Decorin core protein secretion is regulated by N-linked oligosaccharide and glycosaminoglycan additions

Small leucine rich proteoglycans: Biology, function and their therapeutic potential in the ocular surface

Small leucine rich proteoglycans (SLRPs) are the largest family of proteoglycans, with 18 members that are subdivided into five classes. SLRPs are small in size and can be present in tissues as glycosylated and non-glycosylated proteins, and the most studied SLRPs include decorin, biglycan, lumican, keratocan and fibromodulin. SLRPs specifically bind to collagen fibrils, regulating collagen fibrillogenesis and the biomechanical properties of tissues, and are expressed at particularly high levels in fibrous tissues, such as the cornea. However, SLRPs are also very active components of the ECM, interacting with numerous growth factors, cytokines and cell surface receptors. Therefore, SLRPs regulate major cellular processes and have a central role in major fundamental biological processes, such as maintaining corneal homeostasis and transparency and regulating corneal wound healing. Over the years, mutations and/or altered expression of SLRPs have been associated with various corneal diseases, such as congenital stromal corneal dystrophy and cornea plana. Recently, there has been great interest in harnessing the various functions of SLRPs for therapeutic purposes. In this comprehensive review, we describe the structural features and the related functions of SLRPs, and how these affect the therapeutic potential of SLRPs, with special emphasis on the use of SLRPs for treating ocular surface pathologies.

Analysis of Immunogenic Galactose-α-1,3-galactose-Containing N-Glycans in Beef, Mutton, and Pork Tenderloin by Combining Matrix-Assisted Laser Desorption/Ionization-Mass Spectroscopy and Capillary Electrophoresis Hyphenated with Mass Spectrometry via Electrospray Ionization

Severe allergic reactions to certain types of meat following tick bites have been reported in geographic regions which are endemic with ticks. This immune response is directed to a carbohydrate antigen (galactose-α-1,3-galactose or α-Gal), which is present in glycoproteins of mammalian meats. At the moment, asparagine-linked complex carbohydrates (N-glycans) with α-Gal motifs in meat glycoproteins and in which cell types or tissue morphologies these α-Gal moieties are present in mammalian meats are still unclear. In this study, we analyzed α-Gal-containing N-glycans in beef, mutton, and pork tenderloin and provided for the first time the spatial distribution of these types of N-glycans in various meat samples. Terminal α-Gal-modified N-glycans were found to be highly abundant in all analyzed samples (55, 45, and 36% of N-glycome in beef, mutton, and pork, respectively). Visualizations of the N-glycans with α-Gal modification revealed that this motif was mainly present in the fibroconnective tissue. To conclude, this study contributes to a better understanding of the glycosylation biology of meat samples and provides guidance for processed meat products, in which only meat fibers are required as an ingredient (i.e., sausages or canned meat).

From Translation to Protein Degradation as Mechanisms for Regulating Biological Functions: A Review on the SLRP Family in Skeletal Tissues

The extracellular matrix can trigger cellular responses through its composition and structure. Major extracellular matrix components are the proteoglycans, which are composed of a core protein associated with glycosaminoglycans, among which the small leucine-rich proteoglycans (SLRPs) are the largest family. This review highlights how the codon usage pattern can be used to modulate cellular response and discusses the biological impact of post-translational events on SLRPs, including the substitution of glycosaminoglycan moieties, glycosylation, and degradation. These modifications are listed, and their impacts on the biological activities and structural properties of SLRPs are described. We narrowed the topic to skeletal tissues undergoing dynamic remodeling.

Deep Sequencing of Complex Proteoglycans: A Novel Strategy for High Coverage and Site-specific Identification of Glycosaminoglycan-linked Peptides

Proteoglycans are distributed in all animal tissues and play critical, multifaceted, physiological roles. Expressed in a spatially and temporally regulated manner, these molecules regulate interactions among growth factors and cell surface receptors and play key roles in basement membranes and other extracellular matrices. Because of the high degree of glycosylation by glycosaminoglycan (GAG), N-glycan and mucin-type O-glycan classes, the peptide sequence coverage of complex proteoglycans is revealed poorly by standard mass spectrometry-based proteomics methods. As a result, there is little information concerning how proteoglycan site specific glycosylation changes during normal and pathological processes. Here, we developed a workflow to improve sequence coverage and identification of glycosylated peptides in proteoglycans. We applied this workflow to the small leucine-rich proteoglycan decorin and three hyalectan proteoglycans: neurocan, brevican, and aggrecan.We characterized glycosylation of these proteoglycans using LC-MS methods easily implemented on instruments widely used in proteomics laboratories. For decorin, we assigned the linker-glycosite and three N-glycosylation sites. For neurocan and brevican, we identified densely glycosylated mucin-like regions in the extended domains. For aggrecan, we identified 50 linker-glycosites and mucin-type O-glycosites in the extended region and N-glycosites in the globular domains, many of which are novel and have not been observed previously. Most importantly, we demonstrate an LC-MS and bioinformatics approach that will enable routine analysis of proteoglycan glycosylation from biological samples to assess their role in pathophysiology.

Sequencing the Dermatan Sulfate Chain of Decorin

Glycomics represents one of the last frontiers and most challenging in omic analysis. Glycosylation occurs in the endoplasmic reticulum and the Golgi organelle and its control is neither well-understood nor predictable based on proteomic or genomic analysis. One of the most structurally complex classes of glycoconjugates is the proteoglycans (PGs) and their glycosaminoglycan (GAG) side chains. Previously, our laboratory solved the structure of the chondroitin sulfate chain of the bikunin PG. The current study examines the much more complex structure of the dermatan sulfate GAG chain of decorin PG. By utilizing sophisticated separation methods followed by compositional analysis, domain mapping, and tandem mass spectrometry coupled with analysis by a modified genetic algorithm approach, the structural motif for the decorin dermatan sulfate chain was determined. This represents the second example of a GAG with a prominent structural motif, suggesting that the structural variability of this class of glycoconjugates is somewhat simpler than had been expected.

Activation of Parathyroid Hormone 2 Receptor Induces Decorin Expression and Promotes Wound Repair

In this study, we report that TIP39, a parathyroid hormone ligand family member that was recently identified to be expressed in the skin, can induce decorin expression and enhance wound repair. Topical treatment of mice with TIP39 accelerated wound repair, whereas TIP39-deficient mice had delayed repair that was associated with formation of abnormal collagen bundles. To study the potential mechanism responsible for the action of TIP39 in the dermis, fibroblasts were cultured in three-dimensional collagen gels, a process that results in enhanced decorin expression unless activated to differentiate to adipocytes, whereupon these cells reduce expression of several proteoglycans, including decorin. Small interfering RNA-mediated silencing of parathyroid hormone 2 receptor (PTH2R), the receptor for TIP39, suppressed the expression of extracellular matrix-related genes, including decorin, collagens, fibronectin, and matrix metalloproteases. Skin wounds in TIP39^-/- mice had decreased decorin expression, and addition of TIP39 to cultured fibroblasts induced decorin and increased phosphorylation and nuclear translocation of CREB. Fibroblasts differentiated to adipocytes and treated with TIP39 also showed increased decorin and production of chondroitin sulfate. Furthermore, the skin of PTH2R^-/- mice showed abnormal extracellular matrix structure, decreased decorin expression, and skin hardness. Thus, the TIP39-PTH2R system appears to be a previously unrecognized mechanism for regulation of extracellular matrix formation and wound repair.

A comparison of the behavioral and anatomical outcomes in sub-acute and chronic spinal cord injury models following treatment with human mesenchymal precursor cell transplantation and recombinant decorin

This study assessed the potential of highly purified (Stro-1(+)) human mesenchymal precursor cells (hMPCs) in combination with the anti-scarring protein decorin to repair the injured spinal cord (SC). Donor hMPCs isolated from spinal cord injury (SCI) patients were transplanted into athymic rats as a suspension graft, alone or after previous treatment with, core (decorin(core)) and proteoglycan (decorin(pro)) isoforms of purified human recombinant decorin. Decorin was delivered via mini-osmotic pumps for 14 days following sub-acute (7 day) or chronic (1 month) SCI. hMPCs were delivered to the spinal cord at 3 weeks or 6 weeks after the initial injury at T9 level. Behavioral and anatomical analysis in this study showed statistically significant improvement in functional recovery, tissue sparing and cyst volume reduction following hMPC therapy. The combination of decorin infusion followed by hMPC therapy did not improve these measured outcomes over the use of cell therapy alone, in either sub-acute or chronic SCI regimes. However, decorin infusion did improve tissue sparing, reduce spinal tissue cavitation and increase transplanted cell survivability as compared to controls. Immunohistochemical analysis of spinal cord sections revealed differences in glial, neuronal and extracellular matrix molecule expression within each experimental group. hMPC transplanted spinal cords showed the increased presence of serotonergic (5-HT) and sensory (CGRP) axonal growth within and surrounding transplanted hMPCs for up to 2 months; however, no evidence of hMPC transdifferentiation into neuronal or glial phenotypes. The number of hMPCs was dramatically reduced overall, and no transplanted cells were detected at 8 weeks post-injection using lentiviral GFP labeling and human nuclear antigen antibody labeling. The presence of recombinant decorin in the cell transplantation regimes delayed in part the loss of donor cells, with small numbers remaining at 2 months after transplantation. In vitro co-culture experiments with embryonic dorsal root ganglion explants revealed the growth promoting properties of hMPCs. Decorin did not increase axonal outgrowth from that achieved by hMPCs. We provide evidence for the first time that (Stro-1(+)) hMPCs provide: i) an advantageous source of allografts for stem cell transplantation for sub-acute and chronic spinal cord therapy, and (ii) a positive host microenvironment that promotes tissue sparing/repair that subsequently improves behavioral outcomes after SCI. This was not measurably improved by recombinant decorin treatment, but does provide important information for the future development and potential use of decorin in contusive SCI therapy.

Sequence analysis and domain motifs in the porcine skin decorin glycosaminoglycan chain

Decorin proteoglycan is comprised of a core protein containing a single O-linked dermatan sulfate/chondroitin sulfate glycosaminoglycan (GAG) chain. Although the sequence of the decorin core protein is determined by the gene encoding its structure, the structure of its GAG chain is determined in the Golgi. The recent application of modern MS to bikunin, a far simpler chondroitin sulfate proteoglycans, suggests that it has a single or small number of defined sequences. On this basis, a similar approach to sequence the decorin of porcine skin much larger and more structurally complex dermatan sulfate/chondroitin sulfate GAG chain was undertaken. This approach resulted in information on the consistency/variability of its linkage region at the reducing end of the GAG chain, its iduronic acid-rich domain, glucuronic acid-rich domain, and non-reducing end. A general motif for the porcine skin decorin GAG chain was established. A single small decorin GAG chain was sequenced using MS/MS analysis. The data obtained in the study suggest that the decorin GAG chain has a small or a limited number of sequences.

The regulatory roles of small leucine-rich proteoglycans in extracellular matrix assembly

Small leucine-rich proteoglycans (SLRPs) are involved in a variety of biological and pathological processes. This review focuses on their regulatory roles in matrix assembly. SLRPs have protein cores and hypervariable glycosylation with multivalent binding abilities. During development, differential interactions of SLRPs with other molecules result in tissue-specific spatial and temporal distributions. The changing expression patterns play a critical role in the regulation of tissue-specific matrix assembly and therefore tissue function. SLRPs play significant structural roles within extracellular matrices. In addition, they play regulatory roles in collagen fibril growth, fibril organization and extracellular matrix assembly. Moreover, they are involved in mediating cell-matrix interactions. Abnormal SLRP expression and/or structures result in dysfunctional extracellular matrices and pathophysiology. Altered expression of SLRPs has been found in many disease models, and structural deficiency also causes altered matrix assembly. SLRPs regulate assembly of the extracellular matrix, which defines the microenvironment, modulating both the extracellular matrix and cellular functions, with an impact on tissue function.

Regulation of xylosyltransferase I gene expression by interleukin 1β in human primary chondrocyte cells: mechanism and impact on proteoglycan synthesis

Xylosyltransferase I (XT-I) is an essential enzyme of proteoglycan (PG) biosynthesis pathway catalyzing the initial and rate-limiting step in glycosaminoglycan chain assembly. It plays a critical role in the regulation of PG synthesis in cartilage; however, little is known about underlying mechanism. Here, we provide evidence that, in human primary chondrocytes, IL-1β regulates XT-I gene expression into an early phase of induction and a late phase of down-regulation. Based on promoter deletions, the region up to -850 bp was defined as a major element of XT-I gene displaying both constitutive and IL-1β-regulated promoter activity. Point mutation and signaling analyses revealed that IL-1β-induced promoter activity is achieved through AP-1 response elements and mediated by SAP/JNK and p38 signaling pathways. Transactivation and chromatin immunoprecipitation assays indicated that AP-1 is a potent transactivator of XT-I promoter and that IL-1β-induced activity is mediated through increased recruitment of AP-1 to the promoter. Finally, we show that Sp3 is a repressor of XT-I promoter and bring evidence that the repressive effect of IL-1β during the late phase is mediated through Sp3 recruitment to the promoter. This suggests that modulation of Sp3 in cartilage could prevent IL-1β inhibition of PG synthesis and limit tissue degradation.

Umbilical cord blood mesenchymal stem cells protect amyloid-β42 neurotoxicity via paracrine

AIM: To understand the neuroprotective mechanism of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) against amyloid-β42 (Aβ42) exposed rat primary neurons.

METHODS: To evaluate the neuroprotective effect of hUCB-MSCs, the cells were co-cultured with Aβ42-exposed rat primary neuronal cells in a Transwell apparatus. To assess the involvement of soluble factors released from hUCB-MSCs in neuroprotection, an antibody-based array using co-cultured media was conducted. The neuroprotective roles of the identified hUCB-MSC proteins was assessed by treating recombinant proteins or specific small interfering RNAs (siRNAs) for each candidate protein in a co-culture system.

RESULTS: The hUCB-MSCs secreted elevated levels of decorin and progranulin when co-cultured with rat primary neuronal cells exposed to Aβ42. Treatment with recombinant decorin and progranulin protected from Aβ42-neurotoxicity in vitro. In addition, siRNA-mediated knock-down of decorin and progranulin production in hUCB-MSCs reduced the anti-apoptotic effects of hUCB-MSC in the co-culture system.

CONCLUSION: Decorin and progranulin may be involved in anti-apoptotic activity of hUCB-MSCs exposed to Aβ42.

More than matrix: the multifaceted role of decorin in cancer

The small leucine-rich proteoglycan, decorin, has incrementally been shown to be a powerful inhibitor of growth in a wide variety of tumour cells, an effect specifically mediated by the interaction of decorin core protein with the epidermal growth factor receptor (EGFR) and other ErbB family proteins. Nowadays, this matrikine has become the main focus of various cancer studies. Decorin is an important component of the cellular microenvironment or extracellular matrix (ECM). Its interactions with matrix and cell membrane components have been implicated in many physiological and pathophysiological processes including matrix organisation, signal transduction, wound healing, cell migration, inhibition of metastasis, and angiogenesis. This review summarises recent findings on decorin's interactions and behaviour related to cancer. Highlighted are key functions of decorin such as interaction with cell surface receptors, as well as with ECM components, and the therapeutic potential of this multifunctional molecule.

The structural role of N-linked glycans on human glypican-1

Glypicans are cell-surface heparan sulfate proteoglycans that regulate developmental signaling pathways by binding growth factors to their heparan sulfate chains. The primary structures of glypican core proteins contain potential N-glycosylation sites, but the importance of N-glycosylation in glypicans has never been investigated in detail. Here, we studied the role of the possible N-glycosylation sites at Asn-79 and Asn-116 in recombinant anchorless glypican-1 expressed in eukaryotic cells. Mutagenesis and enzymatic cleavage indicated that the potential N-glycosylation sites are invariably occupied. Experiments using the drug tunicamycin to inhibit the N-linked glycosylation of glypican-1 showed that secretion of anchorless glypican-1 was reduced and that the protein did not accumulate inside the cells. Heparan sulfate substitution of N-glycosylation mutant N116Q was similar to wild-type glypican-1 while the N79Q mutant and also the double mutant N79Q,N116Q were mostly secreted as high-molecular-weight heparan sulfate proteoglycan. N-Glycosylation mutants and N-deglycosylated glypican-1 had far-UV circular dichroism and fluorescence emission spectra that were highly similar to those of N-glycosylated glypican-1. A single unfolding transition at high concentrations of urea was found for both N-deglycosylated glypican-1 and glypican-1 in which the N-glycosylation sites had been removed by mutagenesis when chemical denaturation was monitored by circular dichroism and fluorescence emission spectroscopy. In summary, we have found that the potential N-glycosylation sites in glypican-1 are invariably occupied and that the N-linked glycans on glypican-1 affect protein expression and heparan sulfate substitution but that correct folding can be obtained in the absence of N-linked glycans.

Fibroblast growth factor 2 and protein kinase C alpha are involved in syndecan-4 cytoplasmic domain modulation of turkey myogenic satellite cell proliferation

Syndecan-4 core protein is composed of extracellular, transmembrane, and cytoplasmic domains. The cytoplasmic domain functions in transmitting signals into the cell through the protein kinase C alpha (PKCα) pathway. The glycosaminoglycan (GAG) and N-linked glycosylated (N-glycosylated) chains attached to the extracellular domain influence cell proliferation. The current study investigated the function of syndecan-4 cytoplasmic domain in combination with GAG and N-glycosylated chains in turkey muscle cell proliferation, differentiation, fibroblast growth factor 2 (FGF2) responsiveness, and PKCα membrane localization. Syndecan-4 or syndecan-4 without the cytoplasmic domain and with or without the GAG and N-glycosylated chains were transfected or co-transfected with a small interfering RNA targeting syndecan-4 cytoplasmic domain into turkey muscle satellite cells. The overexpression of syndecan-4 mutants increased cell proliferation but did not change differentiation. Syndecan-4 mutants had increased cellular responsiveness to FGF2 during proliferation. Syndecan-4 increased PKCα cell membrane localization, whereas the syndecan-4 mutants decreased PKCα cell membrane localization compared to syndecan-4. However, compared to the cells without transfection, syndecan-4 mutants increased cell membrane localization of PKCα. These data indicated that the syndecan-4 cytoplasmic domain and the GAG and N-glycosylated chains are critical in syndecan-4 regulating satellite cell proliferation, responsiveness to FGF2, and PKCα cell membrane localization.

Role of syndecan-4 side chains in turkey satellite cell growth and development

Syndecan-4 is a cell membrane heparan sulfate proteoglycan that is composed of a core protein and covalently attached glycosaminoglycans (GAG) and N-linked glycosylated (N-glycosylated) chains. Syndecan-4 has been shown to function independent of its GAG chains. Syndecan-4 may derive its biological function from the N-glycosylated chains due to the biological role of N-glycosylated chains in protein folding and cell membrane localization. The objective of the current study was to investigate the role of syndecan-4 N-glycosylated chains and the interaction between GAG and N-glycosylated chains in turkey myogenic satellite cell proliferation, differentiation, and fibroblast growth factor 2 (FGF2) responsiveness. The wild type turkey syndecan-4 and the syndecan-4 without GAG chains were cloned into the expression vector pCMS-EGFP and used as templates to generate syndecan-4 N-glycosylated one-chain and no-chain mutants with or without GAG chains. The wild type syndecan-4, all of the syndecan-4 N-glycosylated chain mutants were transfected into turkey myogenic satellite cells. Cell proliferation, differentiation, and responsiveness to FGF2 were measured. The overexpression of syndecan-4 N-glycosylated mutants with or without GAG chains did not change cell proliferation, differentiation, and responsiveness to FGF2 compared to the wild type syndecan-4 except that the overexpression of syndecan-4 N-glycosylated mutants without GAG chains increased cell proliferation at 48 and 72 h post-transfection. These data suggest that syndecan-4 functions in an FGF2-independent manner, and the N-glycosylated and GAG chains are required for syndecan-4 to regulate turkey myogenic satellite cell proliferation, but not differentiation.

Regulation of intracellular decorin via proteasome degradation in rat mesangial cells

Decorin (DCN) is a member of small leucine-rich proteoglycan family that neutralizes the bioactivity of transforming growth factor-beta1 (TGF-β1). It has been proven to be a promising anti-fibrotic agent to treat glomerulonephritis. But the underlining mechanism for regulating and degrading intracellular DCN is still not fully understood. In this study, we investigated the roles of ubiquitination in the regulation of cytoplasmic DCN metabolism in rat mesangial cells (MC) by immunoprecipitation and Western blot. The results showed that a proportion of cytoplasmic DCN was ubiquitinated in normal MC and was enhanced in N-glycosylation inhibitor (tunicamycin)-treated MC. After being treated with the proteasome inhibitor MG132, ubiquitinated DCN accumulated and displayed a prolonged half-life, accompanied by decreased TGF-β1 expression and reduced collagen IV mRNA level in MC. This study demonstrated that the stability and function of cytoplasmic DCN can be regulated by ubiquitin-proteasome system (UPS) in MC, which implies that regulating the ubiquitination and degradation of DCN might be a novel approach for modulating MC bioactivity.

Domain structure elucidation of human decorin glycosaminoglycans

The structure of the GAG (glycosaminoglycan) chain of recombinantly expressed decorin proteoglycan was examined using a combination of intact-chain analysis and domain compositional analysis. The GAG had a number-average molecular mass of 22 kDa as determined by PAGE. NMR spectroscopic analysis using two-dimensional correlation spectroscopy indicated that the ratio of glucuronic acid to iduronic acid in decorin peptidoglycan was 5 to 1. GAG domains terminated with a specific disaccharide obtained by enzymatic degradation of decorin GAG with highly specific endolytic and exolytic lyases were analysed by PAGE and further depolymerized with the enzymes. The disaccharide compositional profiles of the resulting domains were obtained using LC with mass spectrometric and photometric detection and compared with that of the polysaccharide. The information obtained through the disaccharide compositional profiling was combined with the NMR and PAGE data to construct a map of the decorin GAG sequence motifs.

Expression and purification of secreted recombinant hsp60 from eukaryotic cells

Human heat shock protein 60 (hsp60) is a mitochondrial protein that functions as a molecular chaperone. Recently, it has been observed that hsp60 can become exposed on the cell surface and released into the extracellular space. Extracellular hsp60 is thought to function as a danger signal that activates the immune response. However, concerns have been raised that the effects of recombinant hsp60 on cytokines might be the result of contamination with bacterial components, given that the recombinant hsp60 protein used in these studies was produced with a bacterial expression system. In the present study, recombinant hsp60 was produced using a eukaryotic expression system, and the resulting protein was purified. The results obtained demonstrated that recombinant hsp60 was secreted efficiently from cells when fused to the leader peptide of interleukin-2 and the secreted protein was modified by N-linked glycosylation. Furthermore, we successfully obtained unglycosylated recombinant protein that was capable of binding to macrophages.

Effect of glypican-1 covalently attached chains on turkey myogenic satellite cell proliferation, differentiation, and fibroblast growth factor 2 responsiveness

Glypican-1 is a cell membrane heparan sulfate proteoglycan that is composed of a core protein and covalently attached glycosaminoglycan (GAG) chains and N-linked glycosylated (N-glycosylated) chains. The glypican-1 GAG chains are required for cell differentiation and responsiveness to fibroblast growth factor 2 (FGF2). The role of glypican-1 N-glycosylated chains in regulating cell activities has not been reported. The objective of the current study was to investigate the role of glypican-1 N-glycosylated chains and the interaction between N-glycosylated and GAG chains in turkey myogenic satellite cell proliferation, differentiation, and FGF2 responsiveness. The wild-type turkey glypican-1 and turkey glypican-1 with mutated GAG chain attachment sites were cloned into the pCMS-EGFP mammalian expression vector and were used as templates to generate glypican-1 N-glycosylated 1-chain and no-chain mutants with or without GAG chains by site-directed mutagenesis. The wild-type glypican-1 and all glypican-1 N-glycosylated 1-chain and no-chain mutants with or without GAG chains were transfected into turkey myogenic satellite cells. Cell proliferation, differentiation, and FGF2 responsiveness were measured. The overexpression of glypican-1 N-glycosylated 1-chain and no-chain mutants without GAG chains increased cell proliferation and differentiation compared with the wild-type glypican-1 but not the glypican-1 N-glycosylated mutants with GAG chains attached. Cells overexpressing glypican-1 N-glycosylated mutants with or without GAG chains increased cell responsiveness to FGF2 compared with wild-type glypican-1. These data suggest that glypican-1 N-glycosylated chains and GAG chains are critical in regulating turkey myogenic satellite cell proliferation, differentiation, and responsivness to FGF2.

Xylosyltransferase gene variants and their role in essential hypertension

BACKGROUND

An accumulation of extracellular matrix molecules, such as proteoglycans, is observed in the vascular wall of hypertensive patients. Xylosyltransferases I and II (XT-I and XT-II), the chain-initiating enzymes in the biosynthesis of proteoglycans, catalyze the transfer of D-xylose from UDP-D-xylose to specific serine residues of the core protein. Because associations between XYLT polymorphisms and an altered blood pressure have been observed, genetic variations in the XYLT genes might predispose to essential hypertension. The localization of the XYLT2 gene on chromosome 17q increases its attractiveness as this region has been reported to be a potential candidate locus for essential hypertension.

METHODS

Genotyping of four polymorphisms in the genes XYLT1 and XYLT2 was performed in 150 unrelated essential hypertension patients and 150 age- and sex-matched normotensive controls using restriction fragment length polymorphism analysis.

RESULTS

The allele and genotype frequencies of the XYLT variants investigated did not show any significant differences between patients and controls, among allele-carriers and nonallele-carriers and among recessive and nonrecessive allele-carriers comparing patients and controls. Systolic and diastolic blood pressures did not differ significantly between the genotypes concerning all XYLT variants analyzed. Two XYLT2 variants deviated from Hardy-Weinberg equilibrium (HWE) in the hypertensive group.

CONCLUSIONS

No statistically significant association was found between four XYLT variants and hypertension or blood pressure, suggesting that they do not play a significant role in the development of essential hypertension. The deviation from HWE of two XYLT2 variants might be due to gene-phenotype associations which remain to be explored, as well as the possibility of gene-gene interactions.

High xylosyltransferase activity in children and during mineralization of osteoblast-like SAOS-2 cells

Skeletal growth and tissue remodelling processes are characterized by an elevated collagen and proteoglycan biosynthesis. The xylosyltransferases I and II are the rate-limiting step enzymes in proteoglycan biosynthesis and serum xylosyltransferase (XT) activity has been shown to be a biomarker for the actual proteoglycan biosynthesis rate. Here, XT, alkaline phosphatase (ALP), bone ALP (BALP) activities were measured in 133 juvenile Caucasians. Serum XT activities in juveniles were elevated and significantly correlated with ALP and BALP. In an osteoblast-like cell model using SAOS-2 cells mineralization and bone nodule formation were induced and XT-I, XT-II and ALP were monitored. Induction of mineralization in SAOS-2 cells resulted in a long-term increase of XT-I mRNA and enzyme activity, which could be paralleled with elevated ALP activity. In addition, HGH and IGF-I treatment of SAOS-2 cells led to an increased expression of XT-I and ALP. These results point to skeletal growth and tissue remodeling as a cause of the high XT activity in children.

Identification of a xylosyltransferase II gene haplotype marker for diabetic nephropathy in type 1 diabetes

BACKGROUND

Proteoglycans are major components of the glomerular basement membrane, being responsible for their permeability properties. Type 1 diabetic patients have an altered proteoglycan metabolism, which contributes to microvascular complications like diabetic nephropathy. Xylosyltransferase II (XT-II) is a chain-initiating enzyme in the biosynthesis of basement membrane proteoglycans and catalyzes the transfer of xylose to selected serine residues in the core protein. Thus, genetic variations in the XT-II coding gene XYLT2 might be implicated in the initiation and progression of late diabetic complications.

METHODS

Genotyping of 6 genetic variations in the XYLT2 gene and haplotype analysis was performed in 697 type 1 diabetic patients (358 with and 338 without diabetic nephropathy).

RESULTS

The haplotype analysis of 6 XYLT2 polymorphisms revealed one haplotype (GATTCG) to be significantly less frequent among type 1 patients with diabetic nephropathy (p=0.002, OR=0.13, 95% CI=0.03-0.59). The haplotype GATTCG consist of the XYLT2 variations c.166G>A, c.177A>G, c.342T>C, IVS6-9T>C, c.1569C>T and c.2402C>G. No genotype-phenotype interactions were revealed.

CONCLUSIONS

Our data show that a XYLT2 haplotype is associated with nephropathy in type 1 diabetic patients.

Xylosyltransferase I variants and their impact on abdominal aortic aneurysms

BACKGROUND

The formation of abdominal aortic aneurysm (AAA) is caused by a destructive remodeling of the extracellular matrix in the vascular wall. Proteoglycan content and biosynthesis have been shown to be altered in AAA. Xylosyltransferase I (XT-I) is the initial and rate-limiting enzyme in the biosynthesis of the proteoglycan-linked glycosaminoglycan chains. A familial predisposition to AAA is well recognized. Thus, variations in the XT-I coding gene XYLT1 might be risk factors for AAA formation.

METHODS

We performed genotyping of two genetic variations in the XYLT1 gene which, have been already linked to proteoglycan-associated diseases, in 129 AAA patients and 129 age- and sex-matched healthy controls.

RESULTS

The T-allele of the polymorphism c.343G>T (p.A115S) was found to be significantly more frequent in AAA patients compared to the healthy control group, demonstrating that carriers of the T-allele have a 5-fold increased risk of developing AAA (odds ratio 4.87, 95%-CI 1.38-17.19; p=0.011).

CONCLUSIONS

Our results show that XT-I polymorphisms potentially confer to the genetic susceptibility of AAA.

Human xylosyltransferase II is involved in the biosynthesis of the uniform tetrasaccharide linkage region in chondroitin sulfate and heparan sulfate proteoglycans

Human xylosyltransferase I (XT-I) initiates the biosynthesis of the glycosaminoglycan (GAG) linkage tetrasaccharide in proteoglycans. Xylosyltransferase II (XT-II) is a protein homologous to XT-I but with hitherto unknown activity or physiological function. Here, we report the enzymatic activity of XT-II and provide evidence that XT-II initiates the biosynthesis of both heparan sulfate and chondroitin sulfate GAGs. Transfection of the xylosyltransferase-deficient Chinese hamster ovary mutant pgsA-745 with XT-I or XT-II coding cDNA completely restored GAG biosynthesis. GAG disaccharide analysis revealed that XT-I- and XT-II-transfected pgsA-745 cells produced similar amounts of chondroitin sulfate and heparan sulfate. Furthermore, a high xylosyltransferase activity was measured after transfection with cDNAs encoding either isozyme. Analysis of the enzyme activity revealed that XT-II catalyzes the transfer of xylose to similar peptide acceptors as XT-I but with different efficiency. The optimal XT-II acceptor was observed using a bikunin-related peptide (K(m) 5.2 microM). Analysis of XT-I and XT-II mRNA expression in murine tissues showed a differential expression pattern for both enzymes. In particular, XT-II is highly expressed in liver tissue, where XT-I transcripts were not detected. This is the first report on the enzyme activity of XT-II and its involvement in chondroitin sulfate and heparan sulfate biosynthesis.

Expression of the metastasis suppressor KAI1 in decidual cells at the human maternal-fetal interface: Regulation and functional implications

At the human maternal-fetal interface, the decidua forms a dense matrix that is believed to limit trophoblast invasion. We investigated whether the metastasis suppressor KAI1 (CD82) is expressed at the maternal-fetal interface. Immunohistochemistry showed strong expression of KAI1 in decidual cells, whereas trophoblast cells were negative for KAI1. In luteal phase endometrium, KAI1 was present in decidualizing endometrial stromal cells. We investigated whether KAI1 expression in endometrial stromal cells is regulated by the decidualizing stimuli cAMP and progesterone or by the cytokine interleukin (IL)-1beta. Western blot analysis revealed induction of KAI1 protein by cAMP analog, but not by progesterone, in a delayed fashion. In contrast, IL-1beta rapidly stimulated KAI1 expression at the transcript level and at the protein level. Cultured decidual cells from term placenta expressed a basal level of KAI1 protein that was elevated on cAMP stimulation. Silencing of KAI1 by RNA interference attenuated expression of decorin, a decidual product implicated in limiting trophoblast invasion. This study shows for the first time the expression of KAI1 in decidual cells at the human maternal-fetal interface, where the metastasis suppressor might participate in intercellular communication with trophoblast cells and the control of trophoblast invasion.