A molecular pathway that links N-glycosylation to birth defects

Project Summary A molecular pathway that links N-glycosylation to birth defects Developmental defects are the leading cause of both fetal loss before birth and infant deaths after birth. The immense advances in our genetic understanding of mammalian development over the past four decades have not yet translated into better preventative or therapeutic options for babies with birth defects. Our ability to

address this high unmet need depends critically on the discovery and detailed mechanistic understanding of molecular and cellular pathways that drive human developmental defects. Working with a multidisciplinary investigative team that combines expertise in signal transduction, human genetics and bone biology, we have

discovered an novel inter-organelle communication mechanism that links protein N-glycosylation in the Endoplasmic Reticulum (ER) to the reception of WNT signals at the cell surface. The WNT/β-catenin pathway is a key cell-cell communication system that regulates tissue patterning during development and regenerative

responses in adults. Human genetic studies from our collaborators show that this ER-based pathway is disrupted in a severe, deforming subtype of the inherited bone fragility disorder Osteogenesis Imperfecta (OI) and in subtypes of Congenital Disorders of Glycosylation (CDG), characterized by developmental defects

across tissues. Given that over 25% of proteins encoded in our genomes are N-glycosylated, we propose the existence of a surveillance mechanism (analogous to the unfolded protein response) that ensures WNT-driven differentiation is only allowed to proceed if the ER N-glycosylation machinery is intact. The three goals of this

proposal are to delineate the components and transduction mechanisms of this regulated N-glycosylation pathway, understand its role in osteoblast differentiation and bone matrix production and establish its relevance to human birth defect syndromes. We use genome-wide CRISPR screens and mass spectrometry to identify

pathway components, gene-editing to disrupt or mutate these components in both cell lines and primary cells from human OI patients, and mechanistic studies to understand how N-glycosylation in the ER tunes WNT ligand sensitivity at the cell surface. Successful completion of this project will define a new pathway that

regulates WNT signaling and human development by using N-glycosylation as a regulatory post-translational modification. More broadly, our work will define a largely unexplored signaling function for N-glycosylation, a fundamental cell biological process linked to diseases across multiple organ systems.