Elucidating the Siglec-sialome axis of immune cell regulation with super-resolution microscopy and single-molecule/-particle tracking

• Applicant: Dr. Leonhard Möckl
• Subject Area: Biophysics ; Immunology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 529257351

Siglecs are a family of receptors chiefly found on the surface of immune cells. They bind sialylated species, collectively termed the “sialome”. Most Siglecs exhibit intracellular inhibitory domains, reducing immune cell activity upon ligand binding. Ligand binding can happen in cis (on the same cell) or in trans (with the Siglec and its ligand present on different cells). Both modes are vital for physiological immune system regulation. Moreover, trans interactions are a key strategy utilized by cancer cells to evade the immune response. Recently, I could show that both cis and trans interactions of Siglec-7 with the newly identified ligand CD43 causes substantial reorganization of Siglec-7 on the NK cell membrane, which in turn regulated NK cell activity. This provided first mechanistic connections between Siglec organization and global cellular activity. Despite these findings, we currently lack a comprehensive picture of the functional interplay between cell-surface glycosylation, Siglec organization, and global immune cell activity. This is especially true for presentation of sialylated cis ligands to Siglecs, both on resting and activated immune cells. The proposed project will close this critical knowledge gap. Building on my previous expertise, we will employ cutting-edge super-resolution microscopy techniques to study the spatial organization and the temporal dynamics of Siglecs in dependence on the presentation of sialylated cis ligands. These investigations will be combined with functional assays of immune cell activity. With this integrated approach, we will uncover the mechanistic interplay between Siglec membrane organisation and dynamics, Siglec cis ligand presentation, and global immune cell behavior.

• DFG Programme: Research Grants