Massaging brain vessels with vasomotion: Targeting the vasculature to alter disease progression in mouse models of dementia.

We currently have no treatment that stops or even slows down Alzheimer's disease. Most research since the 1980's has focussed on understanding the role of proteins in the brain called beta-amyloid and Tau. Everybody produces these proteins in their brains throughout the day, but in healthy people they are removed from the brain. In Alzheimer's disease, something goes wrong with the clearance of these proteins and they start to build up over time. Eventually they cause brain nerve cells to die and this is when the symptoms of Alzheimer's disease first become apparent. Despite millions of pounds in funding being invested into how these two proteins build up and ways to remove them, we still do not have a treatment that can affect disease speed or outcome. Recently, other theories about the condition have started to be investigated. One of these suggests that blood flow in the brain may be an important factor. It is well known that patients with Alzheimer's often have lower levels of blood flow in their brains compared to healthy subjects. It was generally assumed that this was due to neurons in the brain dying because of the build-up of the proteins mentioned above. However, scientists are now starting to investigate the potential that it is the reduction in blood flow that is causing the condition. The central idea is that blood flow not only serves to provide energy but also effectively washes the brain of all the waste it produces. If blood flow drops below a certain level, which may be only 5 or 10% less than normal, the washing is less efficient and the waste (in the form of proteins) builds up. It is thought that these changes in blood flow happen very early in the condition, therefore if a treatment can be developed to prevent this blood flow change, a greater proportion of the brain cells can be saved.

For the last few years, our research team has been investigating blood flow in the brains of mice that have Alzheimer's Disease. These mice are bred with genetic changes known to occur in humans who get Alzheimer's very early in life, known as the familial form of the condition. These mice over produce beta-amyloid protein and have similar memory deficits to those seen in humans and, critically for our project, are known to have a lower level of blood flow in their brains compared to animals without the condition. The main aim of this project is to change blood flow in the brains of mice with Alzheimer's disease by either raising the entire baseline or causing blood flow to oscillate. This oscillation is termed vasomotion and it is believed that it might actively massage the brain blood vessels and improve clearance of the toxic proteins. We are going to change blood flow in the brain by two distinct methods. The first is by precise activation of brain cells using a technique called optogenetics. This method works by inserting proteins called opsins into a specific class of neuron in the mouse brain. Once these opsins are in place, we can shine a blue light onto the animal's brain causing the targeted cells to become active. Our recently published work and pilot data shown in this application has shown that stimulation of these neurons robustly increases blood flow and vasomotion. The second method is called hypercapnia, in these experiments the mouse breathes in room air with a small amount of carbon dioxide added (5%), again this has been shown to increase blood flow and vasomotion.

A gradual breakdown in the mechanism matching brain blood flow to neural activity may be an important contributory cause of many brain diseases, maybe even the cognitive decline seen in normal aging. The proposed project seeks to establish in principle whether a treatment that increases brain blood flow can effectively slow or block the development of Alzheimer's Disease-associated symptoms in mouse models of the disease. If successful, this could lead to new vascular-based therapies to be developed for this devastating disease.

Alzheimer's disease (AD) has no cure. The link between impaired cerebral blood flow (CBF) and AD has been understudied in terms of potential AD therapies. Therefore, we aim to identify potential new vascular-based treatment strategies for AD. We will use two mouse models of dementia; the APP/PS1-AD and P301S(PS19) tauopathy models, each replicating a hallmark pathology of AD. The primary objective is to assess the potential disease-modifying effects of new vascular-based interventions which either increase CBF or induce an oscillation in CBF called vasomotion. To do this, we will use one of two methods: the first is to selectively activate nitric oxide synthase interneurons (nNOS-INs). The second will be to use hypercapnia. We will also characterise neurovascular function in the P301S model, assess vascular function throughout the vascular tree in AD, and define the spatial spread of our nNOS-IN stimulation. To achieve these aims we will employ the following array of imaging and electrophysiological techniques, supported by behavioural measures of cognitive function and histological verification of pathology:
1. Optogenetic manipulation: Use of transgenic animals enabling photostimulation of nNOS-INs. Using LED light will eliminate non-specific heat-induced blood flow changes.
2. Mild hypercapnia gas challenges: the animals' air will be supplemented with 5% CO2.
3. 2-dimensional optical imaging spectroscopy (2D-OIS): to measure haemoglobin changes from the cortical surface.
4. Multi-channel electrophysiology: to measure neural activity simultaneously across all cortical layers.
5. 2-photon microscopy: to measure neurovascular responses as a function of depth.
6. Whole brain functional MRI: to assess the spatial extent of optogenetic stimulation effects.
This research will increase our understanding of the involvement of neurovascular components in the aetiology of AD and demonstrate any disease-modifying potential of vascular-based interventions.