Year 2 NRSA Fellowship for Courtney Kloske: Assessing Impaired Neuroinflammation Associated with Apolipoprotein E4

Alzheimer’s Disease (AD) remains the leading cause of dementia worldwide and 6th leading cause of death in the United States. Two neuropathological hallmarks distinguish AD from other dementias: amyloid plaques and neurofibrillary tangles. In addition, the brain experiences a robust inflammatory response to these amyloid-beta plaques inducing the activation and proliferation of microglia. While the majority of AD cases have no clear genetic cause, a few genetic risk factors for developing AD have been identified. One of the most significant genetic risk factors is Apolipoprotein E (ApoE). Of the three identified ApoE isoforms, ApoE4 confers an increased risk of AD, ApoE3 is believed to be the “control” phenotype, and ApoE2 has been shown to be protective for AD. Interestingly, ApoE has been shown to interact with a surface receptor on microglia, triggering receptor expressed on myeloid cells 2 (TREM2) which has also been shown to confer an increased risk of AD. Recent studies have suggested this interaction between ApoE and TREM2 drives microglial gene expression changes and function toward an activated microglial state in the presence of neurodegeneration, suggesting a role for ApoE in the inflammatory response seen in AD. While the AD field has established ApoE and TREM2 as risk factors for developing AD, the mechanistic insights into these risk factors remain murky at best. This project aims to determine the impact of the ApoE isoform on the inflammatory cascade in both mouse and human. We hypothesize that the ApoE isoforms will have differing effects on the neuroinflammatory response seen in AD. In my preliminary results from autopsy tissue, the data suggests ApoE3 patients with AD have a neuroinflammatory response differing from that seen in ApoE3 patients without AD, suggesting that the ApoE3 isoform is responding to amyloid plaques. In contrast, ApoE4 patients with AD tend to be in a state of neuroinflammation similar to that found in ApoE3 patients without AD, suggesting they cannot respond to the amyloid plaques. To further delve into these differences, two approaches will be used to determine the impact of the ApoE isoform dependent mechanism. First, we will continue investigating the neuroinflammatory profile of AD brains by determining microglial morphology in ApoE3/3 and ApoE4/4 patients with AD to compare activation states of the microglia. We will also perform nanoString digital spatial profiling to look at proteins surrounding various AD hallmarks and microglia. These approaches will allow for a deeper understanding of how these changes seen from the preliminary data associate with the pathology. Our second approach will use animal models to target TREM2 and investigate the impact ApoE isoforms have on the activation of the TREM2 cascade. We will target TREM2 activation using two approaches: phosphatidylserine and a TREM2 agonizing antibody provided by Alector. These two approaches will allow for a more comprehensive understanding of the impact of ApoE isoforms on TREM2 activation. Overall, this project aims to dive further into the importance of ApoE isoforms on neuroinflammation to one day help clinicians treat AD in an ApoE genotype specific manner