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Amyloid beta dimers/trimers potently induce cofilin-actin rods that are inhibited by maintaining cofilin-phosphorylation.

Davis RC, Marsden IT, Maloney MT, Minamide LS, Podlisny M, Selkoe DJ, Bamburg JR - Mol Neurodegener (2011)

Bottom Line: Fractions from 7PA2 medium containing Aβ monomers are not active, suggesting oxidized SDS-stable Aβ1-42 dimers in a low-n state are the most active rod-inducing species.Overexpression of cofilin phosphatases increase rod formation when expressed alone and exacerbate rod formation when coupled with Aβd/t, whereas overexpression of a cofilin kinase inhibits Aβd/t-induced rod formation.Together these data support a mechanism by which Aβd/t alters the actin cytoskeleton via effects on cofilin in neurons critical to learning and memory.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870, USA. jbamburg@lamar.colostate.edu.

ABSTRACT

Background: Previously we reported 1 μM synthetic human amyloid beta1-42 oligomers induced cofilin dephosphorylation (activation) and formation of cofilin-actin rods within rat hippocampal neurons primarily localized to the dentate gyrus.

Results: Here we demonstrate that a gel filtration fraction of 7PA2 cell-secreted SDS-stable human Aβ dimers and trimers (Aβd/t) induces maximal neuronal rod response at ~250 pM. This is 4,000-fold more active than traditionally prepared human Aβ oligomers, which contain SDS-stable trimers and tetramers, but are devoid of dimers. When incubated under tyrosine oxidizing conditions, synthetic human but not rodent Aβ1-42, the latter lacking tyrosine, acquires a marked increase (620 fold for EC50) in rod-inducing activity. Gel filtration of this preparation yielded two fractions containing SDS-stable dimers, trimers and tetramers. One, eluting at a similar volume to 7PA2 Aβd/t, had maximum activity at ~5 nM, whereas the other, eluting at the void volume (high-n state), lacked rod inducing activity at the same concentration. Fractions from 7PA2 medium containing Aβ monomers are not active, suggesting oxidized SDS-stable Aβ1-42 dimers in a low-n state are the most active rod-inducing species. Aβd/t-induced rods are predominantly localized to the dentate gyrus and mossy fiber tract, reach significance over controls within 2 h of treatment, and are reversible, disappearing by 24 h after Aβd/t washout. Overexpression of cofilin phosphatases increase rod formation when expressed alone and exacerbate rod formation when coupled with Aβd/t, whereas overexpression of a cofilin kinase inhibits Aβd/t-induced rod formation.

Conclusions: Together these data support a mechanism by which Aβd/t alters the actin cytoskeleton via effects on cofilin in neurons critical to learning and memory.

No MeSH data available.


Related in: MedlinePlus

Three-dimensional reconstruction of cofilin-stained rods in deconvolved confocal image stacks from organotypic slices. Treatment of organotypic slices with Aβd/t results in a profound increase in cofilin-immunostained rods in the dentate gyrus/mossy fiber tract (DG/MFT) and a global change in cofilin distribution in cells in this region. (A) Single focal plane of non-rod-forming region near the CA3 compared to a rod hot spot in the dentate gyrus. Rods are evident in this single plane. (B) Three dimensional stack of planes from a cofilin stained control and Aβd/t-treated slice. Deconvolution of the confocal image stacks and thresholding the image by removing the lowest 20% of signal (lower panels) provides striking evidence of rod formation in this region. Hundreds of rods can be observed, which contain virtually all of the remaining immunostained cofilin.
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Figure 6: Three-dimensional reconstruction of cofilin-stained rods in deconvolved confocal image stacks from organotypic slices. Treatment of organotypic slices with Aβd/t results in a profound increase in cofilin-immunostained rods in the dentate gyrus/mossy fiber tract (DG/MFT) and a global change in cofilin distribution in cells in this region. (A) Single focal plane of non-rod-forming region near the CA3 compared to a rod hot spot in the dentate gyrus. Rods are evident in this single plane. (B) Three dimensional stack of planes from a cofilin stained control and Aβd/t-treated slice. Deconvolution of the confocal image stacks and thresholding the image by removing the lowest 20% of signal (lower panels) provides striking evidence of rod formation in this region. Hundreds of rods can be observed, which contain virtually all of the remaining immunostained cofilin.

Mentions: Rods are not apparent in low magnification images of slices, but become apparent when viewed with a 60x objective, even in single confocal sections (Figure 6A). However, the rod distribution and abundance within the dentate gyrus are more impressive when the confocal image stack is deconvolved and the lowest 20% intensity of immunstaining is removed by resetting the low threshold on an image histogram (Figure 6B). Only a few densely stained cofilin aggregates are observed in the 3D reconstruction of the image stack from control slices whereas rods are abundant throughout the Aβd/t-treated slice.


Amyloid beta dimers/trimers potently induce cofilin-actin rods that are inhibited by maintaining cofilin-phosphorylation.

Davis RC, Marsden IT, Maloney MT, Minamide LS, Podlisny M, Selkoe DJ, Bamburg JR - Mol Neurodegener (2011)

Three-dimensional reconstruction of cofilin-stained rods in deconvolved confocal image stacks from organotypic slices. Treatment of organotypic slices with Aβd/t results in a profound increase in cofilin-immunostained rods in the dentate gyrus/mossy fiber tract (DG/MFT) and a global change in cofilin distribution in cells in this region. (A) Single focal plane of non-rod-forming region near the CA3 compared to a rod hot spot in the dentate gyrus. Rods are evident in this single plane. (B) Three dimensional stack of planes from a cofilin stained control and Aβd/t-treated slice. Deconvolution of the confocal image stacks and thresholding the image by removing the lowest 20% of signal (lower panels) provides striking evidence of rod formation in this region. Hundreds of rods can be observed, which contain virtually all of the remaining immunostained cofilin.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3037337&req=5

Figure 6: Three-dimensional reconstruction of cofilin-stained rods in deconvolved confocal image stacks from organotypic slices. Treatment of organotypic slices with Aβd/t results in a profound increase in cofilin-immunostained rods in the dentate gyrus/mossy fiber tract (DG/MFT) and a global change in cofilin distribution in cells in this region. (A) Single focal plane of non-rod-forming region near the CA3 compared to a rod hot spot in the dentate gyrus. Rods are evident in this single plane. (B) Three dimensional stack of planes from a cofilin stained control and Aβd/t-treated slice. Deconvolution of the confocal image stacks and thresholding the image by removing the lowest 20% of signal (lower panels) provides striking evidence of rod formation in this region. Hundreds of rods can be observed, which contain virtually all of the remaining immunostained cofilin.
Mentions: Rods are not apparent in low magnification images of slices, but become apparent when viewed with a 60x objective, even in single confocal sections (Figure 6A). However, the rod distribution and abundance within the dentate gyrus are more impressive when the confocal image stack is deconvolved and the lowest 20% intensity of immunstaining is removed by resetting the low threshold on an image histogram (Figure 6B). Only a few densely stained cofilin aggregates are observed in the 3D reconstruction of the image stack from control slices whereas rods are abundant throughout the Aβd/t-treated slice.

Bottom Line: Fractions from 7PA2 medium containing Aβ monomers are not active, suggesting oxidized SDS-stable Aβ1-42 dimers in a low-n state are the most active rod-inducing species.Overexpression of cofilin phosphatases increase rod formation when expressed alone and exacerbate rod formation when coupled with Aβd/t, whereas overexpression of a cofilin kinase inhibits Aβd/t-induced rod formation.Together these data support a mechanism by which Aβd/t alters the actin cytoskeleton via effects on cofilin in neurons critical to learning and memory.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870, USA. jbamburg@lamar.colostate.edu.

ABSTRACT

Background: Previously we reported 1 μM synthetic human amyloid beta1-42 oligomers induced cofilin dephosphorylation (activation) and formation of cofilin-actin rods within rat hippocampal neurons primarily localized to the dentate gyrus.

Results: Here we demonstrate that a gel filtration fraction of 7PA2 cell-secreted SDS-stable human Aβ dimers and trimers (Aβd/t) induces maximal neuronal rod response at ~250 pM. This is 4,000-fold more active than traditionally prepared human Aβ oligomers, which contain SDS-stable trimers and tetramers, but are devoid of dimers. When incubated under tyrosine oxidizing conditions, synthetic human but not rodent Aβ1-42, the latter lacking tyrosine, acquires a marked increase (620 fold for EC50) in rod-inducing activity. Gel filtration of this preparation yielded two fractions containing SDS-stable dimers, trimers and tetramers. One, eluting at a similar volume to 7PA2 Aβd/t, had maximum activity at ~5 nM, whereas the other, eluting at the void volume (high-n state), lacked rod inducing activity at the same concentration. Fractions from 7PA2 medium containing Aβ monomers are not active, suggesting oxidized SDS-stable Aβ1-42 dimers in a low-n state are the most active rod-inducing species. Aβd/t-induced rods are predominantly localized to the dentate gyrus and mossy fiber tract, reach significance over controls within 2 h of treatment, and are reversible, disappearing by 24 h after Aβd/t washout. Overexpression of cofilin phosphatases increase rod formation when expressed alone and exacerbate rod formation when coupled with Aβd/t, whereas overexpression of a cofilin kinase inhibits Aβd/t-induced rod formation.

Conclusions: Together these data support a mechanism by which Aβd/t alters the actin cytoskeleton via effects on cofilin in neurons critical to learning and memory.

No MeSH data available.


Related in: MedlinePlus