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NLRP3 Inflammasome Is Expressed and Functional in Mouse Brain Microglia but Not in Astrocytes
Audrey Gustin1, Mélanie Kirchmeyer1, Eric Koncina1
1Life Sciences Research Unit, Faculty of Science, Technology and Communication, University of Luxembourg, Luxembourg, Luxembourg.
Abstract:
Neuroinflammation is the local reaction of the brain to infection, trauma, toxic molecules or protein aggregates. The brain resident macrophages, microglia, are able to trigger an appropriate response involving secretion of cytokines and chemokines, resulting in the activation of astrocytes and recruitment of peripheral immune cells. IL-1β plays an important role in this response; yet its production and mode of action in the brain are not fully understood and its precise implication in neurodegenerative diseases needs further characterization. Our results indicate that the capacity to form a functional NLRP3 inflammasome and secretion of IL-1β is limited to the microglial compartment in the mouse brain. We were not able to observe IL-1β secretion from astrocytes, nor do they express all NLRP3 inflammasome components. Microglia were able to produce IL-1β in response to different classical inflammasome activators, such as ATP, Nigericin or Alum. Similarly, microglia secreted IL-18 and IL-1α, two other inflammasome-linked pro-inflammatory factors. Cell stimulation with α-synuclein, a neurodegenerative disease-related peptide, did not result in the release of active IL-1β by microglia, despite a weak pro-inflammatory effect. Amyloid-β peptides were able to activate the NLRP3 inflammasome in microglia and IL-1β secretion occurred in a P2X7 receptor-independent manner. Thus microglia-dependent inflammasome activation can play an important role in the brain and especially in neuroinflammatory conditions.
Insights
Microglia, the brain's immune cells, are the primary source of Interleukin-1 beta (IL-1β) in neuroinflammation. This study clarifies their role in activating the NLRP3 inflammasome and secreting inflammatory factors in response to stimuli like amyloid-beta.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Neuroinflammation involves microglia, the brain's resident macrophages, releasing cytokines and activating other cells.
- Interleukin-1 beta (IL-1β) is crucial in neuroinflammation, but its brain production and role in neurodegenerative diseases require further study.
- The NLRP3 inflammasome is a key mediator of IL-1β production.
Purpose of the Study:
- To investigate the specific cell types responsible for NLRP3 inflammasome activation and IL-1β secretion in the mouse brain.
- To characterize the response of microglia and astrocytes to various inflammasome activators, including neurodegenerative disease-related peptides.
- To determine the role of the P2X7 receptor in amyloid-beta-induced NLRP3 inflammasome activation.
Main Methods:
- Primary mouse microglia and astrocyte cultures were used.
- Cells were stimulated with classical inflammasome activators (ATP, Nigericin, Alum), α-synuclein, and amyloid-β peptides.
- IL-1β, IL-18, and IL-1α secretion were measured.
- The involvement of the P2X7 receptor was assessed.
Main Results:
- NLRP3 inflammasome formation and IL-1β secretion were confined to microglia, not astrocytes.
- Microglia secreted IL-1β, IL-18, and IL-1α in response to classical activators.
- α-synuclein induced a weak pro-inflammatory effect but not active IL-1β release from microglia.
- Amyloid-β peptides activated the NLRP3 inflammasome in microglia, leading to IL-1β secretion independently of the P2X7 receptor.
Conclusions:
- Microglia are the main cells responsible for NLRP3 inflammasome-mediated IL-1β production in the brain.
- Microglia-dependent inflammasome activation is significant in neuroinflammatory conditions.
- Amyloid-β peptides can trigger microglial inflammasome activation, highlighting a potential mechanism in Alzheimer's disease pathogenesis.
