Decoding the role of follicle stimulating hormone in ovarian ageing

Ageing of the ovary is a naturally occurring process that results in changes in the hormones produced and ultimately in the cessation of ovarian function, termed menopause. Ovarian ageing not only results in declining fertility, but also increases the risk of developing several life-changing diseases, e.g., brittle bone disease, heart disease and impaired cognitive functions. This not only impacts on quality of life, but also results in a significant cost burden to the NHS. Despite this, our current understanding of how the ovary ages and what determines the lifespan of the ovary remains limited. Currently there is only one treatment option available for alleviating menopausal symptoms and preventing related diseases, hormone replacement therapy (HRT). However, HRT has a poor sign-up rate due to safety concerns, and according to current guidelines, can only be taken for a maximum of 10 years, due to adverse health risks of long-term HRT. The ability to extend ovarian lifespan offers a new treatment strategy for preventing/delaying such life-changing diseases, eliminating the problems surrounding HRT, and underpins the long-term goal of this project.

Declining ovarian function can be detected by measuring the hormone, follicle stimulating hormone (FSH) in blood samples. FSH is a master controller of ovarian function, promoting the growth and health of ovarian follicles, the oocyte containing spherical cellular structures that provide hormonal support and signals to the growing oocyte. FSH mediates its function by binding to its receptor, FSHR, located on the surface of granulosa cells within the follicles , which generates different signals inside the cell to control the function and fate of the growing ovarian follicle. On the cell surface, FSHR have been shown to associate with each other. For other receptors belonging to the same family as FSHR, termed G protein-coupled receptors, this is an important way of generating different signals inside cells to mediate different physiological responses. Our data supporting this application suggests that this is also the case for FSH, and that changes in FSHR-FSHR association may alter the signals activated inside cells, to modulate ovarian function.

Within the body, FSH is not produced as a single form. Two forms of FSH have been identified, based on the different sugar attachments formed to the structure of FSH. These forms of FSH are termed 'hyper-glycosylated FSH' (FSH24) and 'hypo-glycosylated FSH' (FSH21). FSH21 and FSH24 have been shown to have different potencies, with FSH21 more potent than FSH24 at activated cell signals and at binding to FSHR. Interestingly, the ratios of FSH21:FSH24 detected have been shown to change with age, with high FSH21:24 in young women, and low FSH21:FSH24 in menopausal women. Our studies using granulosa cells isolated from mouse ovaries suggest that the signal responses to FSH21 and FSH24 differ in mice in their reproductive prime versus menopausal mice. We therefore suspect that changes in the ratio of FSH21:FSH24 that occurs with ageing may in part cause the decline in ovarian function observed in the lead up to menopause.

This application will explore how FSH21 and FSH24 regulate ovarian follicle function and signal activation from puberty to menopause. We will also how changes in genes effect the production of FSH21 and FSH24 with age. This will determine how these key hormonal factors that change with age affect ovarian function and ultimately lead to therapeutic strategies to extend ovarian function to improve quality of life and promote healthy ageing.

Ovarian ageing is naturally occurring process, resulting in altered patterns of hormone secretion and physiological changes. Whilst this is synonymous with declining fertility, the development of co-morbidities e.g., osteoporosis, as a result of ovarian ageing impact on quality of life and represent a significant cost to the NHS. Yet, the mechanisms governing ovarian ageing remain poorly defined. The extension of ovarian lifespan offers an alternative therapeutic strategy to delay/prevent such physiological changes.

One of the earliest biomarkers of ovarian ageing is elevated serum follicle stimulating hormone (FSH). Secreted by the anterior pituitary under the control of the hypothalamic-pituitary-ovarian axis, FSH is critical for ovarian function, with FSH inactivating mutations resulting in premature ovarian ageing and infertility. FSH actions are mediated via its ovarian receptor, FSHR, which elicits the activation of multiple signalling pathways to mediate the diverse ovarian actions of FSH/FSHR. In humans, two predominant forms of FSH have been described, hyperglycosylated FSH (FSH24) and hypoglycosylated FSH (FSH21). Interestingly, the production of FSH glycosylation variants changes with age, with high FSH21:FSH24 observed in young women and low FSH21:FSH24 in women of menopausal age. In vitro, FSH21 and FSH24 have very different bioactivities, with FSH21 the more potent agonist. Our pilot data suggests that ovarian signalling responses to FSH21 and FSH24 differ with age, and we suspect that these age-related changes may underpin the decline in ovarian function observed with ageing.

This project will determine how FSH glycosylation impacts on FSHR di/oligomerisation, ovarian signal activation and follicle function across ovarian lifespan. We will also determine how the secretion pattern of FSH21 and FSH24 is altered with age. These approach will highlight therapeutic targets for extending ovarian function and promote women's health and wellbeing.

Outside of the academic arena, there are several groups that the proposed research will benefit.

1. Patients. Premature ovarian ageing affects 1% of women under the age of 40 and is a life-changing diagnosis for many patients. Despite this being a relatively common disorder, our understanding of what cause premature ovarian ageing remains poor. This project will explore how FSH glycosylation impacts on ovarian ageing, and will highlight key mechanisms underpinning the ovarian senescence. From a medium to long term perspective, this program of work, will yield potential therapeutic targets for lengthening ovarian lifespan, something that would have significant impact to this patient group.

2. Clinical practice. Modulation of FSHR activity using FSH analogues is a fundamental part of IVF treatment regimens. Currently a 'one size fits all' approach is taken to IVF protocols, however, this approach doesn't work for all patient groups, especially women over 35, who tend to have a diminished reserve of ovarian follicles, and higher serum FSH. This project will investigate how ovarian responses to FSH glycosylation variants changes with age, and uncover the relative roles of FSH21 and FSH24 through ovarian lifespan. As FSH analogues used in IVF tend to be fully glycosylated (FSH24), this work will shed light on potential new, more efficacious treatment regimens for treating women with a diminished ovarian reserve, from a medium-longer term perspective.

3. Pharmaceutical Industry. The findings of this project will have clear translational findings. Deciphering the impact of FSH glycosylation on ovarian ageing will have the potential for therapeutic interventions for extending ovarian lifespan, thereby delaying the co-morbidities associated with ovarian ageing. These will be deliverable from a long term perspective.

4. Educational. There are multiple educational beneficiaries of this project. From a training perspective, the PDRA will receive training in cutting-edge super resolution imaging, RNAseq and cell biological techniques. Moreover, their involvement in planned public engagement activities (outlined in pathways to impact) and student project supervision will, together with presentation of project findings at conferences and via publication of first author papers in high impact multidisciplinary journals will enhance their career, and enrich the UK workforce with highly trained research scientists. Additionally, this work will be of great benefit to undergraduate and postgraduate students studying at SGUL and Imperial College, particularly those undertaking research projects with the PI and PDRA. This will be deliverable in the short term.