Effect of maternal aging and vitrification on mitochondrial DNA copy number in embryos and spent culture medium

Effect of paternal aging and vitrification on mitochondrial DNA copy number and telomere length of mouse blastocysts

In this study, we examined the effects of paternal aging on the mitochondrial DNA copy number (mt-cn), telomere length (TL), and gene expression in mouse embryos. The effects of vitrification on the mt-cn and TL of the embryos derived from young and aged male parents (YF and AF, respectively) were examined. C57BL/6N male mice were used for embryo production at 13-23 and 50-55 weeks of age. Two-cell stage embryos were collected from the oviducts of superovulated female mice (8-15 weeks old) and cultured for 24 h until the 8-cell stage, followed by embryo vitrification. Fresh and vitrified-warmed embryos were incubated for 2 days until the blastocyst stage, and mt-cn and TL were investigated. The cell-free mitochondrial DNA copy number (cf-mt-cn) in the spent culture medium (SCM) of the embryos was then investigated. RNA sequencing of blastocysts revealed that metabolic pathways, including oxidative phosphorylation and mTOR pathways, were enriched in differentially expressed genes. The mt-cn and TL of AF-derived blastocysts were lower and shorter, respectively, than those of YF-derived blastocysts. Paternal aging did not affect the blastocyst rate after vitrification. Vitrification of the 8-cell stage embryos did not affect the mt-cn of the blastocysts. However, it increased the cf-mt-cn (cell-free mt-cn) in the SCM of both YF- and AF-derived embryos. Vitrification did not affect the TL of either YF- or AF-derived embryos. Thus, paternal aging affected the mt-cn and TL of the embryos, but vitrification did not affect these parameters in either age groups.

Age-related advanced glycation end-product accumulation impairs mitochondrial regulation after vitrification†

Vitrification is an important assisted reproductive technology, although it induces mitochondrial dysfunction in embryos. Herein, we aimed to investigate whether age-associated accumulation of advanced glycation end-products (AGEs) in oocytes impairs the recovery of embryos from cryopreservation-induced mitochondrial dysfunction/damage. Mouse eight-cell stage embryos developed in vitro were vitrified and warmed and incubated up to the blastocyst stage. AGE levels in oocytes were higher in both aged mice and AGE accumulation mouse models (MGO-mice) than those in young and control mice. In addition, the level of SIRT1 upregulation was lower for embryos of aged and MGO-mice than that for embryos of young and control mice. The highest mitochondrial DNA (mtDNA) content was detected in blastocysts derived from vitrified embryos of aged and MGO-mice. The spent culture medium of blastocysts derived from both aged and MGO-mice contained higher mtDNA content than that of the blastocysts derived from young and control mice. EX527 increased mtDNA content in the spent culture medium of vitrified embryos derived from young mice. In addition, p62 aggregate levels were higher in vitrified embryos of control mice than those in vitrified embryos of MGO-mice. The SIRT1 activator, resveratrol, increased p62 aggregation levels in vitrified embryos derived from young and aged mice, whereas vitrification did not affect p62 aggregation levels in embryos from aged mice. Therefore, age-associated AGE accumulation induces decreased responsive SIRT1 upregulation following vitrified-warmed treatment and impairs mitochondrial quality control activity in vitrified embryos.

Aging and oocyte competence: A molecular cell perspective

Follicular microenvironment is paramount in the acquisition of oocyte competence, which is dependent on two interconnected and interdependent processes: nuclear and cytoplasmic maturation. Extensive research conducted in human and model systems has provided evidence that those processes are disturbed with female aging. In fact, advanced maternal age (AMA) is associated with a lower chance of pregnancy and live birth, explained by the age-related decline in oocyte quality/competence. This decline has largely been attributed to mitochondria, essential for oocyte maturation, fertilization, and embryo development; with mitochondrial dysfunction leading to oxidative stress, responsible for nuclear and mitochondrial damage, suboptimal intracellular energy levels, calcium disturbance, and meiotic spindle alterations, that may result in oocyte aneuploidy. Nuclear-related mechanisms that justify increased oocyte aneuploidy include deoxyribonucleic acid (DNA) damage, loss of chromosomal cohesion, spindle assembly checkpoint dysfunction, meiotic recombination errors, and telomere attrition. On the other hand, age-dependent cytoplasmic maturation failure is related to mitochondrial dysfunction, altered mitochondrial biogenesis, altered mitochondrial morphology, distribution, activity, and dynamics, dysmorphic smooth endoplasmic reticulum and calcium disturbance, and alterations in the cytoskeleton. Furthermore, reproductive somatic cells also experience the effects of aging, including mitochondrial dysfunction and DNA damage, compromising the crosstalk between granulosa/cumulus cells and oocytes, also affected by a loss of gap junctions. Old oocytes seem therefore to mature in an altered microenvironment, with changes in metabolites, ribonucleic acid (RNA), proteins, and lipids. Overall, understanding the mechanisms implicated in the loss of oocyte quality will allow the establishment of emerging biomarkers and potential therapeutic anti-aging strategies. This article is categorized under: Reproductive System Diseases > Molecular and Cellular Physiology.

Beneficial Effect of Polysaccharide Gel Made of Xanthan Gum and Locust Bean Gum on Bovine Oocytes

The present study examined the effect of polysaccharides gels made of xanthan gum and locust bean gum (gel culture system) on oocyte maturation and explored the molecules causing the beneficial effect of the gel culture system. Oocytes and cumulus cells complexes were collected from slaughterhouse-derived ovaries and cultured on a plastic plate or gel. The gel culture system improved the rate of development to the blastocyst stage. The oocytes that matured on the gel contained high lipid contents and F-actin formation, and the resultant 8-cell stage embryos had low DNA methylation levels compared to their plate counterparts. RNA sequencing of the oocytes and embryos revealed the differentially expressed genes between the gel and plate culture systems, and upstream regulator analysis revealed estradiol and TGFB1 as top activated upstream molecules. The medium of the gel culture system contained higher concentrations of estradiol and TGFB1 than that of the plate cultures system. Supplementation of the maturation medium with either estradiol or TGFB1 resulted in high lipid content in oocytes. In addition, TGFB1 improved the developmental ability of the oocytes and increased F-actin content while reducing DNA methylation levels in the 8-cell stage embryos. In conclusion, the gel culture system is useful for embryo production, potentially through the upregulation of TGFB1.

Comparison of oocyte vitrification using a semi-automated or a manual closed system in human siblings: survival and transcriptomic analyses

BACKGROUND

Indications of oocyte vitrification increased substantially over the last decades for clinical and ethical reasons. A semi-automated vitrification system was recently developed making each act of vitrification reproducible. In this study, we evaluated the efficiency of the semi-automated technique of oocyte vitrification by survival rate, morphometric assessment and resistance to empty micro-injection gesture as compared with a manual method. Additionally, we intended to evaluate transcriptomic consequences of both techniques using single-cell RNA-seq technology.

RESULTS

Post-warming survival rate, oocyte surfaces and resistance to empty micro-injection were comparable between semi-automated and manual vitrification groups. Both oocyte vitrification techniques showed limited differences in the resulting transcriptomic profile of sibling oocytes since only 5 differentially expressed genes were identified. Additionally, there was no difference in median transcript integrity number or percentage of mitochondrial DNA between the two groups. However, a total of 108 genes were differentially expressed between fresh and vitrified oocytes (FDR < 0.05) and showed over-represented of genes related to important cellular process.

CONCLUSIONS

Our results provide reassurance about the influence of semi-automation as compared with the manual vitrification method. Concerning oocyte vitrification itself, no tight common transcriptomic signature associated has been observed across studies.

TRIAL REGISTRATION

NCT03570073.

Resveratrol enhanced mitochondrial recovery from cryopreservation-induced damages in oocytes and embryos

BACKGROUND

Mitochondria play a crucial role in nuclear maturation, fertilization, and subsequent embryo development. Cryopreservation is an important assisted reproductive technology that is used worldwide for humans and domestic animals. Although mitochondrial quantity and quality are decisive factors for successful development of oocytes and embryos, cryopreservation induces mitochondrial dysfunction. Upon thawing, the damaged mitochondria are removed, and de novo synthesis occurs to restore the function of mitochondria. Resveratrol, 3,5,4'-trihydroxystilbene, is a polyphenolic antioxidant that has versatile target proteins, among which sirtuin-1 (SIRT1) is a key regulator of in mitochondrial biogenesis and degradation.

METHODS

The present study is a literature review focusing on experiments involving the hypothesis that the activation of mitochondrial biogenesis and degradation following cryopreservation and warming by resveratrol may help mitochondrial recovery and improve oocyte and embryo development.

MAIN FINDINGS AND CONCLUSION

Resveratrol improves oocyte maturation and development and upregulates mitochondrial biogenesis and degradation. When vitrified-warmed embryos are treated with resveratrol, it helps in mitochondrial regulation and recovery of embryos from cryopreservation-induced damage.

CONCLUSION

Resveratrol treatment is a possible countermeasure against cryopreservation-induced mitochondrial damage.