Glycosaminoglycans in extracellular matrix organisation: are concepts from soft matter physics key to understanding the formation of perineuronal nets?

Vacuum Ultraviolet (VUV)-Induced Physicochemical Engineering of Titanium: Enhanced Fibroblast Activity, Redox System, and Glycosaminoglycan Binding for Soft Tissue Integration

Bacterial invasion at the titanium-tissue interface causes peri-implant inflammation, posing challenges for implants in orthopedics, maxillofacial prosthetics, and dentistry. This study hypothesized that titanium surface decarbonization improves soft tissue cell adhesion and growth. One-minute vacuum ultraviolet (VUV) light treatment at 172 nm reduced surface carbon from 60% to 29% without altering surface topography, making surfaces hydrophilic and hydro-attractive. Human fibroblasts attached to VUV-treated surfaces 2-4 times more frequently than untreated surfaces, with an even greater increase on tilted and curved surfaces. Fibroblast proliferation rose 2-6 times, with an expedited G1-to-S phase transition. Cell retention under dislodging forces increased 2-5 times on VUV-treated surfaces. RNA sequencing showed upregulation of extracellular matrix production, growth factors, cell cycle progression, antioxidant defenses, and proteoglycan/glycosaminoglycan (GAG)-binding, alongside downregulation of the inflammatory response on VUV-treated titanium surfaces. An oxidative stress test showed minimal adverse effects from hydrogen peroxide on cells on VUV-treated surfaces, attributed to increased intracellular glutathione reserves. Enhanced adhesion on VUV-treated titanium was negated by treating the cells with GAG-cleaving enzymes. These findings demonstrate that VUV-mediated decarbonization enhances fibroblast attachment, proliferation, and adhesion by fostering homeostatic cellular phenotypes involving proteoglycan/GAG interactions and antioxidant defense, offering a strategy to improve the soft tissue sealing around titanium implants.

The structural organisation of pentraxin-3 and its interactions with heavy chains of inter-α-inhibitor regulate crosslinking of the hyaluronan matrix

Pentraxin-3 (PTX3) is an octameric protein, comprised of eight identical protomers, that has diverse functions in reproductive biology, innate immunity and cancer. PTX3 interacts with the large polysaccharide hyaluronan (HA) to which heavy chains (HCs) of the inter-α-inhibitor (IαI) family of proteoglycans are covalently attached, playing a key role in the (non-covalent) crosslinking of HC•HA complexes. These interactions stabilise the cumulus matrix, essential for ovulation and fertilisation in mammals, and are also implicated in the formation of pathogenic matrices in the context of viral lung infections. To better understand the physiological and pathological roles of PTX3 we have analysed how its quaternary structure underpins HA crosslinking via its interactions with HCs. A combination of X-ray crystallography, cryo-electron microscopy (cryo-EM) and AlphaFold predictive modelling revealed that the C-terminal pentraxin domains of the PTX3 octamer are arranged in a central cube, with two long extensions on either side, each formed from four protomers assembled into tetrameric coiled-coil regions, essentially as described by (Noone et al., 2022; doi:10.1073/pnas.2208144119). From crystallography and cryo-EM data, we identified a network of inter-protomer salt bridges that facilitate the assembly of the octamer. Small angle X-ray scattering (SAXS) validated our model for the octameric protein, including the analysis of two PTX3 constructs: a tetrameric 'Half-PTX3' and a construct missing the 24 N-terminal residues (Δ1-24_PTX3). SAXS determined a length of ∼520 Å for PTX3 and, combined with 3D variability analysis of cryo-EM data, defined the flexibility of the N-terminal extensions. Biophysical analyses revealed that the prototypical heavy chain HC1 does not interact with PTX3 at pH 7.4, consistent with our previous studies showing that, at this pH, PTX3 only associates with HC•HA complexes if they are formed in its presence. However, PTX3 binds to HC1 at acidic pH, and can also be incorporated into pre-formed HC•HA complexes under these conditions. This provides a novel mechanism for the regulation of PTX3-mediated HA crosslinking (e.g., during inflammation), likely mediated by a pH-dependent conformational change in HC1. The PTX3 octamer was found to associate simultaneously with up to eight HC1 molecules and, thus, has the potential to form a major crosslinking node within HC•HA matrices, i.e., where the physical and biochemical properties of resulting matrices could be tuned by the HC/PTX3 composition.

Versican controlled by Lmx1b regulates hyaluronate density and hydration for semicircular canal morphogenesis

During inner ear semicircular canal morphogenesis in zebrafish, patterned canal-genesis zones express genes for extracellular matrix component synthesis. These include hyaluronan and the hyaluronan-binding chondroitin sulfate proteoglycan Versican, which are abundant in the matrices of many developing organs. Charged hyaluronate polymers play a key role in canal morphogenesis through osmotic swelling. However, the developmental factor(s) that pattern the synthesis of the matrix components and regulation of hyaluronate density and swelling are unknown. Here, we identify the transcription factor Lmx1b as a positive transcriptional regulator of hyaluronan, Versican, and chondroitin synthesis genes crucial for canal morphogenesis. We show that Versican regulates hyaluronan density through its protein core, whereas the charged chondroitin side chains contribute to the hydration of hyaluronate-containing extracellular matrices. Versican-tuned properties of hyaluronate matrices may be a broadly used mechanism in morphogenesis with important implications for understanding diseases in which these matrices are impaired, and for hydrogel engineering for tissue regeneration.

Modulation of electrical activity of proteinoid microspheres with chondroitin sulfate clusters

Proteinoids-thermal proteins-are produced by heating amino acids to their melting point and initiation of polymerisation to produce polymeric chains. Proteinoids swell in aqueous solution into hollow microspheres. The proteinoid microspheres produce endogenous burst of electrical potential spikes and change patterns of their electrical activity in response to illumination. These microspheres were proposed as proto-neurons in 1950s. To evaluate pathways of potential evolution of these proto-neurons and their applicability of chimera neuromorphic circuits we decided to hybridise them with hondroitin sulphate (CS) clusters, which form a part of the brain extracellular matrix. We found a novel synergistic interaction between CS clusters and proteinoids that dramatically affects patterns of electrical activity of proteinoid microspheres. Our study might shed light on evolution of synaptic plasticity's molecular mechanisms and the role of extracellular matrix-protein interactions in learning, and open up possibilities for novel methods in unconventional computing and the development of adaptable, brain-inspired computational systems.

Improved Detection of Polysulfated Oligosaccharides by Mass Spectrometry Applicable to Miniaturized Samples

The study of biomolecules and their interactions in their natural environment requires increasingly sophisticated technological and methodological developments. The complexity of these developments is due, among other things, to the nature of these molecules and the small quantities available depending on their origin. In this context, this study focuses on the conditions for improving the detection of glycosaminoglycans on a miniaturized scale by mass spectrometry. These multicharged anionic linear polysaccharides are in fact difficult to study by mass spectrometry and can present, for a given molecule, a large number of signals linked to different charge states, to the loss of one or more sulfate groups and to the presence of different adducts, which reduces sensitivity and complicates the interpretation of the spectra. In order to reduce this complexity, we have investigated different sample preparation methods applicable to small sample volumes. The development of home-made capillary ion-exchange columns, for example, makes it possible to control the adducts formed in nano-ESI coupling. However, their use on a miniaturized scale for detection by MALDI-TOF-MS does not allow for performances as high as those obtained with treatment with a commercial DOWEXTM resin. However, experimental results allowed us to demonstrate that the presence of DOWEXTM resin colloid residues in the aqueous phase greatly improves the quality of the spectra obtained by MALDI-TOFMS on a Fondaparinux model glycosaminoglycan.

Chemical modification of hyaluronan oligosaccharides differentially modulates hyaluronan-hyaladherin interactions

The glycosaminoglycan hyaluronan (HA) is a ubiquitous, nonsulfated polysaccharide with diverse biological roles mediated through its interactions with HA-binding proteins (HABPs). Most HABPs belong to the Link module superfamily, including the major HA receptor, CD44, and secreted protein TSG-6, which catalyzes the covalent transfer of heavy chains from inter-α-inhibitor onto HA. The structures of the HA-binding domains (HABDs) of CD44 (HABD_CD44) and TSG-6 (Link_TSG6) have been determined and their interactions with HA extensively characterized. The mechanisms of binding are different, with Link_TSG6 interacting with HA primarily via ionic and CH-π interactions, whereas HABD_CD44 binds solely via hydrogen bonds and van der Waals forces. Here, we exploit these differences to generate HA oligosaccharides, chemically modified at their reducing ends, that bind specifically and differentially to these target HABPs. Hexasaccharides (HA6AN) modified with 2- or 3-aminobenzoic acid (HA6-2AA, HA6-3AA) or 2-amino-4-methoxybenzoic acid (HA6-2A4MBA), had increased affinities for Link_TSG6 compared to unmodified HA6AN. These modifications did not increase the affinity for CD44_HABD. A model of HA6-2AA (derived from the solution dynamic 3D structure of HA4-2AA) was docked into the Link_TSG6 structure, providing evidence that the 2AA-carboxyl forms a salt bridge with Arginine-81. These modeling results informed a second series of chemical modifications for HA oligosaccharides, which again showed differential binding to the two proteins. Several modifications to HA4 and HA6 were found to convert the oligosaccharide into substrates for heavy chain transfer, whereas unmodified HA4 and HA6 are not. This study has generated valuable research tools to further understand HA biology.

Versican controlled by Lmx1b regulates hyaluronate density and hydration for semicircular canal morphogenesis

During inner ear semicircular canal morphogenesis in zebrafish, patterned canal-genesis zones express genes for extracellular matrix component synthesis. These include hyaluronan and the hyaluronan-binding chondroitin sulfate proteoglycan Versican, which are abundant in the matrices of many developing organs. Charged hyaluronate polymers play a key role in canal morphogenesis through osmotic swelling. However, the developmental factor(s) that control the synthesis of the matrix components and regulation of hyaluronate density and swelling are unknown. Here, we identify the transcription factor, Lmx1b, as a positive transcriptional regulator of hyaluronan, Versican, and chondroitin synthesis genes crucial for canal morphogenesis. We show that Versican regulates hyaluronan density through its protein core, whereas the charged chondroitin side chains contribute to the osmotic swelling of hyaluronate. Versican-tuned properties of hyaluronate matrices may be a broadly used mechanism in morphogenesis with important implications for understanding diseases where these matrices are impaired, and for hydrogel engineering for tissue regeneration.

Rapid alkalinization factor 22 has a structural and signalling role in root hair cell wall assembly

Pressurized cells with strong walls make up the hydrostatic skeleton of plants. Assembly and expansion of such stressed walls depend on a family of secreted RAPID ALKALINIZATION FACTOR (RALF) peptides, which bind both a membrane receptor complex and wall-localized LEUCINE-RICH REPEAT EXTENSIN (LRXs) in a mutually exclusive way. Here we show that, in root hairs, the RALF22 peptide has a dual structural and signalling role in cell expansion. Together with LRX1, it directs the compaction of charged pectin polymers at the root hair tip into periodic circumferential rings. Free RALF22 induces the formation of a complex with LORELEI-LIKE-GPI-ANCHORED PROTEIN 1 and FERONIA, triggering adaptive cellular responses. These findings show how a peptide simultaneously functions as a structural component organizing cell wall architecture and as a feedback signalling molecule that regulates this process depending on its interaction partners. This mechanism may also underlie wall assembly and expansion in other plant cell types.

Inter-alpha-trypsin inhibitor (IαI) and hyaluronan modifications enhance the innate immune response to influenza virus in the lung

The inter-alpha-trypsin inhibitor (IαI) complex is composed of the bikunin core protein with a single chondroitin sulfate (CS) attached and one or two heavy chains (HCs) covalently linked to the CS chain. The HCs from IαI can be transferred to hyaluronan (HA) through a TNFα-stimulated gene-6 (TSG-6) dependent process to form an HC•HA matrix. Previous studies reported increased IαI, HA, and HC•HA complexes in mouse bronchoalveolar lavage fluid (BALF) post-influenza infection. However, the expression and incorporation of HCs into the HA matrix of the lungs during the clinical course of influenza A virus (IAV) infection and the biological significance of the HC•HA matrix are poorly understood. The present study aimed to better understand the composition of HC•HA matrices in mice infected with IAV and how these matrices regulate the host pulmonary immune response. In IAV infected mice bikunin, HC1-3, TSG-6, and HAS1-3 all show increased gene expression at various times during a 12-day clinical course. The increased accumulation of IαI and HA was confirmed in the lungs of infected mice using immunohistochemistry and quantitative digital pathology. Western blots confirmed increases in the IαI components in BALF and lung tissue at 6 days post-infection (dpi). Interestingly, HCs and bikunin recovered from BALF and plasma from mice 6 dpi with IAV, displayed differences in the HC composition by Western blot analysis and differences in bikunin's CS chain sulfation patterns by mass spectrometry analysis. This strongly suggests that the IαI components were synthesized in the lungs rather than translocated from the vascular compartment. HA was significantly increased in BALF at 6 dpi, and the HA recovered in BALF and lung tissues were modified with HCs indicating the presence of an HC•HA matrix. In vitro experiments using polyinosinic-polycytidylic acid (poly(I:C)) treated mouse lung fibroblasts (MLF) showed that modification of HA with HCs increased cell-associated HA, and that this increase was due to the retention of HA in the MLF glycocalyx. In vitro studies of leukocyte adhesion showed differential binding of lymphoid (Hut78), monocyte (U937), and neutrophil (dHL60) cell lines to HA and HC•HA matrices. Hut78 cells adhered to immobilized HA in a size and concentration-dependent manner. In contrast, the binding of dHL60 and U937 cells depended on generating a HC•HA matrix by MLF. Our in vivo findings, using multiple bronchoalveolar lavages, correlated with our in vitro findings in that lymphoid cells bound more tightly to the HA-glycocalyx in the lungs of influenza-infected mice than neutrophils and mononuclear phagocytes (MNPs). The neutrophils and MNPs were associated with a HC•HA matrix and were more readily lavaged from the lungs. In conclusion, this work shows increased IαI and HA accumulation and the formation of a HC•HA matrix in mouse lungs post-IAV infection. The formation of HA and HC•HA matrices could potentially create specific microenvironments in the lungs for immune cell recruitment and activation during IAV infection.

Targeted Analysis of the Size Distribution of Heavy Chain-Modified Hyaluronan with Solid-State Nanopores

The glycosaminoglycan hyaluronan (HA) plays important roles in diverse physiological functions where the distribution of its molecular weight (MW) can influence its behavior and is known to change in response to disease conditions. During inflammation, HA undergoes a covalent modification in which heavy chain subunits of the inter-alpha-inhibitor family of proteins are transferred to its structure, forming heavy chain-HA (HC•HA) complexes. While limited assessments of HC•HA have been performed previously, determining the size distribution of its HA component remains a challenge. Here, we describe a selective method for extracting HC•HA from mixtures that yields material amenable to MW analysis with a solid-state nanopore sensor. After demonstrating the approach in vitro, we validate extraction of HC•HA from osteoarthritic human synovial fluid as a model complex biological matrix. Finally, we apply our technique to pathophysiology by measuring the size distributions of HC•HA and total HA in an equine model of synovitis.

Competitive Specific Anchorage of Molecules onto Surfaces: Quantitative Control of Grafting Densities and Contamination by Free Anchors

The formation of surfaces decorated with biomacromolecules such as proteins, glycans, or nucleic acids with well-controlled orientations and densities is of critical importance for the design of in vitro models, e.g., synthetic cell membranes and interaction assays. To this effect, ligand molecules are often functionalized with an anchor that specifically binds to a surface with a high density of binding sites, providing control over the presentation of the molecules. Here, we present a method to robustly and quantitatively control the surface density of one or several types of anchor-bearing molecules by tuning the relative concentrations of target molecules and free anchors in the incubation solution. We provide a theoretical background that relates incubation concentrations to the final surface density of the molecules of interest and present effective guidelines toward optimizing incubation conditions for the quantitative control of surface densities. Focusing on the biotin anchor, a commonly used anchor for interaction studies, as a salient example, we experimentally demonstrate surface density control over a wide range of densities and target molecule sizes. Conversely, we show how the method can be adapted to quality control the purity of end-grafted biopolymers such as biotinylated glycosaminoglycans by quantifying the amount of residual free biotin reactant in the sample solution.

Plant cell wall patterning and expansion mediated by protein-peptide-polysaccharide interaction

Assembly of cell wall polysaccharides into specific patterns is required for plant growth. A complex of RAPID ALKALINIZATION FACTOR 4 (RALF4) and its cell wall-anchored LEUCINE-RICH REPEAT EXTENSIN 8 (LRX8)-interacting protein is crucial for cell wall integrity during pollen tube growth, but its molecular connection with the cell wall is unknown. Here, we show that LRX8-RALF4 complexes adopt a heterotetrametric configuration in vivo, displaying a dendritic distribution. The LRX8-RALF4 complex specifically interacts with demethylesterified pectins in a charge-dependent manner through RALF4's polycationic surface. The LRX8-RALF4-pectin interaction exerts a condensing effect, patterning the cell wall's polymers into a reticulated network essential for wall integrity and expansion. Our work uncovers a dual structural and signaling role for RALF4 in pollen tube growth and in the assembly of complex extracellular polymers.

Computational modeling of protein-carbohydrate interactions: Current trends and future challenges

The article leads the reader through an up-to-date presentation of the concepts, developments, and main applications of computational modeling to study protein-carbohydrate interactions. It follows with the presentation of some current issues and perspectives arising from the expected evolution of generic methodological developments in deep learning, immersive analytics, and virtual reality for molecular visualization and data management. Such methodological developments for macromolecular interactions would greatly benefit a wide range of scientific endeavors in the field of carbohydrate chemistry and biochemistry, including the following interrelated efforts dealing with highly crowded media, with examples concerning glycoside transferases, the extracellular matrix, and the exploration of interactions between complex carbohydrates and intrinsically disordered proteins.

A One-Bead-Per-Saccharide (1BPS) Model for Glycosaminoglycans

Glycosaminoglycans (GAGs) are polysaccharide compounds that play key roles in various biological processes. GAGs are important structural components of cartilage and the extracellular matrix of the brain. Due to the large size of these polysaccharides, coarse-grained approaches are indispensable for modeling these biopolymers. We develop a one-bead-per-saccharide model of chondroitin sulfates and hyaluronic acid based on an existing three-bead-per-saccharide coarse-grained model. Our coarse graining is carried out by using iterative Boltzmann inversion (IBI), including an additional coupling potential to incorporate the correlation between dihedral angles. The predictions of the model are verified against those of the existing three-bead-per-saccharin model and the experimental radius of gyration for hyaluronic acid.

V3: an enigmatic isoform of the proteoglycan versican

V3 is an isoform of the extracellular matrix (ECM) proteoglycan (PG) versican generated through alternative splicing of the versican gene such that the two major exons coding for sequences in the protein core that support chondroitin sulfate (CS) glycosaminoglycan (GAG) chain attachment are excluded. Thus, versican V3 isoform carries no GAGs. A survey of PubMed reveals only 50 publications specifically on V3 versican, so it is a very understudied member of the versican family, partly because to date there are no antibodies that can distinguish V3 from the CS-carrying isoforms of versican, that is, to facilitate functional and mechanistic studies. However, a number of in vitro and in vivo studies have identified the expression of the V3 transcript during different phases of development and in disease, and selective overexpression of V3 has shown dramatic phenotypic effects in "gain and loss of function" studies in experimental models. Thus, we thought it would be useful and instructive to discuss the discovery, characterization, and the putative biological importance of the enigmatic V3 isoform of versican.

Hyaluronan hydrates and compartmentalises the CNS/PNS extracellular matrix and provides niche environments conducive to the optimisation of neuronal activity

The central nervous system/peripheral nervous system (CNS/PNS) extracellular matrix is a dynamic and highly interactive space-filling, cell-supportive, matrix-stabilising, hydrating entity that creates and maintains tissue compartments to facilitate regional ionic micro-environments and micro-gradients that promote optimal neural cellular activity. The CNS/PNS does not contain large supportive collagenous and elastic fibrillar networks but is dominated by a high glycosaminoglycan content, predominantly hyaluronan (HA) and collagen is restricted to the brain microvasculature, blood-brain barrier, neuromuscular junction and meninges dura, arachnoid and pia mater. Chondroitin sulphate-rich proteoglycans (lecticans) interactive with HA have stabilising roles in perineuronal nets and contribute to neural plasticity, memory and cognitive processes. Hyaluronan also interacts with sialoproteoglycan associated with cones and rods (SPACRCAN) to stabilise the interphotoreceptor matrix and has protective properties that ensure photoreceptor viability and function is maintained. HA also regulates myelination/re-myelination in neural networks. HA fragmentation has been observed in white matter injury, multiple sclerosis, and traumatic brain injury. HA fragments (2 × 105  Da) regulate oligodendrocyte precursor cell maturation, myelination/remyelination, and interact with TLR4 to initiate signalling cascades that mediate myelin basic protein transcription. HA and its fragments have regulatory roles over myelination which ensure high axonal neurotransduction rates are maintained in neural networks. Glioma is a particularly invasive brain tumour with extremely high mortality rates. HA, CD44 and RHAMM (receptor for HA-mediated motility) HA receptors are highly expressed in this tumour. Conventional anti-glioma drug treatments have been largely ineffective and surgical removal is normally not an option. CD44 and RHAMM glioma HA receptors can potentially be used to target gliomas with PEP-1, a cell-penetrating HA-binding peptide. PEP-1 can be conjugated to a therapeutic drug; such drug conjugates have successfully treated dense non-operative tumours in other tissues, therefore similar applications warrant exploration as potential anti-glioma treatments.

Glycosaminoglycans: What Remains To Be Deciphered?

Glycosaminoglycans (GAGs) are complex polysaccharides exhibiting a vast structural diversity and fulfilling various functions mediated by thousands of interactions in the extracellular matrix, at the cell surface, and within the cells where they have been detected in the nucleus. It is known that the chemical groups attached to GAGs and GAG conformations comprise "glycocodes" that are not yet fully deciphered. The molecular context also matters for GAG structures and functions, and the influence of the structure and functions of the proteoglycan core proteins on sulfated GAGs and vice versa warrants further investigation. The lack of dedicated bioinformatic tools for mining GAG data sets contributes to a partial characterization of the structural and functional landscape and interactions of GAGs. These pending issues will benefit from the development of new approaches reviewed here, namely (i) the synthesis of GAG oligosaccharides to build large and diverse GAG libraries, (ii) GAG analysis and sequencing by mass spectrometry (e.g., ion mobility-mass spectrometry), gas-phase infrared spectroscopy, recognition tunnelling nanopores, and molecular modeling to identify bioactive GAG sequences, biophysical methods to investigate binding interfaces, and to expand our knowledge and understanding of glycocodes governing GAG molecular recognition, and (iii) artificial intelligence for in-depth investigation of GAGomic data sets and their integration with proteomics.

The extracellular matrix and the immune system: A mutually dependent relationship

For decades, immunologists have studied the role of circulating immune cells in host protection, with a more recent appreciation of immune cells resident within the tissue microenvironment and the intercommunication between nonhematopoietic cells and immune cells. However, the extracellular matrix (ECM), which comprises at least a third of tissue structures, remains relatively underexplored in immunology. Similarly, matrix biologists often overlook regulation of complex structural matrices by the immune system. We are only beginning to understand the scale at which ECM structures determine immune cell localization and function. Additionally, we need to better understand how immune cells dictate ECM complexity. This review aims to highlight the potential for biological discovery at the interface of immunology and matrix biology.

Perineuronal nets restrict transport near the neuron surface: A coarse-grained molecular dynamics study

Perineuronal nets (PNNs) are mesh-like extracellular matrix structures that wrap around certain neurons in the central nervous system. They are hypothesized to stabilize memories in the brain and act as a barrier between cell and extracellular space. As a means to study the impact of PNNs on diffusion, the nets were approximated by negatively charged polymer brushes and simulated by coarse-grained molecular dynamics. Diffusion constants of single neutral and single charged particles were obtained in directions parallel and perpendicular to the brush substrate. The results for the neutral particle were compared to different theories of diffusion in a heuristic manner. Diffusion was found to be considerably reduced for brush spacings smaller than 10 nm, with a pronounced anisotropy for dense brushes. The exact dynamics of the chains was found to have a negligible impact on particle diffusion. The resistance of the brush proved small compared to typical values of the membrane resistance of a neuron, indicating that PNNs likely contribute little to the total resistance of an enwrapped neuron.

Presence of chondroitin sulphate and requirement for heparan sulphate biosynthesis in the developing zebrafish inner ear

Epithelial morphogenesis to form the semicircular canal ducts of the zebrafish inner ear depends on the production of the large glycosaminoglycan hyaluronan, which is thought to contribute to the driving force that pushes projections of epithelium into the lumen of the otic vesicle. Proteoglycans are also implicated in otic morphogenesis: several of the genes coding for proteoglycan core proteins, together with enzymes that synthesise and modify their polysaccharide chains, are expressed in the developing zebrafish inner ear. In this study, we demonstrate the highly specific localisation of chondroitin sulphate to the sites of epithelial projection outgrowth in the ear, present before any morphological deformation of the epithelium. Staining for chondroitin sulphate is also present in the otolithic membrane, whereas the otoliths are strongly positive for keratan sulphate. We show that heparan sulphate biosynthesis is critical for normal epithelial projection outgrowth, otolith growth and tethering. In the ext2 mutant ear, which has reduced heparan sulphate levels, but continues to produce hyaluronan, epithelial projections are rudimentary, and do not grow sufficiently to meet and fuse to form the pillars of tissue that normally span the otic lumen. Staining for chondroitin sulphate and expression of versican b, a chondroitin sulphate proteoglycan core protein gene, persist abnormally at high levels in the unfused projections of the ext2 mutant ear. We propose a model for wild-type epithelial projection outgrowth in which hyaluronan and proteoglycans are linked to form a hydrated gel that fills the projection core, with both classes of molecule playing essential roles in zebrafish semicircular canal morphogenesis.

A quartz crystal microbalance method to quantify the size of hyaluronan and other glycosaminoglycans on surfaces

Hyaluronan (HA) is a major component of peri- and extra-cellular matrices and plays important roles in many biological processes such as cell adhesion, proliferation and migration. The abundance, size distribution and presentation of HA dictate its biological effects and are also useful indicators of pathologies and disease progression. Methods to assess the molecular mass of free-floating HA and other glycosaminoglycans (GAGs) are well established. In many biological and technological settings, however, GAGs are displayed on surfaces, and methods to obtain the size of surface-attached GAGs are lacking. Here, we present a method to size HA that is end-attached to surfaces. The method is based on the quartz crystal microbalance with dissipation monitoring (QCM-D) and exploits that the softness and thickness of films of grafted HA increase with HA size. These two quantities are sensitively reflected by the ratio of the dissipation shift (ΔD) and the negative frequency shift (- Δf) measured by QCM-D upon the formation of HA films. Using a series of size-defined HA preparations, ranging in size from ~ 2 kDa tetrasaccharides to ~ 1 MDa polysaccharides, we establish a monotonic yet non-linear standard curve of the ΔD/ - Δf ratio as a function of HA size, which reflects the distinct conformations adopted by grafted HA chains depending on their size and surface coverage. We demonstrate that the standard curve can be used to determine the mean size of HA, as well as other GAGs, such as chondroitin sulfate and heparan sulfate, of preparations of previously unknown size in the range from 1 to 500 kDa, with a resolution of better than 10%. For polydisperse samples, our analysis shows that the process of surface-grafting preferentially selects smaller GAG chains, and thus reduces the average size of GAGs that are immobilised on surfaces comparative to the original solution sample. Our results establish a quantitative method to size HA and other GAGs grafted on surfaces, and also highlight the importance of sizing GAGs directly on surfaces. The method should be useful for the development and quality control of GAG-based surface coatings in a wide range of research areas, from molecular interaction analysis to biomaterials coatings.

Extracellular Matrix in Neural Plasticity and Regeneration

The extracellular matrix (ECM) is a fundamental component of biological tissues. The ECM in the central nervous system (CNS) is unique in both composition and function. Functions such as learning, memory, synaptogenesis, and plasticity are regulated by numerous ECM molecules. The neural ECM acts as a non-specific physical barrier that modulates neuronal plasticity and axon regeneration. There are two specialized types of ECM in the CNS, diffuse perisynaptic ECM and condensed ECM, which selectively surround the perikaryon and initial part of dendritic trees in subtypes of neurons, forming perineuronal nets. This review presents the current knowledge about the role of important neuronal ECM molecules in maintaining the basic functions of a neuron, including electrogenesis and the ability to form neural circuits. The review mainly focuses on the role of ECM components that participate in the control of key events such as cell survival, axonal growth, and synaptic remodeling. Particular attention is drawn to the numerous molecular partners of the main ECM components. These regulatory molecules are integrated into the cell membrane or disposed into the matrix itself in solid or soluble form. The interaction of the main matrix components with molecular partners seems essential in molecular mechanisms controlling neuronal functions. Special attention is paid to the chondroitin sulfate proteoglycan 4, type 1 transmembrane protein, neural-glial antigen 2 (NG2/CSPG4), whose cleaved extracellular domain is such a molecular partner that it not only acts directly on neural and vascular cells, but also exerts its influence indirectly by binding to resident ECM molecules.

Role of the Extracellular Matrix in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disease with complex pathological characteristics, whose etiology and pathogenesis are still unclear. Over the past few decades, the role of the extracellular matrix (ECM) has gained importance in neurodegenerative disease. In this review, we describe the role of the ECM in AD, focusing on the aspects of synaptic transmission, amyloid-β-plaque generation and degradation, Tau-protein production, oxidative-stress response, and inflammatory response. The function of ECM in the pathological process of AD will inform future research on the etiology and pathogenesis of AD.

Diverse plasma membrane protrusions act as platforms for extracellular vesicle shedding

Plasma membrane curvature is an important factor in the regulation of cellular phenotype and is critical for various cellular activities including the shedding of extracellular vesicles (EV). One of the most striking morphological features of cells is different plasma membrane-covered extensions supported by actin core such as filopodia and microvilli. Despite the various functions of these extensions are partially unexplained, they are known to facilitate many crucial cellular functions such as migration, adhesion, absorption, and secretion. Due to the rapid increase in the research activity of EVs, there is raising evidence that one of the general features of cellular plasma membrane protrusions is to act as specialized platforms for the budding of EVs. This review will focus on early observations and recent findings supporting this hypothesis, discuss the putative budding and shedding mechanisms of protrusion-derived EVs and their biological significance.

A Shift in Tissue Stiffness During Hippocampal Maturation Correlates to the Pattern of Neurogenesis and Composition of the Extracellular Matrix

Aging changes the mechanical properties of brain tissue, such as stiffness. It has been proposed that the maintenance and differentiation of neural stem cells (NSCs) are regulated in accordance with extracellular stiffness. Neurogenesis is observed in restricted niches, including the dentate gyrus (DG) of the hippocampus, throughout mammalian lifetimes. However, profiles of tissue stiffness in the DG in comparison with the activity of NSCs from the neonatal to the matured brain have rarely been addressed so far. Here, we first applied ultrasound-based shear-wave elasticity imaging (SWEI) in living animals to assess shear modulus as in vivo brain stiffness. To complement the assay, atomic force microscopy (AFM) was utilized to determine the Young’s modulus in the hippocampus as region-specific stiffness in the brain slice. The results revealed that stiffness in the granule cell layer (GCL) and the hilus, including the subgranular zone (SGZ), increased during hippocampal maturation. We then quantified NSCs and immature neural cells in the DG with differentiation markers, and verified an overall decrease of NSCs and proliferative/immature neural cells along stages, showing that a specific profile is dependent on the subregion. Subsequently, we evaluated the amount of chondroitin sulfate proteoglycans (CSPGs), the major extracellular matrix (ECM) components in the premature brain by CS-56 immunoreactivity. We observed differential signal levels of CSPGs by hippocampal subregions, which became weaker during maturation. To address the contribution of the ECM in determining tissue stiffness, we manipulated the function of CSPGs by enzymatic digestion or supplementation with chondroitin sulfate, which resulted in an increase or decrease of stiffness in the DG, respectively. Our results illustrate that stiffness in the hippocampus shifts due to the composition of ECM, which may affect postnatal neurogenesis by altering the mechanical environment of the NSC niche.

Tuning the network charge of biohybrid hydrogel matrices to modulate the release of SDF-1

The delivery of chemotactic signaling molecules via customized biomaterials can effectively guide the migration of cells to improve the regeneration of damaged or diseased tissues. Here, we present a novel biohybrid hydrogel system containing two different sulfated glycosaminoglycans (sGAG)/sGAG derivatives, namely either a mixture of short heparin polymers (Hep-Mal) or structurally defined nona-sulfated tetrahyaluronans (9s-HA4-SH), to precisely control the release of charged signaling molecules. The polymer networks are described in terms of their negative charge, i.e. the anionic sulfate groups on the saccharides, using two parameters, the integral density of negative charge and the local charge distribution (clustering) within the network. The modulation of both parameters was shown to govern the release characteristics of the chemotactic signaling molecule SDF-1 and allows for seamless transitions between burst and sustained release conditions as well as the precise control over the total amount of delivered protein. The obtained hydrogels with well-adjusted release profiles effectively promote MSC migration in vitro and emerge as promising candidates for new treatment modalities in the context of bone repair and wound healing.

Tunable layer-by-layer films containing hyaluronic acid and their interactions with CD44

We report on the development of layer-by-layer (LbL) constructs whose viscoelastic properties and bioactivity can be finely tuned by using polyanions of different size and/or crosslinking. As a polyanion we used hyaluronic acid (HA) - a multi-signaling biomolecule whose bioactivity depends on its molecular weight. We investigated the interplay between the mechanical properties of the LbL systems built using HA of different sizes and the specific HA-mediated biochemical interactions. We characterized the assembled materials and their interactions with CD44, the main HA receptor, by Quartz Crystal Microbalance with Dissipation (QCM-D), Surface Plasmon Resonance (SPR) and Atomic Force Microscopy (AFM). We observed that the presence of CD44 resulted in the disruption of the non-crosslinked multilayers, while crosslinked films remain stable and bind CD44 in a HA molecular weight and charge specific fashion.

The effect of electrospun scaffolds on the glycosaminoglycan profile of differentiating neural stem cells

The use of electrospun scaffolds for neural tissue engineering applications allows a closer mimicry of the native tissue extracellular matrix (ECM), important for the transplantation of cells in vivo. Moreover, the role of the electrospun fiber mat topography on neural stem cell (NSC) differentiation remains to be completely understood. In this work REN-VM cells (NSC model) were differentiated on polycaprolactone (PCL) nanofibers, obtained by wet/wet electrospinning, and on flat glass lamellas. The obtained differentiation profile of NSCs was evaluated using immunofluorescence and qPCR analysis. Glycosaminoglycan (GAG) analysis was successfully emplyed to evaluate changes in the GAG profile of differentiating cells through the use of the highly sensitive liquid chromatography-tandem mass/mass spectrometry (LC-MS/MS) method. Our results show that both culture platforms allow the differentiation of REN-VM cells into neural cells (neurons and astrocytes) similarly. Moreover, LC-MS/MS analysis shows changes in the production of GAGs present both in cell cultures and conditioned media samples. In the media, hyaluronic acid (HA) was detected and correlated with cellular activity and the production of a more plastic extracellular matrix. The cell samples evidence changes in chondroitin sulfate (CS4S, CS6S, CS4S6S) and heparan sulfate (HS6S, HS0S), similar to those previously described in vivo studies and possibly associated with the creation of complex structures, such as perineural networks. The GAG profile of differentiating REN-VM cells on electrospun scaffolds was analyzed for the first time. Our results highlight the advantage of using platforms obtain more reliable and robust neural tissue-engineered transplants.

An Extracellular Perspective on CNS Maturation: Perineuronal Nets and the Control of Plasticity

During restricted time windows of postnatal life, called critical periods, neural circuits are highly plastic and are shaped by environmental stimuli. In several mammalian brain areas, from the cerebral cortex to the hippocampus and amygdala, the closure of the critical period is dependent on the formation of perineuronal nets. Perineuronal nets are a condensed form of an extracellular matrix, which surrounds the soma and proximal dendrites of subsets of neurons, enwrapping synaptic terminals. Experimentally disrupting perineuronal nets in adult animals induces the reactivation of critical period plasticity, pointing to a role of the perineuronal net as a molecular brake on plasticity as the critical period closes. Interestingly, in the adult brain, the expression of perineuronal nets is remarkably dynamic, changing its plasticity-associated conditions, including memory processes. In this review, we aimed to address how perineuronal nets contribute to the maturation of brain circuits and the regulation of adult brain plasticity and memory processes in physiological and pathological conditions.

Connecting the Stimuli-Responsive Rheology of Biopolymer Hydrogels to Underlying Hydrogen-Bonding Interactions

Many biopolymer hydrogels are environmentally responsive because they are held together by physical associations that depend on pH and temperature. Here, we investigate how the pH and temperature responses of the rheology of hyaluronan hydrogels are connected to the underlying molecular interactions. Hyaluronan is an essential structural biopolymer in the human body with many applications in biomedicine. Using two-dimensional infrared spectroscopy, we show that hyaluronan chains become connected by hydrogen bonds when the pH is changed from 7.0 to 2.5 and that the bond density at pH 2.5 is independent of temperature. Temperature-dependent rheology measurements show that because of this hydrogen bonding the stress relaxation at pH 2.5 is strongly slowed down in comparison to pH 7.0, consistent with the sticky reptation model of associative polymers. From the flow activation energy, we conclude that each polymer is cross-linked by multiple (5-15) hydrogen bonds to others, causing slow macroscopic stress relaxation, despite the short time scale of breaking and reformation of each individual hydrogen bond. Our findings can aid the design of stimuli-responsive hydrogels with tailored viscoelastic properties for biomedical applications.

Facilitate Angiogenesis and Neurogenesis by Growth Factors Integrated Decellularized Matrix Hydrogel

Neurological functional recovery depends on the synergistic interaction between angiogenesis and neurogenesis after peripheral nerve injury (PNI). Decellularized nerve matrix hydrogels have drawn much attention and been considered as potential therapeutic biomaterials for neurovascularization, due to their intrinsic advantages in construction of a growth-permissive microenvironment, strong affinity to multiple growth factors (GFs), and promotion of neurite outgrowth. In the present study, nerve growth factor (NGF) and vascular endothelial growth factor (VEGF) were incorporated into porcine decellularized nerve matrix hydrogel (pDNM-gel) for PNI treatment. Both GFs bound strongly to pDNM-gel and underwent a controlled release manner, which showed facilitated axonal extension and vascular-like tube formation in vitro. Especially, a companion growth was identified when human umbilical vein endothelial cells and neurons were cocultured on the GFs containing pDNM-gel. In a crushed rat sciatic nerve model, the incorporated NGF and VEGF appeared to contribute for axonal growth and neovascularization correspondingly but separately. Both GFs were equally important in improving nerve functional recovery after in situ administration. These findings indicate that pDNM-gel is not only a bioactive hydrogel-based material that can be used alone, but also serves as suitable carrier of multiple GFs for promoting an effective PNI repair. Impact statement Decellularized matrix hydrogel derived from nerve tissue has demonstrated its effectiveness in promoting nerve reinnervation, remyelination, and functionalization. Meanwhile, angiogenesis is highly desirable for treatment of long-distance peripheral nerve defects. To this end, we incorporated both vascular endothelial growth factor (VEGF) and nerve growth factor (NGF) into porcine decellularized nerve matrix hydrogel (pDNM-gel) to induce neovascularization and neuroregeneration. At the cellular level, the pDNM-gel with both growth factors (GFs) exhibited significant capability in promoting axonal elongation, Schwann cell proliferation and migration, as well as vessel/nerve interaction. In crushed peripheral nerve injury (PNI) rat model, the integrated VEGF was more favorable for angiogenesis, whereas NGF mainly contributed to neurogenesis. However, the combination of both GFs in pDNM-gel highly facilitated motor functional recovery, highlighting the therapeutic promise of decellularized matrix hydrogel for growth factor delivery toward neuroprotection and neuroregeneration after PNI.

The microvascular extracellular matrix in brains with Alzheimer's disease neuropathologic change (ADNC) and cerebral amyloid angiopathy (CAA)

BACKGROUND

The microvasculature (MV) of brains with Alzheimer's disease neuropathologic change (ADNC) and cerebral amyloid angiopathy (CAA), in the absence of concurrent pathologies (e.g., infarctions, Lewy bodies), is incompletely understood.

OBJECTIVE

To analyze microvascular density, diameter and extracellular matrix (ECM) content in association with ADNC and CAA.

METHODS

We examined samples of cerebral cortex and isolated brain microvasculature (MV) from subjects with the National Institute on Aging-Alzheimer's Association (NIA-AA) designations of not-, intermediate-, or high ADNC and from subjects with no CAA and moderate-severe CAA. Cases for all groups were selected with no major (territorial) strokes, ≤ 1 microinfarct in screening sections, and no Lewy body pathology. MV density and diameter were measured from cortical brain sections. Levels of basement membrane (BM) ECM components, the protein product of TNF-stimulated gene-6 (TSG-6), and the ubiquitous glycosaminoglycan hyaluronan (HA) were assayed by western blots or HA ELISA of MV lysates.

RESULTS

We found no significant changes in MV density or diameter among any of the groups. Levels of BM laminin and collagen IV (col IV) were lower in MV isolated from the high ADNC vs. not-ADNC groups. In contrast, BM laminin was significantly higher in MV from the moderate-severe CAA vs. the no CAA groups. TSG-6 and HA content were higher in the presence of both high ADNC and CAA, whereas levels of BM fibronectin and perlecan were similar among all groups.

CONCLUSIONS

Cortical MV density and diameter are not appreciably altered by ADNC or CAA. TSG-6 and HA are increased in both ADNC and CAA, with laminin and col IV decreased in the BM of high ADNC, but laminin increased in moderate-severe CAA. These results show that changes in the ECM occur in AD and CAA, but independently of one another, and likely reflect on the regional functioning of the brain microvasculature.

The Density and Length of Filopodia Associate with the Activity of Hyaluronan Synthesis in Tumor Cells

Filopodia are multifunctional finger-like plasma membrane protrusions with bundles of actin filaments that exist in virtually all cell types. It has been known for some time that hyaluronan synthesis activity induces filopodial growth. However, because of technical challenges in the studies of these slender and fragile structures, no quantitative analyses have been performed so far to indicate their association with hyaluronan synthesis. In this work we comprehensively address the direct quantification of filopodial traits, covering for the first time length and density measurements in a series of human cancer cell lines with variable levels of hyaluronan synthesis. The synthesis and plasma membrane binding of hyaluronan were manipulated with hyaluronan synthase 3 (HAS3) and hyaluronan receptor CD44 overexpression, and treatments with mannose, 4-methylumbelliferone (4-MU), and glucosamine. The results of this work show that the growth of filopodia was associated with the levels of hyaluronan synthesis but was not dependent on CD44 expression. The results confirm the hypothesis that abundance and length of filopodia in cancer cells is associated with the activity of hyaluronan synthesis.

Synucleinopathy alters nanoscale organization and diffusion in the brain extracellular space through hyaluronan remodeling

In recent years, exploration of the brain extracellular space (ECS) has made remarkable progress, including nanoscopic characterizations. However, whether ECS precise conformation is altered during brain pathology remains unknown. Here we study the nanoscale organization of pathological ECS in adult mice under degenerative conditions. Using electron microscopy in cryofixed tissue and single nanotube tracking in live brain slices combined with super-resolution imaging analysis, we find enlarged ECS dimensions and increased nanoscale diffusion after α-synuclein-induced neurodegeneration. These animals display a degraded hyaluronan matrix in areas close to reactive microglia. Furthermore, experimental hyaluronan depletion in vivo reduces dopaminergic cell loss and α-synuclein load, induces microgliosis and increases ECS diffusivity, highlighting hyaluronan as diffusional barrier and local tissue organizer. These findings demonstrate the interplay of ECS, extracellular matrix and glia in pathology, unraveling ECS features relevant for the α-synuclein propagation hypothesis and suggesting matrix manipulation as a disease-modifying strategy.

The nanoscale organisation of the brain extracellular space can be studied in vivo. Here, the authors investigate how it changes in response to α-synuclein pathology, and identify interactions between microglia and the extracellular matrix.

Extracellular Matrix Mimics Using Hyaluronan-Based Biomaterials

Hyaluronan (HA) is a critical element of the extracellular matrix (ECM). The regulated synthesis and degradation of HA modulates the ECM chemical and physical properties that, in turn, influence cellular behavior. HA triggers signaling pathways associated with the adhesion, proliferation, migration, and differentiation of cells, mediated by its interaction with specific cellular receptors or by tuning the mechanical properties of the ECM. This review summarizes the recent advances on strategies used to mimic the HA present in the ECM to study healthy or pathological cellular behavior. This includes the development of HA-based 2D and 3D in vitro tissue models for the seeding and encapsulation of cells, respectively, and HA particles as carriers for the targeted delivery of therapeutic agents.

Off-line coupling of capillary isotachophoresis separation to IRMPD spectroscopy for glycosaminoglycans analysis: Application to the chondroitin sulfate disaccharides model solutes

Glycans analysis is challenging due to their immense structural diversity. Isotachophoresis was investigated as separation method for the purification of isobaric sulfated disaccharides prior to their characterization by Mass Spectrometry (MS) and tunable IR multiple photon dissociation (IRMPD). This proof of feasibility study was applied to the separation and characterization of chondroitin sulfate (CS) disaccharides. ITP separation conditions were optimized. Separation starts using a 2.5 mM chloride ions and 10 mM glycine at pH 3.2 solution as leading electrolyte and a terminating electrolyte composed of formic acid 2.5 mM and glycine 10 mM at pH 3.5. The CS disaccharides sample were prepared in the terminating electrolyte. The length of injection was also investigated in order to create longer plateau-like bands of pure solutes. This strategy was helpful for collecting fraction at such microseparation scale. Indeed, capillary ITP affords the injection of few tens of nanoliter of sample. Fractionation of the CS disaccharides mixture in isolated ITP bands and collection of solutes were successfully done using a HPC coated fused silica capillary of 1m-length and 75 µm of internal diameter. Collected fractions in a final of volume 10 µL were analyzed by CZE, tandem MS and IRMPD spectroscopy. The purity of each fraction is higher than 90% and is well-adapted to IRMPD characterization.

The role of heparin/heparan sulphate in the IFN-γ-led Arena

IFN-γ (Interferon-gamma) is a pleiotropic cytokine. It is often involved in a variety of physiological processes by binding to the cell surface transmembrane receptor (IFN-γR) to initiate a series of signalling pathways that transmit external signals from cell surface receptors to the cell nucleus. Heparan sulphate (HS), a highly sulphated linear polysaccharide, is ubiquitous on the mammalian cell surface and extracellular matrix. Electrostatic interactions can be generated between the highly sulphated HS region and specific basic amino acid residues in the IFN-γ structure, thereby detaining IFN-γ on the cell surface, and the concentration of IFN-γ on the cell surface is thus, changed. IFN-γ retained on the cell surface will optimize the binding of IFN-γ to the transmembrane receptor resulting in high efficiency signalling. Heparin is a glycosaminoglycan with a structure similar to HS. The structural similarity provides a basis for modelling exogenous heparin dependence for interference with IFN-γ function. This model can be summarized as follows: First, the competitive binding effect; heparin bound to cytokines by competing with membrane-associated HS, causes a decrease in cytokine concentration on the cell surface. Second, the principle of priority occupancy; heparin can occupy the receptor binding site on cytokines, partially preventing the IFN-γ-IFN-γR interaction. These two models interfere with IFN-γ signal transmission. To decipher the mechanism by which heparin influences IFN-γ activity, studies of the structure-activity relationship are in progress. This paper summarizes research progress on the IFN-γ signalling pathway, heparin interference with IFN-γ activity and the structure-activity relationship between heparin and IFN-γ.

Neuronal Pentraxin 2 Binds PNNs and Enhances PNN Formation

The perineuronal net (PNN) is a mesh-like proteoglycan structure on the neuronal surface which is involved in regulating plasticity. The PNN regulates plasticity via multiple pathways, one of which is direct regulation of synapses through the control of AMPA receptor mobility. Since neuronal pentraxin 2 (Nptx2) is a known regulator of AMPA receptor mobility and Nptx2 can be removed from the neuronal surface by PNN removal, we investigated whether Nptx2 has a function in the PNN. We found that Nptx2 binds to the glycosaminoglycans hyaluronan and chondroitin sulphate E in the PNN. Furthermore, in primary cortical neuron cultures, the addition of NPTX2 to the culture medium enhances PNN formation during PNN development. These findings suggest Nptx2 as a novel PNN binding protein with a role in the mechanism of PNN formation.

Hyaluronan Accelerates Intestinal Mucosal Healing through Interaction with TSG-6

Hyaluronan (HA) has proven to be beneficial in the treatment of several diseases. Recently, it has been shown that the local application of HA (IBD98E) improves endoscopic and clinical outcomes in subjects with active distal ulcerative colitis (UC). However, the mechanisms by which this polysaccharide exerts its beneficial effects are unclear. Here, we demonstrated that HA treatment in vitro and in vivo improved mucosal healing by accelerating intestinal epithelial regeneration. Indeed, mice treated with HA showed a faster recovery from colitis and reduced endoscopic signs of mucosal inflammation compared to those receiving saline. Furthermore, histological analysis revealed less ulcerated mucosa in mice treated with HA, characterized by re-epithelialized areas. TSG-6, the secreted product of TNF-stimulated gene-6, is an HA-binding protein shown previously to have tissue-protective properties and promote wound healing. Mucosal levels of TSG-6 increased in UC patients compared to the healthy controls and also after wounding in mice. TSG-6 deletion prevented the beneficial properties of HA in mucosal wound repair, suggesting that the interaction of HA with TSG-6 is crucial for intestinal epithelial regeneration. Overall these results are consistent with HA having a therapeutic effect via the promotion of mucosal healing in patients with ulcerative colitis.

Effect of calcium ions and pH on the morphology and mechanical properties of hyaluronan brushes

Hyaluronan (HA) is a linear, regular polysaccharide that plays as a chief structural and functional component in peri- and extracellular matrices, thus contributing significantly to many basic cellular processes. To understand more comprehensively the response of the supramolecular organization of HA polymers to changes in their aqueous environment, we study the effects of Ca2+ concentration and pH on the morphology and rigidity of films of end-grafted HA polymers on planar supports (HA brushes), as a well-defined in vitro model system of HA-rich matrices, by reflection interference contrast microscopy and quartz crystal microbalance. The thickness and softness of HA brushes decrease significantly with Ca2+ concentration but do not change with pH, within the physiological ranges of these parameters. The effect of Ca2+ on HA brush thickness is virtually identical to the effect of Na+ at 10-fold higher concentrations. Moreover, the thickness and softness of HA brushes decrease appreciably upon HA protonation at pH less than 6. Effects of pH and calcium ions are fully reversible over large parameter ranges. These findings are relevant for understanding the supramolecular organization and dynamics of HA-rich matrices in biological systems and will also benefit the rational design of synthetic HA-rich materials with tailored properties.

Microglia: Brain cells on the move

In the last decade, tremendous progress has been made in understanding the biology of microglia - i.e. the fascinating immigrated resident immune cell population of the central nervous system (CNS). Recent literature reviews have largely dealt with the plentiful functions of microglia in CNS homeostasis, development and pathology, and the influences of sex and the microbiome. In this review, the intriguing aspect of their physical plasticity during CNS development will get specific attention. Microglia move around (mobility) and reshape their processes (motility). Microglial migration into and inside the CNS is most prominent throughout development and consequently most of the data described in this review concern mobility and motility in the changing environment of the developing brain. Here, we first define microglia based on their highly specialized age- and region-dependent gene expression signature and associated functional heterogeneity. Next, we describe their origin, the migration route of immature microglial cells towards the CNS, the mechanisms underlying their invasion of the CNS, and their spatiotemporal localization and surveying behaviour inside the developing CNS. These processes are dependent on microglial mobility and motility which are determined by the microenvironment of the CNS. Therefore, we further zoom in on the changing environment during CNS development. We elaborate on the extracellular matrix and the respective integrin receptors on microglia and we discuss the purinergic and molecular signalling in microglial mobility. In the last section, we discuss the physiological and pathological functions of microglia in which mobility and motility are involved to stress the importance of microglial 'movement'.

Charge-tuning of glycosaminoglycan-based hydrogels to program cytokine sequestration

Glycosaminoglycan (GAG)-based biohybrid hydrogels of varied GAG content and GAG sulfation pattern were prepared and applied to sequester cytokines.

Increased Hyaluronan and TSG-6 in Association with Neuropathologic Changes of Alzheimer's Disease

Little is known about the extracellular matrix (ECM) during progression of AD pathology. Brain ECM is abundant in hyaluronan (HA), a non-sulfated glycosaminoglycan synthesized by HA synthases (HAS) 1-3 in a high molecular weight (MW) form that is degraded into lower MW fragments. We hypothesized that pathologic severity of AD is associated with increases in HA and HA-associated ECM molecules. To test this hypothesis, we assessed HA accumulation and size; HA synthases (HAS) 1-3; and the HA-stabilizing hyaladherin, TSG-6 in parietal cortex samples from autopsied research subjects with not AD (CERAD = 0, Braak = 0- II, n = 12-21), intermediate AD (CERAD = 2, Braak = III-IV, n = 13-18), and high AD (CERAD = 3, Braak = V-VI, n = 32-40) neuropathologic change. By histochemistry, HA was associated with deposits of amyloid and tau, and was also found diffusely in brain parenchyma, with overall HA quantity (measured by ELSA) significantly greater in brains with high AD neuropathology. Mean HA MW was similar among the samples. HAS2 and TSG-6 mRNA expression, and TSG-6 protein levels were significantly increased in high AD and both molecules were present in vasculature, NeuN-positive neurons, and Iba1-positive microglia. These results did not change when accounting for gender, advanced age (≥ 90 years versus <90 years), or the clinical diagnosis of dementia. Collectively, our results indicate a positive correlation between HA accumulation and AD neuropathology, and suggest a possible role for HA synthesis and metabolism in AD progression.

Exploring Structure⁻Property Relationships of GAGs to Tailor ECM-Mimicking Hydrogels

Glycosaminoglycans (GAGs) are a class of linear polysaccharides that are ubiquitous in the extracellular matrix (ECM) and on cell surfaces. Due to their key role in development, homeostasis, pathogenesis, and regeneration, GAGs are increasingly used in the design of ECM-mimicking hydrogels to stimulate tissue formation and regenerative processes via specifically orchestrated cell-instructive signals. These applications first and foremost build on the ability of GAGs to effectively bind, protect, and release morphogens. The specificity and strength of morphogen-GAG interactions are largely governed by the number and spatial distribution of negatively charged sulfate groups carried by GAGs. Herein, we summarize a mean-field approach to quantify the density of ionizable groups, GAG concentration, and cross-linking degree of GAG-containing hydrogels on the basis of microslit electrokinetic experiments. We further present and discuss a continuum model of mucosa that accounts for charge regulation by glycan-ion pairing in biological contexts and under conditions of macromolecular crowding. Finally, we discuss the modulation of the morphogen binding and transport in GAG hydrogels by selective desulfation of the GAG component.

WITHDRAWN: An extremely low frequency-weak magnetic field can induce alterations in a biological system: A case study in chick embryo development

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). These articles are retracted at the request of the authors. The joint Editors-in-Chief agree with this decision.

Single-Molecule Unbinding Forces between the Polysaccharide Hyaluronan and Its Binding Proteins

The extracellular polysaccharide hyaluronan (HA) is ubiquitous in all vertebrate tissues, where its various functions are encoded in the supramolecular complexes and matrices that it forms with HA-binding proteins (hyaladherins). In tissues, these supramolecular architectures are frequently subjected to mechanical stress, yet how this affects the intermolecular bonding is largely unknown. Here, we used a recently developed single-molecule force spectroscopy platform to analyze and compare the mechanical strength of bonds between HA and a panel of hyaladherins from the Link module superfamily, namely the complex of the proteoglycan aggrecan and cartilage link protein, the proteoglycan versican, the inflammation-associated protein TSG-6, the HA receptor for endocytosis (stabilin-2/HARE), and the HA receptor CD44. We find that the resistance to tensile stress for these hyaladherins correlates with the size of the HA-binding domain. The lowest mean rupture forces are observed for members of the type A subgroup (i.e., with the shortest HA-binding domains; TSG-6 and HARE). In contrast, the mechanical stability of the bond formed by aggrecan in complex with cartilage link protein (two members of the type C subgroup, i.e., with the longest HA-binding domains) and HA is equal or even superior to the high affinity streptavidin⋅biotin bond. Implications for the molecular mechanism of unbinding of HA⋅hyaladherin bonds under force are discussed, which underpin the mechanical properties of HA⋅hyaladherin complexes and HA-rich extracellular matrices.

TSG-6: A multifunctional protein with anti-inflammatory and tissue-protective properties

Tumor necrosis factor- (TNF) stimulated gene-6 (TSG-6) is an inflammation-associated secreted protein that has been implicated as having important and diverse tissue protective and anti-inflammatory properties, e.g. mediating many of the immunomodulatory and beneficial activities of mesenchymal stem/stromal cells. TSG-6 is constitutively expressed in some tissues, which are either highly metabolically active or subject to challenges from the environment, perhaps providing protection in these contexts. The diversity of its functions are dependent on the binding of TSG-6 to numerous ligands, including matrix molecules such as glycosaminoglycans, as well as immune regulators and growth factors that themselves interact with these linear polysaccharides. It is becoming apparent that TSG-6 can directly affect matrix structure and modulate the way extracellular signalling molecules interact with matrix. In this review, we focus mainly on the literature for TSG-6 over the last 10 years, summarizing its expression, structure, ligand-binding properties, biological functions and highlighting TSG-6's potential as a therapeutic for a broad range of disease indications.