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Menopause marks the end of a woman’s reproductive lifetime and can have a significant effect on a woman’s quality of life. Menopause naturally occurs at 51 years of age on average, but recent literature suggests that endocrine disrupting chemicals (EDCs) in our environment can accelerate reproductive aging, causing women to reach menopause at earlier ages. This is concerning as menopause can significantly alter a woman’s quality of life and is associated with an increased risk of conditions such as depression, osteoporosis, and cardiovascular disease. EDC exposures have also been associated with more intense menopausal symptoms, making the menopausal transition more difficult for some women. This review highlights the associations between EDC exposure, early menopause, and reproductive aging, using both epidemiological and experimental studies.
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The ovaries play a critical role in female reproductive health because they are the site of oocyte maturation and sex steroid hormone production. The unique cellular processes that take place within the ovary make it a susceptible target for chemical mixtures. Herein, we review the available data regarding the effects of chemical mixtures on the ovary, focusing on development, folliculogenesis, and steroidogenesis. The chemical mixtures discussed include those to which women are exposed to environmentally, occupationally, and medically. Following a brief introduction to chemical mixture components, we describe the effects of chemical mixtures on ovarian development, folliculogenesis, and steroidogenesis. Further, we discuss the effects of chemical mixtures on corpora lutea and transgenerational outcomes. Identifying the effects of chemical mixtures on the ovaries is paramount to preventing and treating mixture-inducing toxicity of the ovary that has long-term consequences such as infertility and ovarian disease.
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Endocrine-disrupting chemicals (EDCs) are exogenous agents with the ability to interfere with processes regulated by endogenous hormones. One such process is female reproductive function. The major reproductive organ in the female is the ovary. Disruptions in ovarian processes by EDCs can lead to adverse outcomes such as anovulation, infertility, estrogen deficiency, and premature ovarian failure among others. This review summarizes the effects of EDCs on ovarian function by describing how they interfere with hormone signaling via two mechanisms: altering the availability of ovarian hormones, and altering binding and activity of the hormone at the receptor level. Among the chemicals covered are pesticides (e.g. dichlorodiphenyltrichloroethane and methoxychlor), plasticizers (e.g. bisphenol A and phthalates), dioxins, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons (e.g. benzo[a]pyrene).
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Mammalian females are endowed with a finite number of primordial follicles at birth or shortly thereafter. Immediately following the formation of the primordial follicle pool, cohorts of these follicles are recruited to begin growth, and this recruitment continues until the primordial follicle population is depleted. Once recruited, a follicle will either grow and ovulate or undergo atresia. Follicle atresia results from the apoptotic death of follicular cells. Members of the BCL-2 family of proteins are important regulators of apoptosis in most cells including in the ovary. Here, we tested the hypothesis that the proapoptotic BAX is an important regulator of follicle survival. We used a variety of histological and biochemical techniques to investigate the impact of Bax deletion on follicle growth and death. We observed that the Bax deletion results in delayed vaginal opening and altered follicular growth. Young adult Bax-deficient ovaries contained increased numbers of primordial follicles and a trend towards reduced numbers of growing follicles. Bax deficiency led to a reduction in average litter size, and also a reduction in the number of oocytes ovulated in response to exogenous gonadotropins. In contrast, Bax deficiency did not alter follicle atresia. In conclusion, BAX appears to be an important regulator of follicle growth, but is dispensable for follicle atresia in mice.
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It is believed that the endowment of primordial follicles in mammalian ovaries is finite. Once follicles are depleted, infertility ensues. Thus, the size of the initial endowment has consequences for fertility and reproductive longevity. Follicular endowment is comprised of various processes that culminate with the incorporation of meiosis-arrested oocytes into primordial follicles. Apoptosis is prominent during follicular endowment, and apoptosis regulatory genes are involved in its regulation. Conflicting data exist with regard to the role of the proapoptotic Bcl-2 associated X protein (BAX) in follicular endowment. Therefore, we investigated the role of BAX during follicular endowment in embryonic and neonatal ovaries. We found that BAX is involved in regulating follicular endowment in mice. Deletion of Bax yields increased oocyte numbers in embryonic ovaries and increased follicle numbers in neonatal ovaries when compared with wild-type ovaries. Increased follicular endowment in Bax−/−ovaries is not due to enhanced germ cell viability. Further, it is not due to an increased primordial germ cell (PGC) allotment, a delay in the onset of meiosis, or altered proliferative activity of oogonia. Instead, our data suggest that the regulatory activity of BAX in follicular endowment likely occurs during PGC migration, prior to PGC colonization of the gonad.
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It is estimated that infertility affects 15–20% of couples and can arise from female or male reproductive defects. Mouse models have ascribed roles to over 100 genes in the maintenance of female fertility. Although previous models have determined roles for apoptosis in male and female fertility, we find that compromised autophagy within the perinatal ovary, through the loss of Becn1 or Atg7, results in the premature loss of female germ cells. Becn1 +/− ovaries have a 56% reduction of germ cells compared with control ovaries at post-natal day 1, whereas Atg7 −/− ovaries lack discernable germ cells at this stage. Thus autophagy appears to be a cell survival mechanism to maintain the endowment of female germ cells prior to establishing primordial follicle pools in the ovary.
