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A152T tau allele causes neurodegeneration that can be ameliorated in a zebrafish model by autophagy induction

View Article: PubMed Central - PubMed

ABSTRACT

Mutations in MAPT cause a variety of neurodegenerative disorders. Lopez et al. confirm that A152T-variant tau is associated with increased risk for frontotemporal dementia and progressive supranuclear palsy syndrome. Upregulation of autophagy increases tau clearance and ameliorates pathology in zebrafish expressing A152T-tau, suggesting potential for the treatment of tauopathies.

No MeSH data available.


Related in: MedlinePlus

Tau clearance in vivo and autophagy function. Clearance kinetics of photoconverted Dendra-tau measured in neurons of WT-tau and AT152T-tau fish. Measurement of the intensity of the red Dendra-tau signal over time reflects the clearance or degradation of tau protein. (A) Representative images of photoconverted red Dendra-tau signal comparing a single neuron from WT-tau and A152T-tau fish at three different timepoints: immediately after photoconversion (0 h), 24 h and 48 h after photoconversion. (B) Quantification of red Dendra-tau intensity in photoconverted neurons in the spinal cord of WT-tau and A152T-Tau transgenic fish (representative images shown in Supplementary Fig. 8C). The percentage of residual photoconverted red Dendra-tau was measured over 48 h measured at 12-h intervals. Dendra-tagged A152T-tau clears at a significantly lower rate than WT-tau. (n = 30/group shown as mean ± SD; Student-Newman-Keuls one-way ANOVA, **P < 0.01 and ***P < 0.001 versus WT-tau). (C–F) Western blots for LC3-II, a well-characterized marker of autophagosome number, demonstrate that there are no differences in the levels of this protein between WT-tau and A152T-tau fish either at 24 hpf (pre-phenotype; C and D) or 72 hpf (post-phenotype; E and F). (E and F) Measurements of LC3-II levels in the presence or absence of ammonium chloride provides a method for measuring autophagic flux. No differences were observed between the two transgenic lines at 3 dpf, suggesting that autophagy functions normally in both WT-tau and A152T-tau fish (graph represents mean ± SD of four independent clutches per group for E and F and three for C and D; two-tailed t-test). (G and H) Clearance kinetics of Dendra-tau was measured in the presence or absence of ammonium chloride. Treatment with ammonium chloride blocks autophagic flux and delays the clearance of both WT-tau and A152T-tau to the same extent, indicating that flux occurs at the same rate in these two lines (mean ± SD, n = 62 neurons/group; Student-Newman-Keuls one-way ANOVA, **P < 0.01 and ***P < 0.001 versus untreated group). Note in G and H, the ‘WT-tau + NH4Cl’ (denoted by black squares and black dashed line) overlaps with the ‘A152T-tau’ line (denoted by grey triangles and grey solid line). The graphs in G and H are presented with a different line in the foreground and background to aid interpretation.
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awx005-F5: Tau clearance in vivo and autophagy function. Clearance kinetics of photoconverted Dendra-tau measured in neurons of WT-tau and AT152T-tau fish. Measurement of the intensity of the red Dendra-tau signal over time reflects the clearance or degradation of tau protein. (A) Representative images of photoconverted red Dendra-tau signal comparing a single neuron from WT-tau and A152T-tau fish at three different timepoints: immediately after photoconversion (0 h), 24 h and 48 h after photoconversion. (B) Quantification of red Dendra-tau intensity in photoconverted neurons in the spinal cord of WT-tau and A152T-Tau transgenic fish (representative images shown in Supplementary Fig. 8C). The percentage of residual photoconverted red Dendra-tau was measured over 48 h measured at 12-h intervals. Dendra-tagged A152T-tau clears at a significantly lower rate than WT-tau. (n = 30/group shown as mean ± SD; Student-Newman-Keuls one-way ANOVA, **P < 0.01 and ***P < 0.001 versus WT-tau). (C–F) Western blots for LC3-II, a well-characterized marker of autophagosome number, demonstrate that there are no differences in the levels of this protein between WT-tau and A152T-tau fish either at 24 hpf (pre-phenotype; C and D) or 72 hpf (post-phenotype; E and F). (E and F) Measurements of LC3-II levels in the presence or absence of ammonium chloride provides a method for measuring autophagic flux. No differences were observed between the two transgenic lines at 3 dpf, suggesting that autophagy functions normally in both WT-tau and A152T-tau fish (graph represents mean ± SD of four independent clutches per group for E and F and three for C and D; two-tailed t-test). (G and H) Clearance kinetics of Dendra-tau was measured in the presence or absence of ammonium chloride. Treatment with ammonium chloride blocks autophagic flux and delays the clearance of both WT-tau and A152T-tau to the same extent, indicating that flux occurs at the same rate in these two lines (mean ± SD, n = 62 neurons/group; Student-Newman-Keuls one-way ANOVA, **P < 0.01 and ***P < 0.001 versus untreated group). Note in G and H, the ‘WT-tau + NH4Cl’ (denoted by black squares and black dashed line) overlaps with the ‘A152T-tau’ line (denoted by grey triangles and grey solid line). The graphs in G and H are presented with a different line in the foreground and background to aid interpretation.

Mentions: To study the influence of the A152T variant on tau turnover rate, we expressed Dendra-tau under the control of mosaic ubiquitous EIF1α::Gal4VP16 driver, as the mosaic expression enables analyses in single cells. Quantification of Dendra, a green-to-red photoconvertible fluorescent protein fused to tau, enabled assessment of tau clearance kinetics in individual spinal cord motor neurons in vivo. Mosaic fish were imaged before and after photoconversion then at defined intervals thereafter, to assess clearance of the red, photoconverted, fluorescently-tagged tau protein (Supplementary Fig. 8). Interestingly, A152T-tau showed significantly slower clearance kinetics than the WT-tau in vivo (Fig. 5A and B). As tau protein is known to be a substrate for both the proteasome and for autophagic degradation (Berger et al., 2006), the slower clearance of A152T-tau may be the result of defects in either of these processes. However, autophagy appeared to be normal in WT-tau and A152T-tau fish as we observed no difference in levels of LC3-II, a well-characterized marker of autophagosome number, either in the presence or absence of ammonium chloride (Fig. 5C–F). Furthermore, when clearance experiments were performed in the presence of ammonium chloride, the rate of clearance was slowed to the same extent in both WT-tau and A152T-tau fish, suggesting that autophagy is functioning normally (Fig. 5G and H).Figure 5


A152T tau allele causes neurodegeneration that can be ameliorated in a zebrafish model by autophagy induction
Tau clearance in vivo and autophagy function. Clearance kinetics of photoconverted Dendra-tau measured in neurons of WT-tau and AT152T-tau fish. Measurement of the intensity of the red Dendra-tau signal over time reflects the clearance or degradation of tau protein. (A) Representative images of photoconverted red Dendra-tau signal comparing a single neuron from WT-tau and A152T-tau fish at three different timepoints: immediately after photoconversion (0 h), 24 h and 48 h after photoconversion. (B) Quantification of red Dendra-tau intensity in photoconverted neurons in the spinal cord of WT-tau and A152T-Tau transgenic fish (representative images shown in Supplementary Fig. 8C). The percentage of residual photoconverted red Dendra-tau was measured over 48 h measured at 12-h intervals. Dendra-tagged A152T-tau clears at a significantly lower rate than WT-tau. (n = 30/group shown as mean ± SD; Student-Newman-Keuls one-way ANOVA, **P < 0.01 and ***P < 0.001 versus WT-tau). (C–F) Western blots for LC3-II, a well-characterized marker of autophagosome number, demonstrate that there are no differences in the levels of this protein between WT-tau and A152T-tau fish either at 24 hpf (pre-phenotype; C and D) or 72 hpf (post-phenotype; E and F). (E and F) Measurements of LC3-II levels in the presence or absence of ammonium chloride provides a method for measuring autophagic flux. No differences were observed between the two transgenic lines at 3 dpf, suggesting that autophagy functions normally in both WT-tau and A152T-tau fish (graph represents mean ± SD of four independent clutches per group for E and F and three for C and D; two-tailed t-test). (G and H) Clearance kinetics of Dendra-tau was measured in the presence or absence of ammonium chloride. Treatment with ammonium chloride blocks autophagic flux and delays the clearance of both WT-tau and A152T-tau to the same extent, indicating that flux occurs at the same rate in these two lines (mean ± SD, n = 62 neurons/group; Student-Newman-Keuls one-way ANOVA, **P < 0.01 and ***P < 0.001 versus untreated group). Note in G and H, the ‘WT-tau + NH4Cl’ (denoted by black squares and black dashed line) overlaps with the ‘A152T-tau’ line (denoted by grey triangles and grey solid line). The graphs in G and H are presented with a different line in the foreground and background to aid interpretation.
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awx005-F5: Tau clearance in vivo and autophagy function. Clearance kinetics of photoconverted Dendra-tau measured in neurons of WT-tau and AT152T-tau fish. Measurement of the intensity of the red Dendra-tau signal over time reflects the clearance or degradation of tau protein. (A) Representative images of photoconverted red Dendra-tau signal comparing a single neuron from WT-tau and A152T-tau fish at three different timepoints: immediately after photoconversion (0 h), 24 h and 48 h after photoconversion. (B) Quantification of red Dendra-tau intensity in photoconverted neurons in the spinal cord of WT-tau and A152T-Tau transgenic fish (representative images shown in Supplementary Fig. 8C). The percentage of residual photoconverted red Dendra-tau was measured over 48 h measured at 12-h intervals. Dendra-tagged A152T-tau clears at a significantly lower rate than WT-tau. (n = 30/group shown as mean ± SD; Student-Newman-Keuls one-way ANOVA, **P < 0.01 and ***P < 0.001 versus WT-tau). (C–F) Western blots for LC3-II, a well-characterized marker of autophagosome number, demonstrate that there are no differences in the levels of this protein between WT-tau and A152T-tau fish either at 24 hpf (pre-phenotype; C and D) or 72 hpf (post-phenotype; E and F). (E and F) Measurements of LC3-II levels in the presence or absence of ammonium chloride provides a method for measuring autophagic flux. No differences were observed between the two transgenic lines at 3 dpf, suggesting that autophagy functions normally in both WT-tau and A152T-tau fish (graph represents mean ± SD of four independent clutches per group for E and F and three for C and D; two-tailed t-test). (G and H) Clearance kinetics of Dendra-tau was measured in the presence or absence of ammonium chloride. Treatment with ammonium chloride blocks autophagic flux and delays the clearance of both WT-tau and A152T-tau to the same extent, indicating that flux occurs at the same rate in these two lines (mean ± SD, n = 62 neurons/group; Student-Newman-Keuls one-way ANOVA, **P < 0.01 and ***P < 0.001 versus untreated group). Note in G and H, the ‘WT-tau + NH4Cl’ (denoted by black squares and black dashed line) overlaps with the ‘A152T-tau’ line (denoted by grey triangles and grey solid line). The graphs in G and H are presented with a different line in the foreground and background to aid interpretation.
Mentions: To study the influence of the A152T variant on tau turnover rate, we expressed Dendra-tau under the control of mosaic ubiquitous EIF1α::Gal4VP16 driver, as the mosaic expression enables analyses in single cells. Quantification of Dendra, a green-to-red photoconvertible fluorescent protein fused to tau, enabled assessment of tau clearance kinetics in individual spinal cord motor neurons in vivo. Mosaic fish were imaged before and after photoconversion then at defined intervals thereafter, to assess clearance of the red, photoconverted, fluorescently-tagged tau protein (Supplementary Fig. 8). Interestingly, A152T-tau showed significantly slower clearance kinetics than the WT-tau in vivo (Fig. 5A and B). As tau protein is known to be a substrate for both the proteasome and for autophagic degradation (Berger et al., 2006), the slower clearance of A152T-tau may be the result of defects in either of these processes. However, autophagy appeared to be normal in WT-tau and A152T-tau fish as we observed no difference in levels of LC3-II, a well-characterized marker of autophagosome number, either in the presence or absence of ammonium chloride (Fig. 5C–F). Furthermore, when clearance experiments were performed in the presence of ammonium chloride, the rate of clearance was slowed to the same extent in both WT-tau and A152T-tau fish, suggesting that autophagy is functioning normally (Fig. 5G and H).Figure 5

View Article: PubMed Central - PubMed

ABSTRACT

Mutations in MAPT cause a variety of neurodegenerative disorders. Lopez et al. confirm that A152T-variant tau is associated with increased risk for frontotemporal dementia and progressive supranuclear palsy syndrome. Upregulation of autophagy increases tau clearance and ameliorates pathology in zebrafish expressing A152T-tau, suggesting potential for the treatment of tauopathies.

No MeSH data available.


Related in: MedlinePlus