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Glucagon-like peptide-1 protects beta-cells against apoptosis by increasing the activity of an IGF-2/IGF-1 receptor autocrine loop.

Cornu M, Yang JY, Jaccard E, Poussin C, Widmann C, Thorens B - Diabetes (2009)

Bottom Line: We found that IGF-1 receptor expression was markedly reduced in the mutant islets.We found that GLP-1 robustly stimulated IGF-1 receptor expression and Akt phosphorylation and that increased Akt phosphorylation was dependent on IGF-1 but not insulin receptor expression.We demonstrated, both in MIN6 cell line and primary beta-cells, that reducing IGF-1 receptor or IGF-2 expression or neutralizing secreted IGF-2 suppressed GLP-1-induced protection against apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.

ABSTRACT

Objective: The gluco-incretin hormones glucagon-like peptide (GLP)-1 and gastric inhibitory peptide (GIP) protect beta-cells against cytokine-induced apoptosis. Their action is initiated by binding to specific receptors that activate the cAMP signaling pathway, but the downstream events are not fully elucidated. Here we searched for mechanisms that may underlie this protective effect.

Research design and methods: We performed comparative transcriptomic analysis of islets from control and GipR(-/-);Glp-1-R(-/-) mice, which have increased sensitivity to cytokine-induced apoptosis. We found that IGF-1 receptor expression was markedly reduced in the mutant islets. Because the IGF-1 receptor signaling pathway is known for its antiapoptotic effect, we explored the relationship between gluco-incretin action, IGF-1 receptor expression and signaling, and apoptosis.

Results: We found that GLP-1 robustly stimulated IGF-1 receptor expression and Akt phosphorylation and that increased Akt phosphorylation was dependent on IGF-1 but not insulin receptor expression. We demonstrated that GLP-1-induced Akt phosphorylation required active secretion, indicating the presence of an autocrine activation mechanism; we showed that activation of IGF-1 receptor signaling was dependent on the secretion of IGF-2. We demonstrated, both in MIN6 cell line and primary beta-cells, that reducing IGF-1 receptor or IGF-2 expression or neutralizing secreted IGF-2 suppressed GLP-1-induced protection against apoptosis.

Conclusions: An IGF-2/IGF-1 receptor autocrine loop operates in beta-cells. GLP-1 increases its activity by augmenting IGF-1 receptor expression and by stimulating secretion; this mechanism is required for GLP-1-induced protection against apoptosis. These findings may lead to novel ways of preventing beta-cell loss in the pathogenesis of diabetes.

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Related in: MedlinePlus

GLP-1–increased Akt phosphorylation depends on secreted IGF-2. A: MIN6 cells were transfected with an unrelated (Un) or an IGF-2–specific shRNA. Forty-eight hours later, they were stimulated with GLP-1 for 18 h to increase IGF-1R expression and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose. B: MIN6 cells were stimulated with GLP-1 for 18 h and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose and with nonspecific IgGs or an IGF-2 blocking antibody. C: Pancreatic islets were stimulated with GLP-1 for 18 h and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose and with nonspecific IgGs or an IGF-2 blocking antibody. A–C: Data are means ± SD, n = 3 independent experiments. **P < 0.01; ***P < 0.001. a.u., arbitrary units.
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Figure 5: GLP-1–increased Akt phosphorylation depends on secreted IGF-2. A: MIN6 cells were transfected with an unrelated (Un) or an IGF-2–specific shRNA. Forty-eight hours later, they were stimulated with GLP-1 for 18 h to increase IGF-1R expression and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose. B: MIN6 cells were stimulated with GLP-1 for 18 h and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose and with nonspecific IgGs or an IGF-2 blocking antibody. C: Pancreatic islets were stimulated with GLP-1 for 18 h and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose and with nonspecific IgGs or an IGF-2 blocking antibody. A–C: Data are means ± SD, n = 3 independent experiments. **P < 0.01; ***P < 0.001. a.u., arbitrary units.

Mentions: We thus tested whether IGF-2 was involved in activation of Akt phosphorylation in MIN6 cells exposed to GLP-1. MIN6 cells were first transfected with an IGF-2–specific or an unrelated shRNA, then exposed to GLP-1 for 18 h to induce IGF-1R expression, and finally exposed to 2 or 20 mmol/l glucose before analysis of Akt phosphorylation. Figure 5A shows that expression of pro–IGF-2 and mature IGF-2 was strongly decreased by transfection of the specific shRNA, and this suppressed the induction of Akt phosphorylation in cells exposed to high glucose. As a second test for an autocrine role of IGF-2 secretion in Akt phosphorylation, MIN6 cells were treated as in the previous experiment but the final incubation with 20 mmol/l glucose was conducted in the presence of an IGF-2 blocking antibody or an unrelated IgG fraction. Figure 5B shows that the IGF-2 blocking antibody suppressed Akt phosphorylation. The same inhibition of Akt phosphorylation by the IGF-2 neutralizing antibody was made using primary islets (Fig. 5C). Thus, both in MIN6 cells and primary islets, activation of Akt phosphorylation by GLP-1 requires secretion of IGF-2 under these conditions. These data also indicated that an IGF-2/IGF-1R autocrine loop operated in β-cells, and its activity could be increased by GLP-1 by enhancing IGF-1R expression and by stimulating secretion in the presence of high glucose.


Glucagon-like peptide-1 protects beta-cells against apoptosis by increasing the activity of an IGF-2/IGF-1 receptor autocrine loop.

Cornu M, Yang JY, Jaccard E, Poussin C, Widmann C, Thorens B - Diabetes (2009)

GLP-1–increased Akt phosphorylation depends on secreted IGF-2. A: MIN6 cells were transfected with an unrelated (Un) or an IGF-2–specific shRNA. Forty-eight hours later, they were stimulated with GLP-1 for 18 h to increase IGF-1R expression and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose. B: MIN6 cells were stimulated with GLP-1 for 18 h and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose and with nonspecific IgGs or an IGF-2 blocking antibody. C: Pancreatic islets were stimulated with GLP-1 for 18 h and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose and with nonspecific IgGs or an IGF-2 blocking antibody. A–C: Data are means ± SD, n = 3 independent experiments. **P < 0.01; ***P < 0.001. a.u., arbitrary units.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2712796&req=5

Figure 5: GLP-1–increased Akt phosphorylation depends on secreted IGF-2. A: MIN6 cells were transfected with an unrelated (Un) or an IGF-2–specific shRNA. Forty-eight hours later, they were stimulated with GLP-1 for 18 h to increase IGF-1R expression and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose. B: MIN6 cells were stimulated with GLP-1 for 18 h and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose and with nonspecific IgGs or an IGF-2 blocking antibody. C: Pancreatic islets were stimulated with GLP-1 for 18 h and then incubated with 2 mmol/l glucose for 2 h and for 1 h in either 2 or 20 mmol/l glucose and with nonspecific IgGs or an IGF-2 blocking antibody. A–C: Data are means ± SD, n = 3 independent experiments. **P < 0.01; ***P < 0.001. a.u., arbitrary units.
Mentions: We thus tested whether IGF-2 was involved in activation of Akt phosphorylation in MIN6 cells exposed to GLP-1. MIN6 cells were first transfected with an IGF-2–specific or an unrelated shRNA, then exposed to GLP-1 for 18 h to induce IGF-1R expression, and finally exposed to 2 or 20 mmol/l glucose before analysis of Akt phosphorylation. Figure 5A shows that expression of pro–IGF-2 and mature IGF-2 was strongly decreased by transfection of the specific shRNA, and this suppressed the induction of Akt phosphorylation in cells exposed to high glucose. As a second test for an autocrine role of IGF-2 secretion in Akt phosphorylation, MIN6 cells were treated as in the previous experiment but the final incubation with 20 mmol/l glucose was conducted in the presence of an IGF-2 blocking antibody or an unrelated IgG fraction. Figure 5B shows that the IGF-2 blocking antibody suppressed Akt phosphorylation. The same inhibition of Akt phosphorylation by the IGF-2 neutralizing antibody was made using primary islets (Fig. 5C). Thus, both in MIN6 cells and primary islets, activation of Akt phosphorylation by GLP-1 requires secretion of IGF-2 under these conditions. These data also indicated that an IGF-2/IGF-1R autocrine loop operated in β-cells, and its activity could be increased by GLP-1 by enhancing IGF-1R expression and by stimulating secretion in the presence of high glucose.

Bottom Line: We found that IGF-1 receptor expression was markedly reduced in the mutant islets.We found that GLP-1 robustly stimulated IGF-1 receptor expression and Akt phosphorylation and that increased Akt phosphorylation was dependent on IGF-1 but not insulin receptor expression.We demonstrated, both in MIN6 cell line and primary beta-cells, that reducing IGF-1 receptor or IGF-2 expression or neutralizing secreted IGF-2 suppressed GLP-1-induced protection against apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.

ABSTRACT

Objective: The gluco-incretin hormones glucagon-like peptide (GLP)-1 and gastric inhibitory peptide (GIP) protect beta-cells against cytokine-induced apoptosis. Their action is initiated by binding to specific receptors that activate the cAMP signaling pathway, but the downstream events are not fully elucidated. Here we searched for mechanisms that may underlie this protective effect.

Research design and methods: We performed comparative transcriptomic analysis of islets from control and GipR(-/-);Glp-1-R(-/-) mice, which have increased sensitivity to cytokine-induced apoptosis. We found that IGF-1 receptor expression was markedly reduced in the mutant islets. Because the IGF-1 receptor signaling pathway is known for its antiapoptotic effect, we explored the relationship between gluco-incretin action, IGF-1 receptor expression and signaling, and apoptosis.

Results: We found that GLP-1 robustly stimulated IGF-1 receptor expression and Akt phosphorylation and that increased Akt phosphorylation was dependent on IGF-1 but not insulin receptor expression. We demonstrated that GLP-1-induced Akt phosphorylation required active secretion, indicating the presence of an autocrine activation mechanism; we showed that activation of IGF-1 receptor signaling was dependent on the secretion of IGF-2. We demonstrated, both in MIN6 cell line and primary beta-cells, that reducing IGF-1 receptor or IGF-2 expression or neutralizing secreted IGF-2 suppressed GLP-1-induced protection against apoptosis.

Conclusions: An IGF-2/IGF-1 receptor autocrine loop operates in beta-cells. GLP-1 increases its activity by augmenting IGF-1 receptor expression and by stimulating secretion; this mechanism is required for GLP-1-induced protection against apoptosis. These findings may lead to novel ways of preventing beta-cell loss in the pathogenesis of diabetes.

Show MeSH
Related in: MedlinePlus