Heparan sulfate 6-O-endosulfatases: discrete in vivo activities and functional co-operativity

High sensitivity (zeptomole) detection of BODIPY-labelled heparan sulfate (HS) disaccharides by ion-paired RP-HPLC and LIF detection enables analysis of HS from mosquito midguts

The fine structure of heparan sulfate (HS), the glycosaminoglycan polysaccharide component of cell surface and extracellular matrix HS proteoglycans, coordinates the complex cell signalling processes that control homeostasis and drive development in multicellular animals. In addition, HS is involved in the infection of mammals by viruses, bacteria and parasites. The current detection limit for fluorescently labelled HS disaccharides (low femtomole; 10^-15 mol), has effectively hampered investigations of HS composition in small, functionally-relevant populations of cells and tissues that may illuminate the structural requirements for infection and other biochemical processes. Here, an ultra-high sensitivity method is described that utilises a combination of reverse-phase HPLC, with tetraoctylammonium bromide (TOAB) as the ion-pairing reagent and laser-induced fluorescence detection of BODIPY-FL-labelled disaccharides. The method provides an unparalleled increase in the sensitivity of detection by ∼six orders of magnitude, enabling detection in the zeptomolar range (∼10^-21 moles; <1000 labelled molecules). This facilitates determination of HS disaccharide compositional analysis from minute samples of selected tissues, as demonstrated by analysis of HS isolated from the midguts of Anopheles gambiae mosquitoes that was achieved without approaching the limit of detection.

HS, an Ancient Molecular Recognition and Information Storage Glycosaminoglycan, Equips HS-Proteoglycans with Diverse Matrix and Cell-Interactive Properties Operative in Tissue Development and Tissue Function in Health and Disease

Heparan sulfate is a ubiquitous, variably sulfated interactive glycosaminoglycan that consists of repeating disaccharides of glucuronic acid and glucosamine that are subject to a number of modifications (acetylation, de-acetylation, epimerization, sulfation). Variable heparan sulfate chain lengths and sequences within the heparan sulfate chains provide structural diversity generating interactive oligosaccharide binding motifs with a diverse range of extracellular ligands and cellular receptors providing instructional cues over cellular behaviour and tissue homeostasis through the regulation of essential physiological processes in development, health, and disease. heparan sulfate and heparan sulfate-PGs are integral components of the specialized glycocalyx surrounding cells. Heparan sulfate is the most heterogeneous glycosaminoglycan, in terms of its sequence and biosynthetic modifications making it a difficult molecule to fully characterize, multiple ligands also make an elucidation of heparan sulfate functional properties complicated. Spatio-temporal presentation of heparan sulfate sulfate groups is an important functional determinant in tissue development and in cellular control of wound healing and extracellular remodelling in pathological tissues. The regulatory properties of heparan sulfate are mediated via interactions with chemokines, chemokine receptors, growth factors and morphogens in cell proliferation, differentiation, development, tissue remodelling, wound healing, immune regulation, inflammation, and tumour development. A greater understanding of these HS interactive processes will improve therapeutic procedures and prognoses. Advances in glycosaminoglycan synthesis and sequencing, computational analytical carbohydrate algorithms and advanced software for the evaluation of molecular docking of heparan sulfate with its molecular partners are now available. These advanced analytic techniques and artificial intelligence offer predictive capability in the elucidation of heparan sulfate conformational effects on heparan sulfate-ligand interactions significantly aiding heparan sulfate therapeutics development.

A glycan-based approach to cell characterization and isolation: Hematopoiesis as a paradigm

Cell surfaces display a wide array of molecules that confer identity. While flow cytometry and cluster of differentiation (CD) markers have revolutionized cell characterization and purification, functionally heterogeneous cellular subtypes remain unresolvable by the CD marker system alone. Using hematopoietic lineages as a paradigm, we leverage the extraordinary molecular diversity of heparan sulfate (HS) glycans to establish cellular "glycotypes" by utilizing a panel of anti-HS single-chain variable fragment antibodies (scFvs). Prospective sorting with anti-HS scFvs identifies functionally distinct glycotypes within heterogeneous pools of mouse and human hematopoietic progenitor cells and enables further stratification of immunophenotypically pure megakaryocyte-erythrocyte progenitors. This stratification correlates with expression of a heptad of HS-related genes that is reflective of the HS epitope recognized by specific anti-HS scFvs. While we show that HS glycotyping provides an orthogonal set of tools for resolution of hematopoietic lineages, we anticipate broad utility of this approach in defining and isolating novel, viable cell types across diverse tissues and species.

Genome-wide screens uncover KDM2B as a modifier of protein binding to heparan sulfate

Heparan sulfate (HS) proteoglycans bind extracellular proteins that participate in cell signaling, attachment and endocytosis. These interactions depend on the arrangement of sulfated sugars in the HS chains generated by well-characterized biosynthetic enzymes; however, the regulation of these enzymes is largely unknown. We conducted genome-wide CRISPR-Cas9 screens with a small-molecule ligand that binds to HS. Screening of A375 melanoma cells uncovered additional genes and pathways impacting HS formation. The top hit was the epigenetic factor KDM2B, a histone demethylase. KDM2B inactivation suppressed multiple HS sulfotransferases and upregulated the sulfatase SULF1. These changes differentially affected the interaction of HS-binding proteins. KDM2B-deficient cells displayed decreased growth rates, which was rescued by SULF1 inactivation. In addition, KDM2B deficiency altered the expression of many extracellular matrix genes. Thus, KDM2B controls proliferation of A375 cells through the regulation of HS structure and serves as a master regulator of the extracellular matrix.

Overcoming the inhibitory microenvironment surrounding oligodendrocyte progenitor cells following experimental demyelination

Chronic demyelination in the human CNS is characterized by an inhibitory microenvironment that impairs recruitment and differentiation of oligodendrocyte progenitor cells (OPCs) leading to failed remyelination and axonal atrophy. By network-based transcriptomics, we identified sulfatase 2 (Sulf2) mRNA in activated human primary OPCs. Sulf2, an extracellular endosulfatase, modulates the signaling microenvironment by editing the pattern of sulfation on heparan sulfate proteoglycans. We found that Sulf2 was increased in demyelinating lesions in multiple sclerosis and was actively secreted by human OPCs. In experimental demyelination, elevated OPC Sulf1/2 expression directly impaired progenitor recruitment and subsequent generation of oligodendrocytes thereby limiting remyelination. Sulf1/2 potentiates the inhibitory microenvironment by promoting BMP and WNT signaling in OPCs. Importantly, pharmacological sulfatase inhibition using PI-88 accelerated oligodendrocyte recruitment and remyelination by blocking OPC-expressed sulfatases. Our findings define an important inhibitory role of Sulf1/2 and highlight the potential for modulation of the heparanome in the treatment of chronic demyelinating disease.

Demyelination results in impairments in oligodendrocyte progenitor cell recruitment. Here the authors identify sulfatase 1/2 as a potential modulator of myelination by modulating the microenvironment around oligodendrocyte progenitor cells.

Mobility shift-based electrophoresis coupled with fluorescent detection enables real-time enzyme analysis of carbohydrate sulfatase activity

Sulfated carbohydrate metabolism is a fundamental process, which occurs in all domains of life. Carbohydrate sulfatases are enzymes that remove sulfate groups from carbohydrates and are essential to the depolymerisation of complex polysaccharides. Despite their biological importance, carbohydrate sulfatases are poorly studied and challenges remain in accurately assessing the enzymatic activity, specificity and kinetic parameters. Most notably, the separation of desulfated products from sulfated substrates is currently a time-consuming process. In this paper, we describe the development of rapid capillary electrophoresis coupled to substrate fluorescence detection as a high-throughput and facile means of analysing carbohydrate sulfatase activity. The approach has utility for the determination of both kinetic and inhibition parameters and is based on existing microfluidic technology coupled to a new synthetic fluorescent 6S-GlcNAc carbohydrate substrate. Furthermore, we compare this technique, in terms of both time and resources, to high-performance anion exchange chromatography and NMR-based methods, which are the two current 'gold standards' for enzymatic carbohydrate sulfation analysis. Our study clearly demonstrates the advantages of mobility shift assays for the quantification of near real-time carbohydrate desulfation by purified sulfatases, and will support the search for small molecule inhibitors of these disease-associated enzymes.

Identification of molecular toxicity pathways across early life-stages of zebrafish exposed to PCB126 using a whole transcriptomics approach

Although withdrawn from the market in the 1980s, polychlorinated biphenyls (PCBs) are still found ubiquitously in the aquatic environment and pose a serious risk to biota due to their teratogenic potential. In fish, early life-stages are often considered most sensitive with regard to their exposure to PCBs and other dioxin-like compounds. However, little is known about the molecular drivers of the frequently observed teratogenic effects. Therefore, the aims of our study were to: (1) characterize the baseline transcriptome profiles at different embryonic life-stages in zebrafish (Danio rerio); and (2) to identify the molecular response to PCB exposure and life-stage specific-effects of the chemical on associated processes. For both objectives, embryos were sampled at 12, 48, and 96 h post-fertilization (hpf) and subjected to Illumina sequence-by-synthesis and RNAseq analysis. Results revealed that with increasing age more genes and related pathways were upregulated both in terms of number and magnitude. Yet, other transcripts followed an opposite pattern with greater transcript abundance at the earlier time points. Additionally, embryos were exposed to PCB126, a potent agonist of the aryl hydrocarbon receptor (AHR). ClueGO network analysis revealed significant enrichment of genes associated with basic cell metabolism, communication, and homeostasis as well as eye development, muscle formation, and skeletal formation. We selected eight genes involved in the affected pathways for an in-depth characterization of their regulation throughout normal embryogenesis and after exposure to PCB126 by quantification of transcript abundances every 12 h until 118 hpf. Among these, fgf7 and c9 stood out because of their strong upregulation by PCB126 exposure at 48 and 96 hpf, respectively. Cyp2aa12 was upregulated from 84 hpf on. Fabp10ab, myhz1.1, col8a1a, sulf1, and opn1sw1 displayed specific regulation depending on the developmental stage. Overall, we demonstrate that (1) the developmental transcriptome of zebrafish is highly dynamic, and (2) dysregulation of gene expression by exposure to PCB126 was significant and in several cases not directly connected to AHR-signaling. Hence, this study improves the understanding of linkages between molecular events and apical outcomes that are of regulatory relevance.

Sulf2a controls Shh-dependent neural fate specification in the developing spinal cord

Sulf2a belongs to the Sulf family of extracellular sulfatases which selectively remove 6-O-sulfate groups from heparan sulfates, a critical regulation level for their role in modulating the activity of signalling molecules. Data presented here define Sulf2a as a novel player in the control of Sonic Hedgehog (Shh)-mediated cell type specification during spinal cord development. We show that Sulf2a depletion in zebrafish results in overproduction of V3 interneurons at the expense of motor neurons and also impedes generation of oligodendrocyte precursor cells (OPCs), three cell types that depend on Shh for their generation. We provide evidence that Sulf2a, expressed in a spatially restricted progenitor domain, acts by maintaining the correct patterning and specification of ventral progenitors. More specifically, Sulf2a prevents Olig2 progenitors to activate high-threshold Shh response and, thereby, to adopt a V3 interneuron fate, thus ensuring proper production of motor neurons and OPCs. We propose a model in which Sulf2a reduces Shh signalling levels in responding cells by decreasing their sensitivity to the morphogen factor. More generally, our work, revealing that, in contrast to its paralog Sulf1, Sulf2a regulates neural fate specification in Shh target cells, provides direct evidence of non-redundant functions of Sulfs in the developing spinal cord.

Knockout of sulfatase 2 is associated with decreased steatohepatitis and fibrosis in a mouse model of nonalcoholic fatty liver disease

Sulfatase 2 (SULF2) is a heparan sulfate editing enzyme that regulates the milieu of growth factors and cytokines involved in a variety of cellular processes. We used a murine model of diet-induced steatohepatitis to assess the effect of SULF2 downregulation on the development of nonalcoholic steatohepatitis (NASH) and liver fibrosis. Wild-type B6;129 mice (WT) and Sulf2-knockout B6;129P2-SULF2^{Gt(PST111)Byg} mice (Sulf2-KO) were fed a fast-food diet (FFD) rich in saturated fats, cholesterol, and fructose or a standard chow diet (SC) ad libitum for 9 mo. WT mice on FFD showed a threefold increase in hepatic Sulf2 mRNA expression, and a 2.2-fold increase in hepatic SULF2 protein expression compared with WT mice on SC. Knockout of Sulf2 led to a significant decrease in diet-mediated weight gain and dyslipidemia compared with WT mice on FFD. Knockout of Sulf2 also abrogated diet-induced steatohepatitis and hepatic fibrosis compared with WT mice on FFD. Furthermore, expression levels of the profibrogenic receptors TGFβR2 and PDGFRβ were significantly decreased in Sulf2-KO mice compared with WT mice on FFD. Together, our data suggest that knockout of Sulf2 significantly downregulates dyslipidemia, steatohepatitis, and hepatic fibrosis in a diet-induced mouse model of NAFLD, suggesting that targeting of SULF2 signaling may be a potential therapeutic mechanism in NASH.NEW & NOTEWORTHY We report for the first time that in wild-type (WT) mice, fast-food diet (FFD) induced a threefold increase in hepatic Sulf2 mRNA and a 2.2-fold increase in sulfatase 2 (SULF2) protein expression compared with WT mice on standard chow diet (SC). We showed that knockout of SULF2 ameliorates FFD-induced obesity, hyperlipidemia, steatohepatitis, and fibrosis. These data, along with work from other laboratories, suggest that SULF2 may be critical to the ability of the liver to progress to nonalcoholic steatohepatitis and fibrosis in conditions of overnutrition.

Involvement of Heparan Sulfate and Heparanase in Neural Development and Pathogenesis of Brain Tumors

Brain tumors are aggressive and devastating diseases. The most common type of brain tumor, glioblastoma (GBM), is incurable and has one of the worst five-year survival rates of all human cancers. GBMs are invasive and infiltrate healthy brain tissue, which is one main reason they remain fatal despite resection, since cells that have already migrated away lead to rapid regrowth of the tumor. Curative therapy for medulloblastoma (MB), the most common pediatric brain tumor, has improved, but the outcome is still poor for many patients, and treatment causes long-term complications. Recent advances in the classification of pediatric brain tumors reveal distinct subgroups, allowing more targeted therapy for the most aggressive forms, and sparing children with less malignant tumors the side-effects of massive treatment. Heparan sulfate proteoglycans (HSPGs), main components of the neurogenic niche, interact specifically with a large number of physiologically important molecules and vital roles for HS biosynthesis and degradation in neural stem cell differentiation have been presented. HSPGs are composed of a core protein with attached highly charged, sulfated disaccharide chains. The major enzyme that degrades HS is heparanase (HPSE), an important regulator of extracellular matrix (ECM) remodeling which has been suggested to promote the growth and invasion of other types of tumors. This is of clinical interest because GBM are highly invasive and children with metastatic MB at the time of diagnosis exhibit a worse outcome. Here we review the involvement of HS and HPSE in development of the nervous system and some of its most malignant brain tumors, glioblastoma and medulloblastoma.

Heparan Sulfate-Editing Extracellular Sulfatases Enhance VEGF Bioavailability for Ischemic Heart Repair

RATIONALE

Mechanistic insight into the inflammatory response after acute myocardial infarction may inform new molecularly targeted treatment strategies to prevent chronic heart failure.

OBJECTIVE

We identified the sulfatase SULF2 in an in silico secretome analysis in bone marrow cells from patients with acute myocardial infarction and detected increased sulfatase activity in myocardial autopsy samples. SULF2 (Sulf2 in mice) and its isoform SULF1 (Sulf1) act as endosulfatases removing 6-O-sulfate groups from heparan sulfate (HS) in the extracellular space, thus eliminating docking sites for HS-binding proteins. We hypothesized that the Sulfs have a role in tissue repair after myocardial infarction.

METHODS AND RESULTS

Both Sulfs were dynamically upregulated after coronary artery ligation in mice, attaining peak expression and activity levels during the first week after injury. Sulf2 was expressed by monocytes and macrophages, Sulf1 by endothelial cells and fibroblasts. Infarct border zone capillarization was impaired, scar size increased, and cardiac dysfunction more pronounced in mice with a genetic deletion of either Sulf1 or Sulf2. Studies in bone marrow-chimeric Sulf-deficient mice and Sulf-deficient cardiac endothelial cells established that inflammatory cell-derived Sulf2 and endothelial cell-autonomous Sulf1 promote angiogenesis. Mechanistically, both Sulfs reduced HS sulfation in the infarcted myocardium, thereby diminishing Vegfa (vascular endothelial growth factor A) interaction with HS. Along this line, both Sulfs rendered infarcted mouse heart explants responsive to the angiogenic effects of HS-binding Vegfa₁₆₄ but did not modulate the angiogenic effects of non-HS-binding Vegfa₁₂₀. Treating wild-type mice systemically with the small molecule HS-antagonist surfen (bis-2-methyl-4-amino-quinolyl-6-carbamide, 1 mg/kg/day) for 7 days after myocardial infarction released Vegfa from HS, enhanced infarct border-zone capillarization, and exerted sustained beneficial effects on cardiac function and survival.

CONCLUSIONS

These findings establish HS-editing Sulfs as critical inducers of postinfarction angiogenesis and identify HS sulfation as a therapeutic target for ischemic tissue repair.

Expression and purification of recombinant extracellular sulfatase HSulf-2 allows deciphering of enzyme sub-domain coordinated role for the binding and 6-O-desulfation of heparan sulfate

Through their ability to edit 6-O-sulfation pattern of Heparan sulfate (HS) polysaccharides, Sulf extracellular endosulfatases have emerged as critical regulators of many biological processes, including tumor progression. However, study of Sulfs remains extremely intricate and progress in characterizing their functional and structural features has been hampered by limited access to recombinant enzyme. In this study, we unlock this critical bottleneck, by reporting an efficient expression and purification system of recombinant HSulf-2 in mammalian HEK293 cells. This novel source of enzyme enabled us to investigate the way the enzyme domain organization dictates its functional properties. By generating mutants, we confirmed previous studies that HSulf-2 catalytic (CAT) domain was sufficient to elicit arylsulfatase activity and that its hydrophilic (HD) domain was necessary for the enzyme 6-O-endosulfatase activity. However, we demonstrated for the first time that high-affinity binding of HS substrates occurred through the coordinated action of both domains, and we identified and characterized 2 novel HS binding sites within the CAT domain. Altogether, our findings contribute to better understand the molecular mechanism governing HSulf-2 substrate recognition and processing. Furthermore, access to purified recombinant protein opens new perspectives for the resolution of HSulf structure and molecular features, as well as for the development of Sulf-specific inhibitors.

Metabolic engineering of mammalian cells to produce heparan sulfates

Heparan sulfate (HS) is a glycosaminoglycan produced by all mammalian cells that plays important roles in physiology and various pathologies. Heparin is a highly sulfated form of HS that is used clinically as an anticoagulant. Heparin and HSs may also have therapeutic benefits for a wide variety of other indications. Cultured mammalian cells produce HS and, through genetic modification, have been used to elucidate the biosynthetic pathway. Recently, metabolic engineering has been used to produce HS from cultured mammalian cells for clinical purposes. This review describes the HS biosynthetic pathway and its manipulation through metabolic engineering to produce bioengineered HSs. We also discuss current challenges and opportunities to advance the field of HS metabolic engineering.

Desulfation of Heparan Sulfate by Sulf1 and Sulf2 Is Required for Corticospinal Tract Formation

Heparan sulfate (HS) has been implicated in a wide range of cell signaling. Here we report a novel mechanism in which extracellular removal of 6-O-sulfate groups from HS by the endosulfatases, Sulf1 and Sulf2, is essential for axon guidance during development. In Sulf1/2 double knockout (DKO) mice, the corticospinal tract (CST) was dorsally displaced on the midbrain surface. In utero electroporation of Sulf1/2 into radial glial cells along the third ventricle, where Sulf1/2 mRNAs are normally expressed, rescued the CST defects in the DKO mice. Proteomic analysis and functional testing identified Slit2 as the key molecule associated with the DKO phenotype. In the DKO brain, 6-O-sulfated HS was increased, leading to abnormal accumulation of Slit2 protein on the pial surface of the cerebral peduncle and hypothalamus, which caused dorsal repulsion of CST axons. Our findings indicate that postbiosynthetic desulfation of HS by Sulfs controls CST axon guidance through fine-tuning of Slit2 presentation.

High sodium diet converts renal proteoglycans into pro-inflammatory mediators in rats

BACKGROUND

High dietary sodium aggravates renal disease by affecting blood pressure and by its recently shown pro-inflammatory and pro-fibrotic effects. Moreover, pro-inflammatory modification of renal heparan sulfate (HS) can induce tissue remodeling. We aim to investigate if high sodium intake in normotensive rats converts renal HS into a pro-inflammatory phenotype, able to bind more sodium and orchestrate inflammation, fibrosis and lymphangiogenesis.

METHODS

Wistar rats received a normal diet for 4 weeks, or 8% NaCl diet for 2 or 4 weeks. Blood pressure was monitored, and plasma, urine and tissue collected. Tissue sodium was measured by flame spectroscopy. Renal HS and tubulo-interstitial remodeling were studied by biochemical, immunohistochemical and qRT-PCR approaches.

RESULTS

High sodium rats showed a transient increase in blood pressure (week 1; p<0.01) and increased sodium excretion (p<0.05) at 2 and 4 weeks compared to controls. Tubulo-interstitial T-cells, myofibroblasts and mRNA levels of VCAM1, TGF-β1 and collagen type III significantly increased after 4 weeks (all p<0.05). There was a trend for increased macrophage infiltration and lymphangiogenesis (both p = 0.07). Despite increased dermal sodium over time (p<0.05), renal concentrations remained stable. Renal HS of high sodium rats showed increased sulfation (p = 0.05), increased L-selectin binding to HS (p<0,05), and a reduction of sulfation-sensitive anti-HS mAbs JM403 (p<0.001) and 10E4 (p<0.01). Hyaluronan expression increased under high salt conditions (p<0.01) without significant changes in the chondroitin sulfate proteoglycan versican. Statistical analyses showed that sodium-induced tissue remodeling responses partly correlated with observed HS changes.

CONCLUSION

We show that high salt intake by healthy normotensive rats convert renal HS into high sulfated pro-inflammatory glycans involved in tissue remodeling events, but not in increased sodium storage.

The function of heparan sulfate during branching morphogenesis

Branching morphogenesis is a fundamental process in the development of diverse epithelial organs such as the lung, kidney, liver, pancreas, prostate, salivary, lacrimal and mammary glands. A unifying theme during organogenesis is the importance of epithelial cell interactions with the extracellular matrix (ECM) and growth factors (GFs). The diverse developmental mechanisms giving rise to these epithelial organs involve many organ-specific GFs, but a unifying paradigm during organogenesis is the regulation of GF activity by heparan sulfates (HS) on the cell surface and in the ECM. This primarily involves the interactions of GFs with the sulfated side-chains of HS proteoglycans. HS is one of the most diverse biopolymers and modulates GF binding and signaling at the cell surface and in the ECM of all tissues. Here, we review what is known about how HS regulates branching morphogenesis of epithelial organs with emphasis on the developing salivary gland, which is a classic model to investigate epithelial-ECM interactions. We also address the structure, biosynthesis, turnover and function of HS during organogenesis. Understanding the regulatory mechanisms that control HS dynamics may aid in the development of therapeutic interventions for diseases and novel strategies for tissue engineering and regenerative medicine.

Drosophila Sulf1 is required for the termination of intestinal stem cell division during regeneration

Stem cell division is activated to trigger regeneration in response to tissue damage. The molecular mechanisms by which this stem cell mitotic activity is properly repressed at the end of regeneration are poorly understood. Here, we show that a specific modification of heparan sulfate is crucial for regulating Drosophila intestinal stem cell (ISC) division during normal midgut homeostasis and regeneration. Loss of the extracellular heparan sulfate endosulfatase Sulf1 resulted in increased ISC division during normal homeostasis, which was caused by upregulation of mitogenic signaling including the JAK-STAT, EGFR and Hedgehog pathways. Using a regeneration model, we found that ISCs failed to properly halt division at the termination stage in Sulf1 mutants, showing that Sulf1 is required for terminating ISC division at the end of regeneration. We propose that post-transcriptional regulation of mitogen signaling by heparan sulfate structural modifications provides a new regulatory step for precise temporal control of stem cell activity during regeneration.

The "in and out" of glucosamine 6-O-sulfation: the 6th sense of heparan sulfate

The biological properties of Heparan sulfate (HS) polysaccharides essentially rely on their ability to bind and modulate a multitude of protein ligands. These interactions involve internal oligosaccharide sequences defined by their sulfation patterns. Amongst these, the 6-O-sulfation of HS contributes significantly to the polysaccharide structural diversity and is critically involved in the binding of many proteins. HS 6-O-sulfation is catalyzed by 6-O-sulfotransferases (6OSTs) during biosynthesis, and it is further modified by the post-synthetic action of 6-O-endosulfatases (Sulfs), two enzyme families that remain poorly characterized. The aim of the present review is to summarize the contribution of 6-O-sulfates in HS structure/function relationships and to discuss the present knowledge on the complex mechanisms regulating HS 6-O-sulfation.

Sulfatase 2 facilitates lymphangiogenesis in breast cancer by regulating VEGF-D

In our previous studies, sulfatase 2 (Sulf2) was found to upregulate vascular endothelial growth factor-D (VEGF-D) expression in breast cancer. As VEGF-D plays an important role in lymphangiogenesis, we hypothesized that Sulf2 facilitates lymphangiogenesis in breast cancer by regulating VEGF-D. To evaluate the functions of Sulf2 on lymphangiogenesis in breast cancer, proliferation, apoptosis, cell cycle, cell mobility and tube-formation of lymphatic endothelial cells (LECs) were measured in vitro. Lymphangiogenesis in nude mouse ears and breast cancer xenografts were examined in vivo. Furthermore, the expression levels of related signaling pathway genes were screened and verified in LECs. We found that Sulf2 significantly increased the mobility and tube formation of the LECs, inhibited cisplatin-induced LEC apoptosis, but had no effect on cell proliferation and the cell cycle. Moreover, recombinant Sulf2 (rSulf2) combined with VEGF-D further promoted the proliferation, cell cycle, mobility and tube-like structure formation in the LECs, and at the same time inhibited cisplatin-induced apoptosis especially in the late stage. Sulf2 also significantly increased the density of lymphatic vessels in mouse ears and breast cancer xenografts in vivo. AKT1 was also shown to be upregulated and activated by Sulf2. Our results confirmed that Sulf2 facilitated lymphangiogenesis in breast cancer cells by regulating VEGF-D and that the AKT1-related signaling pathway was involved.

HSulf-1 deficiency dictates a metabolic reprograming of glycolysis and TCA cycle in ovarian cancer

Warburg effect has emerged as a potential hallmark of many cancers. However, the molecular mechanisms that led to this metabolic state of aerobic glycolysis, particularly in ovarian cancer (OVCA) have not been completely elucidated. HSulf-1 predominantly functions by limiting the bioavailability of heparan binding growth factors and hence their downstream signaling. Here we report that HSulf-1, a known putative tumor suppressor, is a negative regulator of glycolysis. Silencing of HSulf-1 expression in OV202 cell line increased glucose uptake and lactate production by upregulating glycolytic genes such as Glut1, HKII, LDHA, as well as metabolites. Conversely, HSulf-1 overexpression in TOV21G cells resulted in the down regulation of glycolytic enzymes and reduced glycolytic phenotype, supporting the role of HSulf-1 loss in enhanced aerobic glycolysis. HSulf-1 deficiency mediated glycolytic enhancement also resulted in increased inhibitory phosphorylation of pyruvate dehydrogenase (PDH) thus blocking the entry of glucose flux into TCA cycle. Consistent with this, metabolomic and isotope tracer analysis showed reduced glucose flux into TCA cycle. Moreover, HSulf-1 loss is associated with lower oxygen consumption rate (OCR) and impaired mitochondrial function. Mechanistically, lack of HSulf-1 promotes c-Myc induction through HB-EGF-mediated p-ERK activation. Pharmacological inhibition of c-Myc reduced HB-EGF induced glycolytic enzymes implicating a major role of c-Myc in loss of HSulf-1 mediated altered glycolytic pathway in OVCA. Similarly, PG545 treatment, an agent that binds to heparan binding growth factors and sequesters growth factors away from their ligand also blocked HB-EGF signaling and reduced glucose uptake in vivo in HSulf-1 deficient cells.

Sulfatase-mediated manipulation of the astrocyte-Schwann cell interface

Schwann cell (SC) transplantation following spinal cord injury (SCI) may have therapeutic potential. Functional recovery is limited however, due to poor SC interactions with host astrocytes and the induction of astrogliosis. Olfactory ensheathing cells (OECs) are closely related to SCs, but intermix more readily with astrocytes in culture and induce less astrogliosis. We previously demonstrated that OECs express higher levels of sulfatases, enzymes that remove 6-O-sulfate groups from heparan sulphate proteoglycans, than SCs and that RNAi knockdown of sulfatase prevented OEC-astrocyte mixing in vitro. As human OECs are difficult to culture in large numbers we have genetically engineered SCs using lentiviral vectors to express sulfatase 1 and 2 (SC-S1S2) and assessed their ability to interact with astrocytes. We demonstrate that SC-S1S2s have increased integrin-dependent motility in the presence of astrocytes via modulation of NRG and FGF receptor-linked PI3K/AKT intracellular signaling and do not form boundaries with astrocytes in culture. SC-astrocyte mixing is dependent on local NRG concentration and we propose that sulfatase enzymes influence the bioavailability of NRG ligand and thus influence SC behavior. We further demonstrate that injection of sulfatase expressing SCs into spinal cord white matter results in less glial reactivity than control SC injections comparable to that of OEC injections. Our data indicate that sulfatase-mediated modification of the extracellular matrix can influence glial interactions with astrocytes, and that SCs engineered to express sulfatase may be more OEC-like in character. This approach may be beneficial for cell transplant-mediated spinal cord repair. GLIA 2016 GLIA 2017;65:19-33.

Expression of Sulf1 and Sulf2 in cartilage, bone and endochondral fracture healing

SULF1/SULF2 enzymes regulate cell signalling that impacts the growth and differentiation of many tissues. To determine their possible role in cartilage and bone growth or repair, their expression was examined during development and bone fracture healing using RT-PCR and immunochemical analyses. Examination of epiphyseal growth plates revealed differential, inverse patterns of SULF1 and SULF2 expressions, with the former enriched in quiescent and the latter in hypertrophic chondrocyte zones. Markedly higher levels of both SULFs, however, were expressed in osteoblasts actively forming bone when compared with proliferating pre-osteoblasts in the periosteum or the entombed osteocytes which express the lowest levels. The increased expression of Sulf1 and Sulf2 in differentiating osteoblasts was further confirmed by RT-PCR analysis of mRNA levels in rat calvarial osteoblast cultures. SULF1 and SULF2 were expressed in most foetal articular chondrocytes but down-regulated in a larger subset of cells in the post-natal articular cartilage. Unlike adult articular chondrocytes, SULF1/SULF2 expression varied markedly in post-natal hypertrophic chondrocytes in the growth plate, with very high SULF2 expression compared with SULF1 apparent during neonatal growth in both primary and secondary centres of ossification. Similarly, hypertrophic chondrocytes expressed greatly higher levels of SULF2 but not SULF1 during bone fracture healing. SULF2 expression unlike SULF1 also spread to the calcifying matrix around the hypertrophic chondrocytes indicating its possible ligand inhibiting role through HSPG desulphation. Higher levels of SULF2 in both developing and healing bone closely correlated with parallel increases in hedgehog signalling analysed by ptc1 receptor expression.

Sulf1 and Sulf2 Differentially Modulate Heparan Sulfate Proteoglycan Sulfation during Postnatal Cerebellum Development: Evidence for Neuroprotective and Neurite Outgrowth Promoting Functions

Introduction

Sulf1 and Sulf2 are cell surface sulfatases, which remove specific 6-O-sulfate groups from heparan sulfate (HS) proteoglycans, resulting in modulation of various HS-dependent signaling pathways. Both Sulf1 and Sulf2 knockout mice show impairments in brain development and neurite outgrowth deficits in neurons.

Methodology and Main Findings

To analyze the molecular mechanisms behind these impairments we focused on the postnatal cerebellum, whose development is mainly characterized by proliferation, migration, and neurite outgrowth processes of precursor neurons. Primary cerebellar granule cells isolated from Sulf1 or Sulf2 deficient newborns are characterized by a reduction in neurite length and cell survival. Furthermore, Sulf1 deficiency leads to a reduced migration capacity. The observed impairments in cell survival and neurite outgrowth could be correlated to Sulf-specific interference with signaling pathways, as shown for FGF2, GDNF and NGF. In contrast, signaling of Shh, which determines the laminar organization of the cerebellar cortex, was not influenced in either Sulf1 or Sulf2 knockouts. Biochemical analysis of cerebellar HS demonstrated, for the first time in vivo, Sulf-specific changes of 6-O-, 2-O- and N-sulfation in the knockouts. Changes of a particular HS epitope were found on the surface of Sulf2-deficient cerebellar neurons. This epitope showed a restricted localization to the inner half of the external granular layer of the postnatal cerebellum, where precursor cells undergo final maturation to form synaptic contacts.

Conclusion

Sulfs introduce dynamic changes in HS proteoglycan sulfation patterns of the postnatal cerebellum, thereby orchestrating fundamental mechanisms underlying brain development.

Sonic hedgehog processing and release are regulated by glypican heparan sulfate proteoglycans

All Hedgehog morphogens are released from producing cells, despite being synthesized as N- and C-terminally lipidated molecules, a modification that firmly tethers them to the cell membrane. We have previously shown that proteolytic removal of both lipidated peptides, called shedding, releases bioactive Sonic hedgehog (Shh) morphogens from the surface of transfected Bosc23 cells. Using in vivo knockdown together with in vitro cell culture studies, we now show that glypican heparan sulfate proteoglycans regulate this process, through their heparan sulfate chains, in a cell autonomous manner. Heparan sulfate specifically modifies Shh processing at the cell surface, and purified glycosaminoglycans enhance the proteolytic removal of N- and C-terminal Shh peptides under cell-free conditions. The most likely explanation for these observations is direct Shh processing in the extracellular compartment, suggesting that heparan sulfate acts as a scaffold or activator for Shh ligands and the factors required for their turnover. We also show that purified heparan sulfate isolated from specific cell types and tissues mediates the release of bioactive Shh from pancreatic cancer cells, revealing a previously unknown regulatory role for these versatile molecules in a pathological context.

Distinct patterns of heparan sulphate in pancreatic islets suggest novel roles in paracrine islet regulation

Heparan sulphate proteoglycans (HSPGs) exist in pancreatic beta cells, and HS seems to modulate important interactions in the islet microenvironment. However, the intra-islet structures of HS in health or altered glucose homeostasis are currently unknown. Here we show that distinct spatial distribution of HS motifs is present in islets in the adult, that intra-islet HS motifs are mostly conserved between rodents and humans, and that HS is abundant in glucagon producing islet alpha cells. In beta cells HS is characterised by 2-O, 6-O and N-sulphated moieties, whereas HS in alpha cells is N-acetylated, N-, and 2-O sulphated and low in 6-O groups. Differential expression of three HS modifying genes in alpha and beta cells was observed and may account for the different HS patterns. Furthermore, we found that FGF1 and FGF2 were present in alpha cells, whereas functional FGFRs exist in beta cells, but not in the alpha cell line aTC1-6, or in primary alpha cells in islets. FGF1 induced signalling was dependent on 2-O, and 6-O HS sulphation in beta cells, and HS desulphation reduced beta cell proliferation and potentiated oxidant induced apoptosis. In leptin resistant animals and in islets from streptozotocin treated rats there was a reduction in alpha cell HS expression. These data demonstrate the distinct HS expression patterns in alpha and beta islet cells and propose a novel role for alpha cells as a source of paracrine FGF ligands to neighbouring beta cells with specific cell-associated HS domains mediating the activation and diffusion of paracrine ligands.

Use of flow cytometry for characterization and fractionation of cell populations based on their expression of heparan sulfate epitopes

The ability to characterize alterations in heparan sulfate (HS) structure during development or as a result of loss or mutation of one or more components of the HS biosynthetic pathway is essential for broad understanding of the effects these changes may have on cell/tissue function. The use of anti-HS antibodies provides an opportunity to study HS chain composition in situ, with a multitude of different antibodies having been generated that recognize subtle differences in HS patterning, with the number and positioning of sulfate groups influencing antibody binding affinity. Flow cytometry is a valuable technique to enable the rapid characterization of the changes in HS-specific antibody binding in situ, allowing multiple cell types to be directly compared. Additionally fluorescent-activated cell sorting (FACS) allows fractionation of cells based on their HS-epitope expression.

The Sulfs: expression, purification, and substrate specificity

Sulf-1 and Sulf-2 are endo-acting extracellular sulfatases. The Sulfs liberate 6-O sulfate groups, mainly from N, 6-O, and 2-O trisulfated disaccharides of heparan sulfate (HS)/heparin chains. The Sulfs have been shown to modulate the interaction of a number of protein ligands including growth factors and morphogens with HS/heparin and thus regulate the signaling of these ligands. They also play important roles in development and are dysregulated in many cancers. The establishment of the expression of the Sulfs and methods of assaying them has been desirable to investigate these enzymes. In this chapter, methods to express and purify recombinant Sulfs and to analyze HS structures in an extracellular fraction of HSulf-transfected HEK293 cells are described. The application of these enzymes for ex vivo degradation of an anti-HS epitope accumulated in the brain of a neurodegenerative disease model mouse is also described.

The heparan sulfate editing enzyme Sulf1 plays a novel role in zebrafish VegfA mediated arterial venous identity

Arterial and venous specification is critical for establishing and maintaining a functioning vascular system, and defects in key arteriovenous signaling pathways including VEGF (vascular endothelial growth factor) lead to congenital arteriopathies. The activities of VEGF, are in part controlled by heparan sulfate (HS) proteoglycans, significant components of the endothelial glycocalyx. The level of 6-O sulfation on HS polysaccharide chains, that mediate the interaction between HS and VEGFA, is edited at the cell surface by the enzyme SULF1. We investigated the role of sulf1 in vascular development. In zebrafish sulf1 is expressed in the head and tail vasculature, corresponding spatially and temporally with vascular development. Targeted knockdown of sulf1 by antisense morpholinos resulted in severe vascular patterning and maturation defects. 93 % of sulf1 morphants show dysmorphogenesis in arterial development leading to occlusion of the distal aorta and lack of axial and cranial circulation. Co-injection of vegfa165 mRNA rescued circulatory defects. While the genes affecting haematopoiesis are unchanged, expression of several arterial markers downstream of VegfA signalling such as notch and ephrinB2 are severely reduced in the dorsal aorta, with a concomitant increase in expression of the venous markers flt4 in the dorsal aorta of the morphants. Furthermore, in vitro, lack of SULF1 expression downregulates VEGFA-mediated arterial marker expression, confirming that Sulf1 mediates arterial specification by regulating VegfA165 activity. This study provides the first in vivo evidence for the integral role of the endothelial glycocalyx in specifying arterial-venous identity, vascular patterning and arterial integrity, and will help to better understand congenital arteriopathies.

Oligosaccharide substrate preferences of human extracellular sulfatase Sulf2 using liquid chromatography-mass spectrometry based glycomics approaches

Sulfs are extracellular endosulfatases that selectively remove the 6-O-sulfate groups from cell surface heparan sulfate (HS) chain. By altering the sulfation at these particular sites, Sulfs function to remodel HS chains. As a result of the remodeling activity, HSulf2 regulates a multitude of cell-signaling events that depend on interactions between proteins and HS. Previous efforts to characterize the substrate specificity of human Sulfs (HSulfs) focused on the analysis of HS disaccharides and synthetic repeating units. In this study, we characterized the substrate preferences of human HSulf2 using HS oligosaccharides with various lengths and sulfation degrees from several naturally occurring HS sources by applying liquid chromatography mass spectrometry based glycomics methods. The results showed that HSulf2 preferentially digests highly sulfated HS oligosaccharides with zero acetyl groups and this preference is length dependent. In terms of length of oligosaccharides, HSulf2 digestion induced more sulfation decrease on DP6 (DP: degree of polymerization) compared to DP2, DP4 and DP8. In addition, the HSulf2 preferentially digests the oligosaccharide domain located at the non-reducing end (NRE) of the HS and heparin chain. In addition, the HSulf2 digestion products were altered only for specific isomers. HSulf2 treated NRE oligosaccharides also showed greater decrease in cell proliferation than those from internal domains of the HS chain. After further chromatographic separation, we identified the three most preferred unsaturated hexasaccharide for HSulf2.

Human genetic disorders and knockout mice deficient in glycosaminoglycan

Glycosaminoglycans (GAGs) are constructed through the stepwise addition of respective monosaccharides by various glycosyltransferases and maturated by epimerases and sulfotransferases. The structural diversity of GAG polysaccharides, including their sulfation patterns and sequential arrangements, is essential for a wide range of biological activities such as cell signaling, cell proliferation, tissue morphogenesis, and interactions with various growth factors. Studies using knockout mice of enzymes responsible for the biosynthesis of the GAG side chains of proteoglycans have revealed their physiological functions. Furthermore, mutations in the human genes encoding glycosyltransferases, sulfotransferases, and related enzymes responsible for the biosynthesis of GAGs cause a number of genetic disorders including chondrodysplasia, spondyloepiphyseal dysplasia, and Ehlers-Danlos syndromes. This review focused on the increasing number of glycobiological studies on knockout mice and genetic diseases caused by disturbances in the biosynthetic enzymes for GAGs.

Role of 6-O-sulfated heparan sulfate in chronic renal fibrosis

Heparan sulfate (HS) plays a crucial role in the fibrosis associated with chronic allograft dysfunction by binding and presenting cytokines and growth factors to their receptors. These interactions critically depend on the distribution of 6-O-sulfated glucosamine residues, which is generated by glucosaminyl-6-O-sulfotransferases (HS6STs) and selectively removed by cell surface HS-6-O-endosulfatases (SULFs). Using human renal allografts we found increased expression of 6-O-sulfated HS domains in tubular epithelial cells during chronic rejection as compared with the controls. Stimulation of renal epithelial cells with TGF-β induced SULF2 expression. To examine the role of 6-O-sulfated HS in the development of fibrosis, we generated stable HS6ST1 and SULF2 overexpressing renal epithelial cells. Compared with mock transfectants, the HS6ST1 transfectants showed significantly increased binding of FGF2 (p = 0.0086) and pERK activation. HS6ST1 transfectants displayed a relative increase in mono-6-O-sulfated disaccharides accompanied by a decrease in iduronic acid 2-O-sulfated disaccharide structures. In contrast, SULF2 transfectants showed significantly reduced FGF2 binding and phosphorylation of ERK. Structural analysis of HS showed about 40% down-regulation in 6-O-sulfation with a parallel increase in iduronic acid mono-2-O-sulfated disaccharides. To assess the relevance of these data in vivo we established a murine model of fibrosis (unilateral ureteric obstruction (UUO)). HS-specific phage display antibodies (HS3A8 and RB4EA12) showed significant increase in 6-O-sulfation in fibrotic kidney compared with the control. These results suggest an important role of 6-O-sulfation in the pathogenesis of fibrosis associated with chronic rejection.

Using embryonic stem cells to understand how glycosaminoglycans regulate differentiation

Differentiation and subsequent specialization of every cell within an organism is an intricate interwoven process. A complex network of signalling pathways eventually leads to the specification of a multitude of different cell types able to function co-operatively. HS (heparan sulfate) is a highly sulfated linear polysaccharide that resides at the pericellular cell–matrix interface where it dictates the binding and activity of a large number of proteins, including growth factors and morphogens such as members of the FGF (fibroblast growth factor) and BMP (bone morphogenetic protein) families. Embryonic stem cells derived from mice with mutations in components of the HS biosynthetic pathway provide an opportunity to dissect the contribution of HS to signalling pathways critical for regulating stem cell maintenance and differentiation. In addition to improving our understanding of signalling mechanisms, this knowledge enables the selection of exogenous HS saccharides to improve the efficiency and selectivity of directed differentiation protocols, offering a cost-effective alternative to high concentrations of expensive growth factors to drive differentiation towards a particular therapeutically relevant cell type.

Post-Synthetic Regulation of HS Structure: The Yin and Yang of the Sulfs in Cancer

Heparan sulfate (HS) is a complex polysaccharide that takes part in most major cellular processes, through its ability to bind and modulate a very large array of proteins. These interactions involve saccharide domains of specific sulfation pattern (S-domains), the assembly of which is tightly orchestrated by a highly regulated biosynthesis machinery. Another level of structural control does also take place at the cell surface, where degrading enzymes further modify HS post-synthetically. Amongst them are the Sulfs, a family of extracellular sulfatases (two isoforms in human) that catalyze the specific 6-O-desulfation of HS. By targeting HS functional sulfated domains, Sulfs dramatically alter its ligand binding properties, thereby modulating a broad range of signaling pathways. Consequently, Sulfs play major roles during development, as well as in tissue homeostasis and repair. Sulfs have also been associated with many pathologies including cancer, but despite increasing interest, the role of Sulfs in tumor development still remains unclear. Studies have been hindered by a poor understanding of the Sulf enzymatic activities and conflicting data have shown either anti-oncogenic or tumor-promoting effects of these enzymes, depending on the tumor models analyzed. These opposite effects clearly illustrate the fine tuning of HS functions by the Sulfs, and the need to clarify the mechanisms involved. In this review, we will detail the present knowledge on the structural and functional properties of the Sulfs, with a special focus on their implication during tumor progression. Finally, we will discuss attempts and perspectives of using the Sulfs as a biomarker of cancer prognosis and diagnostic and as a target for anti-cancer therapies.

The role of syndecan-1 in cellular signaling and its effects on heparan sulfate biosynthesis in mesenchymal tumors

Proteoglycans (PGs) and in particular the syndecans are involved in the differentiation process across the epithelial-mesenchymal axis, principally through their ability to bind growth factors and modulate their downstream signaling. Malignant tumors have individual proteoglycan profiles, which are closely associated with their differentiation and biological behavior, mesenchymal tumors showing a different profile from that of epithelial tumors. Syndecan-1 is the main syndecan of epithelial malignancies, whereas in sarcomas its expression level is generally low, in accordance with their mesenchymal phenotype and highly malignant behavior. This proteoglycan is often overexpressed in adenocarcinoma cells, whereas mesothelioma and fibrosarcoma cells express syndecan-2 and syndecan-4 more abundantly. Increased expression of syndecan-1 in mesenchymal tumors changes the tumor cell morphology to an epithelioid direction whereas downregulation results in a change in shape from polygonal to spindle-like morphology. Although syndecan-1 plays major roles on the cell-surface, there are also intracellular functions, which are not very well studied. On the functional level, syndecan-1 affects mesenchymal tumor cell proliferation, adhesion, migration and motility, and the effect varies with the different domains of the core protein. Syndecan-1 may exert stimulatory or inhibitory effects, depending on the concentration of various mitogens, enzymes, and signaling molecules, the ratio between the shed and membrane-associated syndecan-1 and histological grade of the tumour. Growth factor signaling seems to be delicately controlled by regulatory loops involving the syndecan expression levels and their sulfation patterns. Overexpression of syndecan-1 modulates the biosynthesis and sulfation of heparan sulfate and it also affects the expression of other PGs. On transcriptomic level, syndecan-1 modulation results in profound effects on genes involved in regulation of cell growth.

Arylsulfatase K, a novel lysosomal sulfatase

The human sulfatase family has 17 members, 13 of which have been characterized biochemically. These enzymes specifically hydrolyze sulfate esters in glycosaminoglycans, sulfolipids, or steroid sulfates, thereby playing key roles in cellular degradation, cell signaling, and hormone regulation. The loss of sulfatase activity has been linked to severe pathophysiological conditions such as lysosomal storage disorders, developmental abnormalities, or cancer. A novel member of this family, arylsulfatase K (ARSK), was identified bioinformatically through its conserved sulfatase signature sequence directing posttranslational generation of the catalytic formylglycine residue in sulfatases. However, overall sequence identity of ARSK with other human sulfatases is low (18-22%). Here we demonstrate that ARSK indeed shows desulfation activity toward arylsulfate pseudosubstrates. When expressed in human cells, ARSK was detected as a 68-kDa glycoprotein carrying at least four N-glycans of both the complex and high-mannose type. Purified ARSK turned over p-nitrocatechol and p-nitrophenyl sulfate. This activity was dependent on cysteine 80, which was verified to undergo conversion to formylglycine. Kinetic parameters were similar to those of several lysosomal sulfatases involved in degradation of sulfated glycosaminoglycans. An acidic pH optimum (~4.6) and colocalization with LAMP1 verified lysosomal functioning of ARSK. Further, it carries mannose 6-phosphate, indicating lysosomal sorting via mannose 6-phosphate receptors. ARSK mRNA expression was found in all tissues tested, suggesting a ubiquitous physiological substrate and a so far non-classified lysosomal storage disorder in the case of ARSK deficiency, as shown before for all other lysosomal sulfatases.

The SULFs, extracellular sulfatases for heparan sulfate, promote the migration of corneal epithelial cells during wound repair

Corneal epithelial wound repair involves the migration of epithelial cells to cover the defect followed by the proliferation of the cells to restore thickness. Heparan sulfate proteoglycans (HSPGs) are ubiquitous extracellular molecules that bind to a plethora of growth factors, cytokines, and morphogens and thereby regulate their signaling functions. Ligand binding by HS chains depends on the pattern of four sulfation modifications, one of which is 6-O-sulfation of glucosamine (6OS). SULF1 and SULF2 are highly homologous, extracellular endosulfatases, which post-synthetically edit the sulfation status of HS by removing 6OS from intact chains. The SULFs thereby modulate multiple signaling pathways including the augmentation of Wnt/ß-catenin signaling. We found that wounding of mouse corneal epithelium stimulated SULF1 expression in superficial epithelial cells proximal to the wound edge. Sulf1^−/−, but not Sulf2^−/−, mice, exhibited a marked delay in healing. Furthermore, corneal epithelial cells derived from Sulf1^−/− mice exhibited a reduced rate of migration in repair of a scratched monolayer compared to wild-type cells. In contrast, human primary corneal epithelial cells expressed SULF2, as did a human corneal epithelial cell line (THCE). Knockdown of SULF2 in THCE cells also slowed migration, which was restored by overexpression of either mouse SULF2 or human SULF1. The interchangeability of the two SULFs establishes their capacity for functional redundancy. Knockdown of SULF2 decreased Wnt/ß-catenin signaling in THCE cells. Extracellular antagonists of Wnt signaling reduced migration of THCE cells. However in SULF2- knockdown cells, these antagonists exerted no further effects on migration, consistent with the SULF functioning as an upstream regulator of Wnt signaling. Further understanding of the mechanistic action of the SULFs in promoting corneal repair may lead to new therapeutic approaches for the treatment of corneal injuries.

Activation of the transcription factor GLI1 by WNT signaling underlies the role of SULFATASE 2 as a regulator of tissue regeneration

Tissue regeneration requires the activation of a set of specific growth signaling pathways. The identity of these cascades and their biological roles are known; however, the molecular mechanisms regulating the interplay between these pathways remain poorly understood. Here, we define a new role for SULFATASE 2 (SULF2) in regulating tissue regeneration and define the WNT-GLI1 axis as a novel downstream effector for this sulfatase in a liver model of tissue regeneration. SULF2 is a heparan sulfate 6-O-endosulfatase, which releases growth factors from extracellular storage sites turning active multiple signaling pathways. We demonstrate that SULF2-KO mice display delayed regeneration after partial hepatectomy (PH). Mechanistic analysis of the SULF2-KO phenotype showed a decrease in WNT signaling pathway activity in vivo. In isolated hepatocytes, SULF2 deficiency blocked WNT-induced β-CATENIN nuclear translocation, TCF activation, and proliferation. Furthermore, we identified the transcription factor GLI1 as a novel target of the SULF2-WNT cascade. WNT induces GLI1 expression in a SULF2- and β-CATENIN-dependent manner. GLI1-KO mice phenocopied the SULF2-KO, showing delayed regeneration and decreased hepatocyte proliferation. Moreover, we identified CYCLIN D1, a key mediator of cell growth during tissue regeneration, as a GLI1 transcriptional target. GLI1 binds to the cyclin d1 promoter and regulates its activity and expression. Finally, restoring GLI1 expression in the liver of SULF2-KO mice after PH rescues CYCLIN D1 expression and hepatocyte proliferation to wild-type levels. Thus, together these findings define a novel pathway in which SULF2 regulates tissue regeneration in part via the activation of a novel WNT-GLI1-CYCLIN D1 pathway.

Sulf1 modulates BMP signaling and is required for somite morphogenesis and development of the horizontal myoseptum

Heparan sulfate proteoglycans (HSPGs) are glycosylated extracellular or membrane-associated proteins. Their unbranched heparan sulfate (HS) disaccharide chains interact with many growth factors and receptors, modifying their activity or diffusion. The pattern of HS sulfation can be altered by the enzymes Sulf1 and Sulf2, secreted extracellular 6-O endosulfatases, which remove specific sulfate groups from HS. Modification by Sulf enzymes changes the binding affinity of HS for protein such as ligands and receptors, affecting growth factor gradients and activities. The precise expression of these sulfatases are thought to be necessary for normal development. We have examined the role of the sulf1 gene in trunk development of zebrafish embryos. sulf1 is expressed in the developing trunk musculature and as well as in midline structures such as the notochord, floorplate and hypochord. Knockdown of sulf1 with antisense morpholinos results in poor differentiation of the somitic trunk muscle, loss of the horizontal myoseptum, lack of pigmentation along the mediolateral stripe, and improper migration of the lateral line primordium. sulf1 knockdown results in a decrease in the number of Pax7-expressing dermomyotome cells, particularly along the midline where the horizontal myoseptum develops. It also leads to decreased sdf1/cxcl12 expression along the mediolateral trunk musculature. Both the Pax7 and cxcl12 expression can be restored by inhibition pharmacological inhibition of BMP signaling, which also restores formation of the myoseptum, fast muscle development, and pigmentation patterning. Lateral line migration and neuromast deposition depend on sdf1/cxcl12 and FGF signaling respectively, both of which are disrupted in sulf1 morphants. Pharmacological activation of FGF signaling can rescue the spacing of neuromast deposition in these fish. Together this data indicate that sulf1 plays a crucial role in modulating both BMP and FGF signaling along the developing myoseptum to coordinate the morphogenesis of trunk musculature, associated pigment cells, and lateral line neuromasts.

Endosulfatases SULF1 and SULF2 limit Chlamydia muridarum infection

The first step in attachment of Chlamydia to host cells is thought to involve reversible binding to host heparan sulfate proteoglycans (HSPGs), polymers of variably sulfated repeating disaccharide units coupled to diverse protein backbones. However, the key determinants of HSPG structure that are involved in Chlamydia binding are incompletely defined. A previous genome-wide Drosophila RNAi screen suggested that the level of HSPG 6-O sulfation rather than the identity of the proteoglycan backbone maybe a critical determinant for binding. Here, we tested in mammalian cells whether SULF1 or SULF2, human endosulfatases, which remove 6-O sulfates from HSPGs, modulate Chlamydia infection. Ectopic expression of SULF1 or SULF2 in HeLa cells, which decreases cell surface HSPG sulfation, diminished C. muridarum binding and decreased vacuole formation. ShRNA depletion of endogenous SULF2 in a cell line that primarily expresses SULF2 augmented binding and increased vacuole formation. C. muridarum infection of diverse cell lines resulted indownregulation of SULF2 mRNA. In a murine model of acute pneumonia, mice genetically deficient in both endosulfatases or in SULF2 alone demonstrated increased susceptibility to C. muridarum lung infection. Collectively, these studies demonstrate that the level of HSPG 6-O sulfation is a critical determinant of C. muridarum infection in vivo and that 6-O endosulfatases are previously unappreciated modulators of microbial pathogenesis.

HSulf sulfatases catalyze processive and oriented 6-O-desulfation of heparan sulfate that differentially regulates fibroblast growth factor activity

Sulfs are extracellular sulfatases that have emerged recently as critical regulators of heparan sulfate (HS) activities through their ability to catalyze specific 6-O-desulfation of the polysaccharide. Consequently, Sulfs have been involved in many physiological and pathological processes, and notably for Sulf-2, in the development of cancers with poor prognosis. Despite growing interest, little is known about the structure and activity of these enzymes and the way they induce dynamic remodeling of HS 6-O-sulfation status. Here, we have combined an array of analytical approaches, including mass spectrometry, NMR, HS oligosaccharide sequencing, and FACS, to dissect HSulf-2 sulfatase activity, either on a purified octasaccharide used as a mimic of HS functional domains, or on intact cell-surface HS chains. In parallel, we have studied the functional consequences of HSulf-2 activity on fibroblast growth factor (FGF)-induced mitogenesis and found that the enzyme could differentially regulate FGF1 and FGF2 activities. Notably, these data supported the existence of precise 6-O-sulfation patterns for FGF activation and provided new insights into the saccharide structures involved. Altogether, our data bring to light an original processive enzymatic mechanism, by which HSulfs catalyze oriented alteration of HS 6-O-desulfation patterns and direct fine and differential regulation of HS functions.

Sulfatase 1 promotes the motor neuron-to-oligodendrocyte fate switch by activating Shh signaling in Olig2 progenitors of the embryonic ventral spinal cord

In the developing ventral spinal cord, motor neurons (MNs) and oligodendrocyte precursor cells (OPCs) are sequentially generated from a common pool of neural progenitors included in the so-called pMN domain characterized by Olig2 expression. Here, we establish that the secreted Sulfatase 1 (Sulf1) is a major component of the mechanism that causes these progenitors to stop producing MNs and change their fate to generate OPCs. We show that specification of OPCs is severely affected in sulf1-deficient mouse embryos. This defect does not rely on abnormal patterning of the spinal cord or failure in maintenance of pMN progenitors at the onset of OPC specification. Instead, the efficiency of OPC induction is reduced, only few Olig2 progenitors are recruited to generate OPCs, meanwhile they continue to produce MNs beyond the normal timing of the neuroglial switch. Using the chicken embryo, we show that Sulf1 activity is required precisely at the stage of the MN-to-OPC fate switch. Finally, we bring arguments supporting the view that Sulf1 controls the level of Sonic Hedgehog (Shh) signaling activity, behaving as an enhancer rather than an obligatory component in the Shh pathway. Our study provides additional insights into the temporal control of Olig2 progenitor cell fate change by the identification of Sulf1 as an extracellular timing signal in the ventral spinal cord.

Overexpression of Sulf2 in idiopathic pulmonary fibrosis

Previously, we have shown that heparan sulfate (HS) 6-O-endosulfatase 1 (Sulf1) is a transforming growth factor-β1 (TGF-β1)-responsive gene in normal human lung fibroblasts and functions as a negative feedback regulator of TGF-β1 and that TGF-β1 induces the expression of Sulf1 as well as that of the closely related Sulf2 in a murine model of pulmonary fibrosis. In this study, we focused on the role of Sulf2 in modulating TGF-β1 function and the development of pulmonary fibrosis. We found that Sulf2 mRNA was overexpressed in lung samples from human patients with idiopathic pulmonary fibrosis (IPF), and Sulf2 protein was specifically localized to the hyperplastic type II alveolar epithelial cells (AECs). In vitro, TGF-β1 induced the expression of Sulf2 with accompanied HS 6-O-desulfation in A549 cells, adenocarcinoma cells derived from the type II alveolar epithelium. Using small interference RNA to block Sulf2 expression, we observed a biphasic TGF-β1 response with early enhanced Smad activation, but eventually reduced TGF-β1 target gene expression in Sulf2 knockdown A549 cells compared with the control cells. To study the role of Sulf2 in normal type II AECs, we isolated primary type II cells from wild-type and Sulf2 knockout mice. We observed enhanced Smad activation as well as enhanced TGF-β1 target gene expression in Sulf2 knockout type II AECs compared with wild-type type II AECs. In conclusion, Sulf2 is overexpressed in IPF and may play a role in regulating TGF-β1 signaling in type II AECs.

Immobilization of heparan sulfate on electrospun meshes to support embryonic stem cell culture and differentiation

As our understanding of what guides the behavior of multi- and pluripotent stem cells deepens, so too does our ability to utilize certain cues to manipulate their behavior and maximize their therapeutic potential. Engineered, biologically functionalized materials have the capacity to influence stem cell behavior through a powerful combination of biological, mechanical, and topographical cues. Here, we present the development of a novel electrospun scaffold, functionalized with glycosaminoglycans (GAGs) ionically immobilized onto the fiber surface. Bound GAGs retained the ability to interact with GAG-binding molecules and, crucially, presented GAG sulfation motifs fundamental to mediating stem cell behavior. Bound GAG proved to be biologically active, rescuing the neural differentiation capacity of heparan sulfate-deficient mouse embryonic stem cells and functioning in concert with FGF4 to facilitate the formation of extensive neural processes across the scaffold surface. The combination of GAGs with electrospun scaffolds creates a biomaterial with potent applicability for the propagation and effective differentiation of pluripotent stem cells.

Glycomics approaches for the bioassay and structural analysis of heparin/heparan sulphates

The glycosaminoglycan heparan sulphate (HS) has a heterogeneous structure; evidence shows that specific structures may be responsible for specific functions in biological processes such as blood coagulation and regulation of growth factor signalling. This review summarises the different experimental tools and methods developed to provide more rapid methods for studying the structure and functions of HS. Rapid and sensitive methods for the facile purification of HS, from tissue and cell sources are reviewed. Data sets for the structural analysis are often complex and include multiple sample sets, therefore different software and tools have been developed for the analysis of different HS data sets. These can be readily applied to chromatographic data sets for the simplification of data (e.g., charge separation using strong anion exchange chromatography and from size separation using gel filtration techniques. Finally, following the sequencing of the human genome, research has rapidly advanced with the introduction of high throughput technologies to carry out simultaneous analyses of many samples. Microarrays to study macromolecular interactions (including glycan arrays) have paved the way for bioassay technologies which utilize cell arrays to study the effects of multiple macromolecules on cells. Glycan bioassay technologies are described in which immobilisation techniques for saccharides are exploited to develop a platform to probe cell responses such as signalling pathway activation. This review aims at reviewing available techniques and tools for the purification, analysis and bioassay of HS saccharides in biological systems using "glycomics" approaches.

Heparan sulfate 6-O-endosulfatases (Sulfs) coordinate the Wnt signaling pathways to regulate myoblast fusion during skeletal muscle regeneration

Skeletal muscle regeneration is mediated by satellite cells (SCs). Upon injury, SCs undergo self-renewal, proliferation, and differentiation into myoblasts followed by myoblast fusion to form new myofibers. We previously showed that the heparan sulfate (HS) 6-O-endosulfatases (Sulf1 and -2) repress FGF signaling to induce SC differentiation during muscle regeneration. Here, we identify a novel role of Sulfs in myoblast fusion using a skeletal muscle-specific Sulf double null (Sulf(SK)-DN) mouse. Regenerating Sulf(SK)-DN muscles exhibit reduced canonical Wnt signaling and elevated non-canonical Wnt signaling. In addition, we show that Sulfs are required to repress non-canonical Wnt signaling to promote myoblast fusion. Notably, skeletal muscle-relevant non-canonical Wnt ligands lack HS binding capacity, suggesting that Sulfs indirectly repress this pathway. Mechanistically, we show that Sulfs reduce the canonical Wnt-HS binding and regulate colocalization of the co-receptor LRP5 with caveolin3. Therefore, Sulfs may increase the bioavailability of canonical Wnts for Frizzled receptor and LRP5/6 interaction in lipid raft, which may in turn antagonize non-canonical Wnt signaling. Furthermore, changes in subcellular distribution of active focal adhesion kinase (FAK) are associated with the fusion defect of Sulf-deficient myoblasts and upon non-canonical Wnt treatment. Together, our findings uncover a critical role of Sulfs in myoblast fusion by promoting antagonizing canonical Wnt signaling activities against the noncanonical Wnt pathway during skeletal muscle regeneration.

New negative feedback regulators of Egfr signaling in Drosophila

The highly conserved epidermal growth factor receptor (Egfr) pathway is required in all animals for normal development and homeostasis; consequently, aberrant Egfr signaling is implicated in a number of diseases. Genetic analysis of Drosophila melanogaster Egfr has contributed significantly to understanding this conserved pathway and led to the discovery of new components and targets. Here we used microarray analysis of third instar wing discs, in which Egfr signaling was perturbed, to identify new Egfr-responsive genes. Upregulated transcripts included five known targets, suggesting the approach was valid. We investigated the function of 29 previously uncharacterized genes, which had pronounced responses. The Egfr pathway is important for wing-vein patterning and using reverse genetic analysis we identified five genes that showed venation defects. Three of these genes are expressed in vein primordia and all showed transcriptional changes in response to altered Egfr activity consistent with being targets of the pathway. Genetic interactions with Egfr further linked two of the genes, Sulfated (Sulf1), an endosulfatase gene, and CG4096, an A Disintegrin And Metalloproteinase with ThromboSpondin motifs (ADAMTS) gene, to the pathway. Sulf1 showed a strong genetic interaction with the neuregulin-like ligand vein (vn) and may influence binding of Vn to heparan-sulfated proteoglycans (HSPGs). How Drosophila Egfr activity is modulated by CG4096 is unknown, but interestingly vertebrate EGF ligands are regulated by a related ADAMTS protein. We suggest Sulf1 and CG4096 are negative feedback regulators of Egfr signaling that function in the extracellular space to influence ligand activity.