PODXL regulates the neuronal entry of α-synuclein aggregates
Cell-to-cell transmission of -synuclein (-Syn) aggregates is a key event in Parkinson's disease (PD) pathogenesis, yet the neuronal surface factors that govern uptake of pathogenic -Syn fibrils remain undefined. We developed a flow cytometry-based CRISPR activation screen for modifiers of -Syn preformed fibril (PFF) uptake by human iPSC-derived cortical neurons. By interrogating 68 genes encoding cell-surface proteins prioritised by PD genetic associations, we identified podocalyxin-like protein 1 (PODXL) as a strong suppressor of -Syn fibril uptake. High-content imaging and PODXL cDNA overexpression confirmed reduced PFF uptake. Stable PODXL overexpression also reduced PFF-seeded pSynSer129 accumulation and uptake of structurally distinct recombinant and disease-derived -Syn fibrils. Conversely, shRNA-mediated PODXL knockdown increased -Syn PFF uptake, and analysis of PODXL domain-deletion and N-glycosylation mutants suggested that the ectodomain and N-glycosylation contribute to the PODXL-mediated reduction in uptake. Transcriptomic profiling further identified membrane metalloendopeptidase (MME) as a PODXL-responsive candidate mediator. MME activation and treatment with conditioned medium from MME-activated neurons reduced PFF uptake. Thiorphan, an MME inhibitor, partially attenuated the PODXL-associated reduction in uptake. Together, our findings identify PODXL as a neuronal brake on -Syn uptake and implicate its glycan-dependent surface properties together with MME-associated extracellular activity.