Importance of γ-secretase in the regulation of liver X receptor and cellular lipid metabolism

Abstract

Presenilins (PS) are the catalytic components of γ-secretase complexes that mediate intramembrane proteolysis. Mutations in the PS genes are a major cause of familial early-onset Alzheimer disease and affect the cleavage of the amyloid precursor protein, thereby altering the production of the amyloid β-peptide. However, multiple additional protein substrates have been identified, suggesting pleiotropic functions of γ-secretase. Here, we demonstrate that inhibition of γ-secretase causes dysregulation of cellular lipid homeostasis, including up-regulation of liver X receptors, and complex changes in the cellular lipid composition. Genetic and pharmacological inhibition of γsecretase leads to strong accumulation of cytoplasmic lipid droplets, associated with increased levels of acylglycerols, but lowered cholesteryl esters. Furthermore, accumulation of lipid droplets was augmented by increasing levels of amyloid precursor protein C-terminal fragments, indicating a critical involvement of this γ-secretase substrate. Together, these data provide a mechanism that functionally connects γ-secretase activity to cellular lipid metabolism. These effects were also observed in human astrocytic cells, indicating an important function of γ-secretase in cells critical for lipid homeostasis in the brain.

The C99 domain of the amyloid precursor protein is a disordered membrane phase-preferring protein

“…C99 also contains another structural feature that at first glance might be expected to endow the protein with a significant affinity for cholesterol-rich raft domains: a cholesterol binding site (18,45,86,110). The functional consequences of cholesterol binding by C99 are incompletely understood, but recent work suggests C99 regulates cholesterol trafficking and cellular lipid metabolism (74,111,112). Key residues in C99 involved in cholesterol binding lie in the N-terminal helix, N-terminal loop, and extracellular end of the TMD (45).…”

“…g-secretase activity as well as g-secretase inhibitors are known to modulate cholesterol and lipid metabolism as well as membrane phase behavior (47,(72)(73)(74). We therefore considered the possibility that the inhibitor treatments could themselves be impacting the phase preference of C99 by changing the properties of the membrane itself.…”

An advanced method for propargylcholine phospholipid detection by direct-infusion MS

“…The residue was separated by silica column chromatography (CHCl 3 /methanol/water 65/35/8) to yield LpPC O-16:0. The synthetic pPC 31:1 used as internal standard for MS analysis was synthesized from PC 31:1 ( 7 ) analogously to the method described for pPC O-16:0/18:1. Alike, the synthetic pPC 18:0/18:0, pPC 18:1/18:1, pPC 18:2/18:2, pPC 18:3/18:3, pPC 20:4/20:4, and pPC 22:6/22:6 used for testing the performance of the method were synthesized from PC 18:0/18:0 (Avanti; 850365), PC 18:1/18:1 (Avanti; 850375), PC 18:2/18:2 (Avanti; 850385), PC 18:3/18:3 (Avanti; 850395), PC 20:4/20:4 (Avanti; 850397), and PC 22:6/22:6 (Avanti; 850400), respectively.…”

“…S2 ) were washed once with ice-cold PBS (Sigma; 806552) and quickly once with 155 mM ammonium acetate, taking care to remove the liquid after the last wash as completely as possible. The lipids were extracted by addition of 500 μL methanol:CHCl 3 5/1 containing 240 pmol pPC 31:1, 210 pmol phosphatidylethanolamine (PE) 31:1, 396 pmol PC 31:1, 98 pmol phosphatidylserine (PS) 31:1, 56 pmol phosphatidic acid 31:1, 51 pmol phosphatidylglycerol 28:0, 39 pmol lysophosphatidate 17:0, 35 pmol lysophosphatidylcholine; 17:1, 38 pmol lysophosphatidylethanolamine (LPE) 17:1, 32 pmol ceramide 17:0, 99 pmol SM 17:0, 55 pmol glucosylceramide 12:0, 339.7 pmol triglyceride (TG) 50:1, 111 pmol cholesteryl ester 17:1, 64 pmol diglyceride 31:1, and 103 pmol monoglyceride 17:1 as internal standard ( 7 ). Culture dishes were sonicated in a bath sonicator for 30 s before lipid collection.…”

Recent Advances of DNA Nanostructure‐Based Cell Membrane Engineering

“…[ 7–10 ] For example, the Presenilins protein in the γ ‐secretase complex balances the lipid homeostasis in the cell through hydrolyzing the discard proteins in the cell membrane. [ 11 ] However, due to the structural and chemical complexity of membrane proteins, it is difficult to do univariate analysis for the effects of proteins on cell membrane properties, such as size effect or chemical composition effect. After development of DNA nanotechnology for decades, it is feasible to construct DNA nanostructures of arbitrary sizes and morphologies with near‐atomic scale precision.…”