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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 overexpression of G6PD on the phenotype of HQ93 flies.(A): Lifespan of flies carrying two neuronal transgenes G6PD and HQ93 (open circles) was extended in comparison with flies carrying only HQ93 (filled triangles) with Elav-Gal4, n = 102 and 126 flies respectively. Survival curves were highly significantly different by log-rank test (***, p<0.0001). (B): Photoreceptor frequency distributions in 1- or 4-day old flies expressing HQ93 alone (black bars), or G6PD and HQ93 (grey bars). The median value of photoreceptor number per ommatidium between the two lines was statistically significant at the 1st and 4th day after adult emergence (Mann-Whitney test; at day 1, p = 0.0104; at day 4, p< 0.0003). (C): Lifespan of HQ93 flies carrying hGluT3 and G6PD (filled diamonds) was not different from the lifespan of HQ93 flies carrying only hGluT3 (open diamonds) with Elav-Gal4, n = 117 and 181 flies respectively.
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pone.0118765.g004: Effect of overexpression of G6PD on the phenotype of HQ93 flies.(A): Lifespan of flies carrying two neuronal transgenes G6PD and HQ93 (open circles) was extended in comparison with flies carrying only HQ93 (filled triangles) with Elav-Gal4, n = 102 and 126 flies respectively. Survival curves were highly significantly different by log-rank test (***, p<0.0001). (B): Photoreceptor frequency distributions in 1- or 4-day old flies expressing HQ93 alone (black bars), or G6PD and HQ93 (grey bars). The median value of photoreceptor number per ommatidium between the two lines was statistically significant at the 1st and 4th day after adult emergence (Mann-Whitney test; at day 1, p = 0.0104; at day 4, p< 0.0003). (C): Lifespan of HQ93 flies carrying hGluT3 and G6PD (filled diamonds) was not different from the lifespan of HQ93 flies carrying only hGluT3 (open diamonds) with Elav-Gal4, n = 117 and 181 flies respectively.

Mentions: G6PD activity, by counteracting oxidative stress, can protect neuronal cells [15, 53]. We hypothesized that overexpression of G6PD would extend the lifespan of HQ93 flies and enhance their resistance to oxidative stress by its ability to produce NADPH. To perform these experiments, we used a Drosophila transgenic line previously characterized, exhibiting a high enzyme activity in the brain and an increase of NADPH content; this line also presented an extension of lifespan and an enhanced resistance to oxidative stress generators as hyperoxia and paraquat treatments [54, 55]. As shown in Fig. 4A, increased expression of G6PD in HD flies was significantly associated with an extension of lifespan: this increase was up to 33% in comparison with flies expressing only the HQ93 transgene. The mHtt-induced neurodegeneration in eyes was significantly rescued by the overexpression of G6PD as seen in Fig. 4B; flies expressing both HQ93 and G6PD have more intact photoreceptor cells (17%) at day 4 after adult eclosion than flies expressing HQ93 alone (5%). To investigate the effects of G6PD on HD fly survival in the presence of hGluT3, we overexpressed HQ93 and G6PD together with hGluT3. As shown in the Fig. 4C, lethality of these flies was not statistically different from that of HD flies expressing hGluT3 alone. This suggests that the co-expression of hGluT3 and G6PD has no cumulative effect on survival rate.


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 overexpression of G6PD on the phenotype of HQ93 flies.(A): Lifespan of flies carrying two neuronal transgenes G6PD and HQ93 (open circles) was extended in comparison with flies carrying only HQ93 (filled triangles) with Elav-Gal4, n = 102 and 126 flies respectively. Survival curves were highly significantly different by log-rank test (***, p<0.0001). (B): Photoreceptor frequency distributions in 1- or 4-day old flies expressing HQ93 alone (black bars), or G6PD and HQ93 (grey bars). The median value of photoreceptor number per ommatidium between the two lines was statistically significant at the 1st and 4th day after adult emergence (Mann-Whitney test; at day 1, p = 0.0104; at day 4, p< 0.0003). (C): Lifespan of HQ93 flies carrying hGluT3 and G6PD (filled diamonds) was not different from the lifespan of HQ93 flies carrying only hGluT3 (open diamonds) with Elav-Gal4, n = 117 and 181 flies respectively.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0118765.g004: Effect of overexpression of G6PD on the phenotype of HQ93 flies.(A): Lifespan of flies carrying two neuronal transgenes G6PD and HQ93 (open circles) was extended in comparison with flies carrying only HQ93 (filled triangles) with Elav-Gal4, n = 102 and 126 flies respectively. Survival curves were highly significantly different by log-rank test (***, p<0.0001). (B): Photoreceptor frequency distributions in 1- or 4-day old flies expressing HQ93 alone (black bars), or G6PD and HQ93 (grey bars). The median value of photoreceptor number per ommatidium between the two lines was statistically significant at the 1st and 4th day after adult emergence (Mann-Whitney test; at day 1, p = 0.0104; at day 4, p< 0.0003). (C): Lifespan of HQ93 flies carrying hGluT3 and G6PD (filled diamonds) was not different from the lifespan of HQ93 flies carrying only hGluT3 (open diamonds) with Elav-Gal4, n = 117 and 181 flies respectively.
Mentions: G6PD activity, by counteracting oxidative stress, can protect neuronal cells [15, 53]. We hypothesized that overexpression of G6PD would extend the lifespan of HQ93 flies and enhance their resistance to oxidative stress by its ability to produce NADPH. To perform these experiments, we used a Drosophila transgenic line previously characterized, exhibiting a high enzyme activity in the brain and an increase of NADPH content; this line also presented an extension of lifespan and an enhanced resistance to oxidative stress generators as hyperoxia and paraquat treatments [54, 55]. As shown in Fig. 4A, increased expression of G6PD in HD flies was significantly associated with an extension of lifespan: this increase was up to 33% in comparison with flies expressing only the HQ93 transgene. The mHtt-induced neurodegeneration in eyes was significantly rescued by the overexpression of G6PD as seen in Fig. 4B; flies expressing both HQ93 and G6PD have more intact photoreceptor cells (17%) at day 4 after adult eclosion than flies expressing HQ93 alone (5%). To investigate the effects of G6PD on HD fly survival in the presence of hGluT3, we overexpressed HQ93 and G6PD together with hGluT3. As shown in the Fig. 4C, lethality of these flies was not statistically different from that of HD flies expressing hGluT3 alone. This suggests that the co-expression of hGluT3 and G6PD has no cumulative effect on survival rate.

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