Enterovirus infection of human islets of Langerhans affects β-cell function resulting in disintegrated islets, decreased glucose stimulated insulin secretion and loss of Golgi structure

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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Rice Bran Phenolic Extracts Modulate Insulin Secretion and Gene Expression Associated with β-Cell Function

Nutrients ◽

10.3390/nu12061889 ◽

2020 ◽

Vol 12 (6) ◽

pp. 1889 ◽

Cited By ~ 1

Author(s):

Nancy Saji ◽

Nidhish Francis ◽

Lachlan J. Schwarz ◽

Christopher L. Blanchard ◽

Abishek B. Santhakumar

Keyword(s):

Insulin Secretion ◽

Rice Bran ◽

Cell Function ◽

Β Cell ◽

Free Radical Damage ◽

Glucose Transporter 2 ◽

Expression Of Genes ◽

Β Cell Function ◽

Glucose Stimulated Insulin Secretion ◽

Phenolic Extracts

Oxidative stress is known to modulate insulin secretion and initiate gene alterations resulting in impairment of β-cell function and type 2 diabetes mellitus (T2DM). Rice bran (RB) phenolic extracts contain bioactive properties that may target metabolic pathways associated with the pathogenesis of T2DM. This study aimed to examine the effect of stabilized RB phenolic extracts on the expression of genes associated with β-cell function such as glucose transporter 2 (Glut2), pancreatic and duodenal homeobox 1 (Pdx1), sirtuin 1 (Sirt1), mitochondrial transcription factor A (Tfam), and insulin 1 (Ins1) in addition to evaluating its impact on glucose-stimulated insulin secretion. It was observed that treatment with different concentrations of RB phenolic extracts (25-250 µg/mL) significantly increased the expression of Glut2, Pdx1, Sirt1, Tfam, and Ins1 genes and glucose-stimulated insulin secretion under both normal and high glucose conditions. RB phenolic extracts favourably modulated the expression of genes involved in β-cell dysfunction and insulin secretion via several mechanisms such as synergistic action of polyphenols targeting signalling molecules, decreasing free radical damage by its antioxidant activity, and stimulation of effectors or survival factors of insulin secretion.

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PKA-dependent potentiation of glucose-stimulated insulin secretion by Epac activator 8-pCPT-2′-O-Me-cAMP-AM in human islets of Langerhans

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00630.2009 ◽

2010 ◽

Vol 298 (3) ◽

pp. E622-E633 ◽

Cited By ~ 57

Author(s):

Oleg G. Chepurny ◽

Grant G. Kelley ◽

Igor Dzhura ◽

Colin A. Leech ◽

Michael W. Roe ◽

...

Keyword(s):

Insulin Secretion ◽

Islets Of Langerhans ◽

Human Islets ◽

Human Islet ◽

Second Phase ◽

Acetoxymethyl Ester ◽

Insulin Secretagogue ◽

Camp Analog ◽

Human Islets Of Langerhans ◽

Glucose Stimulated Insulin Secretion

Potential insulin secretagogue properties of an acetoxymethyl ester of a cAMP analog (8-pCPT-2′- O-Me-cAMP-AM) that activates the guanine nucleotide exchange factors Epac1 and Epac2 were assessed using isolated human islets of Langerhans. RT-QPCR demonstrated that the predominant variant of Epac expressed in human islets was Epac2, although Epac1 was detectable. Under conditions of islet perifusion, 8-pCPT-2′- O-Me-cAMP-AM (10 μM) potentiated first- and second-phase 10 mM glucose-stimulated insulin secretion (GSIS) while failing to influence insulin secretion measured in the presence of 3 mM glucose. The insulin secretagogue action of 8-pCPT-2′- O-Me-cAMP-AM was associated with depolarization and an increase of [Ca2+]i that reflected both Ca2+ influx and intracellular Ca2+ mobilization in islet β-cells. As expected for an Epac-selective cAMP analog, 8-pCPT-2′- O-Me-cAMP-AM (10 μM) failed to stimulate phosphorylation of PKA substrates CREB and Kemptide in human islets. Furthermore, 8-pCPT-2′- O-Me-cAMP-AM (10 μM) had no significant ability to activate AKAR3, a PKA-regulated biosensor expressed in human islet cells by viral transduction. Unexpectedly, treatment of human islets with an inhibitor of PKA activity (H-89) or treatment with a cAMP antagonist that blocks PKA activation (Rp-8-CPT-cAMPS) nearly abolished the action of 8-pCPT-2′- O-Me-cAMP-AM to potentiate GSIS. It is concluded that there exists a permissive role for PKA activity in support of human islet insulin secretion that is both glucose dependent and Epac regulated. This permissive action of PKA may be operative at the insulin secretory granule recruitment, priming, and/or postpriming steps of Ca2+-dependent exocytosis.

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Protein restriction in early life is associated with changes in insulin sensitivity and pancreatic β-cell function during pregnancy

British Journal Of Nutrition ◽

10.1017/s000711451200089x ◽

2012 ◽

Vol 109 (2) ◽

pp. 236-247 ◽

Cited By ~ 7

Author(s):

Letícia Martins Ignácio-Souza ◽

Sílvia Regina Reis ◽

Vanessa Cristina Arantes ◽

Bárbara Laet Botosso ◽

Roberto Vilela Veloso ◽

...

Keyword(s):

Insulin Secretion ◽

Protein Kinase ◽

Early Life ◽

Cell Function ◽

Secretory Process ◽

Insulin Biosynthesis ◽

Β Cell ◽

Pregnant Rats ◽

Β Cell Function ◽

Glucose Stimulated Insulin Secretion

Malnutrition in early life impairs glucose-stimulated insulin secretion in adulthood. Conversely, pregnancy is associated with a significant increase in glucose-stimulated insulin secretion under conditions of normoglycaemia. A failure in β-cell adaptive changes may contribute to the onset of diabetes. Thus, glucose homeostasis and β-cell function were evaluated in control-fed pregnant (CP) and non-pregnant (CNP) or protein-restricted pregnant (LPP) and non-pregnant (LPNP) rats, from fetal to adult life, and in protein-restricted rats that were recovered after weaning (RP and RNP). The typical insulin resistance of pregnancy was not observed in the RP rats, nor did pregnancy increase the insulin content/islet in the LPP group. The glucose dose–response curves from pregnant rats were shifted to the left in relation to the non-pregnant rats, except in the recovered group. Glucose utilisation but not oxidation in islets from the RP and LPP groups was reduced at a concentration of 8·3 mm-glucose compared with islets from the CP group. Cyclic AMP content and the potentiation of glucose-stimulated insulin secretion by isobutylmethylxanthine at a concentration of 2·8 mm-glucose indicated increased adenylyl cyclase 3 activity but reduced protein kinase A-α activity in islets from the RP and LPP rats. Protein kinase C (PKC)-α but not phospholipase C (PLC)-β1 expression was reduced in islets from the RP group. Phorbol-12-myristate 13-acetate produced a less potent stimulation of glucose-stimulated insulin secretion in the RP group. Thus, the alterations exhibited by islets from the LPP group appeared to be due to reduced islet mass and/or insulin biosynthesis. In the RP group the loss of the adaptive capacity apparently resulted from uncoupling between glucose metabolism and the amplifying signals of the secretory process, as well as a severe attenuation of the PLC/PKC pathway.

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Resveratrol and curcumin enhance pancreatic β-cell function by inhibiting phosphodiesterase activity

Journal of Endocrinology ◽

10.1530/joe-14-0335 ◽

2014 ◽

Vol 223 (2) ◽

pp. 107-117 ◽

Cited By ~ 53

Author(s):

Michael Rouse ◽

Antoine Younès ◽

Josephine M Egan

Keyword(s):

Insulin Secretion ◽

Cell Lines ◽

Cell Function ◽

Human Islets ◽

Dependent Manner ◽

Pancreatic Β Cell ◽

Β Cells ◽

Β Cell ◽

Pde Inhibitors ◽

Β Cell Function

Resveratrol (RES) and curcumin (CUR) are polyphenols that are found in fruits and turmeric, and possess medicinal properties that are beneficial in various diseases, such as heart disease, cancer, and type 2 diabetes mellitus (T2DM). Results from recent studies have indicated that their therapeutic properties can be attributed to their anti-inflammatory effects. Owing to reports stating that they protect against β-cell dysfunction, we studied their mechanism(s) of action in β-cells. In T2DM, cAMP plays a critical role in glucose- and incretin-stimulated insulin secretion as well as overall pancreatic β-cell health. A potential therapeutic target in the management of T2DM lies in regulating the activity of phosphodiesterases (PDEs), which degrade cAMP. Both RES and CUR have been reported to act as PDE inhibitors in various cell types, but it remains unknown if they do so in pancreatic β-cells. In our current study, we found that both RES (0.1–10 μmol/l) and CUR (1–100 pmol/l)-regulated insulin secretion under glucose-stimulated conditions. Additionally, treating β-cell lines and human islets with these polyphenols led to increased intracellular cAMP levels in a manner similar to 3-isobutyl-1-methylxanthine, a classic PDE inhibitor. When we investigated the effects of RES and CUR on PDEs, we found that treatment significantly downregulated the mRNA expression of most of the 11 PDE isozymes, including PDE3B, PDE8A, and PDE10A, which have been linked previously to regulation of insulin secretion in islets. Furthermore, RES and CUR inhibited PDE activity in a dose-dependent manner in β-cell lines and human islets. Collectively, we demonstrate a novel role for natural-occurring polyphenols as PDE inhibitors that enhance pancreatic β-cell function.

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Spontaneous restoration of functional β-cell mass in obese SM/J mice

10.1101/2020.05.19.104588 ◽

2020 ◽

Author(s):

Mario A Miranda ◽

Caryn Carson ◽

Celine L St Pierre ◽

Juan F Macias-Velasco ◽

Jing W Hughes ◽

...

Keyword(s):

Insulin Secretion ◽

Mitotic Index ◽

Cell Function ◽

Cell Mass ◽

Β Cell ◽

Physiological Mechanisms ◽

Β Cell Function ◽

Basal Insulin Secretion ◽

Glucose Stimulated Insulin Secretion ◽

Mass Expansion

AbstractMaintenance of functional β-cell mass is critical to preventing diabetes, but the physiological mechanisms that cause β-cell populations to thrive or fail in the context of obesity are unknown. High fat-fed SM/J mice spontaneously transition from hyperglycemic-obese to normoglycemic-obese with age, providing a unique opportunity to study β-cell adaptation. Here, we characterize insulin homeostasis, islet morphology, and β-cell function during SM/J’s diabetic remission. As they resolve hyperglycemia, obese SM/J mice dramatically increase circulating and pancreatic insulin levels while improving insulin sensitivity. Immunostaining of pancreatic sections reveals that obese SM/J mice selectively increase β-cell mass but not α-cell mass. Obese SM/J mice do not show elevated β-cell mitotic index, but rather elevated α-cell mitotic index. Functional assessment of isolated islets reveals that obese SM/J mice increase glucose stimulated insulin secretion, decrease basal insulin secretion, and increase islet insulin content. These results establish that β-cell mass expansion and improved β-cell function underlie the resolution of hyperglycemia, indicating that obese SM/J mice are a valuable tool for exploring how functional β-cell mass can be recovered in the context of obesity.

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Emerging role of testosterone in pancreatic β cell function and insulin secretion

Journal of Endocrinology ◽

10.1530/joe-18-0573 ◽

2019 ◽

Vol 240 (3) ◽

pp. R97-R105 ◽

Cited By ~ 10

Author(s):

Weiwei Xu ◽

Jamie Morford ◽

Franck Mauvais-Jarvis

Keyword(s):

Insulin Secretion ◽

Metabolic Regulation ◽

Cell Function ◽

Visceral Obesity ◽

Β Cells ◽

Β Cell ◽

Β Cell Function ◽

Glucagon Like Peptide 1 ◽

Glucose Stimulated Insulin Secretion

One of the most sexually dimorphic aspects of metabolic regulation is the bidirectional modulation of glucose homeostasis by testosterone in male and females. Severe testosterone deficiency predisposes men to type 2 diabetes (T2D), while in contrast, androgen excess predisposes women to hyperglycemia. The role of androgen deficiency and excess in promoting visceral obesity and insulin resistance in men and women respectively is well established. However, although it is established that hyperglycemia requires β cell dysfunction to develop, the role of testosterone in β cell function is less understood. This review discusses recent evidence that the androgen receptor (AR) is present in male and female β cells. In males, testosterone action on AR in β cells enhances glucose-stimulated insulin secretion by potentiating the insulinotropic action of glucagon-like peptide-1. In females, excess testosterone action via AR in β cells promotes insulin hypersecretion leading to oxidative injury, which in turn predisposes to T2D.

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Glucose Responsiveness of β-Cells Depends on Fatty Acids

Experimental and Clinical Endocrinology & Diabetes ◽

10.1055/a-0884-2919 ◽

2019 ◽

Vol 128 (10) ◽

pp. 644-653

Author(s):

Felicia Gerst ◽

Christine Singer ◽

Katja Noack ◽

Dunia Graf ◽

Gabriele Kaiser ◽

...

Keyword(s):

Fatty Acids ◽

Insulin Secretion ◽

Cell Function ◽

Human Islets ◽

In Vitro Tests ◽

High Concentration ◽

Β Cell Function ◽

Glucose Stimulated Insulin Secretion ◽

Glucose Responsiveness

AbstractGlucose-stimulated insulin secretion (GSIS) is the gold standard for β-cell function. Both experimental and clinical diabetology, i. e., preceding transplantation of isolated human islets, depend on functional testing. However, multiple factors influence GSIS rendering the comparison of different in vitro tests of glucose responsiveness difficult. This study examined the influence of bovine serum albumin (BSA)-coupled fatty acids on GSIS. Isolated islet preparations of human donors and of 12-months old mice displayed impaired GSIS in the presence of 0.5% FFA-free BSA compared to 0.5% BSA (fraction V, not deprived from fatty acids). In aged INS-1E cells, i. e. at a high passage number, GSIS became highly sensitive to FFA-free BSA. Readdition of 30 µM palmitate or 30 µM oleate to FFA-free BSA did not rescue GSIS, while the addition of 100 µM palmitate and the raise of extracellular Ca2+from 1.3 to 2.6 mM improved glucose responsiveness. A high concentration of palmitate (600 µM), which fully activates FFA1, largely restored insulin secretion. The FFA1-agonist TUG-469 also increased insulin secretion but to a lesser extent than palmitate. Glucose- and TUG-induced Ca2+oscillations were impaired in glucose-unresponsive, i. e., aged INS-1E cells. These results suggest that fatty acid deprivation (FFA-free BSA) impairs GSIS mainly through an effect on Ca2+sensitivity.

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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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