Abstract IA017: Dnmt3a and Tet2-driven clonal hematopoiesis have opposing effects on the pathogenesis of Alzheimer’s disease

Abstract While the clonal expansion of mutant hematopoietic stem cells (HSCs) known as clonal hematopoiesis (CH) is associated with many age-associated diseases, the connection to neurodegenerative diseases including Alzheimer’s Disease (AD) is less clear. Prior evidence suggests systemic inflammatory signals can be transmitted to the central nervous system (CNS), where they trigger microglia activation and amyloid-beta clearance. Here we investigated the role of the two most commonly mutated clonal hematopoiesis-associated genes, DNMT3A and TET2, in the pathogenesis of AD using a mouse model. We utilized 5xFAD (Familial Alzheimer’s Disease) mice which express human disease variants of amyloid precursor protein and presenilin and develop b-amyloid plaques and cognitive decline by 6-9 months of age. At 6-8 weeks of age, 5xFAD mice were non-competitively transplanted with Dnmt3a-/-, Tet2-/- or wildtype (WT) bone marrow (BM). Mice were then challenged weekly with LPS to mimic age-associated chronic inflammation. At 6 months of age, transplanted mice were assessed for signs of AD pathogenesis as well as the presence of infiltrating peripheral immune cells within the brain. 5xFAD mice transplanted with Dnmt3a-/- BM displayed exacerbated AD, including worsened cognitive impairment and decreased microglia activation compared to those transplanted with WT BM. They also had fewer peripheral immune cells infiltrating the brain compared to WT-transplanted recipients. In contrast, 5xFAD mice transplanted with Tet2-/- BM showed improved cognitive status, decreased amyloid plaques, and increased microglia activation. Tet2-/- transplanted mice had a higher percentage of activated infiltrating myeloid cells in the brain compared to WT controls. To assess whether peripherally derived immune cells directly replace microglia in the CNS, we quantified donor-derived peripheral immune cells positive for the microglia marker Tmem119 within the brain using flow cytometry. Interestingly, mice transplanted with Tet2-/- BM, had a higher proportion of donor-derived mutant microglia-like cells when compared to mice transplanted with WT BM. To evaluate the impact of DNMT3A or TET2 mutation on human microglial function, we utilized microglia derived from isogenic human iPSC lines harboring DNMT3A (DNMT3AR882H/WT) or TET2 mutations (TET2DelE3-E11/WT). Cytokine bead array of culture supernatant showed that TET2-mutant induced microglia (iMGs) released significantly more inflammatory cytokines and demonstrated a greater capacity to phagocytose both myelin and b-amyloid upon LPS activation compared to WT or DNMT3A-mutant iMGs. In summary, Tet2 provided protection against AD through increased myeloid cell infiltration and microglia activation, leading to more efficient amyloid plaque clearance and improved cognitive performance; while the opposite was true for loss of Dnmt3a. Our study of CH and AD marks the first report in which DNMT3A and TET2, which have opposite roles in DNA methylation, induced opposing effects on disease progression. Citation Format: Katherine Y King. Dnmt3a and Tet2-driven clonal hematopoiesis have opposing effects on the pathogenesis of Alzheimer’s disease [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Methylation, Clonal Hematopoiesis, and Cancer; 2025 Feb 1-4; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2025;85(3 Suppl):Abstract nr IA017