heparitin-sulfate and Hypertriglyceridemia

We recently showed that the heparan sulfate proteoglycan syndecan-1 mediates hepatic clearance of triglyceride-rich lipoproteins in mice based on systemic deletion of syndecan-1 and hepatocyte-specific inactivation of sulfotransferases involved in heparan sulfate biosynthesis. Here, we show that syndecan-1 expressed on primary human hepatocytes and Hep3B human hepatoma cells can mediate binding and uptake of very low density lipoprotein (VLDL). Syndecan-1 also undergoes spontaneous shedding from primary human and murine hepatocytes and Hep3B cells. In human cells, phorbol myristic acid induces syndecan-1 shedding, resulting in accumulation of syndecan-1 ectodomains in the medium. Shedding occurs through a protein kinase C-dependent activation of ADAM17 (a disintegrin and metalloproteinase 17). Phorbol myristic acid stimulation significantly decreases DiD (1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine perchlorate)-VLDL binding to cells, and shed syndecan-1 ectodomains bind to VLDL. Although mouse hepatocytes appear resistant to induced shedding in vitro, injection of lipopolysaccharide into mice results in loss of hepatic syndecan-1, accumulation of ectodomains in the plasma, impaired VLDL catabolism, and hypertriglyceridemia.. These findings suggest that syndecan-1 mediates hepatic VLDL turnover in humans as well as in mice and that shedding might contribute to hypertriglyceridemia in patients with sepsis.

Topics: Animals; Carcinogens; Cell Line, Tumor; Heparitin Sulfate; Hepatocytes; Humans; Hypertriglyceridemia; Lipopolysaccharides; Lipoproteins, VLDL; Liver Neoplasms; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Protein Kinase C; Sepsis; Syndecan-1; Tetradecanoylphorbol Acetate; Triglycerides

Hepatic clearance of triglyceride-rich lipoproteins depends on heparan sulfate and low density lipoprotein receptors expressed on the basal membrane of hepatocytes. Binding and uptake of the lipoproteins by way of heparan sulfate depends on the degree of sulfation of the chains based on accumulation of plasma triglycerides and delayed clearance of triglyceride-rich lipoproteins in mice bearing a hepatocyte-specific alteration of N-acetylglucosamine (GlcNAc) N-deacetylase-N-sulfotransferase 1 (Ndst1) (MacArthur, J. M., Bishop, J. R., Stanford, K. I., Wang, L., Bensadoun, A., Witztum, J. L., and Esko, J. D. (2007) J. Clin. Invest. 117, 153-164). Inactivation of Ndst1 led to decreased overall sulfation of heparan sulfate due to coupling of uronyl 2-O-sulfation and glucosaminyl 6-O-sulfation to initial N-deacetylation and N-sulfation of GlcNAc residues. To determine whether lipoprotein clearance depends on 2-O-and 6-O-sulfation, we evaluated plasma triglyceride levels in mice containing loxP-flanked conditional alleles of uronyl 2-O-sulfotransferase (Hs2st(f/f)) and glucosaminyl 6-O-sulfotransferase-1 (Hs6st1(f/f)) and the bacterial Cre recombinase expressed in hepatocytes from the rat albumin (Alb) promoter. We show that Hs2st(f/f)AlbCre(+) mice accumulated plasma triglycerides and exhibited delayed clearance of intestinally derived chylomicrons and injected human very low density lipoproteins to the same extent as observed in Ndst1(f/f)AlbCre(+) mice. In contrast, Hs6st1(f/f)AlbCre(+) mice did not exhibit any changes in plasma triglycerides. Chemically modified heparins lacking N-sulfate and 2-O-sulfate groups did not block very low density lipoprotein binding and uptake in isolated hepatocytes, whereas heparin lacking 6-O-sulfate groups was as active as unaltered heparin. Our findings show that plasma lipoprotein clearance depends on specific subclasses of sulfate groups and not on overall charge of the chains.

Topics: Animals; Gene Deletion; Gene Targeting; Heparin; Heparitin Sulfate; Hepatocytes; Humans; Hypertriglyceridemia; Integrases; Iodine Radioisotopes; Lipase; Lipoproteins; Lipoproteins, VLDL; Liver; Mice; Mice, Knockout; Mutation; Organ Specificity; Protein Binding; Rats; Sulfotransferases; Triglycerides

Diabetes -associated hyperlipidemia is generally attributed to reduced clearance of plasma lipoproteins, especially remnant lipoproteins enriched in cholesterol and triglycerides. Hepatic clearance of remnants occurs via low density lipoprotein receptors and the heparan sulfate proteoglycan, syndecan-1. Previous studies have suggested alterations in heparan sulfate proteoglycan metabolism in rat and mouse diabetic models, consistent with the idea that diabetic dyslipidemia might be caused by alterations in proteoglycan expression in the liver. In this study we analyzed the content and composition of liver heparan sulfate in streptozotocin-induced insulin-deficient diabetic mice that displayed fasting hypertriglyceridemia and delayed clearance of dietary triglyceride-rich lipoproteins. No differences between normal and diabetic littermates in liver heparan sulfate content, sulfation, syndecan-1 protein levels, or affinity for heparin-binding ligands, such as apolipoprotein E or fibroblast growth factor-2, were noted. Decreased incorporation of [(35)S]sulfate in insulin-deficient mice in vivo was observed, but the decrease was due to increased plasma inorganic sulfate, which reduced the efficiency of labeling of liver heparan sulfate. These results show that hyperlipidemia in insulin-deficient mice is not due to changes in hepatic heparan sulfate composition.

Topics: Animals; Antibiotics, Antineoplastic; Apolipoproteins E; Blood Glucose; Diabetes Mellitus, Type 1; Fibroblast Growth Factor 2; Heparitin Sulfate; Hypertriglyceridemia; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Streptozocin; Sulfotransferases; Syndecan-1

Heparin is a widely used antithrombotic drug. Besides its anticoagulant properties, it also has a marked influence on lipid metabolism, by decreasing serum lipolytic activity due to lipase depletion from vascular sites and stores. Especially in haemodialysis patients who receive heparin during every dialysis session, and in hypertriglyceridaemic patients, decreasing lipolytic activity can lead to the accumulation of triglyceride-rich lipoproteins, which are atherogenic. Replacement of heparin by an antithrombotic drug with less lipase releasing activity might reduce this risk.. We tested danaparoid, a new antithrombotic drug, and compared its ability to displace biotinylated heparan sulphate from lipoprotein lipase in vitro with heparin. Furthermore we compared the in vivo lipase releasing activity.. Danaparoid displaced significantly less biotinylated heparan sulphate from triglyceride-rich lipoprotein-lipoprotein lipase complexes in vitro than heparin. Intravenous injection of danaparoid released less than 20% (P < 0.05) of the lipolytic activity released by an equivalent anticoagulant dose of heparin.. Danaparoid is the drug of choice during the antithrombotic therapy of hypertriglyceridaemic or haemodialysis patients.

Topics: Adult; Anticoagulants; Chondroitin Sulfates; Dermatan Sulfate; Drug Combinations; Female; Heparin; Heparinoids; Heparitin Sulfate; Humans; Hydrolysis; Hypertriglyceridemia; Lipoprotein Lipase; Reference Values; Renal Dialysis; Triglycerides