| 1. |
- Fex, Malin, et al.
(författare)
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{beta}-Cell Lipases and Insulin Secretion.
- 2006
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Ingår i: Diabetes. - 1939-327X. ; 55:Suppl 2, s. 24-31
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Tidskriftsartikel (refereegranskat)abstract
- Lipids have been implicated in ß-cell stimulus-secretion coupling. Thus, lipases in ß-cells would be required to generate coupling factors from intracellular lipids. Indeed, we found that glucose stimulates lipolysis in rodent islets and clonal ß-cells. Lipolysis and diglyceride lipase activity in islets are abolished by orlistat, a pan-lipase inhibitor. Moreover, orlistat dose-dependently inhibits glucose- and forskolin-stimulated insulin secretion, while leaving glucose oxidation and the rise in ATP-to-ADP ratio intact. In an effort to identify ß-cell lipase(s), we found that hormone-sensitive lipase (HSL), the rate-limiting enzyme for acylglyceride hydrolysis in adipocytes, is active in rodent ß-cells. To further address the role of HSL, a global and ß-cell–specific inactivation, respectively, of the lipase has been created in mice. Whereas our line of HSL null mice is moderately glucose intolerant due to reduced peripheral insulin sensitivity, it exhibits normal islet metabolism and insulin secretion. Preliminary analysis of the ß-cell–specific HSL knockout has revealed no evidence for disturbed islet function. Thus, studies of ours and others indicate that there is a complex lipid regulatory component in ß-cell stimulus-secretion coupling. The role of HSL and other lipases needs to be further clarified to provide a balanced view of the role of lipids and lipolysis in ß-cells.
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| 2. |
- Härndahl, Linda, et al.
(författare)
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Beta-cell-targeted overexpression of phosphodiesterase 3B in mice causes impaired insulin secretion, glucose intolerance, and deranged islet morphology.
- 2004
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Ingår i: The Journal of biological chemistry. - 0021-9258 .- 1083-351X. ; 279:15, s. 15214-22
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Tidskriftsartikel (refereegranskat)abstract
- The second messenger cAMP mediates potentiation of glucose-stimulated insulin release. Use of inhibitors of cAMP-hydrolyzing phosphodiesterase (PDE) 3 and overexpression of PDE3B in vitro have demonstrated a regulatory role for this enzyme in insulin secretion. In this work, the physiological significance of PDE3B-mediated degradation of cAMP for the regulation of insulin secretion in vivo and glucose homeostasis was investigated in transgenic mice overexpressing PDE3B in pancreatic beta-cells. A 2-fold overexpression of PDE3B protein and activity blunted the insulin response to intravenous glucose, resulting in reduced glucose disposal. The effects were "dose"-dependent because mice overexpressing PDE3B 7-fold failed to increase insulin in response to glucose and hence exhibited pronounced glucose intolerance. Also, the insulin secretory response to intravenous glucagon-like peptide 1 was reduced in vivo. Similarly, islets stimulated in vitro exhibited reduced insulin secretory capacity in response to glucose and glucagon-like peptide 1. Perifusion experiments revealed that the reduction specifically affected the first phase of glucose-stimulated insulin secretion. Furthermore, morphological examinations demonstrated deranged islet cytoarchitecture. In conclusion, these results are consistent with an essential role for PDE3B in cAMP-mediated regulation of insulin release and glucose homeostasis.
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| 3. |
- Mulder, Hindrik, et al.
(författare)
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Hormone-sensitive lipase null mice exhibit signs of impaired insulin sensitivity whereas insulin secretion is intact.
- 2003
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Ingår i: Journal of Biological Chemistry. - 1083-351X .- 0021-9258. ; 278:38, s. 36380-36388
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Tidskriftsartikel (refereegranskat)abstract
- Lipid metabolism plays an important role in glucose homeostasis under normal and pathological conditions. In adipocytes, skeletal muscle, and pancreatic beta-cells, lipids are mobilized from acylglycerides by the hormone-sensitive lipase (HSL). Here, the consequences of a targeted disruption of the HSL gene for glucose homeostasis were examined. HSL null mice were slightly hyperglycemic in the fasted, but not fed state, which was accompanied by moderate hyperinsulinemia. During glucose challenges, however, disposal of the sugar was not affected in HSL null mice, presumably because of release of increased amounts of insulin. Impaired insulin sensitivity was further indicated by retarded glucose disposal during an insulin tolerance test. A euglycemic hyperinsulinemic clamp revealed that hepatic glucose production was insufficiently blocked by insulin in HSL null mice. In vitro, insulin-stimulated glucose uptake into soleus muscle, and lipogenesis in adipocytes were moderately reduced, suggesting additional sites of insulin resistance. Morphometric analysis of pancreatic islets revealed a doubling of beta-cell mass in HSL null mice, which is consistent with an adaptation to insulin resistance. Insulin secretion in vitro, examined by perifusion of isolated islets, was not impacted by HSL deficiency. Thus, HSL deficiency results in a moderate impairment of insulin sensitivity in multiple target tissues of the hormone but is compensated by hyperinsulinemia.
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| 4. |
- Mulder, Hindrik, et al.
(författare)
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Hormone-sensitive lipase, the rate-limiting enzyme in triglyceride hydrolysis, is expressed and active in beta-cells
- 1999
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Ingår i: Diabetes. - 1939-327X. ; 48:1, s. 228-232
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Tidskriftsartikel (refereegranskat)abstract
- Triglycerides in the beta-cell may be important for stimulus-secretion coupling, through provision of a lipid-derived signal, and for pathogenetic events in NIDDM, where lipids may adversely affect beta-cell function. In adipose tissues, hormone-sensitive lipase (HSL) is rate-limiting in triglyceride hydrolysis. Here, we investigated whether this enzyme is also expressed and active in beta-cells. Northern blot analysis and reverse transcription-polymerase chain reaction demonstrated that HSL is expressed in rat islets and in the clonal beta-cell lines INS-1, RINm5F, and HIT-T15. Western blot analysis identified HSL in mouse and rat islets and the clonal beta-cells. In mouse and rat, immunocytochemistry showed a predominant occurrence of HSL in beta-cells, with a presumed cytoplasmic localization. Lipase activity in homogenates of the rodent islets and clonal beta-cells constituted 2.1 +/- 0.6% of that in adipocytes; this activity was immunoinhibited by use of antibodies to HSL. The established HSL expression and activity in beta-cells offer a mechanism whereby lipids are mobilized from intracellular stores. Because HSL in adipocytes is activated by cAMP-dependent protein kinase (PKA), PKA-regulated triglyceride hydrolysis in beta-cells may participate in the regulation of insulin secretion, possibly by providing a lipid-derived signal, e.g., long-chain acyl-CoA and diacylglycerol.
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| 5. |
- Mulder, Hindrik, et al.
(författare)
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Inhibition of lipase activity and lipolysis in rat islets reduces insulin secretion.
- 2004
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 53:1, s. 122-128
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Tidskriftsartikel (refereegranskat)abstract
- Lipids may serve as coupling factors in KATP-independent glucose sensing in β-cells. We have previously demonstrated that β-cells harbor lipase activities, one of which is the hormone-sensitive lipase. Whether β-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 KATP-independent glucose sensing has been perturbed. Thus, β-cell lipase activity is involved in GSIS, emphasizing the important role of β-cell lipid metabolism for insulin secretion.
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| 6. |
- Stenson, Lena, et al.
(författare)
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Protein kinase B is expressed in pancreatic beta cells and activated upon stimulation with insulin-like growth factor I
- 1998
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Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 250:1, s. 181-186
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Tidskriftsartikel (refereegranskat)abstract
- Protein kinase B (PKB) is involved in signaling to a multitude of important cellular events and is activated by insulin and growth factors, including insulin-like growth factor I (IGF-I). We show here expression of PKB in pancreatic islets and in the beta cell lines HIT-T15, INS-1, and RINm5F. Expression of PKB mRNA and the presence of PKB isoforms (alpha, beta, and gamma) were assessed by Northern blot analysis and RT-PCR, respectively. Antibodies recognizing different parts of PKB isoforms were employed to demonstrate PKB protein expression by immunoblot analysis. By use of immunohistochemistry in rat and mouse pancreatic tissue sections, PKB was localized to predominantly beta cells. Regulation of PKB was examined in INS-1 and RINm5F cells; upon stimulation with IGF-I (5-10 min), PKB was phosphorylated and activated (approximately 3-fold) by a wortmannin-sensitive mechanism, indicating involvement of phosphatidylinositol-3 kinase. The possible participation of PKB in signal transduction pathways modulating cAMP-dependent insulin secretion and in proliferation of beta cells is discussed.
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