Poly(A)-binding proteins highlight the importance of regulated mRNA translation and stability in determining a functional materno-fetal interface

The proteins that make up our cells are encoded by genes that serve as a genetic blueprint. The information stored in genes is expressed, or decoded, to produce proteins by a multi-step process known as gene expression, with one of the critical steps in this pathway being mRNA translation. In order to function properly, cells and organisms need to make proteins at the right time, place and in the correct amount. Thus it is critical that mRNA translation is carefully regulated, with improper control leading to a wide variety of diseases including cancer, metabolic, neurological and reproductive disorders.
Poly(A)-binding protein (PABP) 1 is a central regulator of multiple steps in the gene expression pathway, including mRNA translation. Mammals contain five genes belonging to the PABP family, two of which (PABP1 and PABP4) are produced in many cell types throughout the body. Although PABP1 has been extensively studied, little is known about the potential roles of PABP1, or other family members, in human health. However, we have recently found that an absence of PABP4 severely reduces mammalian fertility. This appears to be due to problems with the mother which lead to fetal death during the later stages of pregnancy. Interestingly, we see that live births are frequently small suggesting growth problems whilst in the womb (intrauterine growth restriction). Poor intrauterine growth predisposes human babies to health problems in adulthood including cardiovascular disease, stroke and type II diabetes. These important observations suggest that we have a unique opportunity to study the underlying causes of a spectrum of pregnancy complications including stillbirth, late miscarriage and intrauterine growth restriction.
Nearly 3 million third-trimester stillbirths occur worldwide each year, with the UK having a higher rate (1 in 200) than almost every other high-income country. Research has shown that stillbirth can be caused by problems with the placenta, the umbilical cord or by infections, although in many cases the reasons why these problems arose is not understood. Moreover, up to 30% of stillbirths have no obvious cause, emphasising the need for research in this area.
Our research aims to shed light on these issues by performing a detailed analysis of the functions and regulatory targets of PABP4, of which little is presently known, and by further investigating the cellular processes that fail to function normally in the absence of PABP4. Importantly, this will be paralleled by an investigation of PABP4 in human reproductive tissues. Taken together this work presents a unique opportunity to understand the pathways and mechanisms that lead to stillbirth and poor intrauterine growth. This forms the first step towards providing answers to couples that suffer such loss, and in the longer term may identify novel prognostic markers for pregnancy failure that could indicate the need for medical intervention. Ultimately it may offer avenues for therapeutic intervention prior to or during pregnancy.

The majority of mammalian mRNAs are now known to be regulated at the level of mRNA translation and/or stability, with dysregulation contributing to a wide range of diseases e.g. metabolic, neurological, and neoplastic disorders. However, the mechanisms of regulation are poorly understood. Poly(A)-binding protein (PABP) 1, the prototypical member of the PABP family, acts as a global determinant of mRNA translation and stability, regulates mRNA-specific translation and is required for miRNA-mediated repression and nonsense-mediated decay. However little is known about the biological roles of this central regulator of gene expression and other family members remain poorly characterised. As an important step toward determining the role of PABPs in human health, we are exploring their biological functions in vivo, focusing on the two widely expressed PABP proteins, PABP1 and PABP4. Intriguingly, PABP4 deficiency results in a specific defect in mammalian pregnancy, revealing a surprising role for maternally expressed PABP4 in fetal growth and viability during mid to late gestation. Thus, we will investigate the cellular and molecular roles of PABP4, define its mRNA targets and also determine the extent to which they overlap with PABP1 to test their functional relatedness. This will involve developmental, cellular, molecular and systems biology (in vivo; ex vivo; in vitro), patient sample analysis and several specialised techniques e.g. translational profiling using deep sequencing, proteomics, longitudinal analysis of pregnancy/placental function using ultrasound analysis/Doppler imaging. This will shed light on the role of misregulated translation/mRNA stability in intrauterine growth restriction, late miscarriage and stillbirth. Stillbirth affects almost 3 million couples annually and our work may provide a molecular diagnosis and be a first step towards pursuing potential therapeutic avenues, as our model relates not to fetal problems but to the biology of the mother.

1. Academic community. The post-doctoral researchers will benefit from working on a multi-disciplinary program (e.g. post-transcriptional control, reproductive biology, systems biology) in a team composed of non-clinical and clinical scientists, and from methodology training that can be applied to other scientific questions in academic, clinical or industrial settings. The PI's laboratory also has a good track record of hosting and training scientists from other laboratories. The results of the proposal, including large datasets, will be of particular interest to, and serve as a resource for, those in the fields of mRNA translation/mRNA stability and reproductive biology. Indeed, the fundamental contribution of post-transcriptional control to almost every aspect of normal physiology, and increasingly in pathophysiology, makes our research relevant to diverse biological problems. Results will be disseminated to non-clinical, clinical and industrial researchers through publication, presentations, via datasets deposited in public databases and, if appropriate, via press releases coordinated through the University of Edinburgh press office (Pathways to Impact). Materials generated during the research will be made available (Academic Beneficiaries and Data Preservation and Sharing).
2. Clinical and pharmacological impact. Stillbirth affects 1:200 births in the UK and the underlying mechanisms are either unknown or poorly understood, representing an unmet clinical need with large societal costs. In particular, the maternal defects (as in the case of PABP4 deficiency) that underlie stillbirth largely remain to be delineated but potentially offer greater scope for intervention than fetal defects. Consequently, in the longer term our results may benefit the clinical community working with families by providing a molecular diagnosis or by developing a marker for screening or novel therapeutic avenues. Our findings may also shed light on the mechanisms of intrauterine growth restriction (a related feature of PABP4 deficient mice), which predisposes babies to health problems in adulthood, including cardiovascular disease, stroke and type II diabetes.
Moreover, by providing insight into the molecular functions, interactomes and targets of the PABP family, our work may also indirectly impact other clinical areas. For instance, PABPs play key roles in host-viral interactions in a wide range of infections and mRNA-specific regulation by PABP-interacting proteins is critical in fertility (affecting 12-15% couples worldwide). Moreover, PABPs are important for nonsense-mediated decay (NMD) and miRNA-mediated regulation, which are associated with a wide variety of human diseases. Understanding fundamental molecular mechanisms is key to the future development of interventions, as demonstrated by clinical trials manipulating the efficiency of the NMD pathway. Our position in the College of Medicine and Veterinary Medicine and the work of the university technology transfer company, ERI, places us an ideal position to exploit clinical/commercial opportunities (see Pathways to Impact for details).
3. Industry: Translational control (mRNA-specific and global) is central to regulating protein synthesis rates and is linked to bulk cell growth in eukaryotes from yeast to humans. Thus understanding regulatory mechanisms can impact a variety of industrial applications including the production of recombinant proteins, and as a result people working within industry keep abreast of developments within this field via scientific literature and international conferences to which the PI's group regularly contributes.
4. Wider community and public engagement. The University has a press office which can disseminate information in a manner suitable to a wide audience, including patient charities. Moreover, the PI has a strong track record in public engagement and it is likely that this research will form the basis for a public lecture (Pathways to Impact and CV)