👤 Jeffrey A Golden

Apolipoprotein E (ApoE) is the primary, most abundant apolipoprotein of the CNS and plays an important role in brain metabolism and lipid homeostasis. In the CNS, ApoE is primarily secreted by astrocytes under homeostatic conditions and by microglia in certain disease-related conditions. APOE has three major alleles: APOE2, APOE3, and APOE4. APOE4 is the strongest genetic risk factor for late-onset Alzheimer's disease (AD), and APOE2 results in decreased risk relative to APOE3. ApoE derived from astrocytes and microglia have been hypothesized to play different roles in the disease pathogenesis of AD. In this study, we profiled the lipidome and proteome of ApoE lipoproteins secreted by astrocytes or microglia and found that they differed according to the cellular source of ApoE and the ApoE isoform. Lipidomics revealed that microglia-derived ApoE lipoproteins were enriched in cholesteryl esters, whereas astrocyte ApoE lipoproteins were enriched in SM. Proteomics revealed that astrocyte ApoE lipoproteins were enriched in proteins involved in glucose metabolism and acute phase response. Microglia-secreted lipoproteins were enriched in proteins involved in complement activation, synapse pruning, proteolysis, and the innate immune response. Further comparison of ApoE lipoproteins from APOE4 microglia revealed that ApoE4 lipoproteins were enriched in complement component 1q and Lpl compared with ApoE2 and ApoE3 microglial lipoproteins, which were enriched in Ankk1 (ankyrin repeat and kinase domain containing 1) and apolipoprotein C1. These results provide the molecular foundation for better understanding of how ApoE functions as an apolipoprotein with the lipoprotein cargo being dependent on the cellular source and ApoE isoform, ultimately contributing to CNS homeostasis and disease pathogenesis. Show less

Demyelination occurs with aging and is exacerbated in neurodegenerative diseases. During demyelination, microglia upregulate expression of APOE, the gene encoding for the brain's primary lipid transport protein apolipoprotein E (ApoE), which also mediates microglial engulfment and elimination of myelin debris. Compared to the E3 allele of APOE, the E2 allele decreases risk for Alzheimer's disease (AD), while the E4 allele increases AD risk and is associated with an increased severity and progression of multiple sclerosis. Previous work shows that mice expressing E2 exhibit improved microglial function and remyelination compared to mice expressing E4. However, whether microglial-derived APOE is responsible for driving these differences following demyelination, and if microglia-selective expression of E2 is sufficient to provide protection, is unknown. We sought to determine if microglia-specific replacement of the E4 allele with E2 can rescue myelin loss and promote remyelination, even in the presence of continued E4 expression by other central nervous system (CNS) cells. Using a novel APOE allelic "switch" model in which we can induce a replacement of E4 with E2 exclusively in microglia, we characterize the glial cell response and lipid profile of mice that underwent either lysophosphatidylcholine (LPC) or cuprizone (CPZ)-induced demyelination and subsequent remyelination. We found that although alterations to the brain lipid profile were subtle, microglial E2 replacement significantly improved remyelination, lessened microgliosis, and decreased astrocytic lipid droplet load following CPZ-remyelination. Our results indicate that microglia-specific E2 expression, in the presence of continued E4 expression, may provide protection against myelin loss via both cell-autonomous and non-autonomous immunometabolic mechanisms. Show less

Abdominal aortic aneurysm (AAA), a dilatation of the infrarenal aorta, typically affects males >65 years. The pathobiological mechanisms of human AAA are poorly understood. The goal of this study was to identify novel pathways involved in the development of AAAs. A custom-designed 'AAA-chip' was used to assay 43 of the differentially expressed genes identified in a previously published microarray study between AAA (n = 15) and control (n = 15) infrarenal abdominal aorta. Protein analyses were performed on selected genes. Altogether 38 of the 43 genes on the 'AAA-chip' showed significantly different expression. Novel validated genes in AAA pathobiology included ADCY7, ARL4C, BLNK, FOSB, GATM, LYZ, MFGE8, PRUNE2, PTPRC, SMTN, TMODI and TPM2. These genes represent a wide range of biological functions, such as calcium signaling, development and differentiation, as well as cell adhesion not previously implicated in AAA pathobiology. Protein analyses for GATM, CD4, CXCR4, BLNK, PLEK, LYZ, FOSB, DUSP6, ITGA5 and PTPRC confirmed the mRNA findings. The results provide new directions for future research into AAA pathogenesis to study the role of novel genes confirmed here. New treatments and diagnostic tools for AAA could potentially be identified by studying these novel pathways. Show less