All Your Eggs in One Basket: Mechanisms of Xenobiotic Induced Female Reproductive Senescence

The irreplaceable mammalian primordial follicle represents the basic unit of female fertility, serving as the primary source of all developing oocytes in the ovary. These primordial follicles remain quiescent, often for decades, until recruited into the growing pool throughout a woman's adult reproductive years. Once recruited, <1% will reach ovulation, with the remainder undergoing an apoptotic process known as atresia (Hirshfield, 1991). Menopause, or ovarian senescence, occurs when the pool of primordial follicles becomes exhausted

Maternal Smoke Exposure Impairs the Long-Term Fertility of Female Offspring in a Murine Model.

The theory of fetal origins of adult disease was first proposed in 1989, and in the decades since, a wide range of other diseases from obesity to asthma have been found to originate in early development. Because mammalian oocyte development begins in fetal life it has been suggested that environmental and lifestyle factors of the mother could directly impact the fertility of subsequent generations. Cigarette smoke is a known ovotoxicant in active smokers, yet disturbingly 13% of Australian and 12% of US women continue to smoke throughout pregnancy. The focus of our investigation was to characterize the adverse effects of smoking on ovary and oocyte quality in female offspring exposed in utero. Pregnant mice were nasally exposed to cigarette smoke for 12 wk throughout pregnancy/lactation, and ovary and oocyte quality of the F1 (maternal smoke exposed) generation was examined. Neonatal ovaries displayed abnormal somatic cell proliferation and increased apoptosis, leading to a reduction in follicle numbers. Further investigation found that altered somatic cell proliferation and reduced follicle number continued into adulthood; however, apoptosis did not. This reduction in follicles resulted in decreased oocyte numbers, with these oocytes found to have elevated levels of oxidative stress, altered metaphase II spindle, and reduced sperm-egg interaction. These ovarian and oocyte changes ultimately lead to subfertility, with maternal smoke-exposed animals having smaller litters and also taking longer to conceive. In conclusion, our results demonstrate that in utero and lactational exposure to cigarette smoke can have long-lasting effects on the fertility of the next generation of females

Imetelstat-mediated alterations in fatty acid metabolism to induce ferroptosis as a therapeutic strategy for acute myeloid leukemia

Telomerase enables replicative immortality in most cancers including acute myeloid leukemia (AML). Imetelstat is a first-in-class telomerase inhibitor with clinical efficacy in myelofibrosis and myelodysplastic syndromes. Here, we develop an AML patient-derived xenograft resource and perform integrated genomics, transcriptomics and lipidomics analyses combined with functional genetics to identify key mediators of imetelstat efficacy. In a randomized phase II-like preclinical trial in patient-derived xenografts, imetelstat effectively diminishes AML burden and preferentially targets subgroups containing mutant NRAS and oxidative stress-associated gene expression signatures. Unbiased, genome-wide CRISPR/Cas9 editing identifies ferroptosis regulators as key mediators of imetelstat efficacy. Imetelstat promotes the formation of polyunsaturated fatty acid-containing phospholipids, causing excessive levels of lipid peroxidation and oxidative stress. Pharmacological inhibition of ferroptosis diminishes imetelstat efficacy. We leverage these mechanistic insights to develop an optimized therapeutic strategy using oxidative stress-inducing chemotherapy to sensitize patient samples to imetelstat causing substantial disease control in AML

Xenobiotics; effects on female fertility

Research Doctorate - Doctor of Philosophy (PhD)Over the course of the 20th century there has been an increasing trend in western women opting to delay childbirth in the pursuit of social and economic stability. This development has highlighted the need to identify and characterise ovotoxic xenobiotics (foreign chemical compounds) which threaten their fertility. Arguably the most insidious ovotoxic xenobiotics are those which target the irreplaceable primordial follicle pool for destruction, resulting in pre-mature ovarian senescence. Although many of these xenobiotics have been identified, the molecular mechanisms behind their ovotoxicity remain largely unknown. Employing a neonatal mouse model rich in primordial follicles, the studies presented in this thesis were aimed at characterising the mechanisms of ovotoxicity for six xenobiotics known to target immature follicles (4-vinylcyclohexene diepoxide; Methoxychlor; Menadione; Benzo-a-pyrene, 7,12-Dimethylbenz-[a]anthracene; 3-Methylcholanthrene). The effects of short term xenobiotic exposure on long term oocyte viability were also examined to determine whether follicles which survive ovotoxic destruction were still functionally viable. Microarray analysis and quantitative PCR revealed a unique ovarian response to each xenobiotic involving a number of genes linked to follicular growth/development, cell death and tumorigenesis in vitro. Immunohistological and histomorphological analysis confirmed the microarray data, and revealed a consistent mechanism of ovotoxicity involving primordial follicle activation alongside developing follicle atresia in vitro and in vivo. Immunohistological and pharmacological inhibition studies also revealed an essential role for the PI3K/Akt/mTOR signalling pathways in 3-Methylcholanthrene and 7,12-Dimethylbenz-[a]anthracene induced primordial follicle activation and survival. Studies into the effects of short term neonatal exposure on long term female fertility revealed no difference in the number of healthy oocytes ovulated in neonatally treated adults compared to controls. However, comprehensive oocyte viability analysis revealed a decreased capacity for fertilisation caused by oxidative damage to the oolemma membrane due to mitochondrial electron transport chain leakage. The studies conducted in this thesis have identified a common mechanism of xenobiotic induced primordial follicle depletion via a homeostatic mechanism of developing follicle recruitment, with some ovotoxic xenobiotics inducing primordial follicle survival as opposed to atresia. In addition, the contents of this thesis also provide the first documented evidence of short term neonatal exposure causing long term oocyte dysfunction through xenobiotic induced oxidative stress

Contraception targets in mammalian ovarian development

In the human ovary, early in pre-natal life, oocytes are surrounded by pre-granulosa follicular cells to form primordial follicles. These primordial oocytes remain dormant, often for decades, until recruited into the growing pool throughout a woman’s adult reproductive years. Activation of follicle growth and subsequent development of growing oocytes in pre-antral follicles are major biological checkpoints that determine an individual females reproductive potential. In the past decade, great strides have been made in the elucidation of the molecular and cellular mechanisms underpinning maintenance of the quiescent primordial follicle pool and initiation and development of follicle growth. Gaining an in-depth knowledge of the intracellular signalling systems that control oocyte preservation and follicle activation has significant implications for improving female reproductive productivity and alleviating infertility. It also has application in domestic animal husbandry, feral animal population control and contraception in women

Intracellular signalling during female gametogenesis

Female reproductive potential is dictated by the size of the primordial follicle pool and the correct regulation of oocyte maturation and activation-events essential for production of viable offspring. Although a substantial body of work underpins our understanding of these processes, the molecular mechanisms of follicular and oocyte development are not fully understood. This review summarizes recent findings which have improved our conception of how folliculogenesis and oocyte competence are regulated, and discusses their implications for assisted reproductive techniques. We highlight evidence provided by genetically modified mouse models and <i>in vitro</i> studies which have refined our understanding of Pi3k/Akt and mTOR signalling in the oocyte and have discovered a role for Jak/Stat/Socs signalling in granulosa cells during primordial follicle activation. We also appraise a novel role for the metal ion zinc in the regulation of meiosis I and meiosis II progression through early meiosis inhibitor (Emi2) and Mos-Mapk signalling, and examine studies which expand our understanding of intracellular calcium signalling and extrinsic Plcζ in stimulating oocyte activation