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Macroautophagy--a novel Beta-amyloid peptide-generating pathway activated in Alzheimer's disease.

Yu WH, Cuervo AM, Kumar A, Peterhoff CM, Schmidt SD, Lee JH, Mohan PS, Mercken M, Farmery MR, Tjernberg LO, Jiang Y, Duff K, Uchiyama Y, Näslund J, Mathews PM, Cataldo AM, Nixon RA - J. Cell Biol. (2005)

Bottom Line: Purified AVs contain APP and beta-cleaved APP and are highly enriched in PS1, nicastrin, and PS-dependent gamma-secretase activity.Inducing or inhibiting macroautophagy in neuronal and nonneuronal cells by modulating mammalian target of rapamycin kinase elicits parallel changes in AV proliferation and Abeta production.Our results, therefore, link beta-amyloidogenic and cell survival pathways through macroautophagy, which is activated and is abnormal in AD.

View Article: PubMed Central - PubMed

Affiliation: Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY 10962, USA.

ABSTRACT
Macroautophagy, which is a lysosomal pathway for the turnover of organelles and long-lived proteins, is a key determinant of cell survival and longevity. In this study, we show that neuronal macroautophagy is induced early in Alzheimer's disease (AD) and before beta-amyloid (Abeta) deposits extracellularly in the presenilin (PS) 1/Abeta precursor protein (APP) mouse model of beta-amyloidosis. Subsequently, autophagosomes and late autophagic vacuoles (AVs) accumulate markedly in dystrophic dendrites, implying an impaired maturation of AVs to lysosomes. Immunolabeling identifies AVs in the brain as a major reservoir of intracellular Abeta. Purified AVs contain APP and beta-cleaved APP and are highly enriched in PS1, nicastrin, and PS-dependent gamma-secretase activity. Inducing or inhibiting macroautophagy in neuronal and nonneuronal cells by modulating mammalian target of rapamycin kinase elicits parallel changes in AV proliferation and Abeta production. Our results, therefore, link beta-amyloidogenic and cell survival pathways through macroautophagy, which is activated and is abnormal in AD.

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Evidence for the enrichment of PS1-dependent γ-secretase activity in AVs. (A and B) Ultrastructure of AVs (A1 and A2) and lysosomes in subcellular fractions from serum-deprived L/APP cells (A) and Western blot analysis (B) for LC3-II, rab24, APP, βCTF, PS1 (PS1 amino-terminal fragment), and nicastrin (NCT) in L/APP subcellular fractions. AVs, A1 and A2; L, lysosomes; E, tubulovesicular compartments (Golgi/ER/endosomes); P, postnuclear pellet; C, cytosol; M, mitochondria. Empty lanes in the original blot have been removed from the figure and noted with a white line. (C) Rates of cleavage of the fluorogenic substrate in subcellular fractions from L/APP cells grown in −serum media (left) or −Leu/−His media (right). PNP, postnuclear pellet. (D and E) Proportions of the total recovered cell γ-secretase activity in different subcellular fractions after serum deprivation (D) or in uninduced (+serum) or induced (−Leu/−His) cells (E). Comparison of +serum versus −Leu and −His conditions shows the redistribution of γ-secretase activity from the tubulovesicular to AV fractions after macroautophagic induction. G, Golgi; A, AV. (F) Liquid chromatography mass spectrometry analysis of the fluorogenic substrate after incubation with purified AVs. Selected ion chromatogram corresponding to different cleavage products is displayed. Numbers in graph refer to the cleavage/amino acid site from the Aβ peptide. (G) γ-Secretase activity in AV and lysosome fractions from mice blastocysts in which the PS1 and PS2 genes were deleted (PS KO; BD8) or in which human PS1 was stably transfected into the PS KO blastocysts (hPS1; BD8/hPS1). Numbers on x axis are in minutes. (H) Aβ40 and Aβ42 levels in medium from these cells as detected by sandwich ELISA. Values are given as means ± SEM (error bars).
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fig7: Evidence for the enrichment of PS1-dependent γ-secretase activity in AVs. (A and B) Ultrastructure of AVs (A1 and A2) and lysosomes in subcellular fractions from serum-deprived L/APP cells (A) and Western blot analysis (B) for LC3-II, rab24, APP, βCTF, PS1 (PS1 amino-terminal fragment), and nicastrin (NCT) in L/APP subcellular fractions. AVs, A1 and A2; L, lysosomes; E, tubulovesicular compartments (Golgi/ER/endosomes); P, postnuclear pellet; C, cytosol; M, mitochondria. Empty lanes in the original blot have been removed from the figure and noted with a white line. (C) Rates of cleavage of the fluorogenic substrate in subcellular fractions from L/APP cells grown in −serum media (left) or −Leu/−His media (right). PNP, postnuclear pellet. (D and E) Proportions of the total recovered cell γ-secretase activity in different subcellular fractions after serum deprivation (D) or in uninduced (+serum) or induced (−Leu/−His) cells (E). Comparison of +serum versus −Leu and −His conditions shows the redistribution of γ-secretase activity from the tubulovesicular to AV fractions after macroautophagic induction. G, Golgi; A, AV. (F) Liquid chromatography mass spectrometry analysis of the fluorogenic substrate after incubation with purified AVs. Selected ion chromatogram corresponding to different cleavage products is displayed. Numbers in graph refer to the cleavage/amino acid site from the Aβ peptide. (G) γ-Secretase activity in AV and lysosome fractions from mice blastocysts in which the PS1 and PS2 genes were deleted (PS KO; BD8) or in which human PS1 was stably transfected into the PS KO blastocysts (hPS1; BD8/hPS1). Numbers on x axis are in minutes. (H) Aβ40 and Aβ42 levels in medium from these cells as detected by sandwich ELISA. Values are given as means ± SEM (error bars).

Mentions: In further studies, we assayed for the protein components and the γ-secretase activity that are needed for Aβ generation in highly purified fractions of AVs from serum-deprived L/APP cells. The AV and lysosome fractions were isolated, and the identity and purity of AV and lysosome fractions were confirmed by EM (Fig. 7 A) and by immunoblotting using antibodies to LC3-II and rab24, which is a ras-related GTPase that is associated with macroautophagy (Fig. 7 B; Munafo and Colombo, 2002). Consistent with the immunogold studies of L/APP cells in Fig. 6, AV fractions were highly enriched in levels of PS1 and nicastrin relative to the other subcellular fractions. Purified AVs also contained significant levels of APP and βCTF (Fig. 7 B). APP was enriched in the ER/endosome/Golgi fraction as well as the AV isolates in cells that were treated with media lacking Leu and His and cells grown in serum. In uninduced cells, the total amount of AVs recovered was considerably lower. PS1 was most abundant in the AV (A2) fraction after macroautophagic induction by serum deprivation, with lesser amounts in the A1 and lysosome fractions and in the ER/endosome/Golgi.


Macroautophagy--a novel Beta-amyloid peptide-generating pathway activated in Alzheimer's disease.

Yu WH, Cuervo AM, Kumar A, Peterhoff CM, Schmidt SD, Lee JH, Mohan PS, Mercken M, Farmery MR, Tjernberg LO, Jiang Y, Duff K, Uchiyama Y, Näslund J, Mathews PM, Cataldo AM, Nixon RA - J. Cell Biol. (2005)

Evidence for the enrichment of PS1-dependent γ-secretase activity in AVs. (A and B) Ultrastructure of AVs (A1 and A2) and lysosomes in subcellular fractions from serum-deprived L/APP cells (A) and Western blot analysis (B) for LC3-II, rab24, APP, βCTF, PS1 (PS1 amino-terminal fragment), and nicastrin (NCT) in L/APP subcellular fractions. AVs, A1 and A2; L, lysosomes; E, tubulovesicular compartments (Golgi/ER/endosomes); P, postnuclear pellet; C, cytosol; M, mitochondria. Empty lanes in the original blot have been removed from the figure and noted with a white line. (C) Rates of cleavage of the fluorogenic substrate in subcellular fractions from L/APP cells grown in −serum media (left) or −Leu/−His media (right). PNP, postnuclear pellet. (D and E) Proportions of the total recovered cell γ-secretase activity in different subcellular fractions after serum deprivation (D) or in uninduced (+serum) or induced (−Leu/−His) cells (E). Comparison of +serum versus −Leu and −His conditions shows the redistribution of γ-secretase activity from the tubulovesicular to AV fractions after macroautophagic induction. G, Golgi; A, AV. (F) Liquid chromatography mass spectrometry analysis of the fluorogenic substrate after incubation with purified AVs. Selected ion chromatogram corresponding to different cleavage products is displayed. Numbers in graph refer to the cleavage/amino acid site from the Aβ peptide. (G) γ-Secretase activity in AV and lysosome fractions from mice blastocysts in which the PS1 and PS2 genes were deleted (PS KO; BD8) or in which human PS1 was stably transfected into the PS KO blastocysts (hPS1; BD8/hPS1). Numbers on x axis are in minutes. (H) Aβ40 and Aβ42 levels in medium from these cells as detected by sandwich ELISA. Values are given as means ± SEM (error bars).
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fig7: Evidence for the enrichment of PS1-dependent γ-secretase activity in AVs. (A and B) Ultrastructure of AVs (A1 and A2) and lysosomes in subcellular fractions from serum-deprived L/APP cells (A) and Western blot analysis (B) for LC3-II, rab24, APP, βCTF, PS1 (PS1 amino-terminal fragment), and nicastrin (NCT) in L/APP subcellular fractions. AVs, A1 and A2; L, lysosomes; E, tubulovesicular compartments (Golgi/ER/endosomes); P, postnuclear pellet; C, cytosol; M, mitochondria. Empty lanes in the original blot have been removed from the figure and noted with a white line. (C) Rates of cleavage of the fluorogenic substrate in subcellular fractions from L/APP cells grown in −serum media (left) or −Leu/−His media (right). PNP, postnuclear pellet. (D and E) Proportions of the total recovered cell γ-secretase activity in different subcellular fractions after serum deprivation (D) or in uninduced (+serum) or induced (−Leu/−His) cells (E). Comparison of +serum versus −Leu and −His conditions shows the redistribution of γ-secretase activity from the tubulovesicular to AV fractions after macroautophagic induction. G, Golgi; A, AV. (F) Liquid chromatography mass spectrometry analysis of the fluorogenic substrate after incubation with purified AVs. Selected ion chromatogram corresponding to different cleavage products is displayed. Numbers in graph refer to the cleavage/amino acid site from the Aβ peptide. (G) γ-Secretase activity in AV and lysosome fractions from mice blastocysts in which the PS1 and PS2 genes were deleted (PS KO; BD8) or in which human PS1 was stably transfected into the PS KO blastocysts (hPS1; BD8/hPS1). Numbers on x axis are in minutes. (H) Aβ40 and Aβ42 levels in medium from these cells as detected by sandwich ELISA. Values are given as means ± SEM (error bars).
Mentions: In further studies, we assayed for the protein components and the γ-secretase activity that are needed for Aβ generation in highly purified fractions of AVs from serum-deprived L/APP cells. The AV and lysosome fractions were isolated, and the identity and purity of AV and lysosome fractions were confirmed by EM (Fig. 7 A) and by immunoblotting using antibodies to LC3-II and rab24, which is a ras-related GTPase that is associated with macroautophagy (Fig. 7 B; Munafo and Colombo, 2002). Consistent with the immunogold studies of L/APP cells in Fig. 6, AV fractions were highly enriched in levels of PS1 and nicastrin relative to the other subcellular fractions. Purified AVs also contained significant levels of APP and βCTF (Fig. 7 B). APP was enriched in the ER/endosome/Golgi fraction as well as the AV isolates in cells that were treated with media lacking Leu and His and cells grown in serum. In uninduced cells, the total amount of AVs recovered was considerably lower. PS1 was most abundant in the AV (A2) fraction after macroautophagic induction by serum deprivation, with lesser amounts in the A1 and lysosome fractions and in the ER/endosome/Golgi.

Bottom Line: Purified AVs contain APP and beta-cleaved APP and are highly enriched in PS1, nicastrin, and PS-dependent gamma-secretase activity.Inducing or inhibiting macroautophagy in neuronal and nonneuronal cells by modulating mammalian target of rapamycin kinase elicits parallel changes in AV proliferation and Abeta production.Our results, therefore, link beta-amyloidogenic and cell survival pathways through macroautophagy, which is activated and is abnormal in AD.

View Article: PubMed Central - PubMed

Affiliation: Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY 10962, USA.

ABSTRACT
Macroautophagy, which is a lysosomal pathway for the turnover of organelles and long-lived proteins, is a key determinant of cell survival and longevity. In this study, we show that neuronal macroautophagy is induced early in Alzheimer's disease (AD) and before beta-amyloid (Abeta) deposits extracellularly in the presenilin (PS) 1/Abeta precursor protein (APP) mouse model of beta-amyloidosis. Subsequently, autophagosomes and late autophagic vacuoles (AVs) accumulate markedly in dystrophic dendrites, implying an impaired maturation of AVs to lysosomes. Immunolabeling identifies AVs in the brain as a major reservoir of intracellular Abeta. Purified AVs contain APP and beta-cleaved APP and are highly enriched in PS1, nicastrin, and PS-dependent gamma-secretase activity. Inducing or inhibiting macroautophagy in neuronal and nonneuronal cells by modulating mammalian target of rapamycin kinase elicits parallel changes in AV proliferation and Abeta production. Our results, therefore, link beta-amyloidogenic and cell survival pathways through macroautophagy, which is activated and is abnormal in AD.

Show MeSH
Related in: MedlinePlus