Limits...
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.

Show MeSH

Related in: MedlinePlus

Newly formed α-cells after ablation are not reprogrammed β-cells. A: Transgenes required for the inducible β-cell tracing and α-cell ablation. B: Experimental design for irreversible labeling of adult β-cells before α-cell ablation. C–F: Almost all β-cells were YFP-labeled after tamoxifen (TAM) administration in control animals (DT-untreated). G–J: At 6 months after DT, none of the very rare glucagon-expressing cells were YFP-positive (the arrowhead points to one α-cell, also shown in the top right inset at higher magnification). Scale bars = 20 μm. (A high-quality digital representation of this figure is available in the online issue.)
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3198058&req=5

Figure 5: Newly formed α-cells after ablation are not reprogrammed β-cells. A: Transgenes required for the inducible β-cell tracing and α-cell ablation. B: Experimental design for irreversible labeling of adult β-cells before α-cell ablation. C–F: Almost all β-cells were YFP-labeled after tamoxifen (TAM) administration in control animals (DT-untreated). G–J: At 6 months after DT, none of the very rare glucagon-expressing cells were YFP-positive (the arrowhead points to one α-cell, also shown in the top right inset at higher magnification). Scale bars = 20 μm. (A high-quality digital representation of this figure is available in the online issue.)

Mentions: We recently showed that adult α-cells spontaneously reprogram to acquire β-cell characteristics after extreme, near-total β-cell destruction (13). We have now investigated whether the reverse β-cell to α-cell transdifferentiation also occurs spontaneously after α-cell ablation; that is, if glucagon-expressing cells found several months after DT administration were indeed β-cells that had been reprogrammed to glucagon production after α-cell loss. For this purpose, we performed a conditional cell lineage tracing using RIP-CreERT, Rosa26YFP, Glucagon-DTR transgenic mice (Fig. 5A). We irreversibly labeled β-cells with the yellow fluorescent protein (YFP) by the administration of tamoxifen before α-cell ablation (Fig. 5B). DT was given to ablate α-cells 2 weeks later. At 1 and 6 months after DT, none of the few glucagon-expressing cells found were YFP-positive (634 islets from 6 mice were scored and 256 glucagon-positive cells analyzed), whereas almost all β-cells were fluorescently tagged (Fig. 5C–J). In conclusion, the glucagon-expressing cells present after massive α-cell ablation are not reprogrammed β-cells.


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)

Newly formed α-cells after ablation are not reprogrammed β-cells. A: Transgenes required for the inducible β-cell tracing and α-cell ablation. B: Experimental design for irreversible labeling of adult β-cells before α-cell ablation. C–F: Almost all β-cells were YFP-labeled after tamoxifen (TAM) administration in control animals (DT-untreated). G–J: At 6 months after DT, none of the very rare glucagon-expressing cells were YFP-positive (the arrowhead points to one α-cell, also shown in the top right inset at higher magnification). Scale bars = 20 μm. (A high-quality digital representation of this figure is available in the online issue.)
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198058&req=5

Figure 5: Newly formed α-cells after ablation are not reprogrammed β-cells. A: Transgenes required for the inducible β-cell tracing and α-cell ablation. B: Experimental design for irreversible labeling of adult β-cells before α-cell ablation. C–F: Almost all β-cells were YFP-labeled after tamoxifen (TAM) administration in control animals (DT-untreated). G–J: At 6 months after DT, none of the very rare glucagon-expressing cells were YFP-positive (the arrowhead points to one α-cell, also shown in the top right inset at higher magnification). Scale bars = 20 μm. (A high-quality digital representation of this figure is available in the online issue.)
Mentions: We recently showed that adult α-cells spontaneously reprogram to acquire β-cell characteristics after extreme, near-total β-cell destruction (13). We have now investigated whether the reverse β-cell to α-cell transdifferentiation also occurs spontaneously after α-cell ablation; that is, if glucagon-expressing cells found several months after DT administration were indeed β-cells that had been reprogrammed to glucagon production after α-cell loss. For this purpose, we performed a conditional cell lineage tracing using RIP-CreERT, Rosa26YFP, Glucagon-DTR transgenic mice (Fig. 5A). We irreversibly labeled β-cells with the yellow fluorescent protein (YFP) by the administration of tamoxifen before α-cell ablation (Fig. 5B). DT was given to ablate α-cells 2 weeks later. At 1 and 6 months after DT, none of the few glucagon-expressing cells found were YFP-positive (634 islets from 6 mice were scored and 256 glucagon-positive cells analyzed), whereas almost all β-cells were fluorescently tagged (Fig. 5C–J). In conclusion, the glucagon-expressing cells present after massive α-cell ablation are not reprogrammed β-cells.

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