Physiological role of cholecystokinin in meal-induced insulin secretion in conscious rats. Studies with L 364718, a specific inhibitor of CCK-receptor binding

Whereas ghrelin is produced primarily in the stomach, a small amount of it is produced in pancreatic islets. Although exogenous administration of ghrelin suppresses insulin secretion in vitro or in vivo, the role of intraislet ghrelin in the regulation of insulin secretion in vivo remains unclear. To understand the physiological role of intraislet ghrelin in insulin secretion and glucose metabolism, we developed a transgenic (Tg) mouse model, rat insulin II promoter ghrelin-internal ribosomal entry site-ghrelin O-acyl transferase (RIP-GG) Tg mice, in which mouse ghrelin cDNA and ghrelin O-acyltransferase are overexpressed under the control of the rat insulin II promoter. Although pancreatic desacyl ghrelin levels were elevated in RIP-GG Tg mice, pancreatic ghrelin levels were not altered in animals on a standard diet. However, when Tg mice were fed a medium-chain triglyceride-rich diet (MCTD), pancreatic ghrelin levels were elevated to ∼16 times that seen in control animals. It seems likely that the gastric ghrelin cells possess specific machinery to provide the octanoyl acid necessary for ghrelin acylation but that this machinery is absent from pancreatic β-cells. Despite the overexpression of ghrelin, plasma ghrelin levels in the portal veins of RIP-GG Tg mice were unchanged from control levels. Glucose tolerance, insulin secretion, and islet architecture in RIP-GG Tg mice were not significantly different even when the mice were fed a MCTD. These results indicate that intraislet ghrelin does not play a major role in the regulation of insulin secretion in vivo.

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Fructose-1,6-Bisphosphatase Regulates Glucose-Stimulated Insulin Secretion of Mouse Pancreatic β-Cells

Endocrinology ◽

10.1210/en.2009-1185 ◽

2010 ◽

Vol 151 (10) ◽

pp. 4688-4695 ◽

Cited By ~ 16

Author(s):

Ye Zhang ◽

Zhifang Xie ◽

Guangdi Zhou ◽

Hai Zhang ◽

Jian Lu ◽

...

Keyword(s):

Insulin Secretion ◽

Specific Inhibitor ◽

Physiological Role ◽

Glucose Sensing ◽

Β Cells ◽

Pancreatic Β Cells ◽

Min6 Cells ◽

Fructose 1,6 Bisphosphatase ◽

Glucose Stimulated Insulin Secretion

Pancreatic β-cells can precisely sense glucose stimulation and accordingly adjust their insulin secretion. Fructose-1,6-bisphosphatase (FBPase) is a gluconeogenic enzyme, but its physiological significance in β-cells is not established. Here we determined its physiological role in regulating glucose sensing and insulin secretion of β-cells. Considerable FBPase mRNA was detected in normal mouse islets and β-cell lines, although their protein levels appeared to be quite low. Down-regulation of FBP1 in MIN6 cells by small interfering RNA could enhance the glucose-stimulated insulin secretion (GSIS), whereas FBP1-overexpressing MIN6 cells exhibited decreased GSIS. Inhibition of FBPase activity in islet β-cells by its specific inhibitor MB05032 led to significant increase of their glucose utilization and cellular ATP to ADP ratios and consequently enhanced GSIS in vitro. Pretreatment of mice with the MB05032 prodrug MB06322 could potentiate GSIS in vivo and improve their glucose tolerance. Therefore, FBPase plays an important role in regulating glucose sensing and insulin secretion of β-cells and serves a promising target for diabetes treatment.

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Carnitine palmitoyltransferase 1A prevents fatty acid-induced adipocyte dysfunction through suppression of c-Jun N-terminal kinase

Biochemical Journal ◽

10.1042/bj20101680 ◽

2011 ◽

Vol 435 (3) ◽

pp. 723-732 ◽

Cited By ~ 38

Author(s):

Xuefei Gao ◽

Kuai Li ◽

Xiaoyan Hui ◽

Xiangping Kong ◽

Gary Sweeney ◽

...

Keyword(s):

Insulin Resistance ◽

Fatty Acids ◽

Fatty Acid ◽

Cell Lines ◽

Specific Inhibitor ◽

Physiological Role ◽

Carnitine Palmitoyltransferase ◽

Acid Uptake ◽

Pharmacological Inhibition

The adipocyte is the principal cell type for fat storage. CPT1 (carnitine palmitoyltransferase-1) is the rate-limiting enzyme for fatty acid β-oxidation, but the physiological role of CPT1 in adipocytes remains unclear. In the present study, we focused on the specific role of CPT1A in the normal functioning of adipocytes. Three 3T3-L1 adipocyte cell lines stably expressing hCPT1A (human CPT1A) cDNA, mouse CPT1A shRNA (short-hairpin RNA) or GFP (green fluorescent protein) were generated and the biological functions of these cell lines were characterized. Alteration in CPT1 activity, either by ectopic overexpression or pharmacological inhibition using etomoxir, did not affect adipocyte differentiation. However, overexpression of hCPT1A significantly reduced the content of intracellular NEFAs (non-esterified fatty acids) compared with the control cells when adipocytes were challenged with fatty acids. The changes were accompanied by an increase in fatty acid uptake and a decrease in fatty acid release. Interestingly, CPT1A protected against fatty acid-induced insulin resistance and expression of pro-inflammatory adipokines such as TNF-α (tumour necrosis factor-α) and IL-6 (interleukin-6) in adipocytes. Further studies demonstrated that JNK (c-Jun N terminal kinase) activity was substantially suppressed upon CPT1A overexpression, whereas knockdown or pharmacological inhibition of CPT1 caused a significant enhancement of JNK activity. The specific inhibitor of JNK SP600125 largely abolished the changes caused by the shRNA- and etomoxir-mediated decrease in CPT1 activity. Moreover, C2C12 myocytes co-cultured with adipocytes pre-treated with fatty acids displayed altered insulin sensitivity. Taken together, our findings have identified a favourable role for CPT1A in adipocytes to attenuate fatty acid-evoked insulin resistance and inflammation via suppression of JNK.

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Nuclear Factor Y in Male Mouse pancreatic β-cells Plays a Crucial Role in Glucose Homeostasis by Regulating β-Cell Mass and Insulin Secretion

10.2337/figshare.14547255 ◽

2021 ◽

Author(s):

Yin Liu ◽

Siyuan He ◽

Ruixue Zhou ◽

Xueping Zhang ◽

Shanshan Yang ◽

...

Keyword(s):

Cell Proliferation ◽

Insulin Secretion ◽

Cell Mass ◽

Physiological Role ◽

Nuclear Factor ◽

Β Cells ◽

Β Cell ◽

Pancreatic Β Cells ◽

Nuclear Factor Y

Pancreatic β-cell mass and insulin secretion are determined by the dynamic change of transcription factor expression levels in response to altered metabolic demand. Nuclear factor-Y (NF-Y) is an evolutionarily conserved transcription factor playing critical roles in multiple cellular processes. However, the physiological role of NF-Y in pancreatic β-cells is poorly understood. The present study was undertaken in a conditional knockout of Nf-ya specifically in pancreatic β-cells (Nf-ya βKO) to define the essential physiological role of NF-Y in β-cells. Nf-ya βKO mice exhibited glucose intolerance without changes in insulin sensitivity. Reduced β-cell proliferation resulting in decreased β-cell mass was observed in these mice, which was associated with disturbed actin cytoskeleton. NF-Y-deficient β-cells also exhibited impaired insulin secretion with a reduced Ca2+ influx in response to glucose, which was associated an inefficient glucose uptake into β-cells due to a decreased expression of glucose transporter 2 and a reduction in ATP production resulting from the disruption of mitochondrial integrity. This study is the first to show that NF-Y is critical for pancreatic islets homeostasis and function through regulation in β-cell proliferation, glucose uptake into β-cells, and mitochondrial energy metabolism. Modulating NF-Y expression in β-cells may therefore offer an attractive approach for therapeutic intervention.

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Regulation of insulin secretion by uncoupling protein

Biochemical Society Transactions ◽

10.1042/bst0340802 ◽

2006 ◽

Vol 34 (5) ◽

pp. 802-805 ◽

Cited By ~ 29

Author(s):

C.B. Chan ◽

N. Kashemsant

Keyword(s):

Insulin Secretion ◽

Fatty Acid ◽

Uncoupling Protein ◽

Physiological Role ◽

Atp Production ◽

Ucp2 Expression ◽

Increased Sensitivity ◽

Glucose Stimulated Insulin Secretion

UCPs (uncoupling proteins) can regulate cellular ATP production by uncoupling oxidative phosphorylation. UCP2 is expressed in islet β-cells and its induction reduces glucose-stimulated insulin secretion. Under physiological conditions, superoxide, formed as a by-product of respiration, activates UCP2. This leads to reduced ATP production, which impairs closure of the ATP-dependent K+ channels to prevent insulin secretion. It is suggested that the physiological role of UCP2 is to prevent excessive superoxide generation through a feedback loop. UCP2 induction may also alter fatty acid metabolism by altering NAD/NADH or by facilitating cycling of fatty acid anions. Recently, UCP2 has been proposed to keep insulin secretion low during starvation, a function under the control of the transcription co-repressor, surtuin-1, which has been shown to bind to the UCP2 promoter. Pathological UCP2 expression or activation may suppress glucose-stimulated insulin secretion to the extent that diabetes onset is hastened. In ob/ob mice, induction of UCP2 at age 5 weeks precedes development of insulin secretion defects and hyperglycaemia. Activating protein kinase A-dependent pathways can normalize insulin secretion in UCP2-overexpressing islets. Conversely, lowering UCP2 expression may promote increased insulin secretion. UCP2 knockout mice were protected from the diabetogenic effects of a high-fat diet and their islets exhibited increased sensitivity to glucose and elevated ATP/ADP. These results support a role for UCP2 as a gene contributing to the pathogenesis of Type 2 diabetes.

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Nuclear Factor Y in Male Mouse pancreatic β-cells Plays a Crucial Role in Glucose Homeostasis by Regulating β-Cell Mass and Insulin Secretion

10.2337/figshare.14547255.v1 ◽

2021 ◽

Author(s):

Yin Liu ◽

Siyuan He ◽

Ruixue Zhou ◽

Xueping Zhang ◽

Shanshan Yang ◽

...

Keyword(s):

Cell Proliferation ◽

Insulin Secretion ◽

Cell Mass ◽

Physiological Role ◽

Nuclear Factor ◽

Β Cells ◽

Β Cell ◽

Pancreatic Β Cells ◽

Nuclear Factor Y

Pancreatic β-cell mass and insulin secretion are determined by the dynamic change of transcription factor expression levels in response to altered metabolic demand. Nuclear factor-Y (NF-Y) is an evolutionarily conserved transcription factor playing critical roles in multiple cellular processes. However, the physiological role of NF-Y in pancreatic β-cells is poorly understood. The present study was undertaken in a conditional knockout of Nf-ya specifically in pancreatic β-cells (Nf-ya βKO) to define the essential physiological role of NF-Y in β-cells. Nf-ya βKO mice exhibited glucose intolerance without changes in insulin sensitivity. Reduced β-cell proliferation resulting in decreased β-cell mass was observed in these mice, which was associated with disturbed actin cytoskeleton. NF-Y-deficient β-cells also exhibited impaired insulin secretion with a reduced Ca2+ influx in response to glucose, which was associated an inefficient glucose uptake into β-cells due to a decreased expression of glucose transporter 2 and a reduction in ATP production resulting from the disruption of mitochondrial integrity. This study is the first to show that NF-Y is critical for pancreatic islets homeostasis and function through regulation in β-cell proliferation, glucose uptake into β-cells, and mitochondrial energy metabolism. Modulating NF-Y expression in β-cells may therefore offer an attractive approach for therapeutic intervention.

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Effects of ketone bodies on insulin release and islet-cell metabolism in the rat

Biochemical Journal ◽

10.1042/bj2120371 ◽

1983 ◽

Vol 212 (2) ◽

pp. 371-377 ◽

Cited By ~ 25

Author(s):

T J Biden ◽

K W Taylor

Keyword(s):

Insulin Secretion ◽

Insulin Release ◽

Islet Cell ◽

Response Curve ◽

Ketone Bodies ◽

Cell Metabolism ◽

Insulin Response ◽

Physiological Role ◽

Oxidation Rates

Ketone bodies promote insulin secretion from isolated rat pancreatic islets in the presence of 5 mM-glucose, but are ineffective in its absence. At concentrations of 10 mM or less, the relative abilities of the ketone bodies to potentiate release are in the order D-3-hydroxybutyrate greater than DL-3-hydroxybutyrate greater than acetoacetate. The response curve relating insulin release to D-3-hydroxybutyrate concentration displays a threshold at 1 mM and a maximum at 10 mM. D-3-Hydroxybutyrate (5 mM, but not 10 mM) promotes insulin secretion in the presence of 5 mM concentrations of both L-arginine and DL-glyceraldehyde, but not with L-leucine, L-alanine, L-glutamate or 4-methyl-2-oxopentanoate. The oxidation rates of the exogenous ketone bodies do not correlate well with their capacities to promote insulin release. Moreover, the oxidation of 5 mM-D-3-hydroxybutyrate can be inhibited by 25% with methylmalonate (10 mM) without any diminution of release. The potentiation with D-3-hydroxybutyrate occurs without an observable increase in total islet cyclic AMP. However, a small net efflux matches the relative abilities of the ketone bodies to promote insulin release. With islets from 48 h-starved animals the insulin response is both diminished and less sensitive than in fed animals, since insulin secretion is not significantly raised until a threshold of 5 mM-D-3-hydroxybutyrate is reached. These results suggest that, in the rat at least, there should be a reappraisal of the physiological role of ketone bodies in the promotion of insulin release.

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Role of nitric oxide and prostaglandins in the regulation of blood pressure in conscious rats

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y95-089 ◽

1995 ◽

Vol 73 (6) ◽

pp. 693-698 ◽

Cited By ~ 9

Author(s):

Andrés C. Inglés ◽

Francisco J. Ruiz ◽

Miguel G. Salom ◽

Tomás Quesada ◽

Luis F. Carbonell

Keyword(s):

Nitric Oxide ◽

Blood Pressure ◽

Methyl Ester ◽

Pressor Response ◽

Specific Inhibitor ◽

Renin Angiotensin System ◽

Conscious Rats ◽

Endogenous Nitric Oxide ◽

Regulation Of Blood Pressure

The present study was designed to investigate the possible role of endothelium-derived vasodilators, nitric oxide and prostaglandins, in the regulation of blood pressure during the presence and absence of the major pressor systems. Conscious rats were infused with a cocktail of inhibitors of the sympathetic nervous system, renin–angiotensin system, and V1 vascular receptor to vasopressin (achieved with hexamethonium, captopril, phentolamine, propranolol, and the V1 vasopressin (AVP) antagonist des-(CH2)5Tyr(Me)-AVP). The cocktail of vasoconstrictor inhibitors induced a marked fall of mean arterial pressure (MAP) from 109 ± 2 to 52 ± 2 mmHg (1 mmHg = 133.3 Pa) (n = 24). In animals with blockade, the specific inhibitor of nitric oxide synthesis, NG-nitro-L-arginine methyl ester (L-NAME), induced a significant increase of MAP from 51 ± 1 to 84 ± 2 mmHg (n = 6). In the presence of indomethacin, a cyclooxygenase inhibitor, the pressor response to L-NAME was from 52 ± 2 to 126 ± 4 mmHg (n = 6). Neither indomethacin (n = 6) nor vehicle (n = 6) alone altered MAP. In intact animals without blockade, L-NAME caused a similar increase of MAP when it was injected alone (from 107 ± 3 to 144 ± 4 mmHg, n = 7) or with indomethacin (from 113 ± 3 to 144 ± 3, n = 6). Indomethacin alone (n = 8) did not change MAP. In conclusion, in the absence of the major pressor systems, the pressor effect of the inhibition of the production of endogenous nitric oxide and vasodilator prostanoid synthesis appears to be synergistic. These results suggest that these two endogenous vasodilators are involved in the maintenance of blood pressure.Key words: nitric oxide, NG-nitro-L-arginine methyl ester, prostaglandins, blood pressure.

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