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Beta-cell uncoupling protein 2 regulates reactive oxygen species production, which influences both insulin and glucagon secretion.

Robson-Doucette CA, Sultan S, Allister EM, Wikstrom JD, Koshkin V, Bhattacharjee A, Prentice KJ, Sereda SB, Shirihai OS, Wheeler MB - Diabetes (2011)

Bottom Line: UCP2BKO islets had elevated intracellular ROS levels that associated with enhanced GSIS.UCP2 does not behave as a classical metabolic uncoupler in the β-cell, but has a more prominent role in the regulation of intracellular ROS levels that contribute to GSIS amplification.In addition, β-cell UCP2 contributes to the regulation of intraislet ROS signals that mediate changes in α-cell morphology and glucagon secretion.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Toronto, Toronto, Ontario, Canada.

ABSTRACT

Objective: The role of uncoupling protein 2 (UCP2) in pancreatic β-cells is highly debated, partly because of the broad tissue distribution of UCP2 and thus limitations of whole-body UCP2 knockout mouse models. To investigate the function of UCP2 in the β-cell, β-cell-specific UCP2 knockout mice (UCP2BKO) were generated and characterized.

Research design and methods: UCP2BKO mice were generated by crossing loxUCP2 mice with mice expressing rat insulin promoter-driven Cre recombinase. Several in vitro and in vivo parameters were measured, including respiration rate, mitochondrial membrane potential, islet ATP content, reactive oxygen species (ROS) levels, glucose-stimulated insulin secretion (GSIS), glucagon secretion, glucose and insulin tolerance, and plasma hormone levels.

Results: UCP2BKO β-cells displayed mildly increased glucose-induced mitochondrial membrane hyperpolarization but unchanged rates of uncoupled respiration and islet ATP content. UCP2BKO islets had elevated intracellular ROS levels that associated with enhanced GSIS. Surprisingly, UCP2BKO mice were glucose-intolerant, showing greater α-cell area, higher islet glucagon content, and aberrant ROS-dependent glucagon secretion under high glucose conditions.

Conclusions: Using a novel β-cell-specific UCP2KO mouse model, we have shed light on UCP2 function in primary β-cells. UCP2 does not behave as a classical metabolic uncoupler in the β-cell, but has a more prominent role in the regulation of intracellular ROS levels that contribute to GSIS amplification. In addition, β-cell UCP2 contributes to the regulation of intraislet ROS signals that mediate changes in α-cell morphology and glucagon secretion.

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Total glucagon content and glucagon secretion are augmented in UCP2BKO islets. A: Total glucagon content of isolated RIPCre and UCP2BKO islets. Data for n = 6. *P < 0.05. B: Total insulin content of isolated RIPCre and UCP2BKO islets. n = 4–6. C: Glucagon secretion from isolated RIPCre and UCP2BKO islets after incubation in 16.7 mmol/L glucose with (+) or without (−) DEM or NAC, respectively, for 1 h. n = 3–4. *P < 0.05; **P < 0.01. The error bars show the SEM.
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Figure 7: Total glucagon content and glucagon secretion are augmented in UCP2BKO islets. A: Total glucagon content of isolated RIPCre and UCP2BKO islets. Data for n = 6. *P < 0.05. B: Total insulin content of isolated RIPCre and UCP2BKO islets. n = 4–6. C: Glucagon secretion from isolated RIPCre and UCP2BKO islets after incubation in 16.7 mmol/L glucose with (+) or without (−) DEM or NAC, respectively, for 1 h. n = 3–4. *P < 0.05; **P < 0.01. The error bars show the SEM.

Mentions: Despite having enhanced GSIS in vitro (Fig. 4), oral glucose tolerance tests (OGTTs) revealed that UCP2BKO mice are glucose-intolerant compared with RIPCre mice (Fig. 5A). No differences in body weight, fasting plasma insulin, and glucagon levels or in daily fasting blood glucose were observed between the two genotypes (Supplementary Fig. 2). Insulin tolerance tests (ITTs) revealed no differences in insulin sensitivity (Fig. 5B). Plasma insulin levels during the OGTT were also similar in both genotypes (Fig. 5C); however, plasma glucagon levels measured 10 min after gavage (just before the peak of blood glucose) were suppressed in RIPCre mice but were aberrantly increased in UCP2BKO mice (Fig. 5D). Since islets are anatomically complex microorgans consisting of a heterogeneous population of endocrine cells (all of which can significantly affect glucose homeostasis), the effect of β-cell UCP2-deficiency on the function and morphology of α-cells was investigated. No difference in the number of islets per pancreatic area was observed (Fig. 6A). Insulin-positive areas in UCP2BKO and RIPCre pancreata (Fig. 6B) were similar, suggesting equal β-cell masses. Conversely, UCP2BKO pancreata had a greater glucagon-positive area compared with RIPCre islets (Fig. 6C), indicative of increased α-cell mass. Total islet insulin content (Fig. 7B) was similar between the two genotypes; however, glucagon content was significantly elevated in UCP2BKO islets (Fig. 7A). Overall, UCP2 deficiency in β-cells induced increased α-cell mass and total islet glucagon content.


Beta-cell uncoupling protein 2 regulates reactive oxygen species production, which influences both insulin and glucagon secretion.

Robson-Doucette CA, Sultan S, Allister EM, Wikstrom JD, Koshkin V, Bhattacharjee A, Prentice KJ, Sereda SB, Shirihai OS, Wheeler MB - Diabetes (2011)

Total glucagon content and glucagon secretion are augmented in UCP2BKO islets. A: Total glucagon content of isolated RIPCre and UCP2BKO islets. Data for n = 6. *P < 0.05. B: Total insulin content of isolated RIPCre and UCP2BKO islets. n = 4–6. C: Glucagon secretion from isolated RIPCre and UCP2BKO islets after incubation in 16.7 mmol/L glucose with (+) or without (−) DEM or NAC, respectively, for 1 h. n = 3–4. *P < 0.05; **P < 0.01. The error bars show the SEM.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198081&req=5

Figure 7: Total glucagon content and glucagon secretion are augmented in UCP2BKO islets. A: Total glucagon content of isolated RIPCre and UCP2BKO islets. Data for n = 6. *P < 0.05. B: Total insulin content of isolated RIPCre and UCP2BKO islets. n = 4–6. C: Glucagon secretion from isolated RIPCre and UCP2BKO islets after incubation in 16.7 mmol/L glucose with (+) or without (−) DEM or NAC, respectively, for 1 h. n = 3–4. *P < 0.05; **P < 0.01. The error bars show the SEM.
Mentions: Despite having enhanced GSIS in vitro (Fig. 4), oral glucose tolerance tests (OGTTs) revealed that UCP2BKO mice are glucose-intolerant compared with RIPCre mice (Fig. 5A). No differences in body weight, fasting plasma insulin, and glucagon levels or in daily fasting blood glucose were observed between the two genotypes (Supplementary Fig. 2). Insulin tolerance tests (ITTs) revealed no differences in insulin sensitivity (Fig. 5B). Plasma insulin levels during the OGTT were also similar in both genotypes (Fig. 5C); however, plasma glucagon levels measured 10 min after gavage (just before the peak of blood glucose) were suppressed in RIPCre mice but were aberrantly increased in UCP2BKO mice (Fig. 5D). Since islets are anatomically complex microorgans consisting of a heterogeneous population of endocrine cells (all of which can significantly affect glucose homeostasis), the effect of β-cell UCP2-deficiency on the function and morphology of α-cells was investigated. No difference in the number of islets per pancreatic area was observed (Fig. 6A). Insulin-positive areas in UCP2BKO and RIPCre pancreata (Fig. 6B) were similar, suggesting equal β-cell masses. Conversely, UCP2BKO pancreata had a greater glucagon-positive area compared with RIPCre islets (Fig. 6C), indicative of increased α-cell mass. Total islet insulin content (Fig. 7B) was similar between the two genotypes; however, glucagon content was significantly elevated in UCP2BKO islets (Fig. 7A). Overall, UCP2 deficiency in β-cells induced increased α-cell mass and total islet glucagon content.

Bottom Line: UCP2BKO islets had elevated intracellular ROS levels that associated with enhanced GSIS.UCP2 does not behave as a classical metabolic uncoupler in the β-cell, but has a more prominent role in the regulation of intracellular ROS levels that contribute to GSIS amplification.In addition, β-cell UCP2 contributes to the regulation of intraislet ROS signals that mediate changes in α-cell morphology and glucagon secretion.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Toronto, Toronto, Ontario, Canada.

ABSTRACT

Objective: The role of uncoupling protein 2 (UCP2) in pancreatic β-cells is highly debated, partly because of the broad tissue distribution of UCP2 and thus limitations of whole-body UCP2 knockout mouse models. To investigate the function of UCP2 in the β-cell, β-cell-specific UCP2 knockout mice (UCP2BKO) were generated and characterized.

Research design and methods: UCP2BKO mice were generated by crossing loxUCP2 mice with mice expressing rat insulin promoter-driven Cre recombinase. Several in vitro and in vivo parameters were measured, including respiration rate, mitochondrial membrane potential, islet ATP content, reactive oxygen species (ROS) levels, glucose-stimulated insulin secretion (GSIS), glucagon secretion, glucose and insulin tolerance, and plasma hormone levels.

Results: UCP2BKO β-cells displayed mildly increased glucose-induced mitochondrial membrane hyperpolarization but unchanged rates of uncoupled respiration and islet ATP content. UCP2BKO islets had elevated intracellular ROS levels that associated with enhanced GSIS. Surprisingly, UCP2BKO mice were glucose-intolerant, showing greater α-cell area, higher islet glucagon content, and aberrant ROS-dependent glucagon secretion under high glucose conditions.

Conclusions: Using a novel β-cell-specific UCP2KO mouse model, we have shed light on UCP2 function in primary β-cells. UCP2 does not behave as a classical metabolic uncoupler in the β-cell, but has a more prominent role in the regulation of intracellular ROS levels that contribute to GSIS amplification. In addition, β-cell UCP2 contributes to the regulation of intraislet ROS signals that mediate changes in α-cell morphology and glucagon secretion.

Show MeSH
Related in: MedlinePlus