Abstract 197: Proteomic Characterization Of Human Brain Lipoproteins Speciated By Size Exclusion Chromatography

Abstract

Like plasma, the cerebrospinal fluid (CSF) contains lipid-protein complexes called lipoproteins tasked with transporting lipids and protecting against cerebrovascular dysfunction. These brain lipoproteins (BLps) are generated de novo in the central nervous system (CNS), but little is known about them, because they exist in CSF at <0.5% the concentration of lipoproteins in plasma making them difficult to study. BLps are thought to resemble plasma high-density lipoproteins (HDL), a heterogenous population of compositionally distinct particles important for transporting lipid, protecting against oxidative stress, and modulating immune and inflammatory responses in the periphery. Mass spectrometry (LC-MS/MS) studies have shown that 260 different proteins can interact with different HDLs in the periphery and specific combinations of these proteins cluster on the lipid surface to govern particle function. In the current study, we developed a lipoprotein profiling technology that overcomes the BLp abundance problem in CSF to capture BLp subspecies with unprecedented sensitivity and resolution. Using high-resolution size exclusion chromatography, we identified at least 10 distinctly sized BLp populations in human CSF with a majority of the particles eluting in size ranges between plasma low-density lipoproteins (LDL) and HDL. BLps were isolated from fractionated CSF using a lipid-binding resin. Proteomic analysis of the particles using LC-MS/MS identified 299 different lipid-associated proteins across fractions with 189 of those proteins not currently reported on the human HDL Proteome Watch. Co-migration analysis further revealed at least 27 unique protein communities across the fractions indicating that multiple distinct subspecies exist within the same sized subfractions. DAVID functional analysis shows that the communities are highly enriched in proteins important in the immune response and neurometabolic functions such as neuron generation and development. In summary, our study shows that similar to plasma HDL, BLps are a highly speciated population of compositionally distinct particles but are enriched in CNS-derived proteins that are essential for maintaining cognitive health.