Does PABP4 control diet-induced obesity, by acting as a master regulator of metabolism-related gene expression?

Obesity is a major problem world-wide with 1 in 3 adults being overweight and 1 in 8 obese, equating to >600 million people worldwide. This growing epidemic of obesity represents a massive and rapidly growing health and economic burden for the UK (62.9% of adults in England were overweight or obese in 2015, an increase of 14.9% since 1993), as obesity is associated with serious health issues such as type 2 diabetes, heart disease and stroke. Moreover, there is growing evidence that obesity in pregnant women can affect the lifelong health of their babies, increasing their risk of becoming obese and having cardiovascular disease. This increase in obesity is driven largely by the increasing adoption of a so-called "Western diet" that is high in calories.

However, it is also clear that not everyone on high calorie diets will become obese. This suggests that both diet (environment) and the "genetic make-up" of individuals contribute to their body composition (i.e. fat versus lean mass). Genes are functional units within our DNA that serve as a "genetic blueprint" for instructions to make the different proteins that are required for all the cells of our bodies to be made and carry out their functions.

In this project, we aim to shed light on the genes that determine how the body responds to high calorie diets. Excitingly, our recent experiments show that deletion of a particular gene provides protection against Western diet-induced obesity and the metabolic changes that are associated with obesity such as accumulation of fat in the liver (a hallmark of non alcoholic fatty liver disease) and insulin resistance (a hallmark of type 2 diabetes). We propose that this gene plays a specific role in responding to the Western diet, as its loss did not affect body composition or metabolism on a "normal" calorie diet. Intriguingly, this effect was only seen in males, suggesting a difference between the sexes, which is also observed in people.

Thus we aim to determine how this gene is controlling body composition by performing an in-depth study of the changes that occur in the absence of this gene: in particular, we are interested in following up our pilot studies that suggest it may increase the metabolic rate and therefore result in more calories being "burnt". We propose that these changes are a consequence of the function of our gene as a master "regulator" of other genes whereby it controls when, where and how much of the different components of cells are made. This then determines the function of cells and their ability to adapt to different "environmental" effects (e.g. diet). Therefore, we will determine not only which cells are affected, but also which cellular function within these cells is affected. Finally, we will then determine the genes within these cells that show changes in their regulation. This information is useful, as understanding the details of how things work is an important first step to any future efforts to try and find novel treatments that can manipulate the pathways that influence diet induced obesity. Lastly, because our gene is an example of a large class of functionally related genes (>1,000 family members in humans) that are poorly understood, our results can have relevance to many other diseases (e.g. neurological, reproductive, oncogenic) in which this class of proteins plays a causal role.

Tight regulation of mRNA translation and stability underlies normal cell function and adaptation, and is conferred by a plethora of RNA-binding proteins (RBPs) (>1000 in man). RBP dysfunction is causal in a wide-range of disorders (e.g. neurological, inflammatory), but most RBPs remain unstudied, making studies of their functions/targets/physiological roles a priority. Thus, we focus on poly(A)-binding proteins (PABPs), archetypal multifunctional regulators of mRNA translation/stability, to establish their roles in whole organism biology. Our exciting pilot data reveal that male, but not female Pabp4-/- mice have pronounced resistance to diet-induced obesity and insulin-resistance, suggesting they can inform upon obesity and its co-morbidities/mortalities in man (e.g. type 2 diabetes), which are largely diet driven.
We will address our hypothesis that PABP4 is a master post-transcriptional regulator of sexually dimorphic metabolic gene expression programs that coordinate the response to HFD diet, and which underlie the predisposition to the development of subsequent obesity and associated pathologies in males. Thus, we will identify which aspects of whole body and tissue-specific physiology are affected in male Pabp4-/- mice, the underlying changes in cellular metabolism, dysregulated mRNAs, and which of those are direct PABP4 targets.
This will transform our knowledge of PABP4 function, targets and physiological roles. Providing a detailed molecular explanation for how loss of this RBP affords protection from the effects of HFD and defining the new regulatory network that it controls, stands to create a step-change in our knowledge of post-transcriptional control circuits that predispose/protect against HFD-induced obesity. The recent association of a human PABP4 SNP with dyslipidaemia and altered body composition (both present in our mice), highlights the timeliness and relevance of our proposal to the current diet-induced obesity "epidemic".

1. Competitiveness and excellence in UK science: (see also 2). This project brings together research on two fundamental processes: post-transcriptional control/RNA-binding proteins (RBPs) and obesity/metabolism, both areas of intense international interest and important for lifelong health. As described in Academic Beneficiaries, a wide range of researchers stand to gain from the obtained knowledge, which can inform their science, or lead to new funding applications, thereby strengthening the UK knowledge economy. Moreover, the fundamental role of post-transcriptional control in almost every aspect of cellular function makes our proposal significant to investigators in almost every area of biology (e.g. from synthetic biology, through neuroscience to developmental biology). Additional impacts include secondary use of our omics datasets (e.g. to study networks, develop mathematical models or reveal target mRNAs that function aspects of biology) and generated reagents, such as plasmids, and mouse lines (e.g. to generate compound mice). The PI's lab has an excellent track record in providing tools, reagents, protocols and developing novel techniques, all of which add to the competitiveness of UK science.

2. Training, capacity building: This proposal will provide high quality multidisciplinary training in key areas where capacity building is required (whole organism physiology, omics and bioinformatic analysis, integration of large datasets, see BBSRC "vulnerable skills"), and in the analysis of post-transcriptional regulatory mechanisms and metabolism/obesity; areas of intense focus. Training will be extended to basic/clinical PhD, MReS and undergraduate students, and other researchers as appropriate (e.g. visiting/local scientists). These skills are highly transferable between academic, clinical and industrial settings and such training is pivotal for the success of the UK research community, which contributes substantively to the UK economy.

3. Health and pharma: RBPs (>1,000 in humans) are of intense international interest due to rapidly emerging roles in diverse pathologies (e.g. neurodegenerative, oncogenic), however few have been studied. This project links the PABP family, of which PABP1 has been most intensively studied, to the regulation of gene expression changes that direct alterations in metabolism and body composition in response to high fat diet (HFD). The link between HFD and obesity is an area of global concern, given the current obesity epidemic and its associated co-morbidities and mortalities. This work stands to shed light on the regulatory circuits that influence responses to HFD, and whilst this is early stage research, we will comprehensively map the resultant changes in gene expression. In the longer term, this information could be exploited by those seeking new avenues for drug discovery and/or repurposing.

4. Industry and Biotech: Eukaryotic protein synthesis is critical for diverse economically important industrial/biotech applications (e.g. recombinant protein/antibody production, synthetic biology). As PABPs regulate global and mRNA-specific protein synthesis (and its levels are tightly linked to cell growth), our results have relevance for those aiming to manipulate protein synthesis for commercial purposes (e.g. globally to enhance growth, or to maximise synthesis of specific molecules).

5. Charities and the general public: The clinical and socio-economic relevance of our phenotype serves to illustrate the long-term potential benefit of this research, which may be of most interest to charities that seek to inform those with type 2 diabetes, cardiovascular disease, stroke (e.g. Diabetes UK, BHF, Stroke Association), for which obesity is a major risk factor. More immediately the general public will benefit from our extensive public engagement plans.

6. Commercially exploitable results and/or pharmacological treatments are highly unlikely to arise within the project lifespan.