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Jung SR, Reed BJ, Sweet IR. A highly energetic process couples calcium influx through L-type calcium channels to insulin secretion in pancreatic beta-cells. Am J Physiol Endocrinol Metab 2009; 297:E717-27. [PMID: 19584201 PMCID: PMC2739700 DOI: 10.1152/ajpendo.00282.2009] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Calcium (Ca(2+)) influx is required for the sustained secretion of insulin and is accompanied by a large rate of energy usage. We hypothesize that the energy usage reflects a process [Ca(2+)/metabolic coupling process (CMCP)] that couples Ca(2+) to insulin secretion by pancreatic islets. The aim of the study was to test this hypothesis by testing the effect of inhibiting candidate Ca(2+)-sensitive proteins proposed to play a critical role in the CMCP. The effects of the inhibitors on oxygen consumption rate (OCR), a reflection of ATP usage, and insulin secretion rate (ISR) were compared with those seen when L-type Ca(2+) channels were blocked with nimodipine. We reasoned that if a downstream Ca(2+)-regulated site was responsible for the OCR associated with the CMCP, then its inhibition should mimic the effect of nimodipine. Consistent with previous findings, nimodipine decreased glucose-stimulated OCR by 36% and cytosolic Ca(2+) by 46% and completely suppressed ISR in rat pancreatic islets. Inhibitors of three calmodulin-sensitive proteins (myosin light-chain kinase, calcineurin, and Ca(2+)/calmodulin-dependent protein kinase II) did not meet the criteria. In contrast, KN-62 severed the connection between Ca(2+) influx, OCR, and ISR without interfering with Ca(2+) influx. In the presence of nimodipine or KN-62, potentiators of ISR, acetylcholine, GLP-1, and arginine had little effect on insulin secretion, suggesting that the CMCP is also essential for the amplification of ISR. In conclusion, a KN-62-sensitive process directly mediates the effects of Ca(2+) influx via L-type Ca(2+) channels on OCR and ISR, supporting the essential role of the CMCP in mediating ISR.
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Affiliation(s)
- Seung-Ryoung Jung
- Dept. of Medicine, Diabetes and Obesity Center of Excellence, Univ. of Washington at South Lake Union, 815 Mercer St, Seattle, WA 98195-8055, USA
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52
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Sweet IR, Gilbert M, Maloney E, Hockenbery DM, Schwartz MW, Kim F. Endothelial inflammation induced by excess glucose is associated with cytosolic glucose 6-phosphate but not increased mitochondrial respiration. Diabetologia 2009; 52:921-31. [PMID: 19219423 PMCID: PMC2741088 DOI: 10.1007/s00125-009-1272-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2008] [Accepted: 01/08/2009] [Indexed: 10/21/2022]
Abstract
AIMS/HYPOTHESIS Exposure of endothelial cells to high glucose levels suppresses responses to insulin, including induction of endothelial nitric oxide synthase activity, through pro-inflammatory signalling via the inhibitor of nuclear factor kappaB (IkappaB)alpha-nuclear factor kappaB (NF-kappaB) pathway. In the current study, we aimed to identify metabolic responses to glucose excess that mediate endothelial cell inflammation and insulin resistance. Since endothelial cells decrease their oxygen consumption rate (OCR) in response to glucose, we hypothesised that increased mitochondrial function would not mediate these cells' response to excess substrate. METHODS The effects of glycolytic and mitochondrial fuels on metabolic intermediates and end-products of glycolytic and oxidative metabolism, including glucose 6-phosphate (G6P), lactate, CO(2), NAD(P)H and OCR, were measured in cultured human microvascular endothelial cells and correlated with IkappaBalpha phosphorylation. RESULTS In response to increases in glucose concentration from low to physiological levels (0-5 mmol/l), production of G6P, lactate, NAD(P)H and CO(2) each increased as expected, while OCR was sharply reduced. IkappaBalpha activation was detected at glucose concentrations >5 mmol/l, which was associated with parallel increases of G6P levels, whereas downstream metabolic pathways were insensitive to excess substrate. CONCLUSIONS/INTERPRETATION Phosphorylation of IkappaBalpha by excess glucose correlates with increased levels of the glycolytic intermediate G6P, but not with lactate generation or OCR, which are inhibited well below saturation levels at physiological glucose concentrations. These findings suggest that oxidative stress due to increased mitochondrial respiration is unlikely to mediate endothelial inflammation induced by excess glucose and suggests instead the involvement of G6P accumulation in the adverse effects of hyperglycaemia on endothelial cells.
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Affiliation(s)
- I R Sweet
- Department of Medicine, Diabetes and Obesity Center of Excellence, University of Washington at South Lake Union, Seattle, Washington 98195-8055, USA.
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53
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Orr C, Scott S, Kandeel F, Ferreri K. PFA: program for the quantitative assessment of cell metabolism by spectral data analysis. Bioinformation 2009; 3:65-7. [PMID: 19238198 PMCID: PMC2639676 DOI: 10.6026/97320630003065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Accepted: 09/17/2008] [Indexed: 11/25/2022] Open
Abstract
Assessment of mitochondrial oxidative metabolism has wide-ranging importance, from pharmacokinetic analysis to studies in
cell viability and apoptosis. Here we present the Perfusion File Analyzer (PFA) application for the real-time analysis of
spectral data to measure cytochrome c reduction, cytochrome a3 reduction, and other parameters important to cellular
metabolism, which are collected during tissue perfusion experiments. Our current efforts are focused on quantitating
changes in mitochondrial function by normalizing baseline drift of spectral data while addressing two major challenges:
(1) a lack of real-time feedback from the system when aiming is compromised, and (2) an inability to adjust calculated data
in the event of spectral shift. PFA has been developed to address these issues, and is currently used for quality assessment
of human islets prior to clinical transplantation.
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Affiliation(s)
- Chris Orr
- Southern California Islet Cell Resources Center, Department of Diabetes, Endocrinology, and Metabolism, Beckman Research Institute of the City of Hope, Duarte, CA, USA.
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54
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Suckow AT, Comoletti D, Waldrop MA, Mosedale M, Egodage S, Taylor P, Chessler SD. Expression of neurexin, neuroligin, and their cytoplasmic binding partners in the pancreatic beta-cells and the involvement of neuroligin in insulin secretion. Endocrinology 2008; 149:6006-17. [PMID: 18755801 PMCID: PMC2613060 DOI: 10.1210/en.2008-0274] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The composition of the beta-cell exocytic machinery is very similar to that of neuronal synapses, and the developmental pathway of beta-cells and neurons substantially overlap. beta-Cells secrete gamma-aminobutyric acid and express proteins that, in the brain, are specific markers of inhibitory synapses. Recently, neuronal coculture experiments have identified three families of synaptic cell-surface molecules (neurexins, neuroligins, and SynCAM) that drive synapse formation in vitro and that control the differentiation of nascent synapses into either excitatory or inhibitory fully mature nerve terminals. The inhibitory synapse-like character of the beta-cells led us to hypothesize that members of these families of synapse-inducing adhesion molecules would be expressed in beta-cells and that the pattern of expression would resemble that associated with neuronal inhibitory synaptogenesis. Here, we describe beta-cell expression of the neuroligins, neurexins, and SynCAM, and show that neuroligin expression affects insulin secretion in INS-1 beta-cells and rat islet cells. Our findings demonstrate that neuroligins and neurexins are expressed outside the central nervous system and help confer an inhibitory synaptic-like phenotype onto the beta-cell surface. Analogous to their role in synaptic neurotransmission, neurexin-neuroligin interactions may play a role in the formation of the submembrane insulin secretory apparatus.
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Affiliation(s)
- Arthur T Suckow
- Department of Medicine, Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, California 92093, USA
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55
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Cummings BP, Digitale EK, Stanhope KL, Graham JL, Baskin DG, Reed BJ, Sweet IR, Griffen SC, Havel PJ. Development and characterization of a novel rat model of type 2 diabetes mellitus: the UC Davis type 2 diabetes mellitus UCD-T2DM rat. Am J Physiol Regul Integr Comp Physiol 2008; 295:R1782-93. [PMID: 18832086 PMCID: PMC2685302 DOI: 10.1152/ajpregu.90635.2008] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2008] [Accepted: 09/26/2008] [Indexed: 12/18/2022]
Abstract
The prevalence of type 2 diabetes (T2DM) is increasing, creating a need for T2DM animal models for the study of disease pathogenesis, prevention, and treatment. The purpose of this project was to develop a rat model of T2DM that more closely models the pathophysiology of T2DM in humans. The model was created by crossing obese Sprague-Dawley rats with insulin resistance resulting from polygenic adult-onset obesity with Zucker diabetic fatty-lean rats that have a defect in pancreatic beta-cell function but normal leptin signaling. We have characterized the model with respect to diabetes incidence; age of onset; longitudinal measurements of glucose, insulin, and lipids; and glucose tolerance. Longitudinal fasting glucose and insulin data demonstrated progressive hyperglycemia (with fasting and fed glucose concentrations >250 and >450 mg/dl, respectively) after onset along with hyperinsulinemia resulting from insulin resistance at onset followed by a progressive decline in circulating insulin concentrations, indicative of beta-cell decompensation. The incidence of diabetes in male and female rats was 92 and 43%, respectively, with an average age of onset of 6 mo in males and 9.5 mo in females. Results from intravenous glucose tolerance tests, pancreas immunohistochemistry, and islet insulin content further support a role for beta-cell dysfunction in the pathophysiology of T2DM in this model. Diabetic animals also exhibit glycosuria, polyuria, and hyperphagia. Thus diabetes in the UC Davis-T2DM rat is more similar to clinical T2DM in humans than in other existing rat models and provides a useful model for future studies of the pathophysiology, treatment, and prevention of T2DM.
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Affiliation(s)
- Bethany P Cummings
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, One Shields Ave., Davis, CA 95616, USA
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56
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Gilbert M, Jung SR, Reed BJ, Sweet IR. Islet oxygen consumption and insulin secretion tightly coupled to calcium derived from L-type calcium channels but not from the endoplasmic reticulum. J Biol Chem 2008; 283:24334-42. [PMID: 18593707 DOI: 10.1074/jbc.m802097200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The aim of the study was to test whether the source of intracellular calcium (Ca2+) is a determinant of beta cell function. We hypothesized that elevations in cytosolic Ca2+ caused by the release of Ca2+ from the endoplasmic reticulum (ER) have little physiologic impact on oxygen consumption and insulin secretion. Ca2+ release from the ER was induced in isolated rat islets by acetylcholine and response of oxygen consumption rate (OCR), NAD(P)H, cytosolic Ca2+, and insulin secretory rate (ISR) were measured. Glucose increased all four parameters, and thereafter acetylcholine further increased cytosolic Ca2+, OCR, and ISR. To assess the contribution of Ca2+ release from the ER in mediating the effects of acetylcholine, ER Ca2+ stores were first emptied by inhibiting the sarcoendoplasmic reticulum Ca2+-ATPase, which subsequently reduced the effect of acetylcholine on cytosolic Ca2+ but not its effects on OCR or ISR. As predicted, OCR and ISR were acutely sensitive to changes in L-type Ca2+ channel activity; nimodipine completely inhibited glucose-stimulated ISR and suppressed OCR by 36%, despite only inhibiting cytosolic Ca2+ by 46%. Moreover, in the presence of nimodipine and high glucose, acetylcholine still elevated cytosolic Ca2+ levels above those observed in the presence of high glucose alone but did not significantly stimulate ISR. In conclusion, Ca2+ flux through L-type Ca2+ channels was tightly coupled to changes in OCR and ISR. In contrast, the results obtained support the notion that Ca2+ release from the ER has little or no access to the intracellular machinery that regulates OCR and ISR.
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Affiliation(s)
- Merle Gilbert
- Department of Medicine, University of Washington, Seattle, Washington 98195, USA
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57
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Raffo A, Hancock K, Polito T, Andan G, Witkowski P, Hardy M, Barba P, Ferrara C, Maffei A, Freeby M, Goland R, Leibel RL, Sweet I, Harris PE. Role of vesicular monoamine transporter type 2 in rodent insulin secretion and glucose metabolism revealed by its specific antagonist tetrabenazine. J Endocrinol 2008; 198:41-9. [PMID: 18577569 PMCID: PMC2712213 DOI: 10.1677/joe-07-0632] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Despite different embryological origins, islet beta-cells and neurons share the expression of many genes and display multiple functional similarities. One shared gene product, vesicular monoamine transporter type 2 (VMAT2, also known as SLC18A2), is highly expressed in human beta-cells relative to other cells in the endocrine and exocrine pancreas. Recent reports suggest that the monoamine dopamine is an important paracrine and/or autocrine regulator of insulin release by beta-cells. Given the important role of VMAT2 in the economy of monoamines such as dopamine, we investigated the possible role of VMAT2 in insulin secretion and glucose metabolism. Using a VMAT2-specific antagonist, tetrabenazine (TBZ), we studied glucose homeostasis, insulin secretion both in vivo and ex vivo in cultures of purified rodent islets. During intraperitoneal glucose tolerance tests, control rats showed increased serum insulin concentrations and smaller glucose excursions relative to controls after a single intravenous dose of TBZ. One hour following TBZ administration we observed a significant depletion of total pancreas dopamine. Correspondingly, exogenous L-3,4-dihydroxyphenylalanine reversed the effects of TBZ on glucose clearance in vivo. In in vitro studies of rat islets, a significantly enhanced glucose-dependent insulin secretion was observed in the presence of dihydrotetrabenazine, the active metabolite of TBZ. Together, these data suggest that VMAT2 regulates in vivo glucose homeostasis and insulin production, most likely via its role in vesicular transport and storage of monoamines in beta-cells.
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Affiliation(s)
- Anthony Raffo
- Department of Medicine of Columbia University Medical Center, New York, NY, 10032, USA
| | - Kolbe Hancock
- Barnard College, Columbia University, New York, NY 10027, USA
| | - Teresa Polito
- Department of Medicine of Columbia University Medical Center, New York, NY, 10032, USA
| | - Gordon Andan
- Department of Surgery of Columbia University Medical Center, New York, NY, 10032, USA
| | - Piotr Witkowski
- Department of Surgery of Columbia University Medical Center, New York, NY, 10032, USA
- Dept of Surgery, Medical University of Gdansk, Poland
| | - Mark Hardy
- Department of Surgery of Columbia University Medical Center, New York, NY, 10032, USA
| | - Pasquale Barba
- Institute of Genetics and Biophysics "Adriano Buzzati-Traverso", CNR, Naples, 80131, Italy
| | - Caterina Ferrara
- Institute of Genetics and Biophysics "Adriano Buzzati-Traverso", CNR, Naples, 80131, Italy
| | - Antonella Maffei
- Department of Medicine of Columbia University Medical Center, New York, NY, 10032, USA
- Institute of Genetics and Biophysics "Adriano Buzzati-Traverso", CNR, Naples, 80131, Italy
| | - Matthew Freeby
- Department of Medicine of Columbia University Medical Center, New York, NY, 10032, USA
| | - Robin Goland
- Naomi Berrie Diabetes Center, Columbia University Medical Center, New York, NY 10032, USA
| | - Rudolph L. Leibel
- Naomi Berrie Diabetes Center, Columbia University Medical Center, New York, NY 10032, USA
| | - Ian Sweet
- Department of Medicine, University of Washington, Seattle, WA 98195, USA
| | - Paul E. Harris
- Department of Medicine of Columbia University Medical Center, New York, NY, 10032, USA
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58
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Sweet IR, Yanay O, Waldron L, Gilbert M, Fuller JM, Tupling T, Lernmark A, Osborne WRA. Treatment of diabetic rats with encapsulated islets. J Cell Mol Med 2008; 12:2644-50. [PMID: 18373735 PMCID: PMC3828880 DOI: 10.1111/j.1582-4934.2008.00322.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Immunoprotection of islets using bioisolator systems permits introduction of allogeneic cells to diabetic patients without the need for immunosuppression. Using TheraCyte™ immunoisolation devices, we investigated two rat models of type 1 diabetes mellitus (T1DM), BB rats and rats made diabetic by streptozotocin (STZ) treatment. We chose to implant islets after the onset of diabetes to mimic the probable treatment of children with T1DM as they are usually diagnosed after disease onset. We encapsulated 1000 rat islets and implanted them subcutaneously (SQ) into diabetic biobreeding (BB) rats and STZ-induced diabetic rats, defined as two or more consecutive days of blood glucose >350 mg/dl. Rats were monitored for weight and blood glucose. Untreated BB rats rapidly lost weight and were euthanized at >20% weight loss that occurred between 4 and 10 days from implantation. For period of 30–40 days following islet implantation weights of treated rats remained steady or increased. Rapid weight loss occurred after surgical removal of devices that contained insulin positive islets. STZ-treated rats that received encapsulated islets showed steady weight gain for up to 130 days, whereas untreated control rats showed steady weight loss that achieved >20% at around 55 days. Although islet implants did not normalize blood glucose, treated rats were apparently healthy and groomed normally. Autologous or allogeneic islets were equally effective in providing treatment. TheraCyte™ devices can sustain islets, protect allogeneic cells from immune attack and provide treatment for diabetic-mediated weight loss in both BB rats and STZ-induced diabetic rats.
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Affiliation(s)
- Ian R Sweet
- Department of Medicine, University of Washington, Seattle, WA 98195, USA
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59
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Köhnke R, Mei J, Park M, York DA, Erlanson-Albertsson C. Fatty acids and glucose in high concentration down-regulates ATP synthase beta-subunit protein expression in INS-1 cells. Nutr Neurosci 2008; 10:273-8. [PMID: 18284036 DOI: 10.1080/10284150701745910] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Chronic hyperglycemia and hyperlipidemia exert deleterious effects on beta-cell function and impair glucose-induced insulin release, referred to as glucotoxicity and lipotoxticity. These abnormalities are associated with decreased glucose-induced ATP production; ATP serves as an important signal for insulin secretion. To investigate the mechanism of the impaired ATP formation, we examined the effects of elevated glucose and fatty acids levels on ATP synthase beta-subunit expression, ATP content and insulin secretion in INS-1 insulinoma beta-cells. ATP synthase beta-subunit expression was measured by western blot, ATP content was monitored by ATP luminescence and insulin secretion detected by radio immunoassay. Our result indicated that chronic exposure to high doses of fatty acids together with high levels glucose produced a marked decrease in ATP synthase beta-subunit protein expression. Reduction of ATP synthase beta-subunit protein expression occurred with a decreased intracellular ATP concentration and insulin secretion at high fatty acid concentrations. These results indicate that high glucose together with fatty acids impair the production of ATP in beta-cells through the suppression of mitochondrial ATP synthesis. We conclude that ATP synthase beta-subunit may have an important role in the glucolipotoxicity of islet cells and suggest that ATP synthase beta-subunit might be a target of lipotoxicity in beta-cells.
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Affiliation(s)
- Rickard Köhnke
- Section for Diabetes, Metabolism and Endocrinology, Department of Experimental Medical Science, Lund University, BMC, B11, Lund, Sweden.
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60
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Snider RM, Ciobanu M, Rue AE, Cliffel DE. A multiwalled carbon nanotube/dihydropyran composite film electrode for insulin detection in a microphysiometer chamber. Anal Chim Acta 2008; 609:44-52. [PMID: 18243872 PMCID: PMC2358927 DOI: 10.1016/j.aca.2007.12.032] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2007] [Revised: 12/18/2007] [Accepted: 12/19/2007] [Indexed: 12/26/2022]
Abstract
We have developed a multiwalled carbon nanotube/dihydropyran (MWCNT/DHP) composite sensor for the electrochemical detection of insulin in a microfluidic device. This sensor has been employed for physiological measurements of secreted insulin from pancreatic islets in a Cytosensor previously modified to be a multianalyte microphysiometer (MAMP). When compared with other established electrochemical insulin sensors, the MWCNT/DHP composite film sensor presented improved resistance to fluidic shear forces, while achieving enhanced electrode kinetics. In addition, the preparation of the composite film is straightforward and facile with a self-polymerizing monomer, DHP, used to add mechanical stability to the film. The sensor film was able to detect insulin concentrations as low as 1muM in the MAMP during calibration experiments. The MWCNT/DHP composite sensor has been successfully used for the direct detection of insulin secreted by islets in the microphysiometer.
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Affiliation(s)
- Rachel M. Snider
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235-1822
| | - Madalina Ciobanu
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235-1822
| | - Amy E. Rue
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235-1822
| | - David E. Cliffel
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235-1822
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61
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Papas KK, Pisania A, Wu H, Weir GC, Colton CK. A stirred microchamber for oxygen consumption rate measurements with pancreatic islets. Biotechnol Bioeng 2008; 98:1071-82. [PMID: 17497731 PMCID: PMC2859188 DOI: 10.1002/bit.21486] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Improvements in pancreatic islet transplantation for treatment of diabetes are hindered by the absence of meaningful islet quality assessment methods. Oxygen consumption rate (OCR) has previously been used to assess the quality of organs and primary tissue for transplantation. In this study, we describe and characterize a stirred microchamber for measuring OCR with small quantities of islets. The device has a titanium body with a chamber volume of about 200 microL and is magnetically stirred and water jacketed for temperature control. Oxygen partial pressure (pO(2)) is measured by fluorescence quenching with a fiber optic probe, and OCR is determined from the linear decrease of pO(2) with time. We demonstrate that measurements can be made rapidly and with high precision. Measurements with betaTC3 cells and islets show that OCR is directly proportional to the number of viable cells in mixtures of live and dead cells and correlate linearly with membrane integrity measurements made with cells that have been cultured for 24 h under various stressful conditions.
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Affiliation(s)
- Klearchos K. Papas
- Department of Chemical Engineering, Massachusetts Institute of Technology, 25 Ames St., Cambridge, Massachusetts 02139; telephone: 617-253-4585; fax: 617-252-1651
- Department of Surgery, Diabetes Institute for Immunology and Transplantation, University of Minnesota, Minneapolis, Minnesota
| | - Anna Pisania
- Department of Chemical Engineering, Massachusetts Institute of Technology, 25 Ames St., Cambridge, Massachusetts 02139; telephone: 617-253-4585; fax: 617-252-1651
| | - Haiyan Wu
- Department of Chemical Engineering, Massachusetts Institute of Technology, 25 Ames St., Cambridge, Massachusetts 02139; telephone: 617-253-4585; fax: 617-252-1651
| | - Gordon C. Weir
- Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts 02215
| | - Clark K. Colton
- Department of Chemical Engineering, Massachusetts Institute of Technology, 25 Ames St., Cambridge, Massachusetts 02139; telephone: 617-253-4585; fax: 617-252-1651
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62
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Sweet IR, Gilbert M, Scott S, Todorov I, Jensen R, Nair I, Al-Abdullah I, Rawson J, Kandeel F, Ferreri K. Glucose-stimulated increment in oxygen consumption rate as a standardized test of human islet quality. Am J Transplant 2008; 8:183-92. [PMID: 18021279 DOI: 10.1111/j.1600-6143.2007.02041.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Standardized assessment of islet quality is imperative for clinical islet transplantation. We have previously shown that the increment in oxygen consumption rate stimulated by glucose (DeltaOCR(glc)) can predict in vivo efficacy of islet transplantation in mice. To further evaluate the approach, we studied three factors: islet specificity, islet composition and agreement between results obtained by different groups. Equivalent perifusion systems were set up at the City of Hope and the University of Washington and the values of DeltaOCR(glc) obtained at both institutions were compared. Islet specificity was determined by comparing DeltaOCR(glc) in islet and nonislet tissue. The DeltaOCR(glc) ranged from 0.01 to 0.19 nmol/min/100 islets (n = 14), a wide range in islet quality, but the values obtained by the two centers were similar. The contribution from nonislet impurities was negligible (DeltaOCR(glc) was 0.12 nmol/min/100 islets vs. 0.007 nmol/min/100 nonislet clusters). The DeltaOCR(glc) was statistically independent of percent beta cells, demonstrating that DeltaOCR(glc) is governed more by islet quality than by islet composition. The DeltaOCR(glc), but not the absolute level of OCR, was predictive of reversal of hyperglycemia in diabetic mice. These demonstrations lay the foundation for testing DeltaOCR(glc) as a measurement of islet quality for human islet transplantation.
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Affiliation(s)
- I R Sweet
- Department of Medicine, University of Washington, Seattle, WA, USA.
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63
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Abstract
Pancreatic beta-cells are clustered in islets of Langerhans, which are typically a few hundred micrometers in a variety of mammals. In this study, we propose a theoretical model for the growth of pancreatic islets and derive the islet size distribution, based on two recent observations: First, the neogenesis of new islets becomes negligible after some developmental stage. Second, islets grow via a random process, where any cell in an islet proliferates with the same rate regardless of the present size of the islet. Our model predicts either log-normal or Weibull distributions of the islet sizes, depending on whether cells in an islet proliferate coherently or independently. To confirm this, we also measure the islet size by selectively staining islets, which are exposed from exocrine tissues in mice after enzymatic treatment. Indeed revealed are skewed distributions with the peak size of approximately 100 cells, which fit well to the theoretically derived ones. Interestingly, most islets turned out to be bigger than the expected minimal size (approximately 10 or so cells) necessary for stable synchronization of beta-cells through electrical gap-junction coupling. The collaborative behavior among cells is known to facilitate synchronized insulin secretion and tends to saturate beyond the critical (saturation) size of approximately 100 cells. We further probe how the islets change as normal mice grow from young (6 weeks) to adult (5 months) stages. It is found that islets may not grow too large to maintain appropriate ratios between cells of different types. Our results implicate that growing of mouse islets may be regulated by several physical constraints such as the minimal size required for stable cell-to-cell coupling and the upper limit to keep the ratios between cell types. Within the lower and upper limits the observed size distributions of islets can be faithfully regenerated by assuming random and uncoordinated proliferation of each beta-cell at appropriate rates.
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Affiliation(s)
- Junghyo Jo
- Department of Physics and Astronomy and Center for Theoretical Physics, Seoul National University, Seoul, Korea
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64
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Sweet IR, Gilbert M. Contribution of calcium influx in mediating glucose-stimulated oxygen consumption in pancreatic islets. Diabetes 2006; 55:3509-19. [PMID: 17130499 DOI: 10.2337/db06-0400] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
In brain, muscle, and pancreatic islets, depolarization induces an increase in respiration, which is dependent on calcium influx. The goal of this study was to assess the quantitative significance of this effect in islets relative to glucose-stimulated ATP turnover, to examine the molecular mechanism mediating the changes, and to investigate the functional implications with respect to insulin secretion. Glucose (3-20 mmol/l) increased steady-state levels of cytochrome c reduction (32-66%) in isolated rat islets, reflecting an increased production of NADH, and oxygen consumption rate (OCR) by 0.32 nmol/min/100 islets. Glucose-stimulated OCR was inhibited 30% by inhibitors of calcium influx (diazoxide or nimodipine), whereas a protein synthesis inhibitor (emetine) decreased it by only 24%. None of the inhibitors affected cytochrome c reduction, suggesting that calcium's effect on steady-state OCR is mediated by changes in ATP usage rather than the rate of NADH generation. 3-isobutyl-1-methylxanthine increased insulin secretion but had little effect on OCR, indicating that the processes of movement and exocytosis of secretory granules do not significantly contribute to ATP turnover. At 20 mmol/l glucose, a blocker of sarcoendoplasmic reticulum calcium ATPase (SERCA) had little effect on OCR despite a large increase in cytosolic calcium, further supporting the notion that influx of calcium, not bulk cytosolic calcium, is associated with the increase in ATP turnover. The glucose dose response of calcium influx-dependent OCR showed a remarkable correlation with insulin secretion, suggesting that the process mediating the effect of calcium on ATP turnover has a role in the amplification pathway of insulin secretion.
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Affiliation(s)
- Ian R Sweet
- Robert H. Williams Laboratory, HSB K-165, Box 357710, University of Washington, 1959 NE Pacific St., Seattle, WA 98195-7710, USA.
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Weydt P, Pineda VV, Torrence AE, Libby RT, Satterfield TF, Lazarowski ER, Gilbert ML, Morton GJ, Bammler TK, Strand AD, Cui L, Beyer RP, Easley CN, Smith AC, Krainc D, Luquet S, Sweet IR, Schwartz MW, La Spada AR. Thermoregulatory and metabolic defects in Huntington's disease transgenic mice implicate PGC-1alpha in Huntington's disease neurodegeneration. Cell Metab 2006; 4:349-62. [PMID: 17055784 DOI: 10.1016/j.cmet.2006.10.004] [Citation(s) in RCA: 444] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/11/2006] [Revised: 09/20/2006] [Accepted: 10/09/2006] [Indexed: 01/08/2023]
Abstract
Huntington's disease (HD) is a fatal, dominantly inherited disorder caused by polyglutamine repeat expansion in the huntingtin (htt) gene. Here, we observe that HD mice develop hypothermia associated with impaired activation of brown adipose tissue (BAT). Although sympathetic stimulation of PPARgamma coactivator 1alpha (PGC-1alpha) was intact in BAT of HD mice, uncoupling protein 1 (UCP-1) induction was blunted. In cultured cells, expression of mutant htt suppressed UCP-1 promoter activity; this was reversed by PGC-1alpha expression. HD mice showed reduced food intake and increased energy expenditure, with dysfunctional BAT mitochondria. PGC-1alpha is a known regulator of mitochondrial function; here, we document reduced expression of PGC-1alpha target genes in HD patient and mouse striatum. Mitochondria of HD mouse brain show reduced oxygen consumption rates. Finally, HD striatal neurons expressing exogenous PGC-1alpha were resistant to 3-nitropropionic acid treatment. Altered PGC-1alpha function may thus link transcription dysregulation and mitochondrial dysfunction in HD.
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Affiliation(s)
- Patrick Weydt
- Department of Laboratory Medicine, University of Washington, Seattle, Washington 98195, USA
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66
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Goto M, Holgersson J, Kumagai-Braesch M, Korsgren O. The ADP/ATP ratio: A novel predictive assay for quality assessment of isolated pancreatic islets. Am J Transplant 2006; 6:2483-7. [PMID: 16869808 DOI: 10.1111/j.1600-6143.2006.01474.x] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The current standard assays for islet product release criteria are unable to predict the outcome after clinical islet transplantation. Therefore, establishment of reliable and rapid assays enabling pre-transplantation prediction of islet potency is warranted. In the present study, we have evaluated the adenosine diphosphate (ADP)/adenosine triphosphate (ATP) test, the glucose-stimulated insulin release, the loss of islets during the first 24 h in culture, and the insulin/deoxyribonucleic acid as predictive assays for the ability of isolated porcine islets to cure athymic mice with streptozotocin-induced diabetes. From the results presented, it is concluded that the measurement of the ADP/ATP ratio was the only test that correlated with transplantation outcome. In summary, we propose that the ADP/ATP assay is worthwhile as applied to human islet transplantation and seek to validate it as a rapid and potent predictor of transplant outcome.
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Affiliation(s)
- M Goto
- Tohoku University, Biomedical Engineering Research Organization, Sendai, Japan.
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67
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Grassiolli S, Bonfleur ML, Scomparin DX, de Freitas Mathias PC. Pancreatic islets from hypothalamic obese rats maintain K+ATP channel-dependent but not -independent pathways on glucose-induced insulin release process. Endocrine 2006; 30:191-6. [PMID: 17322578 DOI: 10.1385/endo:30:2:191] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2006] [Revised: 09/02/2006] [Accepted: 10/02/2006] [Indexed: 11/11/2022]
Abstract
One of the main features of obesity is hyperinsulinemia, which is related to insulin oversecretion. Glucose is by far the major physiological stimulator of insulin secretion. Glucose promotes an increase in the ATP/ADP ratio, which inactivates ATP-sensitive K+ channels (K+ATP) and induces beta cell depolarization with consequent calcium influx. Increased intracellular calcium concentration triggers insulin exocytosis. K+ATP channel function is important for K+ATP channel-dependent pathways involved in glucose-stimulated insulin secretion (GSIS). However, K+ATP channel-independent pathway has been identified and it has been found that this pathway sustains GSIS. Both pathways are critical to better GSIS control. GSIS was studied in pancreatic islets from hyperinsulinemic adult obese rats obtained by monosodium L-glutamate (MSG) neonatal treatment. Islets from MSG-obese rats were more glucose responsive than control ones. Diazoxide, a drug which maintains the K+ATP channels open without interfering with cell metabolism, blocked GSIS in islets from both groups. High extracellular potassium concentration plus diazoxide was used to study an alternative to the K+ATP channel pathway; in these conditions islets from MSG-obese rats did not respond, while islets from control animals showed enhanced GSIS. Results indicate that MSG-obese rats oversecreted insulin, even though the K+ATP channel-independent pathway is impaired in their beta cells.
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Affiliation(s)
- Sabrina Grassiolli
- Laboratory of Secretion Cell Biology, Department of Cell Biology and Genetics, State University of Maringá, Maringá, PR, Brazil
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68
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Doliba NM, Qin W, Vatamaniuk MZ, Buettger CW, Collins HW, Magnuson MA, Kaestner KH, Wilson DF, Carr RD, Matschinsky FM. Cholinergic regulation of fuel-induced hormone secretion and respiration of SUR1-/- mouse islets. Am J Physiol Endocrinol Metab 2006; 291:E525-35. [PMID: 16638820 DOI: 10.1152/ajpendo.00579.2005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Neural and endocrine factors (i.e., Ach and GLP-1) restore defective glucose-stimulated insulin release in pancreatic islets lacking sulfonylurea type 1 receptors (SUR1(-/-)) (Doliba NM, Qin W, Vatamaniuk MZ, Li C, Zelent D, Najafi H, Buettger CW, Collins HW, Carr RD, Magnuson MA, and Matschinsky FM. Am J Physiol Endocrinol Metab 286: E834-E843, 2004). The goal of the present study was to assess fuel-induced respiration in SUR1(-/-) islets and to correlate it with changes in intracellular Ca(2+), insulin, and glucagon secretion. By use of a method based on O(2) quenching of phosphorescence, the O(2) consumption rate (OCR) of isolated islets was measured online in a perifusion system. Basal insulin release (IR) was 7-10 times higher in SUR1(-/-) compared with control (CON) islets, but the OCR was comparable. The effect of high glucose (16.7 mM) on IR and OCR was markedly reduced in SUR1(-/-) islets compared with CON. Ach (0.5 microM) in the presence of 16.7 mM glucose caused a large burst of IR in CON and SUR1(-/-) islets with minor changes in OCR in both groups of islets. In SUR1(-/-) islets, high glucose failed to inhibit glucagon secretion during stimulation with amino acids or Ach. We conclude that 1) reduced glucose responsiveness of SUR1(-/-) islets may be in part due to impaired energetics, as evidenced by significant decrease in glucose-stimulated OCR; 2) elevated intracellular Ca(2+) levels may contribute to altered insulin and glucagon secretion in SUR1(-/-) islets; and 3) The amplitudes of the changes in OCR during glucose and Ach stimulation do not correlate with IR in normal and SUR1(-/-) islets suggesting that the energy requirements for exocytosis are minor compared with other ATP-consuming reactions.
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Affiliation(s)
- Nicolai M Doliba
- Dept. of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
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69
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Giroix MH, Agascioglu E, Oguzhan B, Louchami K, Zhang Y, Courtois P, Malaisse WJ, Sener A. Opposite effects of D-fructose on total versus cytosolic ATP/ADP ratio in pancreatic islet cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:773-80. [PMID: 16782044 DOI: 10.1016/j.bbabio.2006.05.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2005] [Revised: 04/12/2006] [Accepted: 05/03/2006] [Indexed: 12/01/2022]
Abstract
D-fructose (10 mM) augments, in rat pancreatic islets, insulin release evoked by 10 mM D-glucose. Even in the absence of D-glucose, D-fructose (100 mM) displays a positive insulinotropic action. It was now examined whether the insulinotropic action of D-fructose could be attributed to an increase in the ATP content of islet cells. After 30-60 min incubation in the presence of D-glucose and/or D-fructose, the ATP and ADP content was measured by bioluminescence in either rat isolated pancreatic islets (total ATP and ADP) or the supernatant of dispersed rat pancreatic islet cells exposed for 30 s to digitonine (cytosolic ATP and ADP). D-fructose (10 and 100 mM) was found to cause a concentration-related decrease in the total ATP and ADP content and ATP/ADP ratio below the basal values found in islets deprived of exogenous nutrient. Moreover, in the presence of 10 mM D-glucose, which augmented both the total ATP content and ATP/ADP ratio above basal value, D-fructose (10 mM) also lowered these two parameters. The cytosolic ATP/ADP ratio, however, was increased in the presence of D-glucose and/or D-fructose. Under the present experimental conditions, a sigmoidal relationship was found between such a cytosolic ATP/ADP ratio and either (86)Rb net uptake by dispersed islet cells or insulin release from isolated islets. These data provide, to our knowledge, the first example of a dramatic dissociation between changes in total ATP content or ATP/ADP ratio and insulin release in pancreatic islets exposed to a nutrient secretagogue. Nevertheless, the cationic and insulinotropic actions of d-glucose and/or d-fructose were tightly related to the cytosolic ATP/ADP ratio.
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Affiliation(s)
- Marie-Hélène Giroix
- Laboratory of Nutrition Physiopathology, CNRS UMR 7059, University of Paris 7, France
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70
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Affourtit C, Brand MD. Stronger control of ATP/ADP by proton leak in pancreatic beta-cells than skeletal muscle mitochondria. Biochem J 2006; 393:151-9. [PMID: 16137248 PMCID: PMC1383673 DOI: 10.1042/bj20051280] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Pancreatic beta cells respond to rising blood glucose concentrations by increasing their oxidative metabolism, which leads to an increased ATP/ADP ratio, closure of K(ATP) channels, depolarization of the plasma membrane potential, influx of calcium and the eventual secretion of insulin. Such a signalling mechanism implies that the ATP/ADP ratio is flexible in beta cells (beta-cells), which is in contrast with other cell types (e.g. muscle and liver) that maintain a stable ATP/ADP poise while respiring at widely varying rates. To determine whether this difference in flexibility is accounted for by mitochondrial peculiarities, we performed a top-down metabolic control analysis to quantitatively assess how ATP/ADP is controlled in mitochondria isolated from rat skeletal muscle and cultured beta cells. We show that the ATP/ADP ratio is more strongly controlled (approx. 7.5-fold) by proton leak in beta cells than in muscle. The comparatively high importance of proton leak in beta cell mitochondria (relative to phosphorylation) is evidenced furthermore by its relatively high level of control over membrane potential and overall respiratory activity. Modular-kinetic analysis of oxidative phosphorylation reveals that these control differences can be fully explained by a higher relative leak activity in beta cell mitochondria, which results in a comparatively high contribution of proton leak to the overall respiratory activity in this system.
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71
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Abstract
Somatostatin potently inhibits insulin secretion from pancreatic beta-cells. It does so via activation of ATP-sensitive K+-channels (KATP) and G protein-regulated inwardly rectifying K+-channels, which act to decrease voltage-gated Ca2+-influx, a process central to exocytosis. Because KATP channels, and indeed insulin secretion, is controlled by glucose oxidation, we investigated whether somatostatin inhibits insulin secretion by direct effects on glucose metabolism. Oxidative metabolism in beta-cells was monitored by measuring changes in the O2 consumption (DeltaO2) of isolated mouse islets and MIN6 cells, a murine-derived beta-cell line. In both models, glucose-stimulated DeltaO2, an effect closely associated with inhibition of KATP channel activity and induction of electrical activity (r > 0.98). At 100 nm, somatostatin abolished glucose-stimulated DeltaO2 in mouse islets (n = 5, P < 0.05) and inhibited it by 80 +/- 28% (n = 17, P < 0.01) in MIN6 cells. Removal of extracellular Ca2+, 5 mm Co2+, or 20 microm nifedipine, conditions that inhibit voltage-gated Ca2+ influx, did not mimic but either blocked or reduced the effect of the peptide on DeltaO2. The nutrient secretagogues, methylpyruvate (10 mm) and alpha-ketoisocaproate (20 mm), also stimulated DeltaO2, but this was unaffected by somatostatin. Somatostatin also reversed glucose-induced hyperpolarization of the mitochondrial membrane potential monitored using rhodamine-123. Application of somatostatin receptor selective agonists demonstrated that the peptide worked through activation of the type 5 somatostatin receptor. In conclusion, somatostatin inhibits glucose metabolism in murine beta-cells by an unidentified Ca2+-dependent mechanism. This represents a new signaling pathway by which somatostatin can inhibit cellular functions regulated by glucose metabolism.
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Affiliation(s)
- Mathew Daunt
- Institute of Cell Signalling, School of Biomedical Sciences, University of Nottingham, Medical School, Nottingham NG7 2UH, United Kingdom
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72
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Niswender CM, Willis BS, Wallen A, Sweet IR, Jetton TL, Thompson BR, Wu C, Lange AJ, McKnight GS. Cre recombinase-dependent expression of a constitutively active mutant allele of the catalytic subunit of protein kinase A. Genesis 2006; 43:109-19. [PMID: 16155866 DOI: 10.1002/gene.20159] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Using the cre-loxP recombination system, we generated a line of mice expressing a constitutively active catalytic subunit of Protein Kinase A (PKA) in a temporally and spatially regulated fashion. In the absence of cre recombinase the modified catalytic subunit allele is functionally silent, but after recombination the mutant allele is expressed, resulting in enhanced PKA effects at basal cAMP levels. Mice expressing the modified protein in hepatocytes using albumin-cre transgenics show defects in glucose homeostasis, glycogen storage, fructose 2,6-bisphosphate levels, and induction of glucokinase mRNA during feeding. Similar to animals lacking glucokinase in the liver (Postic et al.: J Biol Chem 274:305-315, 1999), these mice also have defects in glucose-stimulated insulin secretion, a hallmark of Type II diabetes. The widespread expression of PKA and the involvement of this kinase in a myriad of signaling pathways suggest that these animals will provide critical tools for the study of PKA function in vivo.
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Affiliation(s)
- Colleen M Niswender
- Department of Pharmacology, University of Washington, Seattle, WA 98195, USA
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73
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Sweet IR, Gilbert M, Jensen R, Sabek O, Fraga DW, Gaber AO, Reems J. Glucose stimulation of cytochrome C reduction and oxygen consumption as assessment of human islet quality. Transplantation 2005; 80:1003-11. [PMID: 16278578 DOI: 10.1097/01.tp.0000178381.35014.37] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
BACKGROUND An in vitro method to assess human islets could prevent transplantation of nonviable islets and facilitate the optimization of islet preparation. We hypothesize that glucose-stimulated cytochrome c reduction and oxygen consumption by human islets can be used as predictors of transplant success. METHODS Isolated human islets were obtained from research-grade pancreata. Using a previously developed islet flow culture system, the response of cytochrome c reduction and oxygen consumption to glucose was compared to the ability of islets transplanted into nondiabetic NOD-SCID mice to secrete C-peptide in response to a glucose tolerance test conducted 7 days following transplant (n=10). RESULTS In vitro responses by human islets were qualitatively similar to those seen in rat islets: glucose increased both oxygen consumption and cytochrome c reduction. However, the responses were smaller in magnitude and quite variable. Scatter plots of C-peptide and quantiles for ln(C-peptide) indicated that 12 ng/ml could be used as threshold of transplant success with which to evaluate the diagnostic potential of cytochrome c and oxygen consumption. Data was analyzed by generating receiver operating curves and the area under the curve was 0.889 (95% CI: 0.645-1.000) and 0.738 (95% CI: 0.413-1.000) for cytochrome c reduction and oxygen consumption respectively (1 indicates absolute predictive capability and 0.5 indicates no predictive capability). CONCLUSIONS The detection of glucose-stimulated cytochrome c reduction and oxygen consumption may have utility as criteria for the assessment of human islet quality.
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Affiliation(s)
- Ian R Sweet
- Department of Medicine, University of Washington, Seattle, WA 98195-7710, USA.
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74
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Fridlyand LE, Ma L, Philipson LH. Adenine nucleotide regulation in pancreatic beta-cells: modeling of ATP/ADP-Ca2+ interactions. Am J Physiol Endocrinol Metab 2005; 289:E839-48. [PMID: 15985450 DOI: 10.1152/ajpendo.00595.2004] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Glucose metabolism stimulates insulin secretion in pancreatic beta-cells. A consequence of metabolism is an increase in the ratio of ATP to ADP ([ATP]/[ADP]) that contributes to depolarization of the plasma membrane via inhibition of ATP-sensitive K+ (K(ATP)) channels. The subsequent activation of calcium channels and increased intracellular calcium leads to insulin exocytosis. Here we evaluate new data and review the literature on nucleotide pool regulation to determine the utility and predictive value of a new mathematical model of ion and metabolic flux regulation in beta-cells. The model relates glucose consumption, nucleotide pool concentration, respiration, Ca2+ flux, and K(ATP) channel activity. The results support the hypothesis that beta-cells maintain a relatively high [ATP]/[ADP] value even in low glucose and that dramatically decreased free ADP with only modestly increased ATP follows from glucose metabolism. We suggest that the mechanism in beta-cells that leads to this result can simply involve keeping the total adenine nucleotide concentration unchanged during a glucose elevation if a high [ATP]/[ADP] ratio exits even at low glucose levels. Furthermore, modeling shows that independent glucose-induced oscillations of intracellular calcium can lead to slow oscillations in nucleotide concentrations, further predicting an influence of calcium flux on other metabolic oscillations. The results demonstrate the utility of comprehensive mathematical modeling in understanding the ramifications of potential defects in beta-cell function in diabetes.
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Affiliation(s)
- Leonid E Fridlyand
- Dept. of Medicine, The Univ. of Chicago, 5841 S. Maryland Ave., Chicago, IL 60637, USA
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75
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Leibowitz G, Khaldi MZ, Shauer A, Parnes M, Oprescu AI, Cerasi E, Jonas JC, Kaiser N. Mitochondrial regulation of insulin production in rat pancreatic islets. Diabetologia 2005; 48:1549-59. [PMID: 15986240 DOI: 10.1007/s00125-005-1811-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2004] [Accepted: 03/25/2005] [Indexed: 10/25/2022]
Abstract
AIMS/HYPOTHESIS The study was designed to identify the key metabolic signals of glucose-stimulated proinsulin gene transcription and translation, focusing on the mechanism of succinate stimulation of insulin production. METHODS Wistar rat islets were incubated in 3.3 mmol/l glucose with and without esters of different mitochondrial metabolites or with 16.7 mmol/l glucose. Proinsulin biosynthesis was analysed by tritiated leucine incorporation into newly synthesised proinsulin. Preproinsulin gene transcription was evaluated following transduction with adenoviral vectors expressing the luciferase reporter gene under the control of the rat I preproinsulin promoter. Steady-state preproinsulin mRNA was determined using relative quantitative PCR. The mitochondrial membrane potential was measured by microspectrofluorimetry using rhodamine-123. RESULTS Succinic acid monomethyl ester, but not other mitochondrial metabolites, stimulated preproinsulin gene transcription and translation. Similarly to glucose, succinate increased specific preproinsulin gene transcription and biosynthesis. The inhibitor of succinate dehydrogenase (SDH), 3-nitropropionate, abolished glucose- and succinate-stimulated mitochondrial membrane hyperpolarisation and proinsulin biosynthesis, indicating that stimulation of proinsulin translation depends on SDH activity. Partial inhibition of SDH activity by exposure to fumaric acid monomethyl ester abolished the stimulation of preproinsulin gene transcription, but only partially inhibited the stimulation of proinsulin biosynthesis by glucose and succinate, suggesting that SDH activity is particularly important for the transcriptional response to glucose. CONCLUSIONS/INTERPRETATION Succinate is a key metabolic mediator of glucose-stimulated preproinsulin gene transcription and translation. Moreover, succinate stimulation of insulin production depends on its metabolism via SDH. The differential effect of fumarate on preproinsulin gene transcription and translation suggests that these processes have different sensitivities to metabolic signals.
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Affiliation(s)
- G Leibowitz
- Endocrinology and Metabolism Service, Department of Medicine, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel.
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Ichii H, Inverardi L, Pileggi A, Molano RD, Cabrera O, Caicedo A, Messinger S, Kuroda Y, Berggren PO, Ricordi C. A novel method for the assessment of cellular composition and beta-cell viability in human islet preparations. Am J Transplant 2005; 5:1635-45. [PMID: 15943621 DOI: 10.1111/j.1600-6143.2005.00913.x] [Citation(s) in RCA: 171] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Current methodologies to evaluate islet cell viability are largely based on tests that assess the exclusion of DNA-binding dyes. While these tests identify cells that have lost selective membrane permeability, they do not allow us to recognize apoptotic cells, which do not yet stain with DNA-binding dyes. Furthermore, current methods of analysis do not discriminate between cell subsets in the preparation and, in particular, they do not allow for selectively defining beta-cell viability. For these reasons we have developed novel methods for the specific assessment of beta-cell content and viability in human islets based on cellular composition analysis through laser scanning cytometry (LSC) coupled with identification of beta-cell-specific apoptosis at the mitochondrial level. Our novel analytical methods hold promise to prospectively analyze clinical islet transplantation preparations and predict functional performance, as suggested by the observed correlation with in vivo analysis of islet potency in immunodeficient rodents.
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Affiliation(s)
- Hirohito Ichii
- Diabetes Research Institute, University of Miami, Leonard M. Miller School of Medicine, Miami, FL, USA
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Pancreatic beta-cell failure and diabetes in mice with a deletion mutation of the endoplasmic reticulum molecular chaperone gene P58IPK. Diabetes 2005; 54:1074-81. [PMID: 15793246 DOI: 10.2337/diabetes.54.4.1074] [Citation(s) in RCA: 163] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The endoplasmic reticulum (ER) transmits apoptotic signals in the pancreas during ER stress, implicating ER stress-mediated apoptosis in the development of diabetes. P58(IPK) (DNAJC3) is induced during ER stress and functions as a negative feedback component to inhibit eIF-2alpha signaling and attenuate the later phases of the ER stress response. To gain insight into a more comprehensive role of P58(IPK) function, we generated deletion mutant mice that showed a gradual onset of glucosuria and hyperglycemia associated with increasing apoptosis of pancreatic islet cells. Lack of P58(IPK) had no apparent effect on the functional integrity of viable beta-cells. A set of genes associated with apoptosis showed altered expression in pancreatic islets from P58(IPK)-null mice, further substantiating the apoptosis phenotype. The data provide in vivo evidence to support the concept that P58(IPK) functions as a signal for the downregulation of ER-associated proteins involved in the initial ER stress response, thus preventing excessive cell loss by degradation pathways. Insulin deficiency associated with the absence of P58(IPK) mimics beta-cell failure associated with type 1 and late-stage type 2 diabetes. P58(IPK) function and activity may therefore provide a novel area of investigation into ER-mediated mechanistic and therapeutic approaches for diabetes.
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78
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Current literature in diabetes. Diabetes Metab Res Rev 2004; 20:487-94. [PMID: 15570584 DOI: 10.1002/dmrr.511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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