A1527G variant of ABCA7 increases soluble and insoluble Aβ40‐42 in an animal model for late‐onset Alzheimer's disease

Abstract

Background: The ATP binding cassette (ABC) subfamily A member 7 (ABCA7) gene was identified by Genome‐wide association studies (GWAS) as a risk factor for Alzheimer's disease (AD). ABCA7 is part of the ABC1 subfamily and is expressed in brain cells including neurons, astrocytes, microglia, endothelial cells, and pericytes. Mounting evidence has linked ABCA7 variants to disrupted lipid metabolism, impaired microglia‐mediated phagocytosis, and altered amyloid deposition. However, the mechanisms by which variations in ABCA7 increase risk for AD are not known. Method: The IU/JAX/PITT MODEL‐AD Center identified the A1527G variant in ABCA7 (ABCA7A1527G) as a putative LOAD risk factor. CRISPR/CAS9 was first used to introduce Abca7A1527G variant to B6.APOE4.Trem2R47H (LOAD1) mice to assess the transcriptional profiling on brain hemispheres from different ages. The Abca7A1527G was then incorporated into B6.APOE4.Trem2R47H.hAb (LOAD2) mice to further evaluate its contribution to LOAD. Female and male LOAD2.Abca7A1527G and LOAD2 mice were characterized at 4, 12, and 24 months using the following phenotyping pipeline: behavior, PET/CT, multi‐omics, fluid biomarkers, neuropathology, and targeted protein analysis. Result: While no aging cognitive deficit was observed in LOAD2.Abca7A1527G, PET/CT imaging revealed significant sex‐ and region‐dependent increases in brain glycolysis, accompanied by reduced tissue perfusion. This resulted in a progressive age‐related uncoupled phenotypes between 4‐12 and 4‐24 months. These changes were supported by brain transcriptional profiling showing Abca7A1527G‐associated alterations in granulocyte/neutrophil migration, and insulin receptor signaling. Consistent with the uncoupled phenotype, while the addition of A1527G variant increased the plasma levels of IL6, IL10, and TNFα, brain levels of IL4, IL12, TNFα, and CXCL1 were decreased, and IL2 and IL10 were elevated independent of age. Interestingly, older ABCA7 cohorts had elevated soluble and insoluble Aβ40 and Aβ42 in both plasma and brain samples. Histological assessment of plaque deposition and microglia staining in 24‐month‐cohorts and targeted protein analysis are ongoing to determine the etiology of Aβ deposition. Conclusion: Data collected to date support a model whereby variations in ABCA7 exert risk for AD through interactions between cerebrovasculature, microglia, Aβ deposition, and peripheral immune cells.