Hypothalamic AMP-Activated Protein Kinase Regulates Biphasic Insulin Secretion from Pancreatic β Cells during Fasting and in Type 2 Diabetes

Metformin, a drug widely used in the treatment of type 2 diabetes, has recently been shown to act on skeletal muscle and liver in part through the activation of AMP-activated protein kinase (AMPK). Whether metformin or the satiety factor leptin, which also stimulates AMPK in muscle, regulates this enzyme in pancreatic islets is unknown. We have recently shown that forced increases in AMPK activity inhibit insulin secretion from MIN6 cells (da Silva Xavier G, Leclerc I, Varadi A, Tsuboi T, Moule SK, and Rutter GA. Biochem J 371: 761–774, 2003). Here, we explore whether 1) glucose, metformin, or leptin regulates AMPK activity in isolated islets from rodent and human and 2) whether changes in AMPK activity modulate insulin secretion from human islets. Increases in glucose concentration from 0 to 3 and from 3 to 17 mM inhibited AMPK activity in primary islets from mouse, rat, and human, confirming previous findings in insulinoma cells. Incubation with metformin (0.2–1 mM) activated AMPK in both human islets and MIN6 β-cells in parallel with an inhibition of insulin secretion, whereas leptin (10–100 nM) was without effect in MIN6 cells. These studies demonstrate that AMPK activity is subject to regulation by both glucose and metformin in pancreatic islets and clonal β-cells. The inhibitory effects of metformin on insulin secretion may therefore need to be considered with respect to the use of this drug for the treatment of type 2 diabetes.

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Abstract 34: Apolipoprotein A-I Increases Insulin Secretion from β-cells via a Protein Kinase A Dependent Mechanism

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvb.32.suppl_1.a34 ◽

2012 ◽

Vol 32 (suppl_1) ◽

Author(s):

Blake J Cochran ◽

Kerry-Anne Rye

Keyword(s):

Type 2 Diabetes ◽

Insulin Secretion ◽

Protein Kinase ◽

Protein Kinase A ◽

Adenyl Cyclase ◽

Β Cells ◽

Pancreatic Β Cells ◽

Kinase A ◽

Dependent Mechanism

Introduction: The progression to hyperglycaemia in type 2 diabetes is marked by β-cell insulin secretory dysfunction and cell loss. We have previously demonstrated that apolipoprotein (apo) A-I, the major protein constituent of high density lipoproteins (HDL) increases insulin expression and secretion from β-cells. Clinical data also suggests that pharmacological elevation of HDL levels is associated with improved glycemic control in patients with type 2 diabetes. With the current interest in HDL raising therapeutics, defining the mechanism by which apoA-I acts on insulin secretion is of importance. Objective: To elucidate the cell signalling events responsible for increasing insulin secretion from pancreatic β-cells treated with lipid-free apoA-I. Methods: Ins-1E (rat insulinoma) cells were pre-treated for 30 min with the Protein kinase A (PKA) specific inhibitor H89 (20 μM), soluble and transmembrane adenyl cyclase specific inhibitors (KH7, 30 μM and 2’5’ dideoxyadenosine, 50 μM, respectively) or vehicle control, then incubated for 1 h with lipid-free apoA-I (final concentration 1 mg/mL) under both basal (2.8 mM) and high (25 mM) glucose conditions. The insulin concentration in the culture supernatants was determined by radioimmunoassay and the cells were either lysed for protein analysis by western blotting or treated with 0.1 M HCl for determining cAMP by enzyme immunoassay. Results: Incubation of Ins-1E cells with apoA-I increased insulin secretion up to 3-fold. This increase was no longer apparent when the cells were pre-treated with H89. Incubation with apoA-I increased cAMP accumulation in Ins-1E cells 2.5-fold. This increase was totally inhibited when the cells were pre-incubated with 2’5’ dideoxyadenosine but not by KH7, indicating that transmembrane adenyl cyclase(s) are responsible for this response. ApoA-I also activated the small GTPase Cdc42, which may link cell surface apoA-I receptors with transmembrane adenyl cyclases. Conclusion: ApoA-I increases insulin secretion from pancreatic β-cells via a PKA-dependent mechanism involving transmembrane, but not soluble, adenyl cyclases and possibly Cdc42. This provides a possible explanation of the clinical observations that increased HDL may be beneficial in type 2 diabetes.

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Teucrium polium: Potential Drug Source for Type 2 Diabetes Mellitus

Biology ◽

10.3390/biology11010128 ◽

2022 ◽

Vol 11 (1) ◽

pp. 128

Author(s):

Yaser Albadr ◽

Andrew Crowe ◽

Rima Caccetta

Keyword(s):

Diabetes Mellitus ◽

Type 2 Diabetes ◽

Type 2 Diabetes Mellitus ◽

Insulin Secretion ◽

Β Cells ◽

Pancreatic Β Cells ◽

Glucose Levels ◽

Teucrium Polium

The prevalence of type 2 diabetes mellitus is rising globally and this disease is proposed to be the next pandemic after COVID-19. Although the cause of type 2 diabetes mellitus is unknown, it is believed to involve a complex array of genetic defects that affect metabolic pathways which eventually lead to hyperglycaemia. This hyperglycaemia arises from an inability of the insulin-sensitive cells to sufficiently respond to the secreted insulin, which eventually results in the inadequate secretion of insulin from pancreatic β-cells. Several treatments, utilising a variety of mechanisms, are available for type 2 diabetes mellitus. However, more medications are needed to assist with the optimal management of the different stages of the disease in patients of varying ages with the diverse combinations of other medications co-administered. Throughout modern history, some lead constituents from ancient medicinal plants have been investigated extensively and helped in developing synthetic antidiabetic drugs, such as metformin. Teucrium polium L. (Tp) is a herb that has a folk reputation for its antidiabetic potential. Previous studies indicate that Tp extracts significantly decrease blood glucose levels r and induce insulin secretion from pancreatic β-cells in vitro. Nonetheless, the constituent/s responsible for this action have not yet been elucidated. The effects appear to be, at least in part, attributable to the presence of selected flavonoids (apigenin, quercetin, and rutin). This review aims to examine the reported glucose-lowering effect of the herb, with a keen focus on insulin secretion, specifically related to type 2 diabetes mellitus. An analysis of the contribution of the key constituent flavonoids of Tp extracts will also be discussed.

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Targeted Genetic Inactivation of N-Acetylglucosaminyltransferase-IVa Impairs Insulin Secretion from Pancreatic β Cells and Evokes Type 2 Diabetes

Methods in Enzymology - Functional Glycomics ◽

10.1016/s0076-6879(10)79012-1 ◽

2010 ◽

pp. 205-222 ◽

Cited By ~ 6

Author(s):

Kazuaki Ohtsubo

Keyword(s):

Type 2 Diabetes ◽

Insulin Secretion ◽

Β Cells ◽

Pancreatic Β Cells ◽

Genetic Inactivation

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AMP-activated protein kinase as regulator of P2Y6 receptor-induced insulin secretion in mouse pancreatic β-cells

Biochemical Pharmacology ◽

10.1016/j.bcp.2012.11.029 ◽

2013 ◽

Vol 85 (7) ◽

pp. 991-998 ◽

Cited By ~ 11

Author(s):

Ramachandran Balasubramanian ◽

Hiroshi Maruoka ◽

P. Suresh Jayasekara ◽

Zhan-Guo Gao ◽

Kenneth A. Jacobson

Keyword(s):

Insulin Secretion ◽

Protein Kinase ◽

Β Cells ◽

Pancreatic Β Cells ◽

P2y6 Receptor ◽

Amp Activated Protein Kinase

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BLX-1002, a novel thiazolidinedione with no PPAR affinity, stimulates AMP-activated protein kinase activity, raises cytosolic Ca2+, and enhances glucose-stimulated insulin secretion in a PI3K-dependent manner

AJP Cell Physiology ◽

10.1152/ajpcell.00444.2008 ◽

2009 ◽

Vol 296 (2) ◽

pp. C346-C354 ◽

Cited By ~ 16

Author(s):

Fan Zhang ◽

Deben Dey ◽

Robert Bränström ◽

Lars Forsberg ◽

Ming Lu ◽

...

Keyword(s):

Type 2 Diabetes ◽

Insulin Secretion ◽

High Glucose ◽

Cell Function ◽

Dependent Manner ◽

Β Cells ◽

Β Cell ◽

Β Cell Function ◽

Amp Activated Protein Kinase

BLX-1002 is a novel small thiazolidinedione with no apparent affinity to peroxisome proliferator-activated receptors (PPAR) that has been shown to reduce glycemia in type 2 diabetes without adipogenic effects. Its precise mechanisms of action, however, remain elusive, and no studies have been done with respect to possible effects of BLX-1002 on pancreatic β-cells. We have investigated the influence of the drug on β-cell function in mouse islets in vitro. BLX-1002 enhanced insulin secretion stimulated by high, but not low or intermediate, glucose concentrations. BLX-1002 also augmented cytoplasmic free Ca2+ concentration ([Ca2+]i) at high glucose, an effect that was abolished by pretreatment with the Ca2+-ATPase inhibitor thapsigargin. In contrast, BLX-1002 did not interfere with voltage-gated Ca2+ channel or ATP-sensitive K+ channel activities. In addition, cellular NAD(P)H stimulated by glucose was not affected by the drug. The stimulatory effect of BLX-1002 on insulin secretion at high glucose was completely abolished by treatment with the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY-294002. Stimulation of the β-cells with BLX-1002 also induced activation of AMP-activated protein kinase (AMPK) at high glucose. Our study suggests that BLX-1002 potentiates insulin secretion only at high glucose in β-cells in a PI3K-dependent manner. This effect of BLX-1002 is associated with an increased [Ca2+]i mediated through Ca2+ mobilization, and an enhanced activation of AMPK. The glucose-sensitive stimulatory impact of BLX-1002 on β-cell function may translate into substantial clinical benefits of the drug in the management of type 2 diabetes, by avoidance of hypoglycemia.

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Angiotensin(1–7) activates MAS-1 and upregulates CFTR to promote insulin secretion in pancreatic β-cells: the association with type 2 diabetes

Endocrine Connections ◽

10.1530/ec-21-0357 ◽

2021 ◽

Author(s):

Xue-Lian Zhang ◽

Xinyi Zhao ◽

Yong Wu ◽

Wen-qing Huang ◽

Jun-jiang Chen ◽

...

Keyword(s):

Type 2 Diabetes ◽

Insulin Secretion ◽

Human Blood ◽

Human Subjects ◽

Blood Levels ◽

Intracellular Camp ◽

Β Cells ◽

Pancreatic Β Cells ◽

Glucose Stimulated Insulin Secretion

Objective: The beneficial effect of angiotensin(1–7), via the activation of its receptor, MAS-1, has been noted in diabetes treatment; however, how angiotensin(1–7) or MAS-1 affects insulin secretion remains elusive and whether endogenous level of angiotensin(1–7) or MAS-1 is altered in diabetic individuals remains unexplored. We recently identified an important role of CFTR, a cAMP-activated Cl- channel, in regulation of insulin secretion. Here, we tested possible involvement of CFTR in mediating angiotensin(1–7)’s effect on insulin secretion and measured the level of angiotensin(1–7), MAS-1 as well as CFTR in the blood of individuals with or without type 2 diabetes. Methods: Angiotensin(1–7)/MAS-1/CFTR pathway was determined by specific inhibitors, gene manipulation, western blotting as well as insulin ELISA in a pancreatic β cell line, RINm5F. Human blood samples were collected from 333 individuals with (n=197) and without (n=136) type 2 diabetes. Angiotensin(1–7), MAS-1 and CFTR level in the human blood were determined by ELISA. Results: In RINm5F cells, angiotensin(1–7) induced intracellular cAMP increase, CREB activation, enhanced CFTR expression and potentiated glucose-stimulated insulin secretion, which were abolished by a selective CFTR inhibitor, RNAi-knockdown of CFTR, or inhibition of MAS-1. In human subjects, the blood levels of MAS-1 and CFTR, but not angiotensin(1–7), were significantly higher in individuals with type 2 diabetes as compared to those in non-diabetic healthy subjects. In addition, blood levels of MAS-1 and CFTR were in significant positive correlation in type-2-diabetic but not non-diabetic subjects. Conclusion: These results suggested MAS-1 and CFTR as key players in mediating angiotensin(1–7)-promoted insulin secretion in pancreatic β cells; MAS-1 and CFTR are positively correlated and both upregulated in type 2 diabetes.

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Novel roles of SUMO in pancreatic β-cells: thinking outside the nucleus

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y11-134 ◽

2012 ◽

Vol 90 (6) ◽

pp. 765-770 ◽

Cited By ~ 13

Author(s):

Jocelyn E. Manning Fox ◽

Catherine Hajmrle ◽

Patrick E. MacDonald

Keyword(s):

Type 2 Diabetes ◽

Insulin Secretion ◽

Endocrine Pancreas ◽

Β Cells ◽

Β Cell ◽

Pancreatic Β Cells ◽

Cellular Processes ◽

Wide Range ◽

Cell Gene

The endocrine pancreas is critically important in the regulation of energy metabolism, with defective insulin secretion from pancreatic islet β-cells a major contributing factor to the development of type 2 diabetes. Small ubiquitin-like modifier (SUMO) proteins have been demonstrated to covalently modify a wide range of target proteins, mediating a broad range of cellular processes. While the effects of SUMOylation on β-cell gene transcription have been previously reviewed, recent reports indicate roles for SUMO outside of the nucleus. In this review we shall focus on the reported non-nuclear roles of SUMOylation in the regulation of β-cells, including SUMOylation as a novel signaling pathway in the acute regulation of insulin secretion.

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Granule docking and cargo release in pancreatic β-cells

Biochemical Society Transactions ◽

10.1042/bst0360294 ◽

2008 ◽

Vol 36 (3) ◽

pp. 294-299 ◽

Cited By ~ 9

Author(s):

Sebastian Barg ◽

Anders Lindqvist ◽

Stefanie Obermüller

Keyword(s):

Insulin Secretion ◽

Live Cell Imaging ◽

Cell Imaging ◽

Fusion Pore ◽

Β Cells ◽

Pancreatic Β Cells ◽

Isolated Pancreatic Islets ◽

Biphasic Insulin ◽

Biphasic Insulin Secretion

Biphasic insulin secretion is required for proper insulin action and is observed not only in vivo, but also in isolated pancreatic islets and even single β-cells. Late events in the granule life cycle are thought to underlie this temporal pattern. In the last few years, we have therefore combined live cell imaging and electrophysiology to study insulin secretion at the level of individual granules, as they approach the plasma membrane, undergo exocytosis and finally release their insulin cargo. In the present paper, we review evidence for two emerging concepts that affect insulin secretion at the level of individual granules: (i) the existence of specialized sites where granules dock in preparation for exocytosis; and (ii) post-exocytotic regulation of cargo release by the fusion pore.

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GLP-1 Analog Liraglutide Enhances Proinsulin Processing in Pancreatic β-Cells via a PKA-Dependent Pathway

Endocrinology ◽

10.1210/en.2014-1218 ◽

2014 ◽

Vol 155 (10) ◽

pp. 3817-3828 ◽

Cited By ~ 8

Author(s):

Liang Wang ◽

Ye Liu ◽

Jin Yang ◽

Hejun Zhao ◽

Jing Ke ◽

...

Keyword(s):

Type 2 Diabetes ◽

Protein Kinase ◽

Protein Kinase A ◽

Pancreatic Β Cell ◽

Β Cells ◽

Β Cell ◽

Pancreatic Β Cells ◽

Proinsulin Processing ◽

Kinase A

Abstract Hyperproinsulinemia has gained increasing attention in the development of type 2 diabetes. Clinical studies have demonstrated that glucagon-like peptide-1 (GLP-1)-based therapies significantly decrease plasma proinsulin/insulin ratio in patients with type 2 diabetes. However, the underlying mechanism remains unclear. Prohormone convertase (PC)-1/3 and PC2 are primarily responsible for processing proinsulin to insulin in pancreatic β-cells. We have recently reported that Pax6 mutation down-regulated PC1/3 and PC2 expression, resulting in defective proinsulin processing in Pax6 heterozygous mutant (Pax6m/+) mice. In this study, we investigated whether and how liraglutide, a novel GLP-1 analog, modulated proinsulin processing. Our results showed that liraglutide significantly up-regulated PC1/3 expression and decreased the proinsulin to insulin ratio in both Pax6m/+ and db/db diabetic mice. In the cultured mouse pancreatic β-cell line, Min6, liraglutide stimulated PC1/3 and PC2 expression and lowered the proinsulin to insulin ratio in a dose- and time-dependent manner. Moreover, the beneficial effects of liraglutide on PC1/3 and PC2 expression and proinsulin processing were dependent on the GLP-1 receptor-mediated cAMP/protein kinase A signaling pathway. The same mechanism was recapitulated in isolated mouse islets. In conclusion, liraglutide enhanced PC1/3- and PC2-dependent proinsulin processing in pancreatic β-cells through the activation of the GLP-1 receptor/cAMP/protein kinase A signaling pathway. Our study provides a new mechanism for improvement of pancreatic β-cell function by the GLP-1-based therapy.

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