Project Summary / Abstract Alzheimer's disease (AD) is a devastating dementia with no effective treatment, underscoring the critical need for better understanding the pathogenic mechanisms of this disease and uncovering new molecular vulnerabilities to target for therapy. This project addresses an important yet under-studied area of AD research and aims to discover sialylation-mediated disease processes and novel targets for early diagnosis and intervention. Protein sialylation is a post-translational modification that covalently attaches sialic acids (negatively charged nine-carbon monosaccharides also known as neuraminic acids) onto glycoproteins to generate sialoglycoproteins. Accumulating evidence indicates that sialic acids on sialoglycoproteins not only affect protein conformation, activity, and trafficking, but also serve as regulators of molecular and cellular interactions, acting as a biological mask for blocking molecular recognition and/or as a biological recognition signal for mediating interactions with specific proteins such as Siglecs (sialic-acid-binding immunoglobulin- type lectins). Protein sialylation is vital to brain function and homeostasis, as highlighted by the fact that genetic mutations in enzymes for catalyzing sialylation, desialylation, or sialic acid metabolism cause human diseases with brain dysfunction and neurological abnormalities. Furthermore, GWAS studies have identified Siglec-3 (also known as CD33) as a risk factor for AD, underlining the connection between dysregulated sialylation-mediated signaling and AD pathogenesis. However, very little is currently known about human brain sialoglycoproteome and its alterations in AD. The proposed project will address this knowledge gap and use an innovative, multi-faceted approach that combines sialoglycoproteomics, network biology, cell biology with translational research in human patient specimens to discover and study sialoglycoproteomic networks and sialylation-based molecular mechanisms and pathways underlying brain function in health and Alzheimer's disease. Furthermore, this project will perform large-scale high-resolution analyses of sialoglycoproteome changes in human AD and control cerebrospinal fluid, and blood serum samples to identify novel biomarkers for early diagnosis and monitoring disease progression. Findings from the proposed research will advance our understanding of AD pathogenesis and provide novel targets for AD diagnostic and therapeutic development.