Caspase-1 activation by the inflammasomes is an important innate immune response to tissue damage and infection by microbial or viral pathogens. Caspase-1 is required for production of the active pro-inflammatory cytokines IL-1 and IL-18, and is also important for pyroptosis or inflammatory cell death. The Nlrp3 inflammasome activates caspase-1 in response to diverse signals including infection with intracellular microbial and viral pathogens, TLR agonists combined with potassium-depleting agents or pore forming toxins, and crystalline and aggregated materials. Uncontrolled activation of the Nlrp3 inflammasome can lead to a number of human diseases, including arthritis, atherosclerosis, and type 2 diabetes. Inherited mutations in Nlrp3 can also lead to a number of human autoinflammatory diseases or periodic fever syndromes. So far the mechanism of activation of the Nlrp3 inflammasome by these seemingly unrelated stimuli is poorly understood. Studies in the applicant's laboratory demonstrated that Nlrp3 is rapidly primed by Toll-like receptor (TLR) signaling through a postranslational modification mechanism that depends on the TLR signaling molecules Myd88 and IRAK1. Additional preliminary evidence suggests that brief TLR signaling primes Nlrp3 by a redox- dependent mechanism, whereas prolonged TLR signaling suppresses inflammasome activation. In this renewal application specific aims are proposed to elucidate how the priming signal through TLR signaling contributes together with signaling from purinergic P2X7 receptor, pore forming toxins or crystalline materials towards the assembly of the Nlrp3 inflammasome, ASC oligomerization and caspase-1 activation.
These aims will test the hypothesis that mtROS generation through TLR signaling or direct stimulation of mitochondrial respiratory complexes activates Nlrp3 by a redox-switch mechanism. Additional experiments will extend these findings and will also address alternative possibilities of Nlrp3 priming through IRAK1-dependent phosphorylation and whether the oxidation and phosphorylation mechanisms are interdependent. Experiments are also proposed to define the signaling pathways downstream of Toll-like receptors that mediate ROS production. Additional experiments will investigate how Nlrp3 inflammasome activity is negatively regulated in vitro and in vivo by prolonged TLR signaling, and the role of a number of cellular anti-inflammatory pathways, including autophagosomal and heme oxygenase-1 pathways in this negative regulatory mechanism. Results from this research will provide fundamental new insights into the mechanisms that regulate its activation and those that regulate its suppression. Successful completion of this study should have a high impact on the field by providing a unifying paradigm for how Nlrp3 can be regulated by an exceptionally diverse group of activating stimuli. Understanding these mechanisms is of great scientific and health significance as this should better our understanding of the molecular basis of Nlrp3-related diseases and should in the long term help in the development of therapeutics to alleviate these inflammatory diseases.

Public Health Relevance

Uncontrolled activation of the Nlrp3 inflammasome can lead to a number of human inflammatory diseases including arthritis, atherosclerosis, and type 2 diabetes. Understanding the molecular pathways that regulate Nlrp3 activation is of great health relevance and should facilitate the development of new therapeutics to treat inflammatory diseases in which Nlrp3 is involved.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
2R01AR055398-16A1
Application #
8697777
Study Section
Cellular and Molecular Immunology - A Study Section (CMIA)
Program Officer
Mancini, Marie
Project Start
1996-08-15
Project End
2019-03-31
Budget Start
2014-04-01
Budget End
2015-03-31
Support Year
16
Fiscal Year
2014
Total Cost
$500,359
Indirect Cost
$177,547
Name
Thomas Jefferson University
Department
Biochemistry
Type
Schools of Medicine
DUNS #
053284659
City
Philadelphia
State
PA
Country
United States
Zip Code
19107
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Juliana, Christine; Fernandes-Alnemri, Teresa; Wu, Jianghong et al. (2010) Anti-inflammatory compounds parthenolide and Bay 11-7082 are direct inhibitors of the inflammasome. J Biol Chem 285:9792-802
Wu, Jianghong; Fernandes-Alnemri, Teresa; Alnemri, Emad S (2010) Involvement of the AIM2, NLRC4, and NLRP3 inflammasomes in caspase-1 activation by Listeria monocytogenes. J Clin Immunol 30:693-702
Alnemri, Emad S (2010) Sensing cytoplasmic danger signals by the inflammasome. J Clin Immunol 30:512-9

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