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Urocortin3 mediates somatostatin-dependent negative feedback control of insulin secretion.

van der Meulen T, Donaldson CJ, Cáceres E, Hunter AE, Cowing-Zitron C, Pound LD, Adams MW, Zembrzycki A, Grove KL, Huising MO - Nat. Med. (2015)

Bottom Line: The peptide hormone urocortin3 (Ucn3) is abundantly expressed by mature beta cells, yet its physiological role is unknown.Here we demonstrate that Ucn3 is stored and co-released with insulin and potentiates glucose-stimulated somatostatin secretion via cognate receptors on delta cells.Further, we found that islets lacking endogenous Ucn3 have fewer delta cells, reduced somatostatin content, impaired somatostatin secretion, and exaggerated insulin release, and that these defects are rectified by treatment with synthetic Ucn3 in vitro.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, California, USA. [2] Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, California, USA.

ABSTRACT
The peptide hormone urocortin3 (Ucn3) is abundantly expressed by mature beta cells, yet its physiological role is unknown. Here we demonstrate that Ucn3 is stored and co-released with insulin and potentiates glucose-stimulated somatostatin secretion via cognate receptors on delta cells. Further, we found that islets lacking endogenous Ucn3 have fewer delta cells, reduced somatostatin content, impaired somatostatin secretion, and exaggerated insulin release, and that these defects are rectified by treatment with synthetic Ucn3 in vitro. Our observations indicate that the paracrine actions of Ucn3 activate a negative feedback loop that promotes somatostatin release to ensure the timely reduction of insulin secretion upon normalization of plasma glucose. Moreover, Ucn3 is markedly depleted from beta cells in mouse and macaque models of diabetes and in human diabetic islets. This suggests that Ucn3 is a key contributor to stable glycemic control, whose reduction during diabetes aggravates glycemic volatility and contributes to the pathophysiology of this disease.

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Ucn3– islets are deficient in delta cell number and somatostatin secretion. Transcriptome analysis of Ucn3– islets compared to wild–type littermates for Ucn3 (a) Sst (b), Hhex (c), and Rbp4 (d) (n = 3), data normalized to 1×107 reads. (e) Somatostatin, insulin and glucagon content of Ucn3– and control islets (n = 4). (f) Relative delta, beta and alpha cell number of Ucn3  and control islets (n = 3 control/4 Ucn3 , 5–7 islets/animal). (g) Somatostatin secretion from Ucn3– islets compared to control (n = 4, 95 islets/well, asterisks indicate significance with the 5.5 mM glucose group for the same genotype, unless indicated otherwise). Insulin secretion from Ucn3– islets compared to control in static incubation (h) (n = 4, 7 islets/well) and in islet perfusion (i) (n = 2, 150 islets per chamber, representative of 2 experiments). Significance determined by Student’s t–test (e, f), two–way ANOVA for treatment and genotype, followed by Holm–Sidak’s multiple comparison test (g, h), or two–way ANOVA for genotype and its interaction with time for each block (i); P values for genotype are given (i). All values are mean ± s.e.m., *P < 0.05, **P < 0.01, ***P < 0.001.
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Figure 2: Ucn3– islets are deficient in delta cell number and somatostatin secretion. Transcriptome analysis of Ucn3– islets compared to wild–type littermates for Ucn3 (a) Sst (b), Hhex (c), and Rbp4 (d) (n = 3), data normalized to 1×107 reads. (e) Somatostatin, insulin and glucagon content of Ucn3– and control islets (n = 4). (f) Relative delta, beta and alpha cell number of Ucn3 and control islets (n = 3 control/4 Ucn3 , 5–7 islets/animal). (g) Somatostatin secretion from Ucn3– islets compared to control (n = 4, 95 islets/well, asterisks indicate significance with the 5.5 mM glucose group for the same genotype, unless indicated otherwise). Insulin secretion from Ucn3– islets compared to control in static incubation (h) (n = 4, 7 islets/well) and in islet perfusion (i) (n = 2, 150 islets per chamber, representative of 2 experiments). Significance determined by Student’s t–test (e, f), two–way ANOVA for treatment and genotype, followed by Holm–Sidak’s multiple comparison test (g, h), or two–way ANOVA for genotype and its interaction with time for each block (i); P values for genotype are given (i). All values are mean ± s.e.m., *P < 0.05, **P < 0.01, ***P < 0.001.

Mentions: We next turned to Ucn3– mice27, where transcriptome analysis confirmed the absence of Ucn3 (Fig. 2a) and revealed marked reductions in the expression of known delta cell markers including Sst, Rbp4, and Hhex29,30 compared to wild type littermates (Fig. 2b–d and Supplementary Table 1). These observations suggest that the absence of Ucn3 precipitated relative delta cell deficiency. Indeed, Ucn3– islets displayed selective reductions in somatostatin content (Fig. 2e) and relative delta cell number (Fig. 2f) compared to controls. Ucn3– islets demonstrate impaired basal and glucose–stimulated somatostatin release compared to wild–type islets, which we fully rescued by co–stimulation with synthetic Ucn3 (Fig. 2g). Ucn3– islets hyper–secreted insulin during the first and second phase of secretion compared to controls, which normalized upon addition of synthetic Ucn3 peptide (Fig. 2h, i). Islets from Crhr2– mice31 showed comparable defects in somatostatin content and release compared to wild–type littermate controls (Supplementary Fig. 3).


Urocortin3 mediates somatostatin-dependent negative feedback control of insulin secretion.

van der Meulen T, Donaldson CJ, Cáceres E, Hunter AE, Cowing-Zitron C, Pound LD, Adams MW, Zembrzycki A, Grove KL, Huising MO - Nat. Med. (2015)

Ucn3– islets are deficient in delta cell number and somatostatin secretion. Transcriptome analysis of Ucn3– islets compared to wild–type littermates for Ucn3 (a) Sst (b), Hhex (c), and Rbp4 (d) (n = 3), data normalized to 1×107 reads. (e) Somatostatin, insulin and glucagon content of Ucn3– and control islets (n = 4). (f) Relative delta, beta and alpha cell number of Ucn3  and control islets (n = 3 control/4 Ucn3 , 5–7 islets/animal). (g) Somatostatin secretion from Ucn3– islets compared to control (n = 4, 95 islets/well, asterisks indicate significance with the 5.5 mM glucose group for the same genotype, unless indicated otherwise). Insulin secretion from Ucn3– islets compared to control in static incubation (h) (n = 4, 7 islets/well) and in islet perfusion (i) (n = 2, 150 islets per chamber, representative of 2 experiments). Significance determined by Student’s t–test (e, f), two–way ANOVA for treatment and genotype, followed by Holm–Sidak’s multiple comparison test (g, h), or two–way ANOVA for genotype and its interaction with time for each block (i); P values for genotype are given (i). All values are mean ± s.e.m., *P < 0.05, **P < 0.01, ***P < 0.001.
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Figure 2: Ucn3– islets are deficient in delta cell number and somatostatin secretion. Transcriptome analysis of Ucn3– islets compared to wild–type littermates for Ucn3 (a) Sst (b), Hhex (c), and Rbp4 (d) (n = 3), data normalized to 1×107 reads. (e) Somatostatin, insulin and glucagon content of Ucn3– and control islets (n = 4). (f) Relative delta, beta and alpha cell number of Ucn3 and control islets (n = 3 control/4 Ucn3 , 5–7 islets/animal). (g) Somatostatin secretion from Ucn3– islets compared to control (n = 4, 95 islets/well, asterisks indicate significance with the 5.5 mM glucose group for the same genotype, unless indicated otherwise). Insulin secretion from Ucn3– islets compared to control in static incubation (h) (n = 4, 7 islets/well) and in islet perfusion (i) (n = 2, 150 islets per chamber, representative of 2 experiments). Significance determined by Student’s t–test (e, f), two–way ANOVA for treatment and genotype, followed by Holm–Sidak’s multiple comparison test (g, h), or two–way ANOVA for genotype and its interaction with time for each block (i); P values for genotype are given (i). All values are mean ± s.e.m., *P < 0.05, **P < 0.01, ***P < 0.001.
Mentions: We next turned to Ucn3– mice27, where transcriptome analysis confirmed the absence of Ucn3 (Fig. 2a) and revealed marked reductions in the expression of known delta cell markers including Sst, Rbp4, and Hhex29,30 compared to wild type littermates (Fig. 2b–d and Supplementary Table 1). These observations suggest that the absence of Ucn3 precipitated relative delta cell deficiency. Indeed, Ucn3– islets displayed selective reductions in somatostatin content (Fig. 2e) and relative delta cell number (Fig. 2f) compared to controls. Ucn3– islets demonstrate impaired basal and glucose–stimulated somatostatin release compared to wild–type islets, which we fully rescued by co–stimulation with synthetic Ucn3 (Fig. 2g). Ucn3– islets hyper–secreted insulin during the first and second phase of secretion compared to controls, which normalized upon addition of synthetic Ucn3 peptide (Fig. 2h, i). Islets from Crhr2– mice31 showed comparable defects in somatostatin content and release compared to wild–type littermate controls (Supplementary Fig. 3).

Bottom Line: The peptide hormone urocortin3 (Ucn3) is abundantly expressed by mature beta cells, yet its physiological role is unknown.Here we demonstrate that Ucn3 is stored and co-released with insulin and potentiates glucose-stimulated somatostatin secretion via cognate receptors on delta cells.Further, we found that islets lacking endogenous Ucn3 have fewer delta cells, reduced somatostatin content, impaired somatostatin secretion, and exaggerated insulin release, and that these defects are rectified by treatment with synthetic Ucn3 in vitro.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, California, USA. [2] Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, California, USA.

ABSTRACT
The peptide hormone urocortin3 (Ucn3) is abundantly expressed by mature beta cells, yet its physiological role is unknown. Here we demonstrate that Ucn3 is stored and co-released with insulin and potentiates glucose-stimulated somatostatin secretion via cognate receptors on delta cells. Further, we found that islets lacking endogenous Ucn3 have fewer delta cells, reduced somatostatin content, impaired somatostatin secretion, and exaggerated insulin release, and that these defects are rectified by treatment with synthetic Ucn3 in vitro. Our observations indicate that the paracrine actions of Ucn3 activate a negative feedback loop that promotes somatostatin release to ensure the timely reduction of insulin secretion upon normalization of plasma glucose. Moreover, Ucn3 is markedly depleted from beta cells in mouse and macaque models of diabetes and in human diabetic islets. This suggests that Ucn3 is a key contributor to stable glycemic control, whose reduction during diabetes aggravates glycemic volatility and contributes to the pathophysiology of this disease.

Show MeSH
Related in: MedlinePlus