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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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G6PD and JafracI ameliorate oxidative stress tolerance of HD flies.(A): Representative survival rate of 12 day-old flies expressing no transgene (white bar) or G6PD (grey bar) after 48 hr exposure to 2% sucrose or to 1.5% H2O2 in 2% sucrose. Numbers of flies included in this assay were respectively: 40; 19; 99; 74. Results represented the means + SEM of the percentages obtained from a representative experiment. The Mann-Whitney test indicates a significant difference between the two genotypes for H2O2-exposed flies (*, p = 0.016). (B): Representative survival rate of 12 day-old flies expressing HQ93 (black bar), or co-expressing HQ93 and G6PD (grey bar) after 48 hr exposure to 2% sucrose or to 1.5% H2O2 in 2% sucrose. Numbers of flies included in this assay were 36; 56; 93; 85 respectively. Results represented the means + SEM of the percentages obtained from a representative experiment. The Mann-Whitney test indicates a significant difference between the two genotypes for non-treated flies (*, p = 0.041) and for H2O2-exposed flies (**, p = 0.006). (C): The survival curve of flies expressing HQ93 as control (squares) or HQ93 and Jafrac I (diamonds) under the neuronal driver Elav-Gal4, with n = 100 and 159 flies respectively. The log-rank test indicates that the two survival curves were very different (***, p<0.0001).
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pone.0118765.g005: G6PD and JafracI ameliorate oxidative stress tolerance of HD flies.(A): Representative survival rate of 12 day-old flies expressing no transgene (white bar) or G6PD (grey bar) after 48 hr exposure to 2% sucrose or to 1.5% H2O2 in 2% sucrose. Numbers of flies included in this assay were respectively: 40; 19; 99; 74. Results represented the means + SEM of the percentages obtained from a representative experiment. The Mann-Whitney test indicates a significant difference between the two genotypes for H2O2-exposed flies (*, p = 0.016). (B): Representative survival rate of 12 day-old flies expressing HQ93 (black bar), or co-expressing HQ93 and G6PD (grey bar) after 48 hr exposure to 2% sucrose or to 1.5% H2O2 in 2% sucrose. Numbers of flies included in this assay were 36; 56; 93; 85 respectively. Results represented the means + SEM of the percentages obtained from a representative experiment. The Mann-Whitney test indicates a significant difference between the two genotypes for non-treated flies (*, p = 0.041) and for H2O2-exposed flies (**, p = 0.006). (C): The survival curve of flies expressing HQ93 as control (squares) or HQ93 and Jafrac I (diamonds) under the neuronal driver Elav-Gal4, with n = 100 and 159 flies respectively. The log-rank test indicates that the two survival curves were very different (***, p<0.0001).

Mentions: Next, we tested resistance of HQ93 flies in the presence or not of G6PD to an oxidizing agent, hydrogen peroxide (H2O2). At first, we verified that after 48hr exposure, flies with G6PD-expressing neurons were more tolerant to H2O2 than wild-type flies (Fig. 5A). Secondly, in the presence of HQ93 alone, exposure of 12 day-old flies to H2O2 drastically reduced fly survival from 70 to 22% (Fig. 5B). Flies with neuronal HQ93 and G6PD transgenes presented a significantly enhanced resistance to oxidant compared to flies carrying only HQ93: 63% of flies with the two transgenes survived in the presence of H2O2 whereas 22% of HQ93 flies remained alive (Fig. 5B). The amplitude of the decreased lifespan was only 30% with G6PD instead of 48% without G6PD. This result suggests that G6PD was able to rescue fly survival by exerting its anti-oxidative activity even in the presence of mHtt. By contrast, we observed that 6 day-old HQ93 flies were insensitive to oxidative stress generated by oxidative treatment (S5 Fig.), but it is noteworthy that these flies did not yet present pathological symptoms. Further, to determine whether the antioxidant capacity of G6PD in HQ93 neurons was responsible for its positive action, we analyzed the effects of NADPH-dependent peroxidases on fly survival. Peroxiredoxins and thioredoxins have been identified by their ability to reduce oxidant activities in conjunction with thiol-reducing systems using NADPH pool as electron donor [56, 57, 58]. The neuronal expression of Jafrac1, a Drosophila homologue of the human peroxiredoxin 2 (Fig. 5C) or the Drosophila thioredoxin deadhead (S6 Fig.) significantly extended the fly lifespan in the presence of HQ93. Thus, G6PD expression and, consequently, activation of the PPP, in addition to their anabolic function, were protective by providing antioxidative supply for mHtt-expressing neurons which are particularly vulnerable to oxidative stress.


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)

G6PD and JafracI ameliorate oxidative stress tolerance of HD flies.(A): Representative survival rate of 12 day-old flies expressing no transgene (white bar) or G6PD (grey bar) after 48 hr exposure to 2% sucrose or to 1.5% H2O2 in 2% sucrose. Numbers of flies included in this assay were respectively: 40; 19; 99; 74. Results represented the means + SEM of the percentages obtained from a representative experiment. The Mann-Whitney test indicates a significant difference between the two genotypes for H2O2-exposed flies (*, p = 0.016). (B): Representative survival rate of 12 day-old flies expressing HQ93 (black bar), or co-expressing HQ93 and G6PD (grey bar) after 48 hr exposure to 2% sucrose or to 1.5% H2O2 in 2% sucrose. Numbers of flies included in this assay were 36; 56; 93; 85 respectively. Results represented the means + SEM of the percentages obtained from a representative experiment. The Mann-Whitney test indicates a significant difference between the two genotypes for non-treated flies (*, p = 0.041) and for H2O2-exposed flies (**, p = 0.006). (C): The survival curve of flies expressing HQ93 as control (squares) or HQ93 and Jafrac I (diamonds) under the neuronal driver Elav-Gal4, with n = 100 and 159 flies respectively. The log-rank test indicates that the two survival curves were very different (***, p<0.0001).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0118765.g005: G6PD and JafracI ameliorate oxidative stress tolerance of HD flies.(A): Representative survival rate of 12 day-old flies expressing no transgene (white bar) or G6PD (grey bar) after 48 hr exposure to 2% sucrose or to 1.5% H2O2 in 2% sucrose. Numbers of flies included in this assay were respectively: 40; 19; 99; 74. Results represented the means + SEM of the percentages obtained from a representative experiment. The Mann-Whitney test indicates a significant difference between the two genotypes for H2O2-exposed flies (*, p = 0.016). (B): Representative survival rate of 12 day-old flies expressing HQ93 (black bar), or co-expressing HQ93 and G6PD (grey bar) after 48 hr exposure to 2% sucrose or to 1.5% H2O2 in 2% sucrose. Numbers of flies included in this assay were 36; 56; 93; 85 respectively. Results represented the means + SEM of the percentages obtained from a representative experiment. The Mann-Whitney test indicates a significant difference between the two genotypes for non-treated flies (*, p = 0.041) and for H2O2-exposed flies (**, p = 0.006). (C): The survival curve of flies expressing HQ93 as control (squares) or HQ93 and Jafrac I (diamonds) under the neuronal driver Elav-Gal4, with n = 100 and 159 flies respectively. The log-rank test indicates that the two survival curves were very different (***, p<0.0001).
Mentions: Next, we tested resistance of HQ93 flies in the presence or not of G6PD to an oxidizing agent, hydrogen peroxide (H2O2). At first, we verified that after 48hr exposure, flies with G6PD-expressing neurons were more tolerant to H2O2 than wild-type flies (Fig. 5A). Secondly, in the presence of HQ93 alone, exposure of 12 day-old flies to H2O2 drastically reduced fly survival from 70 to 22% (Fig. 5B). Flies with neuronal HQ93 and G6PD transgenes presented a significantly enhanced resistance to oxidant compared to flies carrying only HQ93: 63% of flies with the two transgenes survived in the presence of H2O2 whereas 22% of HQ93 flies remained alive (Fig. 5B). The amplitude of the decreased lifespan was only 30% with G6PD instead of 48% without G6PD. This result suggests that G6PD was able to rescue fly survival by exerting its anti-oxidative activity even in the presence of mHtt. By contrast, we observed that 6 day-old HQ93 flies were insensitive to oxidative stress generated by oxidative treatment (S5 Fig.), but it is noteworthy that these flies did not yet present pathological symptoms. Further, to determine whether the antioxidant capacity of G6PD in HQ93 neurons was responsible for its positive action, we analyzed the effects of NADPH-dependent peroxidases on fly survival. Peroxiredoxins and thioredoxins have been identified by their ability to reduce oxidant activities in conjunction with thiol-reducing systems using NADPH pool as electron donor [56, 57, 58]. The neuronal expression of Jafrac1, a Drosophila homologue of the human peroxiredoxin 2 (Fig. 5C) or the Drosophila thioredoxin deadhead (S6 Fig.) significantly extended the fly lifespan in the presence of HQ93. Thus, G6PD expression and, consequently, activation of the PPP, in addition to their anabolic function, were protective by providing antioxidative supply for mHtt-expressing neurons which are particularly vulnerable to oxidative stress.

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