Galectin-8 as an effector molecule of T-cell and pro-inflammatory responses

MARIA VIRGINIA TRIBULATTI; CARABELLI, JULIETA; CATTANEO, VALENTINA; FIGINI, MARÍA GABRIELA; SCHROEDER, MATÍAS NICOLÁS; CAMPETELLA, OSCAR

Cannes

Workshop; EMBO Workshop on Transducing glycan information into function: Lessons from galectins; 2016

EMBO

In recent years, our group has led efforts to disclose galectin-8 (Gal-8) expression/function on different cell types. Two distinct activities on mouse naïve CD4+T-lymphocytes were determined: at low concentrations (0.1μM) Gal-8 synergized cognate antigen-signaling while at higher concentrations (0.5-2μM) induces robust antigen-independent proliferation. Interestingly, Gal-8 induced proliferation of human naïve CD4+T-cells, varying from non- to high-responder individuals, while it promoted death of PHA or CD3/CD28 pre-activated cells, suggesting a dual activity relying on cellular activation state. Associated structural requirements were also assessed: N-N and C-C homodimer chimaeras, but not single C- or N-CRDs, induced antigen-independent proliferation while single CRDs induced antigen-specific co-stimulation. These results support that tandem-repeat structure is essential for the proliferative effect, possibly involving lattice formation, whereas co-stimulation seems mediated by agonistic interactions. C-C chimaeras displayed higher activity than Gal-8, demonstrating that C-CRD was mainly involved. Since galectin-stimulatory signals on naïve T-cells were not previously described, except for Gal-8, we searched for Gal-1 and Gal-3 stimulatory effects: only Gal-1 co-stimulated antigen-specific T-cell response, whereas Gal-3 antagonized both Gal-1 and Gal-8 signals. Despite Gal-1 was unable to induce antigen-independent proliferation, a covalent Gal-1-dimer (Gal-1-Gal-1) efficiently promoted proliferation, further stressing the importance of tandem-repeat structure. Remarkably, a single dose of Gal-1 or Gal-8 administered together with suboptimal antigen doses strengthened weak responses in vivo, arguing for its participation in the adaptive immune response elicitation.Human platelets and endothelial cells not only express Gal-8 constitutively, but also expose it after inflammatory activation. Gal-8 binds GPIb at platelet surface through the N-CRD, triggering aggregation, calcium mobilization, spreading and granule-content-secretion. Gal-8 treatment of human microvascular endothelial cells (HMEC-1) cells induced a platelet-pro-adhesive phenotype, von Willebrand factor exposure, NF-kB phosphorylation and production of several pro-inflammatory molecules. Altogether these results support a role for Gal-8 in inflammation, and suggest that this lectin is actually orchestrating leukocyte, platelet and endothelial cells interaction.In general, Gal-8 effects were prevented with lactose or thiodigalactoside, indicating that lectin-glycan interaction is involved. A double-mutant protein (Gal-8mut) generated by replacing canonical arginine residues on each CRD, retained affinity for polylactosamines and blood group antigens. Gal-8mut was unable to induce T-cell proliferation, but efficiently co-stimulated antigen-specific responses, both in vitro and in vivo. Therefore, Gal-8mut represents an interesting tool to dissect the specificities of lectin-glycan interaction underlying distinctive Gal-8 activities. Moreover, given its distinguishing properties, Gal-8mut could be used to enhance borderline immune responses without the non-specific pro-inflammatory activity.