Key Points
Shed PrPC derivatives and PrPC in extracellular vesicles regulate innate immunity.
The macrophage NMDA-R/LRP1 complex mediates the activity of PrPC released by cells.
The NMDA-R/LRP1 complex functions as an extracellular vesicle receptor in target cells.
Abstract
Nonpathogenic cellular prion protein (PrPC) demonstrates anti-inflammatory activity; however, the responsible mechanisms are incompletely defined. PrPC exists as a GPI-anchored membrane protein in diverse cells; however, PrPC may be released from cells by ADAM proteases or when packaged into extracellular vesicles (EVs). In this study, we show that a soluble derivative of PrPC (S-PrP) counteracts inflammatory responses triggered by pattern recognition receptors in macrophages, including TLR2, TLR4, TLR7, TLR9, NOD1, and NOD2. S-PrP also significantly attenuates the toxicity of LPS in mice. The response of macrophages to S-PrP is mediated by a receptor assembly that includes the N-methyl-d-aspartate receptor (NMDA-R) and low-density lipoprotein receptor–related protein-1 (LRP1). PrPC was identified in EVs isolated from human plasma. These EVs replicated the activity of S-PrP, inhibiting cytokine expression and IκBα phosphorylation in LPS-treated macrophages. The effects of plasma EVs on LPS-treated macrophages were blocked by PrPC-specific Ab, by antagonists of LRP1 and the NMDA-R, by deleting Lrp1 in macrophages, and by inhibiting Src family kinases. Phosphatidylinositol-specific phospholipase C dissociated the LPS-regulatory activity from EVs, rendering the EVs inactive as LPS inhibitors. The LPS-regulatory activity that was lost from phosphatidylinositol-specific phospholipase C–treated EVs was recovered in solution. Collectively, these results demonstrate that GPI-anchored PrPC is the essential EV component required for the observed immune regulatory activity of human plasma EVs. S-PrP and EV-associated PrPC regulate innate immunity by engaging the NMDA-R/LRP1 receptor system in macrophages. The scope of pattern recognition receptors antagonized by S-PrP suggests that released forms of PrPC may have broad anti-inflammatory activity.
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Footnotes
This work was supported by National Heart, Lung, and Blood Institute Grant R01 HL136395 (to S.L.G.).
The online version of this article contains supplemental material.
Abbreviations used in this article
- BMDM
- bone marrow–derived macrophage
- DXM
- dextromethorphan hydrobromide
- EI-tPA
- enzymatically inactive tissue-type plasminogen activator
- EV
- extracellular vesicle
- IMQ
- imiquimod
- L18-MDP
- L18-muramyl dipeptide
- LRP1
- low-density lipoprotein receptor–related protein-1
- LTA
- lipoteichoic acid
- α2M
- α2-macroglobulin
- NTA
- nanoparticle tracking analysis
- PI-PLC
- phosphatidylinositol-specific phospholipase C
- pMac
- peritoneal macrophage
- PrPC
- cellular prion protein
- PRR
- pattern recognition receptor
- qPCR
- quantitative PCR
- RAP
- receptor-associated protein
- SFK
- Src family kinase
- SFM
- serum-free medium
- S-PrP
- soluble derivative of PrPC
- TEM
- transmission electron microscopy
- tPA
- tissue-type plasminogen activator
- UC
- ultracentrifugation
- WT
- wild-type
- Received April 30, 2021.
- Accepted October 19, 2021.
- Copyright © 2021 by The American Association of Immunologists, Inc.
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