Effects of Repeated Ovarian Stimulation on Ovarian Function and Aging in Mice

Impact of repeated ovarian hyperstimulation on the reproductive function

One of six couples (17.5 % of the adult population) worldwide is affected by infertility during their lifetime. This number represents a substantial increase in the prevalence of this gynecological condition over the last decade. Ovulatory dysfunction and anovulation are the main causes of female infertility. Timed intercourse, intrauterine insemination, and assisted reproductive technology (ART), such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), are the most common interventions for infertile couples. Ovulation induction protocols for IVF/ICSI routinely use supraphysiological doses of gonadotropins to stimulate many preovulatory follicles. Animal and human studies suggested that ovarian hyperstimulation, alone or repeatedly, for ART cycles can induce changes in the immune response and increase the oxidative stress (OS) in the ovarian microenvironment. The consequences of repeated ovarian hyperstimulation on the human ovary remain poorly understood, particularly in relation to the effects of ovarian stimulation on the immune system and the potential for ovarian stimulation to cause OS. Animal studies have observed that repeated cycles of ovarian hyperstimulation can accelerate ovarian aging. Changes in ovarian hormone levels, accelerated loss of ovarian reserve, disorders in ovarian ultrastructure, ovarian senescence, and decreased reproductive performance represent possible long-term effects of repeated ovarian hyperstimulation. The short and long-term impact of the combination of antioxidant agents in ovarian hyperstimulation protocols in women undergoing ART must urgently be better understood. The recent increase in the number of ART and fertility preservation cycles may accelerate ovarian aging in these women, promoting consequences beyond the reproductive function and including health deterioration.

Tho2-mediated escort of Nrd1 regulates the expression of aging-related genes

The relationship between aging and RNA biogenesis and trafficking is attracting growing interest, yet the precise mechanisms are unknown. The THO complex is crucial for mRNA cotranscriptional maturation and export. Herein, we report that the THO complex is closely linked to the regulation of lifespan. Deficiencies in Hpr1 and Tho2, components of the THO complex, reduced replicative lifespan (RLS) and are linked to a novel Sir2-independent RLS control pathway. Although transcript sequestration in hpr1Δ or tho2Δ mutants was countered by exosome component Rrp6, loss of this failed to mitigate RLS defects in hpr1Δ. However, RLS impairment in hpr1Δ or tho2Δ was counteracted by the additional expression of Nrd1-specific mutants that interacted with Rrp6. This effect relied on the interaction of Nrd1, a transcriptional regulator of aging-related genes, including ribosome biogenesis or RNA metabolism genes, with RNA polymerase II. Nrd1 overexpression reduced RLS in a Tho2-dependent pathway. Intriguingly, Tho2 deletion mirrored Nrd1 overexpression effects by inducing arbitrary Nrd1 chromatin binding. Furthermore, our genome-wide ChIP-seq analysis revealed an increase in the recruitment of Nrd1 to translation-associated genes, known to be related to aging, upon Tho2 loss. Taken together, these findings underscore the importance of Tho2-mediated Nrd1 escorting in the regulation of lifespan pathway through transcriptional regulation of aging-related genes.

Gonadotropins Regulate the mRNA Expression of Gonadotropin-Releasing Hormone and Its Receptors in the Mouse Ovary and Uterus

Gonadotropin-releasing hormone (GnRH), a critical hormone produced in the hypothalamus, is essential for regulating reproductive processes. It has also been demonstrated the presence of GnRH and its receptors (GnRHR) in ovarian and uterine tissues, but little was known about the regulation mechanism of their expression in these organs and ovarian aging. Therefore, the aim of this study was to investigate the expression of GnRHR in the ovary and uterus of mice, particularly after high-dose gonadotropin treatments and in relation to aging. Quantitative real-time-PCR (qRT-PCR) revealed that pituitary gland had the highest GnRHR expression in both young and aged mice. In addition, liver expression was higher in young mice, whereas thymus expression was higher in aged mice. GnRHR mRNA was present in the ovaries of both young and aged mice but nearly undetectable in the uterus of aged mice. We next examined the expression of GnRHR in the ovary and uterus in response to high-dose administration of pregnant mare serum gonadotropin (PMSG). After PMSG administration, GnRH mRNA levels were significantly decreased in the ovary but increased in the uterus. The expression of GnRH mRNA in these organs showed opposite trends to that of GnRHR expression. These results suggest the involvement of GnRH in age-related reproductive decline and the potential effects of high-dose gonadotropin treatments on reproductive organ function.

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.