XPR1 mediates the pancreatic β-cell phosphate flush

Glucose-stimulated insulin secretion is the hallmark of the pancreatic β-cell, a critical player in the regulation of blood glucose concentration. In 1974 Dawson, Freinkel and co-workers made the remarkable observation that an efflux of intracellular inorganic phosphate (Pi) accompanied the events of stimulated insulin secretion. The mechanism behind this ‘phosphate flush’, its association with insulin secretion and its regulation have since then remained a mystery. We recapitulated the phosphate flush in the MIN6m9 β-cell line and pseudoislets. We demonstrated that knockdown of XPR1, a phosphate transporter present in MIN6m9 cells and pancreatic islets, prevented this flush. Concomitantly, XPR1 silencing led to intracellular Pi accumulation and a potential impact on Ca2+ signaling. XPR1 knockdown slightly blunted first phase glucose-stimulated insulin secretion in MIN6m9 cells, but had no significant impact on pseudoislet secretion. In keeping with other cell types, basal Pi efflux was stimulated by inositol pyrophosphates and basal intracellular Pi accumulated following knockdown of inositol hexakisphosphate kinases. However, the glucose-driven phosphate flush occurred despite inositol pyrophosphate depletion. Finally, whilst it is unlikely that XPR1 directly affects exocytosis, it may protect Ca2+ signaling. Thus we have revealed XPR1 as the missing mediator of the phosphate flush, shedding light on a 45-year-old mystery.

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XPR1 mediates the pancreatic β-cell phosphate flush

10.2337/figshare.12821192.v2 ◽

2020 ◽

Author(s):

Ada Admin ◽

Christopher J. Barker ◽

Fernando Henrique Galvão Tessaro ◽

Sabrina de Souza Ferreira ◽

Rafael Simas ◽

...

Keyword(s):

Insulin Secretion ◽

Inorganic Phosphate ◽

Blood Glucose Concentration ◽

Cell Types ◽

Pancreatic Β Cell ◽

Β Cell ◽

Inositol Pyrophosphate ◽

Inositol Pyrophosphates ◽

Potential Impact ◽

Glucose Stimulated Insulin Secretion

Glucose-stimulated insulin secretion is the hallmark of the pancreatic β-cell, a critical player in the regulation of blood glucose concentration. In 1974 Dawson, Freinkel and co-workers made the remarkable observation that an efflux of intracellular inorganic phosphate (Pi) accompanied the events of stimulated insulin secretion. The mechanism behind this ‘phosphate flush’, its association with insulin secretion and its regulation have since then remained a mystery. We recapitulated the phosphate flush in the MIN6m9 β-cell line and pseudoislets. We demonstrated that knockdown of XPR1, a phosphate transporter present in MIN6m9 cells and pancreatic islets, prevented this flush. Concomitantly, XPR1 silencing led to intracellular Pi accumulation and a potential impact on Ca2+ signaling. XPR1 knockdown slightly blunted first phase glucose-stimulated insulin secretion in MIN6m9 cells, but had no significant impact on pseudoislet secretion. In keeping with other cell types, basal Pi efflux was stimulated by inositol pyrophosphates and basal intracellular Pi accumulated following knockdown of inositol hexakisphosphate kinases. However, the glucose-driven phosphate flush occurred despite inositol pyrophosphate depletion. Finally, whilst it is unlikely that XPR1 directly affects exocytosis, it may protect Ca2+ signaling. Thus we have revealed XPR1 as the missing mediator of the phosphate flush, shedding light on a 45-year-old mystery.

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Inhibition of Forkhead Box O1 Protects Pancreatic β-Cells against Dexamethasone-Induced Dysfunction

Endocrinology ◽

10.1210/en.2009-0343 ◽

2009 ◽

Vol 150 (9) ◽

pp. 4065-4073 ◽

Cited By ~ 24

Author(s):

Xiongfei Zhang ◽

Wei Yong ◽

Jinghuan Lv ◽

Yunxia Zhu ◽

Jingjing Zhang ◽

...

Keyword(s):

Insulin Secretion ◽

Cell Types ◽

Pancreatic Β Cell ◽

Rinm5f Cells ◽

Β Cells ◽

Β Cell ◽

Rat Islets ◽

Cell Dysfunction ◽

Forkhead Box ◽

Glucose Stimulated Insulin Secretion

Abstract Forkhead Box O1 (FoxO1) is a key transcription regulator of insulin/IGF-I signaling pathway, and its activity can be increased by dexamethasone (DEX) in several cell types. However, the role of FoxO1 in DEX-induced pancreatic β-cell dysfunction has not been fully understood. Therefore, in this study, we investigated whether FoxO1 could mediate DEX-induced β-cell dysfunction and the possible underlying mechanisms in pancreatic β-cell line RINm5F cells and primary rat islet. We found that DEX markedly increased FoxO1 mRNA and protein expression and decreased FoxO1 phosphorylation through the Akt pathway, which resulted in an increase in active FoxO1 in RINm5F cells and isolated rat islets. Activated FoxO1 subsequently inhibited pancreatic duodenal homeobox-1 expression and induced nuclear exclusion of pancreatic duodenal homeobox-1. Knockdown of FoxO1 by RNA interference restored the expression of pancreatic duodenal homeobox-1 and prevented DEX-induced dysfunction of glucose-stimulated insulin secretion in rat islets. Together, the results of present study demonstrate that FoxO1 is integrally involved in DEX-induced inhibition of pancreatic duodenal homeobox-1 and glucose-stimulated insulin secretion dysfunction in pancreatic islet β-cells. Inhibition of FoxO1 can effectively protect β-cells against DEX-induced dysfunction.

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Ontology of the apelinergic system in mouse pancreas during pregnancy and relationship with β-cell mass

Scientific Reports ◽

10.1038/s41598-021-94725-0 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Brenda Strutt ◽

Sandra Szlapinski ◽

Thineesha Gnaneswaran ◽

Sarah Donegan ◽

Jessica Hill ◽

...

Keyword(s):

Cell Proliferation ◽

Insulin Secretion ◽

Glucose Transporter ◽

Cell Mass ◽

Elevated Serum ◽

Pancreatic Β Cell ◽

Β Cells ◽

Β Cell ◽

Glucose Transporter 2 ◽

Glucose Stimulated Insulin Secretion

AbstractThe apelin receptor (Aplnr) and its ligands, Apelin and Apela, contribute to metabolic control. The insulin resistance associated with pregnancy is accommodated by an expansion of pancreatic β-cell mass (BCM) and increased insulin secretion, involving the proliferation of insulin-expressing, glucose transporter 2-low (Ins+Glut2LO) progenitor cells. We examined changes in the apelinergic system during normal mouse pregnancy and in pregnancies complicated by glucose intolerance with reduced BCM. Expression of Aplnr, Apelin and Apela was quantified in Ins+Glut2LO cells isolated from mouse pancreata and found to be significantly higher than in mature β-cells by DNA microarray and qPCR. Apelin was localized to most β-cells by immunohistochemistry although Aplnr was predominantly associated with Ins+Glut2LO cells. Aplnr-staining cells increased three- to four-fold during pregnancy being maximal at gestational days (GD) 9–12 but were significantly reduced in glucose intolerant mice. Apelin-13 increased β-cell proliferation in isolated mouse islets and INS1E cells, but not glucose-stimulated insulin secretion. Glucose intolerant pregnant mice had significantly elevated serum Apelin levels at GD 9 associated with an increased presence of placental IL-6. Placental expression of the apelinergic axis remained unaltered, however. Results show that the apelinergic system is highly expressed in pancreatic β-cell progenitors and may contribute to β-cell proliferation in pregnancy.

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Bioactive Phytochemicals Isolated from Akebia quinata Enhances Glucose-Stimulated Insulin Secretion by Inducing PDX-1

Plants ◽

10.3390/plants9091087 ◽

2020 ◽

Vol 9 (9) ◽

pp. 1087

Author(s):

Dahae Lee ◽

Jin Su Lee ◽

Jurdas Sezirahiga ◽

Hak Cheol Kwon ◽

Dae Sik Jang ◽

...

Keyword(s):

Insulin Secretion ◽

Cell Function ◽

Experimental Studies ◽

Pancreatic Β Cell ◽

Β Cell ◽

Etoh Extract ◽

Chemical Structures ◽

Β Cell Function ◽

Glucose Stimulated Insulin Secretion ◽

Phosphoinositide 3 Kinase

Chocolate vine (Akebia quinata) is consumed as a fruit and is also used in traditional medicine. In order to identify the bioactive components of A. quinata, a phytosterol glucoside stigmasterol-3-O-β-d-glucoside (1), three triterpenoids maslinic acid (2), scutellaric acid (3), and hederagenin (4), and three triterpenoidal saponins akebia saponin PA (5), hederacoside C (6), and hederacolchiside F (7) were isolated from a 70% EtOH extract of the fruits of A. quinata (AKQU). The chemical structures of isolates 1–7 were determined by analyzing the 1D and 2D nuclear magnetic resonance (NMR) spectroscopic data. Here, we evaluated the effects of AKQU and compounds 1–7 on insulin secretion using the INS-1 rat pancreatic β-cell line. Glucose-stimulated insulin secretion (GSIS) was evaluated in INS-1 cells using the GSIS assay. The expression levels of the proteins related to pancreatic β-cell function were detected by Western blotting. Among the isolates, stigmasterol-3-O-β-d-glucoside (1) exhibited strong GSIS activity and triggered the overexpression of pancreas/duodenum homeobox protein-1 (PDX-1), which is implicated in the regulation of pancreatic β-cell survival and function. Moreover, isolate 1 markedly induced the expression of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), insulin receptor substrate-2 (IRS-2), phosphoinositide 3-kinase (PI3K), and Akt, which regulate the transcription of PDX-1. The results of our experimental studies indicated that stigmasterol-3-O-β-d-glucoside (1) isolated from the fruits of A. quinata can potentially enhance insulin secretion, and might alleviate the reduction in GSIS during the development of T2DM.

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Investigation of Ultrasound-Mediated Intracellular Ca2+ Oscillations in HIT-T15 Pancreatic β-Cell Line

Cells ◽

10.3390/cells9051129 ◽

2020 ◽

Vol 9 (5) ◽

pp. 1129

Author(s):

Chi Woo Yoon ◽

Nan Sook Lee ◽

Kweon Mo Koo ◽

Sunho Moon ◽

Kyosuk Goo ◽

...

Keyword(s):

Insulin Secretion ◽

Cell Line ◽

Purinergic Signaling ◽

Underlying Mechanism ◽

Resting Cells ◽

Pancreatic Β Cell ◽

Pulsed Ultrasound ◽

Β Cell ◽

Secretion Pathways ◽

Glucose Stimulated Insulin Secretion

In glucose-stimulated insulin secretion (GSIS) of pancreatic β-cells, the rise of free cytosolic Ca2+ concentration through voltage-gated calcium channels (VGCCs) triggers the exocytosis of insulin-containing granules. Recently, mechanically induced insulin secretion pathways were also reported, which utilize free cytosolic Ca2+ ions as a direct regulator of exocytosis. In this study, we aimed to investigate intracellular Ca2+ responses on the HIT-T15 pancreatic β-cell line upon low-intensity pulsed ultrasound (LIPUS) stimulation and found that ultrasound induces two distinct types of intracellular Ca2+ oscillation, fast-irregular and slow-periodic, from otherwise resting cells. Both Ca2+ patterns depend on the purinergic signaling activated by the rise of extracellular ATP or ADP concentration upon ultrasound stimulation, which facilitates the release through mechanosensitive hemichannels on the plasma membrane. Further study demonstrated that two subtypes of purinergic receptors, P2X and P2Y, are working in a competitive manner depending on the level of glucose in the cell media. The findings can serve as an essential groundwork providing an underlying mechanism for the development of a new therapeutic approach for diabetic conditions with further validation.

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Bridging the gap between protein carboxyl methylation and phospholipid methylation to understand glucose-stimulated insulin secretion from the pancreatic β cell

Biochemical Pharmacology ◽

10.1016/j.bcp.2007.06.035 ◽

2008 ◽

Vol 75 (2) ◽

pp. 335-345 ◽

Cited By ~ 1

Author(s):

Anjaneyulu Kowluru

Keyword(s):

Insulin Secretion ◽

Pancreatic Β Cell ◽

Β Cell ◽

Carboxyl Methylation ◽

Glucose Stimulated Insulin Secretion

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Loss of Secretory Pathway Ca2+ ATPase (SPCA1) Impairs Insulin Secretion and Reduces Autophagy in the Pancreatic Islet

10.1101/2021.08.30.458203 ◽

2021 ◽

Author(s):

Robert N. Bone ◽

Xin Tong ◽

Staci A. Weaver ◽

Charanya Muralidharan ◽

Preethi Krishnan ◽

...

Keyword(s):

Insulin Secretion ◽

Secretory Pathway ◽

Cell Types ◽

Β Cell ◽

Human Organ ◽

Altered Glucose ◽

Intracellular Ca ◽

Insulin Granule ◽

Granule Maturation ◽

Glucose Stimulated Insulin Secretion

AbstractThe β cell Golgi apparatus serves as a significant store of intracellular Ca2+ and an important site of proinsulin maturation. However, the contribution of Golgi Ca2+ to diabetes pathophysiology is unknown. The Golgi primarily utilizes the Secretory Pathway Ca2+ ATPase (SPCA1) to maintain intraluminal Ca2+ stores, and loss of SPCA1 has been linked to impaired Golgi function in other cell types. Here, we demonstrated that SPCA1 expression is decreased in islets from diabetic mice and human organ donors with type 2 diabetes, suggesting SPCA1 may impact diabetes development. INS-1 β cells lacking SPCA1 (SPCA1KO) showed reduced intraluminal Golgi Ca2+ levels, reduced glucose-stimulated insulin secretion (GSIS), and increased insulin content. Islets from SPCA1 haploinsufficient mice (SPCA1+/-) exhibited reduced GSIS, altered glucose-induced Ca2+ oscillations, and altered insulin granule maturation. Autophagy can regulate granule homeostasis, therefore we induced autophagy with Torin1 and found that SPCA1KO cells and SPCA1+/- islets had reduced levels of the autophagosome marker LC3-II. Furthermore, SPCA1KO LC3-II were unchanged after blocking autophagy initiation or autophagolysosome fusion and acidification. Thus, we concluded that β cell SPCA1 plays an important role in the maintenance of Golgi Ca2+ homeostasis and reduced Golgi Ca2+ impairs autophagy initiation and may impact insulin granule homeostasis.

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Role of the Rho-ROCK (Rho-Associated Kinase) Signaling Pathway in the Regulation of Pancreatic β-Cell Function

Endocrinology ◽

10.1210/en.2008-1135 ◽

2008 ◽

Vol 150 (5) ◽

pp. 2072-2079 ◽

Cited By ~ 31

Author(s):

Eva Hammar ◽

Alejandra Tomas ◽

Domenico Bosco ◽

Philippe A. Halban

Keyword(s):

Extracellular Matrix ◽

Insulin Secretion ◽

Actin Cytoskeleton ◽

Cell Function ◽

Pancreatic Β Cell ◽

Β Cell ◽

Β Cell Function ◽

Glucose Stimulated Insulin Secretion ◽

And Function

Extracellular matrix has a beneficial impact on β-cell spreading and function, but the underlying signaling pathways have yet to be fully elucidated. In other cell types, Rho, a well-characterized member of the family of Rho GTPases, and its effector Rho-associated kinase (ROCK), play an important role as downstream mediators of outside in signaling from extracellular matrix. Therefore, a possible role of the Rho-ROCK pathway in β-cell spreading, actin cytoskeleton dynamics, and function was investigated. Rho was inhibited using a new cell-permeable version of C3 transferase, whereas the activity of ROCK was repressed using the specific ROCK inhibitors H-1152 and Y-27632. Inhibition of Rho and of ROCK increased spreading and improved both short-term and prolonged glucose-stimulated insulin secretion but had no impact on basal secretion. Inhibition of this pathway led to a depolymerization of the actin cytoskeleton. Furthermore, the impact of the inhibition of ROCK on stimulated insulin secretion was acute and reversible, suggesting that rapid signaling such as phosphorylation is involved. Finally, quantification of the activity of RhoA indicated that the extracellular matrix represses RhoA activity. Overall these results show for the first time that the Rho-ROCK signaling pathway contributes to the stabilization of the actin cytoskeleton and inhibits glucose-stimulated insulin secretion in primary pancreatic β-cells. Furthermore, they indicate that inhibition of this pathway might be one of the mechanisms by which the extracellular matrix exerts its beneficial effects on pancreatic β-cell function.

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