Amyloid‐β plus cholesterol treatment impairs the ability of microglia to efflux excess cholesterol

Abstract

AbstractBackgroundMicroglia, specialized phagocytic cells of the brain, play a critical role in the clearance of amyloid beta (Aβ), which is involved in the pathogenesis of Alzheimer’s disease. The ability of microglia to remove Aβ is influenced by their cellular cholesterol clearance capacity. It is not known to what extent Aβ impairs microglial cholesterol efflux capacity, especially in the context of excess cholesterol.MethodHMC3 microglia were treated with Aβ‐oligomer (AβO, 2µM), cholesterol loading (20µg), or AβO + cholesterol in combination, and with or without cholesterol acceptor, high‐density lipoprotein (HDL), at 0.1 mg/mL. Pooled HDL from 18 individuals in a 2‐hour postprandial state and a 36‐hour fasted state were compared. The cellular content of unesterified and esterified cholesterol was measured.ResultsThe addition of cholesterol, AβO, and cholesterol+AβO increased cellular cholesterol content, which was attenuated by the addition of HDL. Importantly, cells treated with cholesterol plus AβO had the highest overall cholesterol content (27.80+/‐2.85µM), and both fasted (20.67+/‐3.04µM, p≥0.05) and postprandial HDL (21.95+/‐3.84µM, p<0.05) were not able to reduce the cellular cholesterol content as well as in the untreated (fasted: 16.17+/‐2.28µM, p<0.05; postprandial: 18.55+/‐2.01µM, p>0.05), cholesterol only (fasted: 17.72+/‐2.17µM, p<0.05; postprandial: 18.14+/‐3.19µM, p<0.05), or AβO only condition (fasted: 16.80+/‐1.40µM, p<0.05; postprandial: 18.42+/‐2.05µM, p>0.05). Fasted HDL more efficiently removed cellular cholesterol in the untreated and in AβO+cholesterol treated cells. Intriguingly, cellular esterified cholesterol content was significantly lowered with fasted HDL but not postprandial HDL in both AβO alone (fasted: 5.73+/‐2.27 µM, p<0.05; postprandial: 10.32+/‐2.70µM, p>0.05) and AβO + cholesterol (fasted: 2.87+/‐2.13µM, p<0.05; postprandial: 9.03+/‐1.74µM, p>0.05).ConclusionThese findings suggest that microglia exposed to a double‐hit of AβO and excess cholesterol experience an impaired ability to efflux excess cholesterol. Additionally, HDL from fasted individuals displayed an enhanced capacity to efflux cholesterol, especially in microglia dually encumbered by AβO + cholesterol. Further studies are needed to examine the impact of this diminished cholesterol efflux capacity and cholesterol accumulation on the phagocytic capacity of microglia.