Microglia in Early Dementia with Lewy Bodies

Aims
The aim of this project is to identify a new treatment target for the early stages of dementia with Lewy bodies.

Background
Dementia affects a person's thinking skills, memory and ability to carry out their day-to-day activities. Around one million people in the UK have dementia. 5-10% of these people have a type of dementia called dementia with Lewy bodies (DLB). In addition to problems with thinking skills, DLB is associated with other symptoms, including visual hallucinations and the symptoms of Parkinson's disease. These symptoms cause significant distress for people with DLB and their loved ones. At present, there is no treatment that can slow the progression of the disease.

Microglia are specialised cells in the brain with a range of roles including controlling brain inflammation and removing unwanted material from around brain cells. Previous research has suggested that microglia may play a role in the early stages of DLB.

The activity of microglia in the brain can be measured using a specialised brain scan called TSPO PET imaging. This allows us to show whether the number of microglia is increased in early DLB.

Toll-like receptors are proteins that sit on the surface of microglia and other cells. They can influence the activity of microglial cells. Microglia and toll-like receptors can be measured in brain tissue from people with DLB after death. The aim of this study is to demonstrate whether toll-like receptors are a good target for drugs aiming to slow the progression of DLB.

Objectives
1. Using TSPO PET imaging: quantify microglia in early DLB and assess the degree to which increased microglia are associated with more rapid disease progression
2. Using brain tissue: quantify microglial cells and toll-like receptors in the brains of people with early DLB and examine the association between microglial toll-like receptors and disease processes in DLB

Design
Objective 1: Brain Imaging
We will recruit 50 participants with early DLB, along with 20 healthy people. All participants will have a thorough clinical assessment including measurements of the severity of dementia at baseline, 12 months and 24 months. Blood samples will be taken from all participants at baseline and 24 months, along with an optional lumbar puncture to obtain cerebrospinal fluid (the fluid that surrounds the brain and spinal cord).
Participants will have a TSPO PET scan. This will allow us to see if there are more microglial cells in the brains of people with early DLB and if microglial cells are associated with faster progression of dementia.
We will repeat the TSPO PET scan after 24 months in participants with DLB. This will allow us to see if microglial cell numbers change over time in DLB.

Objective 2: Brain Tissue Analysis
We will use brain tissue donated by 30 people who died with early DLB and 30 people who died without any brain disease. Special dyes will be used to look at microglial cells and toll-like receptors under a microscope. Chemicals in the brain tissue will also be measured to understand how toll-like receptors and microglia are associated with other disease processes. This will allow us to understand whether influencing toll-like receptors is likely to slow disease progression in DLB.

Patient/service user, carer and public involvement
A patient and public involvement (PPI) group was consulted in the development of this proposal in April 2020. A PPI Reference Group will meet throughout the Fellowship and PPI members will be invited to sit on the project steering group.

Applications and benefits
The findings of this study could rapidly lead to early-stage clinical trials of toll-like receptor-based treatments in early DLB. This study could also lead to the use of TSPO PET imaging to identify appropriate participants and measure treatment response in such trials.

Dementia with Lewy bodies (DLB) is the second most common type of neurodegenerative dementia. The aim of this project is to understand the role of microglia in early DLB and determine if microglial toll-like receptors (TLRs) 2 and 4 are appropriate therapeutic targets in early disease.

Objective 1: 18F-DPA714 PET
18F-DPA714 is a PET marker of the translocator protein (TSPO). TSPO is expressed on the cell surface of activated microglia, astrocytes and endothelial cells. Participants with mild cognitive impairment with Lewy bodies (MCI-LB) or mild DLB (n=50) and healthy controls (n=20) will have 18F-DPA714 PET-MR at baseline; this will be repeated at 24 months in the MCI-LB/mild DLB group. Clinical evaluation will take place at baseline, 12 months and 24 months. Blood and optional cerebrospinal fluid samples will be taken at baseline and 24 months. Specific 18F-DPA714 binding will be measured using a supervised cluster analysis. Mean cortical binding potential will be compared between MCI-LB/mild DLB and healthy controls. Change in binding over time and association with disease progression will be analysed in the MCI-LB/mild DLB group.

Objective 2: Brain tissue
Post-mortem brain tissue from people with MCI-LB/mild DLB (n=30) and controls (n=30) will be co-stained with fluorescent DPA714 and markers of microglia, astrocytes and endothelial cells to determine the cellular correlates of DPA714 binding. Microglial density and the expression of TLR2 and TLR4 in will be compared between MCI-LB/mild DLB and controls. The association between TLR2 and TLR4 expression and pro-inflammatory cytokines (IL1-beta, TNF-alpha and IL6), markers of autophagy (LC3B and p62) and alpha-synuclein will be examined using western blotting and RT-qPCR.

This project will increase understanding of microglial activity in early DLB and could rapidly lead to early-stage clinical trials investigating the effect of TLR2 and TLR4 antagonists on microglia.