Annexin 6 is a putative cell surface receptor for chondroitin sulfate chains

ANXA6: a key molecular player in cancer progression and drug resistance

Annexin-A6 (ANXA6), a Ca²⁺-dependent membrane binding protein, is the largest of all conserved annexin families and highly expressed in the plasma membrane and endosomal compartments. As a multifunctional scaffold protein, ANXA6 can interact with phospholipid membranes and various signaling proteins. These properties enable ANXA6 to participate in signal transduction, cholesterol homeostasis, intracellular/extracellular membrane transport, and repair of membrane domains, etc. Many studies have demonstrated that the expression of ANXA6 is consistently altered during tumor formation and progression. ANXA6 is currently known to mediate different patterns of tumor progression in different cancer types through multiple cancer-type specific mechanisms. ANXA6 is a potentially valuable marker in the diagnosis, progression, and treatment strategy of various cancers. This review mainly summarizes recent findings on the mechanism of tumor formation, development, and drug resistance of ANXA6. The contents reviewed herein may expand researchers' understanding of ANXA6 and contribute to developing ANXA6-based diagnostic and therapeutic strategies.

Surface-Engineered Mucus Penetrating Nucleic Acid Delivery Systems with Cell Penetrating Peptides for the Lungs

Nucleic acids, both DNA and small RNAs, have emerged as potential therapeutics for the treatment of various lung disorders. However, delivery of nucleic acids to the lungs is challenging due to the barrier property imposed by mucus, which is further reinforced in disease conditions such as chronic obstructive pulmonary disease and asthma. The presence of negatively charged mucins imparts the electrostatic barrier property, and the mesh network structure of mucus provides steric hindrance to the delivery system. To overcome this, the delivery system either needs to be muco-inert with a low positive charge such that the interactions with mucus are minimized or should have the ability to transiently dismantle the mucus structure for effective penetration. We have developed a mucus penetrating system for the delivery of both small RNA and plasmid DNA independently. The nucleic acid core consists of a nucleic acid (pDNA/siRNA) and a cationic/amphipathic cell penetrating peptide. The mucus penetrating coating consists of the hydrophilic biopolymer chondroitin sulfate A (CS-A) conjugated with a mucolytic agent, mannitol. We hypothesize that the hydrophilic coating of CS-A would reduce the surface charge and decrease the interaction with negatively charged mucins, while the conjugated mannitol residues would disrupt the mucin-mucin interaction or decrease the viscosity of mucus by increasing the influx of water into the mucus. Our results indicate that CS-A-mannitol-coated nanocomplexes possess reduced surface charge, reduced viscosity of artificial mucus, and increased diffusion in mucin suspension as well as increased penetration through the artificial mucus layer as compared to the non-coated ones. Further, the coated nanocomplexes showed low cytotoxicity as well as higher transfection in A-549 and BEAS-2B cells as compared to the non-coated ones.

Bioactive potential of natural biomaterials: identification, retention and assessment of biological properties

Biomaterials have had an increasingly important role in recent decades, in biomedical device design and the development of tissue engineering solutions for cell delivery, drug delivery, device integration, tissue replacement, and more. There is an increasing trend in tissue engineering to use natural substrates, such as macromolecules native to plants and animals to improve the biocompatibility and biodegradability of delivered materials. At the same time, these materials have favourable mechanical properties and often considered to be biologically inert. More importantly, these macromolecules possess innate functions and properties due to their unique chemical composition and structure, which increase their bioactivity and therapeutic potential in a wide range of applications. While much focus has been on integrating these materials into these devices via a spectrum of cross-linking mechanisms, little attention is drawn to residual bioactivity that is often hampered during isolation, purification, and production processes. Herein, we discuss methods of initial material characterisation to determine innate bioactivity, means of material processing including cross-linking, decellularisation, and purification techniques and finally, a biological assessment of retained bioactivity of a final product. This review aims to address considerations for biomaterials design from natural polymers, through the optimisation and preservation of bioactive components that maximise the inherent bioactive potency of the substrate to promote tissue regeneration.

Osteoblast-Derived Vesicle Protein Content Is Temporally Regulated During Osteogenesis: Implications for Regenerative Therapies

Osteoblast-derived extracellular vesicles (EV) are a collection of secreted (sEVs) and matrix-bound nanoparticles that function as foci for mineral nucleation and accumulation. Due to the fact sEVs can be isolated directly from the culture medium of mineralizing osteoblasts, there is growing interest their application regenerative medicine. However, at present therapeutic advancements are hindered by a lack of understanding of their precise temporal contribution to matrix mineralization. This study advances current knowledge by temporally aligning sEV profile and protein content with mineralization status. sEVs were isolated from mineralizing primary osteoblasts over a period of 1, 2, and 3 weeks. Bimodal particle distributions were observed (weeks 1 and 3: 44 and 164 nm; week 2: 59 and 220 nm), indicating a heterogeneous population with dimensions characteristic of exosome- (44 and 59 nm) and microvesicle-like (164 and 220 nm) particles. Proteomic characterization by liquid chromatography tandem-mass spectrometry (LC-MS/MS) revealed a declining correlation in EV-localized proteins as mineralization advanced, with Pearson correlation-coefficients of 0.79 (week 1 vs. 2), 0.6 (2 vs. 3) and 0.46 (1 vs. 3), respectively. Principal component analysis (PCA) further highlighted a time-dependent divergence in protein content as mineralization advanced. The most significant variations were observed at week 3, with a significant (p < 0.05) decline in particle concentration, visual evidence of EV rupture and enhanced mineralization. A total of 116 vesicle-localized proteins were significantly upregulated at week 3 (56% non-specifically, 19% relative to week 1, 25% relative to week 2). Gene ontology enrichment analysis of these proteins highlighted overrepresentation of genes associated with matrix organization. Of note, increased presence of phospholipid-binding and calcium channeling annexin proteins (A2, A5, and A6) indicative of progressive variations in the nucleational capacity of vesicles, as well as interaction with the surrounding ECM. We demonstrate sEV-mediated mineralization is dynamic process with variations in vesicle morphology and protein content having a potential influence on developmental changes matrix organization. These findings have implications for the selection and application of EVs for regenerative applications.

Identification of dentinogenic cell-specific surface antigens in odontoblast-like cells derived from adult dental pulp

Background

Odontoblast is a unique progenitor that plays a role in dentin formation. So far, the dentinogenic differentiation of dental pulp stem cells and the role of surface molecules of odontoblasts in dentinogenesis are not well known yet. In this study, we obtained odontoblast-like cells from human dental pulp cells and screened odontoblast-specific cell surface antigens by decoy immunization.

Methods

Through decoy immunization with intact odontoblast-like cells derived from human dental pulp cells, we constructed 12 monoclonal antibodies (mAbs) of IgG type, and their binding affinities for cell surface of odontoblast-like cells were analyzed by flow cytometry. Immunoprecipitation, mass spectrometry, and immunohistochemistry were performed to demonstrate odontoblast-specific antigens. Odontoblasts were sorted by these mAbs using magnetic-activated cell sorting system, and their mineralization efficiency was increased after sorting.

Results

We constructed 12 mAbs of IgG type, which had a strong binding affinity for cell surface antigens of odontoblast-like cells. In human adult tooth, these mAbs accumulated in the odontoblastic layer between dentin and pulp and in the perivascular region adjacent to the blood vessels in the pulp core. Cell surface expression of the antigenic molecules was increased during odontogenic cytodifferentiation and decreased gradually as dentinogenic maturation progressed. Proteomic analysis showed that two representative antigenic molecules, OD40 and OD46, had the potential to be components for cell adhesion and extracellular matrix structures.

Conclusion

These results suggest that mAbs will be useful for detecting and separating odontoblasts from the primary pulp cells and other lineage cells and will provide information on the structures of extracellular matrix and microenvironment that appears during the dentinogenic differentiation.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1232-y) contains supplementary material, which is available to authorized users.

Annexin A6-A multifunctional scaffold in cell motility

Annexin A6 (AnxA6) belongs to a highly conserved protein family characterized by their calcium (Ca²⁺)-dependent binding to phospholipids. Over the years, immunohistochemistry, subcellular fractionations, and live cell microscopy established that AnxA6 is predominantly found at the plasma membrane and endosomal compartments. In these locations, AnxA6 acts as a multifunctional scaffold protein, recruiting signaling proteins, modulating cholesterol and membrane transport and influencing actin dynamics. These activities enable AnxA6 to contribute to the formation of multifactorial protein complexes and membrane domains relevant in signal transduction, cholesterol homeostasis and endo-/exocytic membrane transport. Hence, AnxA6 has been implicated in many biological processes, including cell proliferation, survival, differentiation, inflammation, but also membrane repair and viral infection. More recently, we and others identified roles for AnxA6 in cancer cell migration and invasion. This review will discuss how the multiple scaffold functions may enable AnxA6 to modulate migratory cell behavior in health and disease.

Two translation initiation codons direct the expression of annexin VI 64kDa and 68kDa isoforms

Annexin A6 is a multicompetent, multifunctional protein involved in several biological processes within and outside of the cell. Whereas HeLa cells express annexin A6 only as a 68/67-kDa doublet, indicating alternative splicing (Smith PD et al. (1994) Proc Natl Acad Sci USA 91, 2713-2717), the GMO2784 human fibroblast cell line expresses two additional isoforms at 64 and 58kDa. In both cell lines, annexin A6 is located intracellularly and on the plasma membrane. In vitro eukaryotic protein synthesis of pIRESneoAnxA6 cDNA and pIRESneoAnxA6/Met^1- or Met^33- using a reticulocyte lysate coupled transcription/translation system revealed that this gene contains two translation start codons, Met¹ and Met³³. Immunoprecipitation of the products obtained from the transcription/translation system using various anti-annexin A6 antibodies confirmed the presence of several isoforms and suggested that this protein might be present in different configurations.

Osteoarthritis: Pathology, Mouse Models, and Nanoparticle Injectable Systems for Targeted Treatment

Osteoarthritis (OA) is a progressive, degenerative disease of articulating joints that not only affects the elderly, but also involves younger, more active individuals with prolonged participation in high physical-demand activities. Thus, effective therapies that are easy to adopt clinically are critical in limiting the societal burden associated with OA. This review is focused on intra-articular injectable regimens and provides a comprehensive look at existing in vivo models of OA that might be suitable for developing, testing, and finding a cure for OA by intra-articular injections. We first discuss the pathology, molecular mechanisms responsible for the initiation and progression of OA, and challenges associated with disease-specific targeting of OA. We proceed to discuss available animal models of OA and provide a detailed perspective on the use of mouse models in studies of experimental OA. We finally provide a closer look at intra-articular injectable treatments for OA, focusing on biomaterials-based nanoparticles, and provide a comprehensive overview of the various nanometer-size ranges studied.

Annexin A6 and Late Endosomal Cholesterol Modulate Integrin Recycling and Cell Migration

Annexins are a family of proteins that bind to phospholipids in a calcium-dependent manner. Earlier studies implicated annexin A6 (AnxA6) to inhibit secretion and participate in the organization of the extracellular matrix. We recently showed that elevated AnxA6 levels significantly reduced secretion of the extracellular matrix protein fibronectin (FN). Because FN is directly linked to the ability of cells to migrate, this prompted us to investigate the role of AnxA6 in cell migration. Up-regulation of AnxA6 in several cell models was associated with reduced cell migration in wound healing, individual cell tracking and three-dimensional migration/invasion assays. The reduced ability of AnxA6-expressing cells to migrate was associated with decreased cell surface expression of αVβ3 and α5β1 integrins, both FN receptors. Mechanistically, we found that elevated AnxA6 levels interfered with syntaxin-6 (Stx6)-dependent recycling of integrins to the cell surface. AnxA6 overexpression caused mislocalization and accumulation of Stx6 and integrins in recycling endosomes, whereas siRNA-mediated AnxA6 knockdown did not modify the trafficking of integrins. Given our recent findings that inhibition of cholesterol export from late endosomes (LEs) inhibits Stx6-dependent integrin recycling and that elevated AnxA6 levels cause LE cholesterol accumulation, we propose that AnxA6 and blockage of LE cholesterol transport are critical for endosomal function required for Stx6-mediated recycling of integrins in cell migration.

Chondroitin Sulfate Accelerates Trans-Golgi-to-Surface Transport of Proteoglycan Amyloid Precursor Protein

The amyloid precursor protein (APP) is a membrane protein implicated in the pathogenesis of Alzheimer's disease. APP is a part-time proteoglycan, as splice variants lacking exon 15 are modified by a chondroitin sulfate glycosaminoglycan (GAG) chain. Investigating the effect of the GAG chain on the trafficking of APP in non-polarized cells, we found it to increase the steady-state surface-to-intracellular distribution, to reduce the rate of endocytosis and to accelerate transport kinetics from the trans-Golgi network (TGN) to the plasma membrane. Deletion of the cytosolic domain resulted in delayed surface arrival of GAG-free APP, but did not affect the rapid export kinetics of the proteoglycan form. Protein-free GAG chains showed the same TGN-to-cell surface transport kinetics as proteoglycan APP. Endosome ablation experiments were performed to distinguish between indirect endosomal and direct pathways to the cell surface. Surprisingly, TGN-to-cell surface transport of both GAG-free and proteoglycan APP was found to be indirect via transferrin-positive endosomes. Our results show that GAGs act as alternative sorting determinants in cellular APP transport that are dominant over cytoplasmic signals and involve distinct sorting mechanisms.

Cell adhesion properties of neural stem cells in the chick embryo

The nervous system of vertebrates is derived from an early embryonic region referred to as the neural plate. In the chick embryo, the neural plate is populated by neural stem cells specified from the epiblast shortly after the onset of gastrulation. Accompanying the formation of the plate, chondroitin sulfate glycosaminoglycans are expressed in the basal extracellular matrix. We describe in vitro experiments measuring cell adhesion of epiblast cells during the formation of the neural plate. Our findings may suggest that neural stem cells are set apart from non-neural epiblast by changes in relative cell-cell and cell-substrate adhesion. Specifically, changes in cell adhesion separating neural stem cells from the non-neural epiblast may be augmented by the presence of exogenous chondroitin-6-sulfate in the epiblast basal lamina at the time neural progenitors are specified in the epiblast.

Aceclofenac-loaded chondroitin sulfate conjugated SLNs for effective management of osteoarthritis

Abstract Background: In intra-articular drug delivery, there are number of shortcomings such as lymphatic drainage from the synovial cavity, frequent dosing, adverse side effects and patient discomfort in the management of osteoarthritis (OA).

PURPOSE

This research work reports the development and characterization of aceclofenac-loaded chondroitin sulfate (CS) conjugated (CS-SLN) and unconjugated solid lipid nanoparticles (SLN) for the effective management of OA.

METHODS

The SLNs were prepared using modified solvent injection method and coupled with CS. They were further characterized for size and size distribution, zeta potential, surface morphology, % entrapment efficiency and in vitro drug release profile. Anti-inflammatory activity and in vivo performance was also predicted.

RESULTS

The particle size of the SLN and CS-SLN was found to be 143.4 ± 0.9 nm and 154.2 ± 1.1 nm, respectively. SLNs exhibited sustained drug release (SLN, 64.25 ± 0.75%; CS-SLN, 57.82 ± 0.62%) in vitro for more than 24 h. In vivo performance studies revealed the highest uptake of SLNs by the knee joint.

DISCUSSION

SLNs enhanced accumulation at the knee joint due to specific interactions with CD44, annexin and leptin receptors attributed to CS coupling.

CONCLUSION

CS-SLN could be potentially effective vector for the treatment or management of OA.

Imbalanced expression of Vcan mRNA splice form proteins alters heart morphology and cellular protein profiles

The fundamental importance of the proteoglycan versican to early heart formation was clearly demonstrated by the Vcan null mouse called heart defect (hdf). Total absence of the Vcan gene halts heart development at a stage prior to the heart’s pulmonary/aortic outlet segment growth. This creates a problem for determining the significance of versican’s expression in the forming valve precursors and vascular wall of the pulmonary and aortic roots. This study presents data from a mouse model, Vcan^(tm1Zim), of heart defects that results from deletion of exon 7 in the Vcan gene. Loss of exon 7 prevents expression of two of the four alternative splice forms of the Vcan gene. Mice homozygous for the exon 7 deletion survive into adulthood, however, the inability to express the V2 or V0 forms of versican results in ventricular septal defects, smaller cushions/valve leaflets with diminished myocardialization and altered pulmonary and aortic outflow tracts. We correlate these phenotypic findings with a large-scale differential protein expression profiling to identify compensatory alterations in cardiac protein expression at E13.5 post coitus that result from the absence of Vcan exon 7. The Vcan^(tm1Zim) hearts show significant changes in the relative abundance of several cytoskeletal and muscle contraction proteins including some previously associated with heart disease. These alterations define a protein fingerprint that provides insight to the observed deficiencies in pre-valvular/septal cushion mesenchyme and the stability of the myocardial phenotype required for alignment of the outflow tract with the heart ventricles.

Alpha-1 giardin is an annexin with highly unusual calcium-regulated mechanisms

Alpha-giardins constitute the annexin proteome (group E annexins) in the intestinal protozoan parasite Giardia and, as such, represent the evolutionary oldest eukaryotic annexins. The dominance of alpha-giardins in the cytoskeleton of Giardia with its greatly reduced actin content emphasises the importance of the alpha-giardins for the structural integrity of the parasite, which is particularly critical in the transformation stage between cyst and trophozoite. In this study, we report the crystal structures of the apo- and calcium-bound forms of α1-giardin, a protein localised to the plasma membrane of Giardia trophozoites that has recently been identified as a vaccine target. The calcium-bound crystal structure of α1-giardin revealed the presence of a type III site in the first repeat as known from other annexin structures, as well as a novel calcium binding site situated between repeats I and IV. By means of comparison, the crystal structures of three different alpha-giardins known to date indicate that these proteins engage different calcium coordination schemes, among each other, as well as compared to annexins of groups A-D. Evaluation of the calcium-dependent binding to acidic phosphoplipid membranes revealed that this process is not only mediated but also regulated by the environmental calcium concentration. Uniquely within the large family of annexins, α1-giardin disengages from the phospholipid membrane at high calcium concentrations possibly due to formation of a dimeric species. The observed behaviour is in line with changing calcium levels experienced by the parasite during excystation and may thus provide first insights into the molecular mechanisms underpinning the transformation and survival of the parasite in the host.

Scavenger receptor-mediated uptake of cell-penetrating peptide nanocomplexes with oligonucleotides

Cell-penetrating peptides (CPPs) are short cationic peptides that penetrate cells by interacting with the negatively charged plasma membrane; however, the detailed uptake mechanism is not clear. In contrary to the conventional mode of action of CPPs, we show here that a CPP, PepFect14 (PF14), forms negatively charged nanocomplexes with oligonucleotides and their uptake is mediated by class-A scavenger receptors (SCARAs). Specific inhibitory ligands of SCARAs, such as fucoidin, polyinosinic acid, and dextran sulfate, totally inhibit the activity of PF14-oligonucleotide nanocomplexes in the HeLa pLuc705 splice-correction cell model, while nonspecific, chemically related molecules do not. Furthermore, RNA interference (RNAi) knockdown of SCARA subtypes (SCARA3 and SCARA5) that are expressed in this cell line led to a significant reduction of the activity to <50%. In line with this, immunostaining shows prevalent colocalization of the nanocomplexes with the receptors, and electron microscopy images show no binding or internalization of the nanocomplexes in the presence of the inhibitory ligands. Interestingly, naked oligonucleotides also colocalize with SCARAs when used at high concentrations. These results demonstrate the involvement of SCARA3 and SCARA5 in the uptake of PF14-oligonucleotide nanocomplexes and suggest for the first time that some CPP-based systems function through scavenger receptors, which could yield novel possibilities to understand and improve the transfection by CPPs.

Chemical priming for spinal cord injury: a review of the literature part II-potential therapeutics

INTRODUCTION

Spinal cord injury is a complex cascade of reactions secondary to the initial mechanical trauma that puts into action the innate properties of the injured cells, the circulatory, inflammatory, and chemical status around them, into a non-permissive and destructive environment for neuronal function and regeneration. Priming means putting a cell, in a state of "arousal" towards better function. Priming can be mechanical as trauma is known to enhance activity in cells.

MATERIALS AND METHODS

A comprehensive review of the literature was performed to better understand the possible chemical primers used for spinal cord injuries.

CONCLUSIONS

Taken together, many studies have shown various promising results using the substances outlined herein for treating SCI.

Chemical priming for spinal cord injury: a review of the literature. Part I-factors involved

INTRODUCTION

There are significant differences between the propensity of neural regeneration between the central and peripheral nervous systems.

MATERIALS AND METHODS

Following a review of the literature, we describe the role of growth factors, guiding factors, and neurite outgrowth inhibitors in the physiology and development of the nervous system as well as the pathophysiology of the spinal cord. We also detail their therapeutic role as well as those of other chemical substances that have recently been found to modify regrowth following cord injury.

CONCLUSIONS

Multiple factors appear to have promising futures for the possibility of improving spinal cord injury following injury.

Annexin VI is a mannose-6-phosphate-independent endocytic receptor for bovine β-glucuronidase

Endocytosis and transport of bovine liver β-glucuronidase to lysosomes in human fibroblasts are mediated by two receptors: the well-characterized cation-independent mannose 6-phosphate receptor (IGF-II/Man6PR) and an IGF-II/Man6PR-independent receptor, which recognizes a Ser-Trp*-Ser sequence present on the ligand. The latter receptor was detergent extracted from bovine liver membranes and purified. LC/ESI-MS/MS analysis revealed that this endocytic receptor was annexin VI (AnxA6). Several approaches were used to confirm this finding. First, the binding of bovine β-glucuronidase to the purified receptor from bovine liver membranes and His-tagged recombinant human AnxA6 protein was confirmed using ligand-blotting assays. Second, western blot analysis using antibodies raised against IGF-II/Man6PR-independent receptor as well as commercial antibodies against AnxA6 confirmed that the receptor and AnxA6 were indeed the same protein. Third, double immunofluorescence experiments in human fibroblasts confirmed a complete colocalization of the bovine β-glucuronidase and the AnxA6 receptor on the plasma membrane. Lastly, two cell lines were stably transfected with a plasmid containing the cDNA for human AnxA6. In both transfected cell lines, an increase in cell surface AnxA6 and in mannose 6-phosphate-independent endocytosis of bovine β-glucuronidase was detected. These results indicate that AnxA6 is a novel receptor that mediates the endocytosis of the bovine β-glucuronidase.

Engineering the extracellular environment: Strategies for building 2D and 3D cellular structures

Cell fate is regulated by extracellular environmental signals. Receptor specific interaction of the cell with proteins, glycans, soluble factors as well as neighboring cells can steer cells towards proliferation, differentiation, apoptosis or migration. In this review, approaches to build cellular structures by engineering aspects of the extracellular environment are described. These methods include non-specific modifications to control the wettability and stiffness of surfaces using self-assembled monolayers (SAMs) and polyelectrolyte multilayers (PEMs) as well as methods where the temporal activation and spatial distribution of adhesion ligands is controlled. Building on these techniques, construction of two-dimensional cell sheets using temperature sensitive polymers or electrochemical dissolution is described together with current applications of these grafts in the clinical arena. Finally, methods to pattern cells in three-dimensions as well as to functionalize the 3D environment with biologic motifs take us one step closer to being able to engineer multicellular tissues and organs.

Fetuin-A ({alpha}2HS-glycoprotein) is a major serum adhesive protein that mediates growth signaling in breast tumor cells

The identity of the cell adhesive factors in fetal bovine serum, commonly used to supplement growth media, remains a mystery due to the plethora of serum proteins. In the present analyses, we showed that fetuin-A, whose function in cellular attachment in tissue culture has been debated for many years, is indeed a major serum cell attachment factor particularly for tumor cells. We are able to report this because of a new purification strategy that has for the first time given us a homogeneous protein band in colloidal Coomassie-stained gels that retains biological activity. The tumor cells adhered to immobilized fetuin-A and not α(2)-macroglobulin, its major contaminant. The interaction of cells with fetuin-A was driven mainly by Ca(2+) ions, and cells growing in regular medium supplemented with fetal bovine serum were just as sensitive to loss of extracellular Ca(2+) ions as cells growing in fetuin-A. Fractionation of human serum revealed that cell attachment was confined to the fractions that had fetuin-A. Interestingly, the tumor cells also took up fetuin-A and secreted it back to the medium using an unknown mechanism that can be observed in live cells. The attachment of tumor cells to fetuin-A was accompanied by phosphatidylinositol 3-kinase/Akt activation that was down-regulated in cells that lack annexin-A6, one of the cell surface receptors for fetuin-A. Taken together, our data show the significance of fetuin-A in tumor cell growth mechanisms in vitro and open new research vistas for this protein.

Dentin matrix protein-1 isoforms promote differential cell attachment and migration

Dentin matrix protein-1 (DMP1), bone sialoprotein (BSP), and osteopontin (OPN) are three SIBLINGs (small integrin-binding ligand, N-linked glycoproteins) co-expressed/secreted by skeletal and active ductal epithelial cells. Although etiological mechanisms remain unclear, DMP1 is the only one of these three genes currently known to have mutations resulting in human disease, and yet it remains the least studied. All three contain the highly conserved integrin-binding tripeptide, RGD, and experiments comparing the cell attachment and haptotactic migration-enhancing properties of DMP1 to BSP and OPN were performed using human skeletal (MG63 and primary dental pulp cells) and salivary gland (HSG) cells. Mutation of any SIBLING's RGD destroyed all attachment and migration activity. Using its alphaVbeta5 integrin, HSG cells attached to BSP but not to DMP1 or OPN. However, HSG cells could not migrate onto BSP in a modified Boyden chamber assay. Expression of alphaVbeta3 integrin enhanced HSG attachment to DMP1 and OPN and promoted haptotactic migration onto all three proteins. Interchanging the first four coding exons or the conserved amino acids adjacent to the RGD of DMP1 with corresponding sequences of BSP did not enhance the ability of DMP1 to bind alphaVbeta5. For alphaVbeta3-expressing cells, intact DMP1, its BMP1-cleaved C-terminal fragment, and exon six lacking all post-translational modifications worked equally well but the proteoglycan isoform of DMP1 had greatly reduced ability for cell attachment and migration. The sequence specificity of the proposed BMP1-cleavage site of DMP1 was verified by mutation analysis. Direct comparison of the three proteins showed that cells discriminate among these SIBLINGs and among DMP1 isoforms.

Chondroitin sulphate decreases collagen synthesis in normal and scleroderma fibroblasts through a Smad-independent TGF-beta pathway--implication of C-Krox and Sp1

Despite several investigations, the transcriptional mechanisms which regulate the expression of both type I collagen genes (COL1A1 and COL1A2) in either physiological or pathological situations, such as scleroderma, are not completely known. In this study, we determined the effects of both native ichtyan chondroïtin sulphate (CS) and its derived hydrolytic fragments (CSf) on human normal (NF) and scleroderma (SF) fibroblasts. Here, we demonstrate for the first time that CS and CSf exert an inhibitory effect on type I collagen protein synthesis and decrease the corresponding mRNA steady-state levels of COL1A1 and COL1A2 in NF and SF. These glycosaminoglycan molecules repress COL1A1 gene transcription through a -112/-61 bp sequence upstream the start site of transcription and imply hc-Krox and Sp1 transcription factors. In addition, CS and CSf induced a down-regulation of TβRI expression. As a conclusion, our findings highlight a possible new role for CS and CSf as anti-fibrotic molecules and could help in elucidating the mechanisms of action by which CS and CSf exert their inhibitory effect on type I collagen synthesis.

Collagen/annexin V interactions regulate chondrocyte mineralization

Physiological mineralization in growth plate cartilage is highly regulated and restricted to terminally differentiated chondrocytes. Because mineralization occurs in the extracellular matrix, we asked whether major extracellular matrix components (collagens) of growth plate cartilage are directly involved in regulating the mineralization process. Our findings show that types II and X collagen interacted with cell surface-expressed annexin V. These interactions led to a stimulation of annexin V-mediated Ca(2+) influx resulting in an increased intracellular Ca(2+) concentration, [Ca(2+)](i), and ultimately increased alkaline phosphatase activity and mineralization of growth plate chondrocytes. Consequently, stimulation of these interactions (ascorbate to stimulate collagen synthesis, culturing cells on type II collagen-coated dishes, or overexpression of full-length annexin V) resulted in increase of [Ca(2+)](i), alkaline phosphatase activity, and mineralization of growth plate chondrocytes, whereas inhibition of these interactions (3,4-dehydro-l-proline to inhibit collagen secretion, K-201, a specific annexin channel blocker, overexpression of N terminus-deleted mutant annexin V that does not bind to type II collagen and shows reduced Ca(2+) channel activities) decreased [Ca(2+)](i), alkaline phosphatase activity, and mineralization. In conclusion, the interactions between collagen and annexin V regulate mineralization of growth plate cartilage. Because annexin V is up-regulated during pathological mineralization events of articular cartilage, it is possible that these interactions also regulate pathological mineralization.

How does chondroitinase promote functional recovery in the damaged CNS?

A number of recent studies have established that the bacterial enzyme chondroitinase ABC promotes functional recovery in the injured CNS. The issue of how it works is rarely addressed, however. The effects of the enzyme are presumed to be due to the degradation of inhibitory chondroitin sulphate GAG chains. Here we review what is known about the composition, structure and distribution of the extracellular matrix in the CNS, and how it changes in response to injury. We summarize the data pertaining to the ability of chondroitinase to promote functional recovery, both in the context of axon regeneration and the reactivation of plasticity. We also present preliminary data on the persistence of the effects of the enzyme in vivo, and its hyaluronan-degrading activity in CNS homogenates in vitro. We then consider precisely how the enzyme might influence functional recovery in the CNS. The ability of chondroitinase to degrade hyaluronan is likely to result in greater matrix disruption than the degradation of chondroitin sulphate alone.

Fetuin-A uptake in bovine vascular smooth muscle cells is calcium dependent and mediated by annexins

Fetuin-A is a known inhibitor of vascular calcification in vitro. In arteries with calcification, there is increased immunostaining for fetuin-A. However, vascular smooth muscle cells (VSMC) do not synthesize fetuin-A, suggesting fetuin-A may be endocytosed to exert its inhibitory effects. To examine the mechanism by which fetuin-A is taken up in bovine VSMC (BVSMC), we examined living cells by confocal microscopy and determined the uptake of Cy5-labeled fetuin-A. The results demonstrated that fetuin-A was taken up in BVSMC only in the presence of extracellular calcium, whereas phosphorus had no effect. Additional studies demonstrated the calcium-dependent uptake was specific for fetuin-A and only observed in BVSMC and osteoblasts, but not epithelial, endothelial, or adipose cells. The uptake was dose dependent, but could not be inhibited by excess unlabeled fetuin-A, suggesting a fluid phase rather than a receptor-mediated process. Fetuin-A also induced a sustained increase in intracellular calcium in BVSMC in the presence of extracellular calcium, whereas there was no increase in the absence of extracellular calcium. To further characterize the uptake, we utilized an inhibitor of annexin calcium channel activity, demonstrating inhibition of both fetuin-A uptake and intracellular calcium increase. Finally, we demonstrate that fetuin-A binds to annexin II at the cell membrane of BVSMC. In summary, our study demonstrates calcium- and annexin-dependent uptake of fetuin-A that leads to a sustained rise in intracellular calcium. This regulated uptake may be a mechanism by which fetuin-A inhibits VSMC calcification in the presence of excess calcium.

Versican/PG-M regulates chondrogenesis as an extracellular matrix molecule crucial for mesenchymal condensation

Mesenchymal cell condensation is an essential step for cartilage development. Versican/PG-M, a large chondroitin sulfate proteoglycan, is one of the major molecules expressed in the extracellular matrix during condensation. However, its role, especially as an environment for cells being condensed, has not been elucidated. Here we showed several lines of evidence for essential roles of versican/PG-M in chondrogenic condensation using a new chondrocytic cell line, N1511. Chondrogenic stimuli (treatment with parathyroid hormone, dexamethasone, 10% serum) induced a marked increase in the transcription and protein synthesis of versican/PG-M. Stable antisense clones for versican/PG-M, depending on suppression of the expression of versican/PG-M, showed different capacities for chondrogenesis, as indicated by the expression and deposition of aggrecan, a major chondrocytic cell product. The cells in the early stages of the culture only expressed V0 and V1 forms, having more chondroitin sulfate chains among the four variants of versican/PG-M, and treatment of those cells with chondroitinase ABC suppressed subsequent chondrogenesis. Furthermore, treatment with beta-xyloside, an artificial chain initiator of chondroitin sulfate synthesis to consequently inhibit the synthesis on the core proteins, suppressed chondrogenesis. In addition, forced expression of the variant V3, which has no chondroitin sulfate chain, disrupted the deposition and organization of native versican/PG-M (V0/V1) and other extracellular matrix molecules known to be expressed during the mesenchymal condensation and resulted in the inhibition of subsequent chondrogenesis. These results suggest that versican/PG-M is involved in positively regulating the formation of the mesenchymal matrix and the onset of chondrocyte differentiation through the attached chondroitin sulfate chains.

Demonstration of the Pleiotrophin-binding Oligosaccharide Sequences Isolated from Chondroitin Sulfate/Dermatan Sulfate Hybrid Chains of Embryonic Pig Brains

Mammalian brains contain significant amounts of chondroitin sulfate (CS), dermatan sulfate (DS), and CS/DS hybrid chains. CS/DS chains isolated from embryonic pig brains (E-CS/DS) promote the outgrowth of neurites in embryonic mouse hippocampal neurons in culture by interacting with pleiotrophin (PTN), a heparin-binding growth factor. Here, we analyzed oligosaccharides isolated from E-CS/DS, which showed that octasaccharides were the minimal size capable of interacting with PTN at a physiological salt concentration. Five and eight sequences were purified from fluorescently labeled PTN-bound and -unbound octasaccharide fractions, respectively, by enzymatic digestion followed by PTN-affinity chromatography. Their sequences were determined by enzymatic digestion in conjunction with high performance liquid chromatography, revealing a critical role for oversulfated D and/or iD disaccharides in the low yet significant affinity for PTN, which is required for neuritogenesis. The critical D and iD units are GlcUA(2-O-sulfate)beta1-3GalNAc(6-O-sulfate) and IdoUA(2-O-sulfate)alpha1-3GalNAc(6-O-sulfate), respectively, where IdoUA represents L-iduronic acid. In contrast, high affinity interactions with PTN required decasaccharides with E units (GlcUAbeta1-3GalNAc(4, 6-O-disulfate)), B units (GlcUA(2-O-sulfate)beta1-3GalNAc(4-O-sulfate)), and/or their IdoUA-containing counterparts (iE and iB) in addition to D/iD units, although the biological significance of such strong interactions remains to be investigated. Thus, chain size and composition are crucial to the interaction with PTN, and PTN binds to multiple sequences in E-CS/DS chains with distinct affinity. Notably, not only heparan sulfate but also CS/DS hybrid chain structures of mammalian brains contain a high degree of microheterogeneity with a cluster of oversulfated disaccharides and appear to play roles in regulating the functions of PTN.

Effect of chondroitin sulfate and hyaluronic acid on gene expression in a three-dimensional culture of chondrocytes

The effect of glycosaminoglycan addition on a three-dimensional (3D) culture of porcine chondrocyte cells was investigated with a view to use in cartilage regenerative medicine. Chondroitin sulfate C increased the mRNA expression of type 2 collagen, while chondroitin sulfate A did not. Hyaluronic acid of high molecular weight markedly decreased the mRNA expression of both aggrecan and type 2 collagen, although hyaluronic acid of low molecular weight showed no apparent effect.

Annexins expressed on the cell surface serve as receptors for adhesion to immobilized fetuin-A

Fetuin-A is a major constituent of the fetal bovine serum used extensively in cell culture media. We hereby present data demonstrating that breast carcinoma cells can adhere to immobilized fetuin-A in a calcium-dependent fashion. Interestingly, the cells can also divide and attain confluency under these conditions. Using a proteomic approach, we have identified annexin-II and -VI as the putative cell surface receptors for fetuin-A in the presence of Ca2+ ions. Biotinylation of cell surface proteins followed by immunoprecipitation revealed that annexin-VI was expressed on the extracytoplasmic surface of the cell membranes. Finally, to demonstrate that annexin-II and -VI were the adhesive receptors for fetuin-A, siRNA knockdown of expression of the annexins significantly reduced the calcium-mediated adhesion. Interestingly, we demonstrated that the tumor cells could also adhere to immobilized fetuin-A in the presence of magnesium ions, and that this adhesion was most likely mediated by integrins because neutralizing antibodies against beta1 integrins substantially reduced the adhesion. Our studies suggest that the expression of annexin-II and -VI and possibly other members of the family mediate novel adhesion and signaling mechanisms in tumor cells.

Identification and Characterization of the Acidic pH Binding Sites for Growth Regulatory Ligands of Low Density Lipoprotein Receptor-related Protein-1

The type V TGF-beta receptor (TbetaR-V) plays an important role in growth inhibition by IGFBP-3 and TGF-beta in responsive cells. Unexpectedly, TbetaR-V was recently found to be identical to the LRP-1/alpha(2)M receptor; this has disclosed previously unreported growth regulatory functions of LRP-1. Here we demonstrate that, in addition to expressing LRP-1, all cells examined exhibit low affinity but high density acidic pH binding sites for LRP-1 growth regulatory ligands (TGF-beta(1), IGFBP-3, and alpha(2)M(*)). These sites, like LRP-1, are sensitive to receptor-associated protein and calcium depletion but, unlike LRP-1, are also sensitive to chondroitin sulfate and heparin and capable of directly binding ligands, which do not bind to LRP-1. Annexin VI has been identified as a major membrane-associated protein capable of directly binding alpha(2)M(*) at acidic pH. This is evidenced by: 1) structural and Western blot analyses of the protein purified from bovine liver plasma membranes by alpha(2)M(*) affinity column chromatography at acidic pH, and 2) dot blot analysis of the interaction of annexin VI and (125)I-alpha(2)M(*). Cell surface annexin VI is involved in (125)I-TGF-beta(1) and (125)I-alpha(2)M(*) binding to the acidic pH binding sites and (125)I-alpha(2)M(*) binding to LRP-1 at neutral pH as demonstrated by the sensitivity of cells to pretreatment with anti-annexin VI IgG. Cell surface annexin VI is also capable of mediating internalization and degradation of cell surface-bound (125)I-TGF-beta(1) and (125)I-alpha(2)M(*) at pH 6 and of forming ternary complexes with (125)I-alpha(2)M(*) and LRP-1 at neutral pH as demonstrated by co-immunoprecipitation. Trifluoperazine and fluphenazine, which inhibit ligand binding to the acidic pH binding sites, block degradation after internalization of cell surface-bound (125)I-TGF-beta(1) or (125)I-alpha(2)M(*). These results suggest that cell surface annexin VI may function as an acidic pH binding site or receptor and may also function as a co-receptor with LRP-1 at neutral pH.

Proteoglycans in Atherosclerosis and Restenosis

The proteoglycan versican is one of several extracellular matrix (ECM) molecules that accumulate in lesions of atherosclerosis and restenosis. Its unique structural features create a highly interactive molecule that binds growth factors, enzymes, lipoproteins, and a variety of other ECM components to influence fundamental events involved in vascular disease. Versican is one of the principal genes that is upregulated after vascular injury and is a prominent component in stented and nonstented restenotic lesions. The synthesis of versican is highly regulated by specific growth factors and cytokines and the principal source of versican is the smooth muscle cell. Versican interacts with hyaluronan, a long chain glycosaminoglycan, to create expanded viscoelastic pericellular matrices that are required for arterial smooth muscle cell (ASMC) proliferation and migration. Versican is also prominent in advanced lesions of atherosclerosis, at the borders of lipid-filled necrotic cores as well as at the plaque-thrombus interface, suggesting roles in lipid accumulation, inflammation, and thrombosis. Versican influences the assembly of ECM and controls elastic fiber fibrillogenesis, which is of fundamental importance in ECM remodeling during vascular disease. Collectively, these studies highlight the critical importance of this specific ECM component in atherosclerosis and restenosis.

Macrocyclic proteoglycan mimics. Potent inhibition of cell adhesion by a bundle of chondroitin sulfate chains assembled on the calix[4]resorcarene platform

Tailed calix[4]resorcarene macrocycle (tail=undecyl) can be used as a platform to assemble four glycosaminoglycan polysaccharide chains to give a new type of proteoglycan mimics. A tetra(chondroitin sulfate) derivative thus obtained from the reaction of macrocyclic octaamine and chondroitin sulfate lactone is readily immobilized on a tissue culture plastic (polystyrene) plate and inhibits fibronectin-mediated adhesion of BHK (baby hamster kidney) cells thereon remarkably strongly with 50% inhibition occurring at a 10 ng/mL or 40 pM concentration range.