Elucidating the Pathomechanisms of APOE4 in Lewy Body Dementia - PROJECT SUMMARY The proposed studies seek to investigate the underlying disease mechanisms of Lewy body dementia (LBD) associated with the apolipoprotein E4 (APOE4) isoform. APOE4 is a major genetic risk factor for LBD, and our recent research has shown a direct influence of APOE4 on α-synuclein (αSyn) pathology in the human brain and mouse models. However, the mechanistic relationship between APOE4 and LBD remains unclear. APOE, primarily produced by astrocytes, mediates cell-to-cell lipid transport in an isoform-dependent manner. APOE4 is known to disrupt brain lipid homeostasis and compromise the endosomal-lysosomal system, which are pathways also associated with other LBD hits, GBA and BIN1. This suggests that these pathways may be key mechanisms linking APOE4 to LBD. Moreover, APOE4 is associated with the risk and severity of LBD, but not necessarily Parkinson’s disease (PD). This leads to the speculation that the effects of APOE4 on αSyn pathology may manifest more in the neocortex where LBD pathologies are found and have minimal impact on subcortical or brainstem structures where Lewy pathology is predominant in PD. Therefore, the proposed research aims to investigate the role of APOE4 in αSyn pathogenesis and define the underlying molecular pathways and brain region vulnerability using human postmortem brains, astrocyte-specific APOE3 or APOE4 deletion mouse models, and human induced pluripotent stem cell (iPSC)-derived organoid models. In Aim 1, we will perform multi-omics profiling (bulk RNA iso-seq, single nuclei RNA-seq, proteomics, and lipidomics) of the superior temporal cortex and midbrain of human LBD cases from APOE3/3 and APOE4/4 individuals. We will conduct network analysis to uncover lipid and endosomal-lysosomal related dysfunction, and other pathways associated to LBD and APOE4. In Aim 2, conditional mouse models will be used to delete APOE3 or APOE4 in astrocytes by crossing human APOE knock-in mice, where murine Apoe is replaced with floxed APOE3 or APOE4 gene, with Aldh1l1-CreER mice and human SNCA-overexpression mice. Deletion of APOE will be induced by tamoxifen treatment at different stages of αSyn pathogenesis. The αSyn pathology related phenotypes will be evaluated and multi-omics profiling will be conducted in the experimental mice. In Aim 3, we will validate the cellular mechanisms of APOE4 on affecting αSyn pathogenesis, lipid homeostasis, and endosomal-lysosomal functions using iPSC-derived cortical and midbrain-like organoid models from patients carrying SNCA triplication and different APOE genotypes edited by CRISPR/Cas9 technology. Together, this innovative proposal will utilize unique human brain resources, mouse models, and human iPSC- derived models, and combine state-of-the-art approaches for multi-dimensional integration of molecular profiling to comprehensively investigate the pathomechanisms of APOE4 in LBD. These efforts will contribute to our understanding of the APOE4-mediated pathways involved in αSyn pathology, providing valuable insights for the development of future therapeutic strategies targeting APOE in the treatment of LBD.
