Project Summary/Abstract Sialidases (also called neuraminidases) are glycosidases responsible for the removal of sialic acid (Sia) residues (desialylation) from glycan portions of glycocojugates. By desialylation, sialidases are able to modulate the functionality and stability of the Sia-containing molecules and are involved in both physiological and pathological pathways. Previous and our recent study indicate that lysosomal Neu1 sialidase could relocate to the cell surface of macrophages upon LPS stimulation, where it causes desialylation of TLR4 receptor, leading to TLR4 activation and subsequent production of pro-inflammatory cytokines. Dysregulation of TLR4 activation by LPS is responsible for chronic and acute inflammatory disorders that often causes dangerous disease like sepsis that still lacks specific pharmacological treatment. The first objective of this application is to quantitatively profile the location-specific expression of Neu1 sialidase that is critical for TLR4 activation and its subsequent signal transduction. Sialidase inhibitors are useful tools for studying sialidase function and related mechanisms of the biological pathways. More importantly, effective sialidase inhibitors can be used as drugs to regulate the pathological pathways caused by sialidase, such as dysregulated TLR4 activation. Our recent study indicates that currently available pan sialidase inhibitor and microbial sialidase inhibitors could not inhibit mammalian sialidase effectively. Several mammalian sialidase inhibitors have been reported. However, current sialidase inhibitor design has usually focused on active-site binding, neglecting the subcellular localization of the active enzyme, therefore, they are less effective in vivo or may be even toxic as they will affect other sialidases inside of the cells. The second objective of this application is to develop location-specific inhibitor for Neu1 sialidase and define the Neu1 sialidase’s involvement in LPS/TLR4 signaling pathway. The objectives of this project will be accomplished by three specific aims: (1) Profile Neu1 sialidase expression and cell surface relocation in macrophages upon LPS stimulation; (2) Develop lysosome-targeting Neu1 sialidase inhibitors for effective regulating desialylation in LPS/TLR4 signaling pathway; (3) Develop cell surface-targeting Neu1 sialidase inhibitors for effective regulating desialylation in LPS/TLR4 signaling pathway. This study is innovative because it uses a novel approach that overcomes the current limitations in (a) profiling sialidase expression and relocation and (b) inhibiting sialidase at subcellular location. The proposed project is significant because it will (i) uncover specific desialylation that is critical to the LPS/TLR4 signal pathway and (ii) develop novel sialidase inhibitors for effective regulation of desialylation in LPS/TLR4 signaling pathway. Finally, this proposal will enhance the infrastructure of research and education at Cleveland State Un...