Influence of APOE genotype on cerebrovascular cell pathobiology in AD, and the contribution of microglia inflammation - Alzheimer’s disease (AD) is an age-related neurodegenerative disorder and the predominant type of
dementia, marked by brain deposits of amyloid plaques and neurofibrillary tangles. An often overlooked
pathognomonic lesion of AD is cerebrovascular degeneration. Abnormalities in cerebral blood flow are a
preclinical feature of AD that manifest many years before symptom onset. Vascular lesions are also routinely
observed in AD brains at different stages of the disease. Disruptions to cerebrovascular integrity can impact on
neuronal function, however, the main driver of these vascular changes in AD remains elusive.
The Apolipoprotein E4 (APOE4) allele is one of the strongest risk factors for AD, and has been shown to
significantly impact on cerebrovascular health, precipitating deficits in cerebral perfusion, vascular lesions and
damage to the blood brain barrier. Yet, more longitudinal studies are needed to better understand how APOE4
can significantly impact on cerebrovascular cell pathobiology in the sequelae of AD pathogenesis.
In the brain, APOE is produced primarily by glial cells, and in AD, disease associated microglia (DAM’s)
are known to upregulate APOE expression, which mediates the transcriptional proinflammatory phenotype of
these cells. DAM’s have been shown to drive the outcome and pace of APOE-mediated neuronal dysfunction,
but very little is currently known about the role they play in contributing to cerebrovascular changes in AD,
particularly, how this is influenced by APOE genotype.
To address these questions, we plan to use mouse models expressing human forms of APOE and A to
clarify the role played by APOE4 as a molecular driver of cerebrovascular cell pathobiology, and how this is
influenced by DAM’s. We will explore longitudinal cerebrovascular cell pathobiology at timepoints
representing pre, peri and post onset of
A
pathology using histopathological and ultrastructural analyses. We
will also confirm the contribution of DAMs on cerebrovascular pathobiology by utilizing microglia ablation
techniques to depopulate DAMs and also repopulate newborn microglia in our mouse models. To date, no
studies have characterized the molecular transcripts of reactive cerebrovascular cell phenotypes in these
combined models. Thus, we will conclude our studies using single cell gene analyses of cerebrovascular cells
(endothelial cells, pericytes, smooth muscle cells) to reveal their unique and detailed time-course of responses.
We will confirm differentially expressed genes in autopsied cerebrovascular tissue from staged AD cases to
validate the translational relevance of our findings and map against mouse AD-related pathogenic timelines.
From this proposal, we aim to identify novel (cerebrovascular) cell specific targets in the early stages of
disease through which the APOE4 allele confers neurological risk. Our future goal will be to explore the
functional effects of these targets, and to provide new therapeutic opportunities to promote cerebrovascular
health and restoration of cognitive function in AD.
