Gonadotrophin receptors as rodels for the physiological significance of GPCR dimerisation

Cells communicate to each other by sending and responding to chemical messages. Coordinating this communication is essential for all systems in the body including those controlling reproduction. Here the chemical messages, called hormones, determine the onset of puberty, release of an egg from the ovary or in making sperm and maintenance of early pregnancy. The targeted messages are received when hormones bind to the cell surface through proteins called receptors, which relay the message in to the cell. The group of receptors, which is the focus of our research, are called G protein-coupled receptors (GPCRs), so called due to the mechanism of how these receptors communicate chemical messages in to the cell. Our genes encode for more than 800 different kinds of GPCRs, found throughout the body, with one organ having many different GPCRs. Disrupting the function of these receptors is known to be involved in a number of diseases and disabilities; including cancer, obesity, diabetes, heart disease, depression, Parkinson's Disease and infertility, to name only a few. Although many currently prescribed drugs target some of these receptors, there is a constant demand for drugs where treatments are more specific, have fewer side effects, and that are active for longer. Therefore the goal of this project is to understand how the these receptors are controlled, as this will help us understand how cells communicate and may also be an explanation for diseases where control of these receptors is abnormal. To do this we must first understand how these receptors are activated and controlled by the cell machinery. Once any cell receives external messages that bind to GPCRs, they are activated to relay further signals in to the cell. The cell tightly controls this signalling. One process that has become increasingly appreciated as an important part in determining control of this signalling and in drug specificity is that GPCRs can self associate (homodimerisation) and also interact with distinct GPCRs (heterodimerisation), essentially creating receptors with distinct properties from the homodimer. Many hormones important to reproduction, pregnancy and development also activate GPCRs, such as the receptors for gonadotrophin hormones. Using the GPCRs for gonadotrophin hormones, our recent studies have demonstrated the physiological importance of homodimerisation. Therefore the goal of this project is to understand how dimerisation controls receptor activation in terms of signalling magnitude, duration and specificity. The outcome of this work will help us understand how these clinically and pharmacologically important receptors communicate at a single cell level and in more complex organ systems, such as the ovary, and may also be an explanation for diseases where control of these receptors is abnormal. Furthermore, detailed knowledge of how GPCRs are regulated by dimerisation may provide key information in designing new drugs. These drugs could be highly selective by targeting receptor homo-or heterodimers, which can provide more effective and specific treatments of conditions that require control of gonadotrophin hormone action (e.g. hormone-dependent cancers, infertility, contraception, premature ovarian failure) and applied to a number of other diseases that involve this superfamily of receptors.

It is becoming increasingly apparent that many G protein-coupled receptors (GPCRs) can exist as dimers or higher order oligomers that may provide a mechanism for regulating and/or diversifying cellular signalling at the receptor level. However it is still debated whether monomers or dimers represent the functional signalling unit in vivo. While the majority of in vivo evidence for dimerization has been demonstrated for Class C GPCRs, we have recently provided the first physiological requirement for Class A GPCR dimerisation. Using the receptor for luteinising hormone/chorionic gonadotrophin hormone (LHCGR) as a model GPCR we demonstrated, via functional complementation, that two mutant LHCGRs in transgenic mouse models were able to rescue the male infertility and hypogonadism phenotype of the LHCGR knockout mice. Using the LHCGR, this project will investigate the role of GPCR dimerisation via intermolecular functional complementation as a mode of receptor activation, and to explore how dimerisation affects ligand specificity, signal amplification and diversification of intracellular responses in vivo. We will complement our in vitro molecular approaches with our various LHCGR mouse models to dissect the molecular basis of LHCGR dimerisation, its requirement in female reproductive health, its potential role in vivo for ligand directed signalling (biased agonism) of its hormonal ligands and in regulating signal amplification. We will also examine the potential of LHCGR to heterodimerise with the GPCR for follicle-stimulating hormone (FSHR) as a means of signal diversity or amplification in the mouse ovary. As GPCRs represent the single most common therapeutic target, studies investigating GPCR dimerization, particular such as ours that will use a combination of in vitro and in vivo studies, will be key in the current exploration of dimers as a target in the design of the next generation of novel therapeutic analogs.

Who will benefit from this research? The identified beneficiaries outside of the academic arena include those in industry and commercial sector. New basic science findings in G protein-coupled receptor (GPCR) research are of great interest to those in this sector. Because of the many diseases that GPCRs are implicated, this work could also be of interest to the Health sector and to the general public, either from a general science education benefit, or those who are impacted by disease with which this kind of research would be implicated in. This work has also identified those involved in education as a beneficiary, e.g. in educating and inspiring children into scientific career paths, information resource of public and patient education via the third sector (e.g. Women-for-Women charity, Orchid prostate cancer charity) to the training and skills that will be received by the named posts on this project. The project will also impact veterinarian medicine, which in turn has impact on farming industry and conservation practices, both in the UK and internationally. How will they benefit from this research? GPCRs are the most numerous and diverse family of receptors, responsible for controlling the physiology of the major organ systems. Therefore, GPCRs are an important target for therapeutic intervention and many successful drugs on the market today modulate their activity. The research in this proposal could identify a novel target point or pathway, which could be developed commercially as an assay, used in industry or academic labs or, in identification of small molecule compounds that have a more defined modulation on GPCR dimers. It is also possible to develop the commercial/economical impact level of our research independent of the industry sector. We anticipate this could be initiated during the first half of the award period with current industry collaborators of the PI. If such collaborations are successful this could escalate in to long-term benefits in UK economy from revenue, employment and ultimately in health benefits initially for gonadotrophin-dependent therapies, but could be expanded to other GPCRs in treatment of a number of different diseases. Veterinarians could benefit from our research for assisted reproduction management of domesticated and wild species. The training that the named posts will receive would potentially benefit areas outside of academia by the development of transferable skills that they could then use and benefit in any employment sector. These include key oral and written communication skills, project and time management, problem solving, information technology and mentoring skills. What will be done to ensure that they have the opportunity to benefit from this research? Communication of findings to interested parties is key in developing the impact to industry and health sectors using resources such as established collaborators of the PI at companies such as Organon-Schering-Plough within this sector, seeking new ones via Imperial Business Development and attendance at conferences. Commercial impact of the research could be initially realized via aid of the College's 'Imperial Innovations', which aid with patent development and application to development of spin-out companies and the Drug Discovery centre, part of the UK Drug Discovery Consortium (see Impact plan). Opportunities to develop impacts to health will also be explored by collaborations with clinicians at Queen Charlotte's and Hammersmith Hospitals that our institute has close ties with. In regards to impact on public awareness of health benefits of this research and in Education, we will continue to participate in the IRDB's Open Days to the public and secondary school students, ensure our websites contain summaries (including layman's summaries) of our research and that our publications are open access articles. The named postdoc will be involved in all of these activities as part of her transferable skills training.