Sulfated oligosaccharides (heparin and fucoidan) binding and dimerization of stromal cell-derived factor-1 (SDF-1/CXCL 12) are coupled as evidenced by affinity CE-MS analysis

An emerging paradigm of CXCL12 involvement in the metastatic cascade

The chemokine CXCL12, also known as stromal cell-derived factor 1 (SDF1), has emerged as a pivotal regulator in the intricate molecular networks driving cancer progression. As an influential factor in the tumor microenvironment, CXCL12 plays a multifaceted role that spans beyond its traditional role as a chemokine inducing invasion and metastasis. Indeed, CXCL12 has been assigned functions related to epithelial-to-mesenchymal transition, cancer cell stemness, angiogenesis, and immunosuppression, all of which are currently viewed as specialized biological programs contributing to the "metastatic cascade" among other cancer hallmarks. Its interaction with its cognate receptor, CXCR4, initiates a cascade of events that not only shapes the metastatic potential of tumor cells but also defines the niches within the secondary organs that support metastatic colonization. Given the profound implications of CXCL12 in the metastatic cascade, understanding its mechanistic underpinnings is of paramount importance for the targeted elimination of rate-limiting steps in the metastatic process. This review aims to provide a comprehensive overview of the current knowledge surrounding the role of CXCL12 in cancer metastasis, especially its molecular interactions rationalizing its potential as a therapeutic target.

Rongjin Niantong Fang ameliorates cartilage degeneration by regulating the SDF-1/CXCR4-p38MAPK signalling pathway

CONTEXT

Rongjin Niantong Fang (RJNTF) is a Traditional Chinese Medicine formulation with a good therapeutic effect on osteoarthritis (OA). However, the underlying mechanisms remain unclear.

OBJECTIVE

This study investigates whether RJNTF could delay OA cartilage degeneration by regulating the SDF-1/CXCR4-p38MAPK signalling pathway.

MATERIALS AND METHODS

The Sprague-Dawley (SD) rats were used to establish the OA model by a modified Hulth's method. SD rats were divided into three groups (n = 10): blank group, model group (0.9% saline, 10 mL/kg/day), and treatment group (RJNTF, 4.5 g/kg/day). After 12 weeks of treatment, each group was analysed by H&E, Safranine-O solid green, ELISA, Immunohistochemistry, and Western blot. An in vitro model was induced with 100 ng/mL SDF-1 by ELISA, the blank group, model group, RJNTF group, and inhibitor group with intervention for 12 h, each group was analysed by Immunofluorescence staining and Western blot.

RESULTS

SDF-1 content in the synovium was reduced in RJNTF treatment group compared to non-treatment model group (788.10 vs. 867.32 pg/mL) and down-regulation of CXCR4, MMP-3, MMP-9, MMP-13 protein expression, along with p38 protein phosphorylated were observed in RJNTF treatment group. In vitro results showed that RJNTF (IC₅₀ = 8.925 mg/mL) intervention could down-regulate SDF-1 induced CXCR4 and p38 protein phosphorylated and reduce the synthesis of MMP-3, MMP-9, and MMP-13 proteins of chondrocytes from SD rat cartilage tissues.

DISCUSSION AND CONCLUSION

RJNTF alleviates OA cartilage damage by SDF-1/CXCR4-p38MAPK signalling pathway inhibition. Our ongoing research focuses on Whether RJNTF treats OA through alternative pathways.

Studying protein structure and function by native separation–mass spectrometry

Alterations in protein structure may have profound effects on biological function. Analytical techniques that permit characterization of proteins while maintaining their conformational and functional state are crucial for studying changes in the higher order structure of proteins and for establishing structure-function relationships. Coupling of native protein separations with mass spectrometry is emerging rapidly as a powerful approach to study these aspects in a reliable, fast and straightforward way. This Review presents the available native separation modes for proteins, covers practical considerations on the hyphenation of these separations with mass spectrometry and highlights the involvement of affinity-based separations to simultaneously obtain structural and functional information of proteins. The impact of these approaches is emphasized by selected applications addressing biomedical and biopharmaceutical research questions.

Affinity Capillary Electrophoresis-Mass Spectrometry as a Tool to Unravel Proteoform-Specific Antibody-Receptor Interactions

Monoclonal antibody (mAb) pharmaceuticals consist of a plethora of different proteoforms with different functional characteristics, including pharmacokinetics and pharmacodynamics, requiring their individual assessment. Current binding techniques do not distinguish between coexisting proteoforms requiring tedious production of enriched proteoforms. Here, we have developed an approach based on mobility shift-affinity capillary electrophoresis-mass spectrometry (ACE-MS), which permitted us to determine the binding of coexisting mAb proteoforms to Fc receptors (FcRs). For high-sensitivity MS analysis, we used a sheathless interface providing adequate mAb sensitivity allowing functional characterization of mAbs with a high sensitivity and dynamic range. As a model system, we focused on the interaction with the neonatal FcR (FcRn), which determines the half-life of mAbs. Depending on the oxidation status, proteoforms exhibited different electrophoretic mobility shifts in the presence of FcRn, which could be used to determine their affinity. We confirmed the decrease of the FcRn affinity with antibody oxidation and observed a minor glycosylation effect, with higher affinities for galactosylated glycoforms. Next to relative binding, the approach permits the determination of individual K_D values in solution resulting in values of 422 and 139 nM for double-oxidized and non-oxidized variants. Hyphenation with native MS provides unique capabilities for simultaneous heterogeneity assessment for mAbs, FcRn, and complexes formed. The latter provides information on binding stoichiometry revealing 1:1 and 1:2 for antibody/FcRn complexes. The use of differently engineered Fc-only constructs allowed distinguishing between symmetric and asymmetric binding. The approach opens up unique possibilities for proteoform-resolved antibody binding studies to FcRn and can be extended to other FcRs and protein interactions.

RHAMM Is a Multifunctional Protein That Regulates Cancer Progression

The functional complexity of higher organisms is not easily accounted for by the size of their genomes. Rather, complexity appears to be generated by transcriptional, translational, and post-translational mechanisms and tissue organization that produces a context-dependent response of cells to specific stimuli. One property of gene products that likely increases the ability of cells to respond to stimuli with complexity is the multifunctionality of expressed proteins. Receptor for hyaluronan-mediated motility (RHAMM) is an example of a multifunctional protein that controls differential responses of cells in response-to-injury contexts. Here, we trace its evolution into a sensor-transducer of tissue injury signals in higher organisms through the detection of hyaluronan (HA) that accumulates in injured microenvironments. Our goal is to highlight the domain and isoform structures that generate RHAMM's function complexity and model approaches for targeting its key functions to control cancer progression.

The dimeric form of CXCL12 binds to atypical chemokine receptor 1

The pleiotropic chemokine CXCL12 is involved in diverse physiological and pathophysiological processes, including embryogenesis, hematopoiesis, leukocyte migration, and tumor metastasis. It is known to engage the classical receptor CXCR4 and the atypical receptor ACKR3. Differential receptor engagement can transduce distinct cellular signals and effects as well as alter the amount of free, extracellular chemokine. CXCR4 binds both monomeric and the more commonly found dimeric forms of CXCL12, whereas ACKR3 binds monomeric forms. Here, we found that CXCL12 also bound to the atypical receptor ACKR1 (previously known as Duffy antigen/receptor for chemokines or DARC). In vitro nuclear magnetic resonance spectroscopy and isothermal titration calorimetry revealed that dimeric CXCL12 bound to the extracellular N terminus of ACKR1 with low nanomolar affinity, whereas the binding affinity of monomeric CXCL12 was orders of magnitude lower. In transfected MDCK cells and primary human Duffy-positive erythrocytes, a dimeric, but not a monomeric, construct of CXCL12 efficiently bound to and internalized with ACKR1. This interaction between CXCL12 and ACKR1 provides another layer of regulation of the multiple biological functions of CXCL12. The findings also raise the possibility that ACKR1 can bind other dimeric chemokines, thus potentially further expanding the role of ACKR1 in chemokine retention and presentation.

Surface plasmon resonance imaging coupled to on-chip mass spectrometry: a new tool to probe protein-GAG interactions

A biosensor device for the detection and characterization of protein-glycosaminoglycan interactions is being actively sought and constitutes the key to identifying specific carbohydrate ligands, an important issue in glycoscience. Mass spectrometry (MS) hyphenated methods are promising approaches for carbohydrate enrichment and subsequent structural characterization. In the study herein, we report the analysis of interactions between the glycosaminoglycans (GAGs) heparin (HP) and heparan sulfate (HS) and various cytokines by coupling surface plasmon resonance imaging (SPRi) for thermodynamic analysis method and MALDI-TOF MS for structural determination. To do so, we developed an SPR biochip in a microarray format and functionalized it with a self-assembled monolayer of short poly(ethylene oxide) chains for grafting the human cytokines stromal cell-derived factor-1 (SDF-1α), monocyte chemotactic protein-1 (MCP-1), and interferon-γ. The thermodynamic parameters of the interactions between these cytokines and unfractionated HP/HS and derived oligosaccharides were successively determined using SPRi monitoring, and the identification of the captured carbohydrates was carried out directly on the biochip surface using MALDI-TOF MS, revealing cytokine preferential affinity for GAGs. The MS identification was enhanced by on-chip digestion of the cytokine-bound GAGs with heparinase, leading to the detection of oligosaccharides likely involved in the binding sequence of GAG ligands. Although several carbohydrate array-based assays have been reported, this study is the first report of the successful analysis of protein-GAG interactions using SPRi-MS coupling.

Fucoidan-coated coral-like Pt nanoparticles for computed tomography-guided highly enhanced synergistic anticancer effect against drug-resistant breast cancer cells

Chemotherapy, the most commonly applied cancer treatment, often causes unexpected failure due to multidrug resistance (MDR). To overcome MDR, we have designed a platform to realize a combinational synergistic effect of a natural bioactive product (fucoidan), anticancer small compound (doxorubicin), and photothermal nanocarrier (Pt nanoparticle) to treat drug-resistant breast cancer cells. Especially, fucoidan, a sulfated, polysaccharide-structured, therapeutic biopolymer, has been recently recognized as a potential anticancer compound; however, its cancer-inhibiting efficacy has been regarded as low owing to its insufficient level in serum following its conventional oral ingestion. To enhance its potency, fucoidan was applied as a biocompatible surfactant and surface-coating biopolymer in nanocarrier synthesis to manufacture coral-like, fucoidan-coated Pt nanoparticles with a rough surface morphology by a one-pot method. As a result, the biological-thermo-chemo trimodal combination treatment showed excellent therapeutic efficiency against the MDR breast cancer cell MCF-7 ADR both in vitro and in vivo, and the computed tomography contrast effect was also confirmed from the constituent element Pt. Beyond universal application in drug delivery and photothermal therapy, the present approach of applying a MDR modulating/anticancer natural product from nanoparticle synthesis to theranostics will contribute greatly to maximizing their potential through interdisciplinary convergence in the near future.

Pathological roles of the homeostatic chemokine CXCL12

CXCL12 is a CXC chemokine that traditionally has been classified as a homeostatic chemokine. It contributes to physiological processes such as embryogenesis, hematopoiesis and angiogenesis. In contrast to these homeostatic functions, increased expression of CXCL12 in general, or of a specific CXCL12 splicing variant has been demonstrated in various pathologies. In addition to this increased or differential transcription of CXCL12, also upregulation of its receptors CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3) contributes to the onset or progression of diseases. Moreover, posttranslational modification of CXCL12 during disease progression, through interaction with locally produced molecules or enzymes, also affects CXCL12 activity, adding further complexity. As CXCL12, CXCR4 and ACKR3 are broadly expressed, the number of pathologies wherein CXCL12 is involved is growing. In this review, the role of the CXCL12/CXCR4/ACKR3 axis will be discussed for the most prevalent pathologies. Administration of CXCL12-neutralizing antibodies or small-molecule antagonists of CXCR4 or ACKR3 delays disease onset or prevents disease progression in cancer, viral infections, inflammatory bowel diseases, rheumatoid arthritis and osteoarthritis, asthma and acute lung injury, amyotrophic lateral sclerosis and WHIM syndrome. On the other hand, CXCL12 has protective properties in Alzheimer's disease and multiple sclerosis, has a beneficial role in wound healing and has crucial homeostatic properties in general.

Natural nitration of CXCL12 reduces its signaling capacity and chemotactic activity in vitro and abrogates intra-articular lymphocyte recruitment in vivo

The chemokine CXCL12/stromal cell-derived factor-1 is important for leukocyte migration to lymphoid organs and inflamed tissues and stimulates tumor development. In vitro, CXCL12 activity through CXCR4 is abolished by proteolytic processing. However, limited information is available on in vivo effects of posttranslationally modified CXCL12. Natural CXCL12 was purified from the coculture supernatant of stromal cells stimulated with leukocytes and inflammatory agents. In this conditioned medium, CXCL12 with a nitration on Tyr⁷, designated [3-NT⁷]CXCL12, was discovered via Edman degradation. CXCL12 and [3-NT⁷]CXCL12 were chemically synthesized to evaluate the biological effects of this modification. [3-NT⁷]CXCL12 recruited β-arrestin 2 and phosphorylated the Akt kinase similar to CXCL12 in receptor-transfected cells. Also the affinity of CXCL12 and [3-NT⁷]CXCL12 for glycosaminoglycans, the G protein-coupled chemokine receptor CXCR4 and the atypical chemokine receptor ACKR3 were comparable. However, [3-NT⁷]CXCL12 showed a reduced ability to enhance intracellular calcium concentrations, to generate inositol triphosphate, to phosphorylate ERK1/2 and to induce monocyte and lymphocyte chemotaxis in vitro. Moreover, nitrated CXCL12 failed to induce in vivo extravasation of lymphocytes to the joint. In summary, nitration on Tyr⁷ under inflammatory conditions is a novel natural posttranslational regulatory mechanism of CXCL12 which may downregulate the CXCR4-mediated inflammatory and tumor-promoting activities of CXCL12.

The unique structural and functional features of CXCL12

The CXC chemokine CXCL12 is an important factor in physiological and pathological processes, including embryogenesis, hematopoiesis, angiogenesis and inflammation, because it activates and/or induces migration of hematopoietic progenitor and stem cells, endothelial cells and most leukocytes. Therefore, CXCL12 activity is tightly regulated at multiple levels. CXCL12 has the unique property of existing in six splice variants in humans, each having a specific tissue distribution and in vivo activity. Controlled splice variant transcription and mRNA stability determine the CXCL12 expression profile. CXCL12 fulfills its functions in homeostatic and pathological conditions by interacting with its receptors CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3) and by binding to glycosaminoglycans (GAGs) in tissues and on the endothelium to allow a proper presentation to passing leukocytes. Homodimerizaton and heterodimerization of CXCL12 and its receptors can alter their signaling activity, as exemplified by the synergy between CXCL12 and other chemokines in leukocyte migration assays. Receptor binding may also initiate CXCL12 internalization and its subsequent removal from the environment. Furthermore, CXCL12 activity is regulated by posttranslational modifications. Proteolytic removal of NH₂- or COOH-terminal amino acids, citrullination of arginine residues by peptidyl arginine deiminases or nitration of tyrosine residues reduce CXCL12 activity. This review summarizes the interactions of CXCL12 with the cellular environment and discusses the different levels of CXCL12 activity regulation.

Using biomaterials to rewire the process of wound repair

Wound healing is one of the most complex processes that our bodies must perform. While our ability to repair wounds is often taken for granted, conditions such as diabetes, obesity, or simply old age can significantly impair this process. With the incidence of all three predicted to continue growing into the foreseeable future, there is an increasing push to develop strategies that facilitate healing. Biomaterials are an attractive approach for modulating all aspects of repair, and have the potential to steer the healing process towards regeneration. In this review, we will cover recent advances in developing biomaterials that actively modulate the process of wound healing, and will provide insight into how biomaterials can be used to simultaneously rewire multiple phases of the repair process.

Binding of the chemokine CXCL12α to its natural extracellular matrix ligand heparan sulfate enables myoblast adhesion and facilitates cell motility

The chemokine CXCL12α is a potent chemoattractant that guides the migration of muscle precursor cells (myoblasts) during myogenesis and muscle regeneration. To study how the molecular presentation of chemokines influences myoblast adhesion and motility, we designed multifunctional biomimetic surfaces as a tuneable signalling platform that enabled the response of myoblasts to selected extracellular cues to be studied in a well-defined environment. Using this platform, we demonstrate that CXCL12α, when presented by its natural extracellular matrix ligand heparan sulfate (HS), enables the adhesion and spreading of myoblasts and facilitates their active migration. In contrast, myoblasts also adhered and spread on CXCL12α that was quasi-irreversibly surface-bound in the absence of HS, but were essentially immotile. Moreover, co-presentation of the cyclic RGD peptide as integrin ligand along with HS-bound CXCL12α led to enhanced spreading and motility, in a way that indicates cooperation between CXCR4 (the CXCL12α receptor) and integrins (the RGD receptors). Our findings reveal the critical role of HS in CXCL12α induced myoblast adhesion and migration. The biomimetic surfaces developed here hold promise for mechanistic studies of cellular responses to different presentations of biomolecules. They may be broadly applicable for dissecting the signalling pathways underlying receptor cross-talks, and thus may guide the development of novel biomaterials that promote highly specific cellular responses.

Incorporation of heparin-binding proteins into preformed dextran sulfate-chitosan nanoparticles

Incorporation of proteins into dextran sulfate (DS)-chitosan (CS) nanoparticles (DSCS NPs) is commonly performed using entrapment procedures, in which protein molecules are mixed with DS and CS until particle formation occurs. As DS is an analog of heparin, the authors examined whether proteins could be directly incorporated into preformed DSCS NPs through a heparin binding domain-mediated interaction. The authors formulated negatively-charged DSCS NPs, and quantified the amount of charged DS in the outer shell of the particles. The authors then mixed the DSCS NPs with heparin-binding proteins (SDF-1α, VEGF, FGF-2, BMP-2, or lysozyme) to achieve incorporation. Data show that for DSCS NPs containing 100 nmol charged glucose sulfate units in DS, up to ~1.5 nmol of monomeric or ~0.75 nmol of dimeric heparin-binding proteins were incorporated without significantly altering the size or zeta potential of the particles. Incorporation efficiencies of these proteins were 95%–100%. In contrast, serum albumin or serum globulin showed minimal incorporation (8% and 4%, respectively) in 50% physiological saline, despite their large adsorption in water (80% and 92%, respectively). The NP-incorporated SDF-1α and VEGF exhibited full activity and sustained thermal stability. An in vivo aerosolization study showed that NP-incorporated SDF-1α persisted in rat lungs for 72 h (~34% remaining), while free SDF-1α was no longer detectable after 16 h. As many growth factors and cytokines contain heparin-binding sites/domains, incorporation into preformed DSCS NPs could facilitate in vivo applications of these proteins.

Effects of Platelet-Rich Plasma & Platelet-Rich Fibrin with and without Stromal Cell-Derived Factor-1 on Repairing Full-Thickness Cartilage Defects in Knees of Rabbits

BACKGROUND

The purpose of this study was to create biomaterial scaffolds like platelet-rich plasma (PRP) and platelet-rich fibrin (PRF) containing stromal cell-derived factor-1 (SDF1) as a chemokine to induce hyaline cartilage regeneration of rabbit knee in a full thickness defect.

METHODS

We created a full thickness defect in the trochlear groove of thirty-six bilateral knees of eighteen mature male rabbits. The knees were randomly divided into six groups (group I: untreated control, group II: PRP, group III: PRF, group IV: Gelatin+SDF1, group V: PRP+SDF1, and group VI: PRF+SDF1). After four weeks, the tissue specimens were evaluated by macroscopic examination and histological grading, immunofluorescent staining for collagen type II, and analyzed for cartilage marker genes by real-time PCR. The data were compared using statistical methods (SPSS 20, Kruskal-Wallis test, Bonferroni post hoc test and P<0.05).

RESULTS

Macroscopic evaluations revealed that international cartilage repair society (ICRS) scores of the PRF+SDF1 group were higher than other groups. Microscopic analysis showed that the ICRS score of the PRP group was significantly lower than other groups. Immunofluorescent staining for collagen II demonstrated a remarkable distribution of type II collagen in the Gel+SDF1, PRP+SDF1 and PRF+SDF1 groups compared with other groups. Real-time PCR analysis revealed that mRNA expression of SOX9 and aggrecan were significantly greater in the PRF+SDF1, PRP+SDF1, Gel+SDF1 and PRF groups than the control group (P<0.05).

CONCLUSION

Our results indicate that implantation of PRF scaffold containing SDF1 led to the greatest evaluation scores of full-thickness lesions in rabbits.

Identification of a Pro-Angiogenic Potential and Cellular Uptake Mechanism of a LMW Highly Sulfated Fraction of Fucoidan from Ascophyllum nodosum

Herein we investigate the structure/function relationships of fucoidans from Ascophyllum nodosum to analyze their pro-angiogenic effect and cellular uptake in native and glycosaminoglycan-free (GAG-free) human endothelial cells (HUVECs). Fucoidans are marine sulfated polysaccharides, which act as glycosaminoglycans mimetics. We hypothesized that the size and sulfation rate of fucoidans influence their ability to induce pro-angiogenic processes independently of GAGs. We collected two fractions of fucoidans, Low and Medium Molecular Weight Fucoidan (LMWF and MMWF, respectively) by size exclusion chromatography and characterized their composition (sulfate, fucose and uronic acid) by colorimetric measurement and Raman and FT-IR spectroscopy. The high affinities of fractionated fucoidans to heparin binding proteins were confirmed by Surface Plasmon Resonance. We evidenced that LMWF has a higher pro-angiogenic (2D-angiogenesis on Matrigel) and pro-migratory (Boyden chamber) potential on HUVECs, compared to MMWF. Interestingly, in a GAG-free HUVECs model, LMWF kept a pro-angiogenic potential. Finally, to evaluate the association of LMWF-induced biological effects and its cellular uptake, we analyzed by confocal microscopy the GAGs involvement in the internalization of a fluorescent LMWF. The fluorescent LMWF was mainly internalized through HUVEC clathrin-dependent endocytosis in which GAGs were partially involved. In conclusion, a better characterization of the relationships between the fucoidan structure and its pro-angiogenic potential in GAG-free endothelial cells was required to identify an adapted fucoidan to enhance vascular repair in ischemia.

Therapies from Fucoidan: An Update

Fucoidans are a class of sulfated fucose-rich polysaccharides found in brown marine algae and echinoderms. Fucoidans have an attractive array of bioactivities and potential applications including immune modulation, cancer inhibition, and pathogen inhibition. Research into fucoidan has continued to gain pace over the last few years and point towards potential therapeutic or adjunct roles. The source, extraction, characterization and detection of fucoidan is discussed.

Novel stable cytokine delivery system in physiological pH solution: chitosan oligosaccharide/heparin nanoparticles

Background

Cell therapy is a promising strategy for tissue regeneration. Key to this strategy is mobilization and recruitment of exogenous or autologous stem/progenitor cells by cytokines. However, there is no effective cytokine delivery system available for clinic application, in particular for myocardial regeneration. The aim of this study was to develop a novel cytokine delivery system that is stable in solution at physiological pH.

Methods

Four groups of self-assembled chitosan oligosaccharide/heparin (CSO/H) nanoparticles were prepared with various volume ratios of chitosan oligosaccharide to heparin (5:2, 5:4, 4:15, 1:5) and characterized by laser diffraction, particle size analysis, and transmission electron microscopy. The encapsulation efficiency and loading content of two cytokines, ie, stromal cell-derived factor (SDF)-1α and vascular endothelial growth factor (VEGF) were quantified using an enzyme-linked immunosorbent assay. The biological activity of the loaded SDF-1α and VEGF was evaluated using the transwell migration assay and MTT assay. The dispersion profiles for the cytokine-loaded nanoparticles were quantified using fluorescence molecular tomography.

Results

CSO/H nanoparticles were prepared successfully in solution with physiological pH. The particle sizes in the four treatment groups were in the range of 96.2–210.5 nm and the zeta potential ranged from −29.4 mV to 24.2 mV. The loading efficiency in the CSO/H nanoparticle groups with the first three ratios was more than 90%. SDF-1α loaded into CSO/H nanoparticles retained its migration activity and VEGF loaded into CSO/H nanoparticles continued to show proliferation activity. The in vivo dispersion test showed that the CSO/H nanoparticles enabled to VEGF to accumulate locally for a longer period of time.

Conclusion

CSO/H nanoparticles have a high cytokine loading capacity and allow cytokines to maintain their bioactivity for longer, are stable in an environment with physiological pH, and may be a promising cytokine delivery system for tissue regeneration.

Cell, isoform, and environment factors shape gradients and modulate chemotaxis

Chemokine gradient formation requires multiple processes that include ligand secretion and diffusion, receptor binding and internalization, and immobilization of ligand to surfaces. To understand how these events dynamically shape gradients and influence ensuing cell chemotaxis, we built a multi-scale hybrid agent-based model linking gradient formation, cell responses, and receptor-level information. The CXCL12/CXCR4/CXCR7 signaling axis is highly implicated in metastasis of many cancers. We model CXCL12 gradient formation as it is impacted by CXCR4 and CXCR7, with particular focus on the three most highly expressed isoforms of CXCL12. We trained and validated our model using data from an in vitro microfluidic source-sink device. Our simulations demonstrate how isoform differences on the molecular level affect gradient formation and cell responses. We determine that ligand properties specific to CXCL12 isoforms (binding to the migration surface and to CXCR4) significantly impact migration and explain differences in in vitro chemotaxis data. We extend our model to analyze CXCL12 gradient formation in a tumor environment and find that short distance, steep gradients characteristic of the CXCL12-γ isoform are effective at driving chemotaxis. We highlight the importance of CXCL12-γ in cancer cell migration: its high effective affinity for both extracellular surface sites and CXCR4 strongly promote CXCR4+ cell migration. CXCL12-γ is also more difficult to inhibit, and we predict that co-inhibition of CXCR4 and CXCR7 is necessary to effectively hinder CXCL12-γ-induced migration. These findings support the growing importance of understanding differences in protein isoforms, and in particular their implications for cancer treatment.

On-line capillary isoelectric focusing hyphenated to native electrospray ionization mass spectrometry for the characterization of interferon-γ and variants

The on-line hyphenation of Capillary IsoElectric Focusing (CIEF) with ElectroSpray Ionization Mass Spectrometry (ESI/MS) has been carried out in a non-denaturing detection mode at the CIEF-MS interface.

Microfluidic source-sink model reveals effects of biophysically distinct CXCL12 isoforms in breast cancer chemotaxis

Chemokines critically regulate chemotaxis in normal and pathologic states, but there is limited understanding of how multicellular interactions generate gradients needed for cell migration. Previous studies of chemotaxis of CXCR4+ cells toward chemokine CXCL12 suggest the requirement of cells expressing scavenger receptor CXCR7 in a source-sink system. We leveraged an established microfluidic device to discover that chemotaxis of CXCR4 cells toward distinct isoforms of CXCL12 required CXCR7 scavenging only under conditions with higher than optimal levels of CXCL12. Chemotaxis toward CXCL12-β and -γ isoforms, which have greater binding to extracellular molecules and have been largely overlooked, was less dependent on CXCR7 than the more commonly studied CXCL12-α. Chemotaxis of CXCR4+ cells toward even low levels of CXCL12-γ and CXCL12-β still occurred during treatment with a FDA-approved inhibitor of CXCR4. We also detected CXCL12-γ only in breast cancers from patients with advanced disease. Physiological gradient formation within the device facilitated interrogation of key differences in chemotaxis among CXCL12 isoforms and suggests CXCL12-γ as a biomarker for metastatic cancer.

Preparation and characterization of antioxidant nanoparticles composed of chitosan and fucoidan for antibiotics delivery

In this study, we developed novel chitosan/fucoidan nanoparticles (CS/F NPs) using a simple polyelectrolyte self-assembly method and evaluated their potential to be antioxidant carriers. As the CS/F weight ratio was 5/1, the CS/F NPs were spherical and exhibited diameters of approximately 230-250 nm, as demonstrated by TEM. These CS/F NPs maintained compactness and stability for 25 day in phosphate-buffered saline (pH 6.0-7.4). The CS/F NPs exhibited highly potent antioxidant effects by scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH), reducing the concentration of intracellular reactive oxygen species (ROS) and superoxide anion (O2-) in stimulated macrophages. The DPPH scavenging effect of CS/F NPs primarily derives from fucoidan. Furthermore, these CS/F NPs activated no host immune cells into inflammation-mediated cytotoxic conditions induced by IL-6 production and NO generation. The MTT cell viability assay revealed an absence of toxicity in A549 cells after exposure to the formulations containing 0.375 mg NPs/mL to 3 mg NPs/mL. Gentamicin (GM), an antibiotic, was used as a model drug for an in vitro releasing test. The CS/F NPs controlled the release of GM for up to 72 h, with 99% of release. The antioxidant CS/F NPs prepared in this study could thus be effective in delivering antibiotics to the lungs, particularly for airway inflammatory diseases.

New targets for glycosaminoglycans and glycosaminoglycans as novel targets

Biological functions of a variety of proteins are mediated via their interaction with glycosaminoglycans (GAGs). The structural diversity within the wide GAG landscape provides individual interaction sites for a multitude of proteins involved in several pathophysiological processes. This 'GAG angle' of such proteins as well as their specific GAG ligands give rise to novel therapeutic concepts for drug development. Current glycomic technologies to elucidate the glycan structure-function relationships, methods to investigate the selectivity and specificity of glycan-protein interactions and existing therapeutic approaches to interfere with GAG-protein interactions are discussed.

Progenitor Cell Therapy to Treat Acute Myocardial Infarction: The Promise of High-Dose Autologous CD34(+) Bone Marrow Mononuclear Cells

ST elevation myocardial infarction (STEMI) is associated with an increased risk for congestive heart failure and long-term mortality despite the widespread use of thrombolysis and catheter-based revascularization. The need for improved post-STEMI therapies has led to a surge of novel therapeutics, especially regenerative approaches using autologous mononuclear cells. Indeed, the past decade has been marked by a number of human trials studying the safety and efficacy of progenitor cell delivery in the post-STEMI setting. While a variety of cell types and delivery techniques have been utilized, directed therapy to the infarct-related artery has been the most widely used approach. From over 1300 subjects randomized in these studies, there is sufficient evidence to conclude that cell therapy after STEMI is uniformly safe, while the efficacy of this intervention for improving outcomes is less clear. Recent meta-analyses have highlighted the importance of both timing of cell delivery, as well as the type, quantity, and mobility of delivered cells as determinants of response. Here, we show the case in which higher doses of CD34⁺ cells, which are more potent in terms of their migratory capacity, offer the best hope for preserving cardiac function following STEMI.

Heparin oligosaccharides inhibit chemokine (CXC motif) ligand 12 (CXCL12) cardioprotection by binding orthogonal to the dimerization interface, promoting oligomerization, and competing with the chemokine (CXC motif) receptor 4 (CXCR4) N terminus

The ability to interact with cell surface glycosaminoglycans (GAGs) is essential to the cell migration properties of chemokines, but association with soluble GAGs induces the oligomerization of most chemokines including CXCL12. Monomeric CXCL12, but not dimeric CXCL12, is cardioprotective in a number of experimental models of cardiac ischemia. We found that co-administration of heparin, a common treatment for myocardial infarction, abrogated the protective effect of CXCL12 in an ex vivo rat heart model for myocardial infarction. The interaction between CXCL12 and heparin oligosaccharides has previously been analyzed through mutagenesis, in vitro binding assays, and molecular modeling. However, complications from heparin-induced CXCL12 oligomerization and studies using very short oligosaccharides have led to inconsistent conclusions as to the residues involved, the orientation of the binding site, and whether it overlaps with the CXCR4 N-terminal site. We used a constitutively dimeric variant to simplify the NMR analysis of CXCL12-binding heparin oligosaccharides of varying length. Biophysical and mutagenic analyses reveal a CXCL12/heparin interaction surface that lies perpendicular to the dimer interface, does not involve the chemokine N terminus, and partially overlaps with the CXCR4-binding site. We further demonstrate that heparin-mediated enzymatic protection results from the promotion of dimerization rather than direct heparin binding to the CXCL12 N terminus. These results clarify the structural basis for GAG recognition by CXCL12 and lend insight into the development of CXCL12-based therapeutics.

Attenuation of osteoarthritis via blockade of the SDF-1/CXCR4 signaling pathway

Introduction

This study was performed to evaluate the attenuation of osteoarthritic (OA) pathogenesis via disruption of the stromal cell-derived factor-1 (SDF-1)/C-X-C chemokine receptor type 4 (CXCR4) signaling with AMD3100 in a guinea pig OA model.

Methods

OA chondrocytes and cartilage explants were incubated with SDF-1, siRNA CXCR4, or anti-CXCR4 antibody before treatment with SDF-1. Matrix metalloproteases (MMPs) mRNA and protein levels were measured with real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. The 35 9-month-old male Hartley guinea pigs (0.88 kg ± 0.21 kg) were divided into three groups: AMD-treated group (n = 13); OA group (n = 11); and sham group (n = 11). At 3 months after treatment, knee joints, synovial fluid, and serum were collected for histologic and biochemical analysis. The severity of cartilage damage was assessed by using the modified Mankin score. The levels of SDF-1, glycosaminoglycans (GAGs), MMP-1, MMP-13, and interleukin-1 (IL-1β) were quantified with ELISA.

Results

SDF-1 infiltrated cartilage and decreased proteoglycan staining. Increased glycosaminoglycans and MMP-13 activity were found in the culture media in response to SDF-1 treatment. Disrupting the interaction between SDF-1 and CXCR4 with siRNA CXCR4 or CXCR4 antibody attenuated the effect of SDF-1. Safranin-O staining revealed less cartilage damage in the AMD3100-treated animals with the lowest Mankin score compared with the control animals. The levels of SDF-1, GAG, MMP1, MMP-13, and IL-1β were much lower in the synovial fluid of the AMD3100 group than in that of control group.

Conclusions

The binding of SDF-1 to CXCR4 induces OA cartilage degeneration. The catabolic processes can be disrupted by pharmacologic blockade of SDF-1/CXCR4 signaling. Together, these findings raise the possibility that disruption of the SDF-1/CXCR4 signaling can be used as a therapeutic approach to attenuate cartilage degeneration.

Secreted CXCL12 (SDF-1) forms dimers under physiological conditions

Chemokine CXCL12 (CXC chemokine ligand 12) signalling through CXCR (CXC chemokine receptor) 4 and CXCR7 has essential functions in development and underlies diseases including cancer, atherosclerosis and autoimmunity. Chemokines may form homodimers that regulate receptor binding and signalling, but previous studies with synthetic CXCL12 have produced conflicting evidence for homodimerization. We used bioluminescence imaging with GL (Gaussia luciferase) fusions to investigate dimerization of CXCL12 secreted from mammalian cells. Using column chromatography and GL complementation, we established that CXCL12 was secreted from mammalian cells as both monomers and dimers. Secreted CXCL12 also formed homodimers in the extracellular space. Monomeric CXCL12 preferentially activated CXCR4 signalling through Gαi and Akt, whereas dimeric CXCL12 more effectively promoted recruitment of β-arrestin 2 to CXCR4 and chemotaxis of CXCR4-expressing breast cancer cells. We also showed that CXCR7 preferentially sequestered monomeric CXCL12 from the extracellular space and had minimal effects on dimeric CXCL12 in cell-based assays and an orthotopic tumour xenograft model of human breast cancer. These studies establish that CXCL12 secreted from mammalian cells forms homodimers under physiological conditions. Since monomeric and dimeric CXCL12 have distinct effects on cell signalling and function, our results have important implications for ongoing efforts to target CXCL12 pathways for therapy.

Mobilization of mesenchymal stem cells by stromal cell-derived factor-1 released from chitosan/tripolyphosphate/fucoidan nanoparticles

Stromal cell-derived factor 1 (SDF-1) is an important chemokine in stem cell mobilization, and plays a critical role in the biological and physiological functions of mesenchymal stem cells (MSC). However, the use of SDF-1 in tissue regeneration is limited by two drawbacks, which are its short half-life and ready degradation by enzymes. This study investigates the release of SDF-1 from chitosan-based nanoparticles (NP) and evaluates the effect of released SDF-1 on the migration of MSC. Among the prepared chitosan-based NP a chitosan/tripolyphosphate/fucoidan (CS/TPP/F) NP is the most effective carrier for SDF-1 release. CS/TPP/F NP are spherical and effectively encapsulate SDF-1. The CS/TPP/F NP protected SDF-1 against proteolysis and heat treatment and controlled its release for up to 7 days. The concentration of released SDF-1 reached 23 ng ml(-1). According to in vitro experiments on cells the released SDF-1 retained its mitogenic activity, promoted the migration of MSC and enhanced PI3K expression. Biocompatible CS/TPP/F NP may be effective as carriers for the delivery and controlled release of SDF-1 to mobilize stem cells in tissue engineering applications.

Enhancement of chemokine function as an immunomodulatory strategy employed by human herpesviruses

Herpes simplex virus (HSV) types 1 and 2 are highly prevalent human neurotropic pathogens that cause a variety of diseases, including lethal encephalitis. The relationship between HSV and the host immune system is one of the main determinants of the infection outcome. Chemokines play relevant roles in antiviral response and immunopathology, but the modulation of chemokine function by HSV is not well understood. We have addressed the modulation of chemokine function mediated by HSV. By using surface plasmon resonance and crosslinking assays we show that secreted glycoprotein G (SgG) from both HSV-1 and HSV-2 binds chemokines with high affinity. Chemokine binding activity was also observed in the supernatant of HSV-2 infected cells and in the plasma membrane of cells infected with HSV-1 wild type but not with a gG deficient HSV-1 mutant. Cell-binding and competition experiments indicate that the interaction takes place through the glycosaminoglycan-binding domain of the chemokine. The functional relevance of the interaction was determined both in vitro, by performing transwell assays, time-lapse microscopy, and signal transduction experiments; and in vivo, using the air pouch model of inflammation. Interestingly, and in contrast to what has been observed for previously described viral chemokine binding proteins, HSV SgGs do not inhibit chemokine function. On the contrary, HSV SgGs enhance chemotaxis both in vitro and in vivo through increasing directionality, potency and receptor signaling. This is the first report, to our knowledge, of a viral chemokine binding protein from a human pathogen that increases chemokine function and points towards a previously undescribed strategy of immune modulation mediated by viruses.

Chemokines are chemotactic cytokines that direct the flux of leukocytes to the site of injury and infection, playing a relevant role in the antiviral response. An uncontrolled, unorganized chemokine response is beneath the onset and maintenance of several immunopathologies. During millions of years of evolution, viruses have developed strategies to modulate the host immune system. One of such strategies consists on the secretion of viral proteins that bind to and inhibit the function of chemokines. However, the modulation of the chemokine network mediated by the highly prevalent human pathogen herpes simplex virus (HSV) is unknown. We have addressed this issue and show that HSV-1, causing cold sores and encephalitis and HSV-2, causing urogenital tract infections, interact with chemokines. We determined that the viral protein responsible for such activity is glycoprotein G (gG). gG binds chemokines with high affinity and, in contrast to all viral chemokine binding proteins described to date that inhibit chemokine function, we found that HSV gG potentiates chemokine function in vitro and in vivo. The implications of such potentiation in HSV viral cycle, pathogenesis and chemokine function are discussed.

Therapies from fucoidan; multifunctional marine polymers

Published research on fucoidans increased three fold between 2000 and 2010. These algal derived marine carbohydrate polymers present numerous valuable bioactivities. This review discusses the role for fucoidan in the control of acute and chronic inflammation via selectin blockade, enzyme inhibition and inhibiting the complement cascade. The recent data on toxicology and uptake of fucoidan is detailed together with a discussion on the comparative activities of fractions of fucoidan from different sources. Recent in vivo, in vitro and clinical research related to diverse clinical needs is discussed. Targets include osteoarthritis, kidney and liver disease, neglected infectious diseases, hemopoietic stem cell modulation, protection from radiation damage and treatments for snake envenomation. In recent years, the production of well characterized reproducible fucoidan fractions on a commercial scale has become possible making therapies from fucoidan a realizable goal.

Molecular modeling of the interaction between heparan sulfate and cellular growth factors: bringing pieces together

Heparan sulfate is a polysaccharide belonging to the glycaminoglycan family. It interacts with numerous proteins of the extracellular matrix, in particular cellular growth factors. The number of experimental protein-heparin sulfate complexes obtained by crystallography or nuclear magnetic resonance is limited. Alternatively, computational approaches can be employed. Generally, they restrain the conformation of the glycosidic rings and linkages in order to reduce the complexity of the problem. Modeling the interaction between protein and heparan sulfate is indeed challenging because of the large size of the fragment needed for a strong binding, the flexibility brought by the glycosidic rings and linkages and the high density of negative charges. We propose a two-step method based on molecular docking and molecular dynamics simulation. Molecular docking allows exploring the positioning of a rigid heparin sulfate fragment on the protein surface. Molecular dynamics refine selected docking models by explicitly representing solvent molecules and not restraining the polysaccharide backbone. The interaction of a hexamer of heparin sulfate was studied in interaction with fibroblast growth factor 2 and stromal cell-derived factor 1α. This approach shed light on the plasticity of the growth factors interacting with heparan sulfate. This approach can be extended to the study of other protein/glycosaminoglycan complexes.

Hyphenated techniques for the analysis of heparin and heparan sulfate

The elucidation of the structure of glycosaminoglycan has proven to be challenging for analytical chemists. Molecules of glycosaminoglycan have a high negative charge and are polydisperse and microheterogeneous, thus requiring the application of multiple analytical techniques and methods. Heparin and heparan sulfate are the most structurally complex of the glycosaminoglycans and are widely distributed in nature. They play critical roles in physiological and pathophysiological processes through their interaction with heparin-binding proteins. Moreover, heparin and low-molecular weight heparin are currently used as pharmaceutical drugs to control blood coagulation. In 2008, the health crisis resulting from the contamination of pharmaceutical heparin led to considerable attention regarding their analysis and structural characterization. Modern analytical techniques, including high-performance liquid chromatography, capillary electrophoresis, mass spectrometry, and nuclear magnetic resonance spectroscopy, played critical roles in this effort. A successful combination of separation and spectral techniques will clearly provide a critical advantage in the future analysis of heparin and heparan sulfate. This review focuses on recent efforts to develop hyphenated techniques for the analysis of heparin and heparan sulfate.

Capillary electrophoresis-mass spectrometry for the analysis of intact proteins 2007-2010

CE coupled to MS has proven to be a powerful analytical tool for the characterization of intact proteins, as it combines the high separation efficiency of CE with the selectivity of MS. This review provides an overview of the development and application of CE-MS methods within the field of intact protein analysis as published between January 2007 and June 2010. Ongoing technological developments with respect to CE-MS interfacing, capillary coatings for CE-MS, coupling of CIEF with MS and chip-based CE-MS are treated. Furthermore, CE-MS of intact proteins involving ESI, MALDI and ICP ionization is outlined and overviews of the use of the various CE-MS methods are provided by tables. Representative examples illustrate the applicability of CE-MS for the characterization of proteins, including glycoproteins, biopharmaceuticals, protein-ligand complexes, biomarkers and dietary proteins. It is concluded that CE-MS is a valuable technique with high potential for intact protein analysis, providing useful information on protein identity and purity, including modifications and degradation products.

Constitutive and chemokine-dependent internalization and recycling of CXCR7 in breast cancer cells to degrade chemokine ligands

CXCR7 is a receptor for chemokines including CXCL12 (stromal-derived factor-1), a molecule that promotes tumor growth and metastasis in breast cancer and other malignancies. Building on the recent observation that CXCR7 sequesters CXCL12, we investigated mechanisms for CXCR7-dependent uptake of chemokines. Breast cancer cells expressing CXCR7 accumulated chemokines CXCL12 and CXC11 present at concentrations <1 ng/ml, unlike cells expressing CXCR4. CXCR7-dependent accumulation of chemokines was reduced by inhibitors of clathrin-mediated endocytosis. After CXCR7-mediated internalization, CXCL12 trafficked to lysosomes and was degraded, although levels of CXCR7 remained stable. CXCR7 reduced CXCL12 in the extracellular space, limiting the amounts of chemokine available to acutely stimulate signaling through CXCR4. CXCR7 constitutively internalized and recycled to the cell membrane even in the absence of ligand, and addition of chemokines did not significantly enhance receptor internalization. Chemokines at concentrations less than the Kd values for ligand-receptor binding did not alter levels of CXCR7 at the cell surface. Higher concentrations of chemokine ligands reduced the total cell surface expression of CXCR7 without affecting receptor internalization, indicating that receptor recycling was inhibited. CXCR7-dependent uptake of chemokines and receptor trafficking were regulated by beta-arrestin 2. These studies establish mechanisms through which CXCR7 regulates the availability of chemokine ligands in the extracellular space.

Stimulation of chondrocyte hypertrophy by chemokine stromal cell-derived factor 1 in the chondro-osseous junction during endochondral bone formation

During endochondral bone formation, chondrocytes undergo differentiation toward hypertrophy before they are replaced by bone and bone marrow. In this study, we found that a G-protein coupled receptor CXCR4 is predominantly expressed in hypertrophic chondrocytes, while its ligand, chemokine stromal cell-derived factor 1 (SDF-1) is expressed in the bone marrow adjacent to hypertrophic chondrocytes. Thus, they are expressed in a complementary pattern in the chondro-osseous junction of the growth plate. Transfection of a CXCR4 cDNA into pre-hypertrophic chondrocytes results in a dose-dependent increase of hypertrophic markers including Runx2, Col X, and MMP-13 in response to SDF-1 treatment. In organ culture SDF-1 infiltrates cartilage and accelerates growth plate hypertrophy. Furthermore, a continuous infusion of SDF-1 into the rabbit proximal tibial physis results in early physeal closure, which is accompanied by a transient elevation of type X collagen expression. Blocking SDF-1/CXCR4 interaction suppresses the expression of Runx2. Thus, interaction of SDF-1 and CXCR4 is required for Runx2 expression. Interestingly, knocking down Runx2 gene expression results in a decrease of CXCR4 mRNA levels in hypertrophic chondrocytes. This suggests a positive feedback loop of stimulation of chondrocyte hypertrophy by SDF-1/CXCR4, which is mediated by Runx2.

Chapter 2. Homo- and hetero-oligomerization of chemokines

Chemokines function in cell migration by binding and activating seven transmembrane G protein-coupled receptors (GPCRs) on leukocytes and many other diverse cell types. The extracellular binding event stabilizes specific conformations of the receptor that trigger cascades of intracellular signaling pathways involved in cell movement and activation (Baggiolini, 1998; Baggiolini et al., 1997; Charo and Ransohoff, 2006; Hartley et al., 2003; Kunkel and Butcher, 2002; Loetscher and Clark-Lewis, 2001). Although the current consensus is that monomeric forms of chemokines are necessary for receptor binding to induce cell migration, oligomeric states of chemokines may be associated with other complex functional roles such as regulation, haptotactic gradient formation, protection from proteolysis, and signaling related to processes distinct from migration. Accordingly, diverse biophysical methods have been used to identify and characterize the details of these quaternary interactions. This chapter aims to summarize these methods and to provide guidelines for their application in future studies.