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Abeta42-induced neurodegeneration via an age-dependent autophagic-lysosomal injury in Drosophila.

Ling D, Song HJ, Garza D, Neufeld TP, Salvaterra PM - PLoS ONE (2009)

Bottom Line: Abeta(1-42)-induced impairment of the degradative function, as well as the structural integrity, of post-lysosomal autophagic vesicles triggers a neurodegenerative cascade that can be enhanced by autophagy activation or partially rescued by autophagy inhibition.Neuronal autophagy initially appears to play a pro-survival role that changes in an age-dependent way to a pro-death role in the context of Abeta(1-42) expression.Our in vivo observations provide a mechanistic understanding for the differential neurotoxicity of Abeta(1-42) and Abeta(1-40), and reveal an Abeta(1-42)-induced death execution pathway mediated by an age-dependent autophagic-lysosomal injury.

View Article: PubMed Central - PubMed

Affiliation: Division of Neuroscience, Beckman Research Institute of the City of Hope, Duarte, California, United States of America.

ABSTRACT
The mechanism of widespread neuronal death occurring in Alzheimer's disease (AD) remains enigmatic even after extensive investigation during the last two decades. Amyloid beta 42 peptide (Abeta(1-42)) is believed to play a causative role in the development of AD. Here we expressed human Abeta(1-42) and amyloid beta 40 (Abeta(1-40)) in Drosophila neurons. Abeta(1-42) but not Abeta(1-40) causes an extensive accumulation of autophagic vesicles that become increasingly dysfunctional with age. Abeta(1-42)-induced impairment of the degradative function, as well as the structural integrity, of post-lysosomal autophagic vesicles triggers a neurodegenerative cascade that can be enhanced by autophagy activation or partially rescued by autophagy inhibition. Compromise and leakage from post-lysosomal vesicles result in cytosolic acidification, additional damage to membranes and organelles, and erosive destruction of cytoplasm leading to eventual neuron death. Neuronal autophagy initially appears to play a pro-survival role that changes in an age-dependent way to a pro-death role in the context of Abeta(1-42) expression. Our in vivo observations provide a mechanistic understanding for the differential neurotoxicity of Abeta(1-42) and Abeta(1-40), and reveal an Abeta(1-42)-induced death execution pathway mediated by an age-dependent autophagic-lysosomal injury.

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Aβ1–42 induces an age-dependent dysfunction in autophagic degradation.(A) Control flies fed with 1 µM rapamycin up to 16 days exhibit no accumulation of fluorescent puncta in neurons, suggesting that induction of normal autophagy in healthy neurons is not sufficient to induce formation of fluorescent puncta. (B–C) Neurons from 1-day-old Aβ1–42 flies exhibit numerous autophagic vesicles (arrows) in electron micrographs (B) but no fluorescent puncta in confocal micrographs (C), suggesting that autophagic vesicles at an early age can efficiently digest GFP. (D) Confocal micrograph of neurons from 16-day-old Aβ1–42 flies exhibit an extensive accumulation of fluorescent puncta (arrows). (E) Fluorescent puncta (left panel, arrows) colocalize with Aβ1–42 immunostaining (middle panel, arrows) suggesting an association between the two. Scale bars = 5 µm (A, C–E) or 1 µm (B).
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pone-0004201-g003: Aβ1–42 induces an age-dependent dysfunction in autophagic degradation.(A) Control flies fed with 1 µM rapamycin up to 16 days exhibit no accumulation of fluorescent puncta in neurons, suggesting that induction of normal autophagy in healthy neurons is not sufficient to induce formation of fluorescent puncta. (B–C) Neurons from 1-day-old Aβ1–42 flies exhibit numerous autophagic vesicles (arrows) in electron micrographs (B) but no fluorescent puncta in confocal micrographs (C), suggesting that autophagic vesicles at an early age can efficiently digest GFP. (D) Confocal micrograph of neurons from 16-day-old Aβ1–42 flies exhibit an extensive accumulation of fluorescent puncta (arrows). (E) Fluorescent puncta (left panel, arrows) colocalize with Aβ1–42 immunostaining (middle panel, arrows) suggesting an association between the two. Scale bars = 5 µm (A, C–E) or 1 µm (B).

Mentions: Healthy neurons are thought to have a high efficiency of autophagy degradation; thus autophagic vesicles are usually undetectable due to their rapid turnover[9], [24]. To test if induction of normal autophagy could result in accumulation of fluorescent puncta in the absence of Aβ1–42 expression, we fed 1 µM rapamycin, an autophagy inducer[25], to control flies. Continuous rapamycin feeding does not result in puncta formation in neurons examined in up to 16-day-old adults (Fig. 3A), suggesting that induction of normal autophagy per se does not result in puncta accumulation. Therefore, the numerous puncta in Aβ1–42-targeted neurons (Fig. 3D) are abnormal autophagic vesicles with undigested cargo as indexed by GFP. Electron micrographs reveal numerous autophagic vesicles in neurons from 1-day-old Aβ1–42 flies (Fig. 3B); however, no fluorescent puncta are detectible in neurons at this age (Fig. 3C), suggesting that autophagic vesicles in young Aβ1–42 flies (1–5 days) are functionally normal. The age-dependent increase of fluorescent puncta in Aβ1–42-targeted neurons (Fig. 1F) indicates that the degradative function of autophagy is likely to become progressively impaired with aging. Anti-Aβ immunostaining shows colocalization between fluorescent puncta and Aβ1–42 (Fig. 3E), indicating an accumulation of Aβ1–42 along with other undigested cargo. Aβ1–40 expression under the same experimental conditions does not result in an age-dependent accumulation of fluorescent puncta.


Abeta42-induced neurodegeneration via an age-dependent autophagic-lysosomal injury in Drosophila.

Ling D, Song HJ, Garza D, Neufeld TP, Salvaterra PM - PLoS ONE (2009)

Aβ1–42 induces an age-dependent dysfunction in autophagic degradation.(A) Control flies fed with 1 µM rapamycin up to 16 days exhibit no accumulation of fluorescent puncta in neurons, suggesting that induction of normal autophagy in healthy neurons is not sufficient to induce formation of fluorescent puncta. (B–C) Neurons from 1-day-old Aβ1–42 flies exhibit numerous autophagic vesicles (arrows) in electron micrographs (B) but no fluorescent puncta in confocal micrographs (C), suggesting that autophagic vesicles at an early age can efficiently digest GFP. (D) Confocal micrograph of neurons from 16-day-old Aβ1–42 flies exhibit an extensive accumulation of fluorescent puncta (arrows). (E) Fluorescent puncta (left panel, arrows) colocalize with Aβ1–42 immunostaining (middle panel, arrows) suggesting an association between the two. Scale bars = 5 µm (A, C–E) or 1 µm (B).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2626277&req=5

pone-0004201-g003: Aβ1–42 induces an age-dependent dysfunction in autophagic degradation.(A) Control flies fed with 1 µM rapamycin up to 16 days exhibit no accumulation of fluorescent puncta in neurons, suggesting that induction of normal autophagy in healthy neurons is not sufficient to induce formation of fluorescent puncta. (B–C) Neurons from 1-day-old Aβ1–42 flies exhibit numerous autophagic vesicles (arrows) in electron micrographs (B) but no fluorescent puncta in confocal micrographs (C), suggesting that autophagic vesicles at an early age can efficiently digest GFP. (D) Confocal micrograph of neurons from 16-day-old Aβ1–42 flies exhibit an extensive accumulation of fluorescent puncta (arrows). (E) Fluorescent puncta (left panel, arrows) colocalize with Aβ1–42 immunostaining (middle panel, arrows) suggesting an association between the two. Scale bars = 5 µm (A, C–E) or 1 µm (B).
Mentions: Healthy neurons are thought to have a high efficiency of autophagy degradation; thus autophagic vesicles are usually undetectable due to their rapid turnover[9], [24]. To test if induction of normal autophagy could result in accumulation of fluorescent puncta in the absence of Aβ1–42 expression, we fed 1 µM rapamycin, an autophagy inducer[25], to control flies. Continuous rapamycin feeding does not result in puncta formation in neurons examined in up to 16-day-old adults (Fig. 3A), suggesting that induction of normal autophagy per se does not result in puncta accumulation. Therefore, the numerous puncta in Aβ1–42-targeted neurons (Fig. 3D) are abnormal autophagic vesicles with undigested cargo as indexed by GFP. Electron micrographs reveal numerous autophagic vesicles in neurons from 1-day-old Aβ1–42 flies (Fig. 3B); however, no fluorescent puncta are detectible in neurons at this age (Fig. 3C), suggesting that autophagic vesicles in young Aβ1–42 flies (1–5 days) are functionally normal. The age-dependent increase of fluorescent puncta in Aβ1–42-targeted neurons (Fig. 1F) indicates that the degradative function of autophagy is likely to become progressively impaired with aging. Anti-Aβ immunostaining shows colocalization between fluorescent puncta and Aβ1–42 (Fig. 3E), indicating an accumulation of Aβ1–42 along with other undigested cargo. Aβ1–40 expression under the same experimental conditions does not result in an age-dependent accumulation of fluorescent puncta.

Bottom Line: Abeta(1-42)-induced impairment of the degradative function, as well as the structural integrity, of post-lysosomal autophagic vesicles triggers a neurodegenerative cascade that can be enhanced by autophagy activation or partially rescued by autophagy inhibition.Neuronal autophagy initially appears to play a pro-survival role that changes in an age-dependent way to a pro-death role in the context of Abeta(1-42) expression.Our in vivo observations provide a mechanistic understanding for the differential neurotoxicity of Abeta(1-42) and Abeta(1-40), and reveal an Abeta(1-42)-induced death execution pathway mediated by an age-dependent autophagic-lysosomal injury.

View Article: PubMed Central - PubMed

Affiliation: Division of Neuroscience, Beckman Research Institute of the City of Hope, Duarte, California, United States of America.

ABSTRACT
The mechanism of widespread neuronal death occurring in Alzheimer's disease (AD) remains enigmatic even after extensive investigation during the last two decades. Amyloid beta 42 peptide (Abeta(1-42)) is believed to play a causative role in the development of AD. Here we expressed human Abeta(1-42) and amyloid beta 40 (Abeta(1-40)) in Drosophila neurons. Abeta(1-42) but not Abeta(1-40) causes an extensive accumulation of autophagic vesicles that become increasingly dysfunctional with age. Abeta(1-42)-induced impairment of the degradative function, as well as the structural integrity, of post-lysosomal autophagic vesicles triggers a neurodegenerative cascade that can be enhanced by autophagy activation or partially rescued by autophagy inhibition. Compromise and leakage from post-lysosomal vesicles result in cytosolic acidification, additional damage to membranes and organelles, and erosive destruction of cytoplasm leading to eventual neuron death. Neuronal autophagy initially appears to play a pro-survival role that changes in an age-dependent way to a pro-death role in the context of Abeta(1-42) expression. Our in vivo observations provide a mechanistic understanding for the differential neurotoxicity of Abeta(1-42) and Abeta(1-40), and reveal an Abeta(1-42)-induced death execution pathway mediated by an age-dependent autophagic-lysosomal injury.

Show MeSH
Related in: MedlinePlus