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      Very-Low-Density Lipoprotein-Induced Triglyceride Accumulation in Human Mesangial Cells Is Mainly Mediated by Lipoprotein Lipase

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          Abstract

          Background: Very-low-density lipoprotein (VLDL) in vitro can induce foam cell formation in human mesangial cells. Lipoprotein lipase (LPL) expressed in the arterial wall plays a key role in atherogenesis by actions of enzymolysis and ‘molecular bridge’, and, thereby, leads to the formation of lipid-loaded foam cells. It is known that LPL is expressed by glomerular mesangial cells. This study was designed to investigate if LPL plays a role in VLDL-induced lipid accumulation in human mesangial cells and its underlying mechanism. Methods: Human wild-type LPL (hLPLwt), catalytically inactive LPL (hLPL194) or control alkaline phosphatase (hAP) were expressed in human mesangial cell line (HMCLs) via adenoviral vectors. Orlistat (tetrahydrolipstatin), a specific inhibitor of the lipoidolytic activity of endogenous LPL, and heparinase, which degrades cell-surface heparan sulfate proteoglycans, were also used to estimate the role of either the enzymolysis or ‘molecular bridge’ actions of LPL in the uptake of VLDL. Anti-low-density lipoprotein receptor (LDLr) antibody and anti-LDL receptor-related protein antibody were used to evaluate the effect of lipoprotein receptors on VLDL-induced lipid accumulation in HMCLs. Cellular lipid deposition was visualized by Oil Red O staining and analyzed quantitatively by standard enzymatic procedures. LPL protein expression and activity were measured by Western blot and a chemical analysis, respectively. Results: VLDL induced triglyceride accumulation in HMCLs in a time- and dose-dependent manner. Compared with Ad-hAP transfected HMCLs, cellular triglyceride content increased 4.55-fold (p < 0.05) in Ad-hLPLwt-transfected HMCLs and 1.52-fold (p < 0.05) in Ad-hLPL194-transfected HMCLs. Triglyceride accumulation in response to VLDL was mostly blocked by orlistat. Pretreatment of the cells with heparinase slightly reduced cellular triglyceride accumulation in the present of high concentrations of VLDL. The blockade of some lipoprotein receptors, such as LDLr, did not significantly reduce cellular triglyceride accumulation. LPL expression was upregulated by VLDL. Conclusions: VLDL-induced triglyceride accumulation in human mesangial cells is mainly mediated by LPL, and the enzymolysis action of LPL could be a major factor in this process. These results suggest that LPL may be an important factor participating in the initiation and progression of VLDL-mediated lipid renal injury.

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          Most cited references 17

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          The distribution and chemical composition of ultracentrifugally separated lipoproteins in human serum.

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            Triglyceride, but not total cholesterol or low-density lipoprotein cholesterol levels, predict development of proteinuria.

            Epidemiological data about the relationship between dyslipidemia and proteinuria are sparse. We conducted a retrospective and longitudinal study in a large screened cohort to evaluate whether triglyceride, high-density lipoprotein (HDL) cholesterol, total cholesterol, and low-density lipoprotein (LDL) cholesterol levels increase the risk of development of proteinuria and loss of renal function. Post hoc analysis was performed for 4326 subjects who were free from proteinuria (dipstick 1+ or higher) at baseline (1997) with a follow-up period through 2000. Outcome measures were the development of proteinuria (1+ or higher) and change in glomerular filtration rate (GFR). Multiple logistic analysis and multiple regression analysis were used to analyze baseline characteristics related to the outcome measures. During the observational period, 505 (11.7%) of subjects had one or more episodes of proteinuria (>/=1+). Adjusted relative risk of triglycerides for one or more incidences of proteinuria was 1.007 (95% CI 1.000 to 1.105, P = 0.04) in men and 1.032 (95% CI 1.004 to 1.061, P = 0.02) in women. Total cholesterol, HDL cholesterol, and LDL cholesterol were not significant predictors of proteinuria. The mean change in GFR between 1997 and 2000 was -6.3 (SD = 9.0) mL/min/1.73 m2 in men, and -7.8 (SD = 10.7) mL/min/1.73 m2 in women. HDL cholesterol (beta = 0.04, t = 3.7, P = 0.0002) in men and triglycerides (per 10 mg/dL, beta = -0.09, t = -2.2, P = 0.02) in women were correlated with the change in GFR. High triglyceride levels predicted a risk of developing proteinuria in both men and women, but not total cholesterol nor LDL cholesterol. High triglyceride in women and low HDL cholesterol in men predicted the decline of renal function. It remains to be determined whether prospective treatment of dyslipidemia will protect against renal injury.
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              Direct regulatory effect of fatty acids on macrophage lipoprotein lipase: potential role of PPARs.

              Atherosclerosis is a major complication of type 2 diabetes. The pathogenesis of this complication is poorly understood, but it clearly involves production in the vascular wall of macrophage (Mo) lipoprotein lipase (LPL). Mo LPL is increased in human diabetes. Peripheral factors dysregulated in diabetes, including glucose and free fatty acids (FAs), may contribute to this alteration. We previously reported that high glucose stimulates LPL production in both J774 murine and human Mo. In the present study, we evaluated the direct effect of FAs on murine Mo LPL expression and examined the involvement of peroxisome proliferator-activated receptors (PPARs) in this effect. J774 Mo were cultured for 24 h with 0.2 mmol/l unsaturated FAs (arachidonic [AA], eicosapentaenoic [EPA], and linoleic acids [LA]) and monounsaturated (oleic acid [OA]) and saturated FAs (palmitic acid [PA] and stearic acid [SA]) bound to 2% bovine serum albumin. At the end of this incubation period, Mo LPL mRNA expression, immunoreactive mass, activity, and synthetic rate were measured. Incubation of J774 cells with LA, PA, and SA significantly increased Mo LPL mRNA expression. In contrast, exposure of these cells to AA and EPA dramatically decreased this parameter. All FAs, with the exception of EPA and OA, increased extra- and intracellular LPL immunoreactive mass and activity. Intracellular LPL mass and activity paralleled extracellular LPL mass and activity in all FA-treated cells. In Mo exposed to AA, LA, and PA, an increase in Mo LPL synthetic rate was observed. To evaluate the role of PPARs in the modulatory effect of FAs on Mo LPL gene expression, DNA binding assays were performed. Results of these experiments demonstrate an enhanced binding of nuclear proteins extracted from all FA-treated Mo to the peroxisome proliferator-response element (PPRE) consensus sequence of the LPL promoter. PA-, SA-, and OA-stimulated binding activity was effectively diminished by immunoprecipitation of the nuclear proteins with anti-PPAR-alpha antibodies. In contrast, anti-PPAR-gamma antibodies only significantly decreased AA-induced binding activity. Overall, these results provide the first evidence for a direct regulatory effect of FAs on Mo LPL and suggest a potential role of PPARs in the regulation of Mo LPL gene expression by FAs.
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                Author and article information

                Journal
                NEP
                Nephron Physiol
                10.1159/issn.1660-2137
                Nephron Physiology
                S. Karger AG
                1660-2137
                2008
                September 2008
                13 August 2008
                : 110
                : 1
                : p1-p10
                Affiliations
                Division of Nephrology, Department of Internal Medicine, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People’s Republic of China
                Article
                151272 Nephron Physiol 2008;110:p1
                10.1159/000151272
                18698144
                © 2008 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 6, References: 30, Pages: 1
                Categories
                Original Paper

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