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Enhanced neuronal glucose transporter expression reveals metabolic choice in a HD Drosophila model.

Besson MT, Alegría K, Garrido-Gerter P, Barros LF, Liévens JC - PLoS ONE (2015)

Bottom Line: We demonstrated that overexpression of the human glucose transporter in neurons ameliorated significantly the status of HD flies by increasing their lifespan, reducing their locomotor deficits and rescuing eye neurodegeneration.Overexpression of PFK did not affect HQ93 fly survival, but protected from photoreceptor loss.Finally, the PPP and, to a lesser extent, the glycolysis seem to mediate the hGluT3 protective effects, whereas, in addition, the PPP provides increased protection to oxidative stress.

View Article: PubMed Central - PubMed

Affiliation: Aix-Marseille Université, CNRS, CRN2M-UMR7286, 13344 Marseille cedex 15, Marseille, France.

ABSTRACT
Huntington's disease is a neurodegenerative disorder caused by toxic insertions of polyglutamine residues in the Huntingtin protein and characterized by progressive deterioration of cognitive and motor functions. Altered brain glucose metabolism has long been suggested and a possible link has been proposed in HD. However, the precise function of glucose transporters was not yet determined. Here, we report the effects of the specifically-neuronal human glucose transporter expression in neurons of a Drosophila model carrying the exon 1 of the human huntingtin gene with 93 glutamine repeats (HQ93). We demonstrated that overexpression of the human glucose transporter in neurons ameliorated significantly the status of HD flies by increasing their lifespan, reducing their locomotor deficits and rescuing eye neurodegeneration. Then, we investigated whether increasing the major pathways of glucose catabolism, glycolysis and pentose-phosphate pathway (PPP) impacts HD. To mimic increased glycolytic flux, we overexpressed phosphofructokinase (PFK) which catalyzes an irreversible step in glycolysis. Overexpression of PFK did not affect HQ93 fly survival, but protected from photoreceptor loss. Overexpression of glucose-6-phosphate dehydrogenase (G6PD), the key enzyme of the PPP, extended significantly the lifespan of HD flies and rescued eye neurodegeneration. Since G6PD is able to synthesize NADPH involved in cell survival by maintenance of the redox state, we showed that tolerance to experimental oxidative stress was enhanced in flies co-expressing HQ93 and G6PD. Additionally overexpressions of hGluT3, G6PD or PFK were able to circumvent mitochondrial deficits induced by specific silencing of genes necessary for mitochondrial homeostasis. Our study confirms the involvement of bioenergetic deficits in HD course; they can be rescued by specific expression of a glucose transporter in neurons. Finally, the PPP and, to a lesser extent, the glycolysis seem to mediate the hGluT3 protective effects, whereas, in addition, the PPP provides increased protection to oxidative stress.

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Effect of PFK overexpression on the phenotype of HQ93 flies.(A): Lifespans of flies expressing the transgenes PFK and HQ93 (open diamonds) or only HQ93 (filled triangles) were not different as tested by log-rank test. In this representative experiment, 120 and 61 flies respectively were used. (B): Photoreceptor frequency distributions in 1- or 4-day old fly ommatidia expressing HQ93 alone (black bars), or PFK and HQ93 (grey bars) under the control of Elav-Gal4. Statistical significances on median values of photoreceptor numbers per ommatidium were determined by one-tailed Mann-Whitney test (at day 1, p = 0.0033.; at day 4, p< 0.0001). (C): The lifespan of flies expressing HQ93 together with PFK and hGluT3 (filled circles) was not statistically different from that of flies expressing HQ93 and hGluT3 (open circles); in the experiment, 219 and 181 flies were used. (D): Photoreceptor frequency distributions in 1- or 4-day old fly ommatidia expressing HQ93 together with PFK and hGluT3 (white bars), or HQ93 and hGluT3 (grey bars) under the control of Elav-Gal4. The one-tailed Mann-Whitney test indicates no statistical significances between the two fly lines neither at day 1 nor at day 4.
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pone.0118765.g003: Effect of PFK overexpression on the phenotype of HQ93 flies.(A): Lifespans of flies expressing the transgenes PFK and HQ93 (open diamonds) or only HQ93 (filled triangles) were not different as tested by log-rank test. In this representative experiment, 120 and 61 flies respectively were used. (B): Photoreceptor frequency distributions in 1- or 4-day old fly ommatidia expressing HQ93 alone (black bars), or PFK and HQ93 (grey bars) under the control of Elav-Gal4. Statistical significances on median values of photoreceptor numbers per ommatidium were determined by one-tailed Mann-Whitney test (at day 1, p = 0.0033.; at day 4, p< 0.0001). (C): The lifespan of flies expressing HQ93 together with PFK and hGluT3 (filled circles) was not statistically different from that of flies expressing HQ93 and hGluT3 (open circles); in the experiment, 219 and 181 flies were used. (D): Photoreceptor frequency distributions in 1- or 4-day old fly ommatidia expressing HQ93 together with PFK and hGluT3 (white bars), or HQ93 and hGluT3 (grey bars) under the control of Elav-Gal4. The one-tailed Mann-Whitney test indicates no statistical significances between the two fly lines neither at day 1 nor at day 4.

Mentions: To investigate the role of glycolysis, we analyzed whether the up-regulation of the glycolytic flux was beneficial in the Drosophila HQ93 neurons by overexpressing PFK which catalyses a rate-limiting step between fructose-6-phosphate and fructose-1, 6-biphosphate. For this, we used transgenic flies bearing Drosophila PFK [52]. After crossing them with HQ93 flies and Elav-Gal4 as driver, we analyzed lifespan and eye neurodegeneration. The Fig. 3A shows that overexpression of this enzyme in neurons did not change the survival of HQ93 flies. However, statistical analysis of the pseudopupil data (Fig. 3B) showed that PFK overexpression prevented neurodegeneration at day 1 and day 4. Since this result could be interpreted as an inefficient import of glucose in brain sensu stricto in comparison with the photoreceptors, we analyzed the impact of hGluT3 and PFK co-expression on HD toxicity in the brain and eyes. We showed that PFK and hGluT3 co-expression had no additional effect on survival compared to HD flies expressing hGluT3 alone (Fig. 3C). Similarly, the rescue of photoreceptor degeneration was not enhanced when hGluT3 and HQ93 were co-expressed (Fig. 3D). All these results allow to conclude that overexpression of PFK has no sufficient impact in the brain to rescue longevity of HQ93 flies but was able to delay neurodegeneration in photoreceptors.


Enhanced neuronal glucose transporter expression reveals metabolic choice in a HD Drosophila model.

Besson MT, Alegría K, Garrido-Gerter P, Barros LF, Liévens JC - PLoS ONE (2015)

Effect of PFK overexpression on the phenotype of HQ93 flies.(A): Lifespans of flies expressing the transgenes PFK and HQ93 (open diamonds) or only HQ93 (filled triangles) were not different as tested by log-rank test. In this representative experiment, 120 and 61 flies respectively were used. (B): Photoreceptor frequency distributions in 1- or 4-day old fly ommatidia expressing HQ93 alone (black bars), or PFK and HQ93 (grey bars) under the control of Elav-Gal4. Statistical significances on median values of photoreceptor numbers per ommatidium were determined by one-tailed Mann-Whitney test (at day 1, p = 0.0033.; at day 4, p< 0.0001). (C): The lifespan of flies expressing HQ93 together with PFK and hGluT3 (filled circles) was not statistically different from that of flies expressing HQ93 and hGluT3 (open circles); in the experiment, 219 and 181 flies were used. (D): Photoreceptor frequency distributions in 1- or 4-day old fly ommatidia expressing HQ93 together with PFK and hGluT3 (white bars), or HQ93 and hGluT3 (grey bars) under the control of Elav-Gal4. The one-tailed Mann-Whitney test indicates no statistical significances between the two fly lines neither at day 1 nor at day 4.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4356621&req=5

pone.0118765.g003: Effect of PFK overexpression on the phenotype of HQ93 flies.(A): Lifespans of flies expressing the transgenes PFK and HQ93 (open diamonds) or only HQ93 (filled triangles) were not different as tested by log-rank test. In this representative experiment, 120 and 61 flies respectively were used. (B): Photoreceptor frequency distributions in 1- or 4-day old fly ommatidia expressing HQ93 alone (black bars), or PFK and HQ93 (grey bars) under the control of Elav-Gal4. Statistical significances on median values of photoreceptor numbers per ommatidium were determined by one-tailed Mann-Whitney test (at day 1, p = 0.0033.; at day 4, p< 0.0001). (C): The lifespan of flies expressing HQ93 together with PFK and hGluT3 (filled circles) was not statistically different from that of flies expressing HQ93 and hGluT3 (open circles); in the experiment, 219 and 181 flies were used. (D): Photoreceptor frequency distributions in 1- or 4-day old fly ommatidia expressing HQ93 together with PFK and hGluT3 (white bars), or HQ93 and hGluT3 (grey bars) under the control of Elav-Gal4. The one-tailed Mann-Whitney test indicates no statistical significances between the two fly lines neither at day 1 nor at day 4.
Mentions: To investigate the role of glycolysis, we analyzed whether the up-regulation of the glycolytic flux was beneficial in the Drosophila HQ93 neurons by overexpressing PFK which catalyses a rate-limiting step between fructose-6-phosphate and fructose-1, 6-biphosphate. For this, we used transgenic flies bearing Drosophila PFK [52]. After crossing them with HQ93 flies and Elav-Gal4 as driver, we analyzed lifespan and eye neurodegeneration. The Fig. 3A shows that overexpression of this enzyme in neurons did not change the survival of HQ93 flies. However, statistical analysis of the pseudopupil data (Fig. 3B) showed that PFK overexpression prevented neurodegeneration at day 1 and day 4. Since this result could be interpreted as an inefficient import of glucose in brain sensu stricto in comparison with the photoreceptors, we analyzed the impact of hGluT3 and PFK co-expression on HD toxicity in the brain and eyes. We showed that PFK and hGluT3 co-expression had no additional effect on survival compared to HD flies expressing hGluT3 alone (Fig. 3C). Similarly, the rescue of photoreceptor degeneration was not enhanced when hGluT3 and HQ93 were co-expressed (Fig. 3D). All these results allow to conclude that overexpression of PFK has no sufficient impact in the brain to rescue longevity of HQ93 flies but was able to delay neurodegeneration in photoreceptors.

Bottom Line: We demonstrated that overexpression of the human glucose transporter in neurons ameliorated significantly the status of HD flies by increasing their lifespan, reducing their locomotor deficits and rescuing eye neurodegeneration.Overexpression of PFK did not affect HQ93 fly survival, but protected from photoreceptor loss.Finally, the PPP and, to a lesser extent, the glycolysis seem to mediate the hGluT3 protective effects, whereas, in addition, the PPP provides increased protection to oxidative stress.

View Article: PubMed Central - PubMed

Affiliation: Aix-Marseille Université, CNRS, CRN2M-UMR7286, 13344 Marseille cedex 15, Marseille, France.

ABSTRACT
Huntington's disease is a neurodegenerative disorder caused by toxic insertions of polyglutamine residues in the Huntingtin protein and characterized by progressive deterioration of cognitive and motor functions. Altered brain glucose metabolism has long been suggested and a possible link has been proposed in HD. However, the precise function of glucose transporters was not yet determined. Here, we report the effects of the specifically-neuronal human glucose transporter expression in neurons of a Drosophila model carrying the exon 1 of the human huntingtin gene with 93 glutamine repeats (HQ93). We demonstrated that overexpression of the human glucose transporter in neurons ameliorated significantly the status of HD flies by increasing their lifespan, reducing their locomotor deficits and rescuing eye neurodegeneration. Then, we investigated whether increasing the major pathways of glucose catabolism, glycolysis and pentose-phosphate pathway (PPP) impacts HD. To mimic increased glycolytic flux, we overexpressed phosphofructokinase (PFK) which catalyzes an irreversible step in glycolysis. Overexpression of PFK did not affect HQ93 fly survival, but protected from photoreceptor loss. Overexpression of glucose-6-phosphate dehydrogenase (G6PD), the key enzyme of the PPP, extended significantly the lifespan of HD flies and rescued eye neurodegeneration. Since G6PD is able to synthesize NADPH involved in cell survival by maintenance of the redox state, we showed that tolerance to experimental oxidative stress was enhanced in flies co-expressing HQ93 and G6PD. Additionally overexpressions of hGluT3, G6PD or PFK were able to circumvent mitochondrial deficits induced by specific silencing of genes necessary for mitochondrial homeostasis. Our study confirms the involvement of bioenergetic deficits in HD course; they can be rescued by specific expression of a glucose transporter in neurons. Finally, the PPP and, to a lesser extent, the glycolysis seem to mediate the hGluT3 protective effects, whereas, in addition, the PPP provides increased protection to oxidative stress.

Show MeSH
Related in: MedlinePlus