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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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Increased macroautophagy in PS1/APP mice and human brains. (A–D) EM images of cortical neuropil show an absence of AVs and normal neurite profile in 9-mo-old NTg mouse brains (A, arrowheads outline normal neurites) and a marked accumulation of AVs within enlarged or dystrophic neurites in PS1/APP mice (B, arrowheads outline dystrophic neurite profiles in C) and biopsied brain material from an AD patient (B, inset). At higher magnification (C), AVs include autophagosomes (arrows) and multilamellar bodies (arrowhead). In normal dendrites of PS1/APP mice, multiple AVs are frequently seen (D, arrows). (E and F) LC3 quantification analyzed from immunoblots of LC3-I and LC3-II (top) in prefrontal cortical homogenates from cases of nonaffected (Cont), early stage (preclinical) AD (AD-ES), and moderate AD (AD-MS; E), and from brains of 18–22-mo-old PS1/APP (PA) mice (n = 3; F) compared with nontransgenic (NTg) controls (n = 3; *, P < 0.01). Error bars represent SEM. (G–L) LC3 immunofluorescence in 9-mo-old PS1/APP mice can be seen mainly as puncta in dystrophic dendrites of the cortex (G, arrows) and along adjacent dendrites. LC3 (H, arrows) is strong in dystrophic neurites in the periphery (asterisks) of a thioflavin S–labeled plaque core (H, inset) but is less so in neurites closest (H, arrowheads) to the Aβ deposit. LC3 is diffuse and uniform in neurons of NTg mice (I and J) but is predominantly vesicular and distributed more to the dendrites (arrows) than the cell soma (arrowheads) in 9-mo-old PS1/APP cortex (K and L).
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fig1: Increased macroautophagy in PS1/APP mice and human brains. (A–D) EM images of cortical neuropil show an absence of AVs and normal neurite profile in 9-mo-old NTg mouse brains (A, arrowheads outline normal neurites) and a marked accumulation of AVs within enlarged or dystrophic neurites in PS1/APP mice (B, arrowheads outline dystrophic neurite profiles in C) and biopsied brain material from an AD patient (B, inset). At higher magnification (C), AVs include autophagosomes (arrows) and multilamellar bodies (arrowhead). In normal dendrites of PS1/APP mice, multiple AVs are frequently seen (D, arrows). (E and F) LC3 quantification analyzed from immunoblots of LC3-I and LC3-II (top) in prefrontal cortical homogenates from cases of nonaffected (Cont), early stage (preclinical) AD (AD-ES), and moderate AD (AD-MS; E), and from brains of 18–22-mo-old PS1/APP (PA) mice (n = 3; F) compared with nontransgenic (NTg) controls (n = 3; *, P < 0.01). Error bars represent SEM. (G–L) LC3 immunofluorescence in 9-mo-old PS1/APP mice can be seen mainly as puncta in dystrophic dendrites of the cortex (G, arrows) and along adjacent dendrites. LC3 (H, arrows) is strong in dystrophic neurites in the periphery (asterisks) of a thioflavin S–labeled plaque core (H, inset) but is less so in neurites closest (H, arrowheads) to the Aβ deposit. LC3 is diffuse and uniform in neurons of NTg mice (I and J) but is predominantly vesicular and distributed more to the dendrites (arrows) than the cell soma (arrowheads) in 9-mo-old PS1/APP cortex (K and L).

Mentions: AVs are rare in neurons of the normal adult brain (Nixon et al., 2005). In AD, however, AVs appear in neocortical and hippocampal pyramidal neurons and accumulate markedly within the dendritic arbors of these affected cells (Nixon et al., 2005). We observed similar pathological AV accumulation in PS1/APP animals, which is a mouse model of AD that expresses human mutant PS1 and the Swedish variant of Aβ (Duff et al., 1996). PS1/APP mice begin to deposit Aβ after 10 wk of age and progressively develop many neuritic plaques that mainly consist of Aβ and grossly swollen dendrites and axons (Holcomb et al., 1998). AVs were rarely found in the neuropil of nontransgenic (NTg) mice (Fig. 1 A). In contrast, the numbers of AVs were at least 23-fold higher in the neurons of 9-mo-old PS1/APP mice (13.17 ± 1.91 SEM) compared with age-matched NTg controls (0.57 ± 0.08 SEM) based on ultrastructural morphometric analyses of AV numbers in a series of 100 EM images. AV pathology in 9-mo-old mice (Fig. 1, B–D), like that in AD brains (Fig. 1 B, inset), ranged from small numbers of AVs in relatively normal-appearing dendrites (Fig. 1 D) to striking pathologic accumulations of AVs within dystrophic neurites, where AVs were usually the predominant organelles (Fig. 1, B and C). A significant proportion of AVs met the morphologic criteria for autophagosomes, including a size >0.5 μm in diameter, a double limiting membrane, and the presence within a single vacuole of multiple membranous organelle-derived structures (Fig. 1 B; Dunn, 1990a). Other AVs included translucent and dense multivesicular and multilamellar bodies with single or double outer membranes (Fig. 1 C), reflecting later stages of macroautophagy. In AD brain, we identified these AVs as autophagolysosomes (“late” AVs; Dunn, 1990b), which contain acid hydrolases but are distinct from lysosomal dense bodies that are small (<0.3 μm) and uniformly dense (Nixon et al., 2005). Therefore, we documented a robust accumulation of both early and late AVs in AD and PS1/APP brains, reflecting marked macroautophagic induction, failed maturation of AVs to lysosomes, or both (Nixon et al., 2005).


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)

Increased macroautophagy in PS1/APP mice and human brains. (A–D) EM images of cortical neuropil show an absence of AVs and normal neurite profile in 9-mo-old NTg mouse brains (A, arrowheads outline normal neurites) and a marked accumulation of AVs within enlarged or dystrophic neurites in PS1/APP mice (B, arrowheads outline dystrophic neurite profiles in C) and biopsied brain material from an AD patient (B, inset). At higher magnification (C), AVs include autophagosomes (arrows) and multilamellar bodies (arrowhead). In normal dendrites of PS1/APP mice, multiple AVs are frequently seen (D, arrows). (E and F) LC3 quantification analyzed from immunoblots of LC3-I and LC3-II (top) in prefrontal cortical homogenates from cases of nonaffected (Cont), early stage (preclinical) AD (AD-ES), and moderate AD (AD-MS; E), and from brains of 18–22-mo-old PS1/APP (PA) mice (n = 3; F) compared with nontransgenic (NTg) controls (n = 3; *, P < 0.01). Error bars represent SEM. (G–L) LC3 immunofluorescence in 9-mo-old PS1/APP mice can be seen mainly as puncta in dystrophic dendrites of the cortex (G, arrows) and along adjacent dendrites. LC3 (H, arrows) is strong in dystrophic neurites in the periphery (asterisks) of a thioflavin S–labeled plaque core (H, inset) but is less so in neurites closest (H, arrowheads) to the Aβ deposit. LC3 is diffuse and uniform in neurons of NTg mice (I and J) but is predominantly vesicular and distributed more to the dendrites (arrows) than the cell soma (arrowheads) in 9-mo-old PS1/APP cortex (K and L).
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fig1: Increased macroautophagy in PS1/APP mice and human brains. (A–D) EM images of cortical neuropil show an absence of AVs and normal neurite profile in 9-mo-old NTg mouse brains (A, arrowheads outline normal neurites) and a marked accumulation of AVs within enlarged or dystrophic neurites in PS1/APP mice (B, arrowheads outline dystrophic neurite profiles in C) and biopsied brain material from an AD patient (B, inset). At higher magnification (C), AVs include autophagosomes (arrows) and multilamellar bodies (arrowhead). In normal dendrites of PS1/APP mice, multiple AVs are frequently seen (D, arrows). (E and F) LC3 quantification analyzed from immunoblots of LC3-I and LC3-II (top) in prefrontal cortical homogenates from cases of nonaffected (Cont), early stage (preclinical) AD (AD-ES), and moderate AD (AD-MS; E), and from brains of 18–22-mo-old PS1/APP (PA) mice (n = 3; F) compared with nontransgenic (NTg) controls (n = 3; *, P < 0.01). Error bars represent SEM. (G–L) LC3 immunofluorescence in 9-mo-old PS1/APP mice can be seen mainly as puncta in dystrophic dendrites of the cortex (G, arrows) and along adjacent dendrites. LC3 (H, arrows) is strong in dystrophic neurites in the periphery (asterisks) of a thioflavin S–labeled plaque core (H, inset) but is less so in neurites closest (H, arrowheads) to the Aβ deposit. LC3 is diffuse and uniform in neurons of NTg mice (I and J) but is predominantly vesicular and distributed more to the dendrites (arrows) than the cell soma (arrowheads) in 9-mo-old PS1/APP cortex (K and L).
Mentions: AVs are rare in neurons of the normal adult brain (Nixon et al., 2005). In AD, however, AVs appear in neocortical and hippocampal pyramidal neurons and accumulate markedly within the dendritic arbors of these affected cells (Nixon et al., 2005). We observed similar pathological AV accumulation in PS1/APP animals, which is a mouse model of AD that expresses human mutant PS1 and the Swedish variant of Aβ (Duff et al., 1996). PS1/APP mice begin to deposit Aβ after 10 wk of age and progressively develop many neuritic plaques that mainly consist of Aβ and grossly swollen dendrites and axons (Holcomb et al., 1998). AVs were rarely found in the neuropil of nontransgenic (NTg) mice (Fig. 1 A). In contrast, the numbers of AVs were at least 23-fold higher in the neurons of 9-mo-old PS1/APP mice (13.17 ± 1.91 SEM) compared with age-matched NTg controls (0.57 ± 0.08 SEM) based on ultrastructural morphometric analyses of AV numbers in a series of 100 EM images. AV pathology in 9-mo-old mice (Fig. 1, B–D), like that in AD brains (Fig. 1 B, inset), ranged from small numbers of AVs in relatively normal-appearing dendrites (Fig. 1 D) to striking pathologic accumulations of AVs within dystrophic neurites, where AVs were usually the predominant organelles (Fig. 1, B and C). A significant proportion of AVs met the morphologic criteria for autophagosomes, including a size >0.5 μm in diameter, a double limiting membrane, and the presence within a single vacuole of multiple membranous organelle-derived structures (Fig. 1 B; Dunn, 1990a). Other AVs included translucent and dense multivesicular and multilamellar bodies with single or double outer membranes (Fig. 1 C), reflecting later stages of macroautophagy. In AD brain, we identified these AVs as autophagolysosomes (“late” AVs; Dunn, 1990b), which contain acid hydrolases but are distinct from lysosomal dense bodies that are small (<0.3 μm) and uniformly dense (Nixon et al., 2005). Therefore, we documented a robust accumulation of both early and late AVs in AD and PS1/APP brains, reflecting marked macroautophagic induction, failed maturation of AVs to lysosomes, or both (Nixon et al., 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.

Show MeSH
Related in: MedlinePlus