction clinics.

Mitochondrial transfer from induced pluripotent stem cells rescues developmental potential of in vitro fertilized embryos from aging females†

Conventional heterologous mitochondrial replacement therapy is clinically complicated by "tri-parental" ethical concerns and limited source of healthy donor oocytes or zygotes. Autologous mitochondrial transfer is a promising alternative in rescuing poor oocyte quality and impaired embryo developmental potential associated with mitochondrial disorders, including aging. However, the efficacy and safety of mitochondrial transfer from somatic cells remains largely controversial, and unsatisfying outcomes may be due to distinct mitochondrial state in somatic cells from that in oocytes. Here, we propose a potential strategy for improving in vitro fertilization (IVF) outcomes of aging female patients via mitochondrial transfer from induced pluripotent stem (iPS) cells. Using naturally aging mice and well-established cell lines as models, we found iPS cells and oocytes share similar mitochondrial morphology and functions, whereas the mitochondrial state in differentiated somatic cells is substantially different. By microinjection of isolated mitochondria into fertilized oocytes following IVF, our results indicate that mitochondrial transfer from iPS, but not MEF cells, can rescue the impaired developmental potential of embryos from aging female mice and obtain an enhanced implantation rate following embryo transfer. The beneficial effect may be explained by the fact that mitochondrial transfer from iPS cells not only compensates for aging-associated loss of mtDNA, but also rescues mitochondrial metabolism of subsequent preimplantation embryos. Using mitochondria from iPS cells as the donor, our study not only proposes a promising strategy for improving IVF outcomes of aging females, but also highlights the importance of synchronous mitochondrial state in supporting embryo developmental potential.

Mitochondrial Ca2 + Is Related to Mitochondrial Activity and Dynamic Events in Mouse Oocytes

Mitochondrial energy insufficiency is strongly associated with oocyte activation disorders. Ca²⁺, especially that in the mitochondrial matrix, plays a pivotal role in mitochondrial energy supplementation, but the underlying mechanisms are still only poorly understood. An encoded mitochondrial matrix Ca²⁺ probe (Mt-GCaMP6s) was introduced to observe mitochondrial Ca²⁺ ([Ca²⁺]_m) dynamic changes during oocyte maturation and activation. We found that active mitochondria surrounding the nucleus showed a higher [Ca²⁺]_m than those distributed in the cortex during oocyte maturation. During oocyte partheno-activation, the patterns of Ca²⁺ dynamic changes were synchronous in the cytoplasm and mitochondria. Such higher concentration of mitochondrial matrix Ca²⁺ was closely related to the distribution of mitochondrial calcium uptake (MICU) protein. We further showed that higher [Ca²⁺]_m mitochondria around the chromosomes in oocytes might have a potential role in stimulating mitochondrial energy for calmodulin-responsive oocyte spindle formation, while synchronizing Ca²⁺ functions in the cytoplasm and nuclear area are important for oocyte activation.

Effects of mitochondria-associated Ca2+ transporters suppression on oocyte activation

Oocyte activation deficiency leads to female infertility. [Ca²⁺ ]_i oscillations are required for mitochondrial energy supplement transition from the resting to the excited state, but the underlying mechanisms are still very little known. Three mitochondrial Ca²⁺ channels, Mitochondria Calcium Uniporter (MCU), Na⁺ /Ca²⁺ Exchanger (NCLX) and Voltage-dependent Ca²⁺ Channel (VDAC), were deactivated by inhibitors RU360, CGP37157 and Erastin, respectively. Both Erastin and CGP37157 inhibited mitochondrial activity significantly while attenuating [Ca²⁺ ]_i and [Ca²⁺ ]_m oscillations, which caused developmental block of pronuclear formation. Thus, NCLX and VDAC are two mitochondria-associated Ca²⁺ transporter proteins regulating oocyte activation, which may be used as potential targets to treat female infertility. SIGNIFICANCE OF THE STUDY: NCLX and VDAC are two mitochondria-associated Ca²⁺ transporter proteins regulating oocyte activation.

Transfer of autologous mitochondria from adipose tissue-derived stem cells rescues oocyte quality and infertility in aged mice

Elder women suffer from low or loss of fertility because of decreasing oocyte quality as maternal aging. As energy resource, mitochondria play pivotal roles in oocyte development, determining oocyte quality. With advanced maternal age, increased dysfunctions emerge in oocyte mitochondria, which decrease oocyte quality and its developmental potential. Mitochondria supplement as a possible strategy for improving egg quality has been in debate due to ethnic problems. Heterogeneity is an intractable problem even transfer of germinal vesicle, spindle, pronuclei or polar body is employed. We proposed that the autologous adipose tissue-derived stem cell (ADSC) mitochondria could improve the fertility in aged mice. We found that autologous ADSC mitochondria could promote oocyte quality, embryo development and fertility in aged mice, which may provide a promising strategy for treatment of low fertility or infertility in elder women.

Acanthopanax senticosus Protects Structure and Function of Mesencephalic Mitochondria in A Mouse Model of Parkinson's Disease

OBJECTIVE

To investigate the neuro-protective effects of Acanthopanax senticosus Harms (EAS) on mesencephalic mitochondria and the mechanism of action, using a mouse model of Parkinson's disease (PD).

METHODS

The chemical fingerprint analysis of the extract of Acanthopanax senticosus Harms (EAS) was performed using the ultra performance liquid chromatograph and time of flight mass spectrometry. Thirty mice were randomly divided into the control group, the MPTP model group, and the EAS treated group with MPTP (MPTP+EAS group, 10 in each group). The MPTP model group and the MPTP+EAS group received MPTP-HCl (30 mg/kg i.p) once a day for 5 days. The control group received an equal volume of saline (20 mL/kg i.p) once a day for 5 days. Induced by 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine hydrochloride daily (MPTP-HCl, 30 mg/kg) for 5 days, the PD mice were treated with EAS at 45.5 mg/kg daily for 20 days. The behavioral testing of mice was carried out using the pole-climbing test. The integrity and functions of neurons were examined in mesencephalic mitochondria in a PD mouse model, including nicotinamide adenine dinucleotide dehydrogenase ubiquinone flavoprotein 2 (NDUFV2), mitochondrially encoded nicotinamide adenine dinucleotide dehydrogenase 1 (MT-ND1), succinate dehydrogenase complex subunit A (SDHA), and succinate dehydrogenase cytochrome b560 subunit (SDHC).

RESULTS

After treatment with EAS, the behavioral changes induced by MPTP were attenuated significantly (P<0.05). EAS protected the mesencephalic mitochondria from swelling and attenuated the decreases in their membrane potential (both P<0.05), which was supported by an ultra-structural level analysis. The changes in reactive oxygen species (ROS), malonic dialdehyde (MDA), oxidative phosphorylation (OXPHOS) system 4 subunits levels and PD-related proteins expressions (parkin, Pink1, DJ-1, α-synuclein, and Lrrk2) reverted to near normal levels (all P<0.05), based on the results of immune-histological and Western blotting observations.

CONCLUSIONS

The neuro-protective effects of EAS are linked to protecting mice against MPTP-induced mitochondrial dysfunction and structural damage. Therefore, EAS is a promising candidate for the prevention or treatment of mitochondrial neurodegenerative disorders, such as PD.

Mitochondrial regulation of [Ca2+]i oscillations during cell cycle resumption of the second meiosis of oocyte

Oocyte is arrested at metaphase of the second meiosis until fertilization switching on [Ca²⁺]i oscillations. Oocyte activation inefficiency is the most challenging problem for failed fertilization and embryonic development. Mitochondrial function and intracellular [Ca²⁺]i oscillations are two critical factors for the oocyte's developmental potential. We aimed to understand the possible correlation between mitochondrial function and [Ca²⁺]i oscillations in oocytes. To this end, mitochondrial uncoupler CCCP which damages mitochondrial function and two small molecule mitochondrial agonists, L-carnitine (LC) and BGP-15, were used to examine the regulation of [Ca²⁺]i by mitochondrial functions. With increasing CCCP concentrations, [Ca²⁺]i oscillations were gradually diminished and high concentrations of CCCP led to oocyte death. LC enhanced mitochondrial membrane potential and [Ca²⁺]i oscillations and even improved the damage induced by CCCP, however, BGP-15 had no beneficial effect on oocyte activation. We have found that mitochondrial function plays a vital role in the generation of [Ca²⁺]i oscillations in oocytes, and thus mitochondria may interact with the ER to generate [Ca²⁺]i oscillations during oocyte activation. Improvement of mitochondrial functions with small molecules can be expected to improve oocyte activation and embryonic development in infertile patients without invasive micromanipulation.