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Normal glucagon signaling and β-cell function after near-total α-cell ablation in adult mice.

Thorel F, Damond N, Chera S, Wiederkehr A, Thorens B, Meda P, Wollheim CB, Herrera PL - Diabetes (2011)

Bottom Line: We observed that 2% of the normal α-cell mass produced enough glucagon to ensure near-normal glucagonemia. β-Cell function and blood glucose homeostasis remained unaltered after α-cell loss, indicating that direct local intraislet signaling between α- and β-cells is dispensable.Escaping α-cells increased their glucagon content during subsequent months, but there was no significant α-cell regeneration.We previously reported that α-cells reprogram to insulin production after extreme β-cell loss and now conjecture that the low α-cell requirement could be exploited in future diabetic therapies aimed at regenerating β-cells by reprogramming adult α-cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland.

ABSTRACT

Objective: To evaluate whether healthy or diabetic adult mice can tolerate an extreme loss of pancreatic α-cells and how this sudden massive depletion affects β-cell function and blood glucose homeostasis.

Research design and methods: We generated a new transgenic model allowing near-total α-cell removal specifically in adult mice. Massive α-cell ablation was triggered in normally grown and healthy adult animals upon diphtheria toxin (DT) administration. The metabolic status of these mice was assessed in 1) physiologic conditions, 2) a situation requiring glucagon action, and 3) after β-cell loss.

Results: Adult transgenic mice enduring extreme (98%) α-cell removal remained healthy and did not display major defects in insulin counter-regulatory response. We observed that 2% of the normal α-cell mass produced enough glucagon to ensure near-normal glucagonemia. β-Cell function and blood glucose homeostasis remained unaltered after α-cell loss, indicating that direct local intraislet signaling between α- and β-cells is dispensable. Escaping α-cells increased their glucagon content during subsequent months, but there was no significant α-cell regeneration. Near-total α-cell ablation did not prevent hyperglycemia in mice having also undergone massive β-cell loss, indicating that a minimal amount of α-cells can still guarantee normal glucagon signaling in diabetic conditions.

Conclusions: An extremely low amount of α-cells is sufficient to prevent a major counter-regulatory deregulation, both under physiologic and diabetic conditions. We previously reported that α-cells reprogram to insulin production after extreme β-cell loss and now conjecture that the low α-cell requirement could be exploited in future diabetic therapies aimed at regenerating β-cells by reprogramming adult α-cells.

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Extreme α-cell loss moderately decreases circulating glucagon and has no effect on the counter-regulatory response. Evolution of body weight (A) and glycemia (B) in fasted controls (n = 3; DT-untreated, black ♦) and DT-treated (n = 3; red ▲) Glucagon-DTR mice. C: Glycemia after insulin-induced hypoglycemia 1 week after α-cell ablation. Blood glucose increased in both DT-treated mice (red ▲) and controls (black ♦) after an insulin challenge (n = 3/group). D: Plasma glucagon 1 week and 6 months after DT (red □) injections and in control (black □) mice. Glucagonemia was significantly reduced by 35% 1 week after DT (***P = 0.001) but returned to normal levels 6 months later (values in Supplementary Table 2). Confocal images of pancreatic sections stained for insulin (green) and glucagon (red) in controls (E) and Glucagon-DTR mice (F). Very few pancreatic α-cells can be observed 1 week after DT. E’ and F’: higher magnification of the dotted areas depicted in E and F, respectively. Scale bars = 100 μm in E and F and 20 μm in E’ and F’. G: Arginine-induced glucagon secretion from perfused pancreas 1 week after DT or in controls. H: Quantification of arginine-induced glucagon secretion upon arginine stimulation (1,290.2 ± 281.9 for controls, and 423.3 ± 85.3 pg/mL for DT-treated Glucagon-DTR mice; *P = 0.014). (A high-quality digital representation of this figure is available in the online issue.)
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Figure 2: Extreme α-cell loss moderately decreases circulating glucagon and has no effect on the counter-regulatory response. Evolution of body weight (A) and glycemia (B) in fasted controls (n = 3; DT-untreated, black ♦) and DT-treated (n = 3; red ▲) Glucagon-DTR mice. C: Glycemia after insulin-induced hypoglycemia 1 week after α-cell ablation. Blood glucose increased in both DT-treated mice (red ▲) and controls (black ♦) after an insulin challenge (n = 3/group). D: Plasma glucagon 1 week and 6 months after DT (red □) injections and in control (black □) mice. Glucagonemia was significantly reduced by 35% 1 week after DT (***P = 0.001) but returned to normal levels 6 months later (values in Supplementary Table 2). Confocal images of pancreatic sections stained for insulin (green) and glucagon (red) in controls (E) and Glucagon-DTR mice (F). Very few pancreatic α-cells can be observed 1 week after DT. E’ and F’: higher magnification of the dotted areas depicted in E and F, respectively. Scale bars = 100 μm in E and F and 20 μm in E’ and F’. G: Arginine-induced glucagon secretion from perfused pancreas 1 week after DT or in controls. H: Quantification of arginine-induced glucagon secretion upon arginine stimulation (1,290.2 ± 281.9 for controls, and 423.3 ± 85.3 pg/mL for DT-treated Glucagon-DTR mice; *P = 0.014). (A high-quality digital representation of this figure is available in the online issue.)

Mentions: Fasting and random-fed body weights were not affected after α-cell ablation (Fig. 2A and Supplementary Fig 3A). Surprisingly, DT-treated animals did not exhibit reduced glycemia compared with controls during fasting or in random-fed conditions (Fig. 2B and Supplementary Fig. 3B). In addition, glycemia was not significantly changed, even after a prolonged starvation (27-h fasting; Supplementary Fig. 3C). Furthermore, DT-treated Glucagon-DTR mice displayed normal insulin sensitivity and were able to recover a normal glycemic level after an insulin-induced hypoglycemia (Fig. 2C).


Normal glucagon signaling and β-cell function after near-total α-cell ablation in adult mice.

Thorel F, Damond N, Chera S, Wiederkehr A, Thorens B, Meda P, Wollheim CB, Herrera PL - Diabetes (2011)

Extreme α-cell loss moderately decreases circulating glucagon and has no effect on the counter-regulatory response. Evolution of body weight (A) and glycemia (B) in fasted controls (n = 3; DT-untreated, black ♦) and DT-treated (n = 3; red ▲) Glucagon-DTR mice. C: Glycemia after insulin-induced hypoglycemia 1 week after α-cell ablation. Blood glucose increased in both DT-treated mice (red ▲) and controls (black ♦) after an insulin challenge (n = 3/group). D: Plasma glucagon 1 week and 6 months after DT (red □) injections and in control (black □) mice. Glucagonemia was significantly reduced by 35% 1 week after DT (***P = 0.001) but returned to normal levels 6 months later (values in Supplementary Table 2). Confocal images of pancreatic sections stained for insulin (green) and glucagon (red) in controls (E) and Glucagon-DTR mice (F). Very few pancreatic α-cells can be observed 1 week after DT. E’ and F’: higher magnification of the dotted areas depicted in E and F, respectively. Scale bars = 100 μm in E and F and 20 μm in E’ and F’. G: Arginine-induced glucagon secretion from perfused pancreas 1 week after DT or in controls. H: Quantification of arginine-induced glucagon secretion upon arginine stimulation (1,290.2 ± 281.9 for controls, and 423.3 ± 85.3 pg/mL for DT-treated Glucagon-DTR mice; *P = 0.014). (A high-quality digital representation of this figure is available in the online issue.)
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Figure 2: Extreme α-cell loss moderately decreases circulating glucagon and has no effect on the counter-regulatory response. Evolution of body weight (A) and glycemia (B) in fasted controls (n = 3; DT-untreated, black ♦) and DT-treated (n = 3; red ▲) Glucagon-DTR mice. C: Glycemia after insulin-induced hypoglycemia 1 week after α-cell ablation. Blood glucose increased in both DT-treated mice (red ▲) and controls (black ♦) after an insulin challenge (n = 3/group). D: Plasma glucagon 1 week and 6 months after DT (red □) injections and in control (black □) mice. Glucagonemia was significantly reduced by 35% 1 week after DT (***P = 0.001) but returned to normal levels 6 months later (values in Supplementary Table 2). Confocal images of pancreatic sections stained for insulin (green) and glucagon (red) in controls (E) and Glucagon-DTR mice (F). Very few pancreatic α-cells can be observed 1 week after DT. E’ and F’: higher magnification of the dotted areas depicted in E and F, respectively. Scale bars = 100 μm in E and F and 20 μm in E’ and F’. G: Arginine-induced glucagon secretion from perfused pancreas 1 week after DT or in controls. H: Quantification of arginine-induced glucagon secretion upon arginine stimulation (1,290.2 ± 281.9 for controls, and 423.3 ± 85.3 pg/mL for DT-treated Glucagon-DTR mice; *P = 0.014). (A high-quality digital representation of this figure is available in the online issue.)
Mentions: Fasting and random-fed body weights were not affected after α-cell ablation (Fig. 2A and Supplementary Fig 3A). Surprisingly, DT-treated animals did not exhibit reduced glycemia compared with controls during fasting or in random-fed conditions (Fig. 2B and Supplementary Fig. 3B). In addition, glycemia was not significantly changed, even after a prolonged starvation (27-h fasting; Supplementary Fig. 3C). Furthermore, DT-treated Glucagon-DTR mice displayed normal insulin sensitivity and were able to recover a normal glycemic level after an insulin-induced hypoglycemia (Fig. 2C).

Bottom Line: We observed that 2% of the normal α-cell mass produced enough glucagon to ensure near-normal glucagonemia. β-Cell function and blood glucose homeostasis remained unaltered after α-cell loss, indicating that direct local intraislet signaling between α- and β-cells is dispensable.Escaping α-cells increased their glucagon content during subsequent months, but there was no significant α-cell regeneration.We previously reported that α-cells reprogram to insulin production after extreme β-cell loss and now conjecture that the low α-cell requirement could be exploited in future diabetic therapies aimed at regenerating β-cells by reprogramming adult α-cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland.

ABSTRACT

Objective: To evaluate whether healthy or diabetic adult mice can tolerate an extreme loss of pancreatic α-cells and how this sudden massive depletion affects β-cell function and blood glucose homeostasis.

Research design and methods: We generated a new transgenic model allowing near-total α-cell removal specifically in adult mice. Massive α-cell ablation was triggered in normally grown and healthy adult animals upon diphtheria toxin (DT) administration. The metabolic status of these mice was assessed in 1) physiologic conditions, 2) a situation requiring glucagon action, and 3) after β-cell loss.

Results: Adult transgenic mice enduring extreme (98%) α-cell removal remained healthy and did not display major defects in insulin counter-regulatory response. We observed that 2% of the normal α-cell mass produced enough glucagon to ensure near-normal glucagonemia. β-Cell function and blood glucose homeostasis remained unaltered after α-cell loss, indicating that direct local intraislet signaling between α- and β-cells is dispensable. Escaping α-cells increased their glucagon content during subsequent months, but there was no significant α-cell regeneration. Near-total α-cell ablation did not prevent hyperglycemia in mice having also undergone massive β-cell loss, indicating that a minimal amount of α-cells can still guarantee normal glucagon signaling in diabetic conditions.

Conclusions: An extremely low amount of α-cells is sufficient to prevent a major counter-regulatory deregulation, both under physiologic and diabetic conditions. We previously reported that α-cells reprogram to insulin production after extreme β-cell loss and now conjecture that the low α-cell requirement could be exploited in future diabetic therapies aimed at regenerating β-cells by reprogramming adult α-cells.

Show MeSH
Related in: MedlinePlus