Investigating the role of an EIF2B3 variant as an Alzheimer's disease risk modifier

Project Summary Human genetic studies provide a powerful approach to identify genes and pathways associated with Alzheimer's disease (AD). Apolipoprotein E isoform 4 (APOE4) is the strongest genetic risk factor for sporadic Alzheimer's disease. Despite the strong effect of APOE4 on AD risk, a wide range of clinical outcomes exist within APOE4

carriers: some can develop cognitive impairment as early as 30-years of age while other carriers remain cognitively normal beyond 100-years. The large range in clinical manifestation amongst APOE4 carriers suggests that there are genetic variants that modulate APOE-associated risk. To investigate this hypothesis, we conducted

stratified genome-wide association studies of APOE4 carriers at the extremes of age at onset distribution to identify variants that modify risk. We identified a single variant in EIF2B3 encoding the amino acid substitution S404A as a candidate risk modifier. eIF2B3 is a subunit of eIF2B, a guanine exchange factor (GEF) for eIF2 that

is involved in translational control and the integrated stress response. Our lab has recently shown that APOE4 induces a constitutively upregulated ISR and aberrant protein translation in murine and human iPSC-derived microglia, demonstrating that APOE4 alone can lead to increased levels of cellular stress1,2. Furthermore,

EIF2B2, another eIF2B subunit, is an AD risk gene identified in AD GWAS3. The overall goal of this proposal is to directly test the hypothesis that EIF2B3 variants modulate APOE4-associated risk by dysregulating the ISR

and thus alter microglial cell function in the context of disease. In Aim 1, I will combine cell-free in vitro fluorescent GEF assays and structural chemistry to determine the effects of EIF2B3S404A directly on eIF2B structural integrity and enzymatic activity, in the absence of cellular stress. Aim 2 will determine the impact of EIF2B3S404A on

APOE4 microglia cell function in vitro using human induced pluripotent stem cell (iPSCs)- derived microglia and live-cell imaging in the context of disease-related stressors. Lastly, in Aim 3, I will employ novel xenotransplantation methods involving direct injection of human microglia precursor cells into the mouse brain

to evaluate the effect of EIF2B3S404A on APOE4 microglia cell function in vivo and in the context of disease. Together, the results here will confirm or refute the hypothesis that EIF2B3 variants modulate APOE4-associated risk by altering microglial cell function. Throughout the project, I will test the efficacy of an ISR inhibitor (ISRIB)

drug at alleviating EIF2B3S404A -induced effects on EIF2B activity in vitro and in microglia in vitro and in vivo. The work here has the potential to greatly impact public health through understanding the way in which variants affect immune cell function and modify disease risk and by potentially identifying a novel drug for the treatment of AD.

The fellowship training plan proposed here will provide me with the technical skills, scientific knowledge, critical thinking skills gained from Dr. Alison Goate's mentorship and the collaborative environment at the Icahn School of Medicine at Mount Sinai at large, equipping me with the necessary skills for a successful transition to a career

as an independent scientist.