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Pen OV, Antinozzi PA, Kock ND, Robinson MB, Willey JS, Bourland JD. Automated, quantitative assessment of epidermal necrosis expression resulting from skin exposure to beta radiation. Biomed Phys Eng Express 2019; 6:015007. [PMID: 33438595 DOI: 10.1088/2057-1976/ab5612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE Radiation skin injuries are difficult to quantitatively assess. Various scoring scales exist based on visual images and can be used in quantitative form for histological scoring. As an alternative to human scoring systems, an automated, quantitative system is proposed to provide unbiased scoring of radiation skin injury biopsy samples, with comparisons to human-based scoring systems. MATERIALS AND METHODS A unique algorithm was developed and tested on a sample pool obtained from in-vivo beta radiation experiments with a porcine model. The grading results achieved by the developed algorithm and those provided by an expert histopathologist are compared. RESULTS The extent of the epidermal necrosis is quantified in terms of the number of dead cells and their respective distribution across the length of the samples. The accuracy of the grading performed by the automated algorithm is comparable to that of a trained histopathologist, as demonstrated by statistically significant difference between the grades. CONCLUSIONS This study demonstrates the feasibility of the proposed method as a potential tool designed to aid in the histopathological analysis of the tissues affected by beta radiation exposure. An expanded study with a larger sample pool is recommended to further improve the accuracy of the proposed algorithm.
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Affiliation(s)
- Olga V Pen
- Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC, United States of America. Department of Biomedical Engineering, Virginia Tech-Wake Forest University School of Biomedical Sciences and Engineering, Winston-Salem, NC, United States of America
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Palmer ND, Stevens RD, Antinozzi PA, Anderson A, Bergman RN, Wagenknecht LE, Newgard CB, Bowden DW. Metabolomic profile associated with insulin resistance and conversion to diabetes in the Insulin Resistance Atherosclerosis Study. J Clin Endocrinol Metab 2015; 100:E463-8. [PMID: 25423564 PMCID: PMC4333040 DOI: 10.1210/jc.2014-2357] [Citation(s) in RCA: 174] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
CONTEXT Metabolomic profiling of amino acids and acylcarnitines has revealed consistent patterns associated with metabolic disease. OBJECTIVE This study used metabolomic profiling to identify analytes associated with insulin sensitivity (SI) and conversion to type 2 diabetes (T2D). DESIGN A multiethnic cohort from the Insulin Resistance Atherosclerosis Study. SETTING Community-based. PATIENTS A total of 196 subjects (European American, Hispanic, and African American) were selected to represent extremes of the SI distribution and conversion to T2D between baseline and followup exams. MAIN OUTCOME Mass spectrometry-based profiling of 69 metabolites. Subjects participated in a frequently sampled i.v. glucose tolerance test to measure SI and acute insulin response. T2D status was determined by a 2-hour oral glucose tolerance test. RESULTS Logistic regression analysis from 72 high and 75 low SI subjects revealed significantly decreased glycine and increased valine, leucine, phenylalanine, and combined glutamine and glutamate (P = .0079-7.7 × 10(-6)) in insulin-resistant subjects. Ethnic-stratified results were strongest in European Americans. Comparing amino acid profiles between subjects that converted to T2D (76 converters; 70 nonconverters) yielded a similar pattern of associations: decreased glycine and increased valine, leucine, and combined glutamine and glutamate (P = .016-.00010). Importantly, β-cell function as a covariate revealed a similar pattern of association. CONCLUSIONS A distinct pattern of differences in amino acids were observed when comparing subjects with high and low levels of SI. This pattern was associated with conversion to T2D, remaining significant when accounting for β-cell function, emphasizing a link between this metabolic profile and insulin resistance. These results demonstrate a consistent metabolic signature associated with insulin resistance and conversion to T2D, providing potential insight into underlying mechanisms of disease pathogenesis.
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Affiliation(s)
- Nicholette D Palmer
- Department of Biochemistry (N.D.P., P.A.A., D.W.B.), Center for Genomics and Personalized Medicine Research (N.D.P., P.A.A., D.W.B.), and Center for Diabetes Research (N.D.P., P.A.A., D.W.B.), Wake Forest School of Medicine, Winston Salem, North Carolina 27157; Sarah W. Stedman Nutrition and Metabolism Center (R.D.S., C.B.N.), Duke University School of Medicine, Durham, North Carolina 27710; Department of Biostatistical Sciences (A.A.) and Department of Epidemiology & Prevention (L.E.W.), Wake Forest School of Medicine, Winston Salem, North Carolina 27157; and Department of Physiology and Biophysics (R.N.B.), Keck School of Medicine, University of Southern California, Los Angeles, California 90033
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Ma L, Shelness GS, Snipes JA, Murea M, Antinozzi PA, Cheng D, Saleem MA, Satchell SC, Banas B, Mathieson PW, Kretzler M, Hemal AK, Rudel LL, Petrovic S, Weckerle A, Pollak MR, Ross MD, Parks JS, Freedman BI. Localization of APOL1 protein and mRNA in the human kidney: nondiseased tissue, primary cells, and immortalized cell lines. J Am Soc Nephrol 2014; 26:339-48. [PMID: 25012173 DOI: 10.1681/asn.2013091017] [Citation(s) in RCA: 107] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Although APOL1 gene variants are associated with nephropathy in African Americans, little is known about APOL1 protein synthesis, uptake, and localization in kidney cells. To address these questions, we examined APOL1 protein and mRNA localization in human kidney and human kidney-derived cell lines. Indirect immunofluorescence microscopy performed on nondiseased nephrectomy cryosections from persons with normal kidney function revealed that APOL1 protein was markedly enriched in podocytes (colocalized with synaptopodin and Wilms' tumor suppressor) and present in lower abundance in renal tubule cells. Fluorescence in situ hybridization detected APOL1 mRNA in glomeruli (podocytes and endothelial cells) and tubules, consistent with endogenous synthesis in these cell types. When these analyses were extended to renal-derived cell lines, quantitative RT-PCR did not detect APOL1 mRNA in human mesangial cells; however, abundant levels of APOL1 mRNA were observed in proximal tubule cells and glomerular endothelial cells, with lower expression in podocytes. Western blot analysis revealed corresponding levels of APOL1 protein in these cell lines. To explain the apparent discrepancy between the marked abundance of APOL1 protein in kidney podocytes observed in cryosections versus the lesser abundance in podocyte cell lines, we explored APOL1 cellular uptake. APOL1 protein was taken up readily by human podocytes in vitro but was not taken up efficiently by mesangial cells, glomerular endothelial cells, or proximal tubule cells. We hypothesize that the higher levels of APOL1 protein in human cryosectioned podocytes may reflect both endogenous protein synthesis and APOL1 uptake from the circulation or glomerular filtrate.
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Affiliation(s)
| | | | | | | | - Peter A Antinozzi
- Biochemistry, Wake Forest School of Medicine, Winston-Salem, North Carolina
| | | | - Moin A Saleem
- Children's Renal Unit, Bristol Royal Hospital for Children, University of Bristol, Bristol, United Kingdom
| | - Simon C Satchell
- Learning and Research Southmead Hospital Bristol, University of Bristol, Bristol, United Kingdom
| | - Bernhard Banas
- Internal Medicine II-Nephrology/Transplantation, University Medical Center, Regensburg, Germany
| | - Peter W Mathieson
- Children's Renal Unit, Bristol Royal Hospital for Children, University of Bristol, Bristol, United Kingdom
| | - Matthias Kretzler
- Department of Internal Medicine-Nephrology, University of Michigan at Ann Arbor Medical School, Ann Arbor, Michigan
| | | | | | - Snezana Petrovic
- Internal Medicine-Nephrology, Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, North Carolina
| | | | - Martin R Pollak
- Division of Nephrology, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts; and
| | - Michael D Ross
- Renal Division, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts
| | - John S Parks
- Pathology-Lipid Sciences, and Biochemistry, Wake Forest School of Medicine, Winston-Salem, North Carolina
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Ma L, Murea M, Snipes JA, Marinelarena A, Krüger J, Hicks PJ, Langberg KA, Bostrom MA, Cooke JN, Suzuki D, Babazono T, Uzu T, Tang SCW, Mondal AK, Sharma NK, Kobes S, Antinozzi PA, Davis M, Das SK, Rasouli N, Kern PA, Shores NJ, Rudel LL, Blüher M, Stumvoll M, Bowden DW, Maeda S, Parks JS, Kovacs P, Hanson RL, Baier LJ, Elbein SC, Freedman BI. An ACACB variant implicated in diabetic nephropathy associates with body mass index and gene expression in obese subjects. PLoS One 2013; 8:e56193. [PMID: 23460794 PMCID: PMC3584087 DOI: 10.1371/journal.pone.0056193] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Accepted: 01/07/2013] [Indexed: 02/04/2023] Open
Abstract
Acetyl coenzyme A carboxylase B gene (ACACB) single nucleotide polymorphism (SNP) rs2268388 is reproducibly associated with type 2 diabetes (T2DM)-associated nephropathy (DN). ACACB knock-out mice are also protected from obesity. This study assessed relationships between rs2268388, body mass index (BMI) and gene expression in multiple populations, with and without T2DM. Among subjects without T2DM, rs2268388 DN risk allele (T) associated with higher BMI in Pima Indian children (n = 2021; p-additive = 0.029) and African Americans (AAs) (n = 177; p-additive = 0.05), with a trend in European Americans (EAs) (n = 512; p-additive = 0.09), but not Germans (n = 858; p-additive = 0.765). Association with BMI was seen in a meta-analysis including all non-T2DM subjects (n = 3568; p-additive = 0.02). Among subjects with T2DM, rs2268388 was not associated with BMI in Japanese (n = 2912) or EAs (n = 1149); however, the T allele associated with higher BMI in the subset with BMI≥30 kg/m(2) (n = 568 EAs; p-additive = 0.049, n = 196 Japanese; p-additive = 0.049). Association with BMI was strengthened in a T2DM meta-analysis that included an additional 756 AAs (p-additive = 0.080) and 48 Hong Kong Chinese (p-additive = 0.81) with BMI≥30 kg/m(2) (n = 1575; p-additive = 0.0033). The effect of rs2268388 on gene expression revealed that the T risk allele associated with higher ACACB messenger levels in adipose tissue (41 EAs and 20 AAs with BMI>30 kg/m(2); p-additive = 0.018) and ACACB protein levels in the liver tissue (mixed model p-additive = 0.03, in 25 EA bariatric surgery patients with BMI>30 kg/m(2) for 75 exams). The T allele also associated with higher hepatic triglyceride levels. These data support a role for ACACB in obesity and potential roles for altered lipid metabolism in susceptibility to DN.
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Affiliation(s)
- Lijun Ma
- Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America.
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Manring HR, Antinozzi PA. Abstract 2249: Mutations to the GSK3β regulatory region of CTNNB1 increase TCF transcription activity and are resistant to degradation by GSK3β. Cancer Res 2012. [DOI: 10.1158/1538-7445.am2012-2249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Hepatocellular carcinoma (HCC) is currently the third most common cause of cancer related mortality worldwide. As with many cancers, aberrant activation of Wnt/β-catenin signaling plays a critical pathogenic role in the disease. Somatic mutations in genes of the Wnt pathway are widely observed in tumor tissue, where it has been estimated that 15-20% of tumors possess activating mutations in beta-catenin (CTNNB1). The turnover of CTNNB1 protein is tightly regulated in cells by the degradation complex which includes the CK1α and GSK3β kinases in a complex with Axin and APC. Mutations within the CTNNB1 gene at the CK1α phosphorylation site (Ser45) and GSK3β phosphorylation sites (Ser33, Ser37, Thr41) are observed clinically and result in CTNNB1 protein accumulation and enhanced transcription of Wnt target genes. The goal of this study is to characterize additional clinically observed CTNNB1 mutations in HCC. It is hypothesized that mutations within the phosphorylation domain in exon 3 will impact the phosphorylation of these key regulatory sites of CTNNB1. To assess the impact of three observed CTNNB1 mutations (H36P, I35S and S23R) on Wnt signaling activity, mutant CTNNB1 constructs were first created and their impact on Wnt signaling was measured using a luciferase-based Wnt reporter assay in transfected HEK293T cells. Compared to the wild type CTNNB1 control, Wnt transcription activity in the presence of H36P, I35S, and S23R mutants were increased by 6.55 ± 2.08, 6.76 ± 2.44, and 2.36 ± 1.01 fold, respectively. This compared to a 5.91 ± 1.38 fold increase observed with the phosphorylation mutant S45P. To evaluate if these mutations had a measurable impact on GSK3β regulation of CTNNB1 levels, each mutant was coexpressed with a GSK3β expression vector and evaluated using the same Wnt reporter system. As anticipated, GSK3β coexpression reduced Wnt reporter activity of the CTNNB1 control by 3.6 fold ± .33 where the S45P mutant was not affected. Coexpression of GSK3β did not attenuate increased Wnt activity observed with the mutants H36P and I35S, however it did decrease activity observed with the S23R by a similar magnitude of the wild type CTNNB1 control (2.27 fold ± .93). These results describe the activating nature of H36P, S45P, and I35S which likely mediate their effect via impaired CTNNB1 phosphorylation. To a lesser extent, S23R activated Wnt activity, however, is subject to attenuation by GSK3β phosphorylation.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2249. doi:1538-7445.AM2012-2249
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Freedman BI, Langefeld CD, Murea M, Ma L, Otvos JD, Turner J, Antinozzi PA, Divers J, Hicks PJ, Bowden DW, Rocco MV, Parks JS. Apolipoprotein L1 nephropathy risk variants associate with HDL subfraction concentration in African Americans. Nephrol Dial Transplant 2011; 26:3805-10. [PMID: 21931123 DOI: 10.1093/ndt/gfr542] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND Coding variants in the apolipoprotein L1 gene (APOL1) are strongly associated with non-diabetic nephropathy in African Americans. ApoL1 proteins associate with high-density lipoprotein (HDL) particles in the circulation. Plasma HDL particle subclass concentrations were compared in 73 African Americans based on APOL1 genotypes to detect differences potentially contributing to renal disease. METHODS HDL subclass concentrations were measured using nuclear magnetic resonance spectroscopy in African American first-degree relatives of patients with non-diabetic end-stage renal disease. Participants had estimated glomerular filtration rates (GFRs) > 80 mL/min and lacked albuminuria. Additive effects of the number of APOL1 risk variants on natural logarithm-transformed HDL subclass concentrations were computed. RESULTS Participants were 58.9% female with mean ± SD age 47.2 ± 13.3 years and GFR 92.4 ± 18.8 mL/min. The numbers with 2, 1 and 0 APOL1 nephropathy risk variants, respectively, were 36, 17 and 20. Mean ± SD medium-sized HDL concentrations were significantly lower for each additional APOL1 risk variant (2 versus 1 versus 0 risk variants: 9.0 ± 5.6 versus 10.1 ± 5.5 versus 13.1 ± 8.2 μmol/L, respectively; P = 0.0222 unadjusted; P = 0.0162 triglyceride- and ancestry adjusted). CONCLUSIONS Lower medium-sized HDL subclass concentrations are present in African Americans based on increasing numbers of APOL1 nephropathy risk variants. Potential mechanistic roles of altered medium HDL concentrations on APOL1-associated renal microvascular diseases should be evaluated.
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Affiliation(s)
- Barry I Freedman
- Department of Internal Medicine, Section on Nephrology, Wake Forest School of Medicine, Winston-Salem, NC, USA.
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Ma L, Mondal AK, Murea M, Sharma NK, Tönjes A, Langberg KA, Das SK, Franks PW, Kovacs P, Antinozzi PA, Stumvoll M, Parks JS, Elbein SC, Freedman BI. The effect of ACACB cis-variants on gene expression and metabolic traits. PLoS One 2011; 6:e23860. [PMID: 21887335 PMCID: PMC3162605 DOI: 10.1371/journal.pone.0023860] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Accepted: 07/26/2011] [Indexed: 12/30/2022] Open
Abstract
BACKGROUND Acetyl Coenzyme A carboxylase β (ACACB) is the rate-limiting enzyme in fatty acid oxidation, and continuous fatty acid oxidation in Acacb knock-out mice increases insulin sensitivity. Systematic human studies have not been performed to evaluate whether ACACB variants regulate gene expression and insulin sensitivity in skeletal muscle and adipose tissues. We sought to determine whether ACACB transcribed variants were associated with ACACB gene expression and insulin sensitivity in non-diabetic African American (AA) and European American (EA) adults. METHODS ACACB transcribed single nucleotide polymorphisms (SNPs) were genotyped in 105 EAs and 46 AAs whose body mass index (BMI), lipid profiles and ACACB gene expression in subcutaneous adipose and skeletal muscle had been measured. Allelic expression imbalance (AEI) was assessed in lymphoblast cell lines from heterozygous subjects in an additional EA sample (n = 95). Selected SNPs were further examined for association with insulin sensitivity in a cohort of 417 EAs and 153 AAs. RESULTS ACACB transcribed SNP rs2075260 (A/G) was associated with adipose ACACB messenger RNA expression in EAs and AAs (p = 3.8×10(-5), dominant model in meta-analysis, Stouffer method), with the (A) allele representing lower gene expression in adipose and higher insulin sensitivity in EAs (p = 0.04). In EAs, adipose ACACB expression was negatively associated with age and sex-adjusted BMI (r = -0.35, p = 0.0002). CONCLUSIONS Common variants within the ACACB locus appear to regulate adipose gene expression in humans. Body fat (represented by BMI) may further regulate adipose ACACB gene expression in the EA population.
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Affiliation(s)
- Lijun Ma
- Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America.
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Murea M, Freedman BI, Parks JS, Antinozzi PA, Elbein SC, Ma L. Lipotoxicity in Diabetic Nephropathy: The Potential Role of Fatty Acid Oxidation. Clin J Am Soc Nephrol 2010; 5:2373-9. [DOI: 10.2215/cjn.08160910] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Abstract
In most genome-wide linkage studies, implication of a causative disease gene often requires years of expanding the study to more families and finer mapping of the initially described region. Even after such efforts, unobtainable sample sizes can be required to make statistically meaningful conclusions about a single gene. Here we demonstrate that by adding a layer of functional biology to statistical genetic results, this process can be accelerated. The diabetes susceptibility locus (chromosome 18p11) was systematically dissected by using a cell-based secretion assay and RNA interference, and we identified laminin alpha1 to have a role in pancreatic beta cell secretion. The screen was extended to identify laminin receptor 1 as a functional partner in regards to beta cell function. Our approach can potentially be widely used in the setting of high-throughput cellular screening of other loci to identify candidate genes.
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Affiliation(s)
- Peter A. Antinozzi
- The Judith P. Sulzberger, M.D., Columbia Genome Center and Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, 1150 St. Nicholas Avenue, Russ Berrie Pavilion, Floor 5, New York, NY 10032
- *To whom correspondence may be addressed. E-mail:
or
| | - Alejandro Garcia-Diaz
- The Judith P. Sulzberger, M.D., Columbia Genome Center and Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, 1150 St. Nicholas Avenue, Russ Berrie Pavilion, Floor 5, New York, NY 10032
| | - Chuan Hu
- The Judith P. Sulzberger, M.D., Columbia Genome Center and Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, 1150 St. Nicholas Avenue, Russ Berrie Pavilion, Floor 5, New York, NY 10032
| | - James E. Rothman
- The Judith P. Sulzberger, M.D., Columbia Genome Center and Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, 1150 St. Nicholas Avenue, Russ Berrie Pavilion, Floor 5, New York, NY 10032
- *To whom correspondence may be addressed. E-mail:
or
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Wang H, Iezzi M, Theander S, Antinozzi PA, Gauthier BR, Halban PA, Wollheim CB. Suppression of Pdx-1 perturbs proinsulin processing, insulin secretion and GLP-1 signalling in INS-1 cells. Diabetologia 2005; 48:720-31. [PMID: 15756539 DOI: 10.1007/s00125-005-1692-8] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2004] [Accepted: 12/06/2004] [Indexed: 02/05/2023]
Abstract
AIMS/HYPOTHESIS Mutations in genes encoding HNF-4alpha, HNF-1alpha and IPF-1/Pdx-1 are associated with, respectively, MODY subtypes-1, -3 and -4. Impaired glucose-stimulated insulin secretion is the common primary defect of these monogenic forms of diabetes. A regulatory circuit between these three transcription factors has also been suggested. We aimed to explore how Pdx-1 regulates beta cell function and gene expression patterns. METHODS We studied two previously established INS-1 stable cell lines permitting inducible expression of, respectively, Pdx-1 and its dominant-negative mutant. We used HPLC for insulin processing, adenovirally encoded aequorin for cytosolic [Ca2+], and transient transfection of human growth hormone or patch-clamp capacitance recordings to monitor exocytosis. RESULTS Induction of DN-Pdx-1 resulted in defective glucose-stimulated and K+-depolarisation-induced insulin secretion in INS-1 cells, while overexpression of Pdx-1 had no effect. We found that DN-Pdx-1 caused down-regulation of fibroblast growth factor receptor 1 (FGFR1), and consequently prohormone convertases (PC-1/3 and -2). As a result, DN-Pdx-1 severely impaired proinsulin processing. In addition, induction of Pdx-1 suppressed the expression of glucagon-like peptide 1 receptor (GLP-1R), which resulted in marked reduction of both basal and GLP-1 agonist exendin-4-stimulated cellular cAMP levels. Induction of DN-Pdx-1 did not affect glucokinase activity, glycolysis, mitochondrial metabolism or ATP generation. The K+-induced cytosolic [Ca2+] rise and Ca2+-evoked exocytosis (membrane capacitance) were not abrogated. CONCLUSIONS/INTERPRETATION The severely impaired proinsulin processing combined with decreased GLP-1R expression and cellular cAMP content, rather than metabolic defects or altered exocytosis, may contribute to the beta cell dysfunction induced by Pdx-1 deficiency.
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MESH Headings
- Adenosine Triphosphate/metabolism
- Animals
- Calcium Signaling/physiology
- Cell Line, Tumor
- Cyclic AMP/metabolism
- Dose-Response Relationship, Drug
- Doxycycline/pharmacology
- Exocytosis/physiology
- Gene Expression/drug effects
- Gene Expression/genetics
- Gene Expression Regulation, Neoplastic/drug effects
- Glucagon-Like Peptide-1 Receptor
- Glucokinase/genetics
- Glucose/metabolism
- Glucose/pharmacology
- Glycolysis
- Homeodomain Proteins/genetics
- Homeodomain Proteins/metabolism
- Homeodomain Proteins/physiology
- Human Growth Hormone/genetics
- Human Growth Hormone/metabolism
- Insulin/metabolism
- Insulin Secretion
- Islets of Langerhans/drug effects
- Islets of Langerhans/metabolism
- Mitochondria/metabolism
- Mutation
- Proinsulin/metabolism
- Proprotein Convertases/genetics
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Receptor Protein-Tyrosine Kinases/genetics
- Receptor, Fibroblast Growth Factor, Type 1
- Receptors, Fibroblast Growth Factor/genetics
- Receptors, Glucagon/genetics
- Receptors, Glucagon/physiology
- Signal Transduction/physiology
- Time Factors
- Trans-Activators/genetics
- Trans-Activators/metabolism
- Trans-Activators/physiology
- Transfection
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Affiliation(s)
- H Wang
- Department of Cell Physiology and Metabolism, University Medical Center, 1211 Geneva 4, Switzerland.
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Wang H, Maechler P, Antinozzi PA, Herrero L, Hagenfeldt-Johansson KA, Bjorklund A, Wollheim CB. The transcription factor SREBP-1c is instrumental in the development of beta-cell dysfunction. J Biol Chem 2003; 278:16622-9. [PMID: 12600983 DOI: 10.1074/jbc.m212488200] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Accumulation of lipids in non-adipose tissues is often associated with Type 2 diabetes and its complications. Elevated expression of the lipogenic transcription factor, sterol regulatory element binding protein-1c (SREBP-1c), has been demonstrated in islets and liver of diabetic animals. To elucidate the molecular mechanisms underlying SREBP-1c-induced beta-cell dysfunction, we employed the Tet-On inducible system to achieve tightly controlled and conditional expression of the nuclear active form of SREBP-1c (naSREBP-1c) in INS-1 cells. Controlled expression of naSREBP-1c induced massive accumulation of lipid droplets and blunted nutrient-stimulated insulin secretion in INS-1 cells. K(+)-evoked insulin exocytosis was unaltered. Quantification of the gene expression profile in this INS-1 stable clone revealed that naSREBP-1c induced beta-cell dysfunction by targeting multiple genes dedicated to carbohydrate metabolism, lipid biosynthesis, cell growth, and apoptosis. naSREBP-1c elicits cell growth-arrest and eventually apoptosis. We also found that the SREBP-1c processing in beta-cells was irresponsive to acute stimulation of glucose and insulin, which was distinct from that in lipogenic tissues. However, 2-day exposure to these agents promoted SREBP-1c processing. Therefore, the SREBP-1c maturation could be implicated in the pathogenesis of beta-cell glucolipotoxicity.
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Affiliation(s)
- Haiyan Wang
- Department of Internal Medicine, University Medical Centre, Geneva-4 CH-1211, Switzerland.
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Rubí B, Antinozzi PA, Herrero L, Ishihara H, Asins G, Serra D, Wollheim CB, Maechler P, Hegardt FG. Adenovirus-mediated overexpression of liver carnitine palmitoyltransferase I in INS1E cells: effects on cell metabolism and insulin secretion. Biochem J 2002; 364:219-26. [PMID: 11988095 PMCID: PMC1222564 DOI: 10.1042/bj3640219] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Lipid metabolism in the beta-cell is critical for the regulation of insulin secretion. Pancreatic beta-cells chronically exposed to fatty acids show higher carnitine palmitoyltransferase I (CPT I) protein levels, higher palmitate oxidation rates and an altered insulin response to glucose. We examined the effect of increasing CPT I levels on insulin secretion in cultured beta-cells. We prepared a recombinant adenovirus containing the cDNA for the rat liver isoform of CPT I. The overexpression of CPT I in INS1E cells caused a more than a 5-fold increase in the levels of CPT I protein (detected by Western blotting), a 6-fold increase in the CPT activity, and an increase in fatty acid oxidation at 2.5 mM glucose (1.7-fold) and 15 mM glucose (3.1-fold). Insulin secretion was stimulated in control cells by 15 mM glucose or 30 mM KCl. INS1E cells overexpressing CPT I showed lower insulin secretion on stimulation with 15 mM glucose (-40%; P<0.05). This decrease depended on CPT I activity, since the presence of etomoxir, a specific inhibitor of CPT I, in the preincubation medium normalized the CPT I activity, the fatty-acid oxidation rate and the insulin secretion in response to glucose. Exogenous palmitate (0.25 mM) rescued glucose-stimulated insulin secretion (GSIS) in CPT I-overexpressing cells, indicating that the mechanism of impaired GSIS was through the depletion of a critical lipid. Depolarizing the cells with KCl or intermediary glucose concentrations (7.5 mM) elicited similar insulin secretion in control cells and cells overexpressing CPT I. Glucose-induced ATP increase, glucose metabolism and the triacylglycerol content remained unchanged. These results provide further evidence that CPT I activity regulates insulin secretion in the beta-cell. They also indicate that up-regulation of CPT I contributes to the loss of response to high glucose in beta-cells exposed to fatty acids.
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Affiliation(s)
- Blanca Rubí
- Department of Biochemistry and Molecular Biology, University of Barcelona, School of Pharmacy, Diagonal 643, E-08028 Barcelona, Spain
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Antinozzi PA, Ishihara H, Newgard CB, Wollheim CB. Mitochondrial metabolism sets the maximal limit of fuel-stimulated insulin secretion in a model pancreatic beta cell: a survey of four fuel secretagogues. J Biol Chem 2002; 277:11746-55. [PMID: 11821387 DOI: 10.1074/jbc.m108462200] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The precise metabolic steps that couple glucose catabolism to insulin secretion in the pancreatic beta cell are incompletely understood. ATP generated from glycolytic metabolism in the cytosol, from mitochondrial metabolism, and/or from the hydrogen shuttles operating between cytosolic and mitochondrial compartments has been implicated as an important coupling factor. To identify the importance of each of these metabolic pathways, we have compared the fates of four fuel secretagogues (glucose, pyruvate, dihydroxyacetone, and glycerol) in the INS1-E beta cell line. Two of these fuels, dihydroxyacetone and glycerol, are normally ineffective as secretagogues but are enabled by adenovirus-mediated expression of glycerol kinase. Comparison of these two particular fuels allows the effect of redox state on insulin secretion to be evaluated since the phosphorylated products dihydroxyacetone phosphate and glycerol phosphate lie on opposite sides of the NADH-consuming glycerophosphate dehydrogenase reaction. Based upon measurements of glycolytic metabolites, mitochondrial oxidation, mitochondrial matrix calcium, and mitochondrial membrane potential, we find that insulin secretion most tightly correlates with mitochondrial metabolism for each of the four fuels. In the case of glucose stimulation, the high control strength of glucose phosphorylation sets the pace of glucose metabolism and thus the rate of insulin secretion. However, bypassing this reaction with pyruvate, dihydroxyacetone, or glycerol uncovers constraints imposed by mitochondrial metabolism, each of which attains a similar maximal limit of insulin secretion. More specifically, we found that the hyperpolarization of the mitochondrial membrane, related to the proton export from the mitochondrial matrix, correlates well with insulin secretion. Based on these findings, we propose that fuel-stimulated secretion is in fact limited by the inherent thermodynamic constraints of proton gradient formation.
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Affiliation(s)
- Peter A Antinozzi
- Division of Clinical Biochemistry and Experimental Diabetology, Department of Internal Medicine, University Medical Center, CH-1211 Geneva 4, Switzerland.
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Skelly RH, Wicksteed B, Antinozzi PA, Rhodes CJ. Glycerol-stimulated proinsulin biosynthesis in isolated pancreatic rat islets via adenoviral-induced expression of glycerol kinase is mediated via mitochondrial metabolism. Diabetes 2001; 50:1791-8. [PMID: 11473040 DOI: 10.2337/diabetes.50.8.1791] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
In this study, we examined whether adenoviral-mediated glycerol kinase (AdV-CMV-GlyK) expression in isolated rat pancreatic islets could introduce glycerol-induced proinsulin biosynthesis. In AdV-CMV-GlyK-infected islets, specific glycerol-induced proinsulin biosynthesis translation and insulin secretion were observed in parallel from the same islets. The threshold concentration of glycerol required to stimulate proinsulin biosynthesis was lower (0.25-0.5 mmol/l) than that for insulin secretion (1.0-1.5 mmol/l), reminiscent of threshold differences for glucose-stimulated proinsulin biosynthesis versus insulin secretion. The dose-dependent glycerol-induced proinsulin biosynthesis correlated with the rate of glycerol oxidation in AdV-CMV-GlyK-infected islets, indicating that glycerol metabolism was required for the response. However, glycerol did not significantly increase lactate output from AdV-CMV-GlyK-infected islets, but the dihydroxyacetone phosphate (DHAP) to alpha-glycerophosphate (alpha-GP) ratio significantly increased in AdV-CMV-GlyK-infected islets incubated at 2 mmol/l glycerol compared with that at a basal level of 2.8 mmol/l glucose (P < or = 0.05). The DHAP:alpha-GP ratio was unaffected in AdV-CMV-GlyK-infected islets incubated at 2 mmol/l glycerol in the added presence of alpha-cyanohydroxycinnaminic acid (alpha-CHC), an inhibitor of the plasma membrane and mitochondrial lactate/pyruvate transporter. However, alpha-CHC inhibited glycerol-induced proinsulin biosynthesis and insulin secretion in AdV-CMV-GlyK-infected islets (>75%; P = 0.05), similarly to glucose-induced proinsulin biosynthesis and insulin secretion in AdV-CMV-GlyK-infected and control islets. These data indicated that in AdV-CMV-GlyK-infected islets, the importance of mitochondrial metabolism of glycerol was required to generate stimulus-response coupling signals to induce proinsulin biosynthesis and insulin secretion.
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Affiliation(s)
- R H Skelly
- Pacific Northwest Research Institute and Department of Pharmacology, University of Washington, Seattle, WA 98112, USA
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Mulder H, Lu D, Finley J, An J, Cohen J, Antinozzi PA, McGarry JD, Newgard CB. Overexpression of a modified human malonyl-CoA decarboxylase blocks the glucose-induced increase in malonyl-CoA level but has no impact on insulin secretion in INS-1-derived (832/13) beta-cells. J Biol Chem 2001; 276:6479-84. [PMID: 11113153 DOI: 10.1074/jbc.m010364200] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The long-chain acyl-CoA (LC-CoA) model of glucose-stimulated insulin secretion (GSIS) holds that secretion is linked to a glucose-induced increase in malonyl-CoA level and accumulation of LC-CoA in the cytosol. We have previously tested the validity of this proposal by overexpressing goose malonyl-CoA decarboxylase (MCD) in INS-1 cells, but these studies have been criticized due to: 1) the small insulin secretion response (2-4-fold) of the INS-1 cells used; 2) unknown contribution of the ATP-sensitive K(+) (K(ATP)) channel-independent pathway of GSIS in INS-1 cells, which has been implicated as the site at which lipids regulate insulin granule exocytosis; and 3) deletion of the N-terminal mitochondrial targeting sequence, but not the C-terminal peroxisomal targeting sequence in the goose MCD construct, raising the possibility that a significant fraction of the overexpressed enzyme was localized to peroxisomes. To address these outstanding concerns, INS-1-derived 832/13 cells, which exhibit robust K(ATP) channel-dependent and -independent pathways of GSIS, were treated with a new adenovirus encoding human MCD lacking both its mitochondrial and peroxisomal targeting sequences (AdCMV-MCD Delta 5), resulting in large increases in cytosolic MCD activity. Treatment of 832/13 cells with AdCMV-MCD Delta 5 completely blocked the glucose-induced rise in malonyl-CoA and attenuated the inhibitory effect of glucose on fatty acid oxidation. However, MCD overexpression had no effect on K(ATP) channel-dependent or -independent GSIS in 832/13 cells. Furthermore, combined treatment of 832/13 cells with AdCMV-MCD Delta 5 and triacsin C, an inhibitor of long chain acyl-CoA synthetase that reduces LC-CoA levels, did not impair GSIS. These findings extend our previous observations and are not consistent with the LC-CoA hypothesis as originally set forth.
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Affiliation(s)
- H Mulder
- Touchstone Center for Diabetes Research and Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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Wang H, Maechler P, Antinozzi PA, Hagenfeldt KA, Wollheim CB. Hepatocyte nuclear factor 4alpha regulates the expression of pancreatic beta -cell genes implicated in glucose metabolism and nutrient-induced insulin secretion. J Biol Chem 2000; 275:35953-9. [PMID: 10967120 DOI: 10.1074/jbc.m006612200] [Citation(s) in RCA: 163] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutations in the HNF4alpha gene are associated with the subtype 1 of maturity-onset diabetes of the young (MODY1), which is characterized by impaired insulin secretory response to glucose in pancreatic beta-cells. Hepatocyte nuclear factor 4alpha (HNF4alpha) is a transcription factor critical for liver development and hepatocyte-specific gene expression. However, the role of HNF4alpha in the regulation of pancreatic beta-cell gene expression and its correlation with metabolism secretion coupling have not been previously investigated. The tetracycline-inducible system was employed to achieve tightly controlled expression of both wild type (WT) and dominant-negative mutant (DN) of HNF4alpha in INS-1 cells. The induction of WT-HNF4alpha resulted in a left shift in glucose-stimulated insulin secretion, whereas DN-HNF4alpha selectively impaired nutrient-stimulated insulin release. Induction of DN-HNF4alpha also caused defective mitochondrial function substantiated by reduced [(14)C]pyruvate oxidation, attenuated substrate-evoked mitochondrial membrane hyperpolarization, and blunted nutrient-generated cellular ATP production. Quantitative evaluation of HNF4alpha-regulated pancreatic beta-cell gene expression revealed altered mRNA levels of insulin, glucose transporter-2, L-pyruvate kinase, aldolase B, 2-oxoglutarate dehydrogenase E1 subunit, and mitochondrial uncoupling protein-2. The patterns of HNF4alpha-regulated gene expression are strikingly similar to that of its downstream transcription factor HNF1alpha. Indeed, HNF4alpha changed the HNF1alpha mRNA levels and HNF1alpha promoter luciferase activity through altered HNF4alpha binding. These results demonstrate the importance of HNF4alpha in beta-cell metabolism-secretion coupling.
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Affiliation(s)
- H Wang
- Division de Biochimie Clinique, Départment de Médecine Interne, Centre Médical Universitaire, CH-1211 Geneva 4, Switzerland
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Wang H, Antinozzi PA, Hagenfeldt KA, Maechler P, Wollheim CB. Molecular targets of a human HNF1 alpha mutation responsible for pancreatic beta-cell dysfunction. EMBO J 2000; 19:4257-64. [PMID: 10944108 PMCID: PMC302029 DOI: 10.1093/emboj/19.16.4257] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The reverse tetracycline-dependent transactivator system was employed in insulinoma INS-1 cells to achieve controlled inducible expression of hepatocyte nuclear factor-1 alpha (HNF1 alpha)-P291fsinsC, the most common mutation associated with subtype 3 of maturity-onset diabetes of the young (MODY3). Nuclear localized HNF1 alpha-P291fsinsC protein exerts its dominant-negative effects by competing with endogenous HNF1 alpha for the cognate DNA-binding site. HNF1 alpha controls multiple genes implicated in pancreatic beta-cell function and notably in metabolism- secretion coupling. In addition to reduced expression of the genes encoding insulin, glucose transporter-2, L-pyruvate kinase, aldolase B and 3-hydroxy-3-methylglutaryl coenzyme A reductase, induction of HNF1 alpha-P291fsinsC also significantly inhibits expression of mitochondrial 2-oxoglutarate dehydrogenase (OGDH) E1 subunit mRNA and protein. OGDH enzyme activity and [(14)C]pyruvate oxidation were also reduced. In contrast, the mRNA and protein levels of mitochondrial uncoupling protein-2 were dramatically increased by HNF1 alpha-P291fsinsC induction. As predicted from this altered gene expression profile, HNF1 alpha-P291fsinsC also inhibits insulin secretory responses to glucose and leucine, correlated with impaired nutrient-evoked mitochondrial ATP production and mitochondrial membrane hyperpolarization. These unprecedented results suggest the molecular mechanism of HNF1 alpha-P291fsinsC causing beta-cell dysfunction.
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Affiliation(s)
- H Wang
- Division de Biochimie Clinique et de Diabétologie Expérimentale, Départment de Médecine interne, Centre Médical Universitaire, CH-1211 Geneva 4, Switzerland
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Abstract
The mitochondria play a pivotal role in regulating glucose-induced insulin secretion in the pancreatic beta cell. We have recently demonstrated that glutamate derived from mitochondria participates directly in the stimulation of insulin exocytosis. In the present study, mitochondria isolated from the beta cell line INS-1E generated glutamate when incubated with the tricarboxylic acid cycle intermediate succinate. The generation of glutamate correlated with stimulated mitochondrial activity monitored as oxygen consumption and was inhibited by the mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Glutamate is formed by the mitochondrial enzyme glutamate dehydrogenase from alpha-ketoglutarate. Transient overexpression of glutamate dehydrogenase in INS-1E cells resulted in potentiation of glucose-stimulated hormone secretion without affecting basal release. These results further point to glutamate as an intracellular messenger playing a key role in the control of insulin exocytosis.
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Affiliation(s)
- P Maechler
- Department of Internal Medicine, University Medical Center, Geneva, Switzerland.
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Abstract
Fuel homeostasis in mammals is accomplished by the interplay between tissues and organs with distinct metabolic roles. These regulatory mechanisms are disrupted in obesity and diabetes, leading to a renewed emphasis on discovery of molecular and pharmacologic methods for reversing metabolic disorders. In this chapter, we review the use of recombinant adenoviral vectors as tools for delivering metabolic regulatory genes to cells in culture and to tissues of intact animals. Included are studies on the use of these vectors for gaining insights into the biochemical mechanisms that regulate glucose-stimulated insulin secretion from pancreatic islet beta-cells. We also highlight their use for understanding the function of newly discovered genes that regulate glycogen metabolism in liver and other tissues, and for evaluating "candidate" genes such as glucose-6-phosphatase, which may contribute to development of metabolic dysfunction in pancreatic islets and liver. Finally, we discuss the use of adenoviral and related vectors for causing chronic increases in the levels of circulating hormones. These examples serve to highlight the power of viral gene transfer vectors as tools for understanding metabolic regulatory mechanisms.
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Affiliation(s)
- P A Antinozzi
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235, USA
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Antinozzi PA, Segall L, Prentki M, McGarry JD, Newgard CB. Molecular or pharmacologic perturbation of the link between glucose and lipid metabolism is without effect on glucose-stimulated insulin secretion. A re-evaluation of the long-chain acyl-CoA hypothesis. J Biol Chem 1998; 273:16146-54. [PMID: 9632669 DOI: 10.1074/jbc.273.26.16146] [Citation(s) in RCA: 127] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanism by which glucose stimulates insulin secretion from the pancreatic islets of Langerhans is incompletely understood. It has been suggested that malonyl-CoA plays a regulatory role by inhibiting fatty acid oxidation and promoting accumulation of cytosolic long-chain acyl-CoA (LC-CoA). In the current study, we have re-evaluated this "long-chain acyl-CoA hypothesis" by using molecular and pharmacologic methods to perturb lipid metabolism in INS-1 insulinoma cells or rat islets during glucose stimulation. First, we constructed a recombinant adenovirus containing the cDNA encoding malonyl-CoA decarboxylase (AdCMV-MCD), an enzyme that decarboxylates malonyl-CoA to acetyl-CoA. INS-1 cells treated with AdCMV-MCD had dramatically lowered intracellular malonyl CoA levels compared with AdCMV-betaGal-treated cells at both 3 and 20 mM glucose. Further, at 20 mM glucose, AdCMV-MCD-treated cells were less effective at suppressing [1-14C]palmitate oxidation and incorporated 43% less labeled palmitate and 50% less labeled glucose into cellular lipids than either AdCMV-betaGAL-treated or untreated INS-1 cells. Despite the large metabolic changes caused by expression of MCD, insulin secretion in response to glucose was unaltered relative to controls. The alternative, pharmacologic approach for perturbing lipid metabolism was to use triacsin C to inhibit long-chain acyl-CoA synthetase. This agent caused potent attenuation of palmitate oxidation and glucose or palmitate incorporation into cellular lipids and also caused a 47% decrease in total LC-CoA. Despite this, the drug had no effect on glucose-stimulated insulin secretion in islets or INS-1 cells. We conclude that significant disruption of the link between glucose and lipid metabolism does not impair glucose-stimulated insulin secretion in pancreatic islets or INS-1 cells.
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Affiliation(s)
- P A Antinozzi
- Departments of Biochemistry & Internal Medicine and Gifford Laboratories for Diabetes Research, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA
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Noel RJ, Antinozzi PA, McGarry JD, Newgard CB. Engineering of glycerol-stimulated insulin secretion in islet beta cells. Differential metabolic fates of glucose and glycerol provide insight into mechanisms of stimulus-secretion coupling. J Biol Chem 1997; 272:18621-7. [PMID: 9228030 DOI: 10.1074/jbc.272.30.18621] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Insulin secretion from beta cells in the islets of Langerhans can be stimulated by a number of metabolic fuels, including glucose and glyceraldehyde, and is thought to be mediated by metabolism of the secretagogues and an attendant increase in the ATP:ADP ratio. Curiously, glycerol fails to stimulate insulin secretion, even though it has been reported that islets contain abundant glycerol kinase activity and oxidize glycerol efficiently. We have reinvestigated this point and find that rat islets and the well differentiated insulinoma cell line INS-1 contain negligible glycerol kinase activity. A recombinant adenovirus containing the bacterial glycerol kinase gene (AdCMV-GlpK) was constructed and used to express the enzyme in islets and INS-1 cells, resulting in insulin secretion in response to glycerol. In AdCMV-GlpK-treated INS-1 cells a greater proportion of glycerol is converted to lactate and a lesser proportion is oxidized compared with glucose. The two fuels are equally potent as insulin secretagogues, despite the fact that oxidation of glycerol at its maximally effective dose (2-5 mM) occurs at a rate that is similar to the rate of glucose oxidation at its basal, nonstimulatory concentration (3 mM). We also investigated the possibility that glycerol may signal via expansion of the glycerol phosphate pool to allow enhanced fatty acid esterification and formation of complex lipids. Addition of Triacsin-C, an inhibitor of long-chain acyl-CoA synthetase, to AdCMV-GlpK-treated INS-1 cells did not inhibit glycerol-stimulated insulin secretion despite the fact that it blocked glycerol incorporation into cellular lipids. We conclude from these studies that glycerol kinase expression is sufficient to activate glycerol signaling in beta cells, showing that the failure of normal islets to respond to this substrate is due to a lack of this enzyme activity. Further, our studies show that glycerol signaling is not linked to esterification or oxidation of the substrate, but is likely mediated by its metabolism in the glycerol phosphate shuttle and/or the distal portion of the glycolytic pathway, either of which can lead to production of ATP and an increased ATP:ADP ratio.
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Affiliation(s)
- R J Noel
- Gifford Laboratories for Diabetes Research, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA
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