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Published on: January 30, 2014
Hyperammonemia induces microglial NLRP3 inflammasome activation via mitochondrial oxidative stress in hepatic
So Yeong Cheon1, Min-Yu Kim2, Jeongmin Kim2
1Department of Biotechnology, College of Biomedical & Health Science, Konkuk University, Chungju, Republic of Korea.
Background:
The role of nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome in the pathogenesis of hepatic encephalopathy (HE) is unclear. Mitochondrial reactive oxygen species (mtROS) is a signal for NLRP3 inflammasome activation. Therefore, we aimed to determine whether mtROS-dependent NLRP3 inflammasome activation is involved in HE, using in vivo and in vitro models.
Methods:
Bile duct ligation (BDL) in C57/BL6 mice was used as an in vivo HE model. NLRP3 activation was assessed in the hippocampus. Immunofluorescence staining was performed to determine the cellular source of NLRP3 in the hippocampal tissue. For the in vitro experiment, BV-2 microglial cells were primed with lipopolysaccharide (LPS), followed by ammonia treatment. NLRP3 activation and mitochondrial dysfunction were measured. Mito-TEMPO was used to suppress mtROS production.
Results:
BDL mice showed cognitive impairment with hyperammonemia. Both the priming and activation steps of NLRP3 inflammasome activation were processed in the hippocampus of BDL mice. Moreover, intracellular ROS levels increased in the hippocampus, and NLRP3 was mainly expressed in the microglia of the hippocampus. In LPS-primed BV-2 cells, ammonia treatment induced NLRP3 inflammasome activation and pyroptosis, with elevation of mtROS and altered mitochondrial membrane potential. Pretreatment with Mito-TEMPO suppressed mtROS production and the subsequent NLRP3 inflammasome activation and pyroptosis under LPS and ammonia treatment in BV-2 cells.
Conclusions:
Hyperammonemia in HE may be involved in mtROS overproduction and subsequent NLRP3 inflammasome activation. Further studies using NLRP3-specific inhibitor or NLRP3 knockout mice are needed to elucidate the important role of NLRP3 inflammasome in HE development.
Insights
Mitochondrial reactive oxygen species (mtROS) drive NLRP3 inflammasome activation in hepatic encephalopathy (HE). This study shows mtROS-dependent NLRP3 activation in HE models, suggesting a therapeutic target.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Hepatic encephalopathy (HE) pathogenesis involves the NLRP3 inflammasome, but its precise role is unclear.
- Mitochondrial reactive oxygen species (mtROS) are known activators of the NLRP3 inflammasome.
- This study investigates the involvement of mtROS-dependent NLRP3 inflammasome activation in HE.
Purpose of the Study:
- To determine if mtROS-dependent NLRP3 inflammasome activation contributes to hepatic encephalopathy.
- To explore the role of microglia in NLRP3 inflammasome activation within the hippocampus during HE.
- To investigate the impact of ammonia on microglial NLRP3 inflammasome activation and mitochondrial function in vitro.
Main Methods:
- Established an in vivo model of HE using bile duct ligation (BDL) in mice.
- Assessed NLRP3 inflammasome activation and its cellular localization (microglia) in the hippocampus.
- Utilized an in vitro model with LPS-primed BV-2 microglial cells treated with ammonia to measure NLRP3 activation, pyroptosis, and mtROS production.
- Employed Mito-TEMPO to inhibit mtROS production in vitro.
Main Results:
- BDL mice exhibited cognitive impairment and hyperammonemia, with NLRP3 inflammasome activation in the hippocampus, primarily in microglia.
- Ammonia treatment of LPS-primed BV-2 cells induced NLRP3 inflammasome activation, pyroptosis, and increased mtROS with mitochondrial dysfunction.
- Inhibition of mtROS using Mito-TEMPO attenuated NLRP3 inflammasome activation and pyroptosis in the in vitro model.
Conclusions:
- Hyperammonemia in HE may trigger excessive mtROS production, leading to NLRP3 inflammasome activation.
- NLRP3 inflammasome activation, potentially mediated by mtROS, is implicated in HE pathogenesis.
- Further research with NLRP3 inhibitors or knockout models is warranted to confirm the role of NLRP3 in HE development.
