Early stages of trachea healing process: (immuno/lectin) histochemical monitoring of selected markers and adhesion/growth-regulatory endogenous lectins

Tracheotomy may be associated with numerous acute and chronic complications including extensive formation of granulation tissue. The emerging functional versatility of the adhesion/growth-regulatory galectins prompted us to perform a histochemical study of wound healing using rat trachea as model. By using non-cross-reactive antibodies and the labelled tissue lectins we addressed the issue of the presence and regulation of galectin reactivity during trachea wound healing. Beside localization of high-molecular-weight keratin, wide-spectrum cytokeratin, keratins 10 and 14, α-smooth muscle actin, vimentin, fibronectin, and Sox-2, galectins -1, -2, and -3 and their reactivity profiles were measured in frozen sections of wounded and control trachea specimens 7, 14, and 28 days after trauma. A clear trend for decreased galectin-1 presence and increased reactivity for galectin-1 was revealed from day 7 to day 28. Sox-2-positive cells were present after seven days and found in the wound bed. Interestingly, several similarities were observed in comparison to skin wound healing including regulation of galectin-1 parameters.

K. Open Wound Healing In Vivo: Monitoring Binding and Presence of Adhesion/Growth-Regulatory Galectins in Rat Skin during the Course of Complete Re-Epithelialization

Galectins are a family of carbohydrate-binding proteins that modulate inflammation and immunity. This functional versatility prompted us to perform a histochemical study of their occurrence during wound healing using rat skin as an in vivo model. Wound healing is a dynamic process that exhibits three basic phases: inflammation, proliferation, and maturation. In this study antibodies against keratins-10 and -14, wide-spectrum cytokeratin, vimentin, and fibronectin, and non-cross-reactive antibodies to galectins-1, -2, and -3 were applied to frozen sections of skin specimens two days (inflammatory phase), seven days (proliferation phase), and twenty-one days (maturation phase) after wounding. The presence of binding sites for galectins-1, -2, -3, and -7 as a measure for assessing changes in reactivity was determined using labeled proteins as probes. Our study detected a series of alterations in galectin parameters during the different phases of wound healing. Presence of galectin-1, for example, increased during the early phase of healing, whereas galectin-3 rapidly decreased in newly formed granulation tissue. In addition, nuclear reactivity of epidermal cells for galectin-2 occurred seven days post-trauma. The dynamic regulation of galectins during re-epithelialization intimates a role of these proteins in skin wound healing, most notably for galectin-1 increasing during the early phases and galectin-3 then slightly increasing during later phases of healing. Such changes may identify a potential target for the development of novel drugs to aid in wound repair and patients’ care.

Structural aspects of binding of α-linked digalactosides to human galectin-1

By definition, adhesion/growth-regulatory galectins are known for their ability to bind β-galactosides such as Galβ(1 → 4)Glc (lactose). Indications for affinity of human galectin-1 to α-linked digalactosides pose questions on the interaction profile with such bound ligands and selection of the galactose moiety for CH-π stacking. These issues are resolved by a combination of (15)N-(1)H heteronuclear single quantum coherence (HSQC) chemical shift and saturation transfer difference nuclear magnetic resonance (STD NMR) epitope mappings with docking analysis, using the α(1 → 3/4)-linked digalactosides and also Galα(1 → 6)Glc (melibiose) as test compounds. The experimental part revealed interaction with the canonical lectin site, and this preferentially via the non-reducing-end galactose moiety. Low-energy conformers appear to be selected without notable distortion, as shown by molecular dynamics simulations. With the α(1 → 4) disaccharide, however, the typical CH-π interaction is significantly diminished, yet binding appears to be partially compensated for by hydrogen bonding. Overall, these findings reveal that the type of α-linkage in digalactosides has an impact on maintaining CH-π interactions and the pattern of hydrogen bonding, explaining preference for the α(1 → 3) linkage. Thus, this lectin is able to accommodate both α- and β-linked galactosides at the same site, with major contacts to the non-reducing-end sugar unit.

Symmetric dithiodigalactoside: strategic combination of binding studies and detection of selectivity between a plant toxin and human lectins

Thioglycosides offer the advantage over O-glycosides to be resistant to hydrolysis. Based on initial evidence of this recognition ability for glycosyldisulfides by screening dynamic combinatorial libraries, we have now systematically studied dithiodigalactoside on a plant toxin (Viscum album agglutinin) and five human lectins (adhesion/growth-regulatory galectins with medical relevance e.g. in tumor progression and spread). Inhibition assays with surface-presented neoglycoprotein and in solution monitored by saturation transfer difference NMR spectroscopy, flanked by epitope mapping, as well as isothermal titration calorimetry revealed binding properties to VAA (K(a): 1560 ± 20 M(-1)). They were reflected by the structural model and the affinity on the level of toxin-exposed cells. In comparison, galectins were considerably less reactive, with intrafamily grading down to very minor reactivity for tandem-repeat-type galectins, as quantitated by radioassays for both domains of galectin-4. Model building indicated contact formation to be restricted to only one galactose moiety, in contrast to thiodigalactoside. The tested glycosyldisulfide exhibits selectivity between the plant toxin and the tested human lectins, and also between these proteins. Therefore, glycosyldisulfides have potential as chemical platform for inhibitor design.

Galectins as tools for glycan mapping in histology: comparison of their binding profiles to the bovine zona pellucida by confocal laser scanning microscopy

Gene divergence has given rise to the galectin family of mammalian lectins. Since selective binding to distinct β-galactosides underlies the known bioactivities of galectins, they could find application in cyto- and histochemistry. The pertinent question on the characteristics of their individual reactivity profiles therefore needs to be answered. Toward this end, comparative studies of a panel of galectins in defined systems are required. We here characterise the staining profiles of seven human lectins as well as five natural derivatives originating from proteolytic truncation and serine phosphorylation and one engineered variant. As test system, bovine germinal vesicle oocytes with their glycoprotein envelope (zona pellucida), which presents bi- to tetraantennary complex-type N-glycans with N-acetyllactosamine repeats and core fucosylation, were processed. Technically, confocal laser scanning microscopy was used, first with plant lectins to map the sialylation status. Hereby, α2,3/6-sialylation was detected in the superficial filamentous meshwork of the zona pellucida, while sialic acid-free glycan chains were found to characterise the main inner part of the compact layer of the zona pellucida. Galectin staining was specific and non-uniform. Significant differences in reactivity were detected for the superficial filamentous meshwork and the compact layer of the zona pellucida between galectins-1 to -4 versus galectins-8 and -9. The typical staining profiles intimate a spatially organised display of N-glycans in the different layers of the zona pellucida, underscoring the potential of galectins as cyto- and histochemical tools. Our results encourage further comparative analysis and research to trace the underlying structural and/or topological properties.

Combining carbohydrate substitutions at bioinspired positions with multivalent presentation towards optimising lectin inhibitors: case study with calixarenes

Carbohydrate derivatisation and glycocluster formation are both known to enhance avidity for lectin binding. Using a plant toxin and human adhesion/growth-regulatory lectins (inter- and intrafamily comparisons) the effect of their combination is examined. In detail, aromatic substituents were introduced at the 2-N or 3'-positions of N-acetyllactosamine and the products conjugated to two types of calix[n]arenes (n = 4, 6) via thiourea-linker chemistry.

Human galectins induce conversion of dermal fibroblasts into myofibroblasts and production of extracellular matrix: potential application in tissue engineering and wound repair

Members of the galectin family of endogenous lectins are potent adhesion/growth-regulatory effectors. Their multifunctionality opens possibilities for their use in bioapplications. We studied whether human galectins induce the conversion of human dermal fibroblasts into myofibroblasts (MFBs) and the production of a bioactive extracellular matrix scaffold is suitable for cell culture. Testing a panel of galectins of all three subgroups, including natural and engineered variants, we detected activity for the proto-type galectin-1 and galectin-7, the chimera-type galectin-3 and the tandem-repeat-type galectin-4. The activity of galectin-1 required the integrity of the carbohydrate recognition domain. It was independent of the presence of TGF-β1, but it yielded an additive effect. The resulting MFBs, relevant, for example, for tumor progression, generated a matrix scaffold rich in fibronectin and galectin-1 that supported keratinocyte culture without feeder cells. Of note, keratinocytes cultured on this substratum presented a stem-like cell phenotype with small size and keratin-19 expression. In vivo in rats, galectin-1 had a positive effect on skin wound closure 21 days after surgery. In conclusion, we describe the differential potential of certain human galectins to induce the conversion of dermal fibroblasts into MFBs and the generation of a bioactive cell culture substratum.

Bortezomib delays the onset of factor VIII inhibitors in experimental hemophilia A, but fails to eliminate established anti-factor VIII IgG-producing cells

BACKGROUND

Replacement therapy with exogenous factor VIII to treat hemorrhages induces inhibitory anti-FVIII antibodies in up to 30% of patients with hemophilia A. Current approaches to eradicate FVIII inhibitors using high-dose FVIII injection protocols (immune tolerance induction) or anti-CD20 depleting antibodies (Rituximab) demonstrate limited efficacy; they are extremely expensive and/or require stringent compliance from the patients.

OBJECTIVES

To investigate whether the proteasome inhibitor bortezomib, which depletes plasmocytes, modulates the anti-FVIII immune response in FVIII-deficient mice.

METHODS AND RESULTS

Preventive 4-week treatment of naïve mice with bortezomib at the time of FVIII administration delayed the development of inhibitory anti-FVIII IgG, and depleted plasma cells as well as different lymphoid cell subsets. Conversely, curative treatment of inhibitor-positive mice for 10 weeks, along with FVIII administration, failed to eradicate FVIII inhibitors to extents that would be clinically relevant if achieved in patients. Accordingly, bortezomib did not eradicate anti-FVIII IgG-secreting plasmocytes that had homed to survival niches in the bone marrow, despite significant elimination of total plasma cells.

CONCLUSIONS

The data suggest that strategies for the efficient reduction of anti-FVIII IgG titers in patients with hemophilia A should rely on competition for survival niches for plasmocytes in the bone marrow rather than the mere use of proteasome inhibitors.

From lectin structure to functional glycomics: principles of the sugar code

Lectins are carbohydrate-binding proteins which lack enzymatic activity on their ligand and are distinct from antibodies and free mono- and oligosaccharide sensor/transport proteins. Emerging insights into the functional dimension of lectin binding to cellular glycans have strongly contributed to the shaping of the 'sugar code'. Fittingly, over a dozen folds and a broad spectrum of binding site architecture, ranging from shallow grooves to deep pockets, have developed sugar-binding capacity. A central question is how the exquisite target specificity of endogenous lectins for certain cellular glycans can be explained. In this regard, affinity regulation is first systematically dissected into six levels. Experimentally, the strategic combination of methods to monitor distinct aspects of the lectin-glycan interplay offers a promising perspective to answer this question.

Inhibitory potential of chemical substitutions at bioinspired sites of β-D-galactopyranose on neoglycoprotein/cell surface binding of two classes of medically relevant lectins

Galactose is the key contact site for plant AB-toxins and the human adhesion/growth-regulatory galectins. Natural anomeric extensions and 3'-substitutions enhance its reactivity, thus prompting us to test the potential of respective chemical substitutions of galactose in the quest to develop potent inhibitors. Biochemical screening of a respective glycoside library with 60 substances in a solid-phase assay was followed by examining the compounds' activity to protect cells from lectin binding. By testing 32 anomeric extensions, 18 compounds with additional 3'-substitution, three lactosides and two Lewis-type trisaccharides rather mild effects compared to the common haptenic inhibitor lactose were detected in both assays. When using trivalent glycoclusters marked enhancements with 6- to 8-fold increases were revealed for the toxin and three of four tested galectins. Since the most potent compound and also 3'-substituted thiogalactosides reduced cell growth of a human tumor line at millimolar concentrations, biocompatible substitutions and scaffolds will be required for further developments. The synthesis of suitable glycoclusters, presenting headgroups which exploit differences in ligand selection in interlectin comparison to reduce cross-reactivity, and the documented strategic combination of initial biochemical screening with cell assays are considered instrumental to advance inhibitor design.

Comparative analysis of the nuclear presence of adhesion/growth-regulatory galectins and reactivity in the nuclei of interphasic and mitotic cells

Nuclear galectins participate in splicing of pre-mRNA. In this study we detected galectins-1, -2, -3 and -7 and their glycoligands in three types of cells: fibroblasts, cancer epithelial cells and melanoma cells. The results demonstrated that the nuclear expression of distinct types of galectins and their ligands in interphasic nuclei is dependent on the cell type. The extensive binding of labelled galectins-1 and -2 to mitotic cells (around chromosomes, in mitotic spindle and in bridge connecting both daughter cells) suggests their role during the cell division.

Nitric oxide changes distinct aspects of the glycophenotype of human neuroblastoma NB69 cells

It is an open question whether the presence of nitric oxide (NO) affects the cell glycophenotype. A panel of six plant lectins was used in this study to monitor distinct aspects of cell surface glycosylation under nitrosative stress. We determined that treating human neuroblastoma NB69 cells with the long-lived NO donor 2,2'-(hydroxynitrosohydrazono)bis-ethanimine (DETA/NO) and monitoring the non-apoptotic adherent cell population significantly increases the presentation of N-glycans as detected by concanavalin A. Examining fine-structural features, bisected N-glycans and branch-end tailoring including α2,6-sialylation were found to be enhanced. Confocal fluorescence microscopy and cell permeabilization experiments pointed to a major effect of NO on the extent of cell surface N-glycan presentation. We also show that NO increases the level of protein O-GlcNAcylation, a multifunctional post-translational modification. Our results thus establish the first evidence for NO as modulator of distinct aspects of cell glycosylation.

Differential stimulation of VEGF-C production by adhesion/growth-regulatory galectins and plant lectins in human breast cancer cells

The present study tested the hypothesis that the production of vascular endothelial growth factor C (VEGF-C), a key lymphangiogenic factor, by human breast cancer cells can be stimulated by human lectins, using plant lectins as controls.

MATERIALS AND METHODS

The effects of human galectins and five plant lectins reacting with distinct determinants of N- and O-glycans on the accumulation of VEGF-C in serum-free cell culture media of human breast cancer cells endowed with high (MDA-MB-231) and low (MCF7, T-47D, and SK-BR-3) VEGF-C-producing abilities were examined.

RESULTS

All tested lectins stimulated VEGF-C production by MDA-MB-231 cells, albeit with different potency. Concanavalin A, but not galectins, was also able to stimulate VEGF-C production by low VEGF-C-producing cell lines MCF7 and T-47D. Both VEGF-C mRNA and protein were strongly up-regulated in SK-BR-3 cells by concanavalin A and wheat germ agglutinin, but not jacalin.

CONCLUSION

The differential response of breast cancer cell lines separated by the endogenous level of VEGF-C production suggests that galectins may contribute to tumor-associated lymphangiogenesis in a cell-specific manner.

Negative regulation of RPE cell attachment by carbohydrate-dependent cell surface binding of galectin-3 and inhibition of the ERK-MAPK pathway

Adhesion and spreading of retinal pigment epithelial (RPE) cells on fibronectin-rich extracellular matrices is a crucial event in the pathogenesis of proliferative vitreoretinopathy (PVR). In the present study we explored the capacity of galectin-3, a β-galactoside-binding endogenous lectin, to inhibit early PVR-associated cellular events from a therapeutic perspective. We assessed the relative expression levels of galectin-3 in native RPE and dedifferentiated, cultured RPE. Galectin-3 was constitutively expressed under in vivo and in vitro conditions and was abundant in cultured cells. Treatment of human RPE cells with soluble galectin-3 disclosed no toxicity within control limits up to 250 μg/ml. When added to the medium, galectin-3 dose-dependently inhibited attachment and spreading of the cells on fibronectin by more than 75%. When coated on the plastic surface, galectin-3 alone impaired attachment and spreading of RPE cells, and reduced attachment but not spreading on fibronectin. Galectin-3 bound to the cell surface, and, as determined by the use of the competing sugar β-lactose, galectin-3-mediated effects were dependent on carbohydrate binding. To ascertain the role of the ability of galectin-3 to form pentamers, we proteolytically removed the N-terminal, cross-linking section. The remaining C-terminal carbohydrate-binding domain alone failed to bind to cells and was functionally inactive. These results emphasize the relevance of both properties, i.e., glycan-binding and cross-linking of glycan moieties, for the inhibitory activity of galectin-3. Incubation of mobilized RPE cells with galectin-3 significantly disturbed microfilament assembly and, in correlation with decreased attachment, inhibited ERK phosphorylation. Therefore, galectin-3, acting as a cross-linking lectin on the cell surface, negatively regulates attachment and spreading of RPE cells in vitro. This effect, at least in part, is attributed to an inhibition of the ERK-MAPK pathway, which prevents cytoskeletal rearrangements needed for RPE cell attachment and spreading. Further investigation at this pathway may disclose a promising nouveau perspective for treatment and prophylaxis of early PVR.