Soutenance de thèse : Structural and Functional effect of CXCL12/Heparan Sulfate Interactions at the Cell Surface

Par Espérance AHO (IBS/Groupe Structure et Activité des Glycosaminoglycanes )

The glycocalyx is a protective layer covering the surface of cells, particularly endothelial cells, and represents a major regulator of cell-environment interactions. It functions as a mechanical barrier, a mechanosensor, and a signalling platform that controls vascular permeability. In inflammatory and tumor contexts, alterations in glycocalyx structure and density promote increased cell adhesion, extravasation, and metastatic dissemination. Structurally, the glycocalyx is composed of glycolipids, glycoproteins and proteoglycans bearing glycosaminoglycan (GAG) chains, including heparan sulfate (HS). These linear polysaccharides, organized into sulfated and non-sulfated domains, interact with numerous proteins, including growth factors and chemokines, thereby modulating their bioavailability and biological activity. Notably, chemokine-HS interactions are essential for the formation of chemotactic gradients involved in leukocyte recruitment, inflammatory extravasation, and tumor progression. The chemokine CXCL12 (stromal cell-derived factor-1, SDF-1), a member of the CXC chemokine family, exists as six distinct isoforms generated by alternative splicing of the CXCL12 gene. These isoforms share a common N-terminal sequence but differ in their C-terminal extensions, which influence their interactions with HS. Among them, CXCL12γ isoform, characterized by its exceptionally high affinity for HS, represent a particularly relevant candidate.

This work builds upon previous findings from our group showing, using biophysical approaches (QCM-D, FRAP), that CXCL12 is able to induce cross-linking of HS chains on biomimetic surfaces, resulting in HS rigidification, decreased layer thickness, and reduced HS lateral mobility. These observations suggest that chemokine-HS interactions can modify the physical properties of HS beyond a simple ligand-presentation role. The central hypothesis of this project is that binding of the CXCL12γ to HS induces remodelling of the endothelial glycocalyx at the cell surface thereby changing cellular mechanical properties and promoting immune cell adhesion. Here, we investigate the impact of CXCL12γ on HS organization across molecular, nanoscale, and cellular levels by combining biomimetic surfaces, biophysical approaches, super-resolution microscopy, and cell-based assays.

We show that CXCL12γ reorganizes HS chains at the endothelial cell surface and that all HS-binding sites are required for efficient HS rigidification and network reorganization. CXCL12γ-driven remodeling of the glycocalyx reduces HS thickness and alters its nanoscale topology, thereby promoting paracellular permeability and formation of adhesive platforms that facilitate leukocyte capture, and firm adhesion.