scholarly journals N-Type Ca2+-Channels in Murine Pancreatic β-Cells Are Inhibited by an Exclusive Coupling with Somatostatin Receptor Subtype 1

Endocrinology ◽  
2009 ◽  
Vol 150 (2) ◽  
pp. 741-748 ◽  
Author(s):  
Paul A. Smith
Keyword(s):  
Insulin Secretion ◽  
Somatostatin Receptor ◽  
Inhibitory Effect ◽  
Receptor Subtype ◽  
Receptor Subtypes ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Somatostatin Receptor Subtypes ◽  
Perforated Patch Clamp ◽  
Ca2 Channels

Somatostatin (SRIF) is a well-established inhibitor of insulin secretion, an effect in part mediated by a direct inhibition of voltage-operated Ca2+-channels. However, the identity of the somatostatin receptor subtypes (SSTRs) and voltage-operated Ca2+-channels involved in this process are unknown. Whole-cell perforated patch-clamp methods were applied to the murine pancreatic β-cell line, MIN6, to explore the molecular pharmacology of this problem. SRIF-14 inhibited voltage-gated Ca2+ currents (ICa2+) by 19 ± 3% (n=24) with a pEC50 = 9.05 (95% confidence limits 9–9.1). This action was mimicked solely by 100 nm CH-275, a selective agonist at the somatostatin type 1 receptor (SSTR1), but not by 100 nm BIM-23027, L-362855, or NNC-269100; agonists selective for the other four SSTRs known to exist in MIN6. The inhibition of ICa2+ produced by SRIF and CH-275 was insensitive to pertussis toxin but was reversed by a prepulse to +100 mV. The inhibition of ICa2+ by SRIF-14 was unaffected by 20 μm nifedipine, an inhibitor of L-type Ca2+ channels. Application of the specific N-type Ca2+ channel (Cav2.2) inhibitor ω-conotoxin GV1A at 100 nm mimicked, and as a consequence abolished, the inhibitory effect of SRIF-14 on ICa2+. SRIF selectively inhibits N-type Ca2+-channels in murine pancreatic β-cells via exclusive coupling with SSTR1. These findings help explain how SSTR1 activation can inhibit insulin secretion in pancreatic β-cells and suggest a possible new therapeutic lead for treatment of hyperinsulinemia. In pancreatic β-cells, somatostatin selectively inhibits N-type, but not other, Ca2+-channels via a direct and exclusive coupling with somatostatin receptor subtype 1.

scholarly journals Antidiabetic Activity of a Highly Potent and Selective Nonpeptide Somatostatin Receptor Subtype-2 Agonist

Endocrinology ◽  
2006 ◽  
Vol 147 (10) ◽  
pp. 4664-4673 ◽  
Author(s):  
Mathias Z. Strowski ◽  
Doreen E. Cashen ◽  
Elizabeth T. Birzin ◽  
Lihu Yang ◽  
Vandana Singh ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Insulin Secretion ◽  
Somatostatin Receptor ◽  
Glucagon Secretion ◽  
Receptor Subtype ◽  
Receptor Subtypes ◽  
Glucose Levels ◽  
Somatostatin Receptor Subtypes ◽  
Novel Approach

Somatostatin inhibits both glucagon and insulin secretion. Glucagon significantly contributes to hyperglycemia in type 2 diabetes. Despite its function in the inhibition of glucagon secretion, somatostatin fails to reduce hyperglycemia in type 2 diabetes, due to a parallel suppression of insulin secretion. Five pharmacologically distinct somatostatin receptor subtypes (sst1–sst5) mediate the effects of somatostatin on a cellular level. Pancreatic A cells express sst2, whereas B cells express sst5. In this study, we describe a novel approach to the treatment of type 2 diabetes using a highly sst2-selective, nonpeptide agonist (compound 1). Compound 1 effectively inhibited glucagon secretion from pancreatic islets isolated from wild-type mice, whereas glucagon secretion from sst2-deficient islets was not suppressed. Compound 1 did not influence nonfasted insulin concentration. In sst2-deficient mice, compound 1 did not have any effects on glucagon or glucose levels, confirming its sst2 selectivity. In animal models of type 2 diabetes in the nonfasted state, circulating glucagon and glucose levels were decreased after treatment with compound 1. In the fasting state, compound 1 lowered blood glucose by approximately 25%. In summary, small-molecule sst2-selective agonists that suppress glucagon secretion offer a novel approach toward the development of orally bioavailable drugs for treatment of type 2 diabetes.

scholarly journals Selective Somatostatin 5 (SST5) and Somatostatin 2 (SST2) Nonpeptide Agonists Potently Suppress Glucose- and Tolbutamide-Stimulated Dynamic Insulin Secretion From Isolated Human Islets

2021 ◽  
Vol 5 (Supplement_1) ◽  
pp. A325-A325
Author(s):  
Elizabeth Rico ◽  
Jian Zhao ◽  
Mi Chen ◽  
Ana Karin Kusnetzow ◽  
Yun Fei Zhu ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Somatostatin Receptor ◽  
Physiological Role ◽  
Glucagon Secretion ◽  
Receptor Activation ◽  
Human Islets ◽  
Receptor Subtypes ◽  
Congenital Hyperinsulinism ◽  
Somatostatin Receptor Subtypes ◽  
Selective Agonists

Abstract Congenital hyperinsulinism (HI) is the most common cause of persistent hypoglycemia in newborns and infants and arises from dysregulated insulin secretion. Rapid recognition and treatment are vital to prevent seizures, permanent developmental delays, coma, or even death. Very few medical options exist to treat congenital HI patients: the KATP channel activator diazoxide, the injectable somatostatin receptor peptide agonists octreotide and lanreotide, or chronic glucose infusions. However, side effects and/or limited efficacy render these therapies inadequate for many patients. Somatostatin is a 14-amino acid peptide hormone with a broad spectrum of biological actions, which are regulated through five somatostatin receptor subtypes (SST1-SST5). Somatostatin’s common physiological role is to down-regulate secretion of other hormones in various tissues. Its role in the maintenance of euglycemia is to regulate insulin and glucagon secretion from pancreatic β- and α-cells, respectively. Somatostatin regulates insulin secretion by decreasing the intracellular levels of cAMP, inhibition of voltage-gated calcium channels (VGCC), activation of the G protein-activated inward rectifier K+ channel (GIRK), and direct inhibition of insulin exocytosis. Several studies have evaluated the effect of somatostatin, somatostatin peptide analogs, and a limited number of nonpeptide somatostatin receptor agonists on insulin secretion in static assays using isolated human islets. However, the lack of highly selective agonists has made the interpretation of the contribution of SST receptor sub-types difficult to discern. Our programs for the treatment of hyperinsulinism, acromegaly, and other indications have led to the development of selective nonpeptide SST2, SST3, SST4, and SST5 agonists, possessing EC50s < 1 nM in cell-based assays of receptor activation and selectivity > 130 times over the other members of the family. The ability of these selective nonpeptide agonists to regulate glucose- and tolbutamide-stimulated dynamic insulin secretion from human islets was evaluated using a perifusion system (Biorep, FL). We found that selective SST2 and SST5 agonists potently suppressed dynamic insulin secretion in contrast to SST3 or SST4 selective agonists. Importantly, SST5 agonists were shown to have a greater effect than selective SST2 agonists or diazoxide, demonstrating their potential utility in human conditions such as congenital HI. In addition, SST5 activation is also known to have a smaller effect on glucagon secretion and is also less prone to agonist-driven desensitization than SST2 activation. Taken together, these studies support our program to identify, characterize, and develop potent, nonpeptide, orally-bioavailable, selective SST5 agonists with appropriate pharmaceutical and safety characteristics for the treatment of congenital HI.

scholarly journals Intracellular ATP Signaling Contributes to FAM3A-Induced PDX1 Upregulation in Pancreatic Beta Cells

2021 ◽  
Author(s):  
Han Yan ◽  
Zhenzhen Chen ◽  
Haizeng Zhang ◽  
Weili Yang ◽  
Xiangyang Liu ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Beta Cells ◽  
Mitochondrial Protein ◽  
Extracellular Atp ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Intracellular Atp ◽  
Pdx1 Expression ◽  
Ca2 Channels

AbstractFAM3A is a recently identified mitochondrial protein that stimulates pancreatic-duodenal homeobox 1 (PDX1) and insulin expressions by promoting ATP release in islet β cells. In this study, the role of intracellular ATP in FAM3A-induced PDX1 expression in pancreatic β cells was further examined. Acute FAM3A inhibition using siRNA transfection in mouse pancreatic islets significantly reduced PDX1 expression, impaired insulin secretion, and caused glucose intolerance in normal mice. In vitro, FAM3A overexpression elevated both intracellular and extracellular ATP contents and promoted PDX1 expression and insulin secretion. FAM3A-induced increase in cellular calcium (Ca2+) levels, PDX1 expression, and insulin secretion, while these were significantly repressed by inhibitors of P2 receptors or the L-type Ca2+ channels. FAM3A-induced PDX1 expression was abolished by a calmodulin inhibitor. Likewise, FAM3A-induced β-cell proliferation was also inhibited by a P2 receptor inhibitor and an L-type Ca2+ channels inhibitor. Both intracellular and extracellular ATP contributed to FAM3A-induced PDX1 expression, insulin secretion, and proliferation of pancreatic β cells.

scholarly journals Selective Regulation of Somatostatin Receptor Subtype Signaling: Evidence for Constitutive Receptor Activation

2007 ◽  
Vol 21 (10) ◽  
pp. 2565-2578 ◽  
Author(s):  
Anat Ben-Shlomo ◽  
Oxana Pichurin ◽  
Nicole J. Barshop ◽  
Kolja A. Wawrowsky ◽  
John Taylor ◽  
...  
Keyword(s):  
Mapk Pathway ◽  
Somatostatin Receptor ◽  
Hormone Secretion ◽  
Receptor Activation ◽  
Receptor Subtype ◽  
Pituitary Hormone ◽  
Receptor Subtypes ◽  
Camp Accumulation ◽  
Acth Secretion ◽  
Somatostatin Receptor Subtypes

Abstract Anterior pituitary hormone secretion is under tonic suppression by hypothalamic somatostatin signaling through somatostatin receptor subtypes (SSTs). Because some hormonal axes are known to be abnormally regulated by ligand-independent constitutively active G protein-coupled receptors, we tested pituitary SSTs for selective constitutive signaling. We therefore differentially silenced endogenous SST2, SST3, and SST5 in somatostatin-sensitive ACTH-secreting mouse AtT-20 pituitary corticotroph cells using small inhibitory RNA (siRNA) and analyzed downstream SSTs-regulated pathways. Transfection with siRNA reduced specific receptor subtype mRNA expression up to 82%. Specificity of receptor silencing was validated against negative controls with different gene-selective siRNAs, concordance of mRNA and cAMP changes, reduced potency of receptor-selective agonists, and phenotype rescue by overexpression of the silenced receptor. Mouse SST3 > SST5 > SST2 knockdown increased basal cAMP accumulation (up to 200%) and ACTH secretion (up to 60%). SST2- and SST5-selective agonist potencies were reduced by SST3- and SST5-silencing, respectively. SST5 > SST2 = SST3 silencing also increased basal levels of ERK1/2 phosphorylation. SST3- and SST5-knockdown increased cAMP was only partially blocked by pertussis toxin. The results show that SST2, SST3, and SST5 exhibit constitutive activity in mouse pituitary corticotroph cells, restraining adenylate cyclase and MAPK activation and ACTH secretion. SST3 mainly inhibits cAMP accumulation and ACTH secretion, whereas SST5 predominantly suppresses MAPK pathway activation. Therefore, SST receptor subtypes control pituitary cell function not only through somatostatin binding to variably expressed cell membrane receptor subtypes, but also by differential ligand-independent receptor-selective constitutive action.

scholarly journals Gene Transcription of Receptors for Growth Hormone-Releasing Peptide and Somatostatin in Human Pituitary Adenomas1

1998 ◽  
Vol 83 (8) ◽  
pp. 2997-3000
Author(s):  
Steen Nielsen ◽  
Søren Mellemkjær ◽  
Lars M. Rasmussen ◽  
Thomas Ledet ◽  
Jens Astrup ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Messenger Rna ◽  
Somatostatin Receptor ◽  
Pituitary Tumors ◽  
Distinct Pattern ◽  
Receptor Subtype ◽  
Receptor Subtypes ◽  
Human Pituitary ◽  
Somatostatin Receptor Subtypes ◽  
Almost All

abstract Growth hormone (GH)-releasing peptides (GHRP) or secretagogs (GHS) constitute a family of synthetic compounds with potent and specific GH releasing activity. The receptor (GHS-R) has recently been cloned even though the endogenous ligand remains to be identified. GHRPs act both at the hypothalamic and the pituitary level through mechanisms involving amplification of GH-releasing hormone activity and functional somatostatin antagonism. In the present study we examined the co-expression of messenger RNA (mRNA) for GHS-R and all 5 somatostatin receptor subtypes (sstr 1–5) in 28 human pituitary tumors by RT-PCR. GHS-R transcription was detected in 11 out of 12 somatotroph adenomas and in 2 out of 2 prolactinomas, whereas GHS-R expression was detected in only 2 out of 14 clinically nonfunctioning adenomas (NFPA), and no expression was seen in the only ACTH secreting adenoma. Almost all tumors expressed sstr 2 mRNA (n = 24), whereas only 1 tumor expressed sstr 4 mRNA. The expression of sstr 3 mRNA was inversely associated with GHS-R expression (P < 0.001), which could be attributed to a high prevalence of sstr 3 expression in NFPA. This study suggests that GHS-R expression is predominantly observed in somatotroph adenomas and much less so in NFPA. Moreover, the presence of a distinct pattern of somatostatin receptor subtype co-expression is suggested, which may provide a molecular basis for the complex interaction between GHRPs and somatostatin.

Structural finding of R/S-3,4-dihydro-2,2-dimethyl-6-halo-4-(substituted phenylaminocarbonylamino)-2H-1-benzopyrans as selective pancreatic β-cells KATP-pβ channel openers

2007 ◽  
Vol 85 (12) ◽  
pp. 1053-1063 ◽  
Author(s):  
Sk. Mahasin Alam ◽  
Soma Samanta ◽  
Amit Kumar Halder ◽  
Soumya Basu ◽  
Tarun Jha
Keyword(s):  
Insulin Secretion ◽  
Negative Impact ◽  
Inhibitory Effect ◽  
Van Der Waals Interactions ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Qsar Study ◽  
Water Partition Coefficient ◽  
Qsar Models ◽  
Leave One Out

R/S-3,4-Dihydro-2,2-dimethyl-6-halo-4-(substituted phenylaminocarbonyl-amino)-2H-1-benzopyrans are pancreatic β-cells potassium (KATP-pβ) channel openers with inhibitory effect on insulin secretion. To find the more active and effective benzopyrans as selective potassium (KATP-pβ) channel openers towards the pancreatic tissues, quantitative structure–activity relationships (QSAR) study was performed using E-state and R-state indices along with Wang–Ford charges, n-octanol/water partition coefficient, molar refractivity, and indicator parameters. QSAR models were developed by statistical techniques, e.g., multiple linear regression (MLR), principle component regression analysis (PCRA), and partial least squares (PLS) analysis. The generated equations were validated by the leave-one-out cross-validation method. The models show the importance of ETSA indices of atom numbers 16, 17, 18, 19, 21 as well as 22. The positive coefficient of S16, S17, S18, S19, S21, and S22 indicate that with the increase of the value of E-state indices, desired activity decreases. RTSA index is also important for the biological activity, and the atom numbers 16, 17, 18, 19, 20 and 22 are involved in van der Waals interactions. RTSA index also possesses negative impact on the inhibition of residual insulin secretion. Wang–Ford charges of some particular atoms are also important for the inhibition. Increase of n-octanol/water partition coefficients of compounds inhibit insulin secretion, and the presence of chlorine atom at m- and p- positions of the phenyl ring B is necessary for the inhibition of residual insulin secretion.Key words: benzopyran derivatives, potassium channel openers, PCRA, PLS, QSAR.

scholarly journals Expression of somatostatin receptor subtypes 1–5 in pancreatic islets of normoglycaemic and diabetic NOD mice

2005 ◽  
Vol 153 (3) ◽  
pp. 445-454 ◽  
Author(s):  
E Ludvigsen ◽  
M Stridsberg ◽  
E T Janson ◽  
S Sandler
Keyword(s):  
Pancreatic Islets ◽  
Islet Cells ◽  
Somatostatin Receptor ◽  
Nod Mice ◽  
Receptor Subtypes ◽  
Β Cells ◽  
Somatostatin Receptor Subtypes ◽  
Icr Mouse ◽  
The Difference ◽  
Cell Expression

Objective: Somatostatin acts on five specific receptors (sst1–5) to elicit different biological functions. The non-obese diabetic (NOD) mouse is an experimental model of type 1 diabetes. The aim of this study was to investigate whether the islet expression of sst1–5 is affected during the development of diabetes in NOD mice, with insulitis accompanied by spontaneous hyperglycaemia. Methods: By immunostaining for sst1–5 the expression and co-expression together with the four major islet hormones in pancreatic islets were investigated in female and male NOD mice at different stages of disease. The NOD related non-diabetic ICR mouse was also examined. Results: The islet cells of diabetic NOD mice showed an increased islet cell expression of sst2–5 compared with normoglycaemic female NOD mice. This correlated to increasing age and extent of insulitis. Major findings from the co-expression investigations were that sst2 was expressed in a majority of β-cells in the normoglycaemic NOD mice, but absent in the β-cells in the diabetic NOD mice. A majority of the α-cells expressed sst2 and 5 in normoglycaemic and diabetic NOD mice. About 60% of δ-cells showed co-expression of sst4 and 5 in both normoglycaemic and diabetic NOD mice. 60% of pancreatic polypeptide (PP)-cells expressed sst4 in both groups. Insulitis was found to be accompanied by a down-regulation of sst in normoglycaemic animals. Conclusions: The difference in sst expression in the islets cells of diabetic mice may suggest either a contributing factor in the process leading to diabetes, or a defence response against ongoing β-cell destruction.

scholarly journals Constitutive Somatostatin Receptor Subtype-3 Signaling Suppresses Growth Hormone Synthesis

2014 ◽  
Vol 28 (4) ◽  
pp. 554-564 ◽  
Author(s):  
Tamar Eigler ◽  
Anat Ben-Shlomo ◽  
Cuiqi Zhou ◽  
Ramtin Khalafi ◽  
Song-Guang Ren ◽  
...  
Keyword(s):  
Transcriptional Repression ◽  
Glycogen Synthase ◽  
Somatostatin Receptor ◽  
Pituitary Tumors ◽  
Serine Phosphorylation ◽  
Receptor Subtype ◽  
Receptor Subtypes ◽  
Hormone Synthesis ◽  
Gh Secretion ◽  
Somatostatin Receptor Subtypes

Abstract Somatostatin signals through somatostatin receptor subtypes (SSTR) 2 and 5 to attenuate GH secretion. Although expressed in normal pituitary glands and in GH-secreting pituitary tumors, SSTR3 function was unclear, and we have now determined the role of SSTR3 in somatotroph function. Stable rat pituitary tumor cell (GC) transfectants of human SSTR3 (GpSSTR3WT) showed suppression of rat (r) GH promoter activity, GH mRNA expression, and secreted GH concordant with suppressed cAMP/protein kinase A (PKA) signaling. In contrast, cAMP levels and GH expression were unchanged in cells expressing a mutant SSTR3 DRY motif (GpSSTR3R141A). GH expression was rescued by treatment of GpSSTR3WT with forskolin and 8-bromo-cAMP. GpSSTR3WT exhibited activation of glycogen synthase kinase3-β (GSK3-β), a PKA substrate, which was also reversed by 8-Bromo-cAMP treatment. Moreover, SSTR3-dependent GH transcriptional inhibition was rescued by inhibition of GSK3-β. GpSSTR3WT exhibited elevated Pit-1 serine phosphorylation and decreased Pit-1 occupancy of the rGH promoter with sustained Pit-1 expression. GSK3-β and Pit-1 physically interacted with each other, indicating that Pit-1 may be a GSK3-β phosphorylation substrate. In conclusion, constitutive SSTR3 activity mediates transcriptional repression of GH through cAMP/PKA, leading to subsequent activation of GSK3-β and increased Pit-1 phosphorylation and ultimately attenuating Pit-1 binding to the rGH promoter.

scholarly journals Expression and Functional Analysis of Dopamine Receptor Subtype 2 and Somatostatin Receptor Subtypes in Canine Cushing’s Disease

Endocrinology ◽  
2008 ◽  
Vol 149 (9) ◽  
pp. 4357-4366 ◽  
Author(s):  
C. de Bruin ◽  
J. M. Hanson ◽  
B. P. Meij ◽  
H. S. Kooistra ◽  
A. M. Waaijers ◽  
...  
Keyword(s):  
Medical Treatment ◽  
Dopamine Receptor ◽  
Anterior Pituitary ◽  
Dopamine Agonists ◽  
Somatostatin Receptor ◽  
Somatostatin Analogs ◽  
Receptor Subtype ◽  
Receptor Subtypes ◽  
Somatostatin Receptor Subtypes ◽  
Corticotroph Adenomas

Cushing’s disease (CD) is a severe disorder characterized by chronic hypercortisolism due to an ACTH-secreting pituitary adenoma. Transsphenoidal adenomectomy is the treatment of choice in humans with CD, but recurrences occur frequently. Finding an effective and safe medical treatment for CD may improve long-term clinical outcome. The recent demonstration of expression of somatostatin receptor subtypes (mainly sst5) and dopamine receptor subtype 2 (D2) in human corticotroph adenomas offers the possibility for medical treatment of CD with novel somatostatin analogs and dopamine agonists. Investigation of the effects of these drugs is hampered by the low incidence of CD in humans. Interestingly, CD is a frequent disorder in dogs with striking clinical similarities with CD in humans. Therefore, we investigated the expression and functional role of D2 and somatostatin receptors in corticotroph adenoma cells from 13 dogs with active CD that underwent therapeutic hypophysectomy and normal anterior pituitary cells from five dogs. Quantitative RT-PCR and immunohistochemistry revealed that both in CD and normal anterior pituitary, sst2 was the predominant receptor subtype expressed, whereas D2 was modestly expressed and sst5 was expressed only at very low levels. In primary cultures of canine adenomas (n = 7), the sst2-preferring agonist octreotide also showed the strongest ACTH-suppressive effects. In conclusion, canine corticotroph adenomas provide an interesting model to study CD, but differences in somatostatin and dopamine receptor expression between humans and dogs should be taken into account when using dogs with CD as a model to evaluate efficacy of novel somatostatin analogs and dopamine agonists for human CD.

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