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GSK-3beta phosphorylation of functionally distinct tau isoforms has differential, but mild effects.

Voss K, Gamblin TC - Mol Neurodegener (2009)

Bottom Line: We have found that each isoform has a unique microtubule binding and polymerization profile that is altered by GSK-3beta.These results indicate that tau phosphorylation by a single kinase can have isoform specific outcomes.The mild nature of these changes, however, makes it unlikely that differential effects of GSK-3beta phosphorylation on the isoforms are causative in neurodegenerative disease.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Molecular Biosciences, University of Kansas, 1200 Sunnyside Avenue, Lawrence, KS 66045, USA. gamblin@ku.edu.

ABSTRACT

Background: Tau protein exists as six different isoforms that differ by the inclusion or exclusion of exons 2, 3 and 10. Exon 10 encodes a microtubule binding repeat, thereby resulting in three isoforms with three microtubule binding repeats (3R) and three isoforms that have four microtubule binding repeats (4R). In normal adult brain, the relative amounts of 3R tau and 4R tau are approximately equal. These relative protein levels are preserved in Alzheimer's disease, although in other neurodegenerative tauopathies such as progressive supranuclear palsy, corticobasal degeneration and Pick's disease, the ratio of 3R:4R is frequently altered. Because tau isoforms are not equally involved in these diseases, it is possible that they either have inherently unique characteristics owing to their primary structures or that post-translational modification, such as phosphorylation, differentially affects their properties.

Results: We have determined the effects of phosphorylation by a kinase widely believed to be involved in neurodegenerative processes, glycogen synthase kinase-3beta (GSK-3beta), on the microtubule binding and inducer-initiated polymerization of these isoforms in vitro. We have found that each isoform has a unique microtubule binding and polymerization profile that is altered by GSK-3beta. GSK-3beta phosphorylation had differential effects on the isoforms although there were similarities between isoforms and the effects were generally mild.

Conclusion: These results indicate that tau phosphorylation by a single kinase can have isoform specific outcomes. The mild nature of these changes, however, makes it unlikely that differential effects of GSK-3beta phosphorylation on the isoforms are causative in neurodegenerative disease. Instead, the inherent differences in the isoform interactions themselves and local conditions in the diseased cells are likely the major determinant of isoform involvement in various neurodegenerative disorders.

No MeSH data available.


Related in: MedlinePlus

TEM analysis of ARA induction of GSK-3β phosphorylated tau isoforms. Images are as follows: (A) 0N3R, (B) 0N4R, (C) 1N3R, (D) 1N4R, (E) 2N3R, and (F) 2N4R. Images were recorded at a magnification of 20,000× (A-F) and are representative of polymerized material from 75 μM ARA induced-reactions presented in Figure 6. Scale bars represent 1 μm.
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Figure 7: TEM analysis of ARA induction of GSK-3β phosphorylated tau isoforms. Images are as follows: (A) 0N3R, (B) 0N4R, (C) 1N3R, (D) 1N4R, (E) 2N3R, and (F) 2N4R. Images were recorded at a magnification of 20,000× (A-F) and are representative of polymerized material from 75 μM ARA induced-reactions presented in Figure 6. Scale bars represent 1 μm.

Mentions: Because LLS readings can be influenced by the size and length of the particles [29] and it is not clear to which molecular species ThS binds [30-32], samples of phosphorylated tau isoform filaments were viewed by TEM to determine whether phosphorylation induces significant changes in filament morphology, as has been observed with 2N4R tau [13,19]. Representative micrographs of phosphorylated samples polymerized in the presence of 75 μM ARA indicate distinct morphological changes from unphosphorylated tau isoforms (Compare Figure 7 and Figure 2). Phosphorylated 0N3R and 0N4R (Figure 7a, b) isoforms had increases in the relative length and number of filaments formed as compared to non-phosphorylated (Figure 2c, f). Filaments formed from phosphorylated 1N3R and 1N4R (Figure 7c, d) isoforms also appeared to be relatively more numerous, and longer than non-phosphorylated (Figure 2d, g), although these changes were less dramatic than for the 0N isoforms. Phosphorylated 2N3R and 2N4R (Figure 7e, f) appeared to be relatively unchanged in the length and number of filaments (Figure 3e, h). Filaments from phosphorylated 0N3R, 1N4R, and 2N4R, had an increased tendency to cluster in close association to form "tangle-like" structures, similar to those seen previously with phosphorylated 2N4R induced with lower (25 μM) ARA concentrations [13,19]. It is apparent that isoform and inducer concentration, as well as phosphorylation, affect filament interactions promoting "tangle-like" structures.


GSK-3beta phosphorylation of functionally distinct tau isoforms has differential, but mild effects.

Voss K, Gamblin TC - Mol Neurodegener (2009)

TEM analysis of ARA induction of GSK-3β phosphorylated tau isoforms. Images are as follows: (A) 0N3R, (B) 0N4R, (C) 1N3R, (D) 1N4R, (E) 2N3R, and (F) 2N4R. Images were recorded at a magnification of 20,000× (A-F) and are representative of polymerized material from 75 μM ARA induced-reactions presented in Figure 6. Scale bars represent 1 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2683827&req=5

Figure 7: TEM analysis of ARA induction of GSK-3β phosphorylated tau isoforms. Images are as follows: (A) 0N3R, (B) 0N4R, (C) 1N3R, (D) 1N4R, (E) 2N3R, and (F) 2N4R. Images were recorded at a magnification of 20,000× (A-F) and are representative of polymerized material from 75 μM ARA induced-reactions presented in Figure 6. Scale bars represent 1 μm.
Mentions: Because LLS readings can be influenced by the size and length of the particles [29] and it is not clear to which molecular species ThS binds [30-32], samples of phosphorylated tau isoform filaments were viewed by TEM to determine whether phosphorylation induces significant changes in filament morphology, as has been observed with 2N4R tau [13,19]. Representative micrographs of phosphorylated samples polymerized in the presence of 75 μM ARA indicate distinct morphological changes from unphosphorylated tau isoforms (Compare Figure 7 and Figure 2). Phosphorylated 0N3R and 0N4R (Figure 7a, b) isoforms had increases in the relative length and number of filaments formed as compared to non-phosphorylated (Figure 2c, f). Filaments formed from phosphorylated 1N3R and 1N4R (Figure 7c, d) isoforms also appeared to be relatively more numerous, and longer than non-phosphorylated (Figure 2d, g), although these changes were less dramatic than for the 0N isoforms. Phosphorylated 2N3R and 2N4R (Figure 7e, f) appeared to be relatively unchanged in the length and number of filaments (Figure 3e, h). Filaments from phosphorylated 0N3R, 1N4R, and 2N4R, had an increased tendency to cluster in close association to form "tangle-like" structures, similar to those seen previously with phosphorylated 2N4R induced with lower (25 μM) ARA concentrations [13,19]. It is apparent that isoform and inducer concentration, as well as phosphorylation, affect filament interactions promoting "tangle-like" structures.

Bottom Line: We have found that each isoform has a unique microtubule binding and polymerization profile that is altered by GSK-3beta.These results indicate that tau phosphorylation by a single kinase can have isoform specific outcomes.The mild nature of these changes, however, makes it unlikely that differential effects of GSK-3beta phosphorylation on the isoforms are causative in neurodegenerative disease.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Molecular Biosciences, University of Kansas, 1200 Sunnyside Avenue, Lawrence, KS 66045, USA. gamblin@ku.edu.

ABSTRACT

Background: Tau protein exists as six different isoforms that differ by the inclusion or exclusion of exons 2, 3 and 10. Exon 10 encodes a microtubule binding repeat, thereby resulting in three isoforms with three microtubule binding repeats (3R) and three isoforms that have four microtubule binding repeats (4R). In normal adult brain, the relative amounts of 3R tau and 4R tau are approximately equal. These relative protein levels are preserved in Alzheimer's disease, although in other neurodegenerative tauopathies such as progressive supranuclear palsy, corticobasal degeneration and Pick's disease, the ratio of 3R:4R is frequently altered. Because tau isoforms are not equally involved in these diseases, it is possible that they either have inherently unique characteristics owing to their primary structures or that post-translational modification, such as phosphorylation, differentially affects their properties.

Results: We have determined the effects of phosphorylation by a kinase widely believed to be involved in neurodegenerative processes, glycogen synthase kinase-3beta (GSK-3beta), on the microtubule binding and inducer-initiated polymerization of these isoforms in vitro. We have found that each isoform has a unique microtubule binding and polymerization profile that is altered by GSK-3beta. GSK-3beta phosphorylation had differential effects on the isoforms although there were similarities between isoforms and the effects were generally mild.

Conclusion: These results indicate that tau phosphorylation by a single kinase can have isoform specific outcomes. The mild nature of these changes, however, makes it unlikely that differential effects of GSK-3beta phosphorylation on the isoforms are causative in neurodegenerative disease. Instead, the inherent differences in the isoform interactions themselves and local conditions in the diseased cells are likely the major determinant of isoform involvement in various neurodegenerative disorders.

No MeSH data available.


Related in: MedlinePlus