Galectin-3 in osteoarthritis: when the fountain of youth doesn't deliver its promises

Galectin network in osteoarthritis: galectin-4 programs a pathogenic signature of gene and effector expression in human chondrocytes in vitro

Galectin-4 (Gal-4) is a member of the galectin family, which have been identified as galactose-binding proteins. Gal-4 possesses two tandem repeat carbohydrate recognition domains and acts as a cross-linking bridge in sulfatide-dependent glycoprotein routing. We herein document its upregulation in osteoarthritis (OA) in correlation with the extent of cartilage degradation in vivo. Primary human OA chondrocytes in vitro respond to carbohydrate-inhibitable Gal-4 binding with the upregulation of pro-degradative/-inflammatory proteins such as interleukin-1β (IL-1β) and matrix metalloproteinase-13 (MMP-13), as documented by RT-qPCR-based mRNA profiling and transcriptome data processing. Activation of p65 by phosphorylation of Ser536 within the NF-κB pathway and the effect of three p65 inhibitors on Gal-4 activity support downstream involvement of such signaling. In 3D (pellet) cultures, Gal-4 presence causes morphological and biochemical signs of degradation. Taken together, our findings strongly support the concept of galectins acting as a network in OA pathogenesis and suggest that blocking their activity in disease progression may become clinically relevant in the future.

The Role of Galectins in Chronic Lung Allograft Dysfunction

Background

Galectins are proteins that bind β-galactosides such as N-acetyllactosamine present in N-linked and O-linked glycoproteins and that seem to be implicated in inflammatory and immune responses as well as fibrotic mechanisms. This preliminary study investigated serum galectins as clinical biomarkers in lung transplant patients with chronic lung allograft dysfunction (CLAD), phenotype bronchiolitis obliterans syndrome (BOS).

Materials and Methods

Nineteen lung transplant patients [median age (IQR), 55 (45–62) years; 53% males] were enrolled in the study. Peripheral blood concentrations of galectins-1, 3 and 9 were determined with commercial ELISA kits.

Results

Galectin-1 concentrations were higher in BOS than in stable LTX patients (p = 0.0394). In logistic regression analysis, testing BOS group as dependent variable with Gal-1 and 3 as independent variables, area under the receiver operating characteristics (AUROC) curve was 98.9% (NPV 90% and PPV 88.9%, p = 0.0003). With the stable LTX group as dependent variable and Gal-1, 3 and 9 as independent variables, AUROC was 92.6% (NPV 100% and PPV 90%, p = 0.0023). In stable patients were observed an inverse correlation of Gal-3 with DLCO% and KCO%, and between Gal-9 and KCO%.

Conclusion

Galectins-1, 3 and 9 are possible clinical biomarkers in lung transplant patients with diagnostic and prognostic meaning. These molecules may be directly implicated in the pathological mechanisms of BOS. The hypothesis that they could be new therapeutic targets in BOS patients is intriguing and also worth exploring.

Blocking extracellular Galectin-3 in patients with osteoarthritis

Objective

This pilot clinical trial examined the efficacy of blocking extracellular Galectin-3 (Gal-3) with modified citrus pectin (MCP), in patients suffering from knee osteoarthritis (OA).

Methods

50 patients were randomized in a 1:1 ratio to receive MCP or placebo at a dose of 4 g (5 capsules) twice daily for 12 weeks. Serum Gal-3 levels and OA severity were evaluated at baseline and 12 weeks. Gal-3 levels were detected by sandwich ELISA and OA severity was determined using WOMAC-knee, SF-36, and RAPID3 surveys during these visits. MCP tolerability was assessed by a basic metabolic panel during a week 6 follow up visit.

Results

Patients enrolled in both the MCP treatment and placebo groups shared similar baseline characteristics in OA severity, serum Gal-3 levels, and pain management. Improvement across all surveys was noted independent of supplement or placebo treatment. No significant change in Gal-3 levels were observed in either cohort over the 12-week study.

Conclusion

Treatment of knee OA with a 12-week course of MCP did not significantly improve disease burden compared to placebo.

Elevated Galectin-9 Suppresses Th1 Effector Function and Induces Apoptosis of Activated CD4+ T Cells in Osteoarthritis

T cell immunoglobulin and mucin domain 3 (Tim-3) is a critical regulatory molecule found on activated Th1 cells, exhausted CD8⁺ T cells, and resting monocytes/macrophages. Galectin-9 (Gal-9) is an identified ligand for Tim-3. Interaction between Tim-3 and Gal-9 is thought to inhibit Th1 responses. The regulation and function of Tim-3 and Gal-9 in osteoarthritis (OA) have not been intensively investigated. We found that in peripheral blood, CD4⁺ T cells, but not CD8⁺ T cells or CD14⁺ monocytes, from OA patients presented significantly elevated Tim-3 and Gal-9 expression compared to those from healthy controls (HC). The CD4⁺ T cells from OA did not present altered Th1, Th2, and Th17 composition in the peripheral blood, but secreted less Th1 cytokine interleukin 2 (IL-2) and interferon gamma (IFN-γ) after activation. Further investigation demonstrated that Gal-9 induced high levels of apoptosis in activated CD4⁺ T cells from OA patients. Inhibition of Gal-9 resulted in significantly higher IL-2 and IFN-γ expression that was directly correlated with the number of non-apoptotic cells. In the synovial fluid, both secreted Gal-9 and surface Gal-9 levels were significantly higher in less-severe grade 2 OA patients than in more-severe grade 4 OA patients. Surface Tim-3 was also higher in synovial fluid CD8⁺ T cells and CD14⁺ monocytes from grade 2 OA patients and lower in grade 4 OA patients. Together, these results suggested that Tim-3 and Gal-9 could downregulate T cell inflammation in OA, and could be utilized as a novel therapeutic strategy.

Galectin-3 Binds to Lubricin and Reinforces the Lubricating Boundary Layer of Articular Cartilage

Lubricin is a mucinous, synovial fluid glycoprotein that enables near frictionless joint motion via adsorption to the surface of articular cartilage and its lubricating properties in solution. Extensive O-linked glycosylation within lubricin’s mucin-rich domain is critical for its boundary lubricating function; however, it is unknown exactly how glycosylation facilitates cartilage lubrication. Here, we find that the lubricin glycome is enriched with terminal β-galactosides, known binding partners for a family of multivalent lectins called galectins. Of the galectin family members present in synovial fluid, we find that galectin-3 is a specific, high-affinity binding partner for lubricin. Considering the known ability of galectin-3 to crosslink glycoproteins, we hypothesized that galectins could augment lubrication via biomechanical stabilization of the lubricin boundary layer. We find that competitive inhibition of galectin binding results in lubricin loss from the cartilage surface, and addition of multimeric galectin-3 enhances cartilage lubrication. We also find that galectin-3 has low affinity for the surface layer of osteoarthritic cartilage and has reduced affinity for sialylated O-glycans, a glycophenotype associated with inflammatory conditions. Together, our results suggest that galectin-3 reinforces the lubricin boundary layer; which, in turn, enhances cartilage lubrication and may delay the onset and progression of arthritis.

Immunohistochemical identification of notochordal markers in cells in the aging human lumbar intervertebral disc

The fate of notochord cells during disc development and aging is still a subject of debate. Cells with the typical notochordal morphology disappear from the disc within the first decade of life. However, the pure morphologic differentiation of notochordal from non-notochordal disc cells can be difficult, prompting the use of cellular markers. Previous reports on these notochordal cell markers only explored the occurrence in young age groups without considering changes during disc degeneration. The aim of this study, therefore, was to investigate presence, localization, and abundance of cells expressing notochordal cell markers in human lumbar discs during disc development and degeneration. Based on pilot studies, cytokeratins CK-8, -18 and -19 as well as Galectin-3 were chosen from a broad panel of potential notochordal cell markers and used for immunohistochemical staining of 30 human lumbar autopsy samples (0-86 years) and 38 human surgical disc samples (26-69 years). In the autopsy group, 80% of fetal to adolescent discs (0-17 years) and 100% of young adult discs (18-30 years) contained many cells with positive labeling. These cells were strongly clustered and nearly exclusively located in areas with granular changes (or other matrix defects), showing predominantly a chondrocytic morphology as well as (in a much lesser extent) a fibrocytic phenotype. In mature discs (31-60 years) and elderly discs (≥ 60 years) only 25 and 22-33%, respectively, contained few stained nuclear cells, mostly associated with matrix defects. In the surgical group, only 16% of samples from young adults (≤ 47 years) exhibited positively labeled cells whereas mature to old surgical discs (>47 years) contained no labeled cells. This is the first study describing the presence and temporo-spatial localization of cells expressing notochordal cell markers in human lumbar intervertebral discs of all ages and variable degree of disc degeneration. Our findings indicate that cells with a (immunohistochemically) notochord-like phenotype are present in a considerable fraction of adult lumbar intervertebral discs. The presence of these cells is associated with distinct features of (early) age-related disc degeneration, particularly with granular matrix changes.