A 3D Neurosterol Atlas of Mouse Brain

Lead Research Organisation: University of Edinburgh
Department Name: Centre for Cardiovascular Science

Abstract

The sterol category of lipids, including cholesterol, its precursors and metabolites (oxysterols and steroids), are important biomolecules in the brain. Cholesterol is the major component of the myelin sheaths which surround neurons. Many sterols are biologically active molecules regulating many brain functions and behaviours, such as memory, cognition, stress and mood. These molecules are localized and enriched in different brain regions according to the biological roles they play. However, sterol distributions in brain are poorly defined due to lack of technology which has hampered our understanding about how the brain functions and loses function with ageing.
Bioimaging provides an image of biomolecular abundance, molecule by molecule, in a tissue, allowing visualization of the quantitative and spatial distribution of different molecules within a tissue. Mass spectrometry imaging is an emerging powerful tool for bioimaging. We will use this technology to construct a 3D map or atlas of sterol molecules in the brains of mice from developmental stage to young adult to aged mice. Scientists will use our Atlas to find out where different sterol molecules are located in the brain and how their abundance correlates with brain functional region. The resource will support many aspects of neuroscience research which address healthy aging.

Technical Summary

The brain is a remarkably complex organ. To understand brain function, it requires multidisciplinary technologies and multiple levels of data. There are a number of big initiatives worldwide to map the brain. Current activities are focused on mapping gene expression, cell type and connectivity across the entire brain. Despite these efforts, little is known about the landscape of the metabolome or lipidome across the brain. The sterol category of lipids, including cholesterol, its precursors, and oxysterols and steroids, represent one of the dominating lipid classes in brain and sterol homeostasis plays a critical role in neurophysiology. It is recognised that a lack of quantitative spatial information on steroids and sterols/oxysterols in brain subregions is a key gap in our understanding of the mechanisms underlying health and healthy aging. The aim of this proposal is to create a web-based 3D Neurosterol Atlas of Mouse Brains utilising our recently-developed on tissue derivatisation and mass spectrometry imaging (MSI) technology.
On-tissue derivatisation overcomes the limitations of previous MSI techniques for analysis of low abundance and difficult to ionise sterol molecules. We have successfully combined on-tissue derivatisation with MALDI-MSI to image neurosteroids and cholesterol, and combined it with liquid-extraction for surface analysis (LESA) and liquid chromatography - mass spectrometry (LC-MS), i.e. LESA-LC-MS, to image cholesterol precursors and oxysterols, allowing isomer differentiation and structure identification. Here we will scale up our effort and use the Allen Mouse Brain Atlas as a template to create a web-based interactive 3D Neurosterol Atlas of Mouse Brain including developmental, young adult and aged mice of both sexes. The resource will support neuroscience research in many areas, including myelination and repair, neurotransmitter receptors, stress response and neuroprotection and regeneration.

Planned Impact

Understanding brain development and how the brain is affected by ageing is a vital key to unlock strategies to sustain a healthy lifespan. Key players in central neural pathways are sterols and steroids. To find out the location and in situ concentration of sterols/steroids in the brain requires specialised mass spectrometry technology and expertise which are not widely available. A free to access web-based 3D Neurosterol Atlas of Mouse Brain, across three life stages and both sexes, will provide researchers with easy access to this information. Females have long been under-represented in many areas of animal research. Gender-related differences in sterol metabolism and the glucocorticoid stress response have been reported, hence having access to female brains in the Atlas is of crucial importance. It will have significant impact on basic neuroscience, public health life-style recommendations, medical research and drug discovery.
Corticosteroid receptors are expressed in the CNS and are important in regulating the stress response, memory and behaviour. Glucocorticoid levels are locally controlled by enzymes, such as 11beta-HSD1 which generates activate glucocorticoids. Early life events programme stress responses and overexposure to elevated glucocorticoids with ageing accelerates cognitive decline. As such, inhibitors of 11beta-HSD1 are in clinical trials to treat dementia. A knowledge of glucocorticoid concentrations in the different regions of male and female brains throughout life, as provided by our Atlas, will provide baseline data to understand how the environment during pregnancy programmes the brain, how the stress axis is influenced by ageing and which areas of the brain are at greater risk. This will enable further investigations into how the stress axis can be optimised to extend health and independence.
N-Methyl-D-aspartate receptors (NMDARs) and GABA-A-type receptors (GABA-ARs) are implicated in neurological disorders including schizophrenia, epilepsy, depression, Alzheimer's disease (AD) and traumatic brain injury. Neurosteroids are endogenous allosteric modulators of NMDARs and GABA-ARs. Currently there is considerable interests in exploring the use of neurosteroids to treat these conditions and a number of ongoing clinical trials are in progress. Knowing the distribution of endogenous neurosteroids in the male and female brain in health and how they correlate to the location of interacting receptors is important for the design and optimisation of synthetic analogues which will improve the efficiency of drug development.
For many years cholesterol metabolism has been linked to AD and other neurodegenerative and cognitive disorders. Recently, a gene-therapy approach to increase the local expression of CYP46A1, the enzyme primarily responsible for cholesterol metabolism in brain, has shown promising effects in slowing down disease progression in mouse models of AD. Our Neurosterol Atlas of the healthy brain will provide an essential baseline to understand how cholesterol homeostasis varies between distinct functional regions of brain and with age. With this information, researchers can apply more targeted approaches to design novel therapeutic treatments and monitor sterol changes in focussed lesions.
This is an exciting opportunity for PDRAs to be involved in building the first 3D Neurosterol Atlas of Mouse Brain. Mass spectrometry imaging is an emerging and cutting-edge technology, pioneered in the sterol/steroid field by the applicants. The PDRAs will work closely with analytical scientists, neuroscientists and bioinformaticians. The experience they gain and the networks they will build will enhance their career development.
The Neurosterol Atlas can also be used as a teaching resource for undergraduate students and to engage public attention in understanding of the how brain works.

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