Stefan Amisten

Activation of G protein-coupled receptor 30 modulates hormone secretion and counteracts cytokine-induced apoptosis in pancreatic islets of female mice ☆

The role of the newly discovered estrogen receptor GPR30 in islet physiology and pathophysiology is unclear. We examined GPR30 expression in relation to hormone secretion and possible anti-apoptotic effects in isolated mouse islets using the synthetic GPR30 ligand G-1. The mRNA and protein expression of GPR30 was analyzed by qPCR, Western blot and confocal microscopy. Hormone secretion and cAMP content were determined with RIA and apoptosis in islet cells with the Annexin-V method. GPR30 mRNA and protein expression was markedly higher in islets from females compared to male. This gender difference was not found for the genomic estrogen receptors ER alpha and ER beta, the ER alpha expression being 10-fold higher than ER beta in both genders. Confocal microscopy revealed abounden GPR30 expression in insulin, glucagon and somatostatin cells. Dose-response studies of G-1 vs 17beta-estradiol in isolated islets at 1 or 12 mM glucose showed an almost identical pattern in that both compounds increased insulin and inhibited glucagon and somatostatin secretion. ICI-182,780 and EM-652, potent antagonists of the 17beta-estradiol receptors (ER alpha and ER beta) did not influence the amplifying effect of G-1 or 17beta-estradiol on cAMP content or insulin secretion from isolated islets. Cytokine-induced (IL-1 beta+TNFalpha+INF gamma) apoptosis in islets, cultured for 24h at 5mM glucose, was almost abolished by G-1 or 17beta-estradiol treatment. Addition of ICI-182,780 or EM-652 did not affect this beneficial effect of G-1 or 17beta-estradiol. Taken together, our findings show that GPR30 is expressed in most islet endocrine cells. The synthetic GPR30 ligand G-1 mimics the non-genomic effects of 17beta-estradiol on islet hormone secretion, cAMP content in islets and its anti-apoptotic effects. G-1 or analogs thereof might be new potential candidates in the therapeutic strategy for type 2 diabetes in women.

Expression profiling and electrophysiological studies suggest a major role for Orai1 in the store-operated Ca2+ influx pathway of platelets and megakaryocytes

Store-operated Ca2+ influx represents a major route by which cytosolic Ca2+ can be elevated during platelet activation, yet its molecular identity in this cell type remains highly controversial. Using quantitative RT-PCR analysis of candidate receptor-operated cation entry pathways in human platelets, we show a >30-fold higher expression of message for the recently discovered Orai1 store-operated Ca2+ channel, and also the store Ca2+ sensor STIM1, when compared to the non-selective cation channels TRPC1, TRPC6 and TRPM2. Orai1 and STIM1 gene transcripts were also detected at higher levels than TRPC1, TRPC6 and TRPM2 in primary murine megakaryocytes and human megakaryocytic cell lines. In direct electrophysiological recordings from murine megakaryocytes, Ca2+ ionophore-induced store depletion stimulated CRAC currents, which are known to require Orai1, and these overlapped with TRPC6-like currents following P2Y receptor activation. Together with recent transgenic studies, these data provide evidence for STIM1:Orai1 as a primary pathway for agonist-evoked Ca2+ influx in the platelet and megakaryocyte.

Insulinotropic and Antidiabetic Effects of 17β-Estradiol and the GPR30 Agonist G-1 on Human Pancreatic Islets

We have recently shown that 17β-estradiol (E2) and the synthetic G protein-coupled receptor 30 (GPR30) ligand G-1 have antiapoptotic actions in mouse pancreatic islets, raising the prospect that they might exert beneficial effects also in human islets. The objective of the present study was to identify the expression of GPR30 in human islets and clarify the role of GPR30 in islet hormone secretion and β-cell survival. GPR30 expression was analyzed by confocal microscopy, Western blot, and quantitative PCR in islets from female and male donors. Hormone secretion, phosphatidylinositol hydrolysis, cAMP content, and caspase-3 activity in female islets were determined with conventional methods and apoptosis with the annexin-V method. Confocal microscopy revealed GPR30 expression in islet insulin, glucagon, and somatostatin cells. GPR30 mRNA and protein expression was markedly higher in female vs. male islets. An amplifying effect of G-1 or E2 on cAMP content and insulin secretion from isolated female islets was not influenced by the E2 genomic receptor (ERα and ERβ) antagonists ICI 182,780 and EM-652. Cytokine-induced (IL-1β plus TNFα plus interferon-γ) apoptosis in islets cultured for 24 h at 5 mmol/liter glucose was almost abolished by G-1 or E2 treatment and was not affected by the nuclear estrogen receptor antagonists. Concentration-response studies on female islets from healthy controls and type 2 diabetic subjects showed that both E2 and G-1 displayed important antidiabetic actions by improving glucose-stimulated insulin release while suppressing glucagon and somatostatin secretion. In view of these findings, we propose that small molecules activating GPR30 could be promising in the therapy of diabetes mellitus.

ADP mediates inhibition of insulin secretion by activation of P2Y13 receptors in mice

Aims/hypothesesTo investigate the effects of extracellular purines on insulin secretion from mouse pancreatic islets.MethodsMouse islets and beta cells were isolated and examined with mRNA real-time quantification, cAMP quantification and insulin and glucagon secretion. ATP release was measured in MIN6c4 cells. Insulin and glucagon secretion were measured in vivo after glucose injection.ResultsEnzymatic removal of extracellular ATP at low glucose levels increased the secretion of both insulin and glucagon, while at high glucose levels insulin secretion was reduced and glucagon secretion was stimulated, indicating an autocrine effect of purines. In MIN6c4 cells it was shown that glucose does induce release of ATP into the extracellular space. Quantitative real-time PCR demonstrated the expression of the ADP receptors P2Y1 and P2Y13 in both intact mouse pancreatic islets and isolated beta cells. The stable ADP analogue 2-MeSADP had no effect on insulin secretion. However, co-incubation with the P2Y1 antagonist MRS2179 inhibited insulin secretion, while co-incubation with the P2Y13 antagonist MRS2211 stimulated insulin secretion, indicating that ADP acting via P2Y1 stimulates insulin secretion, while signalling via P2Y13 inhibits the secretion of insulin. P2Y13 antagonism through MRS2211 per se increased the secretion of both insulin and glucagon at intermediate (8.3xa0mmol/l) and high (20xa0mmol/l) glucose levels, confirming an autocrine role for ADP. Administration of MRS2211 during glucose injection in vivo resulted in both increased secretion of insulin and reduced glucose levels.Conclusions/interpretationIn conclusion, ADP acting on the P2Y13 receptors inhibits insulin release. An antagonist to P2Y13 increases insulin release and could be evaluated for the treatment of diabetes.

Uridine diphosphate (UDP) stimulates insulin secretion by activation of P2Y6 receptors

We examined the transcriptional expression and functional effects of receptors for the extracellular pyrimidines uridine triphosphate (UTP) and uridine diphosphate (UDP), on insulin and glucagon secretion in isolated mouse pancreatic islets and purified beta-cells. Using real-time PCR, the UDP receptor P2Y(6) was found to be highly expressed in both whole islets and beta-cells purified by repeated counter-flow elutriation, whereas no mRNA expression for UTP receptors P2Y(4) and P2Y(2) could be detected. Functional in vitro experiments revealed that the P2Y(6) agonist UDPbetaS dose-dependently enhanced insulin and glucagon release during short-term incubation (1h), while P2Y(6) activation during a longer period (24h), selectively increased insulin release, especially at high glucose levels. The corresponding EC(50) value for UDPbetaS ranged from 3.2 x 10(-8)M to 1.6 x 10(-8)M for both glucose concentrations. The P2Y(6) antagonist MRS2578 inhibited the effects of UDPbetaS, supporting a P2Y(6) specific effect. In addition to negative RT-PCR results, the lack of response to UTPgammaS a selective P2Y(2/4) agonist further rule out the involvement of P2Y(2/4) receptors in the islet hormone release. Our results suggest a modulatory role for UDP via a functional active P2Y(6) receptor in the regulation of islet hormone release.

LPS induces GROalpha chemokine production via NF-kappaB in oral fibroblasts.

Objective and designChemotaxis of neutrophils from blood to the inflammation process plays an important role in development of periodontal inflammation. The novel chemokine GROα, also named CXCL1, is a strong chemoattractant for neutrophils. Data on production and regulation of GROα by oral fibroblasts have not previously been presented.Materials and methodsGROα mRNA and protein levels were determined in human periodontal ligament cells and mouse gingival fibroblasts by quantitative real-time PCR and ELISA.ResultsWe disclose that both human periodontal ligament cells and mouse gingival fibroblasts produce GROα in response to LPS stimulation. Stimulation with LPS for 24xa0h increased both mRNA for GROα and GROα protein. The steroid hormone estrogen had no effect on LPS-induced GROα mRNA expression. Treatment with the glucocorticoid dexamethasone attenuated LPS-induced GROα production, and the NF-κB blocker MG 132 fully prevented LPS-induced GROα.ConclusionsOral fibroblasts respond to LPS stimulation by increasing GROα production via the transcription factor NF-κB, suggesting that this mechanism may be involved in development of periodontal inflammation.

GPR40 protein levels are crucial to the regulation of stimulated hormone secretion in pancreatic islets. Lessons from spontaneous obesity-prone and non-obese type 2 diabetes in rats.

The role of islet GPR40 protein in the pathogenesis of diabetes is unclear. We explored the influence of GPR40 protein levels on hormone secretion in islets from two rat models of spontaneous type 2 diabetes displaying either hyperlipidaemia or hyperglycaemia. GPR40 expression was analysed by confocal microscopy, Western blot and qPCR in islets from preobese Zucker (fa/fa) rats, diabetic Goto-Kakizaki (GK) rats, and controls. Confocal microscopy of control islets showed expression of GPR40 protein in insulin, glucagon and somatostatin cells. GPR40 expression was strongly increased in islets of hyperlipidaemic fa/fa rats and coincided with a concentration-related increase in palmitate-induced release of insulin and glucagon and its inhibition of somatostatin release. Conversely, hyperglycaemic GK islets displayed an extremely faint expression of GPR40 as did high-glucose-cultured control islets. This was reflected in abolished palmitate-induced hormone response in GK islets and high-glucose-cultured control islets. The palmitate antagonist rosiglitazone promoted reappearance of GPR40 in high-glucose-cultured islets and served as partial agonist in glucose-stimulated insulin release. GPR40 protein is abundantly expressed in pancreatic islets and modulates stimulated hormone secretion. Mild hyperlipidaemia in obesity-prone diabetes creates increased GPR40 expression and increased risk for an exaggerated palmitate-induced insulin response and lipotoxicity, a metabolic situation suitable for GPR40 antagonist treatment. Chronic hyperglycaemia creates abrogated GPR40 expression and downregulated insulin release, a metabolic situation suitable for GPR40 agonist treatment to avoid glucotoxicity. GPR40 protein is interactively modulated by both free fatty acids and glucose and is a promising target for pharmacotherapy in different variants of type 2 diabetes.

Residual platelet ADP reactivity after clopidogrel treatment is dependent on activation of both the unblocked P2Y(1) and the P2Y (12) receptor and is correlated with protein expression of P2Y (12).

Two ADP receptors have been identified on human platelets: P2Y1 and P2Y12. The P2Y12 receptor blocker clopidogrel is widely used to reduce the risks in acute coronary syndromes, but, currently, there is no P2Y1 blocker in clinical use. Evidence for variable responses to clopidogrel has been described in several reports. The mechanistic explanation for this phenomenon is not fully understood. The aim of this study was to examine mechanisms responsible for variability of 2MeS-ADP, a stable ADP analogue, induced platelet reactivity in clopidogrel-treated patients. Platelet reactivity was assessed by flow cytometry measurements of P-selectin (CD62P) and activated GpIIb/IIIa complex (PAC-1). Residual 2MeS-ADP activation via the P2Y12 and P2Y1 receptors was determined by co-incubation with the selective antagonists AR-C69931 and MRS2179 in vitro. P2Y1 and P2Y12 receptor expression on both RNA and protein level were determined, as well as the P2Y12 H1 or H2 haplotypes. Our data suggest that the residual platelet activation of 2MeS-ADP after clopidogrel treatment is partly due to an inadequate antagonistic effect of clopidogrel on the P2Y12 receptor and partly due to activation of the P2Y1 receptor, which is unaffected by clopidogrel. Moreover, a correlation between increased P2Y12 protein expression on platelets and decreased response to clopidogrel was noticed, r2=0.43 (P<0.05). No correlation was found between P2Y12 mRNA levels and clopidogrel resistance, indicating post-transcriptional mechanisms. To achieve additional ADP inhibition in platelets, antagonists directed at the P2Y1 receptor could be more promising than the development of more potent P2Y12 receptor antagonists.

The P2Y(13) Met-158-Thr Polymorphism, Which Is in Linkage Disequilibrium with the P2Y(12) Locus, Is Not Associated with Acute Myocardial Infarction.

Background and Aims The aims of this study were to investigate (1) if P2Y12 polymorphisms defining the P2Y12 H2 allele are associated with any other SNPs that may explain the previously reported association with increased ADP induced platelet activation and association with peripheral arterial disease and coronary artery disease and (2) if such variants are associated with acute myocardial infarction (AMI) or classical risk factors for AMI. Methods and Results The P2Y13 Met-158-Thr polymorphism was found to be in linkage disequilibrium (LD) with the P2Y12 H2 haplotype (all examined SNPs: D′u200a=u200a1.0, r2u200a=u200a0.936–1.0), defining a novel P2Y12 H2/P2Y13 Thr-158 haplotype. Genotyping of an AMI case control population (nu200a=u200a1244 cases, 2488 controls) revealed no association of the P2Y13 Thr-158 allele with AMI (ORu200a=u200a0.96, 95% C.I. 0.82–1.12, Pu200a=u200a0.63). Also, no differences between the genotype frequencies of P2Y13 Met-158-Met and Met-158-Thr/Thr-158-Thr were seen in AMI case-control subpopulations (early onset AMI ORu200a=u200a1.06, 95% C.I. 0.85–1.31, Pu200a=u200a0.62); family history of AMI (ORu200a=u200a0.98, 95% C.I. 0.78–1.22, Pu200a=u200a0.83) nor in early onset AMIs with family history of AMI (ORu200a=u200a1.0, 95% C.I. 0.74–1.36, Pu200a=u200a1.0). Genotyping of the P2Y13 Met-158-Thr polymorphism in a population based sample (nu200a=u200a6055) revealed no association with cardiovascular risk factors. In addition, the P2Y13 Met-158-Thr polymorphism was genotyped in a diabetes case-control population, and associations were found neither with DM nor with any examined DM risk factors. Conclusion Genotyping The P2Y13 Met-158-Thr polymorphism is in tight LD with the P2Y12 locus but is not associated with AMI or classical cardiovascular risk factors.

Activation of imidazoline receptor I 2 , and improved pancreatic β-cell function in human islets

AIMnThe impact of BL11282, an imidazoline receptor (NISCH) agonist, on potentiation of glucose-stimulated insulin secretion (GSIS) from isolated human non-diabetic (ND) and type 2 diabetic (T2D) islets was investigated.nnnMETHODSnAnalysis of mRNA was performed by RNA-sequencing and qPCR. Insulin and cAMP by RIA and ELISA respectively.nnnRESULTSnRNA-sequencing data revealed that NISCH is highly expressed in fat tissues, islets, liver and muscles, with eight detectable splice variants of transcripts in islets. NISCH had a positive correlation with GLP-1 (GLP1R) and GIP (GIPR) receptor transcripts. The expression of NISCH was confirmed by qPCR in human islets. NISCH and GLP1R were comparably higher expressed in mouse islets compared to human islets. GSIS was dose-dependently potentiated by BL11282 from incubated islets of ND and T2D human islet donors. The insulinotropic action of BL11282 was associated with increased cAMP. While the harmful effect of high glucose on reductive capacity of islet cells was enhanced by glibenclamide during long-term culture, it was counteracted by BL11282 or Bt2-cAMP. BL11282 also increased proliferation of INS-1 cells during long-time culture.nnnCONCLUSIONnOur data suggest that BL11282 potentiates GSIS by an action involving cAMP/PKA system and BL11282 could be an attractive insulinotropic and β-cell protective agent.