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Post-conversion sialylation of prions in lymphoid tissues.

ABSTRACT: Sialylated glycans on the surface of mammalian cells act as part of a "self-associated molecular pattern," helping the immune system to recognize "self" from "altered self" or "nonself." To escape the host immune system, some bacterial pathogens have evolved biosynthetic pathways for host-like sialic acids, whereas others recruited host sialic acids for decorating their surfaces. Prions lack nucleic acids and are not conventional pathogens. Nevertheless, prions might use a similar strategy for invading and colonizing the lymphoreticular system. Here we show that the sialylation status of the infectious, disease-associated state of the prion protein (PrP(Sc)) changes with colonization of secondary lymphoid organs (SLOs). As a result, spleen-derived PrP(Sc) is more sialylated than brain-derived PrP(Sc). Enhanced sialylation of PrP(Sc) is recapitulated in vitro by incubating brain-derived PrP(Sc) with primary splenocytes or cultured macrophage RAW 264.7 cells. General inhibitors of sialyltranserases (STs), the enzymes that transfer sialic acid residues onto terminal positions of glycans, suppressed extrasialylation of PrP(Sc). A fluorescently labeled precursor of sialic acid revealed ST activity associated with RAW macrophages. This study illustrates that, upon colonization of SLOs, the sialylation status of prions changes by host STs. We propose that this mechanism is responsible for camouflaging prions in SLOs and has broad implications.

SUBMITTER: Srivastava S

PROVIDER: S-EPMC4672809 | biostudies-other | 2015 Dec

REPOSITORIES: biostudies-other

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Project description:Neuroinflammation is recognized as one of the obligatory pathogenic features of neurodegenerative diseases including Alzheimer's, Parkinson's or prion diseases. In prion diseases, space and time correlations between deposition of disease-associated, pathogenic form of the prion protein or PrPSc and microglial-mediated neuroinflammation has been established. Yet, it remains unclear whether activation of microglia is triggered directly by a contact with PrPSc, and what molecular features of PrPSc microglia sense and respond to that drive microglia to inflammatory states. The current study asked the questions whether PrPSc can directly trigger activation of microglia and whether the degree of microglia response depends on the nature of terminal carbohydrate groups on the surface of PrPSc particles. PrPSc was purified from brains of mice infected with mouse-adapted prion strain 22L or neuroblastoma N2a cells stably infected with 22L. BV2 microglial cells or primary microglia were cultured in the presence of purified 22L. We found that exposure of BV2 cells or primary microglia to purified PrPSc triggered proinflammatory responses characterized by an increase in the levels of TNFα, IL6, nitric oxide (NO) and expression of inducible Nitric Oxide Synthase (iNOS). Very similar patterns of inflammatory response were induced by PrPSc purified from mouse brains and neuroblastoma cells arguing that microglia response is independent of the source of PrPSc. To test whether the microglial response is mediated by carbohydrate epitopes on PrPSc surface, the levels of sialylation of PrPSc N-linked glycans was altered by treatment of purified PrPSc with neuraminidase. Partial cleavage of sialic acid residues was found to boost the inflammatory response of microglia to PrPSc. Moreover, transient degradation of Iκβα observed upon treatment with partially desialylated PrPSc suggests that canonical NFκB activation pathway is involved in inflammatory response. The current study is the first to demonstrate that PrPSc can directly trigger inflammatory response in microglia. In addition, this work provides direct evidence that the chemical nature of the carbohydrate groups on PrPSc surface is important for microglial activation.

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Post-conversion sialylation of prions in lymphoid tissues.

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