Abstract
Although intracellular cholesterol levels are known to influence the proteolysis of beta-amyloid precursor protein (APP), the effect of specific genes that regulate cholesterol metabolism on APP processing remains poorly understood. The cholesterol transporter ABCG1 facilitates cholesterol efflux to HDL and is expressed in brain. Notably, the human ABCG1 gene maps to chromosome 21q22.3, and individuals with Down syndrome (DS) typically manifest with Alzheimer's disease (AD) neuropathology in their 30s. Here, we demonstrate that expression of ABCG1 enhances amyloid-beta protein (Abeta) production in transfected HEK cells in a manner that requires functional cholesterol transporter activity. ABCG1-expressing cells also exhibit increased secreted APP (sAPP)alpha and sAPPbeta secretion and display increased cell surface-associated APP. These results suggest that ABCG1 increases the availability of APP as a secretase substrate for both the amyloidogenic and nonamyloidogenic pathways. In vivo, ABCG1 mRNA levels are 2-fold more abundant in DS brain compared with age- and sex-matched normal controls. Finally, both Abeta and sAPPalpha levels are increased in DS cortex relative to normal controls. These findings suggest that altered cholesterol metabolism and APP trafficking mediated by ABCG1 may contribute to the accelerated onset of AD neuropathology in DS.
Highlights
Intracellular cholesterol levels are known to influence the proteolysis of b-amyloid precursor protein (APP), the effect of specific genes that regulate cholesterol metabolism on APP processing remains poorly understood
To determine whether ABCG1 affects the secretion of amyloid-b protein (Ab) peptides, HEK293 cells stably expressing APP695 containing the Swedish mutation (HEK-APPswe cells) were transiently transfected with empty vector or human ABCG1 cDNA, and the levels of Ab40 and Ab42 released into the medium were measured over time
These data show that the levels of Ab released from HEK-APPswe cells is augmented in the presence of ABCG1
Summary
Intracellular cholesterol levels are known to influence the proteolysis of b-amyloid precursor protein (APP), the effect of specific genes that regulate cholesterol metabolism on APP processing remains poorly understood. ABCG1-expressing cells exhibit increased secreted APP (sAPP)a and sAPPb secretion and display increased cell surface-associated APP. These results suggest that ABCG1 increases the availability of APP as a secretase substrate for both the amyloidogenic and nonamyloidogenic pathways. ABCG1 mRNA levels are 2-fold more abundant in DS brain compared with age- and sex-matched normal controls. Both Ab and sAPPa levels are increased in DS cortex relative to normal controls. These findings suggest that altered cholesterol metabolism and APP trafficking mediated by ABCG1 may contribute to the accelerated onset of AD neuropathology in DS.—Tansley, G.
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