Analysis of heparan-sulphate chains and oligosaccharides from proliferating and quiescent fibroblasts. A proposed model for endoheparanase activity

Distribution of heparan sulfate correlated with the expression of heparanase-1 and matrix metalloproteinase-9 in an ovariectomized rats skin

There are few studies on heparan sulfate (HS) in the skin, during aging, when estrogen is suppressed. The enzyme heparanase-1 (HPSE-1), has its 17β-estrogen-regulated expression in pathological conditions such as cancer and chronic inflammatory diseases. HPSE-1 is correlated with the matrix metalloproteinase-9 (MMP-9), an endopeptidase that also undergoes estrogen action. We investigated the distribution of HS, expression HPSE-1 and MMP-9 in the skin of adult rats at different ages and in the age-matched ovariectomized rats to evaluate the influence of low estrogen on the distribution of HS. Thirty female Wistar rats were used. Rats underwent to a sham surgery (ctr, n = 15) or to a bilateral ovariectomy (ovx, n = 15) and were euthanized after 45, 75, and 90 days after ovariectomy. Morphological, morphometric, biochemical, and reverse transcriptase polymerase chain reaction (RT-PCR) methodologies were used. A significant decrease (P < 0.001) in total skin thickness was observed in the ctr and ovx animals, being higher in the older animals. The thickness of the epidermis and dermis decreased; however, the proportion in the total skin remained similar comparing ctr and ovx. An increase of HS with increasing age and ovariectomy was observed. The expression of the HPSE-1 and MMP-9 enzymes decreased, being higher in old animals. A correlation between the increase of HS and the decrease of the HPSE-1 was demonstrated in both groups. Overall, these data suggested that estrogen acts in the regulation of the expression of the HPSE-1, not only in pathological states, as already established, but also in aging.

N-unsubstituted glucosamine in heparan sulfate of recycling glypican-1 from suramin-treated and nitrite-deprived endothelial cells. mapping of nitric oxide/nitrite-susceptible glucosamine residues to clustered sites near the core protein

We have analyzed the content of N-unsubstituted glucosamine in heparan sulfate from glypican-1 synthesized by endothelial cells during inhibition of (a) intracellular progression by brefeldin A, (b) heparan sulfate degradation by suramin, and/or (c) endogenous nitrite formation. Glypican-1 from brefeldin A-treated cells carried heparan sulfate chains that were extensively degraded by nitrous acid at pH 3.9, indicating the presence of glucosamines with free amino groups. Chains with such residues were rare in glypican-1 isolated from unperturbed cells and from cells treated with suramin and, surprisingly, when nitrite-deprived. However, when nitrite-deprived cells were simultaneously treated with suramin, such glucosamine residues were more prevalent. To locate these residues, chains were first cleaved at linkages to sulfated l-iduronic acid by heparin lyase and released fragments were separated from core protein carrying heparan sulfate stubs. These stubs were then cleaved off at sites linking N-substituted glucosamines to d-glucuronic acid. These fragments were extensively degraded by nitrous acid at pH 3.9. When purified proteoglycan isolated from brefeldin A-treated cells was incubated with intact cells, endoheparanase-catalyzed degradation generated a core protein with heparan sulfate stubs that were similarly sensitive to nitrous acid. We conclude that there is a concentration of N-unsubstituted glucosamines to the reducing side of the endoheparanase cleavage site in the transition region between unmodified and modified chain segments near the linkage region to the protein. Both sites as well as the heparin lyase-sensitive sites seem to be in close proximity to one another.

Biosynthesis of decorin and glypican

Decorin and glypican are two examples of exclusively chondroitin/dermatan sulfate and heparan sulfate-substituted proteoglycans, respectively. Decorin is a secretory product, whereas glypican is linked to membrane lipids via a glycosyl-phosphatidyl-inositol (GPI) anchor. The nascent decorin protein enters the lumen of the ER, whereas that of glypican is transferred to the preformed GPI-anchors. Both types of glycosaminoglycuronans are initiated on Ser residues located in special consensus sequences, and the first glycosylation steps constitute a common pathway: the generation of the linkage region GlcA-Gal-Gal-Xyl-Ser<. The nature of the enzymes involved will be reviewed with special emphasis on the recently discovered transient 2-phosphorylation of xylose. The initiation enzymes (betaGalNAc-T1 and alphaGlcNAc-T1) then use these tetrasaccharide primers for either chondroitin or heparan sulfate assembly. The selection mechanism is not yet fully understood. The transferases that form the linkage-region and add the first hexosamine, as well as the uronosyl C-5 epimerases, appear to be products of single genes, but many isoforms of the copolymerases and sulfotransferases forming the repetitive part of the glycan chains are currently being discovered. When these enzymes work together, the fine structure of the glycosaminoglycuronans appears to be generated through the selective expression of isoforms that only operate in certain structural contexts. During heparan sulfate assembly, generation of GlcNH(2) as a permanent feature is now well recognised. Studies on glypican-1 glycoforms that recycle suggest that heparan sulfate chains are degraded by endoheparanase at or near GlcNH(2) residues, followed by deaminative cleavage catalysed by NO-derived nitrite. Chain-truncated glypican-1 can serve as a precursor for the reformation of a proteoglycan with full-size chains. Regulation of biosynthesis can be exercised at several levels, such as expression of the core protein, selection for chondroitin or heparan sulfate assembly, expression of modifying enzymes, and degradation and remodelling. Cytokines, growth factors, NO and polyamines may have regulatory roles.

A novel role for nitric oxide in the endogenous degradation of heparan sulfate during recycling of glypican-1 in vascular endothelial cells

We show here that the endothelial cell-line ECV 304 expresses the heparan sulfate proteoglycan glypican-1. The predominant cellular glycoform carries truncated side-chains and is accompanied by heparan sulfate oligosaccharides. Treatment with brefeldin A results in accumulation of a glypican proteoglycan with full-size side-chains while the oligosaccharides disappear. During chase the glypican proteoglycan is converted to partially degraded heparan sulfate chains and chain-truncated proteoglycan, both of which can be captured by treatment with suramin. The heparan sulfate chains in the intact proteoglycan can be depolymerized by nitrite-dependent cleavage at internally located N-unsubstituted glucosamine moieties. Inhibition of NO-synthase or nitrite-deprivation prevents regeneration of intact proteoglycan from truncated precursors as well as formation of oligosaccharides. In nitrite-deprived cells, formation of glypican proteoglycan is restored when NO-donor is supplied. We propose that, in recycling glypican-1, heparan sulfate chains are cleaved at or near glucosamines with unsubstituted amino groups. NO-derived nitrite is then required for the removal of short, nonreducing terminal saccharides containing these N-unsubstituted glucosamine residues from the core protein stubs, facilitating re-synthesis of heparan sulfate chains.

Substrate specificity of heparanases from human hepatoma and platelets

Heparan sulfate proteoglycans, attached to cell surfaces or in the extracellular matrix, interact with a multitude of proteins via their heparan sulfate side chains. Degradation of these chains by limited (endoglycosidic) heparanase cleavage is believed to affect a variety of biological processes. Although the occurrence of heparanase activity in mammalian tissues has been recognized for many years, the molecular characteristics and substrate recognition properties of the enzyme(s) have remained elusive. In the present study, the substrate specificity and cleavage site of heparanase from human hepatoma and platelets were investigated. Both enzyme preparations were found to cleave the single beta-D-glucuronidic linkage of a heparin octasaccharide. A capsular polysaccharide from Escherichia coli K5, with the same (-GlcUAbeta1,4-GlcNAcalpha1,4-)n structure as the unmodified backbone of heparan sulfate, resisted heparanase degradation in its native state as well as after chemical N-deacetylation/N-sulfation or partial enzymatic C-5 epimerization of beta-D-GlcUA to alpha-L-IdceA. By contrast, a chemically O-sulfated (but still N-acetylated) K5 derivative was susceptible to heparanase cleavage. O-Sulfate groups, but not N-sulfate or IdceA residues, thus are essential for substrate recognition by the heparanase(s). In particular, selective O-desulfation of the heparin octasaccharide implicated a 2-O-sulfate group on a hexuronic acid residue located two monosaccharide units from the cleavage site, toward the reducing end.

Generation and application of type-specific anti-heparan sulfate antibodies using phage display technology. Further evidence for heparan sulfate heterogeneity in the kidney

Detailed analysis of various heparan sulfate (HS) species is seriously hampered by a lack of appropriate tools, such as antibodies. We adopted phage display technology to generate anti-HS antibodies. A "single pot" semisynthetic human antibody phage display library was subjected to four rounds of selection on HS from bovine kidney using panning methodology. Three different phage clones expressing anti-HS single chain variable fragment antibodies (HS4C3, HS4D10, and HS3G8) were isolated, with an amino acid sequence of the complementarity-determining region 3 of GRRLKD (VH3 gene, DP-38), SLRMNGCGAHQ (VH3 gene, DP-42), and YYHYKVN (VH1 gene, DP-8), respectively. The antibodies react with HS and heparin, but not with DNA or other glycosaminoglycans. Kd values for HS are about 0.1 microM. The three antibodies react differently toward various HS preparations and show different staining patterns on rat kidney sections, indicating recognition of different HS molecules. This also holds for two described mouse anti-HS IgMs (JM403 and 10E4; both generated by conventional hybridoma technique) and indicates the presence of at least 5 different HS species in the kidney. O- and N-sulfation are important for binding of HS to HS4C3 and HS3G8. The three single chain antibodies, but not JM403, block a basic fibroblast growth factor binding site of HS. It is concluded that phage display technology presents a powerful technique to generate antibodies specific for HS epitopes. This is the first time this technique has been successfully applied to obtain directly antibodies to (poly)saccharides.