Mechanisms underlying the transmission of programming effects

Low birthweight babies are at increased risk of diabetes and heart disease in adulthood. This has led to the concept of 'fetal programming', suggesting that if a developing baby is exposed to an adverse environment during early life this affects early growth and development and also predisposes the individual to heart disease later in life. Studies have shown that this effect is not limited to the individual who was originally exposed but this increased risk of disease can also be passed on to future generations. Importantly, this risk can be passed on by either the mother or the father. The mechanisms underlying 'programming' and the transmission of these effects are not well understood.

We proposed that exposure of the fetus to excess 'stress' steroid hormones (glucocorticoids) might be important in programming. Glucocorticoids are present in mother and baby and are used as treatment during premature labour, but can reduce birthweight and affect later blood pressure. Stress and illnesses increasing a mother's glucocorticoid levels during pregnancy have similar long-term effects. We have shown that exposure of the fetus to glucocorticoids has effects in the directly exposed offspring which are developing in the womb at the time and that these effects are transmitted to the next generation - i.e. the offspring's offspring. We suggest that this might happen because the cells which will form the eggs and sperm which will produce this next generation (called germ cells) are present in the developing ovary and testis from a very early stage of development - in fact while a baby is still developing in the womb. These cells are therefore also exposed to these glucocorticoid hormones.

Studies have shown that the addition or removal of certain chemical groups on genes can have a major affect on the way they function. We propose that these chemical groups might be affected by factors acting in early life, including glucocorticoids, and that this might be a cause of the increased disease risk in later life. These chemical groups are particularly important in the developing germ cells and may also be vulnerable to the effects of glucocorticoids. In this project we wish to increase our knowledge of how overexposure to glucocorticoids impacts on these chemical groups in the germ cells and explain how disease risk can be transmitted across generations.

Crucially, the work may indicate ways for us to prevent the complications associated with low birthweight and prevent these problems being passed on to subsequent generations.

Epidemiological studies demonstrate an association between early life events and cardio-metabolic disorders in adulthood, a phenomenon termed early life 'programming'. Human and animal studies suggest programming effects are not limited to the first generation but may be transmissible to subsequent generations through both male and female lines. The mechanisms accounting for the intergenerational transmission of programmed effects are unclear. We have developed a rat model of fetal glucocorticoid overexposure in which the offspring have reduced birthweight and as adults have hypertension and hyperglycaemia, a phenotype which is transmitted to a second generation.

Alterations in epigenetic modifications have been described in animal models of programming and in humans and the transmission of epigenetic modifications such as DNA methylation (5mC), histone modifications and small RNAs through the germline may be one mechanism accounting for the transmission of programmed effects. We propose there may also be a key role for a newly described DNA modification 5-hydroxymethylation (5hmC). In this project we will test the hypotheses that programming effects are transmitted to a second generation as a consequence of (a) altered epigenetic reprogramming during gametogenesis and/or (b) altered epigenetic modifications in mature germ cells.

This research will increase knowledge and understanding of the role which epigenetic modifications may play in the early life origins of disease and will explore the mechanisms which might account for the transmission of such effects to a second generation, providing a basis for the inherited association between low birthweight and cardiovascular risk factors.

Ultimately, this study may suggest methods that would allow the early identification of individuals at risk of later disease, potential interventions to decrease this risk and interventions to prevent the transmission of disease risk across generations.

Who will benefit from this research?
Academics: The primary beneficiaries will be the research community, i.e. others engaged in understanding the transmission of programmed effects across generations and those who study epigenetic reprogramming in the germline (including researchers at major UK and international institutions). Although we will use a model in which glucocorticoids are the environmental 'programming' agent, the data generated will have wider implications for our understanding of the mechanisms by which disease risk can be transmitted through the germline. The outcomes may also have impact in prompting others to test for similar mechanisms in other models and in future studies in humans.

Clinicians: The work will benefit other clinicians, particularly Paediatric Endocrinologists, Obstetricians and Neonatologists who use glucocorticoids in clinical practice (assisted conception and during pregnancy) - research in this field is already informing the clinical use of glucocorticoids in pregnancy in the management of fetuses at risk of congenital adrenal hyperplasia.

Public health: There are likely to be public health benefits from this work. Cardiovascular disease is the leading cause of death globally and is associated with a large burden of preventable illnesses. Exposure to an adverse environment prenatally is associated with a substantially increased risk of cardiovascular disease so that understanding the mechanisms which account for this 'programming' of disease risk and how this can be transmitted across generations is of great public health importance, allowing early identification of those at risk and the development of intervention strategies. Around 5.6 million people in the UK are currently living with cardiovascular disease, costing the UK approximately £30 billion annually so that this may ultimately lead to reduced costs of care for long-term debilitating diseases.

How will they benefit from this research?
Academics: This interdisciplinary project brings together clinicians and scientists in different fields, ensuring wide dissemination of our findings. We will present our work at national and international scientific conferences and the results will be published in open access format. Our collaboration with CGAT may lead to the development of new analytical pipelines which will benefit the wider academic community. The Edinburgh post-doctoral researcher will receive training in new scientific techniques and will have the opportunity to engage with the transferrable skills programme and with the active post-doc society in Edinburgh to gain skills which will be useful in her future career. Additionally, towards the end of the project she will be preparing a Personal Fellowship application. The CGAT fellow allocated to the project will benefit from working with our unique dataset to answer our particular questions.

Clinicians: Dr Drake is a paediatric endocrinologist who works closely with other paediatricians, neonatologists and obstetricians. She attends clinical meetings at which our work will be disseminated more widely.

Non-Academic: We will disseminate our findings through engagement with the public using various forms of media. Edinburgh University has a strong commitment to engaging the public in its research. Dr Drake has presented her work to public audiences at University seminars, at the Edinburgh International Science Festival, to NIH policy fora and and on local radio. Richard Meehan has presented at international events and workshops, participating in the subsequent press coverage.