Endocrine alterations and signaling changes associated with declining ovarian function and advanced biological aging in follicle-stimulating hormone receptor haploinsufficient mice

Early menarche and childbirth accelerate aging-related outcomes and age-related diseases: Evidence for antagonistic pleiotropy in humans

Aging can be understood as a consequence of the declining force of natural selection with age. Consistent with this the antagonistic pleiotropic theory of aging suggests that aging results from the trade-offs that promote early growth and reproduction. However, evidence for antagonistic pleiotropy in humans is largely lacking. Using Mendelian Randomization (MR), we demonstrated that later ages of menarche or first childbirth were genetically associated with longer parental lifespan, decreased frailty index, slower epigenetic aging, later menopause, and reduced facial aging. Moreover, later menarche or first childbirth were also genetically associated with a lower risk of several age-related diseases, including late-onset Alzheimer's disease (LOAD), type 2 diabetes, heart disease, essential hypertension, and chronic obstructive pulmonary disease (COPD). We validated the associations between the age of menarche, childbirth, and the number of childbirths with several age-related outcomes in the UK Biobank by conducting regression analysis of nearly 200,000 subjects. Our results demonstrated that menarche before the age 11 and childbirth before 21 significantly accelerated the risk of several diseases, and almost doubled the risk for diabetes, heart failure, and quadrupled the risk of obesity, supporting the antagonistic pleiotropy theory. We identified 128 significant single nucleotide polymorphisms (SNPs) that influenced age-related outcomes, some of which were involved in known longevity pathways, including IGF1, growth hormone, AMPK, and mTOR signaling. Our study also identified higher BMI as a mediating factor in causing the increased risk of certain diseases, such as type 2 diabetes and heart failure, in women with early menarche or early pregnancy, emphasizing the importance of the thrifty gene hypothesis in explaining in part the mechanisms behind antagonistic pleiotropy. Our study highlights the complex relationship between genetic legacies and modern diseases, emphasizing the need for gender-sensitive healthcare strategies that consider the unique connections between female reproductive health and aging.

Paeoniflorin Alleviates Cisplatin-Induced Diminished Ovarian Reserve by Restoring the Function of Ovarian Granulosa Cells via Activating FSHR/cAMP/PKA/CREB Signaling Pathway

Paeoniflorin (PAE) is the main active compound of Radix Paeoniae Rubra (a valuable traditional Chinese medicine and a dietary supplement) and exerts beneficial effects on female reproductive function. However, the actions of PAE on diminished ovarian reserve (DOR, a very common ovarian function disorder) are still unclear. Herein, our study investigated the effect and potential mechanism of PAE on DOR by using cisplatin-induced DOR mice and functional impairment of estradiol (E2) synthesis of ovarian granulosa-like KGN cells. Our data show that PAE improved the estrous cycle, ovarian index, and serum hormones levels, including E2, and the number of antral follicles and corpora lutea in DOR mice. Further mechanism results reveal that PAE promoted aromatase expression (the key rate-limiting enzyme for E2 synthesis) and upregulated the FSHR/cAMP/PKA/CREB signaling pathway in the ovaries. Subsequently, PAE improved the levels of E2 and aromatase and activated the FSHR/cAMP/PKA/CREB signaling pathway in KGN cells, while these improving actions were inhibited by the siRNA-FSHR and FSHR antagonist treatments. In sum, PAE restored the function of E2 synthesis in ovarian granulosa cells to improve DOR by activating the FSHR/cAMP/PKA/CREB signaling pathway, which exhibited a new clue for the development of effective therapeutic agents for the treatment of DOR.

Lack of accelerated ovarian aging in a follicle-stimulating hormone receptor haploinsufficiency model

Follicle-stimulation hormone (FSH) and FSH receptor (FSHR) signaling is essential for lifelong ovarian and endocrine functions in females. Previous studies have reported that Fshr haploinsufficiency in female mice led to accelerated ovarian aging, including anticipated progressive fertility decline, irregular estrus cycles, increased follicular atresia and premature ovarian failure at 7 to 9 months of age. Interestingly, these phenotypes resemble key characteristics of human menopause and thus Fshr haploinsufficiency was proposed as a promising research mouse model of menopause. However, the Fshr haploinsufficiency model had not been fully explored, especially at the molecular level. In this study, we characterized the ovarian and endocrine functions of a Fshr heterozygous knockout allele that was generated on the C57BL/6 genetic background as part of the Knockout Mouse Project (KOMP). Based on our analyses of these mice using a breeding assay, ovarian tissue histology and serum hormone quantifications (i.e. FSH, AMH, INHA) analyses, the KOMP Fshr heterozygous knockout female mice do not show the anticipated phenotypes of ovarian aging in terms of fertility and endocrine function. We further confirmed that the expression of Fshr is unaltered in the ovaries of the KOMP Fshr heterozygous knockout animals compared to wild-type. Together, our data suggests that the KOMP Fshr heterozygous knockout strain does not recapitulate the previously reported ovarian aging phenotypes associated to another model of Fshr haploinsufficiency.

The role of cellular senescence in female reproductive aging and the potential for senotherapeutic interventions

BACKGROUND

Advanced maternal age is associated with decreased oocyte quantity and quality as well as uterine and placental dysfunctions. These changes lead to infertility, pregnancy complications and birth defects in the offspring. As the mean age of giving birth is increasing worldwide, prevention of age-associated infertility and pregnancy complications, along with the more frequent use of ART, become extremely important. Currently, significant research is being conducted to unravel the mechanisms underlying female reproductive aging. Among the potential mechanisms involved, recent evidence has suggested a contributing role for cellular senescence, a cellular state of irreversible growth arrest characterized by a hypersecretory and pro-inflammatory phenotype. Elucidating the role of senescence in female reproductive aging holds the potential for developing novel and less invasive therapeutic measures to prevent or even reverse female reproductive aging and increase offspring wellbeing.

OBJECTIVE AND RATIONALE

The review will summarize the positive and negative implications of cellular senescence in the pathophysiology of the female reproductive organs during aging and critically explore the use of novel senotherapeutics aiming to reverse and/or eliminate their detrimental effects. The focus will be on major senescence mechanisms of the ovaries, the uterus, and the placenta, as well as the potential and risks of using senotherapies that have been discovered in recent years.

SEARCH METHODS

Data for this review were identified by searches of MEDLINE, PubMed and Google Scholar. References from relevant articles using the search terms 'Cellular Senescence', 'Aging', 'Gestational age', 'Maternal Age', 'Anti-aging', 'Uterus', 'Pregnancy', 'Fertility', 'Infertility', 'Reproduction', 'Implant', 'Senolytic', 'Senostatic', 'Senotherapy' and 'Senotherapeutic' where selected. A total of 182 articles published in English between 2005 and 2020 were included, 27 of which focus on potential senotherapies for reproductive aging. Exclusion criteria were inclusion of the terms 'male' and 'plants'.

OUTCOMES

Aging is a major determinant of reproductive wellbeing. Cellular senescence is a basic aging mechanism, which can be exploited for therapeutic interventions. Within the last decade, several new strategies for the development and repurposing of drugs targeting senescent cells have emerged, such as modulators of the anti-inflammatory response, oxidative stress, DNA damage, and mitochondria and protein dysfunctions. Several studies of female reproductive aging and senotherapies have been discussed that show promising results for future interventions.

WIDER IMPLICATIONS

In most countries of the Organization for Economic Co-operation and Development, the average age at which women give birth is above 30 years. Currently, in countries such as the Netherlands, Australia, Spain, Finland, Germany and the UK, birth rates among 30- to 34-year-olds are now higher than in any other age groups. This review will provide new knowledge and scientific advancement on the senescence mechanisms during female reproductive aging, and benefit fundamental and clinical scientists and professionals in the areas of reproduction, cancer, immunobiology and fibrosis.

Mtor inhibition by INK128 extends functions of the ovary reconstituted from germline stem cells in aging and premature aging mice

Stem cell transplantation has been generally considered as promising therapeutics in preserving or recovering functions of lost, damaged, or aging tissues. Transplantation of primordial germ cells (PGCs) or oogonia stem cells (OSCs) can reconstitute ovarian functions that yet sustain for only short period of time, limiting potential application of stem cells in preservation of fertility and endocrine function. Here, we show that mTOR inhibition by INK128 extends the follicular and endocrine functions of the reconstituted ovaries in aging and premature aging mice following transplantation of PGCs/OSCs. Follicular development and endocrine functions of the reconstituted ovaries by transplanting PGCs into kidney capsule of the recipient mice were maintained by INK128 treatment for more than 12 weeks, in contrast to the controls for only about 4 weeks without receiving the mTOR inhibitors. Comparatively, rapamycin also can prolong the ovarian functions but for limited time. Furthermore, our data reveal that INK128 promotes mitochondrial function in addition to its known function in suppression of immune response and inflammation. Taken together, germline stem cell transplantation in combination with mTOR inhibition by INK128 improves and extends the reconstituted ovarian and endocrine functions in reproductive aging and premature aging mice.

Functional assessments through novel proteomics approaches: Application to insulin/IGF signaling in neurodegenerative disease'

BACKGROUND

Events that instigate disease may involve biochemical events distinct from changes in the steady-state levels of proteins. Even chronic degenerative disorders appear to involve changes such as post-translational modifications.

NEW METHOD

We have begun a series of proteomics analyses on proteins that have been fractionated by functional status. Because Alzheimer's disease (AD) is associated with metabolic perturbations such as Type-2 diabetes, fractionation hinged on binding to phosphatidylinositol trisphosphate (PIP3), key to insulin/insulin-like growth factor signaling. We compared mice on normal chow to counterparts subjected to diet-induced obesity (DIO) or to mice expressing human Aβ1-42 from a transgene.

RESULTS

The prevailing phenotypic finding in either experimental group was loss of PIP3 binding. Of the 1228 proteins that showed valid PIP3 binding in any group of mice, 55% exhibited a significant quantitative difference in the number of spectral counts as a function of DIO, 63% as function of the Aβ transgene, and 79% as a function of either variable. There was remarkable overlap among the proteins altered in the two experimental groups, and pathway analysis indicated effects on proteostasis, apoptosis, and synaptic vesicles.

COMPARISON WITH EXISTING METHODS

Most proteomics approaches only identify differences in the steady-state levels of proteins. Our overlay of a functional distinction permits new levels of discovery that may achieve novel insights into physiology in an unbiased and inclusive manner.

CONCLUSIONS

Proteomics analyses have revolutionized the discovery phase of biomedical research but are conventionally limited in scope. The creative use of fractionation prior to proteomic discovery is likely to provide important insights into AD and related disorders.

Steroidogenic effect of Erxian decoction for relieving menopause via the p-Akt/PKB pathway in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Erxian decoction (EXD), an empirical Chinese medicine formula, is effectively used in the clinical treatment of menopause-related symptoms in China. Previous data from our group show that EXD has steroidogenic effect on natural menopausal Sprague-Dawley-rats (SD-rats) as an animal model of menopause. However, the mechanistic studies on steroidogenic effects of EXD are still inadequate. Hence, the mechanisms of steroidogenic effects of EXD were studied in vitro and in vivo in this study.

MATERIALS AND METHODS

Menopause causes a decline of endocrine function and a series of symptoms. In this study, 16-20-month-old female SD rats with a low serum estradiol level were employed. Their endocrine functions after treatment with EXD (4.1g/kg) were assessed by determination of their serum estradiol level. Proteins involved in the steroidogenic pathway including StAR, 17βHSD, 3βHSD, aromatase, and activation of phosphorylated Protein Kinase B (p-Akt/PKB), as well as estradiol receptor proteins (ERα & ERβ) after EXD treatment were analyzed. Kinase inhibition assay was conducted to confirm the mechanism of steroidogenic effects of EXD in vitro. MCF-7 and BT-483 cells were used to investigate whether EXD stimulated breast cancer cell proliferation.

RESULTS

Results revealed a significantly ameliorated serum estradiol level, and a significantly increased expression of ovarian aromatase and PKB in the EXD-treated rats. EXD attenuated 17β-estradiol stimulated proliferation of breast cancer cells.

CONCLUSIONS

The results obtained from immunoblotting and measurements of serum estradiol level of the present investigation revealed that EXD may relieve the menopausal syndrome through an upregulation of ovarian aromatase and p-PKB expression without stimulating the growth of breast cancer cells.

Follicular fluid Aβ40 concentrations may be associated with ongoing pregnancy following in vitro fertilization

PURPOSE

To determine whether Aβ40 levels in the follicular fluid (FF) of infertile women undergoing IVF demonstrate a relationship with IVF cycle parameters and outcome.

METHODS

FF Aβ40 levels were compared between patients achieving ongoing pregnancy and those with unsuccessful cycles. Clinical data such as ongoing pregnancy rate, implantation rate, number of oocytes retrieved, number of 8 cells embryos with ≤5 % fragmants, ratio of 8 cells embryos with ≤5 % fragmants to total embryos per patient and cleavage rate were compared among three percentile groups of Aβ40. CCK-8 method was used to measure the effect of Aβ40 on rat granulosa cells proliferation in vitro. RT-PCR was used to detect the mRNA expression levels of steroidogenesis related genes.

RESULTS

Patients achieving ongoing pregnancy (n = 26; 50.98%) demonstrated significantly higher FF Aβ40 levels compared to those with unsuccessful cycles (n = 25; 49.02%; P = 0.024). No significant differences were observed in APP (amyloid precursor protein) and its other proteolysis products including sAPPα, sAPPβand Aβ 42 between the two groups. Statistically significant differences between the three percentile groups of Aβ 40 were observed only in the implantation rates and ongoing pregnancy rates. There were no statistically significant differences between the three percentile groups in the age, No. oocytes retrieved, No. 2 pronucleus, No. embryos transferred, No. 8 cells embryos with ≤5% fragmants and cleavage rate. Significantly negative correlation exists between APP and AFC (antral follicle count) (R =-0.360, P = 0.005) and oocytes retrieved (R =-0.378, P = 0.004). There were also significantly positive correlations between Aβ40 and Aβ42 (R = 0.407, P = 0.000), between AFC and oocytes retrieved (R = 0.476, P = 0.000). Rat granulosa cells treated with Aβ40 of different concentrations have improved their proliferative ability. Cells treated with 200 pg/ml Aβ40 have the strongest ability of proliferation. 200 pg/ml Aβ40 enhanced the expression of key molecules during steroidogenesis such as IGF-1,IGF-1receptor (IGF-1R),FSH receptor (FSHR),P450 aromatase (P450arom),steroidogenic acute regulatory protein (StAR) and cholesterol side-chain cleavage cytochromes P450(P450scc).

CONCLUSIONS

Aβ40 levels in follicle fluid may be associated with ongoing pregnancy and the moderate expression level of Aβ40 is important for oocytes and embryos development.

Primary ovarian insufficiency

Primary ovarian insufficiency is a subclass of ovarian dysfunction in which the cause is within the ovary. In most cases, an unknown mechanism leads to premature exhaustion of the resting pool of primordial follicles. Primary ovarian insufficiency might also result from genetic defects, chemotherapy, radiotherapy, or surgery. The main symptom is absence of regular menstrual cycles, and the diagnosis is confirmed by detection of raised follicle-stimulating hormone and declined oestradiol concentrations in the serum, suggesting a primary ovarian defect. The disorder usually leads to sterility, and has a large effect on reproductive health when it arises at a young age. Fertility-preservation options can be offered to some patients with cancer and those at risk of early menopause, such as those with familial cases of primary ovarian insufficiency. Long-term deprivation of oestrogen has serious implications for female health in general; and for bone density, cardiovascular and neurological systems, wellbeing, and sexual health in particular.

Biological versus chronological ovarian age: implications for assisted reproductive technology

BACKGROUND

Women have been able to delay childbearing since effective contraception became available in the 1960s. However, fertility decreases with increasing maternal age. A slow but steady decrease in fertility is observed in women aged between 30 and 35 years, which is followed by an accelerated decline among women aged over 35 years. A combination of delayed childbearing and reduced fecundity with increasing age has resulted in an increased number and proportion of women of greater than or equal to 35 years of age seeking assisted reproductive technology (ART) treatment.

METHODS

Literature searches supplemented with the authors' knowledge.

RESULTS

Despite major advances in medical technology, there is currently no ART treatment strategy that can fully compensate for the natural decline in fertility with increasing female age. Although chronological age is the most important predictor of ovarian response to follicle-stimulating hormone, the rate of reproductive ageing and ovarian sensitivity to gonadotrophins varies considerably among individuals. Both environmental and genetic factors contribute to depletion of the ovarian oocyte pool and reduction in oocyte quality. Thus, biological and chronological ovarian age are not always equivalent. Furthermore, biological age is more important than chronological age in predicting the outcome of ART. As older patients present increasingly for ART treatment, it will become more important to critically assess prognosis, counsel appropriately and optimize treatment strategies. Several genetic markers and biomarkers (such as anti-Müllerian hormone and the antral follicle count) are emerging that can identify women with accelerated biological ovarian ageing. Potential strategies for improving ovarian response include the use of luteinizing hormone (LH) and growth hormone (GH). When endogenous LH levels are heavily suppressed by gonadotrophin-releasing hormone analogues, LH supplementation may help to optimize treatment outcomes for women with biologically older ovaries. Exogenous GH may improve oocyte development and counteract the age-related decline of oocyte quality. The effects of GH may be mediated by insulin-like growth factor-I, which works synergistically with follicle-stimulating hormone on granulosa and theca cells.

CONCLUSION

Patients with biologically older ovaries may benefit from a tailored approach based on individual patient characteristics. Among the most promising adjuvant therapies for improving ART outcomes in women of advanced reproductive age are the administration of exogenous LH or GH.

A novel mechanism: Erxian Decoction, a Chinese medicine formula, for relieving menopausal syndrome

ETHNOPHARMACOLOGICAL RELEVANCE

Many clinical and experimental reports demonstrated that Erxian Decoction (EXD) was effective in relieving menopausal syndrome.

AIM OF THE STUDY

The mechanisms of action of EXD were explored on the endocrine and antioxidant regimen.

MATERIALS AND METHODS

Menopause causes a decline in both endocrine function and activities of antioxidant enzymes. In this study, 12-month-old female Sprague-Dawley-rats (SD-rats) with a low serum estradiol level were employed. Their endocrine functions after treatment with EXD were assessed by the determination of their serum estradiol level and ovarian mRNA levels of aromatase, which is a key enzyme for biosynthesis of estradiol. Meanwhile, superoxide dismutase-1 (SOD), catalase (CAT) and glutathione peroxidase (GPx-1) in the liver were also determined to assess the effect of EXD on the antioxidant regimen.

RESULTS

Results revealed a significant elevation in serum estradiol level and the mRNA level of ovarian aromatase and liver CAT in the EXD-treated menopausal rat model.

CONCLUSIONS

The results obtained from mRNA and estradiol level of the present investigation revealed that the EXD relieves the menopausal syndrome involved an increase of endocrine and antioxidant function through, at least, the activation of aromatase and CAT detoxifying pathways.

Altered ovarian function affects skeletal homeostasis independent of the action of follicle-stimulating hormone

Osteoporosis is a leading public health problem. Although a major cause in women is thought to be a decline in estrogen, it has recently been proposed that FSH or follitropin is required for osteoporotic bone loss. We examined the FSH receptor null mouse (FORKO mouse) to determine whether altered ovarian function could induce bone loss independent of FSH action. By 3 months of age, FORKO mice developed age-dependent declines in bone mineral density and trabecular bone volume of the lumbar spine and femur, which could be partly reversed by ovarian transplantation. Bilateral ovariectomy reduced elevated circulating testosterone levels in FORKO mice and decreased bone mass to levels indistinguishable from those in ovariectomized wild-type controls. Androgen receptor blockade and especially aromatase inhibition each produced bone volume reductions in the FORKO mouse. The results indicate that ovarian secretory products, notably estrogen, and peripheral conversion of ovarian androgen to estrogen can alter bone homeostasis independent of any bone resorptive action of FSH.

Normalization of hormonal imbalances, ovarian follicular dynamics and metabolic effects in follitrophin receptor knockout mice

Genetically modified follitrophin receptor knockout female mice with total FSH-receptor (FSH-R) deletion are sterile and their combined estrogen deficiency-hyperandrogenemic status provides an experimental paradigm to study the effect of hormonal imbalances on ovarian function and metabolic alterations. Elevated LH levels causing hyperandrogenemia perturb normal folliculogenesis. To control diverse pathophysiology associated with hormonal imbalances, we investigated the effects of transplanting a single normal mouse ovary in young mutants. An intact FSH-R signalling system in the graft responded promptly to the up-regulated pituitary gonadotrophins circulating in the host mutant. Resumption of regular estrous cycles validated stimulation of uterine functions. Secretions from the viable functioning grafts partially corrected follicular abnormalities originally present in host ovaries. Stromal hyperplasia responsible for high ovarian LH-receptor and key enzymes in host thecal/interstitial complex and hyperandrogenemia was reduced in host ovaries. Increases in plasma estradiol and reduced LH and free testosterone re-established the negative-feedback system. Reduced android obesity and activation of mammary glands indicated the combined beneficial effects of normalized steroid hormones on target organs. These data provide evidence that ovarian transplantation in mutants corrects estrogen loss and hyperandrogenemia. However, correction of hormonal imbalances is not sufficient to fully restore effects of FSH-R loss in host granulosa cells.

Sympathetic pharmacological denervation in ageing rats: effects on ovulatory response and follicular population

The present study analyses the participation of ovarian innervation during reproductive senescence. We use the model of acute peripheral pharmacological sympathetic denervation with guanethidine in young (3 months old), middle-aged (12 months old) or old (18 months old) rats with spontaneous or induced ovulation. Ovarian levels of norepinephrine (NE) were measured by HPLC and the oestrous cycle, the number of ovulating animals and the percentage of atretic follicles were also assessed. Aged animals showed a progressive reduction in ovulatory capacity and an increase in ovarian NE content. Acute denervation increased the percentage of healthy follicles in 12- and 18-month-old rats compared with control adult animals. Combined treatment of denervation plus stimulation with gonadotrophins doubled the number of ova shed in young adult rats and restablished a partial ovulation in 12-month-old rats. The results suggest that ovarian noradrenergic innervation plays a modulator role in ovarian physiology during the ageing ovary process. The action of ovarian noradrenergic innervation seems to be associated with folliculogenesis and the ovarian response to gonadotrophins.

Ovarian follicle development and transgenic mouse models

Ovarian follicle development is a complex process that begins with the establishment of what is thought to be a finite pool of primordial follicles and culminates in either the atretic degradation of the follicle or the release of a mature oocyte for fertilization. This review highlights the many advances made in understanding these events using transgenic mouse models. Specifically, this review describes the ovarian phenotypes of mice with genetic mutations that affect ovarian differentiation, primordial follicle formation, follicular growth, atresia, ovulation and corpus luteum (CL) formation. In addition, this review describes the phenotypes of mice with mutations in a variety of genes, which affect the hormones that regulate folliculogenesis. Because studies using transgenic animals have revealed a variety of reproductive abnormalities that resemble many reproductive disorders in women, it is likely that studies using transgenic mouse models will impact our understanding of ovarian function and fertility in women.

Effect of duration of dosing on onset of ovarian failure in a chemical-induced mouse model of perimenopause

OBJECTIVE

Repeated daily dosing with 4-vinylcyclohexene diepoxide (VCD) causes gradual ovarian failure in mice. As a result, the animal undergoes ovarian failure, but retains residual ovarian tissue. The purpose of this study was to use a mouse model to regulate the induction of a period analogous to perimenopause in women.

DESIGN

Female B6C3F1 mice (28 days old; n = 8) were dosed daily for 10 or 20 days with VCD (160 mg/kg/d) or sesame oil. The animals were evaluated for reproductive function on days 10, 20, 35 after the onset of dosing, and on the day of follicle depletion. Each animal was killed at the specified time points, and ovaries, uteri, and plasma were collected.

RESULTS

VCD reduced (P < 0.05) the number of primordial (by 93.2%) and primary (by 85.1%) follicles after 10 days of dosing, whereas essentially all primordial and primary follicles were lost (P < 0.05) after 20 days of dosing. The average time to ovarian failure was on day 135 for 10-day-dosed mice and on day 52 for 20-day-dosed mice. Follicle-depleted mice in both groups had decreased (P < 0.05) ovarian and uterine weights. Circulating follicle-stimulating hormone levels were increased (P < 0.05) on day 44 after the onset of dosing in 10-day-dosed mice and on day 35 in 20-day-dosed mice.

CONCLUSION

These results demonstrate that ovarian failure can be caused by VCD more rapidly if repeated daily dosing occurs for a longer period. Thus, the length of time leading up to ovarian failure (model for perimenopause) can be adjusted by varying the length of exposure.

Oxidative damage and age-related functional declines

Most organisms experience progressive declines in physiological function as they age. Since this senescence of function is thought to underlie the decrease in quality of life in addition to the increase in susceptibility to disease and death associated with aging, identifying the mechanisms involved would be highly beneficial. One of the leading mechanistic theories for aging is the oxidative damage hypothesis. A number of studies in a variety of species support a strong link between oxidative damage and life span determination. The role of oxidative damage in functional senescence has also been investigated, albeit not as comprehensively. Here, we review these investigations. Several studies show that the age-related loss of a number of functions is associated with an accrual of oxidative damage in the tissues mediating those functions. Additionally, treatments that increase the accumulation of oxidative damage with age frequently exacerbate functional losses. Moreover, treatments that reduce the accumulation of oxidative damage often attenuate or delay the loss of function associated with aging. These data provide the foundation for a link between oxidative damage and functional senescence, thereby supporting the oxidative damage hypothesis of aging within the context of age-related functional decline.

Ovarian aging and menopause: current theories, hypotheses, and research models

Aging of the reproductive system has been studied in numerous vertebrate species. Although there are wide variations in reproductive strategies and hormone cycle components, many of the fundamental changes that occur during aging are similar. Evolutionary hypotheses attempt to explain why menopause occurs, whereas cellular hypotheses attempt to explain how it occurs. It is commonly believed that a disruption in the hypothalamic-pituitary-gonadal axis is responsible for the onset of menopause. Data exist to demonstrate that the first signs of menopause occur at the level of the brain or the ovary. Thus, finding an appropriate and representative animal model is especially important for the advancement of menopause research. In primates, there is a gradual decline in the function of the hypothalamic-pituitary-gonadal (HPG) axis ultimately resulting in irregularities in menstrual cycles and increasingly sporadic incidence of ovulation. Rodents also exhibit a progressive deterioration in HPG axis function; however, they also experience a period of constant estrus accompanied by intermittent ovulations, reduced progesterone levels, and elevated circulating estradiol levels. It is remarkable to observe that females of other classes also demonstrate deterioration in HPG axis function and ovarian failure. Comparisons of aging in various taxa provide insight into fundamental biological mechanisms of aging that could underlie reproductive decline.

Bovine model for the study of reproductive aging in women: follicular, luteal, and endocrine characteristics

At present, there is no well-characterized animal model to study the effects of aging on fertility in women. The objectives of the study were to characterize age-related changes in ovarian and endocrine functions in old cows and to investigate the validity of a bovine model for the study of human reproductive aging. We tested the hypotheses that aging in cattle is associated with 1) elevated concentrations of gonadotropins and reduced concentrations of steroid hormones in systemic circulation and 2) increased recruitment of ovarian follicles during wave emergence. Daily ultrasonography was performed in 13- to 14-yr-old cows (n = 10) and their 1- to 4-yr-old daughters (n = 9) for one interovulatory interval to study ovarian function. Plasma samples were obtained every 12 h for determination of FSH, LH, progesterone, and estradiol concentrations. Circulating FSH concentrations were higher (P = 0.009) during follicular waves in old cows than in their daughters, but the number of 4- to 5-mm follicles recruited into a wave was lower (P = 0.04) in old cows. Plasma LH concentrations did not differ between groups (P = 0.4), but the ovulatory follicle in two-wave cycles was smaller in old cows (P = 0.04). Plasma estradiol concentrations were higher (P = 0.01) in old cows, and luteal phase progesterone tended to be lower (P = 0.1). We conclude that these changes are consistent with those reported for women approaching menopause transition. Therefore, our results validate the use of the bovine model to study reproductive aging in women.

Perspectives on reproductive senescence and biological aging: studies in genetically altered follitropin receptor knockout [FORKO] mice

Increased life expectancy leads to increased age-associated health issues in both sexes. For menopausal women the most important of these appear to result from the severe estrogen deficiency caused by ovarian dysfunction. The consequences among others include hot flashes, osteoporosis, obesity, impaired memory, higher incidence of Alzheimer's disease and cardiovascular disease. Ovarian function and steroidogenesis are influenced by pituitary gonadotropins, including follicle-stimulating hormone (FSH), whose actions are mediated through ovarian receptors. This article highlights our recent data pertinent to aging as derived from a novel genetically modified animal model [the FORKO mouse (FOllitropin Receptor KnockOut) lacking the FSH receptor. FORKO female mice experience a chronic depletion of estrogen (E2) from early development, and have phenotypes similar to aging women, with ovarian failure, obesity, skeletal changes, and ovarian tumors. A variety of findings support the conclusion that E2 deficiency in FORKO mice is responsible for their neural impairments associated with glial cell hypertrophy, region-specific brain cells loss, and abnormal behavior. Findings from mice with FSH receptor haploinsufficiency mice ('menopausal mice') are also shedding light on the molecular basis of menopausal conditions that include degeneration of the hippocampus. Many phenotypes noted in the null condition also occur in +/- females but in an age related manner. Thus, the FORKO mouse becomes an excellent model to investigate mechanisms underlying age-related changes especially when these events are accelerated, as in menopausal women. Opportunities abound to assess the potential benefits/adverse effects of hormone replacement regimen on various targets.

Downregulation of Follicle-Stimulating Hormone (FSH)-Receptor Messenger RNA Levels in the Hamster Ovary: Effect of the Endogenous and Exogenous FSH1

Although gonadotropins have been reported to downregulate FSH-receptor (FSHR) mRNA levels in the ovaries of female rats, the effect of the gonadotropin surge, particularly FSH, on hamster follicular FSHR mRNA levels warrants further examination. The objectives of the present study were to clone and determine the complete FSHR cDNA sequence of the hamster and to delineate the effects of endogenous and exogenous FSH on the steady-state levels of ovarian FSHR mRNA. Complete FSHR cDNA was derived from hamster ovarian total RNA by the strategy of 3'- and 5'-rapid amplification of cDNA ends. Ovaries were obtained before and after the endogenous gonadotropin surge or exogenous FSH administration, and the steady-state levels of FSHR mRNA were assessed by Northern blot hybridization. Cloned FSHR cDNA consists of a reading frame corresponding to exons 1-10 of the human FSHR gene and the 5'- and 3'-untranslated regions. The nucleic acid and amino acid sequences of the reading frame were at least 87% and 92% identical, respectively, to that of human, rat, and mouse FSHR. Furthermore, the amino acid sequence contained seven transmembrane domains characteristic of the FSHR. The steady-state levels of FSHR mRNA increased from estrus (Day 1) to reach a peak on proestrus (Day 4) noon; however, significant attenuation was noted following the gonadotropin surge, which was blocked by phenobarbital. Exogenous FSH also downregulated, both dose- and time-dependently, ovarian FSHR mRNA levels. These data indicate that the nucleic acid sequence of hamster FSHR has been identified and that FSH modulates FSHR mRNA levels in the hamster ovary.

Developmental and molecular aberrations associated with deterioration of oogenesis during complete or partial follicle-stimulating hormone receptor deficiency in mice

Targeted disruption of the mouse FSH receptor gene (FSH-R) that mediates the action of the FSH results in a gene dose-related ovarian phenotype in the developing as well as the adult animal. While null females (FORKO) are sterile, the haplo-insufficient mice experience early reproductive senescence. The purpose of this study was to first record changes in oocyte development in the null FORKO and haplo-insufficient mice. Oocyte growth is significantly retarded in the null mutants with thinner zona pellucida in preantral follicles, but thicker zona pellucida in secondary follicles. This morphometric change indicates developmental aberrations in coordination of the germ cell (oocyte) and the somatic granulosa cell (GC) compartments. Markers for primordial germ cell proliferation and oocyte growth, such as the c-Kit/Kit-ligand and bone morphogenetic protein-15 (BMP-15) were downregulated in both null and +/- ovaries, suggesting disrupted communication between oocyte and GCs. Extensive changes in the expression of other oocyte-specific gene products like the zona pellucida glycoproteins (zona pellucida A, B, and C) indicate major alteration in the extracellular matrix surrounding the germ cells. This led to leaky germ cells that allowed infiltration of somatic cells. These results show that the loss of FSH-R signaling alters the follicular environment, where oocyte-granulosa interactions are perturbed, creating an out-of-phase germ cell and somatic cell development. We believe that these data provide an experimental paradigm to explore the mechanisms responsible for preserving the structural integrity and quality of oocytes at different ages.

GCNF-dependent repression of BMP-15 and GDF-9 mediates gamete regulation of female fertility

To determine the function of germ cell nuclear factor (GCNF) in female reproduction, we generated an oocyte-specific GCNF knockout mouse model (GCNF(fl/fl)Zp3Cre(+)). These mice displayed hypofertility due to prolonged diestrus phase of the estrous cycle and aberrant steroidogenesis. These reproductive defects were secondary to a primary defect in the oocytes, in which expression of the paracrine transforming growth factor-beta signaling molecules, bone morphogenetic protein 15 (BMP-15) and growth differentiation factor 9 (GDF-9), were up-regulated in GCNF(fl/fl)Zp3Cre(+) females at diestrus. This was a direct effect of GCNF, as molecular studies showed that GCNF bound to DR0 elements within the BMP-15 and GDF-9 gene promoters and repressed their reporter activities. Consistent with these findings, abnormal double-oocyte follicles, indicative of aberrant BMP-15/GDF-9 expression, were observed in GCNF(fl/fl)Zp3Cre(+) females. The Cre/loxP knockout of GCNF in the oocyte has uncovered a new regulatory pathway in ovarian function. Our results show that GCNF directly regulates paracrine communication between the oocyte and somatic cells by regulating the expression of BMP-15 and GDF-9, to affect female fertility.

The menopausal mouse: a new neural paradigm of a distressing human condition

Progressive and long-term sex hormone imbalance in the FSH-R haploinsufficient menopausal mouse leads to degenerative changes in the CNS associated with increased anxiety. The brain region most affected by aging in these mice is the hippocampus. Choline acetyltransferase (ChAT) enzymatic activity and synapsin immunoreactivity are reduced at 20 months of age. Neurons in the dentate gyrus show signs of progressive degenerative changes, hypertrophy and glyosis, and subsequent cell shrinkage and death. These results suggest that the menopausal mouse mimics degenerative changes in the hippocampus of hormonally imbalanced aging humans. We propose using this animal model to test the effectiveness of potential therapeutics in paradigms of accelerated aging.

Emergence of uterine pathology during accelerated biological aging in FSH receptor-haploinsufficient mice

A fully functional FSH receptor (Fshr) is required for ovarian follicular development and fertility. Fshr null females are sterile because of failure of follicular maturation, ovulation, and estrogen deficiency. Because Fshr-haploinsufficient females also begin to show age-dependent reproductive deficits that mimic biological aging, we have investigated the changes that occur in the uterus of these mice. The uterine weight in 12-month-old Fshr +/- mice increased 2-fold, and most retired breeders (those that stopped breeding earlier than our wild-type females) developed unilateral uterine masses that appeared similar to several abnormalities that also occur in women and associated with infertility. Curiously, there was a tendency for most of the abnormality to occur in the right horn. Up to 25% of the virgin Fshr-haploinsufficient mice also developed pathology. These transformations were not present in either wild-type mice or the estrogen-deficient Fshr null females at any age. In haploinsufficient females, estrogen and progesterone were reduced and testosterone was elevated in circulation by 1 yr. Fshr-haploinsufficient mice developed an imbalance of progesterone receptor isoforms A and B in the uterus. This alteration of progesterone receptors along with an increase in LH receptors in the uterus may contribute to the induction of high frequency of uterine pathology. Angiogenesis, vascular abnormality, and adenomyosis appeared to be increased in the uterine horn bearing pathological mass. The Fshr-haploinsufficient mice might help in understanding the molecular basis of induction of uterine pathology and tissue patterning.

Haploinsufficiency of the follicle-stimulating hormone receptor accelerates oocyte loss inducing early reproductive senescence and biological aging in mice

Female mice that are null for the FSH-receptor (FSH-R) gene are estrogen deficient, acyclic, and sterile. However, the heterozygous (+/-) mice initially have reduced fertility and stop breeding by 7-9 mo. The purpose of this study was to understand the basis of reduced fertility in mice with haploinsufficiency of the FSH-R. Heterozygous females were compared to +/+ females at 3, 7, and 12 mo of age. By 7 mo most of the +/- females were acyclic and <50% delivered pups. The wild-type females were normal in these respects. None of the 1-yr-old +/- females gave viable offspring (73% in +/+). Many degenerative changes, including atresia and apoptosis, and profound loss of oocytes, were apparent in +/- mice by 7 mo. The 1-yr-old +/- ovary had very few follicles and consisted mostly of fibroid tissue and cysts. Our data support the hypothesis that reproductive deficits in +/- FSH-R mice occur because of accelerated oocyte loss due to increased cell death in the ovary. These events contribute to early reproductive senescence and biological aging in mice. Thus FSH-R status is an important determinant of ovarian aging and all phenomena that arise from subsequent estrogen deficiency and other aberrations.