Apolipoprotein E (
apoE) is a major
cholesterol carrier that regulates
lipid homeostasis by mediating
lipid transport from one tissue or cell type to another. In the central neural system (CNS),
apoE is mainly produced by astrocytes, and transports
cholesterol to neurons via
apoE receptors, which are members of the
low-density lipoprotein receptor family. The APOEε4 gene is a strong genetic risk factor for late-onset sporadic
Alzheimer's disease (AD), likely through its strong effect on the accumulation of
amyloid-β (Aβ)
peptide.
ApoE protein levels in cerebrospinal fluid (CSF) and plasma are reduced in APOEε4 carriers and in patients with AD. Furthermore, altered
cholesterol levels are also associated with the risk of AD. Aβ accumulation, oligomerization and deposition in the brain are central to the pathogenesis of AD. Mounting evidence demonstrates that
apoE and
apoE receptors play important roles in these processes. Astrocyte-derived
apoE is pivotal for cerebral
cholesterol metabolism and clearance of Aβ. Thus, we hypothesized that increased
apoE in the brain may be an effective therapeutic strategy for AD. We report here that
quercetin can significantly increase
apoE levels by inhibiting
apoE degradation in immortalized astrocytes. Importantly, we show that
oral administration of
quercetin significantly increased brain
apoE and reduced insoluble Aβ levels in the cortex of 5xFAD
amyloid model mice. Our results demonstrate that
quercetin increases
apoE levels through a novel mechanism and can be explored as a novel class of drug for AD
therapy.