Elucidating and targeting Siglec-9 function on mast cells - PROJECT SUMMARY/ABSTRACT Mast cells have been recognized as key effector cells in urticaria, mastocytosis, and allergic disease. Specifically, studies have shown that the dysregulated expansion and/or activation of mast cells have detrimental consequences in these disorders. Moreover, they have driven the search for effective new strategies to downmodulate mast cell function. Due to their immunoreceptor tyrosine-based inhibitory (ITIM) motifs, pre- clinical and clinical studies support Sialic acid -binding immunoglobulin-like lectins (Siglecs) as an attractive therapeutic target to inhibit mast cell function in mast-associated disorders. However, clinical trials aimed at evaluating the use of antibodies against Siglec-8, one of the most promising inhibitory receptors for mast cell targeting, did not meet primary endpoints for treatment of atopic dermatitis and chronic spontaneous urticaria. These disappointing results highlight the need of our proposed studies to better understand the biology of Siglecs and their ligands in a complex disease microenvironment that can impact Siglec ability to modulate mast cell function. Our published studies and preliminary data demonstrate that: 1-Siglec-9 co-engagement with the high affinity receptor for IgE inhibits human primary mast cell activation, and the severity of systemic anaphylactic reactions; 2-Siglec-9 on mast cells can attenuate the severity of allergic airway immunopathology; and 3-Siglec- 9 interactions with its ligands in cis promote mast cell quiescence. Accordingly, the overall goal of this proposal is to test the hypothesis that Siglec-9 and its ligands play a critical role in mast cell homeostasis, and that Siglec- 9 can be targeted to reduce the severity of mast cell-associated disorders. In Aim 1, we will investigate how Siglec-9 ligand metabolism can modulate human mast cell function in vitro and in mouse models of systemic anaphylaxis. In Aim 2, we will assess Siglec-9 contribution to modulation of mast cell function in a mouse model of allergic airway inflammation. We will also examine whether alterations in the expression of Siglec-9 ligands in airway epithelial cells associate with increased mast cell activation in atopic individuals. In Aim 3, we will examine whether nanoparticles displaying an allergen and Siglec-9 ligands can inhibit IgE-mediated anaphylaxis and can desensitize mice for subsequent challenge with the same allergen. Moreover, we will de novo design minibinders for Siglec-9 clustering to inhibit human mast cell activation. The proposed studies have the potential to uncover novel biological roles for Siglec-9 and its ligands in mast cell function. Finally, these studies will lay the groundwork for future projects aimed at exploring the therapeutic potential of targeting Siglec-9 to modulate disorders in which mast cells play an active role.
