Galectins in the Pathogenesis of Rheumatoid Arthritis

Proteomic analysis of decellularized mice liver and kidney extracellular matrices

BACKGROUND

The extracellular matrix (ECM) is a three-dimensional network of proteins that encases and supports cells within a tissue and promotes physiological and pathological cellular differentiation and functionality. Understanding the complex composition of the ECM is essential to decrypt physiological processes as well as pathogenesis. In this context, the method of decellularization is a useful technique to eliminate cellular components from tissues while preserving the majority of the structural and functional integrity of the ECM.

RESULTS

In this study, we employed a bottom-up proteomic approach to elucidate the intricate network of proteins in the decellularized extracellular matrices of murine liver and kidney tissues. This approach involved the use of a novel, perfusion-based decellularization protocol to generate acellular whole organ scaffolds. Proteomic analysis of decellularized mice liver and kidney ECM scaffolds revealed tissue-specific differences in matrisome composition, while we found a predominantly stable composition of the core matrisome, consisting of collagens, glycoproteins, and proteoglycans. Liver matrisome analysis revealed unique proteins such as collagen type VI alpha-6, fibrillin-2 or biglycan. In the kidney, specific ECM-regulators such as cathepsin z were detected.

CONCLUSION

The identification of distinct proteomic signatures provides insights into how different matrisome compositions might influence the biological properties of distinct tissues. This experimental workflow will help to further elucidate the proteomic landscape of decellularized extracellular matrix scaffolds of mice in order to decipher complex cell-matrix interactions and their contribution to a tissue-specific microenvironment.

Gingival crevicular fluid galectin-3 and interleukin-1 beta levels in stage 3 periodontitis with grade B and C

OBJECTIVES

This study aims to evaluate GCF Galectin-3 and Interleukin-1 beta (IL-β) levels in different grades (B and C) of stage 3 periodontitis, concurrently, and also to investigate their discriminative efficiencies in periodontal diseases.

MATERIALS AND METHODS

A total of 80 systemically healthy and non-smoker individuals, 20 stage 3 grade C (S3GC) periodontitis 20 stage 3 grade B (S3GB) periodontitis, 20 gingivitis, and 20 periodontally healthy were enrolled. Clinical periodontal parameters were recorded and GCF Galectin-3 and IL-1β total amounts were measured by ELISA. Receiver operating characteristics curve was used for estimating the area under the curve (AUC).

RESULTS

Galectin-3 and IL-1β were detected in all participants. Both periodontitis groups had significantly higher GCF Galectin-3 total amounts than periodontally healthy controls (p <0.05). S3GC periodontitis group had also significantly higher GCF Galectin-3 levels than gingivitis group (p <0.05). GCF IL-1β levels in periodontitis groups were higher than gingivitis and periodontally healthy groups (p <0.05). Galectin-3 exhibited an AUC value of 0.89 with 95% sensitivity to discriminate S3GC periodontitis from periodontal health, an AUC value of 0.87 with 80% sensitivity to discriminate S3GC periodontitis versus gingivitis, while an AUC value of 0.85 with 95% sensitivity to discriminate S3GB periodontitis from healthy controls.

CONCLUSIONS

GCF Galectin-3 levels are involved in the pathogenesis of periodontal diseases. Galectin-3 showed excellent diagnostic performances to discriminate S3GB and S3GC periodontitis from periodontal health and gingivitis.

CLINICAL RELEVANCE

The present findings suggest that GCF Galectin-3 levels may be useful in the diagnosis of the periodontal diseases.

BST2, a Novel Inhibitory Receptor, Is Involved in NK Cell Cytotoxicity through Its Cytoplasmic Tail Domain

Bone Marrow Stromal Cell Antigen 2 (BST2) is a type II transmembrane protein expressed on various cell types that tethers the release of viruses. Natural killer (NK) cells express low levels of BST2 under normal conditions but exhibit increased expression of BST2 upon activation. In this study, we show for the first time that murine BST2 can control the cytotoxicity of NK cells. The cytoplasmic tail of murine BST2 contains an immunoreceptor tyrosine-based inhibitory motif (ITIM). The absence of BST2 on NK cells can enhance their cytotoxicity against tumor cells compared to wild type NK cells. NK cells isolated from NZW mice, which express ITIM-deficient BST2, also showed higher cytotoxicity than wild type NK cells. In addition, we found that galectin-8 and galectin-9 were ligands of BST2, since blocking galectin-8 or -9 with monoclonal antibodies enhanced the cytotoxicity of NK cells. These results suggested that BST2 might be a novel NK cell inhibitory receptor as it was involved in regulating NK cell cytotoxicity through its interaction with galectins.

Association between inflammatory cytokines and immune-checkpoint molecule in rheumatoid arthritis

Background

Anti-citrullinated peptide antibodies (ACPA) and inflammatory cytokines play important roles in the development of rheumatoid arthritis (RA). T cell immunoglobulin and mucin–domain containing–3 (TIM–3) is an immune-checkpoint molecule involved in inhibitory signaling. Galectin–9 (Gal–9) mediated ligation of TIM–3 induces the amelioration of autoimmune diseases. TIM–3 is expressed in synovial osteoclasts and involved in the rheumatoid bone destruction. The aim of this study was to investigate the relationships between inflammatory cytokines and immune–checkpoint molecules in RA patients.

Methods

Serum levels of interleukin–6 (IL–6), tumor necrosis factor–α (TNF–α), soluble TIM–3 (sTIM–3) and Gal–9 were determined by ELISA. Patients were stratified into two groups based on ACPA titers: low-medium ACPA (ACPA <200 U/mL) and high ACPA (ACPA ≥200 U/mL). Serum levels of cytokines or immune-checkpoint molecules were evaluated between RA patients with low-medium ACPA titers and high ACPA titers.

Results

Elevated serum levels of inflammatory cytokines were correlated with DAS28–ESR in RA patients. Although serum levels of sTIM–3 were elevated in RA patients, significant correlations between sTIM–3 and cytokines (IL–6 or TNF–α) were observed exclusively in RA patients with low-medium ACPA titers (<200 U/mL). Serum levels of IL–6 and TNF–α levels were significantly correlated with elevated Gal–9 levels regardless of ACPA status. A significant correlation between IL–6 and Gal–9 was observed in RA patients without advanced joint damage. Conversely, a significant correlation between TNF–α and Gal–9 was observed in RA patients with advanced joint damage.

Conclusions

Our data indicated that there are positive correlations between circulating inflammatory cytokines and checkpoint molecules in RA patients and these interactions can be modulated by ACPA status or joint damage stage.

Different Expression Pattern of TIM-3 and Galectin-9 Molecules by Peripheral and Peritoneal Lymphocytes in Women with and without Endometriosis

Endometriosis is a gynecological condition that is associated with chronic pelvic inflammation, pain, and infertility. Although substantial evidence supports that immunological alterations contribute to its pathogenesis and we previously posed a pivotal role of Galectin-9 (Gal-9) in this disorder, the involvement of the TIM-3/Gal-9 pathway in the development of endometriosis-associated immunological abnormalities is not yet known. In the present study, multicolor flow cytometry was used to compare the immunophenotype and cell surface expression of TIM-3 and Gal-9 molecules on peripheral blood (PB) and peritoneal fluid (PF) lymphocytes of women with and without endometriosis. We found an altered distribution of different lymphocyte subpopulations, a markedly decreased TIM-3 labeling on all T and NK subsets and a significantly increased Gal-9 positivity on peripheral CD4+ T and Treg cells of the affected cohort. Furthermore, a significantly increased TIM-3 expression on CD4+T-cells and elevated Gal-9 labeling on all T and NK subsets was also revealed in the PF of the examined patients. In conclusion, our results suggest a persistent activation and disturbed TIM-3/Gal-9-dependent regulatory function in endometriosis, which may be involved in the impaired immune surveillance mechanisms, promotes the survival of ectopic lesions, and aids the evolution of reproductive failures in endometriosis.

A Synthetic Tetramer of Galectin-1 and Galectin-3 Amplifies Pro-apoptotic Signaling by Integrating the Activity of Both Galectins

Galectin-1 (G1) and galectin-3 (G3) are carbohydrate-binding proteins that can signal apoptosis in T cells. We recently reported that a synthetic tetramer with two G1 and two G3 domains ("G1/G3 Zipper") induces Jurkat T cell death more potently than G1. The pro-apoptotic signaling pathway of G1/G3 Zipper was not elucidated, but we hypothesized based on prior work that the G1 domains acted as the signaling units, while the G3 domains served as anchors that increase glycan-binding affinity. To test this, here we studied the involvement of different cell membrane glycoproteins and intracellular mediators in pro-apoptotic signaling via G1/G3 Zipper, G1, and G3. G1/G3 Zipper induced Jurkat T cell death more potently than G1 and G3 alone or in combination. G1/G3 Zipper, G1, and G3 increased caspase-8 activity, yet only G1 and G3 depended on it to induce cell death. G3 increased caspase-3 activity more than G1/G3 Zipper and G1, while all three galectin variants required it to induce cell death. JNK activation had similar roles downstream of G1/G3 Zipper, G1, and G3, whereas ERK had differing roles. CD45 was essential for G1 activity, and was involved in signaling via G1/G3 Zipper and G3. CD7 inhibited G1/G3 Zipper activity at low galectin concentrations but not at high galectin concentrations. In contrast, CD7 was necessary for G1 and G3 signaling at low galectin concentration but antagonistic at high galectin concentrations. Collectively, these observations suggest that G1/G3 Zipper amplifies pro-apoptotic signaling through the integrated activity of both the G1 and G3 domains.

Galectin-3 orchestrates the histology of mesentery and protects liver during lupus-like syndrome induced by pristane

Galectin-3 (Gal-3) controls intercellular and cell-extracellular matrix interactions during immunological responses. In chronic inflammation, Gal-3 is associated with fibrotic events, regulates B cell differentiation and delays lupus progression. Gal-3 deficient mice (Lgals3^−/−) have intense germinal center formation and atypical plasma cell generation correlated to high levels IgG, IgE, and IgA. Here, we used pristane (2,6,10,14-tetramethylpentadecane) to induce lupus-like syndrome in Lgals3^−/− and Lgals3^+/+ BALB/c mice. Mesentery and peritoneal cells were monitored because promptly react to pristane injected in the peritoneal cavity. For the first time, mesenteric tissues have been associated to the pathogenesis of experimental lupus-like syndrome. In Lgals3^+/+ pristane-induced mice, mesentery was hallmarked by intense fibrogranulomatous reaction restricted to submesothelial regions and organized niches containing macrophages and B lymphocytes and plasma cells. In contrast, Lgals3^−/− pristane-treated mice had diffuse mesenteric fibrosis affecting submesothelium and peripheral tissues, atypical M1/M2 macrophage polarization and significant DLL1⁺ cells expansion, suggesting possible involvement of Notch/Delta pathways in the disease. Early inflammatory reaction to pristane was characterized by significant disturbances on monocyte recruitment, macrophage differentiation and dendritic cell (DC) responses in the peritoneal cavity of pristane-induced Lgals3^−/− mice. A correlative analysis showed that mesenteric damages in the absence of Gal-3 were directly associated with severe portal inflammation and hepatitis. In conclusion, it has suggested that Gal-3 orchestrates histological organization in the mesentery and prevents lupoid hepatitis in experimental lupus-like syndrome by controlling macrophage polarization, Notch signaling pathways and DC differentiation in mesenteric structures.

Galectin-9 Is a Possible Promoter of Immunopathology in Rheumatoid Arthritis by Activation of Peptidyl Arginine Deiminase 4 (PAD-4) in Granulocytes

The aetiology of rheumatoid arthritis (RA) is unknown, but citrullination of proteins is thought to be an initiating event. In addition, it is increasingly evident that the lung can be a potential site for the generation of autoimmune triggers before the development of joint disease. Here, we identified that serum levels of galectin-9 (Gal-9), a pleiotropic immunomodulatory protein, are elevated in RA patients, and are even further increased in patients with comorbid bronchiectasis, a lung disease caused by chronic inflammation. The serum concentrations of Gal-9 correlate with C-reactive protein levels and DAS-28 score. Gal-9 activated polymorphonuclear leukocytes (granulocytes) in vitro, which was characterized by increased cytokine secretion, migration, and survival. Further, granulocytes treated with Gal-9 upregulated expression of peptidyl arginine deiminase 4 (PAD-4), a key enzyme required for RA-associated citrullination of proteins. Correspondingly, treatment with Gal-9 triggered citrullination of intracellular granulocyte proteins that are known contributors to RA pathogenesis (i.e., myeloperoxidase, alpha-enolase, MMP-9, lactoferrin). In conclusion, this study identifies for the first time an immunomodulatory protein, Gal-9, that triggers activation of granulocytes leading to increased PAD-4 expression and generation of citrullinated autoantigens. This pathway may represent a potentially important mechanism for development of RA.

Galectin-1, -4, and -7 Were Associated with High Activity of Disease in Patients with Rheumatoid Arthritis

Background

Due to the variety of functions that galectins (Gal) possess, it is clear that they participate in the pathogenesis of rheumatoid arthritis (RA). Although some studies demonstrate their functions, there is still no correlation with the clinical data of the disease, having the physiological meaning still unknown.

Objectives

To compare serum levels of Gal-1, -4, and -7 in patients with RA and healthy controls and to correlate them with clinical parameters.

Methods

Serum samples were collected from patients with RA and healthy donors to determine the serum levels of Gal-1, -4, and -7.

Results

Serum levels of Gal-1, -4, and -7 were significantly higher in RA patients compared to controls. We evaluated disease activity (CDAI) with serum levels of galectins and found that patients who were high in disease activity had high levels of galectin compared to the moderate activity group. Galectin-4 had higher levels in patients who were in high activity when compared to the group in remission or low activity. Evaluating the activity of the individual disease (DAS28), patients in high individual activity had high levels of Gal-4 when compared to the group in remission or low activity. We also found an association between positive rheumatoid factor and Gal-1 and Gal-4 levels.

Conclusion

Our results show for the first time the relationship between serum levels of galectin and the clinical parameters of patients with RA. Demonstrating their role in pathogenesis, new studies with galectins are needed to assess how they function as a biomarker in RA.

Galectins-1 and-3 Increase in Equine Post-traumatic Osteoarthritis

Galectins are potent regulators of cell adhesion, growth and apoptosis in diverse cell types, including chondrocytes and synovial fibroblasts. Elevations in synovial fluid galectin-3 have been observed in rheumatoid arthritis, juvenile idiopathic arthritis and experimental inflammatory arthritis in animal models, whereas galectin-1 is thought to be protective. Less is known about galectins-1 and-3 in osteoarthritis (OA). Therefore, the purpose of this study was: (1) to determine whether galectin-1 and-3 synovial fluid concentrations and synovial membrane and cartilage histochemical staining were altered following osteochondral injury in an experimental equine osteoarthritis (OA) model and (2) to measure galectin-1 and-3 mRNA expression and synovial fluid concentrations in naturally occurring equine carpal OA. Synovial fluid galectin-1 and-3 concentrations were quantified using custom ELISAs in two research horse cohorts undergoing experimental OA induction (n = 5 and 4) and in a cohort of horses with naturally occurring carpal OA (n = 57). Galectin mRNA expression in synovial membrane and cartilage tissue obtained from carpal joints of horses with naturally occurring OA was measured using RT-qPCR, and galectin immunostaining was assessed in synovial membrane and osteochondral tissues in the experimental model (n = 5). Synovial fluid galectin-1 and-3 concentrations increased following experimental carpal osteochondral fragmentation. Cartilage galectin-1 mRNA expression increased with OA severity in naturally occurring disease. The superficial zone of healthy articular cartilage stained intensely for galectin-3 in sham-operated joints, whereas galectin-1 staining was nearly absent. Chondrocyte galectin-1 and-3 immunoreactivity increased following cartilage injury, particularly in galectin-1 positive chondrones. Galectins-1 and-3 are present in healthy equine synovial fluid and increase following post-traumatic OA. Healthy superficial zone chondrocytes express galectin-3, whereas galectin-1 chondrocyte staining is limited predominantly to chondrones and injured cartilage. Further work is needed to clarify the functions of galectins-1 and-3 in healthy and OA joints.

Impaired Gal-9 Dysregulates the PBMC-Induced Th1/Th2 Imbalance in Abortion-Prone Matings

Recurrent miscarriage is defined as the loss of 3 or more consecutive pregnancies; however, the underlying immunologic mechanisms that trigger pregnancy loss remain largely unelucidated. Galectin-9 (Gal-9) may modulate a variety of biologic functions and play an important role in Th1/Th2 immune deviation. To analyze the mechanism of Gal-9 in abortion, we used the classical abortion-prone mouse model (DBA/2-mated CBA/J mice) to detect the expression of Gal-9 at the maternal-fetal interface. We also mimicked the immune environment of pregnancy by culturing trophoblast cells with peripheral blood mononuclear cells (PBMCs) to explore how Gal-9 might be involved in the pathogenesis of abortion. We found that the expression levels of Gal-9 in abortion-prone matings were lower than that for controls. Using a coculture system, we detected a Th1 preponderance in the coculture from abortion-prone matings. Furthermore, Gal-9 blockade augmented the imbalance of Th1/Th2 immunity in abortion-prone matings by promoting the secretion of Th1-derived cytokines in coculture, while there was a Th2 preponderance when we administered recombinant Gal-9. In conclusion, our results suggest that the Gal-9 signal is important for the regulation of PBMC function toward a Th2 bias at the maternal-fetal interface, which is beneficial for the maintenance of a normal pregnancy.

Galectin-3: One Molecule for an Alphabet of Diseases, from A to Z

Galectin-3 (Gal-3) regulates basic cellular functions such as cell-cell and cell-matrix interactions, growth, proliferation, differentiation, and inflammation. It is not surprising, therefore, that this protein is involved in the pathogenesis of many relevant human diseases, including cancer, fibrosis, chronic inflammation and scarring affecting many different tissues. The papers published in the literature have progressively increased in number during the last decades, testifying the great interest given to this protein by numerous researchers involved in many different clinical contexts. Considering the crucial role exerted by Gal-3 in many different clinical conditions, Gal-3 is emerging as a new diagnostic, prognostic biomarker and as a new promising therapeutic target. The current review aims to extensively examine the studies published so far on the role of Gal-3 in all the clinical conditions and diseases, listed in alphabetical order, where it was analyzed.

Galectin-3 Induces a Pro-degradative/inflammatory Gene Signature in Human Chondrocytes, Teaming Up with Galectin-1 in Osteoarthritis Pathogenesis

Inflammatory chemo- and cytokines and matrix-degrading proteases underlie the progression of osteoarthritis (OA). Aiming to define upstream regulators for these disease markers, we pursued initial evidence for an upregulation of members of the adhesion/growth-regulatory galectin family. Immunohistochemical localization of galectin-3 (Gal-3) in sections of human cartilage with increasing levels of degeneration revealed a linear correlation reaching a chondrocyte positivity of 60%. Presence in situ was cytoplasmic, the lectin was secreted from OA chondrocytes in culture and binding of Gal-3 yielded lactose-inhibitable surface staining. Exposure of cells to the lectin led to enhanced gene expression and secretion of functional disease markers. Genome-wide transcriptomic analysis broadened this result to reveal a pro-degradative/inflammatory gene signature under the control of NF-κB. Fittingly, targeting this route of activation by inhibitors impaired the unfavourable response to Gal-3 binding, as also seen by shortening the lectin’s collagen-like repeat region. Gal-3’s activation profile overlaps with that of homodimeric galectin-1 (Gal-1) and also has distinctive (supplementing) features. Tested at subsaturating concentrations in a mixture, we found cooperation between the two galectins, apparently able to team up to promote OA pathogenesis. In summary, our results suggest that a network of endogenous lectins is relevant for initiating this process cascade.

Intra- and intermolecular interactions of human galectin-3: assessment by full-assignment-based NMR

Galectin-3 is an adhesion/growth-regulatory protein with a modular design comprising an N-terminal tail (NT, residues 1-111) and the conserved carbohydrate recognition domain (CRD, residues 112-250). The chimera-type galectin interacts with both glycan and peptide motifs. Complete (13)C/(15)N-assignment of the human protein makes NMR-based analysis of its structure beyond the CRD possible. Using two synthetic NT polypeptides covering residues 1-50 and 51-107, evidence for transient secondary structure was found with helical conformation from residues 5 to 15 as well as proline-mediated, multi-turn structure from residues 18 to 32 and around PGAYP repeats. Intramolecular interactions occur between the CRD F-face (the 5-stranded β-sheet behind the canonical carbohydrate-binding 6-stranded β-sheet of the S-face) and NT in full-length galectin-3, with the sequence P(23)GAW(26)…P(37)GASYPGAY(45) defining the primary binding epitope within the NT. Work with designed peptides indicates that the PGAX motif is crucial for self-interactions between NT/CRD. Phosphorylation at position Ser6 (and Ser12) (a physiological modification) and the influence of ligand binding have minimal effect on this interaction. Finally, galectin-3 molecules can interact weakly with each other via the F-faces of their CRDs, an interaction that appears to be assisted by their NTs. Overall, our results add insight to defining binding sites on galectin-3 beyond the canonical contact area for β-galactosides.

CD154-CD40 T-cell co-stimulation pathway is a key mechanism in kidney ischemia-reperfusion injury

Ischemia-reperfusion occurs in a great many clinical settings and contributes to organ failure or dysfunction. CD154-CD40 signaling in leukocyte–endothelial cell interactions or T-cell activation facilitates tissue inflammation and injury. Here we tested a siRNA anti-CD40 in rodent warm and cold ischemia models to check the therapeutic efficacy and anti-inflammatory outcome of in vivo gene silencing. In the warm ischemia model different doses were used, resulting in clear renal function improvement and a structural renoprotective effect. Renal ischemia activated the CD40 gene and protein expression, which was inhibited by intravenous siRNA administration. CD40 gene silencing improved renal inflammatory status, as seen by the reduction of CD68 and CD3 T-cell infiltrates, attenuated pro-inflammatory, and enhanced anti-inflammatory mediators. Furthermore, siRNA administration decreased a spleen pro-inflammatory monocyte subset and reduced TNFα secretion by splenic T cells. In the cold ischemia model with syngeneic and allogeneic renal transplantation, the most effective dose induced similar functional and structural renoprotective effects. Our data show the efficacy of our siRNA in modulating both the local and the systemic inflammatory milieu after an ischemic insult. Thus, CD40 silencing could emerge as a novel therapeutic strategy in solid organ transplantation.

Tenascin-C aggravates autoimmune myocarditis via dendritic cell activation and Th17 cell differentiation

Background

Tenascin‐C (TN‐C), an extracellular matrix glycoprotein, appears at several important steps of cardiac development in the embryo, but is sparse in the normal adult heart. TN‐C re‐expresses under pathological conditions including myocarditis, and is closely associated with tissue injury and inflammation in both experimental and clinical settings. However, the pathophysiological role of TN‐C in the development of myocarditis is not clear. We examined how TN‐C affects the initiation of experimental autoimmune myocarditis, immunologically.

Methods and Results

A model of experimental autoimmune myocarditis was established in BALB/c mice by immunization with murine α‐myosin heavy chains. We found that TN‐C knockout mice were protected from severe myocarditis compared to wild‐type mice. TN‐C induced synthesis of proinflammatory cytokines, including interleukin (IL)‐6, in dendritic cells via activation of a Toll‐like receptor 4, which led to T‐helper (Th)17 cell differentiation and exacerbated the myocardial inflammation. In the transfer experiment, dendritic cells loaded with cardiac myosin peptide acquired the functional capacity to induce myocarditis when stimulated with TN‐C; however, TN‐C‐stimulated dendritic cells generated from Toll‐like receptor 4 knockout mice did not induce myocarditis in recipients.

Conclusions

Our results demonstrated that TN‐C aggravates autoimmune myocarditis by driving the dendritic cell activation and Th17 differentiation via Toll‐like receptor 4. The blockade of Toll‐like receptor 4‐mediated signaling to inhibit the proinflammatory effects of TN‐C could be a promising therapeutic strategy against autoimmune myocarditis.