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Dietary sugar promotes systemic TOR activation in Drosophila through AKH-dependent selective secretion of Dilp3.

Kim J, Neufeld TP - Nat Commun (2015)

Bottom Line: Here we show that regulation of insulin secretion in Drosophila larvae has been segregated into distinct branches-whereas amino acids promote the secretion of Drosophila insulin-like peptide 2 (Dilp2), circulating sugars promote the selective release of Dilp3.Dilp3 is uniquely required for the sugar-mediated activation of TOR signalling and suppression of autophagy in the larval fat body.Sugar levels are not sensed directly by the IPCs, but rather by the adipokinetic hormone (AKH)-producing cells of the corpora cardiaca, and we demonstrate that AKH signalling is required in the IPCs for sugar-dependent Dilp3 release.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Cell Biology and Development, University of Minnesota, 6-160 Jackson Hall, 321 Church St SE, Minneapolis, Minnesota 55455, USA.

ABSTRACT
Secreted ligands of the insulin family promote cell growth and maintain sugar homeostasis. Insulin release is tightly regulated in response to dietary conditions, but how insulin-producing cells (IPCs) coordinate their responses to distinct nutrient signals is unclear. Here we show that regulation of insulin secretion in Drosophila larvae has been segregated into distinct branches-whereas amino acids promote the secretion of Drosophila insulin-like peptide 2 (Dilp2), circulating sugars promote the selective release of Dilp3. Dilp3 is uniquely required for the sugar-mediated activation of TOR signalling and suppression of autophagy in the larval fat body. Sugar levels are not sensed directly by the IPCs, but rather by the adipokinetic hormone (AKH)-producing cells of the corpora cardiaca, and we demonstrate that AKH signalling is required in the IPCs for sugar-dependent Dilp3 release. Thus, IPCs integrate multiple cues to regulate the secretion of distinct insulin subtypes under varying nutrient conditions.

No MeSH data available.


Related in: MedlinePlus

Trehalose-dependent activation of TOR in the larval fat body requires the brain and insulin signaling(a) Supplementation of M3 medium with trehalose (0, 20, 40 mg/ml) leads to significant increases in fb-TOR activity from whole larval carcasses (left) but not in carcasses from which the brain was surgically removed (right). Data represent mean±s.e.m. of four independent experiments. (b) Trehalose (20 mg/ml in M3) suppresses formation of autophagic vesicles (mCherry-Atg8 punctae) in fat body cells of complete carcasses but not carcasses lacking the brain. Scale bar represents 20 µm. Representative images of three experiments (seven carcasses per condition). (c) Fb-TOR activity of carcasses lacking the brain, incubated in control M3+trehalose medium (−), or in M3+trehalose conditioned medium (C.M.) previously incubated 2h with CNS complexes from wild type larvae (control brain) or from mutant larvae lacking Dilps1–5 and Dilp7 (Dilps−/− brain). Data represent mean±s.e.m. of four independent experiments. *p<0.05, **p<0.01, ***p<0.001, NS p>0.05; Student’s t-test. Full-size immunoblots are shown in Supplementary Figure 4.
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Figure 2: Trehalose-dependent activation of TOR in the larval fat body requires the brain and insulin signaling(a) Supplementation of M3 medium with trehalose (0, 20, 40 mg/ml) leads to significant increases in fb-TOR activity from whole larval carcasses (left) but not in carcasses from which the brain was surgically removed (right). Data represent mean±s.e.m. of four independent experiments. (b) Trehalose (20 mg/ml in M3) suppresses formation of autophagic vesicles (mCherry-Atg8 punctae) in fat body cells of complete carcasses but not carcasses lacking the brain. Scale bar represents 20 µm. Representative images of three experiments (seven carcasses per condition). (c) Fb-TOR activity of carcasses lacking the brain, incubated in control M3+trehalose medium (−), or in M3+trehalose conditioned medium (C.M.) previously incubated 2h with CNS complexes from wild type larvae (control brain) or from mutant larvae lacking Dilps1–5 and Dilp7 (Dilps−/− brain). Data represent mean±s.e.m. of four independent experiments. *p<0.05, **p<0.01, ***p<0.001, NS p>0.05; Student’s t-test. Full-size immunoblots are shown in Supplementary Figure 4.

Mentions: Of the eight Drosophila insulin-like proteins, Dilp2, Dilp3 and Dilp5 are expressed in twin clusters of IPCs within the central nervous system. To examine the potential involvement of these brain-derived Dilps in mediating the systemic effects of trehalose, we first tested whether the CNS itself is required for trehalose-stimulated activation of TOR. Whereas trehalose promoted dose-dependent S6K phosphorylation in the fat body of complete carcasses, removal of the brain and associated ring gland complex abrogated this response (Fig. 2a). Trehalose also failed to suppress autophagy induction in the fat body of brain-less larval carcasses (Fig. 2b). To ask whether soluble factors from the brain are released into the media, we pretreated M3+trehalose medium by incubation with larval brain/ring gland complexes. This conditioned medium was able to fully activate S6K phosphorylation in the fat body of brain-less carcasses (Fig. 2c). In contrast, medium conditioned with CNS complexes from larvae mutant for Dilps1–5 and Dilp7 was significantly less effective in this assay. These results indicate that trehalose-dependent activation of TOR in the larval fat body is a non-autonomous response requiring a CNS-derived signal, and that one or more of the brain-derived Dilps are required for a significant portion of this signal.


Dietary sugar promotes systemic TOR activation in Drosophila through AKH-dependent selective secretion of Dilp3.

Kim J, Neufeld TP - Nat Commun (2015)

Trehalose-dependent activation of TOR in the larval fat body requires the brain and insulin signaling(a) Supplementation of M3 medium with trehalose (0, 20, 40 mg/ml) leads to significant increases in fb-TOR activity from whole larval carcasses (left) but not in carcasses from which the brain was surgically removed (right). Data represent mean±s.e.m. of four independent experiments. (b) Trehalose (20 mg/ml in M3) suppresses formation of autophagic vesicles (mCherry-Atg8 punctae) in fat body cells of complete carcasses but not carcasses lacking the brain. Scale bar represents 20 µm. Representative images of three experiments (seven carcasses per condition). (c) Fb-TOR activity of carcasses lacking the brain, incubated in control M3+trehalose medium (−), or in M3+trehalose conditioned medium (C.M.) previously incubated 2h with CNS complexes from wild type larvae (control brain) or from mutant larvae lacking Dilps1–5 and Dilp7 (Dilps−/− brain). Data represent mean±s.e.m. of four independent experiments. *p<0.05, **p<0.01, ***p<0.001, NS p>0.05; Student’s t-test. Full-size immunoblots are shown in Supplementary Figure 4.
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Figure 2: Trehalose-dependent activation of TOR in the larval fat body requires the brain and insulin signaling(a) Supplementation of M3 medium with trehalose (0, 20, 40 mg/ml) leads to significant increases in fb-TOR activity from whole larval carcasses (left) but not in carcasses from which the brain was surgically removed (right). Data represent mean±s.e.m. of four independent experiments. (b) Trehalose (20 mg/ml in M3) suppresses formation of autophagic vesicles (mCherry-Atg8 punctae) in fat body cells of complete carcasses but not carcasses lacking the brain. Scale bar represents 20 µm. Representative images of three experiments (seven carcasses per condition). (c) Fb-TOR activity of carcasses lacking the brain, incubated in control M3+trehalose medium (−), or in M3+trehalose conditioned medium (C.M.) previously incubated 2h with CNS complexes from wild type larvae (control brain) or from mutant larvae lacking Dilps1–5 and Dilp7 (Dilps−/− brain). Data represent mean±s.e.m. of four independent experiments. *p<0.05, **p<0.01, ***p<0.001, NS p>0.05; Student’s t-test. Full-size immunoblots are shown in Supplementary Figure 4.
Mentions: Of the eight Drosophila insulin-like proteins, Dilp2, Dilp3 and Dilp5 are expressed in twin clusters of IPCs within the central nervous system. To examine the potential involvement of these brain-derived Dilps in mediating the systemic effects of trehalose, we first tested whether the CNS itself is required for trehalose-stimulated activation of TOR. Whereas trehalose promoted dose-dependent S6K phosphorylation in the fat body of complete carcasses, removal of the brain and associated ring gland complex abrogated this response (Fig. 2a). Trehalose also failed to suppress autophagy induction in the fat body of brain-less larval carcasses (Fig. 2b). To ask whether soluble factors from the brain are released into the media, we pretreated M3+trehalose medium by incubation with larval brain/ring gland complexes. This conditioned medium was able to fully activate S6K phosphorylation in the fat body of brain-less carcasses (Fig. 2c). In contrast, medium conditioned with CNS complexes from larvae mutant for Dilps1–5 and Dilp7 was significantly less effective in this assay. These results indicate that trehalose-dependent activation of TOR in the larval fat body is a non-autonomous response requiring a CNS-derived signal, and that one or more of the brain-derived Dilps are required for a significant portion of this signal.

Bottom Line: Here we show that regulation of insulin secretion in Drosophila larvae has been segregated into distinct branches-whereas amino acids promote the secretion of Drosophila insulin-like peptide 2 (Dilp2), circulating sugars promote the selective release of Dilp3.Dilp3 is uniquely required for the sugar-mediated activation of TOR signalling and suppression of autophagy in the larval fat body.Sugar levels are not sensed directly by the IPCs, but rather by the adipokinetic hormone (AKH)-producing cells of the corpora cardiaca, and we demonstrate that AKH signalling is required in the IPCs for sugar-dependent Dilp3 release.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Cell Biology and Development, University of Minnesota, 6-160 Jackson Hall, 321 Church St SE, Minneapolis, Minnesota 55455, USA.

ABSTRACT
Secreted ligands of the insulin family promote cell growth and maintain sugar homeostasis. Insulin release is tightly regulated in response to dietary conditions, but how insulin-producing cells (IPCs) coordinate their responses to distinct nutrient signals is unclear. Here we show that regulation of insulin secretion in Drosophila larvae has been segregated into distinct branches-whereas amino acids promote the secretion of Drosophila insulin-like peptide 2 (Dilp2), circulating sugars promote the selective release of Dilp3. Dilp3 is uniquely required for the sugar-mediated activation of TOR signalling and suppression of autophagy in the larval fat body. Sugar levels are not sensed directly by the IPCs, but rather by the adipokinetic hormone (AKH)-producing cells of the corpora cardiaca, and we demonstrate that AKH signalling is required in the IPCs for sugar-dependent Dilp3 release. Thus, IPCs integrate multiple cues to regulate the secretion of distinct insulin subtypes under varying nutrient conditions.

No MeSH data available.


Related in: MedlinePlus