Mitochondria and reproduction: possibilities for testing and treatment

Mitochondrial deoxyguanosine kinase is required for female fertility in mice

Mitochondrial homeostasis plays a pivotal role in oocyte maturation and embryonic development. Deoxyguanosine kinase (DGUOK) is a nucleoside kinase that salvages purine nucleosides in mitochondria and is critical for mitochondrial DNA replication and homeostasis in non-proliferating cells. Dguok loss-of-function mutations and deletions lead to hepatocerebral mitochondrial DNA deletion syndrome. However, its potential role in reproduction remains largely unknown. In this study, we find that Dguok knockout results in female infertility. Mechanistically, DGUOK deficiency hinders ovarian development and oocyte maturation. Moreover, DGUOK deficiency in oocytes causes a significant reduction in mitochondrial DNA copy number and abnormal mitochondrial dynamics and impairs germinal vesicle breakdown. Only few DGUOK-deficient oocytes can extrude their first polar body during in vitro maturation, and these oocytes exhibit irregular chromosome arrangements and different spindle lengths. In addition, DGUOK deficiency elevates reactive oxygen species levels and accelerates oocyte apoptosis. Our findings reveal novel physiological roles for the mitochondrial nucleoside salvage pathway in oocyte maturation and implicate DGUOK as a potential marker for the diagnosis of female infertility.

Yi Mai granule improve energy supply of endothelial cells in atherosclerosis via miRNA-125a-5p regulating mitochondrial autophagy through Pink1-Mfn2-Parkin pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Yi Mai granule (YMG) consists of two classic Chinese medicine formulas used to treat cardiovascular disease for centuries. The Pink1-Mfn2-Parkin pathway, a well-recognized mechanism that mediates mitochondrial autophagy, plays a big part in mitochondrial quality control and the maintenance of heart function. However, the effects of YMG on endothelial dysfunction and mitochondrial autophagy remain unknown.

AIM OF THE STUDY

Here, we focused on the therapeutic effects of YMG in improving mitochondrial autophagy and the mechanism of YMG against cardiovascular disease.

MATERIALS AND METHODS

In this study, rats were fed high-fat diet (HFD) for 21 weeks and were given high, medium, and low doses of YMG in stomach. The open field test was used to evaluate the rats' behavior. Atherosclerotic plaques, blood lipids, and cytokine levels were measured. Mitochondrial autophagy changes were observed by Transmission electron microscope (TEM). Human umbilical vein endothelial cells (HUVECs) were injured by angiotensinⅡ(AngⅡ) and were given high, medium, and low doses of YMG medicated serum in cell culture medium. Pink1-Mfn2-Parkin expression and miRNA 125a-5p expression were measured by RT-PCR and Western blot.

RESULTS

We demonstrated that the atherosclerosis model group tended to exhibit reduced vitality behaviors. We proved that the atherosclerosis model group showed obvious atherosclerotic plaques, endothelial cells destruction, and high level of blood lipid and cytokines (including hs-CRP, ET). Mitochondria were reduced, and mitophagy was inhibited in aortic cells of the model group. MiRNA-125a-5p was up-regulated; at the same time, Pink1-Mfn2-Parkin-mediated mitochondrial autophagy was prevented. We also proved that AngⅡinjured HUVEC showed obviously low mRNA levels of Pink1, Mfn2, and Parkin. Interestingly, we found that miRNA-125a-5p was significantly down regulated in Ang II-induced HUVECs. In addition, miRNA-125a-5p significantly reduced the protective effect of YiMai Granules against Ang II injury.

CONCLUSION

Our finding indicated that Pink1-Mfn2-Parkin-mediated mitochondrial autophagy plays a crucial role in alleviating atherosclerosis. YMG alleviated atherosclerosis by potentially activating mitochondrial autophagy may via miRNA-125a-5p, regulating Pink1-Mfn2-Parkin pathway, and regulating proinflammatory factors, vasoconstriction cytokine, and blood lipids.

The Role of Mitochondria in Human Fertility and Early Embryo Development: What Can We Learn for Clinical Application of Assessing and Improving Mitochondrial DNA?

Mitochondria are well known as ‘the powerhouses of the cell’. Indeed, their major role is cellular energy production driven by both mitochondrial and nuclear DNA. Such a feature makes these organelles essential for successful fertilisation and proper embryo implantation and development. Generally, mitochondrial DNA is exclusively maternally inherited; oocyte’s mitochondrial DNA level is crucial to provide sufficient ATP content for the developing embryo until the blastocyst stage of development. Additionally, human fertility and early embryogenesis may be affected by either point mutations or deletions in mitochondrial DNA. It was suggested that their accumulation may be associated with ovarian ageing. If so, is mitochondrial dysfunction the cause or consequence of ovarian ageing? Moreover, such an obvious relationship of mitochondria and mitochondrial genome with human fertility and early embryo development gives the field of mitochondrial research a great potential to be of use in clinical application. However, even now, the area of assessing and improving DNA quantity and function in reproductive medicine drives many questions and uncertainties. This review summarises the role of mitochondria and mitochondrial DNA in human reproduction and gives an insight into the utility of their clinical use.

Extensive analysis of mitochondrial DNA quantity and sequence variation in human cumulus cells and assisted reproduction outcomes

STUDY QUESTION

Are relative mitochondrial DNA (mtDNA) content and mitochondrial genome (mtGenome) variants in human cumulus cells (CCs) associated with oocyte reproductive potential and assisted reproductive technology (ART) outcomes?

SUMMARY ANSWER

Neither the CC mtDNA quantity nor the presence of specific mtDNA genetic variants was associated with ART outcomes, although associations with patient body mass index (BMI) were detected, and the total number of oocytes retrieved differed between major mitochondrial haplogroups.

WHAT IS KNOWN ALREADY

CCs fulfil a vital role in the support of oocyte developmental competence. As with other cell types, appropriate cellular function is likely to rely upon adequate energy production, which in turn depends on the quantity and genetic competence of the mitochondria. mtDNA mutations can be inherited or they can accumulate in somatic cells over time, potentially contributing to aging. Such mutations may be homoplasmic (affecting all mtDNA in a cell) or they may display varying levels of heteroplasmy (affecting a proportion of the mtDNA). Currently, little is known concerning variation in CC mitochondrial genetics and how this might influence the reproductive potential of the associated oocyte.

STUDY DESIGN, SIZE, DURATION

This was a prospective observational study involving human CCs collected with 541 oocytes from 177 IVF patients. mtDNA quantity was measured in all the samples with a validated quantitative PCR method and the entire mtGenome was sequenced in a subset of 138 samples using a high-depth massively parallel sequencing approach. Associations between relative mtDNA quantity and mtGenome variants in CCs and patient age, BMI (kg/m2), infertility diagnosis and ART outcomes were investigated.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Massively parallel sequencing permitted not only the accurate detection of mutations but also the precise quantification of levels of mutations in cases of heteroplasmy. Sequence variants in the mtDNA were evaluated using Mitomaster and HmtVar to predict their potential impact.

MAIN RESULTS AND THE ROLE OF CHANCE

The relative mtDNA CC content was significantly associated with BMI. No significant associations were observed between CC mtDNA quantity and patient age, female infertility diagnosis or any ART outcome variable. mtGenome sequencing revealed 4181 genetic variants with respect to a reference genome. The COXI locus contained the least number of coding sequence variants, whereas ATPase8 had the most. The number of variants predicted to affect the ATP production differed significantly between mitochondrial macrohaplogroups. The total number of retrieved oocytes was different between the H-V and J-T as well as the U-K and J-T macrohaplogroups. There was a non-significant increase in mtDNA levels in CCs with heteroplasmic mitochondrial mutations.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Although a large number of samples were analysed in this study, it was not possible to analyse all the CCs from every patient. Also, the results obtained with respect to specific clinical outcomes and macrohaplogroups should be interpreted with caution due to the smaller sample sizes when subdividing the dataset.

WIDER IMPLICATIONS OF THE FINDINGS

These findings suggest that the analysis of mtDNA in CCs is unlikely to provide an advantage in terms of improved embryo selection during assisted reproduction cycles. Nonetheless, our data raise interesting biological questions, particularly regarding the interplay of metabolism and BMI and the association of mtDNA haplogroup with oocyte yield in ovarian stimulation cycles.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by National Institutes of Health grant 5R01HD092550-02. D.J.N. and C.R. co-hold patent US20150346100A1 and D.J.N. holds US20170039415A1, both for metabolic imaging methods. D.W. receives support from the NIHR Oxford Biomedical Research Centre. The remaining authors have no conflicts of interest to declare.

Dynamic changes in mitochondrial DNA, morphology, and fission during oogenesis of a seasonal-breeding teleost, Pampus argenteus

Mitochondria play crucial roles during oocyte development. In this study, we have investigated mitochondrial morphology, mtDNA, Ca²⁺-ATP enzyme activity, and mitochondrial fission factor (mff) expression levels during oogenesis of the silver pomfret Pampus argenteus. The mtDNA increased with oocyte development, and mitochondrial morphology and distribution were stage-specific. In the perinucleolar oocytes, oval mitochondria were dispersed in the cytoplasm. In previtellogenic oocytes, mitochondria massively increased and aggregated, forming mitochondrial clouds. At the same time, two morphologically different types of mitochondria had been distinguished, one of which was elongated with well-developed cristae, and the other was round with distorted and fused cristae. During vitellogenesis, the increases in mitochondria with well-developed cristae and in Ca²⁺-ATPase enzymatic activity were accompanied by an accumulation of yolk substance, suggesting the possible participation of mitochondria in the formation of vitellogenesis. Furthermore, we examined the cDNA of mff its transcript levels in relation to oocyte development. The transcript levels of mff were high in the perinucleolar stage, increasing to the highest level at the previtellogenic stage. Immunocytochemistry showed that MFF was detected in the cytoplasm of previtellogenic and midvitellogenic oocytes. We speculated that the mff-mediated mitochondrial fission may play a crucial role in oocyte development, especially in vitellogenesis.

Mitochondrial DNA Content May Not Be a Reliable Screening Biomarker for Live Birth After Single Euploid Blastocyst Transfer

An increasing number of studies have related the mitochondrial DNA (mtDNA) content to embryo viability and transfer outcomes. However, previous studies have focused more on the relationship between mtDNA and embryo implantation, few studies have studied the effect of the mtDNA content on live birth. In the study, we investigated whether mtDNA content is a reliable screening biomarker for live birth after single blastocyst transfer. A total of 233 couples with 316 blastocyst stage embryos undergoing in vitro fertilization treatment and pre-implantation genetic testing analysis were included in the study. All embryos were chromosomally normal and had undergone single-embryo transfers. There was no significant difference observed in the blastocyst mtDNA content among the live birth, miscarriage and non-implanted groups (p=0.999), and the mtDNA content in blastocysts from the miscarriage and live birth groups was similar [median (interquartile range), 1.00*10⁸(7.59*10⁷- 1.39*10⁸) vs 1.01*10⁸ (7.37*10⁷- 1.32*10⁸)]. Similarly, no significant association was observed between mtDNA content and embryo implantation potential (p=0.965). After adjusting for multiple confounders in a logistic regression analysis with generalized estimating equations, no associations between mtDNA content and live birth were observed in all blastocysts, Day-5 and Day-6 blastocysts (p=0.567, p=0.673, p=0.165, respectively). The live birth rate was not significantly different between blastocysts with an elevated mtDNA content and blastocysts with a normal mtDNA content (26.7% vs 33.6% p=0.780). Additionally, there was no linear correlation between the mtDNA content and maternal age (p=0.570). In conclusion, the mtDNA content does not seem to be a potential biomarker for embryo transfer outcomes (i.e., implantation and live birth) based on the existing testing tools. Embryos with an elevated mtDNA content also have development potential for successful live birth.