NMNAT2-mediated NAD+ generation is essential for quality control of aged oocytes

Exploring nicotinamide adenine dinucleotide precursors across biosynthesis pathways: Unraveling their role in the ovary

Natural Nicotinamide Adenine Dinucleotide (NAD+) precursors have attracted much attention due to their positive effects in promoting ovarian health. However, their target tissue, synthesis efficiency, advantages, and disadvantages are still unclear. This review summarizes the distribution of NAD+ at the tissue, cellular and subcellular levels, discusses its biosynthetic pathways and the latest findings in ovary, include: (1) NAD+ plays distinct roles both intracellularly and extracellularly, adapting its distribution in response to requirements. (2) Different precursors differs in target tissues, synthetic efficiency, biological utilization, and adverse effects. Importantly: tryptophan is primarily utilized in the liver and kidneys, posing metabolic risks in excess; nicotinamide (NAM) is indispensable for maintaining NAD+ levels; nicotinic acid (NA) constructs a crucial bridge between intestinal microbiota and the host with diverse functions; nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) increase NAD+ systemically and can be influenced by delivery route, tissue specificity, and transport efficiency. (3) The biosynthetic pathways of NAD+ are intricately intertwined. They provide multiple sources and techniques for NAD+ synthesis, thereby reducing the dependence on a single molecule to maintain cellular NAD+ levels. However, an excess of a specific precursor potentially influencing other pathways. In addition, Protein expression analysis suggest that ovarian tissues may preferentially utilize NAM and NMN. These findings summarize the specific roles and potential of NAD+ precursors in enhancing ovarian health. Future research should delve into the molecular mechanisms and intervention strategies of different precursors, aiming to achieve personalized prevention or treatment of ovarian diseases, and reveal their clinical application value.

Supplementation with NAD+ and its precursors: A rescue of female reproductive diseases

Nicotinamide adenine dinucleotide (NAD+) is an essential coenzyme involved in many pathophysiological processes. Supplementation with NAD+ and its precursors has been demonstrated as an emerging therapeutic strategy for the diseases. NAD+ also plays an important role in the reproductive system. Here, we summarize the function of NAD+ in various reproductive diseases and review the application of NAD+ and its precursors in the preservation of reproductive capacity and the prevention of embryonic malformations. It is shown that NAD+ shows good promise as a therapeutic approach for saving reproductive capacity.

Understanding oocyte ageing

Females are born with a finite and non-renewable reservoir of oocytes, which therefore decline both in number and quality with advancing age. A striking characteristic of oocyte quality is that "ageing" effects manifest whilst women are in their thirties and are therefore still chronologically and physically young. Furthermore, this decline is unrelenting and not modifiable to any great extent by lifestyle or diet. Since oocyte quality is rate-limiting for pregnancy success, as the proportion of good-quality oocytes progressively deteriorate, the chance of successful pregnancy during each 6-12-month period also decreases, becoming exponential after 37 years. Unlike oocyte quality, age-related attrition in the size of the ovarian reservoir is less impactful for natural fertility since only one mature oocyte is typically ovulated per menstrual cycle. In contrast, oocyte numbers are pivotal for in-vitro fertilization success, since larger numbers enable better-quality oocytes to be found and is important for buffering the inefficiencies of the IVF process. The ageing trajectory is accelerated in ~10% of women, so-called premature ovarian ageing, with ~1% of women at the extreme end of this spectrum with loss of ovarian function occurring before 40 years of age, termed premature ovarian insufficiency. The aim of this review was to analyze how ageing impacts the size and quality of the oocyte pool along with emerging interventions for combating low oocyte numbers and improving quality.

Chemical reversion of age-related oocyte dysfunction fails to enhance embryo development in a bovine model of postovulatory aging

PURPOSE

There are no clinical treatments to prevent/revert age-related alterations associated with oocyte competence decline in the context of advanced maternal age. Those alterations have been attributed to oxidative stress and mitochondrial dysfunction. Our study aimed to test the hypothesis that in vitro maturation (IVM) medium supplementation with antioxidants (resveratrol or phloretin) may revert age-related oocyte competence decline.

METHODS

Bovine immature oocytes were matured in vitro for 23 h (young) and 30 h (aged). Postovulatory aged oocytes (control group) and embryos obtained after fertilization were examined and compared with oocytes supplemented with either 2 μM of resveratrol or 6 μM phloretin (treatment groups) during IVM.

RESULTS

Aged oocytes had a significantly lower mitochondrial mass and proportion of mitochondrial clustered pattern, lower ooplasmic volume, higher ROS, lower sirtuin-1 protein level, and a lower blastocyst rate in comparison to young oocytes, indicating that postovulatory oocytes have a lower quality and developmental competence, thus validating our experimental model. Supplementation of IVM medium with antioxidants prevented the generation of ROS and restored the active mitochondrial mass and pattern characteristic of younger oocytes. Moreover, sirtuin-1 protein levels were also restored but only following incubation with resveratrol. Despite these findings, the blastocyst rate of treatment groups was not significantly different from the control group, indicating that resveratrol and phloretin could not restore the oocyte competence of postovulatory aged oocytes.

CONCLUSION

Resveratrol and phloretin can both revert the age-related oxidative stress and mitochondrial dysfunction during postovulatory aging but were insufficient to enhance embryo developmental rates under our experimental conditions.

NAD+ precursors promote the restoration of spermatogenesis in busulfan-treated mice through inhibiting Sirt2-regulated ferroptosis

Rationale: In recent years, nicotinamide adenine dinucleotide (NAD+) precursors (Npre) have been widely employed to ameliorate female reproductive problems in both humans and animal models. However, whether and how Npre plays a role in the male reproductive disorder has not been fully clarified. Methods: In the present study, a busulfan-induced non-obstructive azoospermic mouse model was used, and Npre was administered for five weeks following the drug injection, with the objective of reinstating spermatogenesis and fertility. Initially, we assessed the NAD+ level, germ cell types, semen parameters and sperm fertilization capability. Subsequently, testis tissues were examined through RNA sequencing analysis, ELISA, H&E, immunofluorescence, quantitative real-time PCR, and Western blotting techniques. Results: The results indicated that Npre restored normal level of NAD+ in blood and significantly alleviated the deleterious effects of busulfan (BU) on spermatogenesis, thereby partially reestablishing fertilization capacity. Transcriptome analysis, along with recovery of testicular Fe2+, GSH, NADPH, and MDA levels, impaired by BU, and the fact that Fer-1, an inhibitor of ferroptosis, restored spermatogenesis and semen parameters close to CTRL values, supported such possibility. Interestingly, the reduction in SIRT2 protein level by the specific inhibitor AGK2 attenuated the beneficial effects of Npre on spermatogenesis and ferroptosis by affecting PGC-1α and ACLY protein levels, thus suggesting how these compounds might confer spermatogenesis protection. Conclusion: Collectively, these findings indicate that NAD+ protects spermatogenesis against ferroptosis, probably through SIRT2 dependent mechanisms. This underscores the considerable potential of Npre supplementation as a feasible strategy for preserving or restoring spermatogenesis in specific conditions of male infertility and as adjuvant therapy to preserve male fertility in cancer patients receiving sterilizing treatments.

β-Nicotinamide mononucleotide supplementation prolongs the lifespan of prematurely aged mice and protects colon function in ageing mice

Ageing is defined as the degeneration of physiological functions in numerous tissues and organs of an organism, which occurs with age. As we age, the gut undergoes a series of changes and weaknesses that may contribute to overall ageing. Emerging evidence suggests that β-nicotinamide mononucleotide (NMN) plays a role in regulating intestinal function, but there is still a lack of literature on its role in maintaining the colon health of ageing mice. In our research, Zmpste24-/- mice proved that NMN prolonged their life span and delayed senescence. This study was designed to investigate the effects of long-term intervention on regulating colon function in ageing mice. Our results indicated that NMN improved the pathology of intestinal epithelial cells and intestinal permeability by upregulating the expression of intestinal tight junction proteins and the number of goblet cells, increasing the release of anti-inflammatory factors, and increasing beneficial intestinal bacteria. NMN increased the expression of the proteins SIRT1, NMNAT2, and NMNAT3 and decreased the expression of the protein P53. It also regulated the activity of ISCs by increasing Wnt/β-catenin and Lgr5. Our findings also revealed that NMN caused a significant increase in the relative abundance of Akkermansia muciniphila and Bifidobacterium pseudolongum and notable differences in metabolic pathways related to choline metabolism in cancer. In summary, NMN supplementation can delay frailty in old age, aid healthy ageing, and delay gut ageing.

Targeting NAD Metabolism for the Therapy of Age-Related Neurodegenerative Diseases

As the aging population continues to grow rapidly, age-related diseases are becoming an increasing burden on the healthcare system and a major concern for the well-being of elderly individuals. While aging is an inevitable process for all humans, it can be slowed down and age-related diseases can be treated or alleviated. Nicotinamide adenine dinucleotide (NAD) is a critical coenzyme or cofactor that plays a central role in metabolism and is involved in various cellular processes including the maintenance of metabolic homeostasis, post-translational protein modifications, DNA repair, and immune responses. As individuals age, their NAD levels decline, and this decrease has been suggested to be a contributing factor to the development of numerous age-related diseases, such as cancer, diabetes, cardiovascular diseases, and neurodegenerative diseases. In pursuit of healthy aging, researchers have investigated approaches to boost or maintain NAD levels. Here, we provide an overview of NAD metabolism and the role of NAD in age-related diseases and summarize recent progress in the development of strategies that target NAD metabolism for the treatment of age-related diseases, particularly neurodegenerative diseases.

Promising anti-ovarian aging herbal formulation He's Yangchao promotes in vitro maturation of oocytes from advanced maternal age mice

ETHNOPHARMACOLOGICAL RELEVANCE

Marveled at the discovery of artemisinin, the world's expectations for traditional Chinese medicine are rising. He's Yangchao formula (HSYC) is a traditional Chinese herbal formula with the effects of tonifying kidney and essence, and reconciling yin and yang. It has been clinically proven to have anti-ovarian aging effects. Age is the primary cause of diminished ovarian reserve and assisted reproductive failure in women, whether HSYC has the potential to improve in vitro maturation of oocytes from advanced maternal age (AMA) mice has yet to be determined.

AIM OF THE STUDY

This study aims to evaluate the efficacy and possible mechanism of HSYC in promoting in vitro maturation of oocytes from AMA mice.

MATERIALS AND METHODS

The GV oocytes were obtained from young and aged mice. The GV oocytes from young mice were cultured in drops of M16 medium, and the GV oocytes from AMA mice were randomly divided four groups: Vehicle group (cultured in 90% M16 medium +10% blank serum), Low HSYC group (cultured in 90% M16 medium + 10% Low HSYC-medicated serum), High-HSYC group (cultured in 90% M16 medium +10% High HSYC-medicated serum), and Quercetin group (cultured in M16 medium supplemented with 10 μM quercetin). The rates of first polar body extrusion, reactive oxygen species (ROS), intracellular calcium, and mitochondrial membrane potential levels in each groups were observed. In addition, expression levels of mitochondrial function, autophagy, DNA damage, and antioxidant-related proteins were assessed.

RESULTS

Supplementation of HSYC in vitro alleviated age-associated meiotic progression defects in maternally aged oocytes. Importantly, HSYC supplementation eliminated the age-related ROS accumulation to suppress DNA damage and autophagy during the in vitro maturation of maternally aged oocytes. Meanwhile, the mitochondrial function was improved after HSYC treatment, as manifested by higher mitochondrial membrane potential and lower Ca2+ levels. Furthermore, we found that HSYC supplementation during in vitro maturation of maternally aged oocytes upregulated the expression level of SIRT3, a crucial protein in regulating mitochondrial function. Consistently, the expression levels of the SOD2, PCG1α, and TFAM were increased, while the SOD2 acetylation level was decreased, which further proved its antioxidant function.

CONCLUSIONS

HSYC supplementation promotes in vitro maturation of oocytes from AMA mice mainly via improving mitochondrial function and alleviating oxidative stress. The mechanism may be related to the regulation of SIRT3-dependent deacetylation of the SOD2 pathway.

Can Nicotinamide Adenine Dinucleotide (NAD+) and Sirtuins Be Harnessed to Improve Mare Fertility?

Years of sire and dam selection based on their pedigree and athletic performance has resulted in a reduction in the reproductive capability of horses. Mare age is considered a major barrier to equine reproduction largely due to an increase in the age at which mares are typically bred following the end of their racing career. Nicotinamide adenine dinucleotide (NAD+) and its involvement in the activation of Sirtuins in fertility are an emerging field of study, with the role of NAD+ in oocyte maturation and embryo development becoming increasingly apparent. While assisted reproductive technologies in equine breeding programs are in their infancy compared to other livestock species such as cattle, there is much more to be learnt, from oocyte maturation to early embryo development and beyond in the mare, which are difficult to study given the complexities associated with mare fertility research. This review examines what is already known about the role of NAD+ and Sirtuins in fertility and discusses how NAD+-elevating agents may be used to activate Sirtuin proteins to improve equine breeding and embryo production programs both in vivo and in vitro.

NADase CD38 is a key determinant of ovarian aging

The ovary ages earlier than most other tissues, yet the underlying mechanisms remain elusive. Here a comprehensive analysis of transcriptomic landscapes in different organs in young and middle-aged mice revealed that the ovaries showed earlier expression of age-associated genes, identifying increased NADase CD38 expression and decreased NAD+ levels in the ovary of middle-aged mice. Bulk and single-cell RNA sequencing revealed that CD38 deletion mitigated ovarian aging, preserving fertility and follicle reserve in aged mice by countering age-related gene expression changes and intercellular communication alterations. Mechanistically, the earlier onset of inflammation induced higher expression levels of CD38 and decreased NAD+ levels in the ovary, thereby accelerating ovarian aging. Consistently, pharmacological inhibition of CD38 enhanced fertility in middle-aged mice. Our findings revealed the mechanisms underlying the earlier aging of the ovary relative to other organs, providing a potential therapeutic target for ameliorating age-related female infertility.

NAD metabolism: Role in senescence regulation and aging

The geroscience hypothesis proposes that addressing the biology of aging could directly prevent the onset or mitigate the severity of multiple chronic diseases. Understanding the interplay between key aspects of the biological hallmarks of aging is essential in delivering the promises of the geroscience hypothesis. Notably, the nucleotide nicotinamide adenine dinucleotide (NAD) interfaces with several biological hallmarks of aging, including cellular senescence, and changes in NAD metabolism have been shown to be involved in the aging process. The relationship between NAD metabolism and cellular senescence appears to be complex. On the one hand, the accumulation of DNA damage and mitochondrial dysfunction induced by low NAD+ can promote the development of senescence. On the other hand, the low NAD+ state that occurs during aging may inhibit SASP development as this secretory phenotype and the development of cellular senescence are both highly metabolically demanding. However, to date, the impact of NAD+ metabolism on the progression of the cellular senescence phenotype has not been fully characterized. Therefore, to explore the implications of NAD metabolism and NAD replacement therapies, it is essential to consider their interactions with other hallmarks of aging, including cellular senescence. We propose that a comprehensive understanding of the interplay between NAD boosting strategies and senolytic agents is necessary to advance the field.

Impact of NAD+ metabolism on ovarian aging

Nicotinamide adenine dinucleotide (NAD+), a crucial coenzyme in cellular redox reactions, is closely associated with age-related functional degeneration and metabolic diseases. NAD exerts direct and indirect influences on many crucial cellular functions, including metabolic pathways, DNA repair, chromatin remodeling, cellular senescence, and immune cell functionality. These cellular processes and functions are essential for maintaining tissue and metabolic homeostasis, as well as healthy aging. Causality has been elucidated between a decline in NAD levels and multiple age-related diseases, which has been confirmed by various strategies aimed at increasing NAD levels in the preclinical setting. Ovarian aging is recognized as a natural process characterized by a decline in follicle number and function, resulting in decreased estrogen production and menopause. In this regard, it is necessary to address the many factors involved in this complicated procedure, which could improve fertility in women of advanced maternal age. Concerning the decrease in NAD+ levels as ovarian aging progresses, promising and exciting results are presented for strategies using NAD+ precursors to promote NAD+ biosynthesis, which could substantially improve oocyte quality and alleviate ovarian aging. Hence, to acquire further insights into NAD+ metabolism and biology, this review aims to probe the factors affecting ovarian aging, the characteristics of NAD+ precursors, and the current research status of NAD+ supplementation in ovarian aging. Specifically, by gaining a comprehensive understanding of these aspects, we are optimistic about the prominent progress that will be made in both research and therapy related to ovarian aging.

Deletion of enzymes for de novo NAD+ biosynthesis accelerated ovarian aging

Recent advances highlight the pivotal role of nicotinamide adenine dinucleotide (NAD+ ) in ovarian aging. However, the roles of de novo NAD+ biosynthesis on ovarian aging are still unknown. Here, we found that genetic ablation of Ido1 (indoleamine-2,3-dioxygenase 1) or Qprt (Quinolinate phosphoribosyl transferase), two critical genes in de novo NAD+ biosynthesis, resulted in decreased ovarian NAD+ levels in middle-aged mice, leading to subfertility, irregular estrous cycles, reduced ovarian reserve, and accelerated aging. Moreover, we observed impaired oocyte quality, characterized by increased reactive oxygen species and spindle anomalies, which ultimately led to reduced fertilization ability and impaired early embryonic development. A transcriptomic analysis of ovaries in both mutant and wild-type mice revealed alterations in gene expression related to mitochondrial metabolism. Our findings were further supported by the observation of impaired mitochondrial distribution and decreased mitochondrial membrane potential in the oocytes of knockout mice. Supplementation with nicotinamide riboside (NR), an NAD+ booster, in mutant mice increased ovarian reserve and improved oocyte quality. Our study highlights the importance of the NAD+ de novo pathway in middle-aged female fertility.

Multi-Omics Analysis Reveals Translational Landscapes and Regulations in Mouse and Human Oocyte Aging

Abnormal resumption of meiosis and decreased oocyte quality are hallmarks of maternal aging. Transcriptional silencing makes translational control an urgent task during meiosis resumption in maternal aging. However, insights into aging-related translational characteristics and underlying mechanisms are limited. Here, using multi-omics analysis of oocytes, it is found that translatomics during aging is related to changes in the proteome and reveals decreased translational efficiency with aging phenotypes in mouse oocytes. Translational efficiency decrease is associated with the N6-methyladenosine (m6A) modification of transcripts. It is further clarified that m6A reader YTHDF3 is significantly decreased in aged oocytes, inhibiting oocyte meiotic maturation. YTHDF3 intervention perturbs the translatome of oocytes and suppress the translational efficiency of aging-associated maternal factors, such as Hells, to affect the oocyte maturation. Moreover, the translational landscape is profiled in human oocyte aging, and the similar translational changes of epigenetic modifications regulators between human and mice oocyte aging are observed. In particular, due to the translational silence of YTHDF3 in human oocytes, translation activity is not associated with m6A modification, but alternative splicing factor SRSF6. Together, the findings profile the specific translational landscapes during oocyte aging in mice and humans, and uncover non-conservative regulators on translation control in meiosis resumption and maternal aging.

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.

Multi-omics reveal the metabolic patterns in mouse cumulus cells during oocyte maturation

Bi-directional communication between cumulus cells and the surrounded oocytes is important for the development and functions of both compartments. However, the metabolic framework in cumulus cells has not been systematically described. In the present study, cumulus cells from cumulus-oocyte complexes (COCs) at three key time points were isolated (arrested GV stage, post-hCG 0h; meiotic resumption GVBD stage, post-hCG 3h; and metaphase II stage, post-hCG 12h), and the temporal metabolomic and proteomic profiling were performed. Integrated multi-omics analysis reveals the global metabolic patterns in cumulus cells during mouse oocyte maturation. In particular, we found the active hyaluronic acid metabolism, steroid hormone synthesis, and prostaglandin E2 (PGE2) production in cumulus cells. Meanwhile, accompanying the oocyte maturation, a progressive increase in nucleotide and amino acid metabolism was detected in the surrounding cumulus cells. In sum, the data serve as a valuable resource for probing metabolism during terminal differentiation of ovarian granulosa cells, and provide the potential biomarkers for improving and predicting oocyte quality.

Growth hormone reduces aneuploidy and improves oocytes quality by JAK2-MAPK3/1 pathway in aged mice

BACKGROUND

The global delay in women's reproductive age has raised concerns about age-related infertility. The decline in oocyte quality is a limiting factor of female fertility, yet there are currently no strategies to preserve oocyte quality in aged women. Here, we investigated the effects of growth hormone (GH) supplementation on aneuploidy of aged oocytes.

METHODS

For the in vivo experiments, the aged mice (8-month-old) were intraperitoneally injected with GH daily for 8 weeks. For the in vitro experiments, germinal vesicle oocytes from aged mice were treated with GH during oocyte maturation. The impacts of GH on ovarian reserve before superovulation was evaluated. Oocytes were retrieved to assess oocyte quality, aneuploidy and developmental potential characteristics. Quantitative proteomics analysis was applied to investigate the potential targets of GH in aged oocytes.

RESULTS

In this study, we demonstrated that GH supplementation in vivo not only alleviated the decline in oocyte number caused by aging, but also improved the quality and developmental potential of aged oocytes. Strikingly, we discovered that GH supplementation reduced aneuploidy in aged oocytes. Mechanically, in addition to improving mitochondrial function, our proteomic analysis indicated that the MAPK3/1 pathway may be involved in the reduction in aneuploidy of aged oocytes, as confirmed both in vivo and in vitro. In addition, JAK2 may also act as a mediator in how GH regulates MAPK3/1.

CONCLUSIONS

In conclusion, our research reveals that GH supplementation protects oocytes against aging-related aneuploidy and enhances the quality of aged oocytes, which has clinical significance for aged women undergoing assisted reproduction technology.

Alpha-ketoglutarate supplementation ameliorates ovarian reserve and oocyte quality decline with aging in mice

Assisted reproductive technology is widely accepted as an effective treatment to improve female fertility, but the decline of aging oocyte quality remains an important factor in the decrease of female fecundity. However, the effective strategies for improving oocyte aging are still not well understood. In the study, we demonstrated that ROS content and abnormal spindle proportion were increased and mitochondrial membrane potential was decreased in aging oocytes. However, supplementation of α-ketoglutarate (α-KG), an immediate metabolite in the tricarboxylic acid cycle (TCA), for 4 months to aging mice, significantly increased the ovarian reserve showed by more follicle numbers observed. In addition, the oocyte quality was significantly improved, as demonstrated by reduced fragmentation rate and decreased reactive oxygen species (ROS) levels, in addition to a lower rate of abnormal spindle assembly, thereby improving the mitochondrial membrane potential. Consistent with the in vivo data, α-KG administration also improved the post-ovulated aging oocyte quality and early embryonic development by improving mitochondrial functions and reducing ROS accumulation and abnormal spindle assembly. Our data revealed that α-KG supplementation might be an effective strategy to improve the quality of aging oocytes in vivo or in vitro.

Mitochondrial activity and redox status in oocytes from old mice: The interplay between maternal and postovulatory aging

Maternal aging has been reported to reduce oocyte quality and, in turn, lower the developmental potential of the resulting embryos. Here, we show that maternally aged oocytes display two strikingly different phenotypes: some have normal morphology, whereas others have significantly shrunk cytoplasm. The latter phenotype usually prevails in aged females. Our objective was to characterize both types of maternally aged oocytes and investigate the origins of this diversity. Importantly, our experiments indicate that shrunk maternally aged oocytes are severely compromised in terms of mitochondrial functionality as compared to their young or morphologically normal maternally aged counterparts: they display significantly decreased mitochondrial activity and lower amounts of ROS. In contrast, morphologically normal maternally aged oocytes had the same mitochondrial activity as young ones, while their ROS levels were higher. Surprisingly, the shrunk phenotype was completely absent in maternally aged oocytes that matured in vitro, suggesting that it is not caused inherently by maternal aging, but may be related to other factors, like postovulatory aging. Indeed, an additional culture of in vitro matured young and old oocytes (i.e., in vitro postovulatory aging) significantly decreased their mitochondrial activity and led to cytoplasm shrinkage. In vivo postovulatory aging had a similar effect on oocytes from both young and old females. Finally, we examined the developmental potential of oocytes obtained from aged females. Shrunk (i.e., most likely postovulatory aged) oocytes failed to become fertilized, whereas morphologically normal ones (i.e., most likely not subjected to postovulatory aging) underwent fertilization and subsequent cleavage divisions, although they achieved the 2-cell stage less frequently than morphologically normal oocytes from young females. Importantly, the quality of blastocysts as well as the live birth rate for morphologically normal oocytes from old and young females were similar. In summary, our data clearly indicate that two pools of oocytes present in oviducts of aged females differ significantly in their quality and developmental potential and that the more severely affected phenotype results most likely from a synergistic action of maternal and postovulatory aging.

Improvement of oocyte quality through the SIRT signaling pathway

Background

Oocyte quality is one of the major deciding factors in female fertility competence.

Methods

PubMed database was searched for reviews by using the following keyword "oocyte quality" AND "Sirtuins". The methodological quality of each literature review was assessed using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) 2020 statement.

Main Findings

Oxidative stress has been recognized as the mechanism attenuating oocyte quality. Increasing evidence from animal experiments and clinical studies has confirmed the protective roles of the sirtuin family in improving oocyte quality via an antioxidant effect.

Conclusion

The protective roles in the oocyte quality of the sirtuin family have been increasingly recognized.

NMNAT2: An important metabolic enzyme affecting the disease progression

Nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) is an evolutionarily conserved nicotinamide adenine dinucleotide (NAD⁺) synthase located in the cytoplasm and Golgi apparatus. NMNAT2 has an important role in neurodegenerative diseases, malignant tumors, and other diseases that seriously endanger human health. NMNAT2 exerts a neuroprotective function through its NAD synthase activity and chaperone function. Among them, the NMNAT2-NAD⁺-Sterile alpha and Toll/interleukin-1 receptor motif-containing 1 (SARM1) axis is closely related to Wallerian degeneration. Physical injury or pathological stimulation will cause a decrease in NMNAT2, which activates SARM1, leading to axonal degeneration and the occurrence of amyotrophic lateral sclerosis (ALS), Alzheimer's disease, peripheral neuropathy, and other neurodegenerative diseases. In addition, NMNAT2 exerts a cancer-promoting role in solid tumors, including colorectal cancer, lung cancer, ovarian cancer, and glioma, and is closely related to tumor occurrence and development. This paper reviews the chromosomal and subcellular localization of NMNAT2 and its basic biological functions. We also summarize the NMNAT2-related signal transduction pathway and the role of NMNAT2 in diseases. We aimed to provide a new perspective to comprehensively understand the relationship between NMNAT2 and its associated diseases.

Development of prognostic indicator based on NAD+ metabolism related genes in glioma

Background

Studies have shown that Nicotinamide adenine dinucleotide (NAD+) metabolism can promote the occurrence and development of glioma. However, the specific effects and mechanisms of NAD+ metabolism in glioma are unclear and there were no systematic researches about NAD+ metabolism related genes to predict the survival of patients with glioma.

Methods

The research was performed based on expression data of glioma cases in the Cancer Genome Atlas (TCGA) and Chinese Glioma Genome Atlas (CGGA) databases. Firstly, TCGA-glioma cases were classified into different subtypes based on 49 NAD+ metabolism-related genes (NMRGs) by consensus clustering. NAD+ metabolism-related differentially expressed genes (NMR-DEGs) were gotten by intersecting the 49 NMRGs and differentially expressed genes (DEGs) between normal and glioma samples. Then a risk model was built by Cox analysis and the least shrinkage and selection operator (LASSO) regression analysis. The validity of the model was verified by survival curves and receiver operating characteristic (ROC) curves. In addition, independent prognostic analysis of the risk model was performed by Cox analysis. Then, we also identified different immune cells, HLA family genes and immune checkpoints between high and low risk groups. Finally, the functions of model genes at single-cell level were also explored.

Results

Consensus clustering classified glioma patients into two subtypes, and the overall survival (OS) of the two subtypes differed. A total of 11 NAD+ metabolism-related differentially expressed genes (NMR-DEGs) were screened by overlapping 5,995 differentially expressed genes (DEGs) and 49 NAD+ metabolism-related genes (NMRGs). Next, four model genes, PARP9, BST1, NMNAT2, and CD38, were obtained by Cox regression and least absolute shrinkage and selection operator (Lasso) regression analyses and to construct a risk model. The OS of high-risk group was lower. And the area under curves (AUCs) of Receiver operating characteristic (ROC) curves were >0.7 at 1, 3, and 5 years. Cox analysis showed that age, grade G3, grade G4, IDH status, ATRX status, BCR status, and risk Scores were reliable independent prognostic factors. In addition, three different immune cells, Mast cells activated, NK cells activated and B cells naive, 24 different HLA family genes, such as HLA-DPA1 and HLA-H, and 8 different immune checkpoints, such as ICOS, LAG3, and CD274, were found between the high and low risk groups. The model genes were significantly relevant with proliferation, cell differentiation, and apoptosis.

Conclusion

The four genes, PARP9, BST1, NMNAT2, and CD38, might be important molecular biomarkers and therapeutic targets for glioma patients.

Novel Role of the SIRT1 in Endocrine and Metabolic Diseases

Silent information regulator 1 (SIRT1), a highly conserved NAD⁺-dependent deacetylase, is a cellular regulator that has received extensive attention in recent years and regarded as a sensor of cellular energy and metabolism. The accumulated evidence suggests that SIRT1 is involved in the development of endocrine and metabolic diseases. In a variety of organisms, SIRT1 regulates gene expression through the deacetylation of histone, transcription factors, and lysine residues of other modified proteins including several metabolic and endocrine signal transcription factors, thereby enhancing the therapeutic effects of endocrine and metabolic diseases. These evidences indicate that targeting SIRT1 has promising applications in the treatment of endocrine and metabolic diseases. This review focuses on the role of SIRT1 in endocrine and metabolic diseases. First, we describe the background and structure of SIRT1. Then, we outline the role of SIRT1 in endocrine and metabolic diseases such as hyperuricemia, diabetes, hypertension, hyperlipidemia, osteoporosis, and polycystic ovarian syndrome. Subsequently, the SIRT1 agonists and inhibitors in the above diseases are summarized and future research directions are proposed. Overall, the information presents here may highlight the potential of SIRT1 as a future biomarker and therapeutic target for endocrine and metabolic diseases.

NAD+, Sirtuins and PARPs: enhancing oocyte developmental competence

Oocyte quality is the limiting factor in female fertility. It is well known that maternal nutrition plays a role in reproductive function, and manipulating nutrition to improve fertility in livestock has been common practice in the past, particularly with respect to negative energy balance in cattle. A deficiency in nicotinamide adenine dinucleotide (NAD⁺) production has been associated with increased incidences of miscarriage and congenital defects in humans and mice, while elevating NAD⁺ through dietary supplements in aged subjects improved oocyte quality and embryo development. NAD⁺ is consumed by Sirtuins and poly-ADP-ribose polymerases (PARPs) within the cell and thus need constant replenishment in order to maintain various cellular functions. Sirtuins and PARPs play important roles in oocyte maturation and embryo development, and their activation may prove beneficial to in vitro embryo production and livestock breeding programs. This review examines the roles of NAD⁺, Sirtuins and PARPs in aspects of fertility, providing insights into the potential use of NAD⁺-elevating treatments in livestock breeding and embryo production programs.

Brain metastases: It takes two factors for a primary cancer to metastasize to brain

Brain metastasis of a cancer is a malignant disease with high mortality, but the cause and the molecular mechanism remain largely unknown. Using the samples of primary tumors of 22 cancer types in the TCGA database, we have performed a computational study of their transcriptomic data to investigate the drivers of brain metastases at the basic physics and chemistry level. Our main discoveries are: (i) the physical characteristics, namely electric charge, molecular weight, and the hydrophobicity of the extracellular structures of the expressed transmembrane proteins largely affect a primary cancer cell’s ability to cross the blood-brain barrier; and (ii) brain metastasis may require specific functions provided by the activated enzymes in the metastasizing primary cancer cells for survival in the brain micro-environment. Both predictions are supported by published experimental studies. Based on these findings, we have built a classifier to predict if a given primary cancer may have brain metastasis, achieving the accuracy level at AUC = 0.92 on large test sets.

NAD+ deficiency in human congenital malformations and miscarriage: A new model of pleiotropy

Pleiotropy is defined as the phenomenon of a single gene locus influencing two or more distinct phenotypic traits. However, nicotinamide adenine dinucleotide (NAD+) deficiency through diet alone can cause multiple or single malformations in mice. Additionally, humans with decreased NAD+ production due to changes in pathway genes display similar malformations. Here, I hypothesize NAD+ deficiency as a pleiotropic mechanism for multiple malformation conditions, including limb-body wall complex (LBWC), pentalogy of Cantrell (POC), omphalocele-exstrophy-imperforate anus-spinal defects (OEIS) complex, vertebral-anal-cardiac-tracheoesophageal fistula-renal-limb (VACTERL) association (hereafter VACTERL), oculoauriculovertebral spectrum (OAVS), Mullerian duct aplasia-renal anomalies-cervicothoracic somite dysplasia (MURCS), sirenomelia, and urorectal septum malformation (URSM) sequence, along with miscarriages and other forms of congenital malformation. The term Congenital NAD Deficiency Disorder (CNDD) could be considered for patients with these malformations; however, it is important to emphasize there have been no confirmatory experimental studies in humans to prove this hypothesis. In addition, these multiple malformation conditions should not be considered individual entities for the following reasons: First, there is no uniform consensus of clinical diagnostic criteria and all of them fail to capture cases with partial expression of the phenotype. Second, reports of individuals consistently show overlapping features with other reported conditions in this group. Finally, what is currently defined as VACTERL is what I would refer to as a default label when more striking features such as body wall defects, caudal dysgenesis, or cloacal exstrophy are not present.

IGF2 reduces meiotic defects in oocytes from obese mice and improves embryonic developmental competency

BACKGROUND

Maternal obesity is a global issue that has devastating effects across the reproductive spectrum such as meiotic defects in oocytes, consequently worsening pregnancy outcomes. Different studies have shown that such types of meiotic defects originated from the oocytes of obese mothers. Thus, there is an urgent need to develop strategies to reduce the incidence of obesity-related oocyte defects that adversely affect pregnancy outcomes. Multiple growth factors have been identified as directly associated with female reproduction; however, the impact of various growth factors on female fertility in response to obesity remains poorly understood.

METHODS

The immature GV-stage oocytes from HFD female mice were collected and cultured in vitro in two different groups (HFD oocytes with and without 50 nM IGF2), however; the oocytes from ND mice were used as a positive control. HFD oocytes treated with or without IGF2 were further used to observe the meiotic structure using different analysis including, the spindle and chromosomal analysis, reactive oxygen species levels, mitochondrial functional activities, and early apoptotic index using immunofluorescence. Additionally, the embryonic developmental competency and embryos quality of IGF2-treated zygotes were also determined.

RESULTS

In our findings, we observed significantly reduced contents of insulin-like growth factor 2 (IGF2) in the serum and oocytes of obese mice. Our data indicated supplementation of IGF2 in a culture medium improves the blastocyst formation: from 46% in the HFD group to 61% in the HFD + IGF2-treatment group (50 nM IGF2). Moreover, adding IGF2 to the culture medium reduces the reactive oxygen species index and alleviates the frequency of spindle/chromosome defects. We found increased mitochondrial functional activity in oocytes from obese mice after treating the oocytes with IGF2: observed elevated level of adenosine triphosphate, increased mitochondrial distribution, higher mitochondrial membrane potentials, and reduced mitochondrial ultrastructure defects. Furthermore, IGF2 administration also increases the overall protein synthesis and decreases the apoptotic index in oocytes from obese mice.

CONCLUSIONS

Collectively, our findings are strongly in favor of adding IGF2 in culture medium to overcome obesity-related meiotic structural-developmental defects by helping ameliorate the known sub-optimal culturing conditions that are currently standard with assisted reproduction technologies.

The effects of nicotinamide adenine dinucleotide in cardiovascular diseases: Molecular mechanisms, roles and therapeutic potential

Recently, cardiovascular diseases (CVDs) were identified as the leading cause of mortality, imposing a heavy burden on health care systems and the social economy. Nicotinamide adenine dinucleotide (NAD⁺), as a pivotal co-substrate for a range of different enzymes, is involved in many signal transduction pathways activated in CVDs. Emerging evidence has shown that NAD⁺ can exert remediating effects on CVDs by regulating metabolism, maintaining redox homeostasis and modulating the immune response. In fact, NAD⁺ might delay ageing through sirtuin and non-sirtuin pathways and thus contribute to interventions for age-related diseases such as CVDs. Considering that robust clinical studies of NAD⁺ are ongoing, we discuss current challenges and the future translational potential of NAD⁺ based on existing studies and our understanding. Despite some remaining gaps in its clinical application, NAD⁺ has been shown to have broad prospects and pan-effects, making it a suitable prophylactic drug for CVDs.

Metabolic control of oocyte development

Well balanced and timed metabolism is essential for oocyte development. The effects of extrinsic nutrients on oocyte maturation have been widely reported. In contrast, intrinsic control of oogenesis by intracellular metabolites and metabolic enzymes has received little attention. The comprehensive characterization of metabolic patterns could lead to more complete understanding of regulatory mechanisms underlying oocyte development. A cell's metabolic state is integrated with epigenetic regulation. Epigenetic modifications in germ cells are therefore sensitive to parental environmental exposures. Nevertheless, direct genetic evidence for metabolites involvement in epigenetic establishment during oocyte development is still lacking. Moreover, metabolic disorder-induced epigenetic perturbations during oogenesis might mediate the inter/transgenerational effects of environmental insults. The molecular mechanisms responsible for this deserve further investigation. Here, we summarize the findings on metabolic regulation in oocyte maturation, and how it contributes to oocyte epigenetic modification. Finally, we propose a mouse model that metabolic disorder in oocyte serves as a potential factor mediating the maternal environment effects on offspring health.

Aberrant Expression of Mitochondrial SAM Transporter SLC25A26 Impairs Oocyte Maturation and Early Development in Mice

The immature germinal vesicle (GV) oocytes proceed through metaphase I (MI) division, extrude the first polar body, and become mature metaphase II (MII) oocytes for fertilization which is followed by preimplantation and postimplantation development until birth. Slc25a26 is the gene encoding S-adenosylmethionine carrier (SAMC), a member of the mitochondrial carrier family. Its major function is to catalyze the uptake of S-adenosylmethionine (SAM) from cytosol into mitochondria, which is the only known mitochondrial SAM transporter. In the present study, we demonstrated that excessive SLC25A26 accumulation in mouse oocytes mimicked naturally aged oocytes and resulted in lower oocyte quality with decreased maturation rate and increased reactive oxygen species (ROS) by impairing mitochondrial function. Increased level of Slc25a26 gene impacted gene expression in mouse oocytes such as mt-Cytb which regulates mitochondrial respiratory chain. Furthermore, increased level of Slc25a26 gene in fertilized oocytes slightly compromised blastocyst formation, and Slc25a26 knockout mice displayed embryonic lethality around 10.5 dpc. Taken together, our results showed that Slc25a26 gene plays a critical role in oocyte maturation and early mouse development.

Insights into the NAD+ biosynthesis pathways involved during meiotic maturation and spindle formation in porcine oocytes

Treatments that elevate NAD⁺ levels have been found to improve oocyte quality in mice, cattle, and pigs, suggesting that NAD⁺ is vital during oocyte maturation. This study aimed to examine the influence of different NAD⁺ biosynthetic pathways on oocyte quality by inhibiting key enzymes. Porcine oocytes from small antral follicles were matured for 44 h in a defined maturation system supplemented with 2-hydroxynicotinic acid [2-HNA, nicotinic acid phosphoribosyltransferase (NAPRT) inhibitor], FK866 [nicotinamide phosphoribosyltransferase (NAMPT) inhibitor], or gallotannin [nicotinamide mononucleotide adenylyltransferase (NMNAT) inhibitor] and their respective NAD⁺ pathway modulators (nicotinic acid, nicotinamide, and nicotinamide mononucleotide, respectively). Cumulus expansion was assessed after 22 h of maturation. At 44 h, maturation rates were determined and mature oocytes were fixed and stained to assess spindle formation. Each enzyme inhibitor reduced oocyte maturation rate and adversely affected spindle formation, indicating that NAD⁺ is required for meiotic spindle assembly. Furthermore, NAMPT and NMNAT inhibition reduced cumulus expansion, whereas NAPRT inhibition affected chromosomal segregation. Treating oocytes with gallotannin and nicotinamide mononucleotide together showed improvements in spindle width, while treating oocytes with 2-HNA and nicotinic acid combined showed an improvement in both spindle length and width. These results indicate that the salvage pathway plays a vital role in promoting oocyte meiotic progression, while the Preiss-Handler pathway is essential for spindle assembly.

In Vivo and In Vitro Matured Oocytes From Mice of Advanced Reproductive Age Exhibit Alternative Splicing Processes for Mitochondrial Oxidative Phosphorylation

The mean age of women seeking infertility treatment has gradually increased over recent years. This has coincided with the emergence of in vitro maturation (IVM), a method used in assisted reproductive technology for patients with special requirements. However, when compared with conventional in vitro fertilization, IVM is associated with poor embryonic development potential and low live birth rates, thus limiting the widespread application of this technique. In this study, we performed RNA-sequencing transcriptomic assays and identified a total of 2,627 significant differentially expressed genes (DEGs) between IVM oocytes and in vivo matured oocytes from mice of advanced reproductive age. Next, Kyoto Encyclopedia of Genes and Genomes pathway analysis was used to identify the potential functions of the DEGs. The most significantly enriched pathway was oxidative phosphorylation (OXPHOS). In addition, we constructed a protein-protein interaction network to identify key genes and determined that most of the hub genes were mtDNA-encoded subunits of respiratory chain complex I. Antioxidant supplementation lead to an increase in ATP production and reduced the gene expression profile of the OXPHOS pathway in the IVM group. Moreover, alternative splicing (AS) events were identified during in vivo or in vitro oocyte maturation; data showed that skipped exons were the most frequent type of AS event. A number of genes associated with the OXPHOS pathway exhibited alterations in AS events, including Ndufa7, Ndufs7, Cox6a2, Ndufs5, Ndufb1, and Uqcrh. Furthermore, the process of IVO promoted the skipping of exon 2 in Ndufa7 and exon 3 in Ndufs7 compared with the IVM oocytes, as determined by semi-quantitative RT-PCR. Collectively, these findings provide potential new therapeutic targets for improving IVM of aged women who undergo infertility treatment.

DNA repair and response to sperm DNA damage in oocytes and embryos, and the potential consequences in ART: a systematic review

Sperm DNA damage is considered a predictive factor for the clinical outcomes of patients undergoing ART. Laboratory evidence suggests that zygotes and developing embryos have adopted specific response and repair mechanisms to repair DNA damage of paternal origin. We have conducted a systematic review in accordance with guidelines from Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) to identify and review the maternal mechanisms used to respond and repair sperm DNA damage during early embryonic development, how these mechanisms operate and their potential clinical implications. The literature search was conducted in Ovid MEDLINE and Embase databases until May 2021. Out of 6297 articles initially identified, 36 studies were found to be relevant through cross referencing and were fully extracted. The collective evidence in human and animal models indicate that the early embryo has the capacity to repair DNA damage within sperm by activating maternally driven mechanisms throughout embryonic development. However, this capacity is limited and likely declines with age. The link between age and decreased DNA repair capacity could explain decreased oocyte quality in older women, poor reproductive outcomes in idiopathic cases, and patients who present high sperm DNA damage. Ultimately, further understanding mechanisms underlying the maternal repair of sperm DNA damage could lead to the development of targeted therapies to decrease sperm DNA damage, improved oocyte quality to combat incoming DNA insults or lead to development of methodologies to identify individual spermatozoa without DNA damage.

The key role of the NAD biosynthetic enzyme nicotinamide mononucleotide adenylyltransferase in regulating cell functions

The enzyme nicotinamide mononucleotide adenylyltransferase (NMNAT) catalyzes a reaction central to all known NAD biosynthetic routes. In mammals, three isoforms with distinct molecular and catalytic properties, different subcellular and tissue distribution have been characterized. Each isoform is essential for cell survival, with a critical role in modulating NAD levels in a compartment‐specific manner. Each isoform supplies NAD to specific NAD‐dependent enzymes, thus regulating their activity with impact on several biological processes, including DNA repair, proteostasis, cell differentiation, and neuronal maintenance. The nuclear NMNAT1 and the cytoplasmic NMNAT2 are also emerging as relevant targets in specific types of cancers and NMNAT2 has a key role in the activation of antineoplastic compounds. This review recapitulates the biochemical properties of the three isoforms and focuses on recent advances on their protective function, involvement in human diseases and role as druggable targets.

NAMPT reduction-induced NAD+ insufficiency contributes to the compromised oocyte quality from obese mice

Maternal obesity is associated with multiple adverse reproductive outcomes, whereas the underlying molecular mechanisms are still not fully understood. Here, we found the reduced nicotinamide phosphoribosyl transferase (NAMPT) expression and lowered nicotinamide adenine dinucleotide (NAD⁺) content in oocytes from obese mice. Next, by performing morpholino knockdown assay and pharmacological inhibition, we revealed that NAMPT deficiency not only severely disrupts maturational progression and meiotic apparatus, but also induces the metabolic dysfunction in oocytes. Furthermore, overexpression analysis demonstrated that NAMPT insufficiency induced NAD⁺ loss contributes to the compromised developmental potential of oocytes and early embryos from obese mice. Importantly, in vitro supplement and in vivo administration of nicotinic acid (NA) was able to ameliorate the obesity‐associated meiotic defects and oxidative stress in oocytes. Our results indicate a role of NAMPT in modulating oocyte meiosis and metabolism, and uncover the beneficial effects of NA treatment on oocyte quality from obese mice.

Supplementing media with NAD+ precursors enhances the in vitro maturation of porcine oocytes

In vitro maturation (IVM) is an important reproductive technology used to produce embryos in vitro. However, the developmental potential of oocytes sourced for IVM is markedly lower than those matured in vivo. Previously, NAD⁺-elevating treatments have improved oocyte quality and embryo development in cattle and mice, suggesting that NAD⁺ is important during oocyte maturation. The aim of this study was to examine the effects of nicotinic acid (NA), nicotinamide (NAM) and nicotinamide mononucleotide (NMN) on oocyte maturation and subsequent embryo development. Porcine oocytes from small antral follicles were matured for 44 h in a defined maturation medium supplemented with NA, NAM and resveratrol or NMN. Mature oocytes were artificially activated and presumptive zygotes cultured for 7 days. Additionally, oocytes were matured without treatment then cultured for 7 days with NMN. Supplementing the IVM medium with NA improved maturation and blastocyst formation while NAM supplementation improved cleavage rates compared with untreated controls. Supplementing the IVM or embryo culture media with NMN had no effect on maturation or embryo development. The results show that supplementing the maturation medium with NA and NAM improved maturation and developmental potential of porcine oocytes.

Nmnat2 attenuates amyloidogenesis and up-regulates ADAM10 in AMPK activity-dependent manner

Amyloid-β (Aβ) accumulating is considered as a causative factor for formation of senile plaque in Alzheimer’s disease (AD), but its mechanism is still elusive. The Nicotinamide mononucleotide adenylyltransferase 2 (Nmnat2), a key redox cofactor for energy metabolism, is reduced in AD. Accumulative evidence has shown that the decrease of α-secretase activity, a disintegrin and metalloprotease domain 10 (ADAM10), is responsible for the increase of Aβ productions in AD patient’s brain. Here, we observe that the activity of α-secretase ADAM10 and levels of Nmnat2 are significantly decreased, meanwhile there is a simultaneous elevation of Aβ in Tg2576 mice. Over-expression of Nmnat2 increases the mRNA expression of α-secretase ADAM10 and its activity and inhibits Aβ production in N2a/APPswe cells, which can be abolished by Compound C, an AMPK antagonist, suggesting that AMPK is involved in over-expression of Nmnat2 against Aβ production. The further assays demonstrate that Nmnat2 activates AMPK by up-regulating the ratio of NAD⁺/NADH, moreover AMPK agonist AICAR can also increase ADAM10 activity and reduces Aβ1-40/1-42. Taken together, Nmnat2 suppresses Aβ production and up-regulates ADAM10 in AMPK activity-dependent manner, suggesting that Nmnat2 may serve as a new potential target in arresting AD.

NAD+ flux is maintained in aged mice despite lower tissue concentrations

NAD⁺ is an essential coenzyme for all living cells. NAD⁺ concentrations decline with age, but whether this reflects impaired production or accelerated consumption remains unclear. We employed isotope tracing and mass spectrometry to probe age-related changes in NAD⁺ metabolism across tissues. In aged mice, we observed modest tissue NAD⁺ depletion (median decrease ∼30%). Circulating NAD⁺ precursors were not significantly changed, and isotope tracing showed the unimpaired synthesis of nicotinamide from tryptophan. In most tissues of aged mice, turnover of the smaller tissue NAD⁺ pool was modestly faster such that absolute NAD⁺ biosynthetic flux was maintained, consistent with more active NAD⁺-consuming enzymes. Calorie restriction partially mitigated age-associated NAD⁺ decline by decreasing consumption. Acute inflammatory stress induced by LPS decreased NAD⁺ by impairing synthesis in both young and aged mice. Thus, the decline in NAD⁺ with normal aging is relatively subtle and occurs despite maintained NAD⁺ production, likely due to increased consumption.

Nampt affects mitochondrial function in aged oocytes by mediating the downstream effector FoxO3a

Maternal aging can impair the quality and decrease the developmental competence of ovulated oocytes. In this study, compromised germinal vesicle breakdown (GVBD) was found in aged mice oocytes. Furthermore, we observed increased reactive oxygen species (ROS) and mitochondrial Ca²⁺ levels, along with reduced mitochondrial temperature in aged oocytes. Maternal aging also changed the crotonylation level in oocytes. Forkhead box O3 (FoxO3a), a member of the forkhead protein family involved in the regulation of cell survival and life span reached a peak level in the metaphase II stage. Compared with a younger group, FoxO3a expression increased in aged oocytes. Intracellular localization of FoxO3a changed from the cytoplasm to chromatin in response to aging. The expression of the upstream regulator nicotinamide-phosphoribosyltransferase (Nampt) peaked in the GVBD stage. Moreover, Nampt expression was increased in aged oocytes, and more intense staining of Nampt was found in aged mice ovary. To further study the role of Nampt in mitochondrial function, specific agonist P7C3 and inhibitor FK866 were applied to aged oocytes, and FK866 significantly decreased adenosine triphosphate and mitochondrial membrane potential. In conclusion, mitochondrial dysfunction in aged oocytes was associated with elevated FoxO3a, and suppression of Nampt could further impair mitochondrial function.

NAD+ deficiency and mitochondrial dysfunction in granulosa cells of women with polycystic ovary syndrome‡

Polycystic ovary syndrome (PCOS) is a prevalent heterogeneous endocrine disorder characterized by ovulation dysfunction, androgen excess, ovarian polycystic changes, insulin resistance, and infertility. Although underlying mechanisms for PCOS are still unknown, inflammation and mitochondrial dysfunction in granulosa cells (GCs) of PCOS patients have been reported. Here, we found that Nicotinamide Adenine Dinucleotide (NAD+) levels in GCs of PCOS patients was significantly decreased when compared with controls. Also, we found that higher expression of inflammation factors, increased reactive oxygen species (ROS) accumulation, lower adenosine triphosphate (ATP) generation, and decreased mitochondrial membrane potential, as well as abnormal mitochondrial dynamics in GCs of PCOS patients. In addition, the NAD+ levels were decreased after activation of inflammation in human granulosa-like tumor cell line (KGN) treated by Lipopolysaccharide (LPS). However, supplementation of nicotinamide riboside (NR), a NAD+ precursor, could largely restore the NAD+ content, reduce ROS levels and improve mitochondrial function demonstrated by increased mitochondrial membrane potential and ATP generation in LPS-treated KGN cells. Our data suggested that inflammation decreased NAD+ levels in GCs of PCOS patients, while supplementation of NR could restore NAD+ levels and alleviated mitochondrial dysfunction in GCs of PCOS patients.

Nicotinamide Mononucleotide Supplementation Reverses the Declining Quality of Maternally Aged Oocytes

Advanced maternal age is highly associated with a decline in oocyte quality, but effective approaches to improve it have still not been fully determined. Here, we report that in vivo supplementation of nicotinamide mononucleotide (NMN) efficaciously improves the quality of oocytes from naturally aged mice by recovering nicotinamide adenine dinucleotide (NAD⁺) levels. NMN supplementation not only increases ovulation of aged oocytes but also enhances their meiotic competency and fertilization ability by maintaining the normal spindle/chromosome structure and the dynamics of the cortical granule component ovastacin. Moreover, single-cell transcriptome analysis shows that the beneficial effect of NMN on aged oocytes is mediated by restoration of mitochondrial function, eliminating the accumulated ROS to suppress apoptosis. Collectively, our data reveal that NMN supplementation is a feasible approach to protect oocytes from advanced maternal age-related deterioration, contributing to the improvement of reproductive outcome of aged women and assisted reproductive technology.

Proteostasis in the Male and Female Germline: A New Outlook on the Maintenance of Reproductive Health

For fully differentiated, long lived cells the maintenance of protein homeostasis (proteostasis) becomes a crucial determinant of cellular function and viability. Neurons are the most well-known example of this phenomenon where the majority of these cells must survive the entire course of life. However, male and female germ cells are also uniquely dependent on the maintenance of proteostasis to achieve successful fertilization. Oocytes, also long-lived cells, are subjected to prolonged periods of arrest and are largely reliant on the translation of stored mRNAs, accumulated during the growth period, to support meiotic maturation and subsequent embryogenesis. Conversely, sperm cells, while relatively ephemeral, are completely reliant on proteostasis due to the absence of both transcription and translation. Despite these remarkable, cell-specific features there has been little focus on understanding protein homeostasis in reproductive cells and how/whether proteostasis is "reset" during embryogenesis. Here, we seek to capture the momentum of this growing field by highlighting novel findings regarding germline proteostasis and how this knowledge can be used to promote reproductive health. In this review we capture proteostasis in the context of both somatic cell and germline aging and discuss the influence of oxidative stress on protein function. In particular, we highlight the contributions of proteostasis changes to oocyte aging and encourage a focus in this area that may complement the extensive analyses of DNA damage and aneuploidy that have long occupied the oocyte aging field. Moreover, we discuss the influence of common non-enzymatic protein modifications on the stability of proteins in the male germline, how these changes affect sperm function, and how they may be prevented to preserve fertility. Through this review we aim to bring to light a new trajectory for our field and highlight the potential to harness the germ cell's natural proteostasis mechanisms to improve reproductive health. This manuscript will be of interest to those in the fields of proteostasis, aging, male and female gamete reproductive biology, embryogenesis, and life course health.

EGCG inhibits pressure overload-induced cardiac hypertrophy via the PSMB5/Nmnat2/SIRT6-dependent signalling pathways

AIM

Epigallocatechin-3-gallate (EGCG), the major polyphenol found in green tea, exerts multiple protective effects against cardiovascular diseases, including cardiac hypertrophy. However, the molecular mechanism underlying its anti-hypertrophic effect has not been clarified. This study revealed that EGCG could inhibit pressure overload-induced cardiac hypertrophy by regulating the PSMB5/Nmnat2/SIRT6-dependent signalling pathway.

METHODS

Quantitative real-time polymerase chain reaction and western blotting were used to determine the expression of mRNA and protein respectively. A fluorometric assay kit was used to determine the activity of SIRT6, a histone deacetylase. Luciferase reporter gene assay and electrophoretic mobility shift assay were employed to measure transcriptional activity and DNA binding activity respectively.

RESULTS

EGCG could significantly increase Nmnat2 protein expression and enzyme activity in cultured neonatal rat cardiomyocytes stimulated with angiotensin II (Ang II) and heart tissues from rats subjected to abdominal aortic constriction. Nmnat2 knockdown by RNA interference attenuated the inhibitory effect of EGCG on cardiac hypertrophy. EGCG blocked NF-κB DNA binding activity induced by Ang II, which was dependent on Nmnat2 and the subsequent SIRT6 activation. Moreover the activation of PSMB5 (20S proteasome subunit β-5, chymotrypsin-like) was required for EGCG-induced Nmnat2 protein expression. Additionally, we demonstrated that EGCG might interact with PSMB5 and inhibit the activation of the proteasome.

CONCLUSIONS

These findings serve as the first evidence that the effect of EGCG against cardiac hypertrophy may be, at least partially, attributed to the modulation of the PSMB5/Nmnat2-dependent signalling pathway, suggesting the therapeutic potential of EGCG in the prevention and treatment of cardiac hypertrophy.

Understanding oocyte ageing: can we influence the process as clinicians?

PURPOSE OF REVIEW

Oocyte quality is rate-limiting for pregnancy success and declines with age. Here, I review animal-study evidence showing dramatic reversal of oocyte ageing with mitochondrial nutrients and explore clinical evidence related to their usage.

RECENT FINDINGS

Oocyte ageing is strongly tied to mitochondrial dysfunction and oxidative stress. Quality-defining events occur over a protracted period (2-3 months in humans) when oocyte volume increases over 100-fold. Treating mice during the growth phase with mitochondrial modifiers such as CoQ10 combats oocyte ageing. Exciting new work shows that raising oocyte NAD+ levels also dramatically rejuvenate aged oocytes. However, evidence that any of these agents can reproducibly improve quality in humans is lacking. This is largely because there has been a focus on patients with poor ovarian response during IVF and/or low ovarian follicular pool size, rather than patients with poor oocyte quality. In addition, studies have used short-term treatment during ovarian stimulation after oocyte growth is already complete.

SUMMARY

Mitochondrial therapeutics such as NAD+-boosting used during the oocyte's growth phase markedly improve oocyte quality in mice. Evaluating them in humans should focus on patients with poor oocyte quality and utilise per-oocyte (rather than per-cycle) endpoints after adequate treatment that captures the growth phase when quality is defined.

Energy sensors and reproductive hypothalamo-pituitary ovarian axis (HPO) in female mammals: Role of mTOR (mammalian target of rapamycin), AMPK (AMP-activated protein kinase) and SIRT1 (Sirtuin 1)

In female, energy metabolism influences reproductive function by modulating the Hypothalamic Pituitary Ovarian axis including the hypothalamic GnRH neuronal network, the pituitary gonadotropin secretion and the ovarian follicle growth and steroidogenesis. Several hormones and neuropeptides or metabolites are important signals between energy balance and reproduction. These energy sensors mediate their action on reproductive cells through specific kinases or signaling pathways. This review focuses on the role of three main enzymes-specifically, mTOR, AMPK, and SIRT1 at the hypothalamic pituitary and ovarian axis in normal female fertility and then we discuss their possible involvement in some women reproductive disorders known to be associated with metabolic complications, such as polycystic ovary syndrome (PCOS) and premature ovarian failure (POF).

IGF2 improves the developmental competency and meiotic structure of oocytes from aged mice

Advanced maternal-age is a major factor adversely affecting oocyte quality, consequently worsening pregnancy outcomes. Thus, developing strategies to reduce the developmental defects associated with advanced maternal-age would benefit older mothers. Multiple growth factors involved in female fertility have been extensively studied; however, the age-related impacts of various growth factors remain poorly studied. In the present study, we identified that levels of insulin-like growth factor 2 (IGF2) are significantly reduced in the serum and oocytes of aged mice. We found that adding IGF2 in culture medium promotes oocyte maturation and significantly increases the proportion of blastocysts: from 41% in the untreated control group to 64% (50 nM IGF2) in aged mice (p < 0.05). Additionally, IGF2 supplementation of the culture medium reduced reactive oxygen species production and the incidence of spindle/chromosome defects. IGF2 increases mitochondrial functional activity in oocytes from aged mice: we detected increased ATP levels, elevated fluorescence intensity of mitochondria, higher mitochondrial membrane potentials, and increased overall protein synthesis, as well as increased autophagy activity and decreased apoptosis. Collectively, our findings demonstrate that IGF2 supplementation in culture media improves oocyte developmental competence and reduces meiotic structure defects in oocytes from aged mice.

Why is oocyte aneuploidy increased with maternal aging?

One of the main causes of pregnancy failure and fetus abortion is oocyte aneuploidy, which is increased with maternal aging. Numerous possible causes of oocyte aneuploidy in aged women have been proposed, including cross-over formation defect, cohesin loss, spindle deformation, spindle assembly checkpoint malfunction, microtubule-kinetochore attachment failure, kinetochore mis-orientation, mitochondria dysfunction-induced increases in reactive oxygen species, protein over-acetylation, and DNA damage. However, it still needs to be answered if these aneuploidization factors have inherent relations, and how to prevent chromosome aneuploidy in aged oocytes. Epidemiologically, oocyte aneuploidy has been found to be weakly associated with higher homocysteine concentrations, obesity, ionizing radiation and even seasonality. In this review, we summarize the research progress and present an integrated view of oocyte aneuploidization.

Dynamic pattern of histone H3 core acetylation in human early embryos

After fertilization, highly differentiated sperm and oocyte are reprogrammed to totipotent embryo, which subsequently cleavages and develops into an individual through spatial-temporal differentiation. Histone modifications play critical roles to coordinate with other reprogramming events in early stages of embryogenesis. However, most of studies focus on modifications at N-terminus of histones, those at nucleosome core were not well understood. Here, we characterize the three key acetylation events in the histone H3 core, H3K56/K64/K122ac, in early human embryos. The three residues localize at DNA entry-exit position of the nucleosome. Globally, H3K56ac, H3K64ac and H3K122ac were detectable throughout preimplantation stages, with H3K64ac levels being relatively stronger and H3K122ac levels being much weaker. Besides, H3K56ac level had a peak at two-cell stage. Moreover, we found that LINEs also peak at two-cell stage, and H3K56ac was enriched at young LINE-1 in human ESCs, supporting that H3K56ac is an important driving force for young LINE-1 activation in human preimplantation embryos. Our results suggest that acetylation in the nucleosome core of histone H3 is dynamic and various during preimplantation development, and may drive diverse chromatin remodeling events in this developmental window.

Nampt-mediated spindle sizing secures a post-anaphase increase in spindle speed required for extreme asymmetry

Meiotic divisions in oocytes are extremely asymmetric and require pre- and post-anaphase-onset phases of spindle migration. The latter induces membrane protrusion that is moulded around the spindle thereby reducing cytoplasmic loss. Here, we find that depleting the NAD biosynthetic enzyme, nicotinamide phosphoribosyl-transferase (Nampt), in mouse oocytes results in markedly longer spindles and compromises asymmetry. By analysing spindle speed in live oocytes, we identify a striking and transient acceleration after anaphase-onset that is severely blunted following Nampt-depletion. Slow-moving midzones of elongated spindles induce cortical furrowing deep within the oocyte before protrusions can form, altogether resulting in larger oocyte fragments being cleaved off. Additionally, we find that Nampt-depletion lowers NAD and ATP levels and that reducing NAD using small molecule Nampt inhibitors also compromises asymmetry. These data show that rapid midzone displacement is critical for extreme asymmetry by delaying furrowing to enable protrusions to form and link metabolic status to asymmetric division.

Meiotic cell division in oocytes is asymmetric and requires microtubule spindle migration after anaphase-onset. Here, the authors show that Nampt, an enzyme of the Nicotinamide adenine dinucleotide (NAD) biosynthetic pathway, contributes to post-anaphase spindle migration and oocyte division asymmetry by controlling spindle length.