Extracellular vesicles from microglial cells activated by abnormal heparan sulfate oligosaccharides from Sanfilippo patients impair neuronal dendritic arborization

Background : In mucopolysaccharidosis type III (MPS III, also known as Sanfilippo syndrome), a pediatric neurodegenerative disorder, accumulation of abnormal glycosaminoglycans (GAGs) induces severe neuroinflammation by triggering the microglial pro-inflammatory cytokines production via a TLR4-dependent pathway. But the extent of the microglia contribution to the MPS III neuropathology remains unclear. Extracellular vesicles (EVs) mediate intercellular communication and are known to participate in the pathogenesis of adult neurodegenerative diseases. However, characterization of the molecular profiles of EVs released by MPS III microglia and their effects on neuronal functions have not been described. Methods : Here, we isolated EVs secreted by the microglial BV-2 cells after treatment with GAGs purified from urines of Sanfilippo patients (MPS-GAGs EVs) or from age-matched healthy subjects (WT-GAGs EVs) to explore the EVs’ proteins and small RNA profiles using LC–MS/MS and RNA sequencing. We next performed a functional assay by immunofluorescence following WT-GAGs- or MPS-GAGs-EVs uptake by WT primary cortical neurons and analyzed their extensions metrics after staining of βIII-tubulin and MAP2 by confocal microscopy. Results : Functional enrichment analysis for both proteomics and RNA sequencing data from MPS-GAGs-EVs revealed a specific content involved in neuroinflammation and neurodevelopment pathways. Treatment of cortical neurons with MPS-GAGs-EVs induced a disease-associated phenotype demonstrated by a lower total neurite surface area, an impaired somatodendritic compartment, and a higher number of immature dendritic spines. Conclusions : This study shows, for the first time, that GAGs from patients with Sanfilippo syndrome can induce microglial secretion of EVs that deliver a specific molecular message to recipient naive neurons, while promoting the neuroinflammation, and depriving neurons of neurodevelopmental factors. This work provides a framework for further studies of biomarkers to evaluate efficiency of emerging therapies. Here, we isolated EVs secreted by the microglial BV-2 cells after treatment with GAGs purified from urines of Sanfilippo patients (MPS-GAGs-EVs) or from age-matched healthy subjects (WT-GAGs-EVs) to explore the EVs’ small RNA profiles using RNA sequencing. EVs were separated by differential ultracentrifugation (dUC) in two different pellets after ultracentrifugation at 12,000g (12K) or 100,000g (100K).