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Insulin downregulates the expression of the Ca2+-activated nonselective cation channel TRPM5 in pancreatic islets from leptin-deficient mouse models.

Colsoul B, Jacobs G, Philippaert K, Owsianik G, Segal A, Nilius B, Voets T, Schuit F, Vennekens R - Pflugers Arch. (2013)

Bottom Line: The glucose-induced Ca(2+) oscillation pattern in db/db and ob/ob islets mimicked those of Trpm5 (-/-) islets.Leptin treatment had no additional effect on Trpm5 expression levels when plasma insulin levels were comparable to those of the vehicle-injected control group.In murine β cell line, MIN6, insulin downregulated TRPM5 expression in a dose-dependent manner, unlike glucose or leptin.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Ion Channel Research, KU Leuven, Herestraat 49, bus 802, Leuven, 3000, Belgium.

ABSTRACT
We recently proposed that the transient receptor potential melastatin 5 (TRPM5) cation channel contributes to glucose-induced electrical activity of the β cell and positively influences glucose-induced insulin release and glucose homeostasis. In this study, we investigated Trpm5 expression and function in pancreatic islets from mouse models of type II diabetes. Gene expression analysis revealed a strong reduction of Trpm5 mRNA levels in pancreatic islets of db/db and ob/ob mice. The glucose-induced Ca(2+) oscillation pattern in db/db and ob/ob islets mimicked those of Trpm5 (-/-) islets. Leptin treatment of ob/ob mice not only reversed the diabetic phenotype seen in these mice but also upregulated Trpm5 expression. Leptin treatment had no additional effect on Trpm5 expression levels when plasma insulin levels were comparable to those of the vehicle-injected control group. In murine β cell line, MIN6, insulin downregulated TRPM5 expression in a dose-dependent manner, unlike glucose or leptin. In conclusion, our data show that increased plasma insulin levels downregulate TRPM5 expression in pancreatic islets from leptin-deficient mouse models of type 2 diabetes.

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Related in: MedlinePlus

Effect of leptin injection on islet Trpm5 expression and circulating insulin levels in control-fed and food-restricted mice. Bodyweight, plasma glucose, plasma insulin, and islet Trpm5 expression in ob/ob mice that were injected for 2 days with either 1 mg leptin/kg bodyweight or vehicle. Mice were divided in two groups: they had either free access to food during the course of the experiment (a) or were put on food restriction (b), meaning that they received 3 g of food per mouse per day and were fasted overnight during the last night before islet isolation. Trpm5 expression in islets from leptin-injected mice was normalized to the average Trpm5 expression in islets from vehicle-injected mice that had followed the same food protocol. N = 4 mice per group, **p < 0.01, ***p < 0.001
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Fig6: Effect of leptin injection on islet Trpm5 expression and circulating insulin levels in control-fed and food-restricted mice. Bodyweight, plasma glucose, plasma insulin, and islet Trpm5 expression in ob/ob mice that were injected for 2 days with either 1 mg leptin/kg bodyweight or vehicle. Mice were divided in two groups: they had either free access to food during the course of the experiment (a) or were put on food restriction (b), meaning that they received 3 g of food per mouse per day and were fasted overnight during the last night before islet isolation. Trpm5 expression in islets from leptin-injected mice was normalized to the average Trpm5 expression in islets from vehicle-injected mice that had followed the same food protocol. N = 4 mice per group, **p < 0.01, ***p < 0.001

Mentions: In order to investigate whether the recovery of the leptin pathway (without altering the metabolic phenotype) would be sufficient to upregulate Trpm5 expression, we injected 9-week-old ob/ob mice for 2 days with either 1 mg leptin per kilogram bodyweight or vehicle. Since leptin will have a dramatic and immediate effect on food intake and consequently on the metabolic phenotype, animals were divided in two groups as follows: one group of mice had free access to food for the whole duration of the experiment (Fig. 6a), whereas a second group was put on food restriction, meaning that they received 3 g of food per day and were fasted overnight during the last night before islet isolation (Fig. 6b). Bodyweight was not altered by this short period of leptin treatment, neither in the fed ad libitum group (vehicle-injected 44.1 ± 1.7 g vs. leptin-injected 42.7 ± 1.1 g; p = 0.52, n = 4 mice per group) nor in the food restriction group (vehicle-injected 41.0 ± 0.7 g vs. leptin-injected 39.2 ± 1.5 g; p = 0.33, n = 4 mice per group). Also, plasma glucose levels did not change after 2 days of leptin treatment for both groups: vehicle-injected 245.5 ± 68.2 mg/dl versus leptin-injected 167.5 ± 4.9 mg/dl; p = 0.30, n = 4 mice per group for the fed ad libitum mice and vehicle-injected 179 ± 18 mg/dl versus leptin-injected 155 ± 17 mg/dl; p = 0.38, n = 4 mice per group for the mice put on food restriction. However, plasma insulin was dramatically decreased by leptin treatment in the fed ad libitum mice (vehicle-injected 16.9 ± 1.4 ng/ml vs. leptin-injected 6.2 ± 1.0 ng/ml; p = 0.0008, n = 4 mice per group). In contrast, the mice that were on food restriction displayed normal insulin levels (4.4 ± 1.6 ng/ml vs. 2.7 ± 1.2 ng/ml, respectively, p = 0.41, n = 4 mice per group). Interestingly, Trpm5 was upregulated by leptin treatment in mice that had free access to food (vehicle-injected 0.96 ± 0.43 vs. leptin-injected 3.65 ± 0.53; p = 0.0092, n = 4 mice per group) but not in mice that were on food restriction (vehicle-injected 0.95 ± 0.36 vs. leptin-injected 1.08 ± 0.31, p = 0.86, n = 4 mice per group). These data strongly suggest that plasma insulin levels are a critical factor in the regulation of islet Trpm5 expression.Fig. 6


Insulin downregulates the expression of the Ca2+-activated nonselective cation channel TRPM5 in pancreatic islets from leptin-deficient mouse models.

Colsoul B, Jacobs G, Philippaert K, Owsianik G, Segal A, Nilius B, Voets T, Schuit F, Vennekens R - Pflugers Arch. (2013)

Effect of leptin injection on islet Trpm5 expression and circulating insulin levels in control-fed and food-restricted mice. Bodyweight, plasma glucose, plasma insulin, and islet Trpm5 expression in ob/ob mice that were injected for 2 days with either 1 mg leptin/kg bodyweight or vehicle. Mice were divided in two groups: they had either free access to food during the course of the experiment (a) or were put on food restriction (b), meaning that they received 3 g of food per mouse per day and were fasted overnight during the last night before islet isolation. Trpm5 expression in islets from leptin-injected mice was normalized to the average Trpm5 expression in islets from vehicle-injected mice that had followed the same food protocol. N = 4 mice per group, **p < 0.01, ***p < 0.001
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig6: Effect of leptin injection on islet Trpm5 expression and circulating insulin levels in control-fed and food-restricted mice. Bodyweight, plasma glucose, plasma insulin, and islet Trpm5 expression in ob/ob mice that were injected for 2 days with either 1 mg leptin/kg bodyweight or vehicle. Mice were divided in two groups: they had either free access to food during the course of the experiment (a) or were put on food restriction (b), meaning that they received 3 g of food per mouse per day and were fasted overnight during the last night before islet isolation. Trpm5 expression in islets from leptin-injected mice was normalized to the average Trpm5 expression in islets from vehicle-injected mice that had followed the same food protocol. N = 4 mice per group, **p < 0.01, ***p < 0.001
Mentions: In order to investigate whether the recovery of the leptin pathway (without altering the metabolic phenotype) would be sufficient to upregulate Trpm5 expression, we injected 9-week-old ob/ob mice for 2 days with either 1 mg leptin per kilogram bodyweight or vehicle. Since leptin will have a dramatic and immediate effect on food intake and consequently on the metabolic phenotype, animals were divided in two groups as follows: one group of mice had free access to food for the whole duration of the experiment (Fig. 6a), whereas a second group was put on food restriction, meaning that they received 3 g of food per day and were fasted overnight during the last night before islet isolation (Fig. 6b). Bodyweight was not altered by this short period of leptin treatment, neither in the fed ad libitum group (vehicle-injected 44.1 ± 1.7 g vs. leptin-injected 42.7 ± 1.1 g; p = 0.52, n = 4 mice per group) nor in the food restriction group (vehicle-injected 41.0 ± 0.7 g vs. leptin-injected 39.2 ± 1.5 g; p = 0.33, n = 4 mice per group). Also, plasma glucose levels did not change after 2 days of leptin treatment for both groups: vehicle-injected 245.5 ± 68.2 mg/dl versus leptin-injected 167.5 ± 4.9 mg/dl; p = 0.30, n = 4 mice per group for the fed ad libitum mice and vehicle-injected 179 ± 18 mg/dl versus leptin-injected 155 ± 17 mg/dl; p = 0.38, n = 4 mice per group for the mice put on food restriction. However, plasma insulin was dramatically decreased by leptin treatment in the fed ad libitum mice (vehicle-injected 16.9 ± 1.4 ng/ml vs. leptin-injected 6.2 ± 1.0 ng/ml; p = 0.0008, n = 4 mice per group). In contrast, the mice that were on food restriction displayed normal insulin levels (4.4 ± 1.6 ng/ml vs. 2.7 ± 1.2 ng/ml, respectively, p = 0.41, n = 4 mice per group). Interestingly, Trpm5 was upregulated by leptin treatment in mice that had free access to food (vehicle-injected 0.96 ± 0.43 vs. leptin-injected 3.65 ± 0.53; p = 0.0092, n = 4 mice per group) but not in mice that were on food restriction (vehicle-injected 0.95 ± 0.36 vs. leptin-injected 1.08 ± 0.31, p = 0.86, n = 4 mice per group). These data strongly suggest that plasma insulin levels are a critical factor in the regulation of islet Trpm5 expression.Fig. 6

Bottom Line: The glucose-induced Ca(2+) oscillation pattern in db/db and ob/ob islets mimicked those of Trpm5 (-/-) islets.Leptin treatment had no additional effect on Trpm5 expression levels when plasma insulin levels were comparable to those of the vehicle-injected control group.In murine β cell line, MIN6, insulin downregulated TRPM5 expression in a dose-dependent manner, unlike glucose or leptin.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Ion Channel Research, KU Leuven, Herestraat 49, bus 802, Leuven, 3000, Belgium.

ABSTRACT
We recently proposed that the transient receptor potential melastatin 5 (TRPM5) cation channel contributes to glucose-induced electrical activity of the β cell and positively influences glucose-induced insulin release and glucose homeostasis. In this study, we investigated Trpm5 expression and function in pancreatic islets from mouse models of type II diabetes. Gene expression analysis revealed a strong reduction of Trpm5 mRNA levels in pancreatic islets of db/db and ob/ob mice. The glucose-induced Ca(2+) oscillation pattern in db/db and ob/ob islets mimicked those of Trpm5 (-/-) islets. Leptin treatment of ob/ob mice not only reversed the diabetic phenotype seen in these mice but also upregulated Trpm5 expression. Leptin treatment had no additional effect on Trpm5 expression levels when plasma insulin levels were comparable to those of the vehicle-injected control group. In murine β cell line, MIN6, insulin downregulated TRPM5 expression in a dose-dependent manner, unlike glucose or leptin. In conclusion, our data show that increased plasma insulin levels downregulate TRPM5 expression in pancreatic islets from leptin-deficient mouse models of type 2 diabetes.

Show MeSH
Related in: MedlinePlus