Interaction Of Proteoglycans Research Articles

Structural Insights into Protein-Ligand Interactions of Small Leucine Rich Repeat Proteoglycans with a Large Number of Binding Partners: An Overview

Small leucine rich repeat proteoglycans (SLRPs) exist in the extracellular matrix. SLRPs contain tandem arrays of LRRs flanked by cysteine clusters at the both N- and C-termini. The extreme N- and/or C-termini contain low complexity sequences, glycosaminoglycan (GAG) chain and/or sulfated tyrosine residues in some members of SLRPs. The LRR solenoid structure may be divided into four parts consisting of a concave surface, an ascending surface, a convex surface, and a descending surface. SLRPs share many biological functions including collagen fibrillogenesis, signaling, innate immunity, and inflammation through the binding of various ligands. We undertake a comprehensive literature search of publications in order to make a list of ligands of SLRPs. We describe and discuss the interacting sites of SLRPs to binding partners. The protein-ligand interactions occur on not only the concave surface but also the ascending surface and the N- or C-terminal capping regions. In addition, the extreme N- and/or C-terminal regions with the GAG chains or sulfated tyrosine residues participate in ligand-interactions.

The centrality of proteoglycan research: Expect the unexpected

The centrality of proteoglycan research: Expect the unexpected

Hydrophilic colloids (Konjac gum/Xanthan gum) in 3D printing of transitional food from fish paste

Hydrocolloids are often used as thickeners to create texture-modified diets for people with dysphagia. The effect of different konjac gum (KGM)/xanthan gum (XG) ratios (12/0, 5/1, 3/1, 1/1, 1/3, 1/5, 0/12, w/w) on rheological properties, 3D printability, textural properties, microstructure, and the proteoglycan interactions of cooked sturgeon pastes were investigated. The sturgeon pastes with different KGM/XG ratios demonstrated shear-thinning behavior and excellent viscoelasticity which made it good feedstock for 3D printing. The texture properties of the sturgeon paste with different KGM/XG ratios were all significantly improved (p < 0.05) comparing to the control, and satisfied the potential transitional foods in the International Dysphagia Diet Standardization Initiative (IDDSI) framework. The hardness (660.62 g) and water holding capacity (98.12%) maximized at the KGM/XG ratio of 1/1. The addition of KGM/XG mainly promotes cross-linking between protein to strength the network structure through hydrogen bonding.

Decorin regulates collagen fibrillogenesis during corneal wound healing in mouse in vivo

A characteristic rigid spatial arrangement of collagen fibrils in the stroma is critical for corneal transparency. This unique organization of collagen fibrils in corneal stroma can be impacted by the presence and interactions of proteoglycans and extracellular matrix (ECM) proteins in a corneal microenvironment. Earlier studies revealed that decorin, a leucine-rich proteoglycan in stroma, regulates keratocyte-collagen matrix assembly and wound healing in the cornea. This study investigated the role of decorin in the regulation of stromal fibrillogenesis and corneal transparency in vivo employing a loss-of-function genetic approach using decorin null (dcn−/−) and wild type (dcn+/+) mice and a standard alkali-injury model. A time-dependent ocular examinations with Slit lamp microscope in live animals assessed corneal clarity, haze, and neovascularization levels in normal and injured eyes. Morphometric changes in normal and injured dcn+/+ and dcn−/− corneas, post-euthanasia, were analyzed with Masson's Trichrome and Periodic Acid-Schiff (PAS) histology evaluations. The ultrastructure changes in all corneas were investigated with transmission electron microscopy (TEM). Injury to eye produced clinically relevant corneal haze and neovascularization in dcn−/− and dcn+/+ mice while corneas of uninjured eyes remained clear and avascular. A clinically significant haze and neovascularization appeared in injured dcn−/- corneas compared to the dcn+/+ corneas at day 21 post-injury and not at early tested times. Histological examinations revealed noticeably abnormal morphology and compromised collagen levels in injured dcn−/− corneas compared to the injured/normal dcn+/+ and uninjured dcn−/− corneas. TEM analysis exhibited remarkably uneven collagen fibrils size and distribution in the stroma with asymmetrical organization and loose packing in injured dcn−/− corneas than injured/normal dcn+/+ and uninjured dcn−/− corneas. The minimum and maximum inter-fibril distances were markedly irregular in injured dcn−/− corneas compared to all other corneas. Together, results of clinical, histological, and ultrastructural investigations in a genetic knockout model suggested that decorin influenced stromal fibrillogenesis and transparency in healing cornea.

Molecular Engineering of Pericellular Microniche via Biomimetic Proteoglycans Modulates Cell Mechanobiology.

Molecular engineering of biological tissues using synthetic mimics of native matrix molecules can modulate the mechanical properties of the cellular microenvironment through physical interactions with existing matrix molecules, and in turn, mediate the corresponding cell mechanobiology. In articular cartilage, the pericellular matrix (PCM) is the immediate microniche that regulates cell fate, signaling, and metabolism. The negatively charged osmo-environment, as endowed by PCM proteoglycans, is a key biophysical cue for cell mechanosensing. This study demonstrated that biomimetic proteoglycans (BPGs), which mimic the ultrastructure and polyanionic nature of native proteoglycans, can be used to molecularly engineer PCM micromechanics and cell mechanotransduction in cartilage. Upon infiltration into bovine cartilage explant, we showed that localization of BPGs in the PCM leads to increased PCM micromodulus and enhanced chondrocyte intracellular calcium signaling. Applying molecular force spectroscopy, we revealed that BPGs integrate with native PCM through augmenting the molecular adhesion of aggrecan, the major PCM proteoglycan, at the nanoscale. These interactions are enabled by the biomimetic "bottle-brush" ultrastructure of BPGs and facilitate the integration of BPGs within the PCM. Thus, this class of biomimetic molecules can be used for modulating molecular interactions of pericellular proteoglycans and harnessing cell mechanosensing. Because the PCM is a prevalent feature of various cell types, BPGs hold promising potential for improving regeneration and disease modification for not only cartilage-related healthcare but many other tissues and diseases.

Physicochemical factors affecting flocculating properties of the proteoglycan isolated from Rhodococcus opacus

The water-soluble fraction of proteoglycan RS-89 isolated from the Rhodococcus opacus FCL89 and composed of 64.6% polysaccharide and 9.44% protein has been studied as regards its flocculating activity. The RS-89 polysaccharide component includes mannose, galactose and glucose at the molar ratio of 2.7: 1.3: 1. The basic factors affecting flocculating activity of the RS-89 have been established. Additionally, the kinetics of kaolin sedimentation without and with the bioflocculant was investigated. The presence of divalent metal ions had a positive effect on the flocculating activity of the RS-89. The addition of Ca2+ increased the RS-89 flocculating activity in comparison to the other studied metals. It was proved that the proteoglycan RS-89 achieved the highest flocculating activity at the concentration equal to 2 mg/L and in the presence of 10 mmol/L of Ca2+. The zeta potential values are less negative when there is an interaction between the kaolin particles and metal ions without the RS-89 in the tested systems. Therefore, the proposed mechanism to describe the proteoglycan interaction with kaolin particles in the presence of divalent ions includes charge neutralization and a bridging mechanism.

Inhibition of Chondroitin Sulfate Proteoglycan Interactions With Receptor PTPσ Promotes Neurogenesis and Recovery From Stroke

Current treatment strategies for stroke primarily focus on reducing the size of ischemic damage and on rescuing dying cells. However, regenerative processes might provide a second target. Neuroregeneration after stroke takes two forms, intrinsic stem cell derived neurons to replace the dead cells and axonal sprouting. Unfortunately, these recuperative efforts are quite inefficient in mammals, leading to only modest improvements in function over time. We have discovered that a major impediment to axon sprouting/regeneration and precursor cell migrations after CNS trauma is a family of potently inhibitory extracellular matrix molecules called chondroitin sulphate proteoglycans. Recently, we have used a small TAT-peptide (Intracellular Sigma Peptide or ISP) that can be administered easily via a systemic route but which enters the CNS to potently and specifically block a major proteoglycan receptor on axons and stem cells (PTPσ) that mediates the inhibition. Utilizing cre mediated inducible gene deletion technology, we have established PTPσ KO adult neural stem cell cultures. We also tested the effects of post-stroke ISP treatment on stroke functional recovery and its influence on neurogenesis and axonal sprouting after stroke. Our results demonstrated that conditional knockout of PTPσ in adult SVZ NSCs has similar effects as ISP peptide inhibition in regulation of adult NSCs neuronal differentiation and migration. In addition, we have also investigated the molecular signaling pathway that might mediate the ISP induced NSCs migration enhancement. Moreover, post-stroke ISP peptide treatment resulted in robust behavioral recovery in an MCAo mouse model, accompanied by extensive axonal sprouting and stem cell migrations into and around the lesion. Transcriptome analyses of peri-lesion cortex at 14 days after stroke in vehicle or ISP treated mice revealed a transcriptional signature of negative regulation of apoptotic pathways and upregulation of axonal development genes. Based on our findings, we propose that CSPGs induced by stroke play a predominant role in the inhibition of neural repair and that blocking CSPG signaling pathways will lead to enhanced neurorepair and functional recovery in stroke.

Human diamine oxidase cellular binding and internalization in vitro and rapid clearance in vivo are not mediated by N-glycans but by heparan sulfate proteoglycan interactions.

Human diamine oxidase (hDAO) rapidly inactivates histamine by deamination. No pharmacokinetic data are available to better understand its potential as a new therapeutic modality for diseases with excess local and systemic histamine, like anaphylaxis, urticaria or mastocytosis. After intravenous administration of recombinant hDAO to rats and mice, more than 90% of the dose disappeared from the plasma pool within 10min. Human DAO did not only bind to various endothelial and epithelial cell lines in vitro, but was also unexpectedly internalized and visible in granule-like structures. The uptake of rhDAO into cells was dependent on neither the asialoglycoprotein-receptor (ASGP-R) nor the mannose receptor (MR) recognizing terminal galactose or mannose residues, respectively. Competition experiments with ASGP-R and MR ligands did not block internalization in vitro or rapid clearance in vivo. The lack of involvement of N-glycans was confirmed by testing various glycosylation mutants. High but not low molecular weight heparin strongly reduced the internalization of rhDAO in HepG2 cells and HUVECs. Human DAO was readily internalized by CHO-K1 cells, but not by the glycosaminoglycan- and heparan sulfate-deficient CHO cell lines pgsA-745 and pgsD-677, respectively. A docked heparin hexasaccharide interacted well with the predicted heparin binding site 568RFKRKLPK575. These results strongly imply that rhDAO clearance in vivo and cellular uptake in vitro is independent of N-glycan interactions with the classical clearance receptors ASGP-R and MR, but is mediated by binding to heparan sulfate proteoglycans followed by internalization via an unknown receptor.

Polyplex transfection from intracerebroventricular delivery is not significantly affected by traumatic brain injury

Traumatic brain injury (TBI) is largely non-preventable and often kills or permanently disables its victims. Because current treatments for TBI merely ameliorate secondary effects of the initial injury like swelling and hemorrhaging, strategies for the induction of neuronal regeneration are desperately needed. Recent discoveries regarding the TBI-responsive migratory behavior and differentiation potential of neural progenitor cells (NPCs) found in the subventricular zone (SVZ) have prompted strategies targeting gene therapies to these cells to enhance neurogenesis after TBI. We have previously shown that plasmid polyplexes can non-virally transfect SVZ NPCs when directly injected in the lateral ventricles of uninjured mice. We describe the first reported intracerebroventricular transfections mediated by polymeric gene carriers in a murine TBI model and investigate the anatomical parameters that dictate transfection through this route of administration. Using both luciferase and GFP plasmid transfections, we show that the time delay between injury and polyplex injection directly impacts the magnitude of transfection efficiency, but that overall trends in the location of transfection are not affected by injury. Confocal microscopy of quantum dot-labeled plasmid uptake in vivo reveals association between our polymers and negatively charged NG2 chondroitin sulfate proteoglycans of the SVZ extracellular matrix. We further validate that glycosaminoglycans but not sulfate groups are required for polyplex uptake and transfection in vitro. These studies demonstrate that non-viral gene delivery is impacted by proteoglycan interactions and suggest the need for improved polyplex targeting materials that penetrate brain extracellular matrix to increase transfection efficiency in vivo.

Defective angiogenesis in CXCL12 mutant mice impairs skeletal muscle regeneration

BackgroundDuring muscle regeneration, the chemokine CXCL12 (SDF-1) and the synthesis of some specific heparan sulfates (HS) have been shown to be critical. CXCL12 activity has been shown to be heavily influenced by its binding to extracellular glycosaminoglycans (GAG) by modulating its presentation to its receptors and by generating haptotactic gradients. Although CXCL12 has been implicated in several phases of tissue repair, the influence of GAG binding under HS influencing conditions such as acute tissue destruction remains understudied.MethodsTo investigate the role of the CXCL12/HS proteoglycan interactions in the pathophysiology of muscle regeneration, we performed two models of muscle injuries (notexin and freeze injury) in mutant CXCL12Gagtm/Gagtm mice, where the CXCL12 gene having been selectively mutated in critical binding sites of CXCL12 to interact with HS. Histological, cytometric, functional transcriptomic, and ultrastructure analysis focusing on the satellite cell behavior and the vessels were conducted on muscles before and after injuries. Unless specified, statistical analysis was performed with the Mann-Whitney test.ResultsWe showed that despite normal histology of the resting muscle and normal muscle stem cell behavior in the mutant mice, endothelial cells displayed an increase in the angiogenic response in resting muscle despite the downregulated transcriptomic changes induced by the CXCL12 mutation. The regenerative capacity of the CXCL12-mutated mice was only delayed after a notexin injury, but a severe damage by freeze injury revealed a persistent defect in the muscle regeneration of CXCL12 mutant mice associated with vascular defect and fibroadipose deposition with persistent immune cell infiltration.ConclusionThe present study shows that CXCL12 is crucial for proper muscle regeneration. We highlight that this homing molecule could play an important role in drastic muscle injuries and that the regeneration defect could be due to an impairment of angiogenesis, associated with a long-lasting fibro-adipogenic scar.

Distinct Binding Interactions of α5β1-Integrin and Proteoglycans with Fibronectin

Dynamic single-molecule force spectroscopy was performed to monitor the unbinding of fibronectin with the proteoglycans syndecan-4 (SDC4) and decorin and to compare this with the unbinding characteristics of α5β1-integrin. A single energy barrier was sufficient to describe the unbinding of both SDC4 and decorin from fibronectin, whereas two barriers were observed for the dissociation of α5β1-integrin from fibronectin. The outer (high-affinity) barriers in the interactions of fibronectin with α5β1-integrin and SDC4 are characterized by larger barrier heights and widths and slower dissociation rates than those of the inner (low-affinity) barriers in the interactions of fibronectin with α5β1-integrin and decorin. These results indicate that SDC4 and (ultimately) α5β1-integrin have the ability to withstand deformation in their interactions with fibronectin, whereas the decorin-fibronectin interaction is considerably more brittle.

Protamine sulfate may prevent infections by pathogens that require heparan sulfate proteoglycan interactions, including high- and low-risk Human Papillomaviruses and Chlamydia trachomatis..

e13065 Background: Human papillomaviruses (HPVs) are the most common pathogens of the reproductive tract with 80% of the population acquiring an infection at least once in their lifetime. Globally, high-risk (oncogenic) HPVs cause 630,000 new cancer cases per year and are responsible for 99% of cervical cancers. Regardless of available screening and preventive measures, cervical cancer is the fourth most common malignancy in women worldwide causing more than 445,000 new cases and 270,000 deaths annually. Like many pathogens of the reproductive tract, initiation of HPV infections require attachment to negatively-charged heparan sulfate proteoglycans (HSPG) present in the extracellular matrix and plasma membrane of host cells. To better define the role of HSPGs in HPV infections, we used protamine sulfate (PrS), a polycationic peptide that is FDA approved to neutralize heparin. Structural similarities between HSPGs and heparin allow PrS to bind HSPGs preventing HPV-HSPG interactions and infection. In order to further evaluate proof of concept for PrS we expanded our investigation to Chlamydia trachomatis, another genital tract pathogen whose mechanism of infection has been reported to rely on HSPGs. Methods: High and low risk HPV viruses were used in prophylactic and post exposure cell-based assays and a preclinical prophylactic mouse vaginal challenge model to evaluate the effects of PrS on infection. Chlamydia trachomatis serovar L2 was also used in prophylactic cell-based assays to evaluate the effects of PrS on infection. Results: A single dose prophylactic application of PrS reduced infection by high- and low-risk HPV genotypes by up to 95% in vitro (p-value &lt; 0.001) in a dose response manner and 60% in vivo (p-value 0.05). In addition, post-HPV exposure PrS treatment significantly decreased infection. PrS showed the greatest effectiveness in the first two hours after HPV exposure. In line with our data on HPV, Chlamydia trachomatis infection showed a statistically significant decrease in cells pretreated with PrS (p-value 0.05). Conclusions: Inhibition of attachment by PrS presents a unique opportunity to provide a new cheap prophylactic modality for HPV infection, which would reduce cervical cancer global burden.

Viral pathogens hitchhike with insect sperm for paternal transmission

Arthropod-borne viruses (arboviruses) can be maternally transmitted by female insects to their offspring, however, it is unknown whether male sperm can directly interact with the arbovirus and mediate its paternal transmission. Here we report that an important rice arbovirus is paternally transmitted by the male leafhoppers by hitchhiking with the sperm. The virus-sperm binding is mediated by the interaction of viral capsid protein and heparan sulfate proteoglycan on the sperm head surfaces. Mating experiments reveal that paternal virus transmission is more efficient than maternal transmission. Such paternal virus transmission scarcely affects the fitness of adult males or their offspring, and plays a pivotal role in maintenance of viral population during seasons unfavorable for rice hosts in the field. Our findings reveal that a preferred mode of vertical arbovirus transmission has been evolved by hitchhiking with insect sperm without disturbing sperm functioning, facilitating the long-term viral epidemic and persistence in nature.

Interaction of poly-l-lysine coating and heparan sulfate proteoglycan on magnetic nanoparticle uptake by tumor cells.

BackgroundPoly-l-lysine (PLL) enhances nanoparticle (NP) uptake, but the molecular mechanism remains unresolved. We asked whether PLL may interact with negatively charged glycoconjugates on the cell surface and facilitate uptake of magnetic NPs (MNPs) by tumor cells.MethodsPLL-coated MNPs (PLL-MNPs) with positive and negative ζ-potential were prepared and characterized. Confocal and transmission electron microscopy was used to analyze cellular internalization of MNPs. A colorimetric iron assay was used to quantitate cell-associated MNPs (MNPcell).ResultsCoadministration of PLL and dextran-coated MNPs in culture enhanced cellular internalization of MNPs, with increased vesicle size and numbers/cell. MNPcell was increased by eight- to 12-fold in response to PLL in a concentration-dependent manner in human glioma and HeLa cells. However, the application of a magnetic field attenuated PLL-induced increase in MNPcell. PLL-coating increased MNPcell regardless of ζ-potential of PLL-MNPs, whereas magnetic force did not enhance MNPcell. In contrast, epigallocatechin gallate and magnetic force synergistically enhanced PLL-MNP uptake. In addition, heparin, but not sialic acid, greatly reduced the enhancement effects of PLL; however, removal of heparan sulfate from heparan sulfate proteoglycans of the cell surface by heparinase III significantly reduced MNPcell.ConclusionOur results suggest that PLL-heparan sulfate proteoglycan interaction may be the first step mediating PLL-MNP internalization by tumor cells. Given these results, PLL may facilitate NP interaction with tumor cells via a molecular mechanism shared by infection machinery of certain viruses.

Effects of Proteoglycans on Oxidative/Nitrative Stress

Objective: Enhanced production of reactive oxygen and/or nitrogen species in biological tissues leads to oxidative and nitrative stress, a general pathophysiological phenomenon playing a role in the development of various human diseases including cardiovascular and neurological disorders. Method: Reactive oxygen and/or nitrogen species interact with lipids, DNA and proteins via oxidative or radical- mediated reactions, potentially leading to cell damage or death. Proteoglycans are among the most important structural and functional macromolecules in most tissues. The chemical structure of these molecules consist of a core protein onto which one or more negatively charged glycosaminoglycan (GAG) chain(s) are covalently attached. Interaction of proteoglycans with oxidative/nitrative stress has been demonstrated in various experimental systems. In this review, we discuss the modulatory effects of proteoglycans on tissue oxidative/ nitrative stress and consequent cellular function especially in cardiovascular and neurological disorders. Conclusion: Proteoglycans have been implicated in both deleterious and potentially cytoprotective mechanisms. The protective mechanisms include chelation of positively charged transitional metal ions (e.g. iron and copper), scavenging superoxide anions by extracellular superoxide dismutase, building pericellular net and mediation of signal transduction pathways. Although these results may implicate proteoglycans as potential therapeutic targets, more research should be done to better explore proteoglycans as modulators of reactive oxygen/nitrogen species and to determine their possible therapeutic value in disorders accompanied by oxidative/ nitrative stress. Keywords: Proteoglycan, mucopolysaccharide, GAG, ROS, EC-SOD, perineural net, chelation, superoxide, nitric oxide, peroxynitrite.

Increased migration of antigen presenting cells to newly-formed lymphatic vessels in transplanted kidneys by glycol-split heparin.

BackgroundChronic renal transplant dysfunction is characterized by loss of renal function and tissue remodeling, including chronic inflammation and lymph vessel formation. Proteoglycans are known for their chemokine presenting capacity. We hypothesize that interruption of the lymphatic chemokine–proteoglycan interaction interferes with the lymphatic outflow of leukocytes from the renal graft and might decrease the anti-graft allo-immune response.MethodsIn a rat renal chronic transplant dysfunction model (female Dark-Agouti to male Wistar Furth), chemokines were profiled by qRT-PCR in microdissected tubulo-interstitial tissue. Disruption of lymphatic chemokine–proteoglycan interaction was studied by (non-anticoagulant) heparin-derived polysaccharides in vitro and in renal allografts. The renal allograft function was assessed by rise in plasma creatinine and urea.ResultsWithin newly-formed lymph vessels of transplanted kidneys, numerous CD45+ leukocytes were found, mainly MHCII+, ED-1-, IDO-, HIS14-, CD103- antigen presenting cells, most likely representing a subset of dendritic cells. Treatment of transplanted rats with regular heparin and two different (non-)anticoagulant heparin derivatives revealed worsening of kidney function only in the glycol-split heparin treated group despite a two-fold reduction of tubulo-interstitial leukocytes (p<0.02). Quantitative digital image analysis however revealed increased numbers of intra-lymphatic antigen-presenting cells only in the glycol-split heparin group (p<0.01). The number of intra-lymphatic leukocytes significantly correlates with plasma creatinine and urea, and inversely with creatinine clearance.ConclusionsTreatment of transplanted rats with glycol-split heparin significantly increases the number of intra-lymphatic antigen presenting cells, by increased renal diffusion of lymphatic chemokines, thereby increasing the activation and recruitment of antigen presenting cells towards the lymph vessel. This effect is unwanted in the transplantation setting, but might be advantageous in e.g., dendritic cell vaccination.

Function of Membrane-Associated Proteoglycans in the Regulation of Satellite Cell Growth.

Muscle growth can be divided into embryonic and postnatal periods. During the embryonic period, mesenchymal stem cells proliferate and differentiate to form muscle fibers. Postnatal muscle growth (hypertrophy) is characterized by the enlargement of existing muscle fiber size. Satellite cells (also known as adult myoblasts) are responsible for hypertrophy. The activity of satellite cells can be regulated by their extracellular matrix (ECM). The ECM is composed of collagens, proteoglycans, non-collagenous glycoproteins, cytokines and growth factors. Proteoglycans contain a central core protein with covalently attached glycosaminoglycans (GAGs: chondroitin sulfate, keratan sulfate, dermatan sulfate, and heparan sulfate) and N- or O-linked glycosylation chains. Membrane-associated proteoglycans attach to the cell membrane either through a glycosylphosphatidylinositol anchor or transmembrane domain. The GAGs can bind proteins including cytokines and growth factors. Both cytokines and growth factors play important roles in regulating satellite cell growth and development. Cytokines are generally associated with immune cells. However, cytokines can also affect muscle cell development. For instance, interleukin-6, tumor necrosis factor-α, and leukemia inhibitory factor have been reported to affect the proliferation and differentiation of satellite cells and myoblasts. Growth factors are potent stimulators or inhibitors of satellite cell proliferation and differentiation. The proper function of some cytokines and growth factors requires an interaction with the cell membrane-associated proteoglycans to enhance the affinity to bind to their primary receptors to initiate downstream signal transduction. This chapter is focused on the interaction of membrane-associated proteoglycans with cytokines and growth factors, and their role in satellite cell growth and development.

The interaction of heparan sulfate proteoglycans with endothelial transglutaminase-2 limits VEGF165-induced angiogenesis.

Sprouting angiogenesis is stimulated by vascular endothelial growth factor (VEGF165) that is localized in the extracellular matrix (ECM) and binds to heparan sulfate (HS)-bearing proteins known as heparan sulfate proteoglycans (HSPGs). VEGF165 presentation by HSPGs enhances VEGF receptor-2 (VEGFR2) signaling. We investigated the effect of TG2, which binds to HSPGs, on the interaction between VEGF165 and HS and angiogenesis. Mice with tg2 deficiency showed transiently enhanced retina vessel formation and increased vascularization of VEGF165-containing Matrigel implants. In addition, endothelial cells in which TG2 was knocked down exhibited enhanced VEGF165-induced sprouting and migration, which was associated with increased phosphorylation of VEGFR2 at Tyr(951) and its targets Src and Akt. TG2 knockdown did not affect the phosphorylation of VEGFR2 at Tyr(1175) or cell proliferation in response to VEGF165 and sprouting or signaling in response to VEGF121. Decreased phosphorylation of VEGFR2 at Tyr(951) was due to ECM-localized TG2, which reduced the binding of VEGF165 to endothelial ECM in a manner that required its ability to bind to HS but not its catalytic activity. Surface plasmon resonance assays demonstrated that TG2 impeded the interaction between VEGF165 and HS. These results show that TG2 controls the formation of VEGF165-HSPG complexes and suggest that this regulation could be pharmacologically targeted to modulate developmental and therapeutic angiogenesis.

Structural basis for extracellular cis and trans RPTPσ signal competition in synaptogenesis.

Receptor protein tyrosine phosphatase sigma (RPTPσ) regulates neuronal extension and acts as a presynaptic nexus for multiple protein and proteoglycan interactions during synaptogenesis. Unknown mechanisms govern the shift in RPTPσ function, from outgrowth promotion to synaptic organization. Here, we report crystallographic, electron microscopic and small-angle X-ray scattering analyses, which reveal sufficient inter-domain flexibility in the RPTPσ extracellular region for interaction with both cis (same cell) and trans (opposite cell) ligands. Crystal structures of RPTPσ bound to its postsynaptic ligand TrkC detail an interaction surface partially overlapping the glycosaminoglycan-binding site. Accordingly, heparan sulphate and heparin oligomers compete with TrkC for RPTPσ binding in vitro and disrupt TrkC-dependent synaptic differentiation in neuronal co-culture assays. We propose that transient RPTPσ ectodomain emergence from the presynaptic proteoglycan layer allows capture by TrkC to form a trans-synaptic complex, the consequent reduction in RPTPσ flexibility potentiating interactions with additional ligands to orchestrate excitatory synapse formation.

Novel insights into matrix pathobiology regulatory mechanisms in health and disease.

Matrix macromolecules exhibit leading roles in tissue properties, physiological processes, as well as the development and progression of several diseases. This thematic series covers emerging areas of research in the matrix macromolecule field and includes epigenetics, stem cells, microRNAs, as well as proteoglycan interactions with proteolytic enzymes. Current knowledge of these aspects will elucidate their regulatory mechanisms in pathophysiology and aid the design of novel pharmacological agents.Accompanied by a podcast, listen now. Or listen in iTunes