The significant role of glycosaminoglycans in tooth development

This review delves into the roles of glycosaminoglycans (GAGs), integral components of proteoglycans, in tooth development. Proteoglycans consist of a core protein linked to GAG chains, comprised of repeating disaccharide units. GAGs are classified into several types, such as hyaluronic acid, heparan sulfate, chondroitin sulfate, dermatan sulfate, and keratan sulfate. Functioning as critical macromolecular components within the dental basement membrane, these GAGs facilitate cell adhesion and aggregation, and play key roles in regulating cell proliferation and differentiation, thereby significantly influencing tooth morphogenesis. Notably, our recent research has identified the hyaluronan-degrading enzyme Transmembrane protein 2 (Tmem2) and we have conducted functional analyses using mouse models. These studies have unveiled the essential role of Tmem2-mediated hyaluronan degradation and its involvement in hyaluronan-mediated cell adhesion during tooth formation. This review provides a comprehensive summary of the current understanding of GAG functions in tooth development, integrating insights from recent research, and discusses future directions in this field.

Identification of kinesin family member (KIF22) homozygous variants in spondyloepimetaphyseal dysplasia with joint laxity, lepdodactylic type and demonstration of proteoglycan biosynthesis impairment

Heterozygous variants in KIF22, encoding a kinesin-like protein, are responsible for spondyloepimetaphyseal dysplasia with joint laxity, leptodactilic type (lepto-SEMDJL), characterized by short stature, flat face, generalized joint laxity with multiple dislocations, and progressive scoliosis and limb deformity. By targeted gene sequencing analysis, we identified a homozygous KIF22 variant (NM_007317.3: c.146G>A, p.Arg49Gln) in 3 patients from 3 unrelated families. The clinical features appeared similar to those of patients carrying heterozygous KIF22 variant (c.443C>T or c.446G>A), although the spinal involvement appeared later and was less severe in patients with a recessive variant. Relatives harboring the c.146G>A variant at the heterozygous state were asymptomatic. The homozygous KIF22 variant c.146G>A affected a conserved residue located in the active site and potentially destabilized ATP binding. RT-PCR and western blot analyses demonstrated that both dominant and recessive KIF22 variants do not affect KIF22 mRNA and protein expression in patient fibroblasts compared to controls. As lepto-SEMDJL presents phenotypic overlap with chondrodysplasias with multiple dislocations (CMD), related to defective proteoglycan biosynthesis, we analyzed proteoglycan synthesis in patient skin fibroblasts. Compared to controls, DMMB assay showed a significant decrease of total sulfated proteoglycan content in culture medium but not in the cell layer, and immunofluorescence demonstrated a strong reduction of staining for chondroitin sulfates but not for heparan sulfates, similarly in patients with recessive or dominant KIF22 variants. These data identify a new recessive KIF22 pathogenic variant and link for the first time KIF22 pathogenic variants to altered proteoglycan biosynthesis and place the lepto-SEMDJL in the CMD spectrum.

Endothelial Glycocalyx Degradation Patterns in Sepsis-Associated Pediatric Acute Respiratory Distress Syndrome: A Single Center Retrospective Observational Study

BACKGROUND

Sepsis-associated destruction of the pulmonary microvascular endothelial glycocalyx (EGCX) creates a vulnerable endothelial surface, contributing to the development of acute respiratory distress syndrome (ARDS). Constituents of the EGCX shed into circulation, glycosaminoglycans and proteoglycans, may serve as biomarkers of endothelial dysfunction. We sought to define the patterns of plasma EGCX degradation products in children with sepsis-associated pediatric ARDS (PARDS), and test their association with clinical outcomes.

METHODS

We retrospectively analyzed a prospective cohort (2018-2020) of children (≥1 month to <18 years of age) receiving invasive mechanical ventilation for acute respiratory failure for ≥72 h. Children with and without sepsis-associated PARDS were selected from the parent cohort and compared. Blood was collected at time of enrollment. Plasma glycosaminoglycan disaccharide class (heparan sulfate, chondroitin sulfate, and hyaluronan) and sulfation subtypes (heparan sulfate and chondroitin sulfate) were quantified using liquid chromatography tandem mass spectrometry. Plasma proteoglycans (syndecan-1) were measured through an immunoassay.

RESULTS

Among the 39 mechanically ventilated children (29 with and 10 without sepsis-associated PARDS), sepsis-associated PARDS patients demonstrated higher levels of heparan sulfate (median 639 ng/mL [interquartile range, IQR 421-902] vs 311 [IQR 228-461]) and syndecan-1 (median 146 ng/mL [IQR 32-315] vs 8 [IQR 8-50]), both p = 0.01. Heparan sulfate subtype analysis demonstrated greater proportions of N-sulfated disaccharide levels among children with sepsis-associated PARDS (p = 0.01). Increasing N-sulfated disaccharide levels by quartile were associated with severe PARDS (n = 9/29) with the highest quartile including >60% of the severe PARDS patients (test for trend, p = 0.04). Higher total heparan sulfate and N-sulfated disaccharide levels were independently associated with fewer 28-day ventilator-free days in children with sepsis-associated PARDS (all p < 0.05).

CONCLUSIONS

Children with sepsis-associated PARDS exhibited higher plasma levels of heparan sulfate disaccharides and syndecan-1, suggesting that EGCX degradation biomarkers may provide insights into endothelial dysfunction and PARDS pathobiology.

Developmental patterns of extracellular matrix molecules in the embryonic and postnatal mouse hindbrain

Normal brain development requires continuous communication between developing neurons and their environment filled by a complex network referred to as extracellular matrix (ECM). The ECM is divided into distinct families of molecules including hyaluronic acid, proteoglycans, glycoproteins such as tenascins, and link proteins. In this study, we characterize the temporal and spatial distribution of the extracellular matrix molecules in the embryonic and postnatal mouse hindbrain by using antibodies and lectin histochemistry. In the embryo, hyaluronan and neurocan were found in high amounts until the time of birth whereas versican and tenascin-R were detected in lower intensities during the whole embryonic period. After birth, both hyaluronic acid and neurocan still produced intense staining in almost all areas of the hindbrain, while tenascin-R labeling showed a continuous increase during postnatal development. The reaction with WFA and aggrecan was revealed first 4th postnatal day (P4) with low staining intensities, while HAPLN was detected two weeks after birth (P14). The perineuronal net appeared first around the facial and vestibular neurons at P4 with hyaluronic acid cytochemistry. One week after birth aggrecan, neurocan, tenascin-R, and WFA were also accumulated around the neurons located in several hindbrain nuclei, but HAPLN1 was detected on the second postnatal week. Our results provide further evidence that many extracellular macromolecules that will be incorporated into the perineuronal net are already expressed at embryonic and early postnatal stages of development to control differentiation, migration, and synaptogenesis of neurons. In late postnatal period, the experience-driven neuronal activity induces formation of perineuronal net to stabilize synaptic connections.

Differential Proteoglycan Expression in Atherosclerosis Alters Platelet Adhesion and Activation

Proteoglycans are differentially expressed in different atherosclerotic plaque phenotypes, with biglycan and decorin characteristic of ruptured plaques and versican and hyaluronan more prominent in eroded plaques. Following plaque disruption, the exposure of extracellular matrix (ECM) proteins triggers platelet adhesion and thrombus formation. In this study, the impact of differential plaque composition on platelet function and thrombus formation was investigated. Platelet adhesion, activation and thrombus formation under different shear stress conditions were assessed in response to individual proteoglycans and composites representing different plaque phenotypes. The results demonstrated that all the proteoglycans tested mediated platelet adhesion but not platelet activation, and the extent of adhesion observed was significantly lower than that observed with type I and type III collagens. Thrombus formation upon the rupture and erosion ECM composites was significantly reduced (p < 0.05) compared to relevant collagen alone, indicating that proteoglycans negatively regulate platelet collagen responses. This was supported by results demonstrating that the addition of soluble biglycan or decorin to whole blood markedly reduced thrombus formation on type I collagen (p < 0.05). Interestingly, thrombus formation upon the erosion composite displayed aspirin sensitivity, whereas the rupture composite was intensive to aspirin, having implications for current antiplatelet therapy regimes. In conclusion, differential platelet responses and antiplatelet efficacy are observed on ECM composites phenotypic of plaque rupture and erosion. Proteoglycans inhibit thrombus formation and may offer a novel plaque-specific approach to limit arterial thrombosis.

Mutable Collagenous Tissue: A Concept Generator for Biomimetic Materials and Devices

Echinoderms (starfish, sea-urchins and their close relations) possess a unique type of collagenous tissue that is innervated by the motor nervous system and whose mechanical properties, such as tensile strength and elastic stiffness, can be altered in a time frame of seconds. Intensive research on echinoderm 'mutable collagenous tissue' (MCT) began over 50 years ago, and over 20 years ago, MCT first inspired a biomimetic design. MCT, and sea-cucumber dermis in particular, is now a major source of ideas for the development of new mechanically adaptable materials and devices with applications in diverse areas including biomedical science, chemical engineering and robotics. In this review, after an up-to-date account of present knowledge of the structural, physiological and molecular adaptations of MCT and the mechanisms responsible for its variable tensile properties, we focus on MCT as a concept generator surveying biomimetic systems inspired by MCT biology, showing that these include both bio-derived developments (same function, analogous operating principles) and technology-derived developments (same function, different operating principles), and suggest a strategy for the further exploitation of this promising biological resource.

Differential heparan sulfate dependency of the Drosophila glypicans

Heparan sulfate proteoglycans (HSPGs) are composed of a core protein and glycosaminoglycan (GAG) chains and serve as coreceptors for many growth factors and morphogens. To understand the molecular mechanisms by which HSPGs regulate morphogen gradient formation and signaling, it is important to determine the relative contributions of the carbohydrate and protein moieties to the proteoglycan function. To address this question, we generated ΔGAG alleles for dally and dally-like protein (dlp), two Drosophila HSPGs of the glypican family, in which all GAG-attachment serine residues are substituted to alanine residues using CRISPR/Cas9 mutagenesis. In these alleles, the glypican core proteins are expressed from the endogenous loci with no GAG modification. Analyses of the dallyΔGAG allele defined Dally functions that do not require heparan sulfate (HS) chains and that need both core protein and HS chains. We found a new, dallyΔGAG-specific phenotype, the formation of a posterior ectopic vein, which we have never seen in the null mutants. Unlike dallyΔGAG, dlpΔGAG mutants do not show most of the dlp null mutant phenotypes, suggesting that HS chains are dispensable for these dlp functions. As an exception, HS is essentially required for Dlp's activity at the neuromuscular junction. Thus, Drosophila glypicans show strikingly different levels of HS dependency. The ΔGAG mutant alleles of the glypicans serve as new molecular genetic toolsets highly useful to address important biological questions, such as molecular mechanisms of morphogen gradient formation.

Prolonged use of temozolomide leads to increased anxiety and decreased content of aggrecan and chondroitin sulfate in brain tissues of aged rats

Chemotherapy with temozolomide (TMZ) is an essential part of anticancer therapy used for malignant tumors (mainly melanoma and glioblastoma); however, the long-term effects on patient health and life quality are not fully investigated. Considering that tumors often occur in elderly patients, the present study was conducted on long-term (4 months) treatment of adult Wistar rats (9 months old, n=40) with TMZ and/or dexamethasone (DXM) to investigate potential behavioral impairments or morphological and molecular changes in their brain tissues. According to the elevated plus maze test, long-term use of TMZ affected the anxiety of the adult Wistar rats, although no significant deterioration of brain morphology or cellular composition of the brain tissue was revealed. The expression levels of all studied heparan sulfate (HS) proteoglycans (HSPGs) (syndecan-1, syndecan-3, glypican-1 and HSPG2) and the majority of the studied chondroitin sulfate (CS) proteoglycans (CSPGs) (decorin, biglycan, lumican, brevican, neurocan aggrecan, versican, Cspg4/Ng2, Cspg5 and phosphacan) were not affected by TMZ/DXM, except for neurocan and aggrecan. Aggrecan was the most sensitive proteoglycan to TMZ/DXM treatment demonstrating downregulation of its mRNA and protein levels following TMZ (-10-fold), DXM (-45-fold) and TMZ-DXM (-80-fold) treatment. HS content was not affected by TMZ/DXM treatment, whereas CS content was decreased 1.5-2.5-fold in the TMZ- and DXM-treated brain tissues. Taken together, the results demonstrated that treatment of adult Wistar rats with TMZ had long-term effects on the brain tissues, such as decreased aggrecan core protein levels and CS chain content and increased anxiety of the experimental animals.

Salmon nasal cartilage proteoglycan stimulates hair growth

Hair loss is a commonly encountered problem. In this study, hair growth was enhanced by daily oral ingestion of salmon nasal cartilage proteoglycan (PG) in mice. Proteoglycan stimulated vesicular endothelial growth factor production in human follicle dermal papilla cells through insulin growth factor-1 receptor signaling, suggesting the possibility of hair loss improvement by PG ingestion.

Chemokine Cxcl1-Cxcl2 heterodimer is a potent neutrophil chemoattractant

Microbial infection is characterized by release of multiple proinflammatory chemokines that direct neutrophils to the insult site. How collective function of these chemokines orchestrates neutrophil recruitment is not known. Here, we characterized the role for heterodimer and show that the Cxcl1-Cxcl2 heterodimer is a potent neutrophil chemoattractant in mice and can recruit more neutrophils than the individual chemokines. Chemokine-mediated neutrophil recruitment is determined by Cxcr2 receptor signaling, Cxcr2 endocytosis, and binding to glycosaminoglycans. We have now determined heterodimer's Cxcr2 activity using cellular assays and Cxcr2 density in blood and recruited neutrophils in heterodimer-treated mice. We have shown that the heterodimer binds glycosaminoglycans with higher affinity and more efficiently than Cxcl1 or Cxcl2. These data collectively indicate that optimal glycosaminoglycan interactions and dampened receptor activity acting in concert in a dynamic fashion promote heterodimer-mediated robust neutrophil recruitment. We propose that this could play a critical role in combating infection.

Investigating the temporal roles of decorin and biglycan in tendon healing

The small leucine-rich proteoglycans, decorin and biglycan, are minor components of the tendon extracellular matrix that regulate fibrillogenesis and matrix assembly. Our study objective was to define the temporal roles of decorin and biglycan during tendon healing using inducible knockout mice to include genetic knockdown at specific phases of healing: time of injury, the proliferative phase, and the remodeling phase. We hypothesized that knockdown of decorin or biglycan would adversely affect tendon healing, and that by prescribing the timing of knockdown, we could elucidate the temporal roles of these proteins during healing. Contrary to our hypothesis, decorin knockdown did not affect tendon healing. However, when biglycan was knocked down, either alone or coupled with decorin, tendon modulus was increased relative to wild-type mice, and this finding was consistent among all induction timepoints. At 6 weeks postinjury, we observed increased expression of genes associated with the extracellular matrix and growth factor signaling in the biglycan knockdown and compound decorin-biglycan knockdown tendons. Interestingly, these groups demonstrated opposing trends in gene expression as a function of knockdown-induction timepoint, highlighting distinct temporal roles for decorin and biglycan. In summary, this study finds that biglycan plays multiple functions throughout tendon healing, with the most impactful, detrimental role likely occurring during late-stage healing. Statement of clinical importance: This study helps to define the molecular factors that regulate tendon healing, which may aid in the development of new clinical therapies.

Regulation of Glycoprotein VI-Dependent Platelet Activation and Thrombus Formation by Heparan Sulfate Proteoglycan Perlecan

Proteoglycans form a heterogeneous family of proteins with covalently bound sulfated glycosaminoglycans. The extracellular matrix proteoglycan perlecan has been proposed to bind to the platelet- and megakaryocyte-specific receptor G6bB, co-regulating platelet glycoprotein VI (GPVI) signaling. The derived non-sulfate proteoglycan endorepellin was previously shown to enhance platelet adhesion via the collagen receptor, integrin α2β1. Here, we compared the roles of perlecan and other matrix proteoglycans in platelet responses and thrombus formation. We used multi-color flow cytometry to measure the degranulation and integrin αIIbβ3 activation of washed platelets in response to various proteoglycans and collagen-related peptide (CRP), the GPVI agonist. Perlecan, but not endorepellin, enhanced the CRP-induced activation of platelets in a time- and concentration-dependent manner. Similar to collagen, immobilized perlecan, but not other proteoglycans, supported static platelet adhesion and spreading. In-flowed whole-blood perlecan diminished shear-dependent platelet adhesion, while it enforced GPVI-dependent thrombus formation-to a larger extent than endorepellin-to induce more contracted aggregates of activated platelets. We concluded that the sulfated proteoglycan perlecan enhances GPVI-dependent platelet responses extending to thrombus formation, but it does so at the expense of reduced adhesion of platelets under flow.

Protein-protein interactions between tenascin-R and RPTPζ/phosphacan are critical to maintain the architecture of perineuronal nets

Neural plasticity, the ability to alter the structure and function of neural circuits, varies throughout the age of an individual. The end of the hyperplastic period in the central nervous system coincides with the appearance of honeycomb-like structures called perineuronal nets (PNNs) that surround a subset of neurons. PNNs are a condensed form of neural extracellular matrix that include the glycosaminoglycan hyaluronan and extracellular matrix proteins such as aggrecan and tenascin-R (TNR). PNNs are key regulators of developmental neural plasticity and cognitive functions, yet our current understanding of the molecular interactions that help assemble them remains limited. Disruption of Ptprz1, the gene encoding the receptor protein tyrosine phosphatase RPTPζ, altered the appearance of nets from a reticulated structure to puncta on the surface of cortical neuron bodies in adult mice. The structural alterations mirror those found in Tnr-/- mice, and TNR is absent from the net structures that form in dissociated cultures of Ptprz1-/- cortical neurons. These findings raised the possibility that TNR and RPTPζ cooperate to promote the assembly of PNNs. Here, we show that TNR associates with the RPTPζ ectodomain and provide a structural basis for these interactions. Furthermore, we show that RPTPζ forms an identical complex with tenascin-C, a homolog of TNR that also regulates neural plasticity. Finally, we demonstrate that mutating residues at the RPTPζ-TNR interface impairs the formation of PNNs in dissociated neuronal cultures. Overall, this work sets the stage for analyzing the roles of protein-protein interactions that underpin the formation of nets.

The Contribution of Vascular Proteoglycans to Atherothrombosis: Clinical Implications

The vascular extracellular matrix (ECM) produced by endothelial and smooth muscle cells is composed of collagens and glycoproteins and plays an integral role in regulating the structure and function of the vascular wall. Alteration in the expression of these proteins is associated with endothelial dysfunction and has been implicated in the development and progression of atherosclerosis. The ECM composition of atherosclerotic plaques varies depending on plaque phenotype and vulnerability, with distinct differences observed between ruptured and erodes plaques. Moreover, the thrombi on the exposed ECM are diverse in structure and composition, suggesting that the best antithrombotic approach may differ depending on plaque phenotype. This review provides a comprehensive overview of the role of proteoglycans in atherogenesis and thrombosis. It discusses the differential expression of the proteoglycans in different plaque phenotypes and the potential impact on platelet function and thrombosis. Finally, the review highlights the importance of this concept in developing a targeted approach to antithrombotic treatments to improve clinical outcomes in cardiovascular disease.

Extracellular Matrix of Echinoderms

This review considers available data on the composition of the extracellular matrix (ECM) in echinoderms. The connective tissue in these animals has a rather complex organization. It includes a wide range of structural ECM proteins, as well as various proteases and their inhibitors. Members of almost all major groups of collagens, various glycoproteins, and proteoglycans have been found in echinoderms. There are enzymes for the synthesis of structural proteins and their modification by polysaccharides. However, the ECM of echinoderms substantially differs from that of vertebrates by the lack of elastin, fibronectins, tenascins, and some other glycoproteins and proteoglycans. Echinoderms have a wide variety of proteinases, with serine, cysteine, aspartic, and metal peptidases identified among them. Their active centers have a typical structure and can break down various ECM molecules. Echinoderms are also distinguished by a wide range of proteinase inhibitors. The complex ECM structure and the variety of intermolecular interactions evidently explain the complexity of the mechanisms responsible for variations in the mechanical properties of connective tissue in echinoderms. These mechanisms probably depend not only on the number of cross-links between the molecules, but also on the composition of ECM and the properties of its proteins.

Conformations, interactions and functions of intrinsically disordered syndecans

Syndecans are transmembrane heparan sulfate proteoglycans present on most mammalian cell surfaces. They have a long evolutionary history, a single syndecan gene being expressed in bilaterian invertebrates. Syndecans have attracted interest because of their potential roles in development and disease, including vascular diseases, inflammation and various cancers. Recent structural data is providing important insights into their functions, which are complex, involving both intrinsic signaling through cytoplasmic binding partners and co-operative mechanisms where syndecans form a signaling nexus with other receptors such as integrins and tyrosine kinase growth factor receptors. While the cytoplasmic domain of syndecan-4 has a well-defined dimeric structure, the syndecan ectodomains are intrinsically disordered, which is linked to a capacity to interact with multiple partners. However, it remains to fully establish the impact of glycanation and partner proteins on syndecan core protein conformations. Genetic models indicate that a conserved property of syndecans links the cytoskeleton to calcium channels of the transient receptor potential class, compatible with roles as mechanosensors. In turn, syndecans influence actin cytoskeleton organization to impact motility, adhesion and the extracellular matrix environment. Syndecan clustering with other cell surface receptors into signaling microdomains has relevance to tissue differentiation in development, for example in stem cells, but also in disease where syndecan expression can be markedly up-regulated. Since syndecans have potential as diagnostic and prognostic markers as well as possible targets in some forms of cancer, it remains important to unravel structure/function relationships in the four mammalian syndecans.

Role of Syndecans in Ovarian Cancer: New Diagnostic and Prognostic Biomarkers and Potential Therapeutic Targets

Ovarian cancer (OC) is the eighth cancer both in prevalence and mortality in women and represents the deadliest female reproductive cancer. Due to generally vague symptoms, OC is frequently diagnosed only at a late and advanced stage, resulting in high mortality. The tumor extracellular matrix and cellular matrix receptors play a key role in the pathogenesis of tumor progression. Syndecans are a family of four transmembrane heparan sulfate proteoglycans (PG), including syndecan-1, -2, -3, and -4, which are dysregulated in a myriad of cancers, including OC. Many clinicopathological studies suggest that these proteins are promising diagnostic and prognostic biomarkers for OC. Furthermore, functions of the syndecan family in the regulation of cellular processes make it an interesting pharmacological target for anticancer therapies.

The C-terminal domains of ADAMTS1 contain exosites involved in its proteoglycanase activity

A disintegrin-like and metalloproteinase with thrombospondin type 1 motifs (ADAMTS1) is a protease involved in fertilization, cancer, cardiovascular development, and thoracic aneurysms. Proteoglycans such as versican and aggrecan have been identified as ADAMTS1 substrates, and Adamts1 ablation in mice typically results in versican accumulation; however, previous qualitative studies have suggested that ADAMTS1 proteoglycanase activity is weaker than that of other family members such as ADAMTS4 and ADAMTS5. Here, we investigated the functional determinants of ADAMTS1 proteoglycanase activity. We found that ADAMTS1 versicanase activity is approximately 1000-fold lower than ADAMTS5 and 50-fold lower than ADAMTS4 with a kinetic constant (kcat/Km) of 3.6 × 103 M-1 s-1 against full-length versican. Studies on domain-deletion variants identified the spacer and cysteine-rich domains as major determinants of ADAMTS1 versicanase activity. Additionally, we confirmed that these C-terminal domains are involved in the proteolysis of aggrecan as well as biglycan, a small leucine-rich proteoglycan. Glutamine scanning mutagenesis of exposed positively charged residues on the spacer domain loops and loop substitution with ADAMTS4 identified clusters of substrate-binding residues (exosites) in β3-β4 (R756Q/R759Q/R762Q), β9-β10 (residues 828-835), and β6-β7 (K795Q) loops. This study provides a mechanistic foundation for understanding the interactions between ADAMTS1 and its proteoglycan substrates and paves the way for development of selective exosite modulators of ADAMTS1 proteoglycanase activity.

Aggrecan accumulates at sites of increased pulmonary arterial pressure in idiopathic pulmonary arterial hypertension

Expansion of extracellular matrix occurs in all stages of pulmonary angiopathy associated with pulmonary arterial hypertension (PAH). In systemic arteries, dysregulation and accumulation of the large chondroitin-sulfate proteoglycan aggrecan is associated with swelling and disruption of vessel wall homeostasis. Whether aggrecan is present in pulmonary arteries, and its potential roles in PAH, has not been thoroughly investigated. Here, lung tissue from 11 patients with idiopathic PAH was imaged using synchrotron radiation phase-contrast microcomputed tomography (TOMCAT beamline, Swiss Light Source). Immunohistochemistry for aggrecan core protein in subsequently sectioned lung tissue demonstrated accumulation in PAH compared with failed donor lung controls. RNAscope in situ hybridization indicated ACAN expression in vascular endothelium and smooth muscle cells. Based on qualitative histological analysis, aggrecan localizes to cellular, rather than fibrotic or collagenous, lesions. Interestingly, ADAMTS15, a potential aggrecanase, was upregulated in pulmonary arteries in PAH. Aligning traditional histological analysis with three-dimensional renderings of pulmonary arteries from synchrotron imaging identified aggrecan in lumen-reducing lesions containing loose, cell-rich connective tissue, at sites of intrapulmonary bronchopulmonary shunting, and at sites of presumed elevated pulmonary blood pressure. Our findings suggest that ACAN expression may be an early response to injury in pulmonary angiopathy and supports recent work showing that dysregulation of aggrecan turnover is a hallmark of arterial adaptations to altered hemodynamics. Whether cause or effect, aggrecan and aggrecanase regulation in PAH are potential therapeutic targets.

Histories of Dermatan Sulfate Epimerase and Dermatan 4-O-Sulfotransferase from Discovery of Their Enzymes and Genes to Musculocontractural Ehlers-Danlos Syndrome

Dermatan sulfate (DS) and its proteoglycans are essential for the assembly of the extracellular matrix and cell signaling. Various transporters and biosynthetic enzymes for nucleotide sugars, glycosyltransferases, epimerase, and sulfotransferases, are involved in the biosynthesis of DS. Among these enzymes, dermatan sulfate epimerase (DSE) and dermatan 4-O-sulfotranserase (D4ST) are rate-limiting factors of DS biosynthesis. Pathogenic variants in human genes encoding DSE and D4ST cause the musculocontractural type of Ehlers-Danlos syndrome, characterized by tissue fragility, joint hypermobility, and skin hyperextensibility. DS-deficient mice exhibit perinatal lethality, myopathy-related phenotypes, thoracic kyphosis, vascular abnormalities, and skin fragility. These findings indicate that DS is essential for tissue development as well as homeostasis. This review focuses on the histories of DSE as well as D4ST, and their knockout mice as well as human congenital disorders.

Sb-Phenyl-N-methyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azastibocine Induces Perlecan Core Protein Synthesis in Cultured Vascular Endothelial Cells

Vascular endothelial cells synthesize and secrete perlecan, a large heparan sulfate proteoglycan that increases the anticoagulant activity of vascular endothelium by inducing antithrombin III and intensifying fibroblast growth factor (FGF)-2 activity to promote migration and proliferation in the repair process of damaged endothelium during the progression of atherosclerosis. However, the exact regulatory mechanisms of endothelial perlecan expression remain unclear. Since organic-inorganic hybrid molecules are being developed rapidly as tools to analyze biological systems, we searched for a molecular probe to analyze these mechanisms using a library of organoantimony compounds and found that the Sb-phenyl-N-methyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azastibocine (PMTAS) molecule promotes the expression of perlecan core protein gene without exhibiting cytotoxicity in vascular endothelial cells. In the present study, we characterized proteoglycans synthesized by cultured bovine aortic endothelial cells using biochemical techniques. The results indicated that PMTAS selectively induced perlecan core protein synthesis, without affecting the formation of its heparan sulfate chain, in vascular endothelial cells. The results also implied that this process is independent of the endothelial cell density, whereas in vascular smooth muscle cells, it occurred only at high cell density. Thus, PMTAS would be a useful tool for further studies on the mechanisms underlying perlecan core protein synthesis in vascular cells, which is critical in the progression of vascular lesions, such as those during atherosclerosis.

Recent Developments in Biopolymer-Based Hydrogels for Tissue Engineering Applications

Hydrogels are being investigated for their application in inducing the regeneration of various tissues, and suitable conditions for each tissue are becoming more apparent. Conditions such as the mechanical properties, degradation period, degradation mechanism, and cell affinity can be tailored by changing the molecular structure, especially in the case of polymers. Furthermore, many high-functional hydrogels with drug delivery systems (DDSs), in which drugs or bioactive substances are contained in controlled hydrogels, have been reported. This review focuses on the molecular design and function of biopolymer-based hydrogels and introduces recent developments in functional hydrogels for clinical applications.

Chemokine CXCL4 interactions with extracellular matrix proteoglycans mediate widespread immune cell recruitment independent of chemokine receptors

Leukocyte recruitment from the vasculature into tissues is a crucial component of the immune system but is also key to inflammatory disease. Chemokines are central to this process but have yet to be therapeutically targeted during inflammation due to a lack of mechanistic understanding. Specifically, CXCL4 (Platelet Factor 4, PF4) has no established receptor that explains its function. Here, we use biophysical, in vitro, and in vivo techniques to determine the mechanism underlying CXCL4-mediated leukocyte recruitment. We demonstrate that CXCL4 binds to glycosaminoglycan (GAG) sugars on proteoglycans within the endothelial extracellular matrix, resulting in increased adhesion of leukocytes to the vasculature, increased vascular permeability, and non-specific recruitment of a range of leukocytes. Furthermore, GAG sulfation confers selectivity onto chemokine localization. These findings present mechanistic insights into chemokine biology and provide future therapeutic targets.

Chondroitin sulfate glycosaminoglycans function as extra/pericellular ligands for cell surface receptors

Chondroitin sulfate (CS) chains, a class of sulfated glycosaminoglycan (GAG) polysaccharides, are ubiquitously distributed in extra/pericellular matrices that establish microenvironmental niches to support a multitude of cellular events. Such wide-ranging functions of CS chains are attributable not only to their sulfation pattern-dependent structural divergence, but also to their multiple modes of action. Although it has long been accepted that CS chains act as passive structural scaffolds that often behave as co-receptors and/or reservoirs for various humoral factors, the discovery of cell surface receptor molecules for distinct CS chains has offered insights into a novel mode of CS function as dynamic extra/pericellular signaling ligands. A recent report by Gong et al. (Identification of PTPR-interacting proteins by proximity-labeling assay. J. Biochem. 2021; 169:187-194) also strongly reinforced the physiological importance of CS receptor-mediated signaling pathways. In this commentary, we briefly introduce the functional aspects of CS chains as extra/pericellular signaling molecules.

Glucocorticoid Effects on Proteoglycans and Glycosaminoglycans

Glucocorticoids are steroid hormones that play diverse roles in numerous normal and pathological processes. They are actively used to treat a wide variety of diseases, including neurodegenerative and inflammatory diseases, cancers, and COVID-19, among others. However, the long-term use of glucocorticoids is associated with numerous side effects. Molecular mechanisms of these negative side effects are not completely understood. Recently, arguments have been made that one such mechanisms may be related to the influence of glucocorticoids on O-glycosylated components of the cell surface and extracellular matrix, in particular on proteoglycans and glycosaminoglycans. The potential toxic effects of glucocorticoids on these glycosylated macromolecules are particularly meaningful for brain physiology because proteoglycans/glycosaminoglycans are the main extracellular components of brain tissue. Here, we aim to review the known effects of glucocorticoids on proteoglycan expression and glycosaminoglycan content in different tissues, with a specific focus on the brain.

Alterations in glycosaminoglycan biosynthesis associated with the Ehlers-Danlos syndromes

Proteoglycans consist of a core protein substituted with one or more glycosaminoglycan (GAG) chains and execute versatile functions during many physiological and pathological processes. The biosynthesis of GAG chains is a complex process that depends on the concerted action of a variety of enzymes. Central to the biosynthesis of heparan sulfate (HS) and chondroitin sulfate/dermatan sulfate (CS/DS) GAG chains is the formation of a tetrasaccharide linker region followed by biosynthesis of HS or CS/DS-specific repeating disaccharide units, which then undergo modifications and epimerization. The importance of these biosynthetic enzymes is illustrated by several severe pleiotropic disorders that arise upon their deficiency. The Ehlers-Danlos syndromes (EDS) constitute a special group among these disorders. Although most EDS types are caused by defects in fibrillar types I, III, or V collagen, or their modifying enzymes, a few rare EDS types have recently been linked to defects in GAG biosynthesis. Spondylodysplastic EDS (spEDS) is caused by defective formation of the tetrasaccharide linker region, either due to β4GalT7 or β3GalT6 deficiency, whereas musculocontractural EDS (mcEDS) results from deficiency of D4ST1 or DS-epi1, impairing DS formation. This narrative review highlights the consequences of GAG deficiency in these specific EDS types, summarizes the associated phenotypic features and the molecular spectrum of reported pathogenic variants, and defines the current knowledge on the underlying pathophysiological mechanisms based on studies in patient-derived material, in vitro analyses, and animal models.

The Human Myofibroblast Marker Xylosyltransferase-I: A New Indicator for Macrophage Polarization

Chronic inflammation and excessive synthesis of extracellular matrix components, such as proteoglycans (PG), by fibroblast- or macrophage-derived myofibroblasts are the hallmarks of fibrotic diseases, including systemic sclerosis (SSc). Human xylosyltransferase-I (XT-I), which is encoded by the gene XYLT1, is the key enzyme that is involved in PG biosynthesis. Increased cellular XYLT1 expression and serum XT-I activity were measured in SSc. Nothing is known so far about the regulation of XT-I in immune cells, and their contribution to the increase in measurable serum XT-I activity. We utilized an in vitro model, with primary human CD14+CD16+ monocyte-derived macrophages (MΦ), in order to investigate the role of macrophage polarization on XT-I regulation. The MΦ generated were polarized towards two macrophage phenotypes that were associated with SSc, which were classified as classical pro-inflammatory (M1-like), and alternative pro-fibrotic (M2-like) MΦ. The fully characterized M1- and M2-like MΦ cultures showed differential XT-I gene and protein expressions. The fibrotic M2-like MΦ cultures exhibited higher XT-I secretion, as well as increased expression of myofibroblast marker α-smooth muscle actin, indicating the onset of macrophage-to-myofibroblast transition (MMT). Thus, we identified XT-I as a novel macrophage polarization marker for in vitro generated M1- and M2-like MΦ subtypes, and broadened the view of XT-I as a myofibroblast marker in the process of MMT.

Biglycan has a major role in maintenance of mature tendon mechanics

Decorin and biglycan are two small leucine-rich proteoglycans (SLRPs) that regulate collagen fibrillogenesis and extracellular matrix assembly in tendon. The objective of this study was to determine the individual roles of these molecules in maintaining the structural and mechanical properties of tendon during homeostasis in mature mice. We hypothesized that knockdown of decorin in mature tendons would result in detrimental changes to tendon structure and mechanics while knockdown of biglycan would have a minor effect on these parameters. To achieve this objective, we created tamoxifen-inducible mouse knockdown models targeting decorin or biglycan inactivation. This enables the evaluation of the roles of these SLRPs in mature tendon without the abnormal tendon development caused by conventional knockout models. Contrary to our hypothesis, knockdown of decorin resulted in minor alterations to tendon structure and no changes to mechanics while knockdown of biglycan resulted in broad changes to tendon structure and mechanics. Specifically, knockdown of biglycan resulted in reduced insertion modulus, maximum stress, dynamic modulus, stress relaxation, and increased collagen fiber realignment during loading. Knockdown of decorin and biglycan produced similar changes to tendon microstructure by increasing the collagen fibril diameter relative to wild-type controls. Biglycan knockdown also decreased the cell nuclear aspect ratio, indicating a more spindle-like nuclear shape. Overall, the extensive changes to tendon structure and mechanics after knockdown of biglycan, but not decorin, provides evidence that biglycan plays a major role in the maintenance of tendon structure and mechanics in mature mice during homeostasis.

Decorin evokes reversible mitochondrial depolarization in carcinoma and vascular endothelial cells

Decorin, a small leucine-rich proteoglycan with multiple biological functions, is known to evoke autophagy and mitophagy in both endothelial and cancer cells. Here, we investigated the effects of soluble decorin on mitochondrial homeostasis using live cell imaging and ex vivo angiogenic assays. We discovered that decorin triggers mitochondrial depolarization in triple-negative breast carcinoma, HeLa, and endothelial cells. This bioactivity was mediated by the protein core in a time- and dose-dependent manner and was specific for decorin insofar as biglycan, the closest homolog, failed to trigger depolarization. Mechanistically, we found that the bioactivity of decorin to promote depolarization required the MET receptor and its tyrosine kinase. Moreover, two mitochondrial interacting proteins, mitostatin and mitofusin 2, were essential for downstream decorin effects. Finally, we found that decorin relied on the canonical mitochondrial permeability transition pore to trigger tumor cell mitochondrial depolarization. Collectively, our study implicates decorin as a soluble outside-in regulator of mitochondrial dynamics.

The INSR/AKT/mTOR pathway regulates the pace of myogenesis in a syndecan-3-dependent manner

Muscle stem cells (MuSCs) are indispensable for muscle regeneration. A multitude of extracellular stimuli direct MuSC fate decisions from quiescent progenitors to differentiated myocytes. The activity of these signals is modulated by coreceptors such as syndecan-3 (SDC3). We investigated the global landscape of SDC3-mediated regulation of myogenesis using a phosphoproteomics approach which revealed, with the precision level of individual phosphosites, the large-scale extent of SDC3-mediated regulation of signal transduction in MuSCs. We then focused on INSR/AKT/mTOR as a key pathway regulated by SDC3 during myogenesis and mechanistically dissected SDC3-mediated inhibition of insulin receptor signaling in MuSCs. SDC3 interacts with INSR ultimately limiting signal transduction via AKT/mTOR. Both knockdown of INSR and inhibition of AKT rescue Sdc3^-/- MuSC differentiation to wild type levels. Since SDC3 is rapidly downregulated at the onset of differentiation, our study suggests that SDC3 acts a timekeeper to restrain proliferating MuSC response and prevent premature differentiation.

Evaluation of Sodium Relaxation Times and Concentrations in the Achilles Tendon Using MRI

Sodium magnetic resonance imaging (MRI) can be used to evaluate the change in the proteoglycan content in Achilles tendons (ATs) of patients with different AT pathologies by measuring the ²³Na signal-to-noise ratio (SNR). As ²³Na SNR alone is difficult to compare between different studies, because of the high influence of hardware configurations and sequence settings on the SNR, we further set out to measure the apparent tissue sodium content (aTSC) in the AT as a better comparable parameter. Ten healthy controls and one patient with tendinopathy in the AT were examined using a clinical 3 Tesla (T) MRI scanner in conjunction with a dual tuned ¹H/²³Na surface coil to measure ²³Na SNR and aTSC in their ATs. ²³Na T₁ and T₂* of the AT were also measured for three controls to correct for different relaxation behavior. The results were as follows: ²³Na SNR = 11.7 ± 2.2, aTSC = 82.2 ± 13.9 mM, ²³Na T₁ = 20.4 ± 2.4 ms, ²³Na T_2s* = 1.4 ± 0.4 ms, and ²³Na T_2l* = 13.9 ± 0.8 ms for the whole AT of healthy controls with significant regional differences. These are the first reported aTSCs and ²³Na relaxation times for the AT using sodium MRI and may serve for future comparability in different studies regarding examinations of diseased ATs with sodium MRI.

N-glycosylation modulates enzymatic activity of Trypanosoma congolense trans-sialidase

Trypanosomes cause the devastating disease trypanosomiasis, in which the action of trans-sialidase (TS) enzymes harbored on their surface is a key virulence factor. TS enzymes are N-glycosylated, but the biological functions of their glycans have remained elusive. In this study, we investigated the influence of N-glycans on the enzymatic activity and structural stability of TconTS1, a recombinant TS from the African parasite Trypanosoma congolense. We expressed the enzyme in Chinese hamster ovary Lec1 cells, which produce high-mannose type N-glycans similar to the TS N-glycosylation pattern in vivo. Our MALDI-TOF mass spectrometry data revealed that up to eight putative N-glycosylation sites were glycosylated. In addition, we determined that N-glycan removal via endoglycosidase H_f treatment of TconTS1 led to a decrease in substrate affinity relative to the untreated enzyme but had no impact on the conversion rate. Furthermore, we observed no changes in secondary structure elements of hypoglycosylated TconTS1 in CD experiments. Finally, our molecular dynamics simulations provided evidence for interactions between monosaccharide units of the highly flexible N-glycans and some conserved amino acids located at the catalytic site. These interactions led to conformational changes, possibly enhancing substrate accessibility and enzyme–substrate complex stability. The here-observed modulation of catalytic activity via N-glycans represents a so-far-unknown structure–function relationship potentially inherent in several members of the TS enzyme family.

Excavating proteoglycan structure-function relationships: Modern approaches to capture the interactions of ancient biomolecules

Proteoglycans are now well regarded as key facilitators of cell biology. While a majority of their interactions and functions are attributed to the decorating glycosaminoglycan chains, there is a growing appreciation for the roles of the proteoglycan core protein and for considering proteoglycans as replete protein-glycan conjugates. This appreciation, seeded by early work in proteoglycan biology, is now being advanced and exalted by modern approaches in chemical glycobiology. In this review, we discuss up-and-coming methods to unearth the fine-scale architecture of proteoglycans that modulate their functions and interactions. Crucial to these efforts is the production of chemically defined materials, including semi-synthetic proteoglycans and the in situ capture of interacting proteins. Together, the integration of chemical biology approaches promises to expedite the dissection of the structural heterogeneity of proteoglycans and deliver refined insight into their functions.

Chondroitin Sulfates Control Invasiveness of the Basal-Like Breast Cancer Cell Line MDA-MB-231 Through ROR1

Extracellular and cell surface chondroitin sulfates (CSs) regulate cancer cell properties, including proliferation and invasion. Thus, it is necessary to understand the mechanisms underlying their roles in cancer. Although we have shown that CS has an inherent ability to enhance the invasive activity of the human triple-negative breast cancer cell line MDA-MB-231, its molecular mechanism remains elusive. Here, we focused on receptor tyrosine kinase-like orphan receptor 1 (ROR1) and dickkopf WNT signaling pathway inhibitor 1 (DKK1). MDA-MB-231 cells express high levels of ROR1; their invasive potential depends on ROR1 signaling. Although accumulating evidence has demonstrated that ROR1 is associated with aggressive breast-cancer phenotypes, the whole picture of its biological function remains poorly understood. In this study, we examined whether CS controls ROR1 function. Surface plasmon resonance analysis indicated that CSs were bound to ROR1 in the presence of WNT5A. The invasive activity of MDA-MB-231 cells enhanced by CSs was completely suppressed by ROR1 knockdown. In addition, knockdown of the CS biosynthetic enzymes CHST11 and CHST15 inhibited invasive activity, even in the presence of ROR1. These results suggest that CS is required to induce an ROR1-dependent, aggressive MDA-MB-231 phenotype. ROR1 signaling in MDA-MB-231 cells activated c-Jun N-terminal kinase (JNK), leading to increased invasive potential; moreover, exogenous CSs activated JNK. MDA-MB-231 cells express DKK1, a tumor suppressor factor that binds to CS, at high levels. Knockdown of DKK1 enhanced CS-stimulated tumor invasion activity of MDA-MB-231 cells, suggesting that DKK1 sequesters CS to block ROR1/JNK signaling. These results showed that CSs promotes cancer aggressiveness through the ROR1−JNK axis in MDA-MB-231 cells.

Biglycan Is a Novel Mineralocorticoid Receptor Target Involved in Aldosterone/Salt-Induced Glomerular Injury

The beneficial effects of mineralocorticoid receptor (MR) antagonists (MRAs) for various kidney diseases are established. However, the underlying mechanisms of kidney injury induced by MR activation remain to be elucidated. We recently reported aldosterone-induced enhancement of proteoglycan expression in mitral valve interstitial cells and its association with fibromyxomatous valvular disorder. As the expression of certain proteoglycans is elevated in several kidney diseases, we hypothesized that proteoglycans mediate kidney injury in the context of aldosterone/MR pathway activation. We evaluated the proteoglycan expression and tissue injury in the kidney and isolated glomeruli of uninephrectomy/aldosterone/salt (NAS) mice. The MRA eplerenone was administered to assess the role of the MR pathway. We investigated the direct effects of biglycan, one of the proteoglycans, on macrophages using isolated macrophages. The kidney samples from NAS-treated mice showed enhanced fibrosis and increased expression of biglycan accompanying glomerular macrophage infiltration and enhanced expression of TNF-α, iNOS, Nox2, CCL3 (C-C motif chemokine ligand 3), and phosphorylated NF-κB. Eplerenone blunted these changes. Purified biglycan stimulated macrophages to express TNF-α, iNOS, Nox2, and CCL3. This was prevented by a toll-like receptor 4 (TLR4) or NF-κB inhibitor, indicating that biglycan stimulation is dependent on the TLR4/NF-κB pathway. We identified the proteoglycan biglycan as a novel target of MR involved in MR-induced glomerular injury and macrophage infiltration via a biglycan/TLR4/NF-κB/CCL3 cascade.

Syndecan-1 in liver pathophysiology

Syndecan-1 is a heparan sulfate/chondroitin sulfate proteoglycan (PG) of the cell surface and the extracellular matrix, which regulates a broad spectrum of physiological and pathological processes such as cell proliferation, migration, inflammation, matrix remodeling, wound healing, or tumorigenesis. Syndecan-1 represents the major PG of the liver, expressed by hepatocytes and cholangiocytes, and its elevated expression is a characteristic feature of liver diseases. The highest syndecan-1 expression is found in liver cirrhosis and in hepatocellular carcinoma (HCC) developed in cirrhotic livers. In addition, as being a hepatitis C receptor, hepatitis C virus (HCV) infected livers produce extremely large amounts of syndecan-1. The serum levels of the cleaved (shedded) extracellular domain has clinical significance, as its increased concentration reflects on poor prognosis in cirrhosis as well as in cancer. In vivo experiments confirmed that syndecan-1 protects against early stages of fibrogenesis mainly by enhanced clearance of transforming growth factor beta (TGFβ1) and thrombospondin-1 via circulation, and against hepatocarcinogenesis by interfering with several signaling pathways and enhancing cell cycle blockade. In addition, syndecan-1 is capable to hinder lipid metabolism and ribosomal biogenesis in induced cancer models.. These observations together with its participation in the uptake of viruses (e.g. HCV, SARS-CoV-2) indicate that syndecan-1 is a central player in liver pathologies.

Bio-orthogonal Click Chemistry Methods to Evaluate the Metabolism of Inflammatory Challenged Cartilage after Traumatic Overloading

During traumatic joint injuries, impact overloading can cause mechanical damage to the cartilage. In the following inflammation phase, excessive inflammatory cytokines (e.g., interleukin-1β (IL-1β)) can act on chondrocytes, causing over-proliferation, apoptosis, and extracellular matrix (ECM) degradation that can lead to osteoarthritis. This study investigated the combined effects of traumatic overloading and IL-1β challenge on the metabolic activities of chondrocytes. Bovine cartilage explants underwent impact overloading followed by IL-1β exposure at a physiologically relevant dosage (1 ng/mL). New click chemistry-based methods were developed to visualize and quantify the proliferation of in situ chondrocytes in a nondestructive manner without the involvement of histological sectioning or antibodies. Click chemistry-based methods were also employed to measure the ECM synthesis and degradation in cartilage explants. As the click reactions are copper-free and bio-orthogonal, i.e., with negligible cellular toxicity, cartilage ECM was cultured and studied for 6 weeks. Traumatic overloading induced significant cell death, mainly in the superficial zone. The high number of dead cells reduced the overall proliferation of chondrocytes as well as the synthesis of glycosaminoglycan (GAG) and collagen contents, but overloading alone had no effects on ECM degradation. IL-1β challenge had little effect on cell viability, proliferation, or protein synthesis but induced over 40% GAG loss in 10 days and 61% collagen loss in 6 weeks. For the overloaded samples, IL-1β induced greater degrees of degradation, with 68% GAG loss in 10 days and 80% collagen loss in 6 weeks. The results imply a necessary immediate ease of inflammation after joint injuries when trauma damage on cartilage is present. The new click chemistry methods could benefit many cellular and tissue engineering studies, providing convenient and sensitive assays of metabolic activities of cells in native three-dimensional (3D) environments.

The heparan sulphate proteoglycan Syndecan-1 (CD138) regulates tumour progression in a 3D model of ductal carcinoma in situ of the breast

Ductal carcinoma in situ (DCIS) is a form of breast cancer that is restricted to the lactiferous ducts and has not yet invaded the surrounding breast tissue. Dysregulation of the transmembrane heparan sulphate proteoglycan Syndecan-1 (Sdc-1) plays a role in tumour progression of invasive breast cancer (IBC). In DCIS, Sdc-1, c-Met and E-cadherin are part of a proangiogenic expression signature. In this study, we employed a siRNA knockdown approach in the DCIS model cell line MCF10A DCIS.com to investigate a potential connection between Sdc-1 and epithelial mesenchymal transition (EMT), proteolysis and the Rho kinase pathway. Analysis of gene expression data of the TNMplot.com database revealed that Sdc-1 expression was higher in primary breast tumours compared to metastases. The impact of Sdc-1-depletion on the cellular phenotype was investigated in a Matrigel-based three-dimensional cell culture model. Sdc-1 depletion resulted in the formation of larger spheroids and the formation of invasive protrusions. Application of matrix metalloproteinase (MMP) and Rho kinase inhibitors could block the Sdc-1-induced phenotype. qPCR analysis of Sdc-1-depleted cells in two-dimensional culture revealed upregulated expression of the EMT-markers CDH1, FN-1, CLDN1, the proteolysis markers MMP3, and MMP9, and HPSE, while MMP2, VIM and ROCK-2 were downregulated. Immunocytochemistry confirmed upregulation of MMP9 and fibronectin, the latter being particular prominent after ROCK inhibition. STRING analysis confirmed an interaction of the investigated gene products at the protein level. Our results suggest that diminished Sdc-1 expression plays a role in DCIS progression to IBC through deregulation of proteolytic factors and a partial EMT.

Integrin α11β1 and syndecan-4 dual receptor ablation attenuates cardiac hypertrophy in the pressure overloaded heart

Pathological myocardial hypertrophy in response to an increase in left ventricular (LV) afterload may ultimately lead to heart failure. Cell surface receptors bridge the interface between the cell and the ECM in cardiac myocytes and cardiac fibroblasts, and have been suggested to be important mediators of pathological myocardial hypertrophy. We identify for the first time that integrin α11 (α11) is preferentially upregulated amongst integrin beta 1 heterodimer-forming α subunits in response to increased afterload induced by aortic banding (AB) in wild type mice (WT). Mice were anesthetized in a chamber with 4% isoflurane and 95% oxygen before being intubated and ventilated with 2.5% isoflurane and 97% oxygen. For pre- and post-operative analgesia, animals were administered 0.02 mL buprenorphine (0.3 mg/mL) subcutaneously. Surprisingly, mice lacking α11 develop myocardial hypertrophy following AB comparable to WT. In the mice lacking α11, we further show a compensatory increase in the expression of another mechanoreceptor, syndecan-4, following AB compared to WT AB mice, indicating that syndecan-4 compensated for lack of α11. Intriguingly, mice lacking mechanoreceptors α11 and syndecan-4 show ablated myocardial hypertrophy following AB compared to WT mice. Expression of the main cardiac collagen isoforms col1a2 and col3a1 was significantly reduced in AB mice lacking mechanoreceptors α11 and syndecan-4 compared to WT AB.

Biglycan as a potential regulator of tumorgenicity and immunogenicity in K-RAS-transformed cells

The extracellular matrix component biglycan (BGN) plays an essential role in various physiological and pathophysiological processes. A deficient BGN expression associated with reduced immunogenicity was found in HER-2/neu-overexpressing cells. To determine whether BGN is suppressed by oncogene-driven regulatory networks, the expression and function of BGN was analyzed in murine and human BGNlow/BGNhigh K-RASG12V-transformed model systems as well as in different patients' datasets of colorectal carcinoma (CRC) lesions. K-RAS-mutated CRC tissues expressed low BGN mRNA and protein levels when compared to normal colon epithelial cells, which was associated with a reduced patients' survival. Transfection of BGN in murine and human BGNlow K-RAS-expressing cells resulted in a reduced growth and migration of BGNhigh vs BGNlow K-RAS cells. In addition, increased MHC class I surface antigens as a consequence of an enhanced antigen processing machinery component expression was found upon restoration of BGN, which was confirmed by RNA-sequencing of BGNlow vs. BGNhigh K-RAS models. Furthermore, a reduced tumor formation of BGNhigh versus BGNlow K-RAS-transformed fibroblasts associated with an enhanced MHC class I expression and an increased frequency of tumor-infiltrating lymphocytes in tumor lesions was found. Our data provide for the first time an inverse link between BGN and K-RAS expression in murine and human K-RAS-overexpressing models and CRC lesions associated with altered growth properties, reduced immunogenicity and worse patients' outcome. Therefore, reversion of BGN might be a novel therapeutic option for K-RAS-associated malignancies.

Angiotensin II Induces Aortic Rupture and Dissection in Osteoprotegerin-Deficient Mice

Background

The biological mechanism of action for osteoprotegerin, a soluble decoy receptor for the receptor activator of nuclear factor‐kappa B ligand in the vascular structure, has not been elucidated. The study aim was to determine if osteoprotegerin affects aortic structural integrity in angiotensin II (Ang II)‐induced hypertension.

Methods and Results

Mortality was higher (P<0.0001 by log‐rank test) in 8‐week‐old male homozygotes of osteoprotegerin gene‐knockout mice given subcutaneous administration of Ang II for 28 days, with an incidence of 21% fatal aortic rupture and 23% aortic dissection, than in age‐matched wild‐type mice. Ang II‐infused aorta of wild‐type mice showed that osteoprotegerin immunoreactivity was present with proteoglycan. The absence of osteoprotegerin was associated with decreased medial and adventitial thickness and increased numbers of elastin breaks as well as with increased periostin expression and soluble receptor activator of nuclear factor‐kappa B ligand concentrations. PEGylated human recombinant osteoprotegerin administration decreased all‐cause mortality (P<0.001 by log‐rank test), the incidence of fatal aortic rupture (P=0.08), and aortic dissection (P<0.001) with decreasing numbers of elastin breaks, periostin expressions, and soluble receptor activator of nuclear factor‐kappa B ligand concentrations in Ang II‐infused osteoprotegerin gene‐knockout mice.

Conclusions

These data suggest that osteoprotegerin protects against aortic rupture and dissection in Ang II‐induced hypertension by inhibiting receptor activator of nuclear factor‐kappa B ligand activity and periostin expression.

Aggrecan and versican: two brothers close or apart

Aggrecan (Acan) and versican (Vcan) are large chondroitin sulfate proteoglycans of the extracellular matrix. They share the same structural domains at both N and C-termini. The N-terminal G1 domain binds hyaluronan (HA), forms an HA-rich matrix, and regulates HA-mediated signaling. The C-terminal G3 domain binds other extracellular matrix molecules and forms a supramolecular structure that stores TGFb and BMPs and regulates their signaling. EGF-like motifs in the G3 domain may directly act like an EGF ligand. Both Acan and Vcan are present in cartilage, intervertebral disc, brain, heart, and aorta. Their localizations are essentially reciprocal. This review describes their structural domains, expression patterns and functions, and regulation of their expression.

Role of extracellular matrix proteoglycans in immune cell recruitment

Leucocyte recruitment is a critical component of the immune response and is central to our ability to fight infection. Paradoxically, leucocyte recruitment is also a central component of inflammatory-based diseases such as rheumatoid arthritis, atherosclerosis and cancer. The role of the extracellular matrix, in particular proteoglycans, in this process has been largely overlooked. Proteoglycans consist of protein cores with glycosaminoglycan sugar side chains attached. Proteoglycans have been shown to bind and regulate the function of a number of proteins, for example chemokines, and also play a key structural role in the local tissue environment/niche. Whilst they have been implicated in leucocyte recruitment and inflammatory disease, their mechanistic function has yet to be fully understood, precluding therapeutic targeting. This review summarizes what is currently known about the role of proteoglycans in the different stages of leucocyte recruitment and proposes a number of areas where more research is needed. A better understanding of the mechanistic role of proteoglycans during inflammatory disease will inform the development of next-generation therapeutics.

Coreceptor Functions of Cell Surface Heparan Sulfate Proteoglycans

Receptor-ligand interactions play an important role in many biological processes by triggering specific cellular responses. These interactions are frequently regulated by coreceptors that facilitate, alter, or inhibit signaling. Coreceptors work in parallel with other specific and accessory molecules to coordinate receptor-ligand interactions. Cell surface heparan sulfate proteoglycans (HSPGs) function as unique coreceptors because they can bind to many ligands and receptors through their HS and core protein motifs. Cell surface HSPGs are typically expressed in abundance of the signaling receptors and, thus, are capable of mediating the initial binding of ligands to the cell surface. HSPG coreceptors do not possess kinase domains or intrinsic enzyme activities and, for the most part, binding to cell surface HSPGs does not directly stimulate intracellular signaling. Because of these features, cell surface HSPGs primarily function as coreceptors for many receptor-ligand interactions. Given that cell surface HSPGs are widely conserved, they likely serve fundamental functions to preserve basic physiological processes. Indeed, cell surface HSPGs can support specific cellular interactions with growth factors, morphogens, chemokines, extracellular matrix (ECM) components, and microbial pathogens and their secreted virulence factors. Through these interactions, HSPG coreceptors regulate cell adhesion, proliferation, migration and differentiation, and impact the onset, progression, and outcome of pathophysiological processes, such as development, tissue repair, inflammation, infection, and tumorigenesis. This review seeks to provide an overview of the various mechanisms of how cell surface HSPGs function as coreceptors.

Extracellular endosulfatase Sulf-2 harbors a chondroitin/dermatan sulfate chain that modulates its enzyme activity

Sulfs represent a class of unconventional sulfatases which provide an original post-synthetic regulatory mechanism for heparan sulfate polysaccharides and are involved in multiple physiopathological processes, including cancer. However, Sulfs remain poorly characterized enzymes, with major discrepancies regarding their in vivo functions. Here we show that human Sulf-2 (HSulf-2) harbors a chondroitin/dermatan sulfate glycosaminoglycan (GAG) chain, attached to the enzyme substrate-binding domain. We demonstrate that this GAG chain affects enzyme/substrate recognition and tunes HSulf-2 activity in vitro and in vivo. In addition, we show that mammalian hyaluronidase acts as a promoter of HSulf-2 activity by digesting its GAG chain. In conclusion, our results highlight HSulf-2 as a proteoglycan-related enzyme and its GAG chain as a critical non-catalytic modulator of the enzyme activity. These findings contribute to clarifying the conflicting data on the activities of the Sulfs.

The function of Glypicans in the mammalian embryo

Glypicans are proteoglycans that are bound to the outer surface of the plasma membrane by a glycosylphosphatidylinositol anchor. The mammalian genome contains six members of the glypican family (GPC1 to GPC6). Although the degree of sequence homology within the family is rather low, the three-dimensional structure of these proteoglycans is highly conserved. Glypicans are predominantly expressed during embryonic development. Genetic and biochemical studies have shown that glypicans can stimulate or inhibit the signaling pathways triggered by Wnts, Hedgehogs, Fibroblast Growth Factors, and Bone Morphogenetic Proteins. The study of mutant mouse strains demonstrated that glypicans have important functions in the developmental morphogenesis of various organs. In addition, a role of glypicans in synapsis formation has been established. Notably, glypican loss-of-function mutations are the cause of three human inherited syndromes. Recent analysis of glypican compound mutant mice have demonstrated that members of this protein family display redundant functions during embryonic development.

Differential Impact of Membrane-Bound and Soluble Forms of the Prognostic Marker Syndecan-1 on the Invasiveness, Migration, Apoptosis, and Proliferation of Cervical Cancer Cells

Cervical cancer ranks fourth among the most commonly diagnosed malignant tumors in women worldwide. Previously published evidence suggested a possible connection between the expression of the membrane-bound heparan sulfate proteoglycan syndecan-1 (Sdc-1) and the development of cervical carcinoma. Sdc-1 serves as a matrix receptor and coreceptor for receptor tyrosine kinases and additional signaling pathways. It influences cell proliferation, adhesion, and migration and is seen as a modulator of the tumor microenvironment. Following proteolytic cleavage of its extracellular domain in a process called shedding, Sdc-1 can act as a paracrine effector. The loss of Sdc-1 expression is associated with low differentiation of cervical carcinoma and with an increased rate of lymph node metastases. Here, we analyzed the clinical impact of Sdc-1 expression by analysis of public gene expression datasets and studied the effect of an overexpression of Sdc-1 and its membrane-bound and soluble forms on the malignant properties of the human cervical carcinoma cell line HeLa through functional analysis. For this purpose, the HeLa cells were stably transfected with the control plasmid pcDNA3.1 and three different Sdc-1-DNA constructs,encoding wild-type, permanently membrane-bound, and constitutively soluble Sdc-1. In clinical specimens, Sdc-1 mRNA was more highly expressed in local tumor tissues than in normal and metastatic cervical cancer tissues. Moreover, high Sdc-1 expression correlated with a poor prognosis in Kaplan-Meier survival analysis, suggesting the important role of Sdc-1 in the progression of this type of cancer. In vitro, we found that the soluble, as well as the permanently membrane-bound forms of Sdc-1 modulated the proliferation and the cell cycle, while membrane-bound Sdc1 regulated HeLa cell apoptosis. The overexpression of Sdc-1 and its soluble form increased invasiveness. In vitro scratch/wound healing assay, showed reduced Sdc-1-dependent cell motility which was linked to the Rho-GTPase signaling pathway. In conclusion, in cervical cancer Sdc-1 modulates pathogenetically relevant processes, which depend on the membrane-association of Sdc-1.

Effects of salmon cartilage proteoglycan on obesity in mice fed with a high-fat diet

This study investigated the effects of salmon nasal cartilage proteoglycan (PG), which shows anti-inflammatory properties, on obesity induced by high-fat diet (HFD) in a mouse model. Mice were fed either a HFD or normal diet (ND), with or without PG, for 8-12 weeks. After 12 weeks, the body weight of mice fed with PG-free HFD was 54.08 ± 4.67 g, whereas that of mice fed with HFD containing PG was 41.83 ± 4.97 g. The results suggest that the increase in body weight was attenuated in mice fed with HFD containing PG. This effect was not observed in mice fed with ND. The PG administration suppressed the elevation of serum lipids (the level of serum lipids ranged between 54% and 69% compared to 100% in mice fed with PG-free HFD) and the upregulated mRNA expression of sterol regulatory element-binding protein-1c (SREBP-1c), which is a transcription factor that acts as a master regulator of lipogenic gene expression in the liver (the expression level was 77.5% compared to 100% in mice fed with PG-free HFD). High leptin levels in mice fed with PG-free HFD were observed during fasting (average at 14,376 ng/ml), and they did not increase after refeeding (average of 14,263 ng/ml), whereas serum leptin levels in mice fed with HFD containing PG were low during fasting (average of 6481 ng/ml) and increased after refeeding (average 13,382 ng/ml). These results suggest that PG feeding has an anti-obesity effect and that the regulation of SREBP-1c and leptin secretion play a role in this effect.