Evidence for a multi‐domain structure for hormone‐sensitive lipase

Smith, Gabriele M.; Garton, Andrew J.; Aitken, Alastair; Yeaman, Stephen J.

doi:10.1016/0014-5793(96)01076-9

Cited by 27 publications

(25 citation statements)

References 22 publications

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“…Despite these features, it is known that orlistat at high concentrations traverses cellular membranes (35) and blocks intracellular lipases (14,36). Orlistat binds irreversibly to the catalytic site of lipases and has been shown to inhibit HSL (13). Here, we were able to show that acute exposure to glucose stimulated lipolysis in rat islets.…”

Section: Fig 3 Diglyceride Lipase Activity In Rat Islets Islets Frmentioning

confidence: 62%

“…To circumvent the issue of which particular lipase accounts for hydrolysis of acylglycerides in pancreatic ␤-cells, we used an inhibitor of a wide spectrum of lipases. Our choice was tetrahydrolipstatin, or orlistat, which is a lipophilic molecule that irreversibly binds to the catalytic site of a great number of lipases (13) and which has previously been shown to inhibit cAMPinduced insulin secretion in the clonal ␤-cell line HIT-T15 (14) and glucagon-like peptide 1 (GLP-1)-stimulated secretion in rat islets (15). The drug is widely used for treatment of obesity (16); it inhibits intestinal lipases, preventing uptake of lipids and thereby restricting caloric input.…”

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confidence: 99%

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Inhibition of Lipase Activity and Lipolysis in Rat Islets Reduces Insulin Secretion

et al. 2004

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Lipids may serve as coupling factors in K ATP -independent glucose sensing in ␤-cells. We have previously demonstrated that ␤-cells harbor lipase activities, one of which is the hormone-sensitive lipase. Whether ␤-cell lipases are critical for glucose-stimulated insulin secretion (GSIS) by providing lipid-derived signals from endogenous lipids is unknown. Therefore, using a lipase inhibitor (orlistat), we examined whether lipase inhibition reduces insulin secretion. Islet lipolysis stimulated by glucose and diglyceride lipase activity was abolished by orlistat. Incubation of rat islets with orlistat dose dependently inhibited GSIS; this inhibition was reversed by 1 mmol/l palmitate, suggesting that orlistat acts via impaired formation of an acylglyceride-derived coupling signal. Orlistat inhibited the potentiating effect of forskolin on GSIS, an effect proposed to be due to activation of a lipase. In perifused islets, orlistat attenuated mainly the second phase of insulin secretion. Because the rise in islet ATP/ADP levels in response to glucose and oxidation of the sugar were unaffected by orlistat whereas the second phase of insulin secretion was reduced, it seems likely that a lipid coupling factor involved in K ATP -independent glucose sensing has been perturbed. Thus, ␤-cell lipase activity is involved in GSIS, emphasizing the important role of ␤-cell lipid metabolism for insulin secretion. Diabetes 53:122-128, 2004A large body of evidence suggests that lipids are required for appropriate glucose sensing in pancreatic ␤-cells. For instance, when triglycerides in pancreatic islets are depleted by hyperleptinemia, pancreatic ␤-cells fail to release insulin (1). Along similar lines, perfused pancreas from fasted rats is unresponsive to a rise in glucose (2). Importantly, in both cases, glucose responsiveness is reinstated by the addition of exogenous fatty acids.The current view holds that lipids serve as coupling factors in glucose-stimulated insulin secretion (GSIS) that does not rely on closure of the ATP-sensitive K ϩ channel (K ATP independent) (3). These putative mechanisms presumably drive the second phase of GSIS and accordingly have been termed as amplifying (4), and the coupling factors have been proposed to emanate from intermediary metabolism in the ␤-cell (5). Against this background, lipids have become attractive candidates for coupling factors in K ATP -independent glucose sensing. In fact, a model has been proposed to delineate the combined events in metabolism of glucose and lipids that result in a dose-dependent regulation of insulin secretion, the socalled long-chain acyl-CoA hypothesis (3). This model is based on the observations that an increase in glucose metabolism in ␤-cells results in decreased oxidation of fats while esterification of lipids increases. As a consequence, the levels of complex lipids rise, perhaps acyl-CoA moieties, which then act as a signaling molecules coupling stimulus to secretion in the ␤-cell. We have previously demonstrated that different preparations of ␤-cells...

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Section: Fig 3 Diglyceride Lipase Activity In Rat Islets Islets Frmentioning

confidence: 62%

mentioning

confidence: 99%

Inhibition of Lipase Activity and Lipolysis in Rat Islets Reduces Insulin Secretion

et al. 2004

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“…Lipolysis inhibition by Orlistat abolishes glucosestimulated lipolysis and markedly reduces insulin secretion in ZF islets Orlistat binds to the catalytic site of numerous lipases, including HSL [17,22]. Previously, inhibition of lipolysis by Orlistat in normal rat islets has been shown to inhibit GSIS, suggesting a role for lipolysis in normal insulin secretion [17].…”

Section: Fatty Acid Partitioning Into Oxidation and Esterification Pamentioning

confidence: 99%

Beta cell compensation for insulin resistance in Zucker fatty rats: increased lipolysis and fatty acid signalling

et al. 2006

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Aims/hypothesis The aim of this study was to determine the role of fatty acid signalling in islet beta cell compensation for insulin resistance in the Zucker fatty fa/fa (ZF) rat, a genetic model of severe obesity, hyperlipidaemia and insulin resistance that does not develop diabetes. Materials and methods NEFA augmentation of insulin secretion and fatty acid metabolism were studied in isolated islets from ZF and Zucker lean (ZL) control rats. Results Exogenous palmitate markedly potentiated glucosestimulated insulin secretion (GSIS) in ZF islets, allowing robust secretion at physiological glucose levels (5-8 mmol/l).Exogenous palmitate also synergised with glucagon-like peptide-1 and the cyclic AMP-raising agent forskolin to enhance GSIS in ZF islets only. In assessing islet fatty acid metabolism, we found increased glucose-responsive palmitate esterification and lipolysis processes in ZF islets, suggestive of enhanced triglyceride-fatty acid cycling. Interruption of glucose-stimulated lipolysis by the lipase inhibitor Orlistat (tetrahydrolipstatin) blunted palmitate-augmented GSIS in ZF islets. Fatty acid oxidation was also higher at intermediate glucose levels in ZF islets and steatotic triglyceride accumulation was absent. Conclusions/interpretationThe results highlight the potential importance of NEFA and glucoincretin enhancement of insulin secretion in beta cell compensation for insulin resistance. We propose that coordinated glucose-responsive fatty acid esterification and lipolysis processes, suggestive of triglyceride-fatty acid cycling, play a role in the coupling mechanisms of glucose-induced insulin secretion as well as in beta cell compensation and the hypersecretion of insulin in obesity.

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“…Forskolin increased glucose-stimulated insulin secretion, and this incretin effect was progressively and largely diminished by 30 min preincubation of the cells with increasing concentrations of the lipase inhibitor orlistat (tetrahydrolipstatin) (26)(27)(28) (Fig. 8).…”

Section: Inhibition Of the Incretin Effect By A Lipase Inhibitormentioning

confidence: 99%

Glucagon-Like Peptide 1 Stimulates Lipolysis in Clonal Pancreatic β-Cells (HIT)

et al. 2001

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Glucagon-like peptide 1 (GLP-1) is the most potent physiological incretin for insulin secretion from the pancreatic ␤-cell, but its mechanism of action has not been established. It interacts with specific cell-surface receptors, generates cAMP, and thereby activates protein kinase A (PKA). Many changes in pancreatic ␤-cell function have been attributed to PKA activation, but the contribution of each one to the secretory response is unknown. We show here for the first time that GLP-1 rapidly released free fatty acids (FFAs) from cellular stores, thereby lowering intracellular pH (pH i ) and stimulating FFA oxidation in clonal ␤-cells (HIT). Similar changes were observed with forskolin, suggesting that stimulation of lipolysis was a function of PKA activation in ␤-cells. G lucagon-like peptide 1 (GLP-1) is the most potent potentiator of glucose-induced insulin secretion that has been described (1,2). This peptide causes the elevation of cAMP and the activation of protein kinase A (PKA) (3); however, it releases insulin only in the presence of stimulatory glucose (4) and thus serves as an incretin rather than a secretagogue (5). Activation of PKA leads to phosphorylation of multiple ␤-cell proteins, many of which have been hypothesized to play a role in insulin secretion (6-8). The nature of the endogenous substrates for PKA that may potentiate insulin secretion is unknown. Because the islet contains large stores of triglycerides (9), particularly in diabetes (10), another possible role of the normal rise in cAMP could be to stimulate lipolysis (via lipase activation), thereby providing the cell with free fatty acids (FFAs). Recent research on hormone-sensitive lipase (HSL) in ␤-cells yielded results consistent with that notion (11). The released FFAs may directly effect secretion, or they may do so indirectly via generation of other lipids, including the putative long-chain acyl CoA (LC-CoA) signal, diacylglycerol (DAG), and phosphatidic acid (PA) (12). The acute addition of exogenous FFAs is also known to enhance glucose-stimulated secretion (9,13-15).We have shown in previous studies that added FFAs cause acidification in ␤-cells (16) and fat cells (17) as a consequence of the flip-flop mechanism of diffusion across the plasma membrane (16,17). Furthermore, we have shown in adipocytes that the elevation of cAMP stimulates lipolysis, with a resulting decrease in the intracellular pH (pH i ) caused by the release of FFAs, which become partially ionized (17). Therefore, in this study we assessed whether GLP-1 has a similar effect on lipolysis in ␤-cells. Our data show a decrease in pH i and a release of FFAs by agents that increase cAMP, presumably via activation of HSL. Furthermore, the incretin effect was largely diminished by a lipase inhibitor, whereas glucose-stimulated secretion was less affected. These findings indicate that cAMP-mediated lipolysis may play an important role in ␤-cell signal transduction and the incretin effect of GLP-1. RESEARCH DESIGN AND METHODSGrowth and incubation of cells. Clonal pancr...

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Evidence for a multi‐domain structure for hormone‐sensitive lipase

Cited by 27 publications

References 22 publications

Inhibition of Lipase Activity and Lipolysis in Rat Islets Reduces Insulin Secretion

Inhibition of Lipase Activity and Lipolysis in Rat Islets Reduces Insulin Secretion

Beta cell compensation for insulin resistance in Zucker fatty rats: increased lipolysis and fatty acid signalling

Glucagon-Like Peptide 1 Stimulates Lipolysis in Clonal Pancreatic β-Cells (HIT)

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