Ensuring quality maternal care in an adverse environment

A critically important adaptation during the mammalian pregnancy is the induction of maternal care. Maternal care is vitally important for the survival of the newborn and the withdrawal of maternal care or poor quality maternal care can result in adverse behavioural and metabolic outcomes later in life. Importantly, prenatal adversities such as suboptimal diet or stress can influence the quality of maternal care. Consequently, understanding how maternal care is induced and how the maternal environment influences the induction of maternal care is of paramount importance.

There is some evidence that the placenta plays a role in instructing the mother to care for her newborns. The placenta is a transient organ of pregnancy that plays a key role in transferring nutrients to the growing fetus. The placenta is also a super endocrine organ that manufactures hormones that flood the maternal system to induce the changes required for a successful, health pregnancy. Studies suggest that some of these hormones, the placental lactogens, may induce maternal care. Given this proposed role for the placenta, placental dysfunction could contribute to poor maternal care.

We have identified a gene called Phlda2 that is important for the production of these placental hormones. Phlda2 regulates the amount of placental hormones that are manufactured by regulating the size of the placental endocrine compartment. Transgenic over expression of Phlda2 results in a smaller endocrine compartment. Mouse mothers exposed to placenta with this much smaller endocrine compartment exhibit changes in gene expression and neurogenesis in the maternal brain during pregnancy and poor maternal care of their offspring, even though they themselves are not mutant for Phlda2. Phlda2 is an imprinted gene whose expression is regulated by epigenetic marks. Remarkably, expression of Phlda2 is altered in the placenta in response to the two different suboptimal maternal diets that have previously been linked to poor maternal care. This leads us to believe that a suboptimal maternal diet may contribute to poor maternal care by altering the expression of Phlda2 in the placenta and thus reducing exposure of the maternal brain to placental lactogens. In this study, we will use a variety of existing experimental models and techniques to test this hypothesis first asking whether we can restore maternal care by manipulating placental expression of Phlda2 in a dietary model, and then by exploring the mechanism initially focusing on placental lactogen signaling via the maternal prolactin receptor. We will also develop a novel imaging tool based on infrared luciferase, to ask whether we can longitudinally bioimage ongoing maternal neurogenesis. A considerable advantage of this tool will be the ability to image the same animal multiple times substantially reducing the number of animals required for our studies.
This work is important not just in helping us to fundamentally understand how maternal care is induced but also how this process may be influenced by the maternal environment, and how we might be able to restore maternal care - work that will have wide relevance to the welfare of experimental, domestic and agricultural animals as well as human health.

Prenatal adversity, specifically diets low in protein or high in fat, have been linked to poor quality maternal care. We have shown that expression of Phlda2 in the placenta can be altered by maternal diet. Phlda2 regulates the expression of placental lactogens. Lactogenic signalling via the maternal prolactin receptor has been implicated in the induction of maternal care in rodents. Dams exposed to Phlda2 mutant placenta display abnormal maternal care. To assess the extent to which elevated placental Phlda2 contributes to abnormal maternal care in response to low protein diet, we will combine maternal low protein with a genetic model in which the elevated expression of Phlda2 from the placenta is prevented by a targeted deletion followed by characterisation using a combination of RNAseq, immunohistochemistry and classic behavioural assays.
In a second aim, we will ask whether we can rescue any aspect of the maternal phenotypes observed independently in prolactin receptor (Prlr) heterozygous knock dams and our dams carrying 2XPhlda2 placenta, which express low levels of placental lactogen, by combining the Prlr receptor heterozygous knockout model (50% receptor) with our 0XPhlda2 placenta (high placental lactogens).
In a third aim, we will use intracerebral ventricular infusion to ask whether we can restore maternal behaviour by a central nervous system infusion of placental lactogen making use of the new iPRECIO programmable infusion pump system. We will also develop a bioimaging system, based on an infrared variant of luciferase, as a quantitative tool to image neurogenesis. The ability to image neurogenesis in vivo, during pregnancy and after delivery, would reduce animal numbers and has the potential transform the research in this area. Overall, this work will identify a novel mechanism linking maternal nutrition to maternal care which will have important implications for the design of interventions aimed at improving maternal care.

Enhancing quality of life, health and well-being:
While our studies are in rodents, which have very different placenta to humans, they may have some relevance to our understanding of human maternal mood disorders. We have some evidence from our MRC funded study that altered expression of certain imprinted genes in the human placenta is associated with self-reported maternal prenatal depression and clinically diagnosed prenatal depression. Thus if our work in rodents leads to a better understanding of the origins of maternal mood disorders, our findings may translate into the human situation to enhance the quality of life. This is particularly important as we are not just studying why maternal care fails but also investigating approaches to restore maternal care in an adverse environment.

The economy:
If our studies translate to humans, our discoveries have the potential to benefit the British economy by reducing costs to the NHS in treating maternal mood disorders and the associated childhood behavioural disorders. According to report by the London School of Economics and Political Science and the Centre for Mental Health in 2014, perinatal mental health problems cost the UK economy >£8 billion each year.

If our studies translate to the other non-human mammals, our work may have relevance to the successful raising and breeding of a number of agricultural, experimental and domestic animals. For example, there is a 15% mortality rate in lambs with an estimated to cost the UK economy >£180M per annum. A very modest 0.5% reduction in mortality rate, potentially by something as simple as a dietary change, would save the UK economy £6M/annum.

Commercialisation:
Although not the focus of this study, there is the potential for the development of biomarkers, which predict abnormal maternal behaviours, and also suggest therapeutic approaches to treating prenatal depression

Contributing towards evidence based policy-making and influencing public policies and legislation at a local, regional, national and international level:
We have found that expression of Phlda2 is up regulated in the placenta in response to a suboptimal maternal diet in rodents. We have also found a similar increase in expression of PHLDA2 in human placenta obtained from women reporting a high fat diet during pregnancy. Our current work suggests this aberrant expression is relevant to both fetal and maternal health, and childhood wellbeing. Our findings may lead to changes advice given to pregnant women.

Contributing to increasing public awareness and understanding of science, economic and societal issues:
News media play a role in informing the way people understand science. The public understanding of issues such as climate change, stem cells and MMR have increased due to media coverage as a consequence of new discoveries reported in scientific journals. The public is likely to be very interested in our work as it concerns the wellbeing of mothers and their children. Our work will raise awareness of epigenetics and, ultimately the role of the environment early in life in shaping later life outcomes

Enhancing the knowledge economy:
Nothing is published linking Phlda2 to maternal care or childhood outcomes. Our scientific discoveries will provide new knowledge.

Worldwide scientific advancement to address issues of importance in other countries or globally: Studies on Phlda2 may provide a tool to address maternal mental health worldwide.

Delivering and training highly skilled researchers:
This work will provide valuable training to a young researcher and a technician in in vivo models (behavioural neuroscience, bio-imaging), molecular and bioinformatics (RNAseq) skills.