"Coding" and "Decoding": hypothesis for the regulatory mechanism involved in heparan sulfate biosynthesis

Chromosome evolution of Escherichia coli Nissle 1917 for high-level production of heparosan

Heparosan is a crucial-polysaccharide precursor for the chemoenzymatic synthesis of heparin, a widely used anticoagulant drug. Presently, heparosan is mainly extracted with the potential risk of contamination from Escherichia coli strain K5, a pathogenic bacterium causing urinary tract infection. Here, a nonpathogenic probiotic, E. coli strain Nissle 1917 (EcN), was metabolically engineered to carry multiple copies of the 19-kb kps locus and produce heparosan to 9.1 g/L in fed-batch fermentation. Chromosome evolution driven by antibiotics was employed to amplify the kps locus, which governed the synthesis and export of heparosan from EcN at 21 mg L^-1  OD^-1 . The average copy number of kps locus increased from 1 to 24 copies per cell, which produced up to 104 mg L^-1  OD^-1 of heparosan in the shaking flask cultures of engineered strains. The following in-frame deletion of recA stabilized the recombinant duplicates of chromosomal kps locus and the productivity of heparosan in continuous culture for at least 56 generations. Fed-batch fermentation of the engineered strain EcN8 was carried out to bring the yield of heparosan up to 9.1 g/L. Heparosan from the fermentation culture was further purified at a 75% overall recovery. The structure of purified heparosan was characterized and further modified by N-sulfotransferase with 3'-phosphoadenosine-5'-phosphosulfate as the sulfo-donor. The analysis of element composition showed that heparosan was N-sulfated by over 80%. These results indicated that duplicating large DNA cassettes up to 19-kb, followed by high-cell-density fermentation, was promising in the large-scale preparation of chemicals and could be adapted to engineer other industrial-interest bacteria metabolically.

Heparan sulfate proteoglycans (HSPGs) of the ocular lens

Heparan sulfate proteoglycans (HSPGs) reside in most cells; on their surface, in the pericellular milieu and/or extracellular matrix. In the eye, HSPGs can orchestrate the activity of key signalling molecules found in the ocular environment that promote its development and homeostasis. To date, our understanding of the specific roles played by individual HSPG family members, and the heterogeneity of their associated sulfated HS chains, is in its infancy. The crystalline lens is a relatively simple and well characterised ocular tissue that provides an ideal stage to showcase and model the expression and unique roles of individual HSPGs. Individual HSPG core proteins are differentially localised to eye tissues in a temporal and spatial developmental- and cell-type specific manner, and their loss or functional disruption results in unique phenotypic outcomes for the lens, and other ocular tissues. More recent work has found that different HS sulfation enzymes are also presented in a cell- and tissue-specific manner, and that disruption of these different sulfation patterns affects specific HS-protein interactions. Not surprisingly, these sulfated HS chains have also been reported to be required for lens and eye development, with dysregulation of HS chain structure and function leading to pathogenesis and eye-related phenotypes. In the lens, HSPGs undergo significant and specific changes in expression and function that can drive pathology, or in some cases, promote tissue repair. As master signalling regulators, HSPGs may one day serve as valuable biomarkers, and even as putative targets for the development of novel therapeutics, not only for the eye but for many other systemic pathologies.

Heparan Sulfate Glycosaminoglycan Is Predicted to Stabilize Inflammatory Infiltrate Formation and RANKL/OPG Ratio in Severe Periodontitis in Humans

Since chronically inflamed periodontal tissue exhibits extracellular matrix (ECM) degradation, the possible alternative to standard periodontitis treatment is to restore ECM by supplementing its components, including heparan sulfate glycosaminoglycan (HS GAG). Supplementation of the degraded ECM with synthetic derivatives of HS GAGs has been shown to be effective for periodontal tissue regeneration in experimental animal models of periodontitis. However, the potential of HS GAG supplementation for the treatment of periodontal disease in humans is still unknown. Here, we used a statistical model to investigate the role of HS GAG on inflammatory infiltrate formation and alveolar bone resorption in humans with severe periodontitis. The model was based on data from immunofluorescence staining (IF) of human gingiva samples, and reconstruction of a subset of HS GAG -related proteins from STRING reactome database. According to predictions, increased expression of native HS GAG might stabilize the accumulation of gingival inflammatory infiltrate (represented by the general inflammatory cell marker CD45) and alveolar bone resorption (represented by Receptor Activator of Nuclear ΚΒ ligand (RANKL) and osteoprotegerin (OPG) ratio) but could not restore them to healthy tissue levels. Therefore, supplementation of native HS GAG may be of limited benefits for the treatment of sever periodontitis in humans.

Heparan Sulfate Biosynthesis and Sulfation Profiles as Modulators of Cancer Signalling and Progression

Heparan Sulfate Proteoglycans (HSPGs) are important cell surface and Extracellular Matrix (ECM) maestros involved in the orchestration of multiple cellular events in physiology and pathology. These glycoconjugates bind to various bioactive proteins via their Heparan Sulfate (HS) chains, but also through the protein backbone, and function as scaffolds for protein-protein interactions, modulating extracellular ligand gradients, cell signalling networks and cell-cell/cell-ECM interactions. The structural features of HS chains, including length and sulfation patterns, are crucial for the biological roles displayed by HSPGs, as these features determine HS chains binding affinities and selectivity. The large HS structural diversity results from a tightly controlled biosynthetic pathway that is differently regulated in different organs, stages of development and pathologies, including cancer. This review addresses the regulatory mechanisms underlying HS biosynthesis, with a particular focus on the catalytic activity of the enzymes responsible for HS glycan sequences and sulfation motifs, namely D-Glucuronyl C5-Epimerase, N- and O-Sulfotransferases. Moreover, we provide insights on the impact of different HS structural epitopes over HSPG-protein interactions and cell signalling, as well as on the effects of deregulated expression of HS modifying enzymes in the development and progression of cancer. Finally, we discuss the clinical potential of HS biosynthetic enzymes as novel targets for therapy, and highlight the importance of developing new HS-based tools for better patients' stratification and cancer treatment.

Biological role of heparan sulfate in osteogenesis: A review

Heparan sulfate (HS) is extensively expressed in cells, for example, cell membrane and extracellular matrix of most mammalian cells and tissues, playing a key role in the growth and development of life by maintaining homeostasis and implicating in the etiology and diseases. Recent studies have revealed that HS is involved in osteogenesis via coordinating multiple signaling pathways. The potential effect of HS on osteogenesis is a complicated and delicate biological process, which involves the participation of osteocytes, chondrocytes, osteoblasts, osteoclasts and a variety of cytokines. In this review, we summarized the structural and functional characteristics of HS and highlighted the molecular mechanism of HS in bone metabolism to provide novel research perspectives for the further medical research.

Novel approach for quantification of multiple immunofluorescent signals using histograms and 2D plot profiling of whole-section panoramic images

We describe a novel approach for quantification and colocalization of immunofluorescence (IF) signals of multiple markers on high-resolution panoramic images of serial histological sections utilizing standard staining techniques and readily available software for image processing and analysis. Human gingiva samples stained with primary antibodies against the common leukocyte antigen CD45 and factors related to heparan sulfate glycosaminoglycans (HS GAG) were used. Expression domains and spatial gradients of IF signals were quantified by histograms and 2D plot profiles, respectively. The importance of histomorphometric profiling of tissue samples and IF signal thresholding is elaborated. This approach to quantification of IF staining utilizes pixel (px) counts and comparison of px grey value (GV) or luminance. No cell counting is applied either to determine the cellular content of a given histological section nor the number of cells positive to the primary antibody of interest. There is no selection of multiple Regions-Of-Interest (ROIs) since the entire histological section is quantified. Although the standard IF staining protocol is applied, the data output enables colocalization of multiple markers (up to 30) from a given histological sample. This can serve as an alternative for colocalization of IF staining of multiple primary antibodies based on repeating cycles of staining of the same histological section since those techniques require non standard staining protocols and sophisticated equipment that can be out of reach for small laboratories in academic settings. Combined with the data from ontological bases, this approach to quantification of IF enables creation of in silico virtual disease models.

Learning from BMPs and their biophysical extracellular matrix microenvironment for biomaterial design

It is nowadays well-accepted that the extracellular matrix (ECM) is not a simple reservoir for growth factors but is an organization center of their biological activity. In this review, we focus on the ability of the ECM to regulate the biological activity of BMPs. In particular, we survey the role of the ECM components, notably the glycosaminoglycans and fibrillary ECM proteins, which can be promoters or repressors of the biological activities mediated by the BMPs. We examine how a process called mechano-transduction induced by the ECM can affect BMP signaling, including BMP internalization by the cells. We also focus on the spatio-temporal regulation of the BMPs, including their release from the ECM, which enables to modulate their spatial localization as well as their local concentration. We highlight how biomaterials can recapitulate some aspects of the BMPs/ECM interactions and help to answer fundamental questions to reveal previously unknown molecular mechanisms. Finally, the design of new biomaterials inspired by the ECM to better present BMPs is discussed, and their use for a more efficient bone regeneration in vivo is also highlighted.

Sanfilippo Syndrome: Molecular Basis, Disease Models and Therapeutic Approaches

Sanfilippo syndrome or mucopolysaccharidosis III is a lysosomal storage disorder caused by mutations in genes responsible for the degradation of heparan sulfate, a glycosaminoglycan located in the extracellular membrane. Undegraded heparan sulfate molecules accumulate within lysosomes leading to cellular dysfunction and pathology in several organs, with severe central nervous system degeneration as the main phenotypical feature. The exact molecular and cellular mechanisms by which impaired degradation and storage lead to cellular dysfunction and neuronal degeneration are still not fully understood. Here, we compile the knowledge on this issue and review all available animal and cellular models that can be used to contribute to increase our understanding of Sanfilippo syndrome disease mechanisms. Moreover, we provide an update in advances regarding the different and most successful therapeutic approaches that are currently under study to treat Sanfilippo syndrome patients and discuss the potential of new tools such as induced pluripotent stem cells to be used for disease modeling and therapy development.

Heparan Sulfate Proteoglycan Signaling in Tumor Microenvironment

In the last few decades, heparan sulfate (HS) proteoglycans (HSPGs) have been an intriguing subject of study for their complex structural characteristics, their finely regulated biosynthetic machinery, and the wide range of functions they perform in living organisms from development to adulthood. From these studies, key roles of HSPGs in tumor initiation and progression have emerged, so that they are currently being explored as potential biomarkers and therapeutic targets for cancers. The multifaceted nature of HSPG structure/activity translates in their capacity to act either as inhibitors or promoters of tumor growth and invasion depending on the tumor type. Deregulation of HSPGs resulting in malignancy may be due to either their abnormal expression levels or changes in their structure and functions as a result of the altered activity of their biosynthetic or remodeling enzymes. Indeed, in the tumor microenvironment, HSPGs undergo structural alterations, through the shedding of proteoglycan ectodomain from the cell surface or the fragmentation and/or desulfation of HS chains, affecting HSPG function with significant impact on the molecular interactions between cancer cells and their microenvironment, and tumor cell behavior. Here, we overview the structural and functional features of HSPGs and their signaling in the tumor environment which contributes to tumorigenesis and cancer progression.

Polysaccharide Sequence Influences the Specificity and Catalytic Activity of Glucuronyl C5-Epimerase

Heparin is a widely used biotherapeutic produced from animal tissues. However, it might be possible to produce a bioengineered version using a multienzyme process, relying on the isolation of the E. coli K5 capsule heparosan and its chemical conversion to N-sulfoheparosan, NSH. Glucuronyl C5-epimerase, the first enzyme that acts on NSH, catalyzes the reversible conversion of glucuronic acid (GlcA) to iduronic acid (IdoA). Using full-length NSH, containing different amounts of N-acetylglucosamine (GlcNAc) residues, we demonstrate that C5-epimerase specificity relates to polysaccharide sequence, particularly the location of GlcNAc residues within the chain. We leveraged the deuterium exchange and the novel β-glucuronidase heparanase BP, which cleaves at the GlcA residue. Liquid chromatography-mass spectrometry and gel permeation chromatography of partial/complete heparanase BP digestion products from various NSH substrates treated with C5-epimerase provide information on C5-epimerase activity and action pattern. This study provides insight into optimizing the large-scale production of bioengineered heparin.

The second member of the bacterial UDP-N-acetyl-d-glucosamine:heparosan alpha-1, 4-N-acetyl-d-glucosaminyltransferase superfamily: GaKfiA from Gallibacterium anatis

Bacterial UDP-N-acetyl-d-glucosamine:heparosan alpha-1, 4-N-acetyl-d-glucosaminyltransferases (KfiAs) are in high demand for the development of animal-free heparin (HP) production. Until now, EcKfiA from Escherichia coli O10:K5:H4 was the sole identified member of this family. The lack of known members has limited research into molecular structure and catalytic mechanism of the KfiA superfamily, and restricted its application in enzymatic glycan synthesis. Herein, we report the identification and characterization of Gallibacterium anatis GaKfiA, doubling the number of known members of the KfiA family. GaKfiA is a monofunctional enzyme that transfers N-acetyl-d-glucosamine (GlcNAc) residues from their nucleotide forms to the nonreducing ends of saccharide chains structurally equivalent to the backbone of HP. The catalytic efficiency of GaKfiA is lower than that of EcKfiA. However, a single mutation of GaKfiA, N56D, resulted in a drastic increase in k_cat/K_m compared with wild-type GaKfiA. These data once again indicate the key role of a complete DXD motif for the catalytic efficiency of glycosyltransferases. This study deepens understanding of the mechanism of KfiA, and will assist in research into animal-free HP production.

Syndecans and Enzymes for Heparan Sulfate Biosynthesis and Modification Differentially Correlate With Presence of Inflammatory Infiltrate in Periodontitis

Periodontitis is a common degenerative disease initiated by the bacteria in subgingival biofilm. The exposure to bacterial biofilm triggers host inflammatory response whose dysregulation is ultimately responsible for the destruction of hard and soft periodontal tissues resulting in tooth loss. To date, significant effort has been invested in the research of the involvement of host cells and inflammatory mediators in regulation of inflammatory response in periodontitis. Syndecans (Sdcs) belong to a four-member family of heparan sulfate proteoglycans (HSPGs). Sdcs are compound molecules comprised of the core protein to which several heparan sulfate (HS) glycosaminoglycan (GAG) chains are attached. The role of Sdcs in pathogenesis of periodontitis is poorly investigated despite the numerous reports from experimental studies about the critical involvement of these factors in modulation of various aspects of inflammatory response, such as the formation of inflammatory mediators gradients, leukocyte recruitment and extracellular matrix remodeling in resolution of inflammation. Most of these functions of Sdcs are HS-related and, thus, dependent upon the structure of HS. This, in turn, is determined by the combinatorial action of enzymes for biosynthesis and modification of HS such as exostosis (EXTs), sulfotransferases (NDSTs), and heparanase 1 (HPSE1). The data presented in this study clearly indicate that some Sdcs display different expression profiles in healthy and diseased periodontal tissue. Additionally, the differences in expression profiles of HS GAG biosynthesis and modification enzymes (EXTs, NDSTs, and HPSE1) in healthy and diseased periodontal tissue imply that changes in HS GAG content and structure might also take place during periodontitis. Most notably, expression profiles of Sdcs, EXTs, NDSTs, and HPSE1 differentially correlate with the presence of inflammatory infiltrate in healthy and diseased periodontal tissue, which might imply that these factors could also be involved in modulation of inflammatory response in periodontitis.

Chemoenzymatic quantification for monitoring unpurified polysaccharide in rich medium

The heparosan polysaccharide serves as the starting carbon backbone for the chemoenzymatic synthesis of heparin, a widely used clinical anticoagulant drug. The previous quantification methods for heparosan rely on time-consuming purification or expensive instruments not readily available for many labs. Here, a chemoenzymatic approach is developed to monitor the production of heparosan in rich medium without purification. After removing the interfering small molecules by ultrafiltration, heparosan was decomposed into oligosaccharides using heparin lyase III. The oligosaccharides were separated from large molecules by ultrafiltration and quantitatively determined by the anthrone-sulfuric acid assay using a spectrophotometer. Based on the different substrate specificity of heparin lyases, the study showed that the concentration of heparosan and heparin in a mixture was discriminatively determined by the two-step chemoenzymatic assay. Furthermore, the anthrone-sulfuric acid assay was observed to be more reliable than the phenol-sulfuric acid assay under these conditions. Besides heparosan and heparin, the chemoenzymatic assay may be adapted to quantify other types of polysaccharides if the specific lyases were available.

Heparan sulfate as a regulator of inflammation and immunity

Heparan sulfate is found on the surface of most cell types, as well as in basement membranes and extracellular matrices. Its strong anionic properties and highly variable structure enable this glycosaminoglycan to provide binding sites for numerous protein ligands, including many soluble mediators of the immune system, and may promote or inhibit their activity. The formation of ligand binding sites on heparan sulfate (HS) occurs in a tissue- and context-specific fashion through the action of several families of enzymes, most of which have multiple isoforms with subtly different specificities. Changes in the expression levels of these biosynthetic enzymes occur in response to inflammatory stimuli, resulting in structurally different HS and acquisition or loss of binding sites for immune mediators. In this review, we discuss the multiple roles for HS in regulating immune responses, and the evidence for inflammation-associated changes to HS structure.

Regulation of eosinophil recruitment and allergic airway inflammation by heparan sulfate proteoglycan (HSPG) modifying enzymes

BACKGROUND

HSPGs are glycoproteins containing covalently attached heparan sulfate (HS) chains which bind to growth factors, chemokines, etc., and regulate various aspects of inflammation including cell recruitment. We previously showed that deletion of endothelial N-acetylglucosamine N-deacetylase-N-sulfotransferase-1 (Ndst1), an enzyme responsible for N-sulfation during HS biosynthesis, reduces allergic airway inflammation (AAI). Here, we investigated the importance of O-sulfation mediated by uronyl 2-O-sulfotransferase (Hs2st) in development of AAI relative to N-sulfation.

METHODS

Mice deficient in endothelial and leukocyte Hs2st (Hs2st^f/fTie2Cre⁺) or Ndst1 (Ndst1^f/fTie2Cre⁺) and WT mice were challenged with Alternaria alternata and evaluated for airway inflammation. Trafficking of murine eosinophils on lung endothelial cells was examined in vitro under conditions of flow.

RESULTS

Exposure to Alternaria decreased expression level of Hs2st in WT mice while level of Ndst1 remained unchanged. Compared to WT mice, Alternaria-challenged Hs2st^f/fTie2Cre⁺ mice exhibited significantly increased eosinophils in the bone marrow, bronchoalveolar lavage fluid [BALF] and lung tissue associated with persistent airway hyperresponsiveness, airway mucus hypersecretion and elevated Th2 cytokines. In contrast, Alternaria-challenged Ndst1^f/fTie2Cre⁺ mice exhibited a marked reduction in airway eosinophilia, mucus secretion and smooth muscle mass compared to WT counterparts. While BALF eotaxins were lower in Alternaria-challenged Hs2st^f/fTie2Cre⁺ relative to WT mice, they were not reduced to background levels as in allergen-challenged Ndst1^f/fTie2Cre⁺ mice. Trafficking of murine eosinophils under conditions of flow in vitro was similar on Hs2st-deficient and WT endothelial cells. Expression of ZO-1 in Hs2st-deficient lung blood vessels in control and allergen-challenged mice was significantly lower than in WT counterparts.

CONCLUSIONS

Our study demonstrates that allergen exposure reduces expression of Hs2st; loss of uronyl 2-O-sulfation in endothelial and leukocyte HSPG amplifies recruitment of eosinophils likely due to a compromised vascular endothelium resulting in persistent inflammation whereas loss of N-sulfation limits eosinophilia and attenuates inflammation underscoring the importance of site-specific sulfation in HSPG to their role in AAI.

Heparan Sulfate Biosynthetic System Is Inhibited in Human Glioma Due to EXT1/2 and HS6ST1/2 Down-Regulation

Heparan sulfate (HS) is an important component of the extracellular matrix and cell surface, which plays a key role in cell–cell and cell–matrix interactions. Functional activity of HS directly depends on its structure, which determined by a complex system of HS biosynthetic enzymes. During malignant transformation, the system can undergo significant changes, but for glioma, HS biosynthesis has not been studied in detail. In this study, we performed a comparative analysis of the HS biosynthetic system in human gliomas of different grades. RT-PCR analysis showed that the overall transcriptional activity of the main HS biosynthesis-involved genes (EXT1, EXT2, NDST1, NDST2, GLCE, HS2ST1, HS3ST1, HS3ST2, HS6ST1, HS6ST2, SULF1, SULF2, HPSE) was decreased by 1.5–2-fold in Grade II-III glioma (p < 0.01) and by 3-fold in Grade IV glioma (glioblastoma multiforme, GBM) (p < 0.05), as compared with the para-tumourous tissue. The inhibition was mainly due to the elongation (a decrease in EXT1/2 expression by 3–4-fold) and 6-O-sulfation steps (a decrease in 6OST1/2 expression by 2–5-fold) of the HS biosynthesis. Heparanase (HPSE) expression was identified in 50% of GBM tumours by immunostaining, and was characterised by a high intratumoural heterogeneity of the presence of the HPSE protein. The detected disorganisation of the HS biosynthetic system in gliomas might be a potential molecular mechanism for the changes of HS structure and content in tumour microenvironments, contributing to the invasion of glioma cells and the development of the disease.

Fibroblast Growth Factor Signaling Mediates Pulmonary Endothelial Glycocalyx Reconstitution

The endothelial glycocalyx is a heparan sulfate (HS)-rich endovascular structure critical to endothelial function. Accordingly, endothelial glycocalyx degradation during sepsis contributes to tissue edema and organ injury. We determined the endogenous mechanisms governing pulmonary endothelial glycocalyx reconstitution, and if these reparative mechanisms are impaired during sepsis. We performed intravital microscopy of wild-type and transgenic mice to determine the rapidity of pulmonary endothelial glycocalyx reconstitution after nonseptic (heparinase-III mediated) or septic (cecal ligation and puncture mediated) endothelial glycocalyx degradation. We used mass spectrometry, surface plasmon resonance, and in vitro studies of human and mouse samples to determine the structure of HS fragments released during glycocalyx degradation and their impact on fibroblast growth factor receptor (FGFR) 1 signaling, a mediator of endothelial repair. Homeostatic pulmonary endothelial glycocalyx reconstitution occurred rapidly after nonseptic degradation and was associated with induction of the HS biosynthetic enzyme, exostosin (EXT)-1. In contrast, sepsis was characterized by loss of pulmonary EXT1 expression and delayed glycocalyx reconstitution. Rapid glycocalyx recovery after nonseptic degradation was dependent upon induction of FGFR1 expression and was augmented by FGF-promoting effects of circulating HS fragments released during glycocalyx degradation. Although sepsis-released HS fragments maintained this ability to activate FGFR1, sepsis was associated with the downstream absence of reparative pulmonary endothelial FGFR1 induction. Sepsis may cause vascular injury not only via glycocalyx degradation, but also by impairing FGFR1/EXT1-mediated glycocalyx reconstitution.

Epigenetic Regulation of the Biosynthesis & Enzymatic Modification of Heparan Sulfate Proteoglycans: Implications for Tumorigenesis and Cancer Biomarkers

Emerging evidence suggests that the enzymes in the biosynthetic pathway for the synthesis of heparan sulfate moieties of heparan sulfate proteoglycans (HSPGs) are epigenetically regulated at many levels. As the exact composition of the heparan sulfate portion of the resulting HSPG molecules is critical to the broad spectrum of biological processes involved in oncogenesis, the epigenetic regulation of heparan sulfate biosynthesis has far-reaching effects on many cellular activities related to cancer progression. Given the current focus on developing new anti-cancer therapeutics focused on epigenetic targets, it is important to understand the effects that these emerging therapeutics may have on the synthesis of HSPGs as alterations in HSPG composition may have profound and unanticipated effects. As an introduction, this review will briefly summarize the variety of important roles which HSPGs play in a wide-spectrum of cancer-related cellular and physiological functions and then describe the biosynthesis of the heparan sulfate chains of HSPGs, including how alterations observed in cancer cells serve as potential biomarkers. This review will then focus on detailing the multiple levels of epigenetic regulation of the enzymes in the heparan sulfate synthesis pathway with a particular focus on regulation by miRNA and effects of epigenetic therapies on HSPGs. We will also explore the use of lectins to detect differences in heparan sulfate composition and preview their potential diagnostic and prognostic use in the clinic.