Moderate caloric restriction initiated in rodents during adulthood sustains function of the female reproductive axis into advanced chronological age

Senolytic treatment fails to improve ovarian reserve or fertility in female mice

Senescent cell number increases with age in different tissues, leading to greater senescent cell load, proinflammatory stress, and tissue dysfunction. In the current study, we tested the efficacy of senolytic drugs to reduce ovarian senescence and improve fertility in reproductive age female mice. In the first experiment, 1-month-old C57BL/6 female mice were treated every other week with D + Q (n = 24) or placebo (n = 24). At 3 and 6 months of age, female mice were mated with untreated males to evaluate pregnancy rate and litter size. In the second experiment, 6-month-old C57BL/6 female mice were treated monthly with D + Q (n = 30), fisetin (n = 30), or placebo (n = 30). Females were treated once a month until 11 months of age, then they were mated with untreated males for 30 days to evaluate pregnancy rate and litter size. In the first experiment, D + Q treatment did not affect pregnancy rate (P = 0.68), litter size (P = 0.58), or ovarian reserve (P > 0.05). Lipofuscin staining was lower in females treated with D + Q (P = 0.04), but expression of senescence genes in ovaries was similar. In the second experiment, D + Q or fisetin treatment also did not affect pregnancy rate (P = 0.37), litter size (P = 0.20), or ovarian reserve (P > 0.05). Lipofuscin staining (P = 0.008) and macrophage infiltration (P = 0.002) was lower in fisetin treated females. Overall, treatment with D + Q or fisetin did not affect ovarian reserve or fertility but did decrease some senescence markers in the ovary.

The impact of maternal age on aneuploidy in oocytes: Reproductive consequences, molecular mechanisms, and future directions

Age-related aneuploidy in human oocytes is a major factor contributing to decreased fertility and adverse reproductive outcomes. As females age, their oocytes are more prone to meiotic chromosome segregation errors, leading primarily to aneuploidy. Elevated aneuploidy rates have also been observed in oocytes from very young, prepubertal conceptions. A key barrier to developing effective treatments for age-related oocyte aneuploidy is our incomplete understanding of the molecular mechanisms involved. The challenge is becoming increasingly critical as more people choose to delay childbearing, a trend that has significant societal implications. In this review, we summarize current knowledge regarding the process of oocyte meiosis and folliculogenesis, highlighting the relationship between age and chromosomal aberrations in oocytes and embryos, and integrate proposed mechanisms of age-related meiotic disturbances across structural, protein, and genomic levels. Our goal is to spur new research directions and therapeutic avenues.

Caloric restriction extends lifespan in a clonal plant

When subjected to dietary caloric restriction (CR), individual animals often outlive well-fed conspecifics. Here, we address whether CR also extends lifespan in plants. Whereas caloric intake in animals comes from ingestion, in plants it derives from photosynthesis. Thus, factors that reduce photosynthesis, such as reduced light intensity, can induce CR. In two lab experiments investigating the aquatic macrophyte Lemna minor, we tracked hundreds of individuals longitudinally, with light intensity-and hence, CR-manipulated using neutral-density filters. In both experiments, CR dramatically increased lifespan through a process of temporal scaling. Moreover, the magnitude of lifespan extension accorded with the assumptions that (a) light intensity positively relates to photosynthesis following Michaelis-Menten kinetics, and (b) photosynthesis negatively relates to lifespan via a power law. Our results emphasize that CR-mediated lifespan extension applies to autotrophs as well as heterotrophs, and suggest that variation in light intensity has quantitatively predictable effects on plant aging trajectories.

Treatment of mice with maternal intermittent fasting to improve the fertilization rate and reproduction

Maternal intermittent fasting (MIF) can have significant effects on several tissue and organ systems of the body, but there is a lack of research on the effects on the reproductive system. So, the aim of our study was to analyze the effects of MIF on fertility. B6C3F1Crl (C57BL/6N × C3H/HeN) male and female mice were selected for the first part of the experiments and were analyzed for body weight and fat weight after administration of the MIF intervention, followed by analysis of sperm counts and activation and embryo numbers. Subsequently, two strains of mice, C57BL/6NCrl and BALB/cJRj, were selected and administered MIF to observe the presence or absence of vaginal plugs for the purposes of mating success, sperm and oocyte quality, pregnancy outcome, fertility status and in vitro fertilization (IVF). Our results showed a significant reduction in body weight and fat content in mice receiving MIF intervention in B6C3F1Crl mice. Comparing the reproduction of the two strains of mice. However, the number of litters was increased in all MIF interventions in C57BL/6NCrl, but not statistically significant. In BALB/cJRj, there was a significant increase in the number of pregnant females as well as litter size in the MIF treatment group, as well as vaginal plugs, and IVF. There was also an increase in sperm activation and embryo number and the MIF intervention significantly increased sperm count and activation. Our results suggest that MIF interventions may be beneficial for reproduction in mice.

Effects of calorie, protein, and branched chain amino acid restriction on ovarian aging in mice

Calorie restriction (CR) is an intervention that promotes longevity and preserves the ovarian reserve. Some studies have observed that the positive impacts of CR can be linked to restriction of protein (PR) and branched-chain amino acids (BCAAs) independent of calorie intake. The aim of this study was to compare the effects of protein and BCAA restriction to 30% CR on the ovarian reserve of female mice. For this, 3 month-old C57BL/6 female mice (n = 35) were randomized into four groups for four months dietary interventions including: control group (CTL; n = 8), 30% CR (CR; n = 9), protein restriction (PR; n = 9) and BCAA restriction (BCAAR; n = 9). Body mass gain, body composition, food intake, serum levels of BCAAs, ovarian reserve and estrous cyclicity were evaluated. We observed that CR, protein and BCAA restriction prevented weight gain and changed body composition compared to the CTL group. The BCAA restriction did not affect the ovarian reserve, while both PR and CR prevented activation of primordial follicles. This prevention occurred in PR group despite the lack of reduction of calorie intake compared to CTL group, and CR did not reduce protein intake in levels similar to the PR group. BCAA restriction resulted in increased calorie intake compared to CTL and PR mice, but only PR reduced serum BCAA levels compared to the CTL group. Our data indicates that PR has similar effects to CR on the ovarian reserve, whereas BCAA restriction alone did not affect it.

17α-estradiol does not adversely affect sperm parameters or fertility in male mice: implications for reproduction-longevity trade-offs

17α-estradiol (17α-E2) is referred to as a nonfeminizing estrogen that was recently found to extend healthspan and lifespan in male, but not female, mice. Despite an abundance of data indicating that 17α-E2 attenuates several hallmarks of aging in male rodents, very little is known with regard to its effects on feminization and fertility. In these studies, we evaluated the effects of 17α-E2 on several markers of male reproductive health in two independent cohorts of mice. In alignment with our previous reports, chronic 17α-E2 treatment prevented gains in body mass, but did not adversely affect testes mass or seminiferous tubule morphology. We subsequently determined that chronic 17α-E2 treatment also did not alter plasma 17β-estradiol or estrone concentrations, while mildly increasing plasma testosterone levels. We also determined that chronic 17α-E2 treatment did not alter plasma follicle-stimulating hormone or luteinizing hormone concentrations, which suggests 17α-E2 treatment does not alter gonadotropin-releasing hormone neuronal function. Sperm quantity, morphology, membrane integrity, and various motility measures were also unaffected by chronic 17α-E2 treatment in our studies. Lastly, two different approaches were used to evaluate male fertility in these studies. We found that chronic 17α-E2 treatment did not diminish the ability of male mice to impregnate female mice, or to generate successfully implanted embryos in the uterus. We conclude that chronic treatment with 17α-E2 at the dose most commonly employed in aging research does not adversely affect reproductive fitness in male mice, which suggests 17α-E2 does not extend lifespan or curtail disease parameters through tradeoff effects with reproduction.

Ovarian aging in humans: potential strategies for extending reproductive lifespan

Ovarian reserve is a term used to estimate the total number of immature follicles present in the ovaries. Between birth and menopause, there is a progressive decrease in the number of ovarian follicles. Ovarian aging is a continuous physiological phenomenon, with menopause being the clinical mark of the end of ovarian function. Genetics, measured as family history for age at the onset of menopause, is the main determinant. However, physical activity, diet, and lifestyle are important factors that can influence the age of menopause. The low estrogen levels after natural or premature menopause increased the risk for several diseases, resulting in increased mortality risk. Besides that, the decreasing ovarian reserve is associated to reduced fertility. In women with infertility undergoing in vitro fertilization, reduced markers of ovarian reserve, including antral follicular count and anti-Mullerian hormone, are the main indicators of reduced chances of becoming pregnant. Therefore, it becomes clear that the ovarian reserve has a central role in women's life, affecting fertility early in life and overall health later in life. Based on this, the ideal strategy for delaying ovarian aging should have the following characteristics: (1) be initiated in the presence of good ovarian reserve; (2) maintained for a long period; (3) have an action on the dynamics of primordial follicles, controlling the rate of activation and atresia; and (4) safe use in pre-conception, pregnancy, and lactation. In this review, we therefore discuss some of these strategies and its feasibility for preventing a decline in the ovarian reserve.

CeLab, a microfluidic platform for the study of life history traits, reveals metformin and SGK-1 regulation of longevity and reproductive span

The potential to carry out high-throughput assays in a whole organism in a small space is one of the benefits of C. elegans, but worm assays often require a large sample size with frequent physical manipulations, rendering them highly labor-intensive. Microfluidic assays have been designed with specific questions in mind, such as analysis of behavior, embryonic development, lifespan, and motility. While these devices have many advantages, current technologies to automate worm experiments have several limitations that prevent widespread adoption, and most do not allow analyses of reproduction-linked traits. We developed a miniature C. elegans lab-on-a-chip device, CeLab, a reusable, multi-layer device with 200 separate incubation arenas that allows progeny removal, to automate a variety of worm assays on both individual and population levels. CeLab enables high-throughput simultaneous analysis of lifespan, reproductive span, and progeny production, refuting assumptions about the disposable soma hypothesis. Because CeLab chambers require small volumes, the chip is ideal for drug screens; we found that drugs previously shown to increase lifespan also increase reproductive span, and we discovered that low-dose metformin increases both. CeLab reduces the limitations of escaping and matricide that typically limit plate assays, revealing that feeding with heat-killed bacteria greatly extends lifespan and reproductive span of mated animals. CeLab allows tracking of life history traits of individuals, which revealed that the nutrient-sensing mTOR pathway mutant, sgk-1, reproduces nearly until its death. These findings would not have been possible to make in standard plate assays, in low-throughput assays, or in normal population assays.

Demographic Determinants of Residue Profiles of Fungicidal Compounds in Common Voles (Microtus arvalis) under Semi-Natural and Natural Conditions

Environmental risks from plant protection products (PPPs) need to be assessed to ensure safe use. The risk assessments are generally carried out using the common vole as a focal species with conservative theoretical estimates of external exposure. These are then compared to dose-related toxicity endpoints established in toxicity studies, often with laboratory species. The aim of the present study was to determine the actual internal dosimetry of PPPs' active ingredients (AIs) in a population of common voles to provide the basis for informed higher tier risk assessment. As a proof of concept, two fungicidal AIs (fludioxonil and cyprodinil) were investigated using a range of application methodologies. Individuals were treated using oral gavage application (AI dose: 100/200 mg/kg) and fed treated grass (AI sprayed at 2 kg/ha) under laboratory, semi-natural, and natural conditions. Our results show that demographic factors play a significant role in the individual residue profile and that age structure is a key aspect that determines the overall exposure risk of a population. These results are consistent from laboratory to field conditions. Future approaches could establish dose-residue relationships that are reflective of natural food intake rates in wild common vole populations in the risk assessment of PPPs.

Reproductive aging: biological pathways and potential interventive strategies

Reproductive aging is a natural process conserved across species and is well-known in females. It shows age-related follicle depletion and reduction of oocyte quality, eventually causing reproductive senescence and menopause. Although reproductive aging in males is not well noticed as in females, it also causes infertility and has deleterious consequences on the offspring. Various factors have been suggested to contribute to reproductive aging, including oxidative stress, mitochondrial defects, telomere shortening, meiotic chromosome segregation errors and genetic alterations. With the increasing trend of pregnancy age, it is particularly crucial to find interventions to preserve or extend human fertility. Studies in humans and model organisms have provided insights into the biological pathways associated with reproductive aging, and a series of potential interventive strategies have been tested. Here, we review factors affecting reproductive aging in females and males and summarize interventive strategies that may help delay or rescue the aging phenotypes of reproduction.

Longevity Science and Women's Health and Wellbeing

In most areas of the world women comprise the majority of older persons (especially at the most advanced ages), but the additional longevity (globally it is 4.8 years) women have often comes with poorer health status compared to age-matched men. This article draws attention to four distinct ways an applied gerontological intervention designed to increase the human healthspan via "rate (of ageing) control" could positively impact the health and wellbeing of women in today's ageing world. The four benefits examined are: (1) improving women's health in late life; (2) increasing reproductive longevity and improving maternal health, (3) reducing the financial vulnerability many women experience at advanced ages (especially in the developing world); and (4) reducing the caring burdens which typically fall, at least disproportionately, on daughters to care for their ageing parents. Highlighting these factors is important as is helps focus geroscience advocacy not only on the potential health dividend age retardation could confer on those in late life, but also the distributional effects on health throughout the lifespan (e.g. improving maternal health) and on helping to ameliorate other important inequalities (e.g. reducing the financial vulnerabilities of late life and easing the burdens on the care givers for ageing parents). By making vivid the benefits "rate (of ageing) control" could confer on women, especially in the developing world, the goal of retarding biological ageing can be rightly construed as a pressing public health priority for the 21st century.

Ce Lab, a Microfluidic Platform for the Study of Life History Traits, reveals Metformin and SGK-1 regulation of Longevity and Reproductive Span

The potential to carry out high-throughput assays in a whole organism in a small space is one of the benefits of C. elegans , but worm assays often require a large sample size with frequent physical manipulations, rendering them highly labor-intensive. Microfluidic assays have been designed with specific questions in mind, such as analysis of behavior, embryonic development, lifespan, and motility. While these devices have many advantages, current technologies to automate worm experiments have several limitations that prevent widespread adoption, and most do not allow analyses of reproduction-linked traits. We developed a miniature C. elegans lab-on-a-chip device, Ce Lab, a reusable, multi-layer device with 200 separate incubation arenas that allows progeny removal, to automate a variety of worm assays on both individual and population levels. Ce Lab enables high-throughput simultaneous analysis of lifespan, reproductive span, and progeny production, refuting assumptions about the Disposable Soma hypothesis. Because Ce Lab chambers require small volumes, the chip is ideal for drug screens; we found that drugs previously shown to increase lifespan also increase reproductive span, and we discovered that low-dose metformin increases both. Ce Lab reduces the limitations of escaping and matricide that typically limit plate assays, revealing that feeding with heat-killed bacteria greatly extends lifespan and reproductive span of mated animals. Ce Lab allows tracking of life history traits of individuals, which revealed that the nutrient-sensing mTOR pathway mutant, sgk-1 , reproduces nearly until its death. These findings would not have been possible to make in standard plate assays, in low-throughput assays, or in normal population assays.

Unraveling female reproductive senescence to enhance healthy longevity

In a society where women often want successful careers and equal opportunities to men, the early nature of ovarian aging often forces women to make difficult life choices between career and family development. Fertility in women begins to decline after the age of 37 years and it is rare for pregnancies to occur after 45. This reproductive decline in women is inevitable and culminates in menopause, which is a major driver of age-related diseases. In a world where biomedical advances are leading to modifiable biological outcomes, it is time to focus on mitigating female reproductive senescence to maintain fertility and preserve age-related hormonal functions, with the goal of providing increased life choices and enhancing healthspan. To date, reproductive longevity research remains an understudied field. More needs to be done to unravel the biology of the ovarian follicles, which are the functional units of reproductive lifespan and are comprised of cell types including the oocyte (female gamete) and a group of specialized supporting somatic cells. Biological attempts to maintain the quality and quantity of follicles in animal models through manipulating pathways involved in aging can potentially prolong female reproductive lifespan and healthspan. Here, we summarize the molecular events driving ovarian aging and menopause and the interventional strategies to offset these events. Developing solutions to female reproductive senescence will open doors to discover ways to enhance true healthy longevity for both men and women.

Fecal microbiota transplantation from young donor mice improves ovarian function in aged mice

Advanced maternal age is characterized by declines in the quantity and quality of oocytes in the ovaries, and the aging process is accompanied by changes in gut microbiota composition. However, little is known about the relationship between gut microbiota and ovarian aging. By using fecal microbiota transplantation (FMT) to transplant material from young (5-week-old) into aged (42-week-old) mice, we find that the composition of gut microbiota in FMT-treated mice presents a "younger-like phenotype" and an increase of commensal bacteria, such as Bifidobacterium and Ruminococcaceae. Moreover, the FMT-treated mice show increased anti-inflammatory cytokine IL-4 and decreased pro-inflammatory cytokine IFN-γ. Fertility tests for assessing ovarian function reveal that the first litter size of female FMT-treated mice is significantly higher than that of the non-FMT group. Morphology analysis demonstrates a dramatic decrease in follicle atresia and apoptosis as well as an increase in cellular proliferation in the ovaries of the FMT-treated mice. Our results also show that FMT improves the immune microenvironment in aged ovaries, with decreased macrophages and macrophage-derived multinucleated giant cells (MNGCs). These results suggest that FMT from young donors could be a good choice for delaying ovarian aging.

Non-neutral clonal selection and its potential role in mammalian germline stem cell dysfunction with advancing age

The concept of natural selection, or "survival of the fittest", refers to an evolutionary process in nature whereby traits emerge in individuals of a population through random gene alterations that enable those individuals to better adapt to changing environmental conditions. This genetic variance allows certain members of the population to gain an advantage over others in the same population to survive and reproduce in greater numbers under new environmental pressures, with the perpetuation of those advantageous traits in future progeny. Here we present that the behavior of adult stem cells in a tissue over time can, in many respects, be viewed in the same manner as evolution, with each stem cell clone being representative of an individual within a population. As stem cells divide or are subjected to cumulative oxidative damage over the lifespan of the organism, random genetic alterations are introduced into each clone that create variance in the population. These changes may occur in parallel to, or in response to, aging-associated changes in microenvironmental cues perceived by the stem cell population. While many of these alterations will be neutral or silent in terms of affecting cell function, a small fraction of these changes will enable certain clones to respond differently to shifts in microenvironmental conditions that arise with advancing age. In some cases, the same advantageous genetic changes that support survival and expansion of certain clones over others in the population (viz. non-neutral competition) could be detrimental to the downstream function of the differentiated stem cell descendants. In the context of the germline, such a situation would be devastating to successful propagation of the species across generations. However, even within a single generation, the “evolution” of stem cell lineages in the body over time can manifest into aging-related organ dysfunction and failure, as well as lead to chronic inflammation, hyperplasia, and cancer. Increased research efforts to evaluate stem cells within a population as individual entities will improve our understanding of how organisms age and how certain diseases develop, which in turn may open new opportunities for clinical detection and management of diverse pathologies.

Oocyte Quiescence: From Formation to Awakening

Decades of work using various model organisms have resulted in an exciting and emerging field of oocyte maturation. High levels of insulin and active mammalian target of rapamycin signals, indicative of a good nutritional environment, and hormones such as gonadotrophin, indicative of the growth of the organism, work together to control oocyte maturation to ensure that reproduction happens at the right timing under the right conditions. In the wild, animals often face serious challenges to maintain oocyte quiescence under long-term unfavorable conditions in the absence of mates or food. Failure to maintain oocyte quiescence will result in activation of oocytes at the wrong time and thus lead to exhaustion of the oocyte pool and sterility of the organism. In this review, we discuss the shared mechanisms in oocyte quiescence and awakening and a conserved role of noradrenergic signals in maintenance of the quiescent oocyte pool under unfavorable conditions in simple model organisms.

Mild calorie restriction, but not 17α-estradiol, extends ovarian reserve and fertility in female mice

Calorie restriction (CR) (25-40%) is the most commonly studied strategy for curtailing age-related disease and has also been found to extend reproductive lifespan in female mice. However, the effects of mild CR (10%), which is sustainable, on ovarian aging has not yet been addressed. 17α-estradiol (17α-E2) is another intervention shown to positively modulate healthspan and lifespan in mice but its effects on female reproduction remain unclear. We evaluated the effects of mild CR (10%) and 17α-E2 treatment on ovarian reserve and female fertility over a 24-week period, and compared these effects with the more commonly employed 30% CR regimen. Both 10% and 30% CR elicited positive effects on the preservation of ovarian reserve, whereas 17α-E2 did not alter parameters associated with ovarian function. Following refeeding, both 10% and 30% increased fertility as evidenced by greater pregnancy rates. In aligned with the ovarian reserve data, 17α-E2 also failed to improve fertility. Collectively, these data indicate that 10% CR is effective in preserving ovarian function and fertility, while 17α-E2 does not appear to have therapeutic potential for delaying ovarian aging.

Mitochondria: Their relevance during oocyte ageing

The oocyte is recognised as the largest cell in mammalian species and other multicellular organisms. Mitochondria represent a high proportion of the cytoplasm in oocytes and mitochondrial architecture is different in oocytes than in somatic cells, characterised by a rounder appearance and fragmented network. Although the number of mitochondria per oocyte is higher than in any other mammalian cell, their number and activity decrease with advancing age. Mitochondria integrate numerous processes essential for cellular function, such as metabolic processes related to energy production, biosynthesis, and waste removal, as well as Ca²⁺ signalling and reactive oxygen species (ROS) homeostasis. Further, mitochondria are responsible for the cellular adaptation to different types of stressors such as oxidative stress or DNA damage. When these stressors outstrip the adaptive capacity of mitochondria to restore homeostasis, it leads to mitochondrial dysfunction. Decades of studies indicate that mitochondrial function is multifaceted, which is reflected in the oocyte, where mitochondria support numerous processes during oocyte maturation, fertilization, and early embryonic development. Dysregulation of mitochondrial processes has been consistently reported in ageing and age-related diseases. In this review, we describe the functions of mitochondria as bioenergetic powerhouses and signal transducers in oocytes, how dysfunction of mitochondrial processes contributes to reproductive ageing, and whether mitochondria could be targeted to promote oocyte rejuvenation.

Reproductive Longevity and Aging: Geroscience Approaches to Maintain Long-Term Ovarian Fitness

Increases in delayed childbearing worldwide have elicited the need for a better understanding of the biological underpinnings and implications of age-related infertility. In women 35 years and older the incidences of infertility, aneuploidy, and birth defects dramatically increase. These outcomes are a result of age-related declines in both ovarian reserve and oocyte quality. In addition to waning reproductive function, the decline in estrogen secretion at menopause contributes to multisystem aging and the initiation of frailty. Both reproductive and hormonal ovarian function are limited by the primordial follicle pool, which is established in utero and declines irreversibly until menopause. Because ovarian function is dependent on the primordial follicle pool, an understanding of the mechanisms that regulate follicular growth and maintenance of the primordial follicle pool is critical for the development of interventions to prolong the reproductive life span. Multiple pathways related to aging and nutrient-sensing converge in the mammalian ovary to regulate quiescence or activation of primordial follicles. The PI3K/PTEN/AKT/FOXO3 and associated TSC/mTOR pathways are central to the regulation of the primordial follicle pool; however, aging-associated systems such as the insulin-like growth factor-1/growth hormone pathway, and transsulfuration/hydrogen sulfide pathways may also play a role. Additionally, sirtuins aid in maintaining developmental metabolic competence and chromosomal integrity of the oocyte. Here we review the pathways that regulate ovarian reserve and oocyte quality, and discuss geroscience interventions that leverage our understanding of these pathways to promote reproductive longevity.

Growth hormone increases DNA damage in ovarian follicles and macrophage infiltration in the ovaries

Evidence points to an important role of the growth hormone (GH) in the aging process and longevity. GH-deficient mice are smaller, live longer than normal littermates, and females have an increased ovarian reserve. The aim of the study was to evaluate the role of GH in the ovarian reserve by evaluating DNA damage, macrophage infiltration, and granulosa cell number in primordial and primary follicles. Experiment 1 used GH-deficient Ames dwarf mice (df/df, n = 12) and their normal littermates (N/df, n = 12), receiving GH or saline injections. Experiment 2 included transgenic mice overexpressing bovine GH (bGH) (n = 6) and normal mice (N, n = 6). DNA damage (anti-γH2AX) and macrophage counting (anti-CD68) were evaluated by immunofluorescence. Female df/df mice had lower γH2AX foci intensity in both oocytes and granulosa cells of primordial and primary follicles (p < 0.05), indicating fewer DNA double-strand breaks (DSBs). GH treatment increased DSBs in both df/df and N/df mice. Inversely, bGH mice had a higher quantity of DSBs in both oocytes and granulosa cells of primordial and primary follicles (p < 0.05). Df/df mice showed ovarian tissue with less macrophage infiltration than N/df mice (p < 0.05) and GH treatment increased macrophage infiltration (p < 0.05). In contrast, bGH mice had ovarian tissue with more macrophage infiltration compared to normal mice (p < 0.05). The current study shows that GH increases DNA DSBs in oocytes and granulosa cells and raises macrophage infiltration in the ovaries, pointing to the role of the GH/IGF-I axis in maintenance of oocyte DNA integrity and ovarian macrophage infiltration in mice.

Pseudo-Starvation Driven Energy Expenditure Negatively Affects Ovarian Follicle Development

In the present investigation, we examined whether a change in whole body energy fluxes could affect ovarian follicular development, employing mice ectopically expressing uncoupling protein 1 in skeletal muscle (UCP1-TG). Female UCP1-TG and wild-type (WT) mice were dissected at the age of 12 weeks. Energy intake and expenditure, activity, body weight and length, and body composition were measured. Plasma insulin, glucose, leptin, plasma fibroblast growth factor 21 (FGF21) and plasma insulin-like growth factor 1 (IGF1) levels were analyzed and ovarian follicle and corpus luteum numbers were counted. IGF1 signaling was analyzed by immunohistochemical staining for the activation of insulin receptor substrate 1/2 (IRS1/2) and AKT. UCP1-TG female mice had increased energy expenditure, reduced body size, maintained adiposity, and decreased IGF1 concentrations compared to their WT littermates, while preantral and antral follicle numbers were reduced by 40% and 60%, respectively. Corpora lutea were absent in 40% of the ovaries of UCP1-TG mice. Phospho-IRS1, phospho-AKT -Ser473 and -Thr308 immunostaining was present in the granulosa cells of antral follicles in WT ovaries, but faint to absent in the antral follicles of UCP1-TG mice. In conclusion, the reduction in circulating IGF1 levels due to the ectopic expression of UCP1 is associated with reduced immunostaining of the IRS1-PI3/AKT pathway, which may negatively affect ovarian follicle development and ovulation.

Cellular hallmarks of aging emerge in the ovary prior to primordial follicle depletion

Decline in ovarian reserve with advancing age is associated with reduced fertility and the emergence of metabolic disturbances, osteoporosis, and neurodegeneration. Recent studies have provided insight into connections between ovarian insufficiency and systemic aging, although the basic mechanisms that promote ovarian reserve depletion remain unknown. Here, we sought to determine if chronological age is linked to changes in ovarian cellular senescence, transcriptomic, and epigenetic mechanisms in a mouse model. Histological assessments and transcriptional analyses revealed the accumulation of lipofuscin aggresomes and senescence-related transcripts (Cdkn1a, Cdkn2a, Pai-1 and Hmgb1) significantly increased with advancing age. Transcriptomic profiling and pathway analyses following RNA sequencing, revealed an upregulation of genes related to pro-inflammatory stress and cell-cycle inhibition, whereas genes involved in cell-cycle progression were downregulated; which could be indicative of senescent cell accumulation. The emergence of these senescence-related markers preceded the dramatic decline in primordial follicle reserve observed. Whole Genome Oxidative Bisulfite Sequencing (WGoxBS) found no genome-wide or genomic context-specific DNA methylation and hydroxymethylation changes with advancing age. These findings suggest that cellular senescence may contribute to ovarian aging, and thus, declines in ovarian follicular reserve. Cell-type-specific analyses across the reproductive lifespan are needed to fully elucidate the mechanisms that promote ovarian insufficiency.

Current mechanisms of primordial follicle activation and new strategies for fertility preservation

Premature ovarian insufficiency (POI) is characterized by symptoms caused by ovarian dysfunction in patients aged <40 years. It is associated with a shortened reproductive lifespan. The only effective treatment for patients who are eager to become pregnant is IVF/Embryo Transfer (ET) using oocytes donated by young women. However, the use of the technique is constrained by the limited supply of oocytes and ethical issues. Some patients with POI still have some residual follicles in the ovarian cortex, which are not regulated by gonadotropin. These follicles are dormant. Therefore, activating dormant primordial follicles (PFs) to obtain high-quality oocytes for assisted reproductive technology may bring new hope for patients with POI. Therefore, this study aimed to explore the factors related to PF activation, such as the intercellular signaling network, the internal microenvironment of the ovary and the environment of the organism. In addition, we discussed new strategies for fertility preservation, such as in vitro activation and stem cell transplantation.

Dietary Restriction Improves Fitness of Aging Parents But Reduces Fitness of Their Offspring in Nematodes

Dietary restriction (DR) is a well-established intervention to extend lifespan across taxa. Recent studies suggest that DR-driven lifespan extension can be cost-free, calling into question a central tenant of the evolutionary theory of aging. Nevertheless, boosting parental longevity can reduce offspring fitness. Such intergenerational trade-offs are often ignored but can account for the "missing costs" of longevity. Here, we use the nematode Caenorhabditis remanei to test for effects of DR by fasting on fitness of females and their offspring. Females deprived of food for 6 days indeed had increased fecundity, survival, and stress resistance after re-exposure to food compared with their counterparts with constant food access. However, offspring of DR mothers had reduced early and lifetime fecundity, slower growth rate, and smaller body size at sexual maturity. These findings support the direct trade-off between investment in soma and gametes challenging the hypothesis that increased somatic maintenance and impaired reproduction can be decoupled.

Caloric restriction in female reproduction: is it beneficial or detrimental?

Caloric restriction (CR), an energy-restricted intervention with undernutrition instead of malnutrition, is widely known to prolong lifespan and protect against the age-related deteriorations. Recently it is found that CR significantly affects female reproduction via hypothalamic (corticotropin releasing hormone, neuropeptide Y, agouti-related peptide) and peripheral (leptin, ghrelin, insulin, insulin-like growth factor) mediators, which can regulate the energy homeostasis. Although CR reduces the fertility in female mammals, it exerts positive effects like preserving reproductive capacity. In this review, we aim to discuss the comprehensive effects of CR on the central hypothalamus-pituitary-gonad axis and peripheral ovary and uterus. In addition, we emphasize the influence of CR during pregnancy and highlight the relationship between CR and reproductive-associated diseases. Fully understanding and analyzing the effects of CR on the female reproduction could provide better strategies for the management and prevention of female reproductive dysfunctions.

The protective effects of rapamycin pretreatment on ovarian damage during ovarian tissue cryopreservation and transplantation

Ovarian tissue cryopreservation and transplantation (OCT) has been sufficiently proven effective and feasible to preserve fertility for women especially for prepubertal girls suffering from cancer with radiotherapy and chemotherapy. However, grafts' survival, significant follicle loss and a delay of revascularization during OCT still need to be resolved no matter what kind of cryopreserved method being used. Different from previous reports about additives treatment on recipient after ovarian transplantation, we here report a new vitrification protocol with pretreatment of rapamycin, an inhibitor of the mTOR signaling pathway. The rapamycin treatment has been shown to inhibit the activation of mTOR signaling pathway in fresh thawed ovaries or in ovaries shortly grafted in the recipient mice. Further study revealed increased percentage of primordial follicles and reduced apoptosis after 5 days of transplantation. Long-term follow up of ovarian development demonstrated the increase of ovarian survival rates in rapamycin treated ovaries after 2 weeks of transplantation. Although follicular development showed a slight delay with more secondary and early antral follicles found in rapamycin treated ovaries, follicular development was not blocked as manifested by the ovarian morphology after 5 weeks of transplantation. Taken together, the pretreatment of rapamycin before vitrification is a good method for clinical application with its effectiveness on preserving follicle reserve and promoting ovarian survival during the process of OCT.

The Relevance of Aquaporins for the Physiology, Pathology, and Aging of the Female Reproductive System in Mammals

Aquaporins constitute a group of water channel proteins located in numerous cell types. These are pore-forming transmembrane proteins, which mediate the specific passage of water molecules through membranes. It is well-known that water homeostasis plays a crucial role in different reproductive processes, e.g., oocyte transport, hormonal secretion, completion of successful fertilization, blastocyst formation, pregnancy, and birth. Further, aquaporins are involved in the process of spermatogenesis, and they have been reported to be involved during the storage of spermatozoa. It is noteworthy that aquaporins are relevant for the physiological function of specific parts in the female reproductive system, which will be presented in detail in the first section of this review. Moreover, they are relevant in different pathologies in the female reproductive system. The contribution of aquaporins in selected reproductive disorders and aging will be summarized in the second section of this review, followed by a section dedicated to aquaporin-related proteins. Since the relevance of aquaporins for the male reproductive system has been reviewed several times in the recent past, this review aims to provide an update on the distribution and impact of aquaporins only in the female reproductive system. Therefore, this paper seeks to determine the physiological and patho-physiological relevance of aquaporins on female reproduction, and female reproductive aging.

Clinical Application of Antioxidants to Improve Human Oocyte Mitochondrial Function: A Review

Mitochondria produce adenosine triphosphate (ATP) while also generating high amounts of reactive oxygen species (ROS) derived from oxygen metabolism. ROS are small but highly reactive molecules that can be detrimental if unregulated. While normally functioning mitochondria produce molecules that counteract ROS production, an imbalance between the amount of ROS produced in the mitochondria and the capacity of the cell to counteract them leads to oxidative stress and ultimately to mitochondrial dysfunction. This dysfunction impairs cellular functions through reduced ATP output and/or increased oxidative stress. Mitochondrial dysfunction may also lead to poor oocyte quality and embryo development, ultimately affecting pregnancy outcomes. Improving mitochondrial function through antioxidant supplementation may enhance reproductive performance. Recent studies suggest that antioxidants may treat infertility by restoring mitochondrial function and promoting mitochondrial biogenesis. However, further randomized, controlled trials are needed to determine their clinical efficacy. In this review, we discuss the use of resveratrol, coenzyme-Q10, melatonin, folic acid, and several vitamins as antioxidant treatments to improve human oocyte and embryo quality, focusing on the mitochondria as their main hypothetical target. However, this mechanism of action has not yet been demonstrated in the human oocyte, which highlights the need for further studies in this field.

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.

The Interconnections Between Somatic and Ovarian Aging in Murine Models

The mammalian female is born with a limited ovarian reserve of primordial follicles. These primordial follicles are slowly activated throughout the reproductive lifecycle, thereby determining lifecycle length. Once primordial follicles are exhausted, women undergo menopause, which is associated with several metabolic perturbations and a higher mortality risk. Long before exhaustion of the reserve, females experience severe declines in fertility and health. As such, significant efforts have been made to unravel the mechanisms that promote ovarian aging and insufficiency. In this review, we explain how long-living murine models can provide insights in the regulation of ovarian aging. There is now overwhelming evidence that most life-span-extending strategies, and long-living mutant models simultaneously delay ovarian aging. Therefore, it appears that the same mechanisms that regulate somatic aging may also be modulating ovarian aging and germ cell exhaustion. We explore several potential contributing mechanisms including insulin resistance, inflammation, and DNA damage-all of which are hallmarks of cellular aging throughout the body including the ovary. These findings are in alignment with the disposable soma theory of aging, which dictates a trade-off between growth, reproduction, and DNA repair. Therefore, delaying ovarian aging will not only increase the fertility window of middle age females, but may also actively prevent menopausal-related decline in systemic health parameters, compressing the period of morbidity in mid-to-late life in females.

Mechanisms of oocyte aneuploidy associated with advanced maternal age

It is well established that maternal age is associated with a rapid decline in the production of healthy and high-quality oocytes resulting in reduced fertility in women older than 35 years of age. In particular, chromosome segregation errors during meiotic divisions are increasingly common and lead to the production of oocytes with an incorrect number of chromosomes, a condition known as aneuploidy. When an aneuploid oocyte is fertilized by a sperm it gives rise to an aneuploid embryo that, except in rare situations, will result in a spontaneous abortion. As females advance in age, they are at higher risk of infertility, miscarriage, or having a pregnancy affected by congenital birth defects such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Turner syndrome (monosomy X). Here, we review the potential molecular mechanisms associated with increased chromosome segregation errors during meiosis as a function of maternal age. Our review shows that multiple exogenous and endogenous factors contribute to the age-related increase in oocyte aneuploidy. Specifically, the weight of evidence indicates that recombination failure, cohesin deterioration, spindle assembly checkpoint (SAC) disregulation, abnormalities in post-translational modification of histones and tubulin, and mitochondrial dysfunction are the leading causes of oocyte aneuploidy associated with maternal aging. There is also growing evidence that dietary and other bioactive interventions may mitigate the effect of maternal aging on oocyte quality and oocyte aneuploidy, thereby improving fertility outcomes. Maternal age is a major concern for aneuploidy and genetic disorders in the offspring in the context of an increasing proportion of mothers having children at increasingly older ages. A better understanding of the mechanisms associated with maternal aging leading to aneuploidy and of intervention strategies that may mitigate these detrimental effects and reduce its occurrence are essential for preventing abnormal reproductive outcomes in the human population.

Glucose activates the primordial follicle through the AMPK/mTOR signaling pathway

Background

We have previously found that the energy level in sows affects the activation of primordial follicles. Glucose is the primary metabolic substrate of dietary energy and its effect and mechanism of action with regards to the activation and development of primordial follicle remain unclear. Studies utilizing several different animal cells have shown that energy stress, induced by glucose starvation, activates AMPK and participates in a variety of cellular processes by regulating the Hippo and mTOR signaling pathways. However, whether glucose can affect primordial follicle activation through the above pathways has not been reported.

Methods

We developed an in vitro culture system for mouse ovaries to investigate the effects of glucose on the primordial follicle activation. Protein expression of AMPK‐Hippo‐YAP and AMPK‐mTOR pathway was investigated under glucose starvation and optimal glucose level treatment. Then, ovaries were treated with AICAR or Compound C in vitro to explore the effect of AMPK activation or inhibition on primordial follicle activation, and the changes of AMPK‐Hippo‐YAP and AMPK‐mTOR signaling pathways. Finally, investigated the signaling pathways affected by glucose potentially affecting the primordial follicle activation in vivo.

Results

The glucose was an essential nutrient for primordial follicle activation and we identified 25 mM glucose as the optimal level (P < .05) for the primordial follicle activation in vitro. The glycolysis pathway was involved in primordial follicle activation (P < .05) of ovaries cultured in vitro. The glucose affected the activation of primordial follicles in vitro through AMPK/mTOR signaling pathway by AMPK activation or inhibition treatment and follicle ratio count (P < .05). Moreover, glucose affected the primordial follicle activation of ovary in vivo via mTOR signaling pathway.

Conclusions

This study demonstrates that glucose affects the primordial follicle activation through the AMPK/mTOR rather than the AMPK/Hippo signaling pathway.

The effect of rapamycin on bovine oocyte maturation success and metaphase telomere length maintenance

Maternal aging-associated reduction of oocyte viability is a common feature in mammals, but more research is needed to counteract this process. In women, the first aging phenotype appears with a decline in reproductive function, and the follicle number gradually decreases from menarche to menopause. Cows can be used as a model of early human embryonic development and reproductive aging because both species share a very high degree of similarity during follicle selection, cleavage, and blastocyst formation. Recently, it has been proposed that the main driver of aging is the mammalian target of rapamycin (mTOR) signaling rather than reactive oxygen species. Based on these observations, the study aimed to investigate for the first time the possible role of rapamycin on oocyte maturation, embryonic development, and telomere length in the bovine species, as a target for future strategies for female infertility caused by advanced maternal age. The 1nm rapamycin in vitro treatment showed the best results for maturation rates (95.21±4.18%) of oocytes and was considered for further experiments. In conclusion, rapamycin influenced maturation rates of oocytes in a concentration-dependent manner. Our results also suggest a possible link between mTOR, telomere maintenance, and bovine blastocyst formation.

The obligate need for accuracy in reporting preclinical studies relevant to clinical trials: autologous germline mitochondrial supplementation for assisted human reproduction as a case study

A now large body of work has solidified the central role that mitochondria play in oocyte development, fertilization, and embryogenesis. From these studies, a new technology termed autologous germline mitochondrial energy transfer was developed for improving pregnancy success rates in assisted reproduction. Unlike prior clinical studies that relied on the use of donor, or nonautologous, mitochondria for microinjection into eggs of women with a history of repeated in vitro fertilization failure to enhance pregnancy success, autologous germline mitochondrial energy transfer uses autologous mitochondria collected from oogonial stem cells of the same woman undergoing the fertility treatment. Initial trials of autologous germline mitochondrial energy transfer during - in vitro fertilization at three different sites with a total of 104 patients indicated a benefit of the procedure for improving pregnancy success rates, with the birth of children conceived through the inclusion of autologous germline mitochondrial energy transfer during in vitro fertilization. However, a fourth clinical study, consisting of 57 patients, failed to show a benefit of autologous germline mitochondrial energy transfer-in vitro fertilization versus in vitro fertilization alone for improving cumulative live birth rates. Complicating this area of work further, a recent mouse study, which claimed to test the long-term safety of autologous mitochondrial supplementation during in vitro fertilization, raised concerns over the use of the procedure for reproduction. However, autologous mitochondria were not actually used for preclinical testing in this mouse study. The unwarranted fears that this new study's erroneous conclusions could cause in women who have become pregnant through the use of autologous germline mitochondrial energy transfer during-in vitro fertilization highlight the critical need for accurate reporting of preclinical work that has immediate bearing on human clinical studies.

Estrogen regulation of germline stem cell differentiation as a mechanism contributing to female reproductive aging

Progressive loss of ovarian estrogen (E2) production is a hallmark feature of, if not a driving force behind, reproductive aging and the menopause. Recent genetic studies in mice have shown that female germline or oogonial stem cells (OSCs) contribute to maintenance of adult ovarian function and fertility under physiological conditions through support of de-novo oogenesis. Here we show that mouse OSCs express E2 receptor-α (ERα). In the presence of E2, ERα interacts with the stimulated by retinoic acid gene 8 (Stra8) promoter to drive Stra8 expression followed by oogenesis. Treatment of mice with E2 in vivo increases Stra8 expression and oogenesis, and these effects are nullified by ERα (Esr1), but not ERβ (Esr2), gene disruption. Although mice lacking ERα are born with a normal quota of oocytes, ERα-deficient females develop premature ovarian insufficiency in adulthood due to impaired oogenesis. Lastly, mice treated with reversible ER antagonists show a loss of Stra8 expression and oocyte numbers; however, both endpoints rebound to control levels after ceasing drug treatment. These findings establish a key physiological role for E2-ERα signaling in promoting OSC differentiation as a potential mechanism to maintain adequate numbers of ovarian follicles during reproductive life.

Primordial follicle reserve, DNA damage and macrophage infiltration in the ovaries of the long-living Ames dwarf mice

The aim of this study was to evaluate the effect of growth hormone (GH) deficiency in primordial follicle reserve, DNA damage and macrophage infiltration in the ovaries of young mice. Ovaries from six-month-old GH-deficient Ames Dwarf (df/df) and Normal (N/df) mice were used. The number of primordial follicles was higher in df/df mice (p = 0.0026). Also, df/df mice had a lower number of primary (p = 0.023), secondary (p = 0.0052) and tertiary (p = 0.019) follicles. These findings indicate a slower rate of primordial follicle activation in df/df mice. Female df/df mice had decreased γH2AX foci intensity in oocytes of primordial (p = 0.015) and primary (p = 0.0004) follicles compared to N/df mice. Also, df/df mice had reduced γH2AX intensity in granulosa cells of primordial (p = 0.0002) and primary (p < 0.0001) follicles. Overall, this indicate to us that df/df mice accumulate less DNA damage in the ovarian reserve compared to N/df mice. Additionally, macrophage infiltration was also reduced in ovaries of df/df mice compared to N/df mice (p = 0.033). Interestingly, df/df mice had a reduced number of granulosa cells around primordial (p = 0.0024) and primary (p = 0.007) follicles compared to N/df mice. Also, df/df mice had a small diameter of primordial follicle nuclei (p = 0.0093), secondary follicle oocyte (p = 0.046) and tertiary follicle (p = 0.012). This points to the role of granulosa cell proliferation and oocyte growth for primordial follicle activation. The current study points to the role of the GH/IGF-I axis in extending lifespan of reproductive health, along with maintenance of oocyte DNA integrity and reduced ovarian inflammation.

Effect of caloric restriction and rapamycin on ovarian aging in mice

Caloric restriction (CR) increases the preservation of the ovarian primordial follicular reserve, which can potentially delay menopause. Rapamycin also increases preservation on the ovarian reserve, with similar mechanism to CR. Therefore, the aim of our study was to evaluate the effects of rapamycin and CR on metabolism, ovarian reserve, and gene expression in mice. Thirty-six female mice were allocated into three groups: control, rapamycin-treated (4 mg/kg body weight every other day), and 30% CR. Caloric restricted females had lower body weight (P < 0.05) and increased insulin sensitivity (P = 0.003), while rapamycin injection did not change body weight (P > 0.05) and induced insulin resistance (P < 0.05). Both CR and rapamycin females displayed a higher number of primordial follicles (P = 0.02 and 0.04, respectively), fewer primary, secondary, and tertiary follicles (P < 0.05) and displayed increased ovarian Foxo3a gene expression (P < 0.05). Despite the divergent metabolic effects of the CR and rapamycin treatments, females from both groups displayed a similar increase in ovarian reserve, which was associated with higher expression of ovarian Foxo3a.

Short-term starvation stress at young adult stages enhances meiotic activity of germ cells to maintain spermatogenesis in aged male Caenorhabditis elegans

To survive and reproduce, living organisms must evolve numerous mechanisms to re‐adjust their physiology when encountering adverse conditions that subject them to severe stress. We found that short‐term starvation (STS) stress in young adult male Caenorhabditis elegans can significantly improve their vitality (relative to nonstressed males) when they are aged. In addition, we found that stress‐treated aged males maintained reproductive activity equivalent to young males, whereas nonstressed aged males quickly lost reproductive ability. STS stress can preserve sperm number and quality in aged male worms. Spermatogenesis involves germ cell mitosis and meiosis. We found that germ cell meiotic activity is more sensitive to aging than mitotic activity and is declining rapidly with age. We examined the role of numerous factors important for spermatogenesis on STS‐preserved spermatogenesis during aging. Our results show that mutant strains deficient in anaphase‐promoting complex/cyclosome (APC/C) function fail to exhibit the STS stress‐enhanced spermatogenesis found in wild‐type N2 worms, suggesting that the mechanism underlying starvation‐induced spermatogenesis involves the APC/C complex, a conserved ubiquitin‐protein ligase E3 complex. Furthermore, transgenic expression of FZY‐1/CDC‐20, a coactivator of APC/C, ameliorated the age‐associated decline of meiosis, similar to the hormetic effect of STS.

SIRT1 knock-in mice preserve ovarian reserve resembling caloric restriction

Previous studies have proposed that caloric restriction (CR) regulates many cell functions and prolongs the lifespan of an organism. Our previous studies proposed that CR also prevents follicular activation and preserves the ovarian reserve in mice by activating SIRT1. To test if SIRT1 preserves the ovarian reserve and prolongs the ovarian longevity, we generated SIRT1 knock-in mice that can overexpress SIRT1 in oocytes of the mouse. Ovaries of the mice at ages 35 days and 15 months were collected, and the follicular development and follicular reserve were examined. The vaginal opening and onset of estrus of transgenic female mice (both the homozygous and heterozygous for SIRT1 overexpression) were later than that of wild-type mice. Both the homozygous and heterozygous SIRT1-overexpressing mice had a larger and stronger reproductive capacity than wild-type mice. Moreover, 35-day-old and 15-month-old homozygous and heterozygous SIRT1-overexpressing mice also had a higher mean number and percentage of healthy follicles, fewer atretic follicles than wild-type mice, and the mean number and percentage of primordial follicles in both the homozygous and heterozygous SIRT1-overexpressing mice were higher than wild-type mice at the same age. However, the phenotypes of heterozygous and homozygous transgenic mice came no difference. Immunohistochemistry showed increased expression of SIRT1 and FOXO3a, and decreased expression of mTOR in both the homozygous and heterozygous SIRT1-overexpressing mice compared with wild-type mice. Thus, oocyte-specific SIRT1-overexpressing mice continuously activate FOXO3a and suppress mTOR and have a larger reproductive capacity, larger follicle reserve and longer ovarian lifespan.

Extension of longevity and reduction of inflammation is ovarian-dependent, but germ cell-independent in post-reproductive female mice

Cardiovascular disease, rare in premenopausal women, increases sharply at menopause and is typically accompanied by chronic inflammation. Previous work in our laboratory demonstrated that replacing senescent ovaries in post-reproductive mice with young, actively cycling ovaries restored many health benefits, including decreased cardiomyopathy and restoration of immune function. Our objective here was to determine if depletion of germ cells from young transplanted ovaries would alter the ovarian-dependent extension of life and health span. Sixty-day-old germ cell-depleted and germ cell-containing ovaries were transplanted to post-reproductive, 17-month-old mice. Mean life span for female CBA/J mice is approximately 644 days. Mice that received germ cell-containing ovaries lived 798 days (maximum = 815 days). Mice that received germ cell-depleted ovaries lived 880 days (maximum = 1046 days), 29% further past the time of surgery than mice that received germ cell-containing ovaries. The severity of inflammation was reduced in all mice that received young ovaries, whether germ cell-containing or germ cell-depleted. Aging-associated inflammatory cytokine changes were reversed in post-reproductive mice by 4 months of new-ovary exposure. In summary, germ cell depletion enhanced the longevity-extending effects of the young, transplanted ovaries and, as with germ cell-containing ovaries, decreased the severity of inflammation, but did so independent of germ cells. Based on these observations, we propose that gonadal somatic cells are programed to preserve the somatic health of the organism with the intent of facilitating future germline transmission. As reproductive potential decreases or is lost, the incentive to preserve the somatic health of the organism is lost as well.

Can ovarian aging be delayed by pharmacological strategies?

Aging has been regarded as a treatable condition, and delaying aging could prevent some diseases. Ovarian aging, a special type of organ senescence, is the earliest-aging organ, as ovaries exhibit an accelerated rate of aging with characteristics of gradual declines in ovarian follicle quantity and quality since birth, compared to other organs. Ovarian aging is considered as the pacemaker of female body aging, which drives the aging of multiple organs of the body. Hence, anti-ovarian aging has become a research topic broadly interesting to both biomedical scientists and pharmaceutical industry. A marked progress has been made in exploration of possible anti-ovarian agents or approaches, such as calorie restriction mimetics, antioxidants, autophagy inducers etc., over the past years. This review is attempted to discuss recent advances in the area of anti-ovarian aging pharmacology and to offer new insights into our better understanding of molecular mechanisms underlying ovarian aging, which might be informative for future prevention and treatment of ovarian aging and its related diseases.

SIRT1 induces resistance to apoptosis in human granulosa cells by activating the ERK pathway and inhibiting NF-κB signaling with anti-inflammatory functions

SIRT1, a member of the sirtuin family, has recently emerged as a vital molecule in controlling ovarian function. The aims of the present study were to investigate SIRT1 expression and analyze SIRT1-mediated apoptosis in human granulosa cells (GCs). Human ovarian tissues were subjected to immunohistochemistry for localization of SIRT1 expression. SIRT1 knockdown in a human ovarian GC tumor line (COV434) was achieved by small interfering RNA, and the relationship between apoptosis and SIRT1 was assessed by quantitative reverse transcription polymerase chain reaction and western blotting. We further detected SIRT1 expression in human luteinized GCs. Associations among SIRT1 knockdown, SIRT1 stimulation (resveratrol) and expression of ERK1/2 and apoptotic regulatory proteins were analyzed in cell lines and luteinized GCs. Resveratrol downregulated the levels of nuclear factor (NF)-κB/p65, but this inhibitory effect was attenuated by suppressing SIRT1 activity. The NF-κB/p65 inhibitor pyrrolidine dithiocarbamate achieved similar anti-apoptosis effects. These results suggest that SIRT1 might play an anti-apoptotic role in apoptosis processes in GCs, possibly by sensing and regulating the ERK1/2 pathway, which has important clinical implications. Thus, our study provides a mechanistic link, whereby activation of SIRT1 function might help to sustain human reproduction by maintaining GCs as well as oocytes, offering a novel approach for developing a new class of therapeutic anti-inflammatory agents.

Influence of Maternal Aging on Mitochondrial Heterogeneity, Inheritance, and Function in Oocytes and Preimplantation Embryos

Contrasting the equal contribution of nuclear genetic material from maternal and paternal sources to offspring, passage of mitochondria, and thus mitochondrial DNA (mtDNA), is uniparental through the egg. Since mitochondria in eggs are ancestral to all somatic mitochondria of the next generation and to all cells of future generations, oocytes must prepare for the high energetic demands of maturation, fertilization and embryogenesis while simultaneously ensuring that their mitochondrial genomes are inherited in an undamaged state. Although significant effort has been made to understand how the mtDNA bottleneck and purifying selection act coordinately to prevent silent and unchecked spreading of invisible mtDNA mutations through the female germ line across successive generations, it is unknown if and how somatic cells of the immediate next generation are spared from inheritance of detrimental mtDNA molecules. Here, we review unique aspects of mitochondrial activity and segregation in eggs and early embryos, and how these events play into embryonic developmental competency in the face of advancing maternal age.

Regulation of reproduction and longevity by nutrient-sensing pathways

Nutrients are necessary for life, as they are a crucial requirement for biological processes including reproduction, somatic growth, and tissue maintenance. Therefore, signaling systems involved in detecting and interpreting nutrient or energy levels-most notably, the insulin/insulin-like growth factor 1 (IGF-1) signaling pathway, mechanistic target of rapamycin (mTOR), and adenosine monophosphate-activated protein kinase (AMPK)-play important roles in regulating physiological decisions to reproduce, grow, and age. In this review, we discuss the connections between reproductive senescence and somatic aging and give an overview of the involvement of nutrient-sensing pathways in controlling both reproductive function and lifespan. Although the molecular mechanisms that affect these processes can be influenced by distinct tissue-, temporal-, and pathway-specific signaling events, the progression of reproductive aging and somatic aging is systemically coordinated by integrated nutrient-sensing signaling pathways regulating somatic tissue maintenance in conjunction with reproductive capacity.

Short-term rapamycin treatment increases ovarian lifespan in young and middle-aged female mice

Although age‐related ovarian failure in female mammals cannot be reversed, recent strategies have focused on improving reproductive capacity with age, and rapamycin is one such intervention that has shown a potential for preserving the ovarian follicle pool and preventing premature ovarian failure. However, the application is limited because of its detrimental effects on follicular development and ovulation during long‐term treatment. Herein, we shortened the rapamycin administration to 2 weeks and applied the protocol to both young (8 weeks) and middle‐aged (8 months) mouse models. Results showed disturbances in ovarian function during and shortly after treatment; however, all the treated animals returned to normal fertility 2 months later. Following natural mating, we observed prolongation of ovarian lifespan in both mouse models, with the most prominent effect occurring in mice older than 12 months. The effects of transient rapamycin treatment on ovarian lifespan were reflected in the preservation of primordial follicles, increases in oocyte quality, and improvement in the ovarian microenvironment. These data indicate that short‐term rapamycin treatment exhibits persistent effects on prolonging ovarian lifespan no matter the age at initiation of treatment. In order not to disturb fertility in young adults, investigators should in the future consider applying the protocol later in life so as to delay menopause in women, and at the same time increase ovarian lifespan.

Age-Related Loss of Cohesion: Causes and Effects

Aneuploidy is a leading genetic cause of birth defects and lower implantation rates in humans. Most errors in chromosome number originate from oocytes. Aneuploidy in oocytes increases with advanced maternal age. Recent studies support the hypothesis that cohesion deterioration with advanced maternal age represents a leading cause of age-related aneuploidy. Cohesin generates cohesion, and is established only during the premeiotic S phase of fetal development without any replenishment throughout a female's period of fertility. Cohesion holds sister chromatids together until meiosis resumes at puberty, and then chromosome segregation requires the release of sister chromatid cohesion from chromosome arms and centromeres at anaphase I and anaphase II, respectively. The time of cohesion cleavage plays an important role in correct chromosome segregation. This review focuses specifically on the causes and effects of age-related cohesion deterioration in female meiosis.

Maternal control of early embryogenesis in mammals

Oocyte quality is a critical factor limiting the efficiency of assisted reproductive technologies (ART) and pregnancy success in farm animals and humans. ART success is diminished with increased maternal age, suggesting a close link between poor oocyte quality and ovarian aging. However, the regulation of oocyte quality remains poorly understood. Oocyte quality is functionally linked to ART success because the maternal-to-embryonic transition (MET) is dependent on stored maternal factors, which are accumulated in oocytes during oocyte development and growth. The MET consists of critical developmental processes, including maternal RNA depletion and embryonic genome activation. In recent years, key maternal proteins encoded by maternal-effect genes have been determined, primarily using genetically modified mouse models. These proteins are implicated in various aspects of early embryonic development, including maternal mRNA degradation, epigenetic reprogramming, signal transduction, protein translation and initiation of embryonic genome activation. Species differences exist in the number of cell divisions encompassing the MET and maternal-effect genes controlling this developmental window. Perturbations of maternal control, some of which are associated with ovarian aging, result in decreased oocyte quality.

Oogonial stem cells as a model to study age-associated infertility in women

Fertility is the first biological process to break down during aging, thereby making it a useful tool to understand fundamental processes of aging. Reproductive aging in females is associated with a loss of ovarian function characterised by a reduction in the number and quality of oocytes. The central dogma, namely that females are born with a fixed pool of oocytes that progressively decline with increasing maternal age, has been challenged by evidence supporting postnatal oogenesis in mammals. Reports demonstrating formation of new oocytes from newly discovered germline stem cells, referred to as oogonial stem cells (OSCs), has opened new avenues for treatment of female infertility. In this review we discuss why the OSCs possibly lose their regenerative potential over time, and focus specifically on the aging process in germline stem cells as a possible mechanism for understanding female age-related infertility and how we can slow or delay ovarian aging.

Pre-breeding food restriction promotes the optimization of parental investment in house mice, Mus musculus

Litter size is one of the most reliable state-dependent life-history traits that indicate parental investment in polytocous (litter-bearing) mammals. The tendency to optimize litter size typically increases with decreasing availability of resources during the period of parental investment. To determine whether this tactic is also influenced by resource limitations prior to reproduction, we examined the effect of experimental, pre-breeding food restriction on the optimization of parental investment in lactating mice. First, we investigated the optimization of litter size in 65 experimental and 72 control families (mothers and their dependent offspring). Further, we evaluated pre-weaning offspring mortality, and the relationships between maternal and offspring condition (body weight), as well as offspring mortality, in 24 experimental and 19 control families with litter reduction (the death of one or more offspring). Assuming that pre-breeding food restriction would signal unpredictable food availability, we hypothesized that the optimization of parental investment would be more effective in the experimental rather than in the control mice. In comparison to the controls, the experimental mice produced larger litters and had a more selective (size-dependent) offspring mortality and thus lower litter reduction (the proportion of offspring deaths). Selective litter reduction helped the experimental mothers to maintain their own optimum condition, thereby improving the condition and, indirectly, the survival of their remaining offspring. Hence, pre-breeding resource limitations may have facilitated the mice to optimize their inclusive fitness. On the other hand, in the control females, the absence of environmental cues indicating a risky environment led to “maternal optimism” (overemphasizing good conditions at the time of breeding), which resulted in the production of litters of super-optimal size and consequently higher reproductive costs during lactation, including higher offspring mortality. Our study therefore provides the first evidence that pre-breeding food restriction promotes the optimization of parental investment, including offspring number and developmental success.