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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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Insulin downregulates Trpm5 expression in Min6 cells. a, bTrpm5 expression in the insulinoma cell line MIN6 incubated for 1 week with 200 ng/ml leptin (a) or with 200 ng/ml leptin + 30 μM Tyrphostin AG490 (b). Control medium contained either no leptin (a) or 200 ng/ml leptin (b). Expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium. N = 3 per group. cTrpm5 expression in ob/ob islets incubated with 200 ng/ml leptin for 48 h. Expression was normalized to expression in islets from the same animal incubated in control medium. N = 4 per group, p = 0.149 (one-paired t test). dTrpm5 expression in MIN6 cells incubated for 1 week with 25 mM glucose + 250 μM diazoxide. Expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium containing 5.5 mM glucose + 250 μM diazoxide. N = 3–7 per group. eTrpm5 expression in MIN6 cells after incubation with either 10 or 100 nM insulin during 1 week. The incubation medium contained 5.5 mM glucose and expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium without insulin. N = 7 per group, **p < 0.01, ***p < 0.001
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Fig7: Insulin downregulates Trpm5 expression in Min6 cells. a, bTrpm5 expression in the insulinoma cell line MIN6 incubated for 1 week with 200 ng/ml leptin (a) or with 200 ng/ml leptin + 30 μM Tyrphostin AG490 (b). Control medium contained either no leptin (a) or 200 ng/ml leptin (b). Expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium. N = 3 per group. cTrpm5 expression in ob/ob islets incubated with 200 ng/ml leptin for 48 h. Expression was normalized to expression in islets from the same animal incubated in control medium. N = 4 per group, p = 0.149 (one-paired t test). dTrpm5 expression in MIN6 cells incubated for 1 week with 25 mM glucose + 250 μM diazoxide. Expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium containing 5.5 mM glucose + 250 μM diazoxide. N = 3–7 per group. eTrpm5 expression in MIN6 cells after incubation with either 10 or 100 nM insulin during 1 week. The incubation medium contained 5.5 mM glucose and expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium without insulin. N = 7 per group, **p < 0.01, ***p < 0.001

Mentions: We incubated the insulinoma cell line MIN6 cells with several factors altered in these mouse models for type 2 diabetes. First of all, both mouse strains suffer from a defect in the leptin signaling pathway. Activation of the leptin pathway in MIN6 cells by incubation with 200 ng/ml leptin for 48 h had no influence on Trpm5 expression (control 1.00 ± 0.05 vs. leptin 1.17 ± 0.13, n = 3 per group, p = 0.22; Fig. 7a). Furthermore, disrupting leptin signaling by adding the compound Tyrphostin AG490 to the incubation medium for 1 week had no effect on Trpm5 expression in MIN6 cells (leptin 1.0 ± 0.08 vs. leptin + AG490 0.85 ± 0.09, n = 3 per group, p = 0.279). Similarly, recovery of the leptin pathway in ob/ob islets by incubation with 200 ng/ml leptin for 48 h had no influence on Trpm5 expression (islet Trpm5 expression 1.27 ± 0.22 vs. control, n = 4, one-paired t test p = 0.30; Fig. 7b, c). These data strongly suggest that the disrupted leptin pathway is not the cause of the downregulation of Trpm5.Fig. 7


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)

Insulin downregulates Trpm5 expression in Min6 cells. a, bTrpm5 expression in the insulinoma cell line MIN6 incubated for 1 week with 200 ng/ml leptin (a) or with 200 ng/ml leptin + 30 μM Tyrphostin AG490 (b). Control medium contained either no leptin (a) or 200 ng/ml leptin (b). Expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium. N = 3 per group. cTrpm5 expression in ob/ob islets incubated with 200 ng/ml leptin for 48 h. Expression was normalized to expression in islets from the same animal incubated in control medium. N = 4 per group, p = 0.149 (one-paired t test). dTrpm5 expression in MIN6 cells incubated for 1 week with 25 mM glucose + 250 μM diazoxide. Expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium containing 5.5 mM glucose + 250 μM diazoxide. N = 3–7 per group. eTrpm5 expression in MIN6 cells after incubation with either 10 or 100 nM insulin during 1 week. The incubation medium contained 5.5 mM glucose and expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium without insulin. N = 7 per group, **p < 0.01, ***p < 0.001
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Fig7: Insulin downregulates Trpm5 expression in Min6 cells. a, bTrpm5 expression in the insulinoma cell line MIN6 incubated for 1 week with 200 ng/ml leptin (a) or with 200 ng/ml leptin + 30 μM Tyrphostin AG490 (b). Control medium contained either no leptin (a) or 200 ng/ml leptin (b). Expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium. N = 3 per group. cTrpm5 expression in ob/ob islets incubated with 200 ng/ml leptin for 48 h. Expression was normalized to expression in islets from the same animal incubated in control medium. N = 4 per group, p = 0.149 (one-paired t test). dTrpm5 expression in MIN6 cells incubated for 1 week with 25 mM glucose + 250 μM diazoxide. Expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium containing 5.5 mM glucose + 250 μM diazoxide. N = 3–7 per group. eTrpm5 expression in MIN6 cells after incubation with either 10 or 100 nM insulin during 1 week. The incubation medium contained 5.5 mM glucose and expression was normalized to Trpm5 expression in MIN6 cells incubated in control medium without insulin. N = 7 per group, **p < 0.01, ***p < 0.001
Mentions: We incubated the insulinoma cell line MIN6 cells with several factors altered in these mouse models for type 2 diabetes. First of all, both mouse strains suffer from a defect in the leptin signaling pathway. Activation of the leptin pathway in MIN6 cells by incubation with 200 ng/ml leptin for 48 h had no influence on Trpm5 expression (control 1.00 ± 0.05 vs. leptin 1.17 ± 0.13, n = 3 per group, p = 0.22; Fig. 7a). Furthermore, disrupting leptin signaling by adding the compound Tyrphostin AG490 to the incubation medium for 1 week had no effect on Trpm5 expression in MIN6 cells (leptin 1.0 ± 0.08 vs. leptin + AG490 0.85 ± 0.09, n = 3 per group, p = 0.279). Similarly, recovery of the leptin pathway in ob/ob islets by incubation with 200 ng/ml leptin for 48 h had no influence on Trpm5 expression (islet Trpm5 expression 1.27 ± 0.22 vs. control, n = 4, one-paired t test p = 0.30; Fig. 7b, c). These data strongly suggest that the disrupted leptin pathway is not the cause of the downregulation of Trpm5.Fig. 7

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