1. Shedding of membrane-associated LDL receptor-related protein-1 from microglia amplifies and sustains neuroinflammation.
- Author
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Brifault C, Gilder AS, Laudati E, Banki M, and Gonias SL
- Subjects
- Animals, Animals, Newborn, Calreticulin genetics, Calreticulin metabolism, Cell-Derived Microparticles drug effects, Cell-Derived Microparticles immunology, Cells, Cultured, Cerebral Cortex cytology, Cerebral Cortex drug effects, Cerebral Cortex immunology, Gene Expression Regulation drug effects, Humans, Inflammation Mediators metabolism, LDL-Receptor Related Protein-Associated Protein metabolism, Ligands, Lipopolysaccharides toxicity, Low Density Lipoprotein Receptor-Related Protein-1, Male, Mice, Inbred C57BL, Mice, Knockout, Mice, Transgenic, Microglia cytology, Microglia drug effects, Microglia immunology, Nerve Tissue Proteins antagonists & inhibitors, Nerve Tissue Proteins chemistry, Nerve Tissue Proteins genetics, Nitric Oxide Synthase Type II chemistry, Nitric Oxide Synthase Type II genetics, Nitric Oxide Synthase Type II metabolism, RNA Interference, Receptors, LDL agonists, Receptors, LDL antagonists & inhibitors, Receptors, LDL genetics, Recombinant Proteins metabolism, Tumor Suppressor Proteins agonists, Tumor Suppressor Proteins antagonists & inhibitors, Tumor Suppressor Proteins genetics, Cell-Derived Microparticles metabolism, Cerebral Cortex metabolism, Inflammation Mediators agonists, Microglia metabolism, Nerve Tissue Proteins metabolism, Receptors, LDL metabolism, Tumor Suppressor Proteins metabolism
- Abstract
In the CNS, microglia are activated in response to injury or infection and in neurodegenerative diseases. The endocytic and cell signaling receptor, LDL receptor-related protein-1 (LRP1), is reported to suppress innate immunity in macrophages and oppose microglial activation. The goal of this study was to identify novel mechanisms by which LRP1 may regulate microglial activation. Using primary cultures of microglia isolated from mouse brains, we demonstrated that LRP1 gene silencing increases expression of proinflammatory mediators; however, the observed response was modest. By contrast, the LRP1 ligand, receptor-associated protein (RAP), robustly activated microglia, and its activity was attenuated in LRP1-deficient cells. An important element of the mechanism by which RAP activated microglia was its ability to cause LRP1 shedding from the plasma membrane. This process eliminated cellular LRP1, which is anti-inflammatory, and generated a soluble product, shed LRP1 (sLRP1), which is potently proinflammatory. Purified sLRP1 induced expression of multiple proinflammatory cytokines and the mRNA encoding inducible nitric-oxide synthase in both LRP1-expressing and -deficient microglia. LPS also stimulated LRP1 shedding, as did the heat-shock protein and LRP1 ligand, calreticulin. Other LRP1 ligands, including α
2 -macroglobulin and tissue-type plasminogen activator, failed to cause LRP1 shedding. Treatment of microglia with a metalloproteinase inhibitor inhibited LRP1 shedding and significantly attenuated RAP-induced cytokine expression. RAP and sLRP1 both caused neuroinflammation in vivo when administered by stereotaxic injection into mouse spinal cords. Collectively, these results suggest that LRP1 shedding from microglia may amplify and sustain neuroinflammation in response to proinflammatory stimuli., (© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.)- Published
- 2017
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