Active gamma-secretase is localized to detergent-resistant membranes in human brain.
Several lines of evidence suggest that polymerization of the amyloid beta-peptide (Abeta) into amyloid plaques is a pathogenic event in Alzheimer's disease (AD). Abeta is produced from the amyloid precursor protein as the result of sequential proteolytic cleavages by beta-secretase and gamma-secretase, and it has been suggested that these enzymes could be targets for treatment of AD. gamma-Secretase is an aspartyl protease complex, containing at least four transmembrane proteins. Studies in cell lines have shown that gamma-secretase is partially localized to lipid rafts, which are detergent-resistant membrane microdomains enriched in cholesterol and sphingolipids. Here, we studied gamma-secretase in detergent-resistant membranes (DRMs) prepared from human brain. DRMs prepared in the mild detergent CHAPSO and isolated by sucrose gradient centrifugation were enriched in gamma-secretase components and activity. The DRM fraction was subjected to size-exclusion chromatography in CHAPSO, and all of the gamma-secretase components and a lipid raft marker were found in the void volume (> 2000 kDa). Co-immunoprecipitation studies further supported the notion that the gamma-secretase components are associated even at high concentrations of CHAPSO. Preparations from rat brain gave similar results and showed a postmortem time-dependent decline in gamma-secretase activity, suggesting that DRMs from fresh rat brain may be useful for gamma-secretase activity studies. Finally, confocal microscopy showed co-localization of gamma-secretase components and a lipid raft marker in thin sections of human brain. We conclude that the active gamma-secretase complex is localized to lipid rafts in human brain.
Hur
Ji-Yeun
JY
Karolinska Institutet (KI) Dainippon Sumitomo Pharma Alzheimer Center, KI-Alzheimer's Disease Research Center, Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Novum, Huddinge, Sweden.
Welander
Hedvig
H
Behbahani
Homira
H
Aoki
Mikio
M
Frånberg
Jenny
J
Winblad
Bengt
B
Frykman
Susanne
S
Tjernberg
Lars O
LO
D053829:Amyloid Precursor Protein Secretases / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification; D000818:Animals; D001921:Brain / Q000201:enzymology*; D045744:Cell Line, Tumor; D002850:Chromatography, Gel; D003902:Detergents / Q000737:chemistry; D006801:Humans; D047468:Immunoprecipitation; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification; D021962:Membrane Microdomains / Q000737:chemistry / Q000201:enzymology*; D008970:Molecular Weight; D051381:Rats
D003902:Detergents; D008562:Membrane Glycoproteins; C413604:nicastrin protein; D053829:Amyloid Precursor Protein Secretases