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Einstein FH, Atzmon G, Yang XM, Ma XH, Rincon M, Rudin E, Muzumdar R, Barzilai N. Differential responses of visceral and subcutaneous fat depots to nutrients. Diabetes 2005; 54:672-8. [PMID: 15734842 DOI: 10.2337/diabetes.54.3.672] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Increased visceral adiposity is a pivotal component of the metabolic syndrome. Differential gene expression patterns of fat-derived peptides (FDPs) in visceral fat and subcutaneous fat have been characterized in the fasting state. Here we examined whether delivery of nutrients differentially affects the expression of FDPs in visceral fat versus subcutaneous fat (in the fed state). We increased the rate of glucose flux into adipose tissue of normal rats (n = 16) by hyperglycemia or hyperinsulinemia using the clamp technique. Glucose uptake was associated with increased expression of FDPs, including resistin ( approximately 5-fold), adiponectin ( approximately 2-fold), leptin ( approximately 15-fold), plasminogen activating inhibitor-1 ( approximately 10-fold), and angiotensinogen ( approximately 4-fold) in visceral fat, but markedly less in subcutaneous fat. Cytokine expression derived mainly from vascular/stromal/macrophage components of adipose tissue was less dramatically increased. Infusion of glucosamine amplified the results obtained by increasing glucose uptake into adipose tissue, suggesting that flux through the hexosamine biosynthetic pathway may serve as a mechanism for "nutrient sensing." Nutrient-dependent expression of FDPs in visceral fat was also associated with increased plasma levels of several FDPs. Because a biologic sensing pathway can dynamically couple daily food intake to abnormal plasma levels of important FDPs, we challenge the practice of obtaining plasma levels after fasting to assess risk factors for metabolic syndrome.
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Affiliation(s)
- Francine H Einstein
- Department of Obstetrics and Gynecology and Women's Health, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA
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52
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Horal M, Zhang Z, Stanton R, Virkamäki A, Loeken MR. Activation of the hexosamine pathway causes oxidative stress and abnormal embryo gene expression: involvement in diabetic teratogenesis. ACTA ACUST UNITED AC 2005; 70:519-27. [PMID: 15329829 DOI: 10.1002/bdra.20056] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND Oxidative stress is critical to the teratogenic effects of diabetic pregnancy, yet the specific biochemical pathways responsible for oxidative stress have not been fully elucidated. The hexosamine pathway is activated in many tissues during diabetes and could contribute to oxidative stress by inhibiting the pentose shunt pathway, thereby diminishing production of the cellular antioxidant, reduced glutathione (GSH). METHODS To test the hypothesis that activation of the hexosamine pathway might contribute to the teratogenic effects of diabetic pregnancy, pregnant mice were injected with glucose, to induce hyperglycemia, or glucosamine, to directly activate the hexosamine pathway. Embryo tissue fragments were also cultured in physiological glucose, high glucose, or physiological glucose plus glucosamine, to test effects on oxidative stress and embryo gene expression. RESULTS Glucosamine increased hexosamine synthesis and inhibited pentose shunt activity. There was a trend for transient hyperglycemia to have the same effects, but they did not reach statistical significance. However, both glucose and glucosamine significantly decreased GSH, and increased oxidative stress, as indicated by 2',7'-dichloro-dihydrofluorescein fluorescence. Glucose and glucosamine inhibited expression of Pax-3, a gene required for neural tube closure both in vivo and in vitro, and increased neural tube defects (NTDs) in vivo; these effects were prevented by GSH ethyl ester. High glucose and glucosamine inhibited Pax-3 expression by embryo culture, but culture in glutamine-free media to block the hexosamine pathway prevented the inhibition of Pax-3 expression by high glucose. CONCLUSIONS Activation of the hexosamine pathway causes oxidative stress through depletion of GSH and consequent disruption of embryo gene expression. Activation of this pathway may contribute to diabetic teratogenesis.
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Affiliation(s)
- Melissa Horal
- Section on Developmental and Stem Cell Biology, Joslin Diabetes Center, Boston, Massachusetts 02215, USA
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53
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Masson E, Wiernsperger N, Lagarde M, El Bawab S. Involvement of gangliosides in glucosamine-induced proliferation decrease of retinal pericytes. Glycobiology 2004; 15:585-91. [PMID: 15625180 DOI: 10.1093/glycob/cwi039] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The hexosamine pathway (HP) is a biochemical hypothesis recently proposed explaining cellular alterations occurring during diabetic microvascular complications. Diabetic retinopathy is a common microvascular complication of diabetes, and it is known that cell proliferation is severely affected during the development of the disease. Particularly, early stages are characterized by death of the retinal microvascular cells, pericytes. Gangliosides have often been described to regulate cell growth; however, very few studies focused on the potential role of gangliosides in diabetic microvascular alterations. The aim of this article was to investigate the effect of the HP activation on pericyte proliferation and determine the potential implication of gangliosides in this process. Results indicate first that HP activation, mimicked by glucosamine treatment, decreased pericyte proliferation. Second, glucosamine treatment induced a modification of gangliosides pattern, particularly GM1 and GD3 were significantly increased. Next, results showed that exogenous addition of a-series gangliosides (GM3, GM2, GM1, GD1a) and b-series ganglioside (GD3) caused a decrease of pericyte proliferation, whereas nonsialylated precursors glucosylceramide and lactosylceramide were without effect. Furthermore, when ganglioside biosynthesis was blocked using PPMP, a glucosylceramide synthase inhibitor, the effects of glucosamine on pericyte proliferation were partially reversed. Our results suggest that in retinal pericytes, gangliosides and particularly GM1 and GD3 that are increased in response to glucosamine, are involved in the antiproliferative effect of glucosamine. These observations also underlie the potential involvement of gangliosides in a pathological context, such as diabetic microvascular complications.
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Affiliation(s)
- Elodie Masson
- Diabetic Microangiopathy Research Unit, Merck Santé-INSERM UMR 585, INSA-Lyon, Louis Pasteur Bldg, 69621 Villeurbanne Cedex, France
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54
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Matthews JA, Acevedo-Duncan M, Potter RL. Selective decrease of membrane-associated PKC-alpha and PKC-epsilon in response to elevated intracellular O-GlcNAc levels in transformed human glial cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2004; 1743:305-15. [PMID: 15843043 DOI: 10.1016/j.bbamcr.2004.11.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2004] [Revised: 10/19/2004] [Accepted: 11/03/2004] [Indexed: 11/19/2022]
Abstract
Increased flux through the hexosamine biosynthetic pathway (HBP) has been shown to affect the activity and translocation of certain protein kinase C (PKC) isoforms. It has been suggested that this effect is due to increases in the beta-O-linked N-acetylglucosamine (O-GlcNAc) modification. Herein, we demonstrate the effect of increasing the O-GlcNAc modification on the translocation of select PKC isozymes in a human astroglial cell line. Treating cells with either 8 mM d-glucosamine (GlcN), 5 mM streptozotocin (STZ), or 80 muM O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc) produced a significant increase in the O-GlcNAc modification on both cytosolic and membrane proteins; however, both the level and rate of O-GlcNAc increase varied with the compound. GlcN treatment resulted in a rapid, transient translocation of PKC-betaII that was maximal after 3 h (73+/-8%) and also produced a 48+/-15% decrease in membrane-associated PKC-epsilon after 9 h of treatment. Similar to GlcN treatment, STZ and PUGNAc treatment also resulted in decreased levels of PKC-epsilon in the membrane fraction. Significant decreases were seen as early as 5 h and, by 9 h of treatment, had decreased by 87+/-6% with STZ and 73+/-7% with PUGNAc. Unlike GlcN, both STZ and PUGNAc produced a decrease in PKC-alpha membrane levels by 9 h posttreatment (78+/-10% with STZ and 66+/-8% with PUGNAc) while neither compound produced any changes in PKC-betaII translocation. In addition, none of the three compounds affected membrane levels of PKC-iota. Altogether, these results demonstrate a novel link between increased levels of the O-GlcNAc modification and the regulation of specific PKC isoforms.
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Affiliation(s)
- Jason A Matthews
- Department of Chemistry, University of South Florida, 4202 East Fowler Ave, SCA 400, Tampa, FL, 33620, USA
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55
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King GL, Loeken MR. Hyperglycemia-induced oxidative stress in diabetic complications. Histochem Cell Biol 2004; 122:333-8. [PMID: 15257460 DOI: 10.1007/s00418-004-0678-9] [Citation(s) in RCA: 330] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/07/2004] [Indexed: 02/02/2023]
Abstract
Reactive oxygen species are increased by hyperglycemia. Hyperglycemia, which occurs during diabetes (both type 1 and type 2) and, to a lesser extent, during insulin resistance, causes oxidative stress. Free fatty acids, which may be elevated during inadequate glycemic control, may also be contributory. In this review, we will discuss the role of oxidative stress in diabetic complications. Oxidative stress may be important in diabetes, not just because of its role in the development of complications, but because persistent hyperglycemia, secondary to insulin resistance, may induce oxidative stress and contribute to beta cell destruction in type 2 diabetes. The focus of this review will be on the role of oxidative stress in the etiology of diabetic complications.
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Affiliation(s)
- George L King
- Section on Vascular Cell Biology and Complications, Joslin Diabetes Center, Boston, Massachusetts, USA
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56
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Zachara NE, O'Donnell N, Cheung WD, Mercer JJ, Marth JD, Hart GW. Dynamic O-GlcNAc modification of nucleocytoplasmic proteins in response to stress. A survival response of mammalian cells. J Biol Chem 2004; 279:30133-42. [PMID: 15138254 DOI: 10.1074/jbc.m403773200] [Citation(s) in RCA: 457] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cellular response to environmental, physiological, or chemical stress is key to survival following injury or disease. Here we describe a unique signaling mechanism by which cells detect and respond to stress in order to survive. A wide variety of stress stimuli rapidly increase nucleocytoplasmic protein modification by O-linked beta-N-acetylglucosamine (O-GlcNAc), an essential post-translational modification of Ser and Thr residues of metazoans. Blocking this post-translational modification, or reducing it, renders cells more sensitive to stress and results in decreased cell survival; and increasing O-GlcNAc levels protects cells. O-GlcNAc regulates both the rates and extent of the stress-induced induction of heat shock proteins, providing a molecular basis for these findings.
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Affiliation(s)
- Natasha E Zachara
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2185, USA
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57
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Ng DPK, Walker WH, Chia KS, Choo S, Warram JH, Krolewski AS. Scrutiny of the glutamine-fructose-6-phosphate transaminase 1 (GFPT1) locus reveals conserved haplotype block structure not associated with diabetic nephropathy. Diabetes 2004; 53:865-9. [PMID: 14988277 DOI: 10.2337/diabetes.53.3.865] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glutamine-fructose-6-phosphate transaminase 1 (GFAT) is the rate-limiting enzyme of the hexosamine pathway that has been implicated in the pathogenesis of diabetic nephropathy. As such, we hypothesized that GFPT1, which encodes for GFAT, may confer genetic susceptibility to this complication among Caucasians. Screening of all known functional regions of GFPT1 revealed six single nucleotide polymorphisms (SNPs) that were located in the promoter, introns, and 3' untranslated region. The approximately 60 kb GFPT1 locus was encompassed in a single conserved haplotype block, and two tagging SNPs were sufficient to capture >90% of the haplotype diversity. Analysis of these SNPs in a case-control study made up of type 1 diabetic subjects (324 case subjects with diabetic nephropathy and 289 control subjects with normoalbuminuria despite >15 years of diabetes) revealed no significant association even after stratification by sex, diabetes duration, glucose control, and blood pressure. Similar results were obtained among type 2 diabetic subjects (202 case and 114 control subjects). Genetic variation in GFPT1 is thus unlikely to have a major impact on susceptibility to diabetic nephropathy.
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Affiliation(s)
- Daniel P K Ng
- Section on Genetics and Epidemiology, Joslin Diabetes Center, Boston, Massachusetts, USA
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58
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Perrini S, Natalicchio A, Laviola L, Belsanti G, Montrone C, Cignarelli A, Minielli V, Grano M, De Pergola G, Giorgino R, Giorgino F. Dehydroepiandrosterone stimulates glucose uptake in human and murine adipocytes by inducing GLUT1 and GLUT4 translocation to the plasma membrane. Diabetes 2004; 53:41-52. [PMID: 14693696 DOI: 10.2337/diabetes.53.1.41] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Dehydroepiandrosterone (DHEA) has been shown to modulate glucose utilization in humans and animals, but the mechanisms of DHEA action have not been clarified. We show that DHEA induces a dose- and time-dependent increase in glucose transport rates in both 3T3-L1 and human adipocytes with maximal effects at 2 h. Exposure of adipocytes to DHEA does not result in changes of total GLUT4 and GLUT1 protein levels. However, it does result in significant increases of these glucose transporters in the plasma membrane. In 3T3-L1 adipocytes, DHEA increases tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2 and stimulates IRS-1- and IRS-2-associated phosphatidylinositol (PI) 3-kinase activity with no effects on either insulin receptor or Akt phosphorylation. In addition, DHEA causes significant increases of cytosolic Ca(2+) concentrations and a parallel activation of protein kinase C (PKC)-beta(2). The effects of DHEA are abrogated by pretreatment of adipocytes with PI 3-kinase and phospholipase C gamma inhibitors, as well as by inhibitors of Ca(2+)-dependent PKC isoforms, including a specific PKC-beta inhibitor. Thus, DHEA increases glucose uptake in both human and 3T3-L1 adipocytes by stimulating GLUT4 and GLUT1 translocation to the plasma membrane. PI 3-kinase, phospholipase C gamma, and the conventional PKC-beta(2) seem to be involved in DHEA effects.
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Affiliation(s)
- Sebastio Perrini
- Department of Emergency and Organ Transplantation, Section on Internal Medicine, Endocrinology and Metabolic Diseases, Bari, Italy
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59
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Singh LP, Green K, Alexander M, Bassly S, Crook ED. Hexosamines and TGF-beta1 use similar signaling pathways to mediate matrix protein synthesis in mesangial cells. Am J Physiol Renal Physiol 2003; 286:F409-16. [PMID: 14559714 DOI: 10.1152/ajprenal.00007.2003] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hyperglycemia-induced alterations in mesangial (MES) cell function and extracellular matrix (ECM) protein accumulation are seen in diabetic glomerulopathy. Transforming growth factor-beta1 (TGF-beta1) mediates high-glucose-induced matrix production in the kidney. Recent studies demonstrated that some of the effects of high glucose on cellular metabolism are mediated by the hexosamine biosynthesis pathway (HBP) in which fructose-6-phosphate is converted to glucosamine (GlcN) 6-phosphate. We previously showed that the high-glucose-mediated fibronectin and laminin synthesis in MES cells is mediated by the HBP and that GlcN is more potent than glucose in inducing TGF-beta1 promoter luciferase activity. In this study, we investigated the hypothesis that the effects of glucose on MES matrix production occur via hexosamine regulation of TGF-beta1. Culturing simian virus (SV)-40-transformed rat kidney MES cells in 25 mM glucose (HG) for 48 h increases cellular fibronectin and laminin levels about twofold on Western blots compared with low glucose (5 mM). GlcN (1.5 mM) or TGF-beta1 (2.5-5 ng/ml) for 24-48 h also increases ECM synthesis. However, the effects of HG or GlcN with TGF-beta1 are not additive. The presence of anti-TGF-beta1 antibodies (20 microg/ml) blocks both TGF-beta1- and GlcN-induced fibronectin synthesis. TGF-beta1 increased ECM levels via PKA (laminin and fibronectin) and PKC (fibronectin) pathways. Similarly, TGF-beta1 and hexosamines led to nonadditive increases in phosphorylation of the cAMP responsive element binding transcription factor. These results suggest that the effects of excess glucose on MES ECM synthesis occur via HBP-mediated regulation of TGF-beta1.
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Affiliation(s)
- Lalit P Singh
- Department of Internal Medicine, Division of Nephrology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
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60
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Ilic MZ, Martinac B, Handley CJ. Effects of long-term exposure to glucosamine and mannosamine on aggrecan degradation in articular cartilage. Osteoarthritis Cartilage 2003; 11:613-22. [PMID: 12880584 DOI: 10.1016/s1063-4584(03)00092-x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
OBJECTIVE To investigate the effect of long-term exposure to glucosamine or mannosamine on the catabolism of aggrecan by explant cultures of bovine articular cartilage maintained in the presence of retinoic acid. DESIGN The kinetics of loss of 35S-labeled and total aggrecan from explant cultures of bovine articular cartilage maintained in the presence of 1 micro M retinoic acid and exposed to varying concentrations of glucosamine or mannosamine was investigated over a 9-day culture period. In other experiments, the reversibility of the inhibition of aggrecan catabolism by glucosamine or mannosamine was investigated in cultures exposed to these amino sugars for the first 5 days of a 15-day culture period. The metabolism of chondrocytes exposed to these amino sugars was evaluated by measurement of lactate production or 3H-serine and 35S-sulfate incorporation into protein and glycosaminoglycans, respectively. The direct effect of these amino sugars on soluble aggrecanase activity was determined from immunoblots of aggrecan digests. RESULTS Glucosamine at 5mM concentration and mannosamine at 2mM concentration inhibited degradation of radiolabeled and chemical levels of aggrecan. At concentrations of up to 10mM amino sugars, the metabolism of chondrocytes was not impaired, as determined by lactate production, protein synthesis and the incorporation of 35S-sulfate into proteoglycans. These amino sugars did not inhibit soluble aggrecanase activity. The exposure of articular cartilage explants to 5mM glucosamine or mannosamine for 5 days in culture in the presence or absence of retinoic acid did not provide long-term suppression of stimulated aggrecan loss. CONCLUSIONS This study indicates that continuous presence of amino sugars is required to protect cartilage from stimulated loss of aggrecan.
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Affiliation(s)
- M Z Ilic
- School of Human Biosciences, La Trobe University, Melbourne, Victoria 3086, Australia.
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61
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Dodge GR, Jimenez SA. Glucosamine sulfate modulates the levels of aggrecan and matrix metalloproteinase-3 synthesized by cultured human osteoarthritis articular chondrocytes. Osteoarthritis Cartilage 2003; 11:424-32. [PMID: 12801482 DOI: 10.1016/s1063-4584(03)00052-9] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
OBJECTIVE The functional integrity of articular cartilage is determined by a balance between chondrocyte biosynthesis of extracellular matrix and its degradation. In osteoarthritis (OA), the balance is disturbed by an increase in matrix degradative enzymes and a decrease in biosynthesis of constitutive extracellular matrix molecules, such as collagen type II and aggrecan. In this study, we examined the effects of the sulfate salt of glucosamine (GS) on the mRNA and protein levels of the proteoglycan aggrecan and on the activity of matrix metalloproteinase (MMP)-3 in cultured human OA articular chondrocytes. DESIGN Freshly isolated chondrocytes were obtained from knee cartilage of patients with OA. Levels of aggrecan and MMP-3 were determined in culture media by employing Western blots after incubation with GS at concentrations ranging from 0.2 to 200 microM. Zymography (casein) was performed to confirm that effects observed at the protein level were reflected at the level of enzymatic activity. Northern hybridizations were used to examine effects of GS on levels of aggrecan and MMP-3 mRNA. Glycosaminoglycan (GAG) assays were performed on the cell layers to determine levels of cell-associated GAG component of proteoglycans. RESULTS Treatment of OA chondrocytes with GS (1.0-150 microM) resulted in a dose-dependent increase in aggrecan core protein levels, which reached 120% at 150 microM GS. These effects appeared to be due to increased expression of the corresponding gene as indicated by an increase in aggrecan mRNA levels in response to GS. MMP-3 levels decreased (18-65%) as determined by Western blots. Reduction of MMP-3 protein was accompanied by a parallel reduction in enzymatic activity. GS caused a dose-dependent increase (25-140%) in cell-associated GAG content. Chondrocytes obtained from 40% of OA patients failed to respond to GS. CONCLUSIONS The results indicate that GS can stimulate mRNA and protein levels of aggrecan core protein and, at the same time, inhibit production and enzymatic activity of matrix-degrading MMP-3 in chondrocytes from OA articular cartilage. These results provide a cogent molecular mechanism to support clinical observations suggesting that GS may have a beneficial effect in the prevention of articular cartilage loss in some patients with OA.
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Affiliation(s)
- G R Dodge
- Bone and Cartilage Research Laboratory, Nemours Children's Clinic--Wilmington, Alfred I. duPont Hospital for Children, Wilmington, DE, USA.
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Haneda M, Koya D, Isono M, Kikkawa R. Overview of glucose signaling in mesangial cells in diabetic nephropathy. J Am Soc Nephrol 2003; 14:1374-82. [PMID: 12707407 DOI: 10.1097/01.asn.0000064500.89551.76] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Affiliation(s)
- Masakazu Haneda
- Department of Medicine, Shiga University of Medical Science, Seta, Otsu, Shiga 520-2192, Japan.
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63
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Lam TKT, Carpentier A, Lewis GF, van de Werve G, Fantus IG, Giacca A. Mechanisms of the free fatty acid-induced increase in hepatic glucose production. Am J Physiol Endocrinol Metab 2003; 284:E863-73. [PMID: 12676648 DOI: 10.1152/ajpendo.00033.2003] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The associations between obesity, insulin resistance, and type 2 diabetes mellitus are well documented. Free fatty acids (FFA), which are often elevated in obesity, have been implicated as an important link in these associations. Contrary to muscle glucose metabolism, the effects of FFA on hepatic glucose metabolism and the associated mechanisms have not been extensively investigated. It is still controversial whether FFA have substantial effects on hepatic glucose production, and the mechanisms responsible for these putative effects remain unknown. We review recent progress in this area and try to clarify controversial issues regarding the mechanisms responsible for the FFA-induced increase in hepatic glucose production in the postabsorptive state and during hyperinsulinemia.
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Affiliation(s)
- Tony K T Lam
- Department of Physiology and Medicine, Medical Science Building, University of Toronto, 1 King's College Circle, Toronto, Ontario M5S 1A8, Canada
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