Investigating And Targeting Microglial Senescence In Alzheimer's Disease

Our immune response is usually a defensive mechanism to prevent the spread of infections and their associated tissue damage. In the brain, inflammation is a double-edge sword mediated by the main resident macrophage population, the microglia. We know that one of the most characteristic responses of microglia in age-related neurological diseases, such as Alzheimer's (AD) or Parkinson's, is the increase in their numbers. Recent data from our research group indicates that this process of expansion, when repeated over time, drives microglial burn-out, in a process known as replicative senescence. This, in turn, has detrimental effects during the progression of chronic neurodegenerative disease like Alzheimer's. However, we do not fully understand how this process develops, and what are the consequence to the roles that microglia usually undertake in the brain. Most importantly, so far most of the knowledge about these mechanisms derives from the study of rodents, and we lack models that would inform about human-relevant biology.
In this proposal we will develop new models in which to study senescence in human microglia, by taking advantage of the culture of induced pluripotent stem cells (iPSCs), which can be turned into any specific cell type of interest. We will convert human iPSCs into human microglia, using validated models thanks to the expertise of Dr Mead and the Oxford Drug Discovery Institute. Once we have obtained these human microglia in a culture dish, we will "wind them up", inducing their increase in numbers, with the expectation that cells will increased replications will become senescent. We will use alternative models to induce senescence, for example using pharmacological agents known to work in others. Once we identify the conditions to induce microglial senescence, we will explore the impact on key house-keeping functions that microglia undertake in order to maintain a normal brain health. These include the ability of microglia to remove (eat) foreign bodies and infectious agents, called phagocytosis, as well as the ability of microglia to engage an inflammatory response to disease. We will check if the changes observed in cultured cells correlate with changes observed in microglia in the brains of patients with AD, thanks to contribution from Prof. Matthews, a leader in the analysis of human microglia at the single-cell level.
Once we have identified effective methods to induce senescence in human microglia, and have also explored what functions are modified as a consequence of senescence, we will screen for drugs able to eliminate or revert senescence microglia. This will be achieved thanks to expertise from Prof. Gil, a leader in the field of understanding and targeting senescence. We will screen a large library of compounds, and identify those able to selectively remove senescent microglia, or revert them to their healthy state, without altering non-senescent cells.
To address our experimental plan, we will use state-of-the-art techniques, fully enabling our approach to have an impact on the academic community. With the proposed approach, we will break new ground into the understanding of the initial events of age-related brain pathology. We have a plan for translating outcomes of the proposed research into the drug discovery phase, with an ambition to improve the quality of life of patients with chronic neurodegeneration in the future.

Recent data supports that senescent microglia contributes to the onset of amyloidosis and neuritic damage that is observed in the early stages of Alzheimer's disease (AD). However, we lack an understanding of the mechanisms driving microglial senescence in humans, and the consequences of this. We will provide human-relevant validation of the mechanistic link of microglial senescence with key functional readouts determining the progression of age-related neurological disorders. We will derive microglial-like cells from human iPSC lines, initially testing if physiological "ageing" of the cells is sufficient to trigger replicative senescence. Alternatively, we will induce senescence in microglia using validated pharmacological agents. We will use a range of techniques to test the onset of senescence, including accumulation of beta-Gal activity or measurement of telomeric length. We will then analyse the functional changes associated with senescence, by studying key microglial functional readouts associated with disease, such as the phagocytic capacity, inflammatory activation and the overall transcriptional profile using single-cell or bulk RNA sequencing. The transcriptional signatures observed in senescent human iPSC-derived microglia will be compared with those exhibited by microglia in the human AD brain, thanks to mining of existing single-nuclei RNAseq data. Finally, we will implement a drug screening approach, using a validated drug library to look for agents capable of selectively eliminate senescent microglia or those able to revert their senescent phenotype.
We have put together a Team with relevant expertise in the different angles explored by this proposal, able to deliver significant impact to the understanding of the contribution of microglial senescence to AD. Finally, the proposal is highly translational, providing a robust data package for target identification and validation, optimising the speed and value of any follow up drug discovery efforts.