Tissue Lectins Research Articles

IgG4 glycosylation contributes to the pathogenesis of IgG4 Hashimoto's thyroiditis via the complement pathway.

To explore whether IgG4 is involved in the pathogenesis of IgG4 HT. Serum TgAb IgG4 and TPOAb IgG4 were measured in IgG4 HT and non-IgG4 HT. C1q, mannose-binding lectin (MBL), Bb, C3d, C4d, and membrane attack complex (MAC) in thyroid tissues from IgG4 HT, non-IgG4 HT, and controls were examined by immunohistochemistry. We assessed IgG4 and MAC deposition in mouse thyroid by immunohistochemistry after injecting purified IgG4 into mice. The glycosylation patterns of TgAb IgG4 from IgG4 HT were identified by MALDI-TOF-MS. The ability of IgG4 to bind to MBL before and after deglycosylation was assessed by ELISA. MBL and MAC fluorescence were detected in thyrocytes after the addition of IgG4 or deglycosylated IgG4. Serum TgAb IgG4 and TPOAb IgG4 levels were significantly higher in the IgG4 HT group. MBL, Bb, C3d, C4d, and MAC levels were significantly higher in the thyroid tissues of IgG4 HT than in non-IgG4 HT (all P < 0.001). IgG4 colocalized with MBL by immunofluorescence. In mice, follicular cell structure disruption was observed after the injection of IgG4 from IgG4 HT, as well as the colocalization of IgG4 with MAC. High levels of TgAb IgG4 glycosylation patterns, including monogalactose glycan (G1F), galactose-deficient glycan (G0F), and high-mannose glycan (M5), were detected in IgG4 HT. After deglycosylation, IgG4 reduced its ability to bind to MBL, and there was low MBL and MAC activation in thyrocytes. High levels of IgG4 glycosylation patterns, including G1F, G0F, and M5, may activate the complement lectin pathway, thereby participating in the pathogenesis of IgG4 HT.

A Siglec3-like lectin from Nile tilapia (Oreochromis niloticus): Transcriptional profiling upon Streptococcus agalactiae infection and its potential role in immune escape

Siglec-3, also known as CD33, is a type of sialic acid binding immunoglobulin-like lectin that plays a role in regulating cellular activation in the innate immune system and subsequent inflammatory responses. In this study, we cloned the cDNA encoding OnSiglec3-like ORF sequence (1170 bp) in Nile tilapia, contained two Ig-like domains in the extracellular region and one inhibitory ITIM-like motif in the intracellular region. Through qRT-PCR analysis, we found that the mRNA of OnSiglec3-like lectin was highly expressed in the brain and head kidney. When challenged with Streptococcus agalactiae both in vivo and in vitro, we observed a significant up-regulation in the expression of OnSiglec3-like lectin in the head kidney tissues and leukocytes, respectively. Additionally, we investigated the interaction between a recombinant extracellular region protein (referred to as (r)exSiglec3-like protein) and three different phenotypes of S. agalactiae: WT (wild type), ∆cps (cps-deficient mutant), and ∆neuA (sia-deficient mutant) using ELISA. We found that the exOnSiglec3-like protein, when combined with RNA interference and bacterial infection, significantly enhanced the phagocytic ability against S. agalactiae. Furthermore, the expression of four common inflammatory factors (OnIL-6, OnIL-10, OnTNF-α, and OnTGF-β) showed a significant up-regulation. Overall, this study suggests that OnSigelc3-like lectin may play a role in host defence against bacterial infection and mediate immune escape in Nile tilapia.

Targeting osteoarthritis-associated galectins and an induced effector class by a ditopic bifunctional reagent: Impact of its glycan part on binding measured in the tissue context

Pairing glycans with tissue lectins controls multiple effector pathways in (patho)physiology. A clinically relevant example is the prodegradative activity of galectins-1 and -3 (Gal-1 and -3) in the progression of osteoarthritis (OA) via matrix metalloproteinases (MMPs), especially MMP-13. The design of heterobifunctional inhibitors that can block galectin binding and MMPs both directly and by preventing their galectin-dependent induction selectively offers a perspective to dissect the roles of lectins and proteolytic enzymes. We describe the synthesis of such a reagent with a bivalent galectin ligand connected to an MMP inhibitor and of two tetravalent glycoclusters with a subtle change in headgroup presentation for further elucidation of influence on ligand binding. Testing was performed on clinical material with mixtures of galectins as occurring in vivo, using sections of fixed tissue. Two-colour fluorescence microscopy monitored binding to the cellular glycome after optimization of experimental parameters. In the presence of the inhibitor, galectin binding to OA specimens was significantly reduced. These results open the perspective to examine the inhibitory capacity of custom-made ditopic compounds on binding of lectins in mixtures using sections of clinical material with known impact of galectins and MMPs on disease progression.

Structure and Biological Properties of Ribosome-Inactivating Proteins and Lectins from Elder (Sambucus nigra L.) Leaves.

Ribosome-inactivating proteins (RIPs) are a group of proteins with rRNA N-glycosylase activity that catalyze the removal of a specific adenine located in the sarcin–ricin loop of the large ribosomal RNA, which leads to the irreversible inhibition of protein synthesis and, consequently, cell death. The case of elderberry (Sambucus nigra L.) is unique, since more than 20 RIPs and related lectins have been isolated and characterized from the flowers, seeds, fruits, and bark of this plant. However, these kinds of proteins have never been isolated from elderberry leaves. In this work, we have purified RIPs and lectins from the leaves of this shrub, studying their main physicochemical characteristics, sequences, and biological properties. In elderberry leaves, we found one type 2 RIP and two related lectins that are specific for galactose, four type 2 RIPs that fail to agglutinate erythrocytes, and one type 1 RIP. Several of these proteins are homologous to others found elsewhere in the plant. The diversity of RIPs and lectins in the different elderberry tissues, and the different biological activities of these proteins, which have a high degree of homology with each other, constitute an excellent source of proteins that are of great interest in diagnostics, experimental therapy, and agriculture.

APPLICATIONS OF PLANT LECTINS IN BIOTECHNOLOGY AND THERAPEUTICS

Lectins are carbohydrate-binding proteins broadly used in various therapeutic and biomedical applications. The variable affinity of lectins towards variety of carbohydrates has raised attention for the biologist to explore functional aspects of lectins. Lectins express specificity to simple carbohydrates for example mannose, lactose, sialic acid, complex glycan, and glycoproteins. Lectins are classified based on their sugar specificity and are used as a tool to study protein-carbohydrate interactions. Lectins are ubiquitous in nature and identified from all sources such as bacteria, fungi, algae, and animals. Plants are the most abundant source of lectins, and till now, more than three hundred lectins were characterized from plants. These are distributed to various parts of a plant according to their requirements and function. The physiological role of lectins in a plant is still not well understood. The overabundant presence of lectins in plant seeds and storage tissues indicated their role in plant development. Plant lectins shows a broad range of activities like antibacterial, antifungal, insecticidal, anticancerous, antileishmanial, antiviral, and anticoagulants. In this review, we aim to highlight the plant lectins classification and their application in various biological aspects.

Exploring the Galectin Network by Light and Fluorescence Microscopy.

Dynamic changes of a cell's glycophenotype are increasingly interpreted as shifts in the capacity to interact with tissue (endogenous) lectins. The status of glycan branching or chain length (e.g., core 1 vs core 2 mucin-type O-glycans and polyLacNAc additions) as well as of sialylation/sulfation has been delineated to convey signals. They are "read" by galectins, for example regulating lattice formation on the membrane and cell growth. Owing to the discovery of the possibility that these effectors act in networks physiologically resulting in functional antagonism or cooperation, their detection and distribution profiling need to be expanded from an individual (single) protein to the-at best-entire family. How to work with non-cross-reactive antibodies and with the labeled tissue-derived proteins (used as probes) is exemplarily documented for chicken and human galectins including typical activity and specificity controls. This description intends to inspire the systematic (network) study of members of a lectin family and also the application of tissue proteins beyond a single lectin category in lectin histochemistry.

APPLICATIONS OF PLANT LECTINS IN BIOTECHNOLOGY AND THERAPEUTICS: Plant lectins application

Lectins are carbohydrate-binding proteins broadly used in various therapeutic and biomedical applications. The variable affinity of lectins towards variety of carbohydrates has raised attention for the biologist to explore functional aspects of lectins. Lectins express specificity to simple carbohydrates for example mannose, lactose, sialic acid, complex glycan, and glycoproteins. Lectins are classified based on their sugar specificity and are used as a tool to study protein-carbohydrate interactions. Lectins are ubiquitous in nature and identified from all sources such as bacteria, fungi, algae, and animals. Plants are the most abundant source of lectins, and till now, more than three hundred lectins were characterized from plants. These are distributed to various parts of a plant according to their requirements and function. The physiological role of lectins in a plant is still not well understood. The overabundant presence of lectins in plant seeds and storage tissues indicated their role in plant development. Plant lectins shows a broad range of activities like antibacterial, antifungal, insecticidal, anticancerous, antileishmanial, antiviral, and anticoagulants. In this review, we aim to highlight the plant lectins classification and their application in various biological aspects.

What Cyto- and Histochemistry Can Do to Crack the Sugar Code.

As letters form the vocabulary of a language, biochemical ‘symbols’ (the building blocks of oligo- and polymers) make writing molecular messages possible. Compared to nucleotides and amino acids, sugars have chemical properties that facilitate to reach an unsurpassed level of oligomer diversity. These glycans are a part of the ubiquitous cellular glycoconjugates. Cyto- and histochemically, the glycans’ structural complexity is mapped by glycophenotyping of cells and tissues using receptors (‘readers’, thus called lectins), hereby revealing its dynamic spatiotemporal regulation: these data support the concept of a sugar code. When proceeding from work with plant (haem)agglutinins as such tools to the discovery of endogenous (tissue) lectins, it became clear that a broad panel of biological meanings can indeed be derived from the sugar-based vocabulary (the natural glycome incl. post-synthetic modifications) by glycan-lectin recognition in situ. As consequence, the immunocyto- and histochemical analysis of lectin expression is building a solid basis for the steps toward tracking down functional correlations, for example in processes leading to cell adhesion, apoptosis, autophagy or growth regulation as well as targeted delivery of glycoproteins. Introduction of labeled tissue lectins to glycan profiling assists this endeavor by detecting counterreceptor(s) in situ. Combining these tools and their applications strategically will help to take the trip toward the following long-range aim: to compile a dictionary for the glycan vocabulary that translates each message (oligosaccharide) into its bioresponse(s), that is to crack the sugar code.

N-Glycan profiling of chondrocytes and fibroblast-like synoviocytes: Towards functional glycomics in osteoarthritis.

PurposeN‐Glycan profiling provides an indicator of the cellular potential for functional pairing with tissue lectins. Following the discovery of galectin expression by chondrocytes as a factor in osteoarthritis pathobiology, mapping of N‐glycans upon their phenotypic dedifferentiation in culture and in fibroblast‐like synoviocytes is a step to better understand glycobiological contributions to disease progression.Experimental designThe profiles of cellular N‐glycans of human osteoarthritic chondrocytes and fibroblast‐like synoviocytes were characterized by mass spectrometry. RT‐qPCR experiments determined mRNA levels of 16 glycosyltransferases. Responsiveness of cells to galectins was quantified by measuring the mRNA level for interleukin‐1β.ResultsThe shift of chondrocytes to a fibroblastic phenotype (dedifferentiation) is associated with changes in N‐glycosylation. The N‐glycan profile of chondrocytes at passage 4 reflects characteristics of synoviocytes. Galectins‐1 and ‐3 enhance expression of interleukin‐1β mRNA in both cell types, most pronounced in primary culture. Presence of interleukin‐1β leads to changes in sialylation in synoviocytes that favor galectin binding.Conclusions and clinical relevanceN‐Glycosylation reflects phenotypic changes of osteoarthritic cells in vitro. Like chondrocytes, fibroblast‐like synoviocytes express N‐glycans that are suited to bind galectins, and these proteins serve as inducers of pro‐inflammatory markers in these cells. Synoviocytes can thus contribute to disease progression in osteoarthritis in situ.

Probing sulfatide-tissue lectin recognition with functionalized glycodendrimersomes.

SummaryThe small 3-O-sulfated galactose head group of sulfatides, an abundant glycosphingolipid class, poses the (sphinx-like) riddle on involvement of glycan bridging by tissue lectins (sugar code). First, synthesis of head group derivatives for functionalization of amphiphilic dendrimers is performed. Aggregation of resulting (biomimetic) vesicles, alone or in combination with lactose, demonstrates bridging by a tissue lectin (galectin-4). Physiologically, this can stabilize glycolipid-rich microdomains (rafts) and associate sulfatide-rich regions with specific glycoproteins. Further testing documents importance of heterobivalency and linker length. Structurally, sulfatide recognition by galectin-8 is shown to involve sphingosine's OH group as substitute for the 3′-hydroxyl of glucose of lactose. These discoveries underscore functionality of this small determinant on biomembranes intracellularly and on the cell surface. Moreover, they provide a role model to examine counterreceptor capacity of more complex glycans of glycosphingolipids and to start their bottom-up glycotope surface programming.

Galectin-Glycan Interactions: Guidelines for Monitoring by 77 Se NMR Spectroscopy, and Solvent (H2 O/D2 O) Impact on Binding.

Functional pairing between cellular glycoconjugates and tissue lectins like galectins has wide (patho)physiological significance. Their study is facilitated by nonhydrolysable derivatives of the natural O‐glycans, such as S‐ and Se‐glycosides. The latter enable extensive analyses by specific 77Se NMR spectroscopy, but still remain underexplored. By using the example of selenodigalactoside (SeDG) and the human galectin‐1 and ‐3, we have evaluated diverse 77Se NMR detection methods and propose selective 1H,77Se heteronuclear Hartmann–Hahn transfer for efficient use in competitive NMR screening against a selenoglycoside spy ligand. By fluorescence anisotropy, circular dichroism, and isothermal titration calorimetry (ITC), we show that the affinity and thermodynamics of SeDG binding by galectins are similar to thiodigalactoside (TDG) and N‐acetyllactosamine (LacNAc), confirming that Se substitution has no major impact. ITC data in D2O versus H2O are similar for TDG and LacNAc binding by both galectins, but a solvent effect, indicating solvent rearrangement at the binding site, is hinted at for SeDG and clearly observed for LacNAc dimers with extended chain length.

Glycobiology of developing chicken kidney: Profiling the galectin family and selected β-galactosides.

The concept of the sugar code interprets the cellular glycophenotype as a rich source of information read by glycan-lectin recognition in situ. This study's aim is the comprehensive characterization of galectin expression by immunohistochemistry during chicken nephrogenesis along with mapping binding sites by (ga)lectin histochemistry. Light and two-color fluorescence microscopy were used. First, six plant/fungal lectins that are specific for galectin-binding parts of N- and O-glycans were applied. The spatiotemporally regulated distributions of these glycans in meso- and metanephros equip cells with potential binding partners for the galectins. Complete galectin profiling from HH Stage 20 (about 70-72 hr) onward revealed cell-, galectin-, and stage-dependent expression patterns. Representatives of all three types of modular architecture of the galectin family are detectable, and overlaps of signal distribution in light and two-color fluorescence microscopy illustrate a possibility for functional cooperation among them. Performing systematic galectin histochemistry facilitated comparisons between staining profiles of plant lectins and galectins. They revealed several cases for differences so that tissue lectins appear to be selective among the β-galactosides. Notably, selectivity is also disclosed in intrafamily comparison. Thus, combining experimental series with plant and tissue lectins is a means to characterize target populations of glycans presented by cellular glycoconjugates for individual galectins. Our results document the presence and sophisticated level of elaboration among β-galactosides and among the members of the family of galectins during organogenesis, using chicken galectins and kidney as model. Thus, they provide a clear guideline for functional assays using supramolecular tools, cells, and organ cultures.

Structural insight into the binding of human galectins to corneal keratan sulfate, its desulfated form and related saccharides

Glycosaminoglycan chains of keratan sulfate proteoglycans appear to be physiologically significant by pairing with tissue lectins. Here, we used NMR spectroscopy and molecular dynamics (MD) simulations to characterize interactions of corneal keratan sulfate (KS), its desulfated form, as well as di-, tetra- (N-acetyllactosamine and lacto-N-tetraose) and octasaccharides with adhesion/growth-regulatory galectins, in particular galectin-3 (Gal-3). The KS contact region involves the lectin canonical binding site, with estimated KD values in the low µM range and stoichiometry of ~ 8 to ~ 20 galectin molecules binding per polysaccharide chain. Compared to Gal-3, the affinity to Gal-7 is relatively low, signaling preferences among galectins. The importance of the sulfate groups was delineated by using desulfated analogs that exhibit relatively reduced affinity. Binding studies with two related di- and tetrasaccharides revealed a similar decrease that underscores affinity enhancement by repetitive arrangement of disaccharide units. MD-based binding energies of KS oligosaccharide-loaded galectins support experimental data on Gal-3 and -7, and extend the scope of KS binding to Gal-1 and -9N. Overall, our results provide strong incentive to further probe the relevance of molecular recognition of KS by galectins in terms of physiological processes in situ, e.g. maintaining integrity of mucosal barriers, intermolecular (lattice-like) gluing within the extracellular meshwork or synaptogenesis.

HIP/PAP protects against bleomycin-induced lung injury and inflammation and subsequent fibrosis in mice.

Hepatocarcinoma‐intestine‐pancreas/pancreatitis‐associated protein (HIP/PAP), a C‐type lectin, exerts anti‐oxidative, anti‐inflammatory, bactericidal, anti‐apoptotic, and mitogenic functions in several cell types and tissues. In this study, we explored the role of HIP/PAP in pulmonary fibrosis (PF). Expression of HIP/PAP and its murine counterpart, Reg3B, was markedly increased in fibrotic human and mouse lung tissues. Adenovirus‐mediated HIP/PAP expression markedly alleviated bleomycin (BLM)‐induced lung injury, inflammation, and fibrosis in mice. Adenovirus‐mediated HIP/PAP expression alleviated oxidative injury and lessened the decrease in pulmonary superoxide dismutase (SOD) activity in BLM‐treated mice, increased pulmonary SOD expression in normal mice, and HIP/PAP upregulated SOD expression in cultured human alveolar epithelial cells (A549) and human lung fibroblasts (HLF‐1). Moreover, in vitro experiments showed that HIP/PAP suppressed the growth of HLF‐1 and ameliorated the H2O2‐induced apoptosis of human alveolar epithelial cells (A549 and HPAEpiC) and human pulmonary microvascular endothelial cells (HPMVEC). In HLF‐1, A549, HPAEpiC, and HPMVEC cells, HIP/PAP did not affect the basal levels, but alleviated the TGF‐β1‐induced down‐regulation of the epithelial/endothelial markers E‐cadherin and vE‐cadherin and the over‐expression of mesenchymal markers, such as α‐SMA and vimentin. In conclusion, HIP/PAP was found to serve as a potent protective factor in lung injury, inflammation, and fibrosis by attenuating oxidative injury, promoting the regeneration of alveolar epithelial cells, and antagonizing the pro‐fibrotic actions of the TGF‐β1/Smad signaling pathway.

Influence of protein (human galectin-3) design on aspects of lectin activity

The concept of biomedical significance of the functional pairing between tissue lectins and their glycoconjugate counterreceptors has reached the mainstream of research on the flow of biological information. A major challenge now is to identify the principles of structure–activity relationships that underlie specificity of recognition and the ensuing post-binding processes. Toward this end, we focus on a distinct feature on the side of the lectin, i.e. its architecture to present the carbohydrate recognition domain (CRD). Working with a multifunctional human lectin, i.e. galectin-3, as model, its CRD is used in protein engineering to build variants with different modular assembly. Hereby, it becomes possible to compare activity features of the natural design, i.e. CRD attached to an N-terminal tail, with those of homo- and heterodimers and the tail-free protein. Thermodynamics of binding disaccharides proved full activity of all proteins at very similar affinity. The following glycan array testing revealed maintained preferential contact formation with N-acetyllactosamine oligomers and histo-blood group ABH epitopes irrespective of variant design. The study of carbohydrate-inhibitable binding of the test panel disclosed up to qualitative cell-type-dependent differences in sections of fixed murine epididymis and especially jejunum. By probing topological aspects of binding, the susceptibility to inhibition by a tetravalent glycocluster was markedly different for the wild-type vs the homodimeric variant proteins. The results teach the salient lesson that protein design matters: the type of CRD presentation can have a profound bearing on whether basically suited oligosaccharides, which for example tested positively in an array, will become binding partners in situ. When lectin-glycoconjugate aggregates (lattices) are formed, their structural organization will depend on this parameter. Further testing (ga)lectin variants will thus be instrumental (i) to define the full range of impact of altering protein assembly and (ii) to explain why certain types of design have been favored during the course of evolution, besides opening biomedical perspectives for potential applications of the novel galectin forms.

How galectins have become multifunctional proteins.

Having identified glycans of cellular glycoconjugates as versatile molecular messages, their recognition by sugar receptors (lectins) is a fundamental mechanism within the flow of biological information. This type of molecular interplay is increasingly revealed to be involved in a wide range of (patho)physiological processes. To do so, it is a vital prerequisite that a lectin (and its expression) can develop more than a single skill, that is the general ability to bind glycans. By studying the example of vertebrate galectins as a model, a total of five relevant characteristics is disclosed: i) access to intra- and extracellular sites, ii) fine-tuned gene regulation (with evidence for co-regulation of counterreceptors) including the existence of variants due to alternative splicing or single nucleotide polymorphisms, iii) specificity to distinct glycans from the glycome with different molecular meaning, iv) binding capacity also to peptide motifs at different sites on the protein and v) diversity of modular architecture. They combine to endow these lectins with the capacity to serve as multi-purpose tools. Underscoring the arising broad-scale significance of tissue lectins, their numbers in terms of known families and group members have steadily grown by respective research that therefore unveiled a well-stocked toolbox. The generation of a network of (ga)lectins by evolutionary diversification affords the opportunity for additive/synergistic or antagonistic interplay in situ, an emerging aspect of (ga)lectin functionality. It warrants close scrutiny. The realization of the enormous potential of combinatorial permutations using the five listed features gives further efforts to understand the rules of functional glycomics/lectinomics a clear direction.

Sensing Glycans as Biochemical Messages by Tissue Lectins: The Sugar Code at Work in Vascular Biology.

Although a plethora of players has already been revealed to be engaged in the haemostatic system, a fundamental consideration of the molecular nature of information coding can give further explorations of the mechanisms of blood clotting, platelet functionality and vascular trafficking direction. By any measures, looking at ranges of occurrence and of potential for structural versatility, at strategic positioning to influence protein and cell sociology as well as at dynamics of processing and restructuring for phenotypic variability, using sugars as an alphabet of life for generating the glycan part of glycoconjugates is a success story. The handiwork by the complex system for glycan biosynthesis renders biochemical messages of exceptionally high coding capacity available. They are read and translated into cellular effects by receptors termed lectins. The different levels of regulation on both sides, that is, glycan and lectin, establish an intriguingly fine-tuned capacity for functional pairing. The emerging insights into the highly branched routes of glycosylation, into lectin structures up to complete characterization in solution and the shape of lectin networks, first obtained for the three selectins, now extended to considering many other C-type lectins, galectins and siglecs, as well as into intra- and inter-family cross-talk and cooperations are sure to push boundaries in our understanding of the molecular basis of haemostasis.

Chicken GRIFIN: binding partners, developmental course of localization and activation of its lens-specific gene expression by L-Maf/Pax6.

Tissue lectins appear to be involved in a broad range of physiological processes, as reflected for the members of the family of galectins by referring to them as adhesion/growth-regulatory effectors. In order to clarify the significance of galectin presence, key challenges are to define their binding partners and the profile of localization. Having identified the chicken galectin-related interfiber protein (C-GRIFIN) as lens-specific protein present in the main body of adult lens, we here report its interaction with lens proteins in ligand blotting. The assumption for pairing with α-, β- and δ-crystallins was ascertained by mass spectrometric detection of their presence in eluted fractions obtained by affinity chromatography. Biochemical and immunohistochemical monitoring revealed protein presence from about 3-day-old embryos onwards, mostly in the cytoplasm of elongated posterior cells, later in secondary lens fiber cells. On the level of gene expression, its promoter was activated by transcription factor L-Maf alone and together with Pax6 like a crystallin gene, substantiating C-GRIFIN's status as lens-specific galectin. Using this combined strategy for counterreceptor and expression profiling by bio- and histochemical methods including light, electron and fluorescence microscopy, respective monitoring in lens development can now be taken to the level of the complete galectin family.

Galectin-8 induces functional disease markers in human osteoarthritis and cooperates with galectins-1 and -3

The reading of glycan-encoded signals by tissue lectins is considered a major route of the flow of biological information in many (patho)physiological processes. The arising challenge for current research is to proceed from work on a distinct protein to family-wide testing of lectin function. Having previously identified homodimeric galectin-1 and chimera-type galectin-3 as molecular switches in osteoarthritis progression, we here provide proof-of-principle evidence for an intra-network cooperation of galectins with three types of modular architecture. We show that the presence of tandem-repeat-type galectin-8 significantly correlated with cartilage degeneration and that it is secreted by osteoarthritic chondrocytes. Glycan-inhibitable surface binding of galectin-8 to these cells increased gene transcription and the secretion of functional disease markers. The natural variant galectin-8 (F19Y) was less active than the prevalent form. Genome-wide array analysis revealed induction of a pro-degradative/inflammatory gene signature, largely under control of NF-κB signaling. This signature overlapped with respective gene-expression patterns elicited by galectins-1 and -3, but also presented supplementary features. Functional assays with mixtures of galectins that mimic the pathophysiological status unveiled cooperation between the three galectins. Our findings shape the novel concept to consider individual galectins as part of a so far not realized teamwork in osteoarthritis pathogenesis, with relevance beyond this disease.

Three-step monitoring of glycan and galectin profiles in the anterior segment of the adult chicken eye

A histochemical three-step approach is applied for processing a panel of sections that covers the different regions of fixed anterior segment of the adult chicken eye. This analysis gains insight into the presence of binding partners for functional pairing by galectin/lectin recognition in situ. Glycophenotyping with 11 fungal and plant lectins (step 1) revealed a complex pattern of reactivity with regional as well as glycan- and cell-type-dependent differences. When characterizing expression of the complete set of the seven adhesion/growth-regulatory chicken galectins immunohistochemically (step 2), the same holds true, clearly demonstrating profiles with individual properties, even for the CG-1A/B paralogue pair. Testing this set of labeled tissue lectins as probes (step 3) detected binding sites in a galectin-type-dependent manner. The results of steps 2 and 3 reflect the divergence of sequences and argue against functional redundancy among the galectins. These data shape the concept of an in situ network of galectins. As consequence, experimental in vitro studies will need to be performed from the level of testing a single protein to work with mixtures that mimic the (patho)physiological situation, a key message of this report.