Introduction:  Recent genetic studies have highlighted that RELN-DAB1 is a novel pathway that significantly modifies disease-risk in both familial and late-onset cases of Alzheimer’s disease (AD)(Bracher-Smith, Leonenko et al. 2022, Lopera, Marino et al. 2023). While preclinical studies have shown that RELN counteracts amyloid and Tau pathology in mice (Lane-Donovan, Philips et al. 2015, Rossi, Gruart et al. 2020), how protection is conferred in the human brain remains unclear. A recent GWAS from the lab predicts that RELN-DAB1 interacts with APOE4 to modify disease-risk(Bracher-Smith, Leonenko et al. 2022).

Aim Here, we aim to investigate how RELN-DAB1/DAB2 and APOE signalling interact to modify microglia and the vasculature.

Methods Publicly available transcriptomic datasets of single-cell RNA sequences from human AD brains and controls were first mined to assess for changes in RELN-DAB1 pathways in AD. We next characterised the microglia in a germline N-Reln knock-down mouse model using immunocytochemistry. Finally, we cultured human APOE iPSC-differentiated microglia in vitro and knocked down DAB1 and DAB2 using siRNA, and characterised changes to microglia in bulk RNA transcriptomic studies and through automated analysis of microglial morphologies and activation states using Opera-Phenix imaging and Harmony analysis.

Results Our analysis of publicly available transcriptomic databases suggests that RELN-DAB1 pathways may alter neuroinflammation and the vascular system in AD, and that DAB1 is down regulated in response to amyloid. In addition, we observe that a Reln deficient environment results in the hypotrophying of microglial processes with indications of their increased phagocytosis within the adolescent brain (n=3-4 Reln wildtype or knock-down mice). We next study how siRNA DAB1 knock-down in human iPSC-differentiated microglial models (n=3 MG differentiations per genotype and siRNA) and upon exposure to AD-relevant stressors in vitro (n=3-4 MG differentiations per genotype and siRNA) alters microglial morphologies, their activation states and phagocytosis.

Conclusion Together, we aim to understand how RELN-DAB1 and APOE genetic status may sensitize microglial responses to stressors in AD. We propose that RELN-DAB1 is a novel immune-modulatory pathway that interacts with APOE to alter AD-risk through its effects on microglial function in the human brain.