Maternal over-nutrition and offspring health: role of translational programming of insulin action

It is well known that lifestyle factors, particularly diet and exercise, have a big effect on long-term health and lifespan. In particular, many scientific studies have established that obesity increases risk of metabolic and cardiovascular diseases and cancer. It is less well known that maternal obesity during pregnancy can permanently influence the health of her offspring including their risk of being obese and developing insulin resistance. This phenomenon, known as developmental programming, has been studied in humans largely by observational and association studies, from which it is difficult to deduce underlying mechanisms. However, laboratory animals show developmental programming as a consequence of maternal obesity that is strikingly similar to that seen in humans, and therefore provide valuable systems in which to investigate mechanisms that will also be applicable in humans. We have been studying the offspring of female mice that have been fed a high-fat/high-sugar diet during pregnancy. We have found evidence that these offspring have impaired metabolic responses to the hormone insulin that persist into adulthood and that are known to increase the risk of metabolic and cardiovascular diseases in later life. Associated with these effects on insulin sensitivity of the whole animal, in fat tissue (which has a central role in orchestrating metabolism of other tissues) we detected changes in the levels of specific proteins that mediate responses to insulin. One of these proteins, IRS-1, was already known to be a key control point for insulin action on fat and muscle cells. By comparing fat cells taken from the offspring of mothers fed high-fat/high-sugar or normal diets, we found evidence that levels of IRS-1 protein are lower in the offspring of obese mothers because the synthesis of the protein is decreased. We believe this reflects the action of a class of small RNA molecules, microRNAs or miRs for short, that inhibit the translation of messenger RNA molecules containing the information required for synthesis of IRS-1 protein. In fact in cells from offspring of mothers fed the high-fat/high-sugar diet we have shown changes in the level of one of the microRNAs (miR-126) that is known to target IRS-1. This is an exciting breakthrough that points the way for further studies that will shed new light on what is happening at a molecular level to cause adverse developmental programming, and what might be done to prevent it.
There are four things we would now like to do. First, we want to identify other microRNAs whose levels are programmed in fat cells by maternal over-nutrition. Advances in genome wide RNA sequencing and array technology make this a relatively straightforward exercise. The results will inform us about the scope of such changes and, using information on potential targets that is available in databases, what the overall effects might be. Second we will carry out experiments to identify targets of programmed microRNAs including miR-126. We have done similar experiments before in other contexts so we are confident of getting clear-cut data. Third, we will investigate the role of miRNAs including miR-126 in programming IRS-1 levels, insulin sensitivity and metabolic function in fat cells. We can by manipulating (up or down) the levels of individual microRNAs. Finally we will investigate whether simple lifestyle interventions, such as increased amounts of exercise during pregnancy, can alleviate developmental programming at the level of microRNAs and proteins in fat cells, and whether this correlates with improved metabolic responses at the whole organism level. We believe these studies will significantly advance understanding of the causes and consequences of developmental programming arising from maternal over-nutrition during pregnancy, and how such programming might be ameliorated. Importantly our experiments in animal models will inform the debate on how to manage the corresponding human condition.

The developmental origins of health and disease hypothesis links the intrauterine environment to long term health of offspring. There is evidence from human and animal studies that metabolic health of offspring is adversely affected by maternal obesity and diabetes during pregnancy. Using a mouse model of maternal diet-induced obesity we found that exposure to an obesogenic environment in utero led to the development of insulin resistance in young adult life. This was associated with altered expression of insulin signalling proteins in muscle, liver and adipose tissue. Notably, there was a marked decrease in IRS-1 protein in adipose tissue without any change in IRS-1 mRNA. Using primary cultured pre-adipocytes we showed that this reflects decreased synthesis of IRS-1 protein and that it is paralleled by an increased level of miRNA-126 that targets IRS-1 mRNA. We therefore hypothesise that maternal diet-induced obesity programmes adipose tissue insulin action in offspring through cell autonomous, post-transcriptional mechanisms that influence levels of IRS-1 and other proteins. The overall aim of this project is to elucidate the molecular mechanisms underlying this programming. We will take a global approach to identify miRNAs in adipose tissue that are programmed by maternal over-nutrition and identify targets of these miRNAs using a combination of bioinformatics, RNA-Seq and Ago2 immunoprecipitation. We will then define the role of selected miRNAs, including miR-126, in programming adipose tissue insulin sensitivity and function, by using miR mimics and antagonists. Finally, we will establish whether normalisation of maternal insulin in obese dams can prevent programming of adipocytes.
These studies will advance understanding of developmental programming arising from maternal over-nutrition and how such programming might be ameliorated. Most importantly, our experiments in animal models will inform debate on how to manage the corresponding human condition.

This proposal falls within the BBSRC strategic priority Ageing Research Lifelong Health and Wellbeing and specifically is within the scope of Fundamental research on the biology of ageing and its modulation by diet, physical activity and developmental factors. The proposal addresses two of the key issues identified and seeks to make an impact on both of these:
i) Diet, physical activity and health during ageing, and the need to understand the mechanisms by which diet and physical activity influence health across the lifecourse.
ii) Developmental factors and health during ageing, and the need to encourage research that investigates how early developmental factors may influence health during ageing, including the specific challenges to understand how nutritional exposures are recorded and transmitted through subsequent generations of cells and how this memory is translated into altered function in later life.

Academic impact: Developmental origins of health and disease is an expanding field in which UK research has so far been at the forefront. It cuts across many disciplines, most obviously physiology, nutrition and public health, with an urgent need for greater understanding at the biochemical level. The proposal therefore has potential to make a major academic impact by increasing knowledge of the molecular mechanisms linking maternal diet to metabolic phenotype of offspring. In addition to advancing knowledge, the research will involve development of new databases of miRNAs and their targets that will be broadly applicable in academia. On-going collaborations with other institutions in the UK and Europe will provide potential for extension of findings into other human cohort studies and animal models and in systems biology approaches. The research will provide cross-disciplinary training for the PDRAs, and opportunities for enhancing teaching and learning of undergraduate and postgraduate students through seminars and projects.

Economic and societal impact: The research aims to define the network of miRNAs and their targets in adipose tissue that are programmed in offspring as a consequence of maternal obesity, predisposing to insulin resistance and metabolic disease in later life. These miRNAs may provide novel targets for therapeutic intervention and patentable discoveries may emerge. Although this application focuses on adipose tissue, we intend in the longer term to establish if miRNAs are also programmed in readily accessible tissues such as white blood cells with potential utility as biomarkers of disease risk that would indicate the need for lifestyle change or other intervention.

The lead researchers are actively engaged with the commercial pharmaceutical sector (including Unilever, Astra Zeneca and Abbott Laboratories) through joint research projects and studentships. The proposed research will inform and benefit this sector through access to new knowledge, technology development and databases. Thus in the longer term we foresee opportunities for commercialization of both diagnostics (identifying individuals at risk of metabolic disease as a consequence of early life nutrition) and therapeutics (targeting specific miRNAs whose programmed expression contributes to adverse metabolic phenotype). Thus the proposed research has potential to enhance the knowledge economy and economic competitiveness of the UK.
The research also has high relevance to the public sector, with potential to inform policy making with regard to advice on nutrition and healthy ageing, by strengthening the evidence base concerning relationships between nutrition during pregnancy and long-term health of offspring. The research is also readily accessible to the general public, because of its immediate relevance to improving health and well being and enhancing quality of life. The research therefore provides an excellent vehicle for increasing public engagement and understanding.