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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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Changes in pancreatic glucagon content and α-cell number after near-total α-cell loss. A: Pancreatic glucagon content was increased almost sevenfold between 1 week and 1 month (from 23.52 to 157.9 pg/mg; **P = 0.0048, one-tailed Mann-Whitney U test) and doubled between 1 and 6 months (157.9 to 331.4 pg/mg; *P = 0.0317, one-tailed Mann-Whitney U test) in DT-treated animals. B: Pancreatic α-cell number was not increased between 1 week and 1 month after DT but was doubled at 6 months. C: The total number of islets (defined as clusters of at least three β-cells) remained unchanged after α-cell ablation. D: The number of islet sections containing at least one α-cell was dramatically reduced after DT treatment, throughout the whole period of analysis. E: The number of α-cells in islet sections containing α-cells after DT treatment was almost doubled at 6 months. F: The number of α-cells located outside of islets was always lower in DT-treated mice than in controls and did not increase significantly with time after DT. A–F: Black ♦: control; red ▲: DT-treated mice.
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Figure 4: Changes in pancreatic glucagon content and α-cell number after near-total α-cell loss. A: Pancreatic glucagon content was increased almost sevenfold between 1 week and 1 month (from 23.52 to 157.9 pg/mg; **P = 0.0048, one-tailed Mann-Whitney U test) and doubled between 1 and 6 months (157.9 to 331.4 pg/mg; *P = 0.0317, one-tailed Mann-Whitney U test) in DT-treated animals. B: Pancreatic α-cell number was not increased between 1 week and 1 month after DT but was doubled at 6 months. C: The total number of islets (defined as clusters of at least three β-cells) remained unchanged after α-cell ablation. D: The number of islet sections containing at least one α-cell was dramatically reduced after DT treatment, throughout the whole period of analysis. E: The number of α-cells in islet sections containing α-cells after DT treatment was almost doubled at 6 months. F: The number of α-cells located outside of islets was always lower in DT-treated mice than in controls and did not increase significantly with time after DT. A–F: Black ♦: control; red ▲: DT-treated mice.

Mentions: One week after DT administration, the total pancreatic glucagon content had dropped to 0.86% of control level, but 1 and 6 months later, it was increased by a factor of 6.7- and 14-fold, respectively (Fig. 4A and Table 1). Basal glucagonemia was normal in Glucagon-DTR mice (n = 4) 6 months after α-cell destruction (63.0 ± 0.9 vs. 64.2 ± 0.4 pg/mL in controls, n = 3; Fig. 2D). These observations are consistent with 1) increased glucagon production and secretion with time, by the few remaining α-cells, and 2) the regeneration of new α-cells, or both. To explore these possibilities, we assessed the number of α-cells present in the pancreas 1 week, 1 month, and 6 months after DT (Supplementary Table 1). The total number of α-cells remained unchanged between 1 week and 1 month after DT, but was doubled at 6 months, from 0.17 at 1 month to 0.35 cells/mm2 5 months later (P = 0.0286; Fig. 4B and Table 1). The number of islets was similar between untreated and DT-treated animals at all intervals, suggesting that new islets are not formed after α-cell ablation (Fig. 4C and Table 1). The number of islet sections containing at least 1 α-cell did not increase during the regeneration period under study: the percentage of sections containing α-cells dropped 1 week after DT by about 10-fold compared with untreated controls and remained stable thereafter (Fig. 4D and Table 1). Nevertheless, among the islets that contained α-cells, the number of α-cells per islet section was almost doubled 6 months after DT, from 1.58 at 1 month to 2.48 α-cells/α-cell–containing islets (P = 0.0286; Fig. 4E and Table 1). These findings suggest that the doubling in α-cells observed 6 months post-DT was not due to the appearance of new glucagon-expressing cells in islets devoid of α-cells. Furthermore, we found that α-cell apoptosis and proliferation were not increased at any time after DT administration, thus suggesting that the low α-cell regeneration observed after massive α-cell ablation was not the consequence of a high rate α-cell turnover (Supplementary Figs. 5 and 6).


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)

Changes in pancreatic glucagon content and α-cell number after near-total α-cell loss. A: Pancreatic glucagon content was increased almost sevenfold between 1 week and 1 month (from 23.52 to 157.9 pg/mg; **P = 0.0048, one-tailed Mann-Whitney U test) and doubled between 1 and 6 months (157.9 to 331.4 pg/mg; *P = 0.0317, one-tailed Mann-Whitney U test) in DT-treated animals. B: Pancreatic α-cell number was not increased between 1 week and 1 month after DT but was doubled at 6 months. C: The total number of islets (defined as clusters of at least three β-cells) remained unchanged after α-cell ablation. D: The number of islet sections containing at least one α-cell was dramatically reduced after DT treatment, throughout the whole period of analysis. E: The number of α-cells in islet sections containing α-cells after DT treatment was almost doubled at 6 months. F: The number of α-cells located outside of islets was always lower in DT-treated mice than in controls and did not increase significantly with time after DT. A–F: Black ♦: control; red ▲: DT-treated mice.
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Figure 4: Changes in pancreatic glucagon content and α-cell number after near-total α-cell loss. A: Pancreatic glucagon content was increased almost sevenfold between 1 week and 1 month (from 23.52 to 157.9 pg/mg; **P = 0.0048, one-tailed Mann-Whitney U test) and doubled between 1 and 6 months (157.9 to 331.4 pg/mg; *P = 0.0317, one-tailed Mann-Whitney U test) in DT-treated animals. B: Pancreatic α-cell number was not increased between 1 week and 1 month after DT but was doubled at 6 months. C: The total number of islets (defined as clusters of at least three β-cells) remained unchanged after α-cell ablation. D: The number of islet sections containing at least one α-cell was dramatically reduced after DT treatment, throughout the whole period of analysis. E: The number of α-cells in islet sections containing α-cells after DT treatment was almost doubled at 6 months. F: The number of α-cells located outside of islets was always lower in DT-treated mice than in controls and did not increase significantly with time after DT. A–F: Black ♦: control; red ▲: DT-treated mice.
Mentions: One week after DT administration, the total pancreatic glucagon content had dropped to 0.86% of control level, but 1 and 6 months later, it was increased by a factor of 6.7- and 14-fold, respectively (Fig. 4A and Table 1). Basal glucagonemia was normal in Glucagon-DTR mice (n = 4) 6 months after α-cell destruction (63.0 ± 0.9 vs. 64.2 ± 0.4 pg/mL in controls, n = 3; Fig. 2D). These observations are consistent with 1) increased glucagon production and secretion with time, by the few remaining α-cells, and 2) the regeneration of new α-cells, or both. To explore these possibilities, we assessed the number of α-cells present in the pancreas 1 week, 1 month, and 6 months after DT (Supplementary Table 1). The total number of α-cells remained unchanged between 1 week and 1 month after DT, but was doubled at 6 months, from 0.17 at 1 month to 0.35 cells/mm2 5 months later (P = 0.0286; Fig. 4B and Table 1). The number of islets was similar between untreated and DT-treated animals at all intervals, suggesting that new islets are not formed after α-cell ablation (Fig. 4C and Table 1). The number of islet sections containing at least 1 α-cell did not increase during the regeneration period under study: the percentage of sections containing α-cells dropped 1 week after DT by about 10-fold compared with untreated controls and remained stable thereafter (Fig. 4D and Table 1). Nevertheless, among the islets that contained α-cells, the number of α-cells per islet section was almost doubled 6 months after DT, from 1.58 at 1 month to 2.48 α-cells/α-cell–containing islets (P = 0.0286; Fig. 4E and Table 1). These findings suggest that the doubling in α-cells observed 6 months post-DT was not due to the appearance of new glucagon-expressing cells in islets devoid of α-cells. Furthermore, we found that α-cell apoptosis and proliferation were not increased at any time after DT administration, thus suggesting that the low α-cell regeneration observed after massive α-cell ablation was not the consequence of a high rate α-cell turnover (Supplementary Figs. 5 and 6).

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