Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2022 Oct 26;23(21):12985.
doi: 10.3390/ijms232112985.

Differential Effects of Human Tau Isoforms to Neuronal Dysfunction and Toxicity in the Drosophila CNS

Ergina Vourkou  1   2   3 , Vassilis Paspaliaris  1   4 , Anna Bourouliti  1   5 , Maria-Christina Zerva  1   6 , Engie Prifti  1   7 , Katerina Papanikolopoulou  1 , Efthimios M C Skoulakis  1
Affiliations

Differential Effects of Human Tau Isoforms to Neuronal Dysfunction and Toxicity in the Drosophila CNS

Ergina Vourkou et al. Int J Mol Sci. .

Abstract

Accumulation of highly post-translationally modified tau proteins is a hallmark of neurodegenerative disorders known as tauopathies, the most common of which is Alzheimer's disease. Although six tau isoforms are found in the human brain, the majority of animal and cellular tauopathy models utilize a representative single isoform. However, the six human tau isoforms present overlapping but distinct distributions in the brain and are differentially involved in particular tauopathies. These observations support the notion that tau isoforms possess distinct functional properties important for both physiology and pathology. To address this hypothesis, the six human brain tau isoforms were expressed singly in the Drosophila brain and their effects in an established battery of assays measuring neuronal dysfunction, vulnerability to oxidative stress and life span were systematically assessed comparatively. The results reveal isoform-specific effects clearly not attributed to differences in expression levels but correlated with the number of microtubule-binding repeats and the accumulation of a particular isoform in support of the functional differentiation of these tau isoforms. Delineation of isoform-specific effects is essential to understand the apparent differential involvement of each tau isoform in tauopathies and their contribution to neuronal dysfunction and toxicity.

Keywords: Drosophila; habituation; learning and memory; neuronal dysfunction; tau isoforms; toxicity.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Variable levels of hTau isoforms in the Drosophila CNS. (A) A representative Western blot of head lysates from animals expressing the different hTau transgenes under the elavGAL4 driver detected with the 5A6 anti-tau antibody. The hTau isoform expressed in the fly CNS is indicated below the quantification. For the quantification, hTau levels were normalized using the Syx loading control and are shown as the mean ± SEM of n = 3 independent experiments. Bars marked with # are not significantly different from each other but are from those marked with ‡ and conversely ‡ marked bars are not significantly different from each other but are from ones marked with #. (B) Quantification of tau mRNA levels by Reverse Transcription followed by the Polymerase Chain Reaction in the CNS of flies expressing the indicated hTau transgenes under elavGAL4. The rp49 RNA served as an internal reference transcript for the reaction and has been used to normalize the quantifications. Bars indicate mean ± SEM relative mRNA levels. n = 4. Statistical details for both experiments are presented in Supplemental Table S1.
Figure 2
Figure 2
Tau isoforms affect differentially mushroom body neurons structurally and functionally. (A) Carnoy’s-fixed paraffin-embedded frontal sections stained with anti-Leonardo antibody at the level of the dendrites (calyces) of MB neurons, from control (elavGAL4/+) and animals expressing the indicated hTau transgenes under elavGal4. The area of the calyx from multiple similar sections per genotype was quantified, averaged below and presented as the mean ± SEM. Stars indicate significant differences from control flies. n ≥ 7 for all genotypes. (B) Learning after 3 and 6 pairings of animals accumulating pan-neuronally the indicated hTau transgenes under elavGAL4 (black bars) compared with driver (grey bars) and transgene heterozygotes (white bars). The means ± SEMs are shown. Stars (*) indicate significant differences from both controls. n ≥ 11 for all genotypes. Statistical details for both experiments are presented in Supplemental Table S2.
Figure 3
Figure 3
PSD memory deficits emerge for all 4R isoforms. The hTau isoform expressed is indicated above each graph. The means ± SEMs for the indicated repetitions are shown. Stars (*) indicate significant differences from both controls. Statistical details in Supplemental Table S3. (A) Protein synthesis-dependent memory of animals accumulating pan-neuronally the indicated hTau isoforms (black bars) compared with driver and transgene heterozygotes (grey and white bars). n ≥ 7 for all genotypes. (B) Protein synthesis independent memory of animals accumulating pan-neuronally the indicated hTau proteins (black bars) compared with driver and transgene heterozygotes (grey and white bars). n ≥ 9 for all genotypes.
Figure 4
Figure 4
Conditioning stimulus perception and mobility is unaffected by hTau isoform accumulation. (A) Odor and electric footshock avoidance of animals accumulating pan-neuronally the indicated hTau isoforms compared with driver and transgene heterozygotes. The means ± SEM are shown for n ≥ 6 for all genotypes. (B) Negative geotaxis (climbing) of flies accumulating pan-neuronally for 5 days at 25 °C the indicated hTau isoforms compared with driver heterozygotes. The hTau isoform expressed is indicated below each bar. The means ± SEMs are shown for n ≥ 12 for all genotypes. Statistical details for both experiments are presented in Supplemental Table S4.
Figure 5
Figure 5
hTau isoforms affect differentially habituation to footshocks. Habituation following exposure to 15 (A) or 2 footshocks (B) of flies accumulating pan-neuronally the indicated hTau isoforms (black bars) compared with driver and transgene heterozygotes (grey and white bars). The means ± SEMs are shown for n ≥ 7 for all genotypes. Stars (*) indicate significant differences from both controls. Statistical details in Supplemental Table S5.
Figure 6
Figure 6
Circadian locomotor activity is affected by all hTau isoforms. Locomotor activity of animals accumulating pan-neuronally the indicated hTau isoforms under elavGAL4 (black bars) compared with driver and transgene heterozygotes (grey and white bars). Flies were monitored for 2 days at 25 °C in a 12 h light/dark cycle. Representations of the average activities of the indicated genotypes monitored in 30-min bins over two days (left panel) divided in four 6-h intervals (early day: 0600–1130, late day: 1200–1730, early night: 1800–2330 and late night 2400–0530 h) as indicted by the light on (white) and off (black) and bar on the bottom of the graph. Total activities shown as means ± SEMs for each quarter day for animals accumulating the indicated isoform and relevant controls are indicated on the right. Stars (*) indicate significant differences from both controls. n ≥ 50 flies per genotype. Statistical details in Supplemental Table S6.
Figure 7
Figure 7
CNS accumulation of all hTau isoforms increases vulnerability to oxidative stress. The mortality of flies accumulating the indicated hTau isoforms and controls upon exposure to 5% H2O2 at 25 °C scored at 24, 48, 52, 58 and 75 h is shown. The bars represent the mean ± SEM from two independent experiments with at least 300 flies assessed per genotype. Stars indicate significant differences from control flies. Statistical details in Supplemental Table S7.
Figure 8
Figure 8
Lifespan is equally decreased by all hTau isoforms. Survival curves for animals accumulating pan-neuronally the six hTau isoforms under elav-GAL4; tub-Gal80ts compared with driver heterozygotes (w1118). Flies were raised at 18 °C, but adults were transferred and maintained at 30 °C until they expired. The data represent the mean ± SEM from two independent experiments with at least 300 flies assessed per genotype. After 27 days, the population of control heterozygotes (w1118) was reduced by 50% (50% attrition) indicated by the dotted line and the number of surviving animals per genotype on that day is quantified in the insert. Stars indicate significant differences from control. Statistical details in Supplemental Table S8.
Figure 9
Figure 9
A summary of hTau steady state levels and isoform specific phenotypes as detailed in the text. Bars marked with # are not significantly different from each other but are from those marked with ‡ and conversely ‡ marked bars are not significantly different from each other but are from ones marked with #. Arrows denote changes in phenotype (up or down) compared to controls, while dashes denote no effect.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Qiang L., Sun X., Austin T.O., Muralidharan H., Jean D.C., Liu M., Yu W., Baas P.W. Tau Does Not Stabilize Axonal Microtubules but Rather Enables Them to Have Long Labile Domains. Curr. Biol. 2018;28:2181–2189. doi: 10.1016/j.cub.2018.05.045. - DOI - PubMed
    1. Sotiropoulos I., Galas M.C., Silva J.M., Skoulakis E., Wegmann S., Maina M.B., Blum D., Sayas C.L., Mandelkow E.M., Mandelkow E., et al. Atypical, non-standard functions of the microtubule associated Tau protein. Acta Neuropathol. Commun. 2017;5:91. doi: 10.1186/s40478-017-0489-6. - DOI - PMC - PubMed
    1. Couchie D., Mavilia C., Georgieff I.S., Liem R.K., Shelanski M.L., Nunez J. Primary structure of high molecular weight tau present in the peripheral nervous system. Proc. Natl. Acad. Sci. USA. 1992;89:4378–4381. doi: 10.1073/pnas.89.10.4378. - DOI - PMC - PubMed
    1. Goedert M., Jakes R. Expression of separate isoforms of human tau protein: Correlation with the tau pattern in brain and effects on tubulin polymerization. Embo J. 1990;9:4225–4230. doi: 10.1002/j.1460-2075.1990.tb07870.x. - DOI - PMC - PubMed
    1. Panda D., Samuel J., Massie M., Feinstein S., Wilson L. Differential regulation of microtubule dynamics by three- and four-repeat tau: Implications for the onset of neurodegenerative disease. Proc. Natl. Acad. Sci. USA. 2003;100:9548–9553. doi: 10.1073/pnas.1633508100. - DOI - PMC - PubMed

LinkOut - more resources