Cerebrospinal fluid lipoprotein-mediated cholesterol delivery to neurons is impaired in Alzheimer's disease and involves APOE4.

In the central nervous system, apolipoprotein (APO)E-containing lipoprotein particles mediate the transport of glial-derived cholesterol to neurons, which is essential for neuronal membrane remodeling and maintenance of the myelin sheath. We aimed to examine cholesterol transport via lipoprotein particles in cerebrospinal fluid (CSF) of Alzheimer's disease (AD) patients compared to control individuals. Additionally, we explored the ability of reconstituted HDL containing different APOE isoforms to regulate cholesterol transport. We evaluated the capacity of CSF lipoprotein particles to facilitate radiolabeled unesterified cholesterol efflux from A172 human glioblastoma astrocytes and to deliver cholesterol to SH-SY5Y human neuronal cells. The CSF lipoprotein proteome was analyzed by LC-MS/MS. Reconstituted HDL nanoparticles were prepared by combining phospholipids and cholesterol with human APOE3 or APOE4, followed by radiolabeling with unesterified cholesterol. Our results showed that cholesterol efflux from astrocytes to CSF were similar between AD patients and controls, both under baseline conditions and after activation of ABCA1 and ABCG1. However, CSF lipoprotein-mediated neuronal cholesterol uptake was significantly reduced in the AD group. LC-MS/MS analysis identified 239 proteins associated with CSF lipoproteins in both groups, with no major alterations in proteins linked to cholesterol metabolism. However, 27 proteins involved in non-cholesterol-related processes were differentially expressed. Notably, synthetic reconstituted HDL particles containing APOE4 exhibited reduced capacity to deliver cholesterol to neurons compared to those with APOE3. These findings indicate that CSF lipoproteins from patients with AD demonstrate impaired cholesterol delivery to neurons. Our study highlights APOE4 as a critical contributor to abnormal neuronal cholesterol uptake in AD pathophysiology.