A stress response pathway in mice upregulates somatostatin level and transcription in pancreatic delta cells through Gs and β-arrestin 1

Abstract

Aims/hypothesis Somatostatin secretion from islet delta cells plays an important role in regulating islet function and is tightly controlled by environmental changes. Activation of the adrenergic system promoted somatostatin secretion from islet delta cells; however, the role of the adrenergic system in regulating somatostatin content and transcription has not been defined. An imbalance between the somatostatin content and its secretion may cause dysfunctions in the islet delta cells. We have investigated the role of the adrenergic system in the modulation of somatostatin content and transcription in pancreatic delta cells and the detailed underlying mechanisms of this regulation. Methods The stress hormone adrenaline (epinephrine), specific adrenergic agonists or specific adrenergic antagonists were applied to islets from either wild-type or specific adrenergic receptor knockout mice and pancreatic delta cell lines to investigate their effects on somatostatin content and transcription. The GloSensor assay, quantitative real-time PCR, western blots and the dual luciferase assay were used to monitor the cAMP level, somatostatin expression, activations of kinases and transcriptional factors. Arrb1 knockout mice, specific Creb or Pax6 mutations and specific kinase inhibitors were used to dissect the signalling pathway. Results Adrenaline and isoprenaline increased somatostatin content and transcription through the activation of β1-/β2-adrenergic receptors (β1-/β2ARs). The somatostatin content in β1AR−/− (Adrb1/Adrb2 knockout) mice was 50% lower than in β1AR +/+ /β2AR +/+ mice. Two parallel signalling pathways, Gs-cAMP-protein kinase A (PKA)-cAMP response element binding protein (CREB) and β-arrestin 1-extracellular signal-related kinase (ERK)-paired box protein 6 (PAX6), cooperatively regulated isoprenaline-induced somatostatin transcription. Conclusions/interpretation A stress pathway increased somatostatin content and transcription through β-adrenergic agonism. β-Arrestin1, ERK and PAX6 are important pancreatic delta cell regulators in addition to cAMP, PKA and CREB. Dysfunction of β-adrenergic agonism may impair pancreatic delta cell function.

A cullin 4B-RING E3 ligase complex fine-tunes pancreatic δ cell paracrine interactions

“…However, although the insulin secretion of islets isolated from Sst-Cre +/-Cul4b fl/Y mice was still much lower than that of their WT littermates after SNX482 treatment, this difference was eliminated after nicardipine treatment ( Figure 3D). These data are in agreement with the observed somatostatin secretion patterns and reinforce the conclusion that L-type calcium channels in pancreatic δ cells are key components mediating the increased somatostatin secretion and impaired glucose metabolism in Sst In addition to intracellular calcium, the second messenger cAMP, the G q -PLC pathway, and kinase signaling are actively involved in hormone secretion from pancreatic islets (5,13,(39)(40)(41). Therefore, we preincubated the islets with several inhibitors, including cAMP-PKA signaling inhibitors Rp-CAMPs and H89, G q -PLC inhibitor U73122, MEK inhibitor U0126, and adenyl cyclase (AC) inhibitor 2′,5′-dideoxyadenosine (DDA), and we examined glucose-induced somatostatin secretion patterns ciency in the pancreatic β cells of Ins2-Cre +/-Cul4b fl/Y mice did not significantly affect insulin and somatostatin secretion levels in response to high glucose relative to trends found for Ins2-Cre +/-mice (Supplemental Figure 3, A and B).…”

“…L-type calcium channels are responsible for the influx of extracellular calcium during hormone secretion. We therefore measured high glucose-and high potassium-induced calcium signals in iso- In addition to intracellular calcium, the second messenger cAMP, the G q -PLC pathway, and kinase signaling are actively involved in hormone secretion from pancreatic islets (5,13,(39)(40)(41). Therefore, we preincubated the islets with several inhibitors, including cAMP-PKA signaling inhibitors Rp-CAMPs and H89, G q -PLC inhibitor U73122, MEK inhibitor U0126, and adenyl cyclase (AC) inhibitor 2′,5′-dideoxyadenosine (DDA), and we examined glucose-induced somatostatin secretion patterns ciency in the pancreatic β cells of Ins2-Cre +/-Cul4b fl/Y mice did not significantly affect insulin and somatostatin secretion levels in response to high glucose relative to trends found for Ins2-Cre +/-mice (Supplemental Figure 3, A and B).…”

“…Recently, the functional importance of pancreatic δ cells in maintaining glucose homeostasis is increasingly being appreciated. More specifically, several studies have shown that somatostatin secretion from pancreatic δ cells is regulated by intracellular calcium and cyclic AMP, whereas somatostatin synthesis in pancreatic δ cells is regulated by the cAMP and β-arrestin1 pathways (12,13). In spite of this progress, whether an epigenetic regulatory mechanism underlies the crosstalk between pancreatic δ and β cells has not been investigated.…”

FFA4 receptor (GPR120): A hot target for the development of anti-diabetic therapies

“…Therefore, a systematic examination of an agonist-induced interaction of FFA4 receptor with different G proteins, GRK or arrestin subtypes and their downstream functions is required. Recently, biophysical and pharmacological studies have revealed that for the same receptor, different ligands could induce significantly different conformations that selectively stimulated the activation of one of the downstream effectors of GPCRs and result in biased signaling (Shenoy and Lefkowitz, 2011;Whalen et al, 2011;Shukla et al, 2014;Strachan et al, 2014;Wang et al, 2014). For example, a β-arrestin2 biased downstream signaling of FFA4 receptor may maintain its beneficial effect in anti-inflammation but decrease its potential for promoting tumor growth and angiogenesis.…”

Adaptive Activation of a Stress Response Pathway Improves Learning and Memory Through Gs and β-Arrestin-1–Regulated Lactate Metabolism

“…G-protein- and β-arrestin–mediated signaling are the two main pathways underlying β2AR function (17,27–29). Application of the protein kinase A (PKA) inhibitor (E)-N-(2-(4-bromocinna-mylamino)ethyl)isoquinoline-5-sulfonamide dihydrochloride (H89) significantly reduced, but did not eliminate, the formoterol-induced lactate release in U251 cells, demonstrating the contribution of Gs-PKA–mediated β2AR signaling in lactate release (Figure 4A).…”