Mapping the human hypothalamic functional architecture underlying food intake control

Obesity is a growing public health problem. While our changing lifestyle and environment have undoubtedly driven this increase, there is a powerful genetic component that underlies the large variation in human body shape and size in this modern environment. Understanding the mechanisms controlling feeding behaviour that lead to this variability in body-weight will be important in informing any strategy to improve our health in this current food environment. While the preferred model in which to study food intake is clearly in humans, the fact that genetic studies point to a region in the brain called the hypothalamus as having a crucial role in modulating appetite has limited the mechanistic insights achievable through human research. The inaccessibility of the human hypothalamus has, to date, meant our understanding of brain circuits controlling food intake has emerged primarily from mouse studies. Now, an important collaboration with the Cambridge Brain Bank, is allowing us access to fresh human donor brain samples. This, coupled with recent developments in single-cell sequencing and in technologies allowing us to visualize single-molecules using fluorescence, provides us with a timely opportunity to map the functional architecture of the human hypothalamus, with a focus on appetitive behaviour. A functioning map requires two key elements; we first need to know the components of the map, and then we need to know where these components sit on the map, with respect to each other. Thus our two objectives are: A) using single-cell technologies, we will sequence 500,000 individual hypothalamic cells, in order to perform a molecular census of cell populations to identify components of the neuro-circuitry controlling food intake; B) using an approach called single-molecule fluorescent in-situ hybridization (smFISH), we will map the different components identified onto both mouse and human brains. We will examine the spatial expression of these genes in the human hypothalamus and compare this to the pattern seen in the mouse brain. Detailed mechanistic studies on the brain using modern genetic manipulation tools will, for obvious reasons, still require mouse models. Our rationale however, is that if a certain neuronal population is ONLY found in mice, then studying it makes little 'translatable' sense. It would be far better to focus finite resources on generating sophisticated mouse models once we can determine that a particular pathway or neuronal type actually exists in the human brain. Our goal of a comprehensive human hypothalamic atlas will be of utility to basic scientists and clinical researchers attempting to better understand the fundamental nature of energy balance regulation by the hypothalamus. This will hopefully allow us to manipulate these systems to improve the health of the population.

Obesity is a growing public health problem, however genetic studies point to the brain, and in particular the hypothalamus, as having a crucial role in modulating appetitive behaviour, which has limited the mechanistic insights achievable from human research. The inaccessibility of the human hypothalamus has, to date, meant our understanding of circuitry controlling food intake has emerged primarily from murine studies. Now, a collaboration with the Cambridge Brain Bank allowing us access to fresh human donor brain samples, coupled with single-nucleus sequencing (NucSeq) technologies and single-molecule fluorescent in-situ hybridization (smFISH), provides us a timely opportunity to map the functional architecture of the human hypothalamus underlying appetitive behaviour. To achieve this, we have two objectives: A) Using NucSeq, we will sequence at least 500,000 individual hypothalamic cells to perform a molecular census of cell populations, and identify components of the neuro-circuitry controlling food intake in humans. B) The second is taking a targeted candidate approach to determine the spatial coordinates of different components. The pro-opiomelanocortin (POMC) and NPY neurons are key energy sensors within the arcuate nucleus of the hypothalamus. We have identified murine POMC and NYP populations expressing distinct pattern of genes involved in the regulation of food intake. We will examine the spatial expression of these genes in the human hypothalamus and compare this to the pattern seen in the murine brain. smFISH allows us to not only to detect low-expression transcripts, but with the capability to image from four different fluorescent channels, will enable us to visualize up to four different transcripts at once. A comprehensive human hypothalamic atlas will be of utility to better understand the fundamental nature of energy balance regulation by the hypothalamus and allow us manipulate these systems to improve the health of the population.

This study integrates two fundamental biomedical topics - neuroscience and metabolism - that will initially impact academic and commercial research communities including post- and under-graduate students working on obesity, neuroanatomy, physiology and gene expression. In the near term, the project will directly impact those focussing on the hypothalamic control energy balance, but as it develops, it will bring an awareness about the importance of neuroscience to the obesity epidemic to an increasingly broad audience locally, nationally and internationally. Between them, Dr Yeo and Prof Rowitch have over four decades of experience working in the US and UK, presenting an ongoing opportunity for knowledge transfer from many centres of excellence. They will seek to publish our findings in high-profile, broadly-read, peer-reviewed international journals such as NPG, Cell Press or AAAS titles; Dr Yeo and Prof Rowitch publish in all three. Work on hypothalamic neuroscience will be communicated to academic audiences nationally at meetings but more often in one-off presentations at UK universities and research institutes. Communication internationally will be at scientific meetings that include Keystone Symposia or Gordon Conferences, whose academic participants often include policy makers; Drs Perry and Yeo have recently presented their work at both. Outreach to potential stake-holders including academics, policy-makers and the commercial sector will be maximised.

The work proposed here is, by its very nature, fundamental. It will have direct efforts on the 3 'Rs', by allowing the field to refine the types of mouse models used, and ultimately reducing the numbers of animals required. Knowledge generated here will eventually inform new health care messages, interventions and treatment regimes, with beneficiaries that include health care professionals, private and public health institutions (NHS, social services), policy makers (Department of Health, Health Authorities), charities (eg WHO, Diabetes UK, British Heart Foundation), pharmaceutical and biotechnology companies and those at risk of developing diet-related illnesses disease. We expect the work to identify novel therapeutic targets of human relevance that directly inform clinical studies, benefiting healthcare workers and some of the 74% of adults in the UK are predicted to be over-weight by 2030. Given that the NHS in England spent ~£5.1 billion on obesity-related ill-health in 2014-15, reducing incidence of this condition will have a major economic impact. The work will benefit the commercial private sector because it will lead to new information on human relevant markers that influence metabolic disease, allowing us to improve the health of the population.