The effects of APOE genotype in homeostatic microglial function in preclinical APOE mouse model

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Project Summary Alzheimer's disease (AD) is a devastating neurodegenerative condition. Aging and the 4 allele of the APOE gene are the strongest genetic risk factor for AD. APOE is the main cholesterol transporter in the brain that promotes neuronal growth, debris clearance, and it is mainly produced by astrocytes. Upon inflammatory insults APOE is produced by microglia to act as an immunomodulator. Chronic inflammation exacerbates the progression of AD pathology. Previous studies show an effect of APOE4 genotype in decreased levels of APOE protein in the brain, increased inflammation at baseline, and simplification of dendritic spines. The studies proposed here aim to understand APOE4-related alteration in microglial function prior AD onset. We generated a novel human APOE knock-in mice expressing GFP under the CX3CR1 promoter to study the effects of APOE genotype in homeostatic microglia function. So far in my thesis, I have examined the disturbances of APOE4 in homeostatic microglial function and found that APOE4 altered microglia surveillance and response to damage through the downregulation of chemotactic purinergic receptors. I have also studied the effects of aging, sex, and APOE genotype in microglial function and found that aging affects microglia response to damage, and these alterations occur earlier in APOE4 brains. This F99/K00 proposal will encompass 2 aims presented in the following research plan. In Aim 1, I will identify the molecular mechanism underlying microglial alteration in homeostatic function and response to amyloid  (A). Aim 1a will examine whole transcriptome RNA-seq from APOE3 and APOE4 microglia. We will identify genes differentially expressed in APOE3 and APOE4 microglia and investigate specific pathways involved in altering homeostatic microglial function. Aim 1b will examine the effects of APOE genotype on microglia's ability to recognize A prior AD onset. We will investigate microglia response to acute exposure to A and if APOE genotype affects microglia affinity to A monomers and oligomers. Aim 1c will study APOE protein interaction with A and its effect on phagocytosis. We will investigate APOE-A interactions and their effect on microglia recognition of A and uptake. In Aim 2, I will continue to build skills in a post-doctoral setting researching the mechanisms underlying microglia crosstalk with the peripheral immune system during aging and neuronal degeneration. To achieve this, I will first identify the ideal postdoctoral lab and then obtain the postdoctoral position. I aim to complete my postdoctoral fellowship in an institution that values innovation, scientific rigor, training, and professional development. To obtain this fellowship, my sponsor and I are working closely in identifying conferences and inviting speakers that will allow me to expand my network and identify the ideal lab setting. The F99/K00 will greatly assist me in both completing my PhD and obtaining the postdoctoral fellowship I am striving for.