What is NLRP3?

NLRP3 (NOD-like receptor family pyrin domain-containing protein 3) is a cytosolic immune sensor that detects signs of infection or cellular stress. Upon activation, it forms a multi-protein complex, called the NLRP3 inflammasome, which processes the inflammatory cytokines IL-1β and IL-18 and can trigger pyroptotic cell death. It plays a vital role in coordinating innate immune responses, but when dysregulated, contributes to chronic inflammatory and degenerative diseases.

Activation involves two steps: first, a priming signal increases NLRP3 expression. Then a second signal, such as mitochondrial or lysosomal damage, triggers inflammasome assembly. This assembly leads to caspase-1 activation and the processing of inflammatory cytokines.  

Yes. NLRP3’s involvement in inflammatory, metabolic, autoimmune, and neurodegenerative diseases makes it a high-priority target for drug development. Multiple small molecules and biologics are being developed to inhibit different stages of its activation.

NLRP3 plays a role in a broad spectrum of diseases and conditions:

• Neurodegenerative: AD, PD, ALS, MS
• Metabolic: Type 2 diabetes, obesity, gout
• Autoimmune/Inflammatory: Rheumatoid arthritis, lupus, inflammatory bowel disease
• Cardiovascular: Atherosclerosis
• Infectious diseases: COVID-19, sepsis, influenza
• Genetic autoinflammatory syndromes: Cryopyrin-associated periodic syndromes

In many cases, NLRP3 works in concert with other inflammasomes, like AIM2 and NLRP1, highlighting the complexity of the innate immune response.  

NLRP3 is a cytosolic pattern recognition receptor (PRR) that detects a variety of pathogen-associated and damage-associated molecular patterns. Upon activation, NLRP3 oligomerizes to form the NLRP3 inflammasome, which recruits the adaptor protein ASC and pro-caspase-1. This leads to caspase-1 activation, resulting in the maturation and secretion of pro-inflammatory cytokines IL-1β and IL-18, and inducing pyroptotic cell death.

In Alzheimer's disease (AD), NLRP3 activation in microglial cells contributes to neuroinflammation. Amyloid-β (Aβ) aggregates and hyperphosphorylated tau can activate the NLRP3 inflammasome, leading to IL-1β release and chronic neuroinflammatory responses. This exacerbates neuronal damage and promotes further Aβ deposition.

Upon sensing danger signals, NLRP3 undergoes conformational changes and forms a multiprotein inflammasome complex with ASC and pro-caspase-1. This results in caspase-1 activation, leading to cleavage of pro-IL-1β and pro-IL-18 into their active forms. Caspase-1 also cleaves gasdermin D, forming pores in the cell membrane, thereby initiating pyroptosis and amplifying the inflammatory response.

Yes, several selective NLRP3 inhibitors are in clinical development. For example, dapansutrile (OLT1177®), an oral NLRP3 inhibitor, has progressed through Phase II trials for conditions including type 2 diabetes (NCT06047262) and acute gout flare (NCT05658575). NLRP3 inhibitors aim to reduce NLRP3-mediated inflammation in diseases such as type 2 diabetes, Alzheimer's, and cardiovascular diseases.

NLRP3 is studied using in vitro cell models stimulated with known inflammasome activators. Cytokine release is measured by ELISA. Western blotting and immunofluorescence are used to detect inflammasome components. In vivo, NLRP3 knockout or transgenic mice help elucidate its role in inflammation and disease pathogenesis.

Blevins, H.M., Xu, Y., Biby, S., Zhang, S. The NLRP3 inflammasome pathway: a review of mechanisms and inhibitors for the treatment of inflammatory diseases. Front. Aging Neurosci., 14: 879021, 2022; doi: 10.3389/fnagi.2022.879021

Clénet, M.L., Keaney, J., Gillet, G., Valadas, J.S., Langlois, J., Cardenas, A., Gasser, J., Kadiu, I. Divergent functional outcomes of NLRP3 blockade downstream of multi-inflammasome activation: therapeutic implications for ALS. Front. Immunol., 14: 1190219, 2023; doi: 10.3389/fimmu.2023.1190219

Gordon, R., Albornoz, E.A., Christie, D.C., Langley, M.R., Kumar, V., Mantovani, S., Robertson, A.A.B., Butler, M.S., Rowe, D.B., O'Neill, L.A., Kanthasamy, A.G., Schroder, K., Cooper, M.A., Woodruff, T.M. Inflammasome inhibition prevents α-synuclein pathology and dopaminergic neurodegeneration in mice. Sci. Transl. Med., 10: eaah4066, 2018; doi: 10.1126/scitranslmed.aah4066

Grotemeyer, A., Fischer, J.F., Koprich, J.B., Brotchie, J.M., Blum, R., Volkmann, J., Ip, C.W. Inflammasome inhibition protects dopaminergic neurons from α-synuclein pathology in a model of progressive Parkinson's disease. J. Neuroinflammation, 20: 79, 2023; doi: 10.1186/s12974-023-02759-0

Heneka, M.T., Kummer, M.P., Stutz, A., Delekate, A., Schwartz, S., Vieira-Saecker, A., Griep, A., Axt, D., Remus, A., Tzeng, T. C., Gelpi, E., Halle, A., Korte, M., Latz, E., Golenbock, D. T. NLRP3 is activated in Alzheimer's disease and contributes to pathology in APP/PS1 mice. Nature, 493: 674-8, 2013; doi: 10.1038/nature11729

Holbrook, J.A., Jarosz-Griffiths, H.H., Caseley, E., Lara-Reyna, S., Poulter, J.A., Williams-Gray, C.H., Peckham, D., McDermott, M.F. Neurodegenerative disease and the NLRP3 inflammasome. Front. Pharmacol., 12: 643254, 2021; doi: 10.3389/fphar.2021.643254

Ising, C., Venegas, C., Zhang, S., Scheiblich, H., Schmidt, S. V., Vieira-Saecker, A., Schwartz, S., Albasset, S., McManus, R.M., Tejera, D., Griep, A., Santarelli, F., Brosseron, F., Opitz, S., Stunden, J., Merten, M., Kayed, R., Golenbock, D.T., Blum, D., Latz, E., Buée, L., Heneka, M.T. NLRP3 inflammasome activation drives tau pathology. Nature, 575: 669-673, 2019; doi: 10.1038/s41586-019-1769-z

Kim, S.K. The mechanism of the NLRP3 inflammasome activation and pathogenic implication in the pathogenesis of gout. J. Rheum. Dis., 29: 140-153, 2022; doi: 10.4078/jrd.2022.29.3.140

Lee, E., Hwang, I., Park, S., Hong, S., Hwang, B., Cho, Y., Son, J., Yu, J.W. MPTP-driven NLRP3 inflammasome activation in microglia plays a central role in dopaminergic neurodegeneration. Cell Death Differ., 26: 213-228, 2019; doi: 10.1038/s41418-018-0124-5

Li, Y., Qiang, R., Cao, Z., Wu, Q., Wang, J., Lyu, W. NLRP3 inflammasomes: dual function in infectious diseases. J. Immunol., 213: 407-417, 2024; doi: 10.4049/jimmunol.2300745

Nițulescu, I.M., Ciulei, G., Cozma, A., Procopciuc, L.M., Orășan, O.H. From innate immunity to metabolic disorder: a review of the NLRP3 inflammasome in diabetes mellitus. J. Clin. Med., 12: 6022, 2023; doi: 10.3390/jcm12186022

Qiao, C., Zhang, L.X., Sun, X.Y., Ding, J.H., Lu, M., Hu, G. Caspase-1 deficiency alleviates dopaminergic neuronal death via inhibiting caspase-7/AIF pathway in MPTP/p mouse model of Parkinson's disease. Mol. Neurobiol., 54: 4292-4302, 2017; doi: 10.1007/s12035-016-9980-5

Singh, J., Habean, M.L., Panicker, N. Inflammasome assembly in neurodegenerative diseases. Trends Neurosci., 46: 814-831, 2023; doi: 10.1016/j.tins.2023.07.009

Tanase, D.M., Valasciuc, E., Gosav, E.M., Ouatu, A., Buliga-Finis, O.N., Floria, M., Maranduca, M.A., Serban, I.L. Portrayal of NLRP3 inflammasome in atherosclerosis: current knowledge and therapeutic targets. Int. J. Mol. Sci., 24: 8162, 2023; doi: 10.3390/ijms24098162

Wang, W., Nguyen, L.T., Burlak, C., Chegini, F., Guo, F., Chataway, T., Ju, S., Fisher, O.S., Miller, D.W., Datta, D., Wu, F., Wu, C. X., Landeru, A., Wells, J. A., Cookson, M.R., Boxer, M. B., Thomas, C.J., Gai, W.P., Ringe, D., Petsko, G.A., Hoang, Q.Q. Caspase-1 causes truncation and aggregation of the Parkinson's disease-associated protein α-synuclein. Proc. Natl. Acad. Sci. U S A., 113: 9587-92, 2016; doi: 10.1073/pnas.1610099113

Yang, K., Wang, X., Pan, H., Wang, X., Hu, Y., Yao, Y., Zhao, X., Sun, T. The roles of AIM2 in neurodegenerative diseases: insights and therapeutic implications. Front. Immunol.,15: 1441385, 2024; doi: 10.3389/fimmu.2024.1441385

Alpha-Synuclein: a presynaptic neuronal protein that is genetically and neuropathologically associated with Parkinson's disease (PD).  

Alzheimer's Disease: a progressive neurodegenerative disorder characterized by cognitive decline, memory loss, and behavioral changes. It is associated with the accumulation of amyloid-beta plaques and tau tangles in the brain, and loss of neurons and synapses in the cerebral cortex and subcortical regions.  

Amyloid-Beta (Aβ): a peptide derived from the amyloid precursor protein (APP) that can aggregate to form plaques.  

Amyotrophic Lateral Sclerosis (ALS): also known as Lou Gehrig's disease, it is the most common form of motor neuron disease and affects the upper and lower motor neurons. This fatal neuromuscular disease is characterized by progressive weakness of the muscles required to move, speak, eat, and breathe. 

DAMPs: Damage-Associated Molecular Patterns are endogenous signals released from injured, stressed, or dying cells, such as extracellular ATP or uric acid crystals, that alert the immune system to tissue damage. These signals can activate the inflammasome, promoting inflammatory responses. 

Frontotemporal Dementia (FTD): a group of neurodegenerative disorders characterized by progressive damage to the frontal and/or temporal lobes of the brain. This damage leads to a variety of symptoms that can include changes in personality, behavior, and language abilities. FTD is distinct from other types of dementia, such as Alzheimer's disease, in that it often affects younger individuals (typically between the ages of 45 and 65) and presents with early and prominent changes in social behavior, executive function, and language, rather than memory loss. The three main subtypes of FTD are Behavioral variant FTD (bvFTD), Non-fluent variant primary progressive aphasia (nfvPPA) and Semantic variant primary progressive aphasia (svPPA). 

Multiple Sclerosis (MS): the most commonly demyelinating disease of the central nervous system (CNS); MS is an immune-mediated disease, involving T cell, B cells, microglia, and macrophages, and characterized by inflammation, demyelination, axonal injury, and neurodegeneration. 

Neurodegeneration: a complex, multifactorial process resulting in the loss of neurons.  

Neuroinflammation: an inflammatory response within the central nervous system (CNS), primarily involving the activation of microglia and astrocytes. This process can be triggered by various factors, including infections, traumatic brain injury, toxic metabolites, and autoimmune diseases.    

NLRP3 Inflammasome: a cytosolic multi-protein complex found primarily in neuroinflammatory cells like microglia and astrocytes, and peripheral immune cells. The NLRP3 inflammasome plays a key role in the immune response by activating caspase-1 in response to various stress signals or infections, leading to the release of proinflammatory cytokines like IL-1β and IL-18, as well as the pore-forming molecule GSDMD. This inflammatory process can contribute to chronic inflammation and neurodegeneration, making NLRP3 a potential target for therapeutic intervention in neurodegenerative diseases.

PAMPs: Pathogen-Associated Molecular Patterns are components of microbes, such as LPS or viral RNA, that are detected by pattern recognition receptors. Their recognition can lead to activation of the inflammasome, a multiprotein complex that drives inflammation.

Parkinson's Disease (PD): a neurodegenerative disease that is characterized by: (a) movement-related (motor) symptoms, including resting tremor, bradykinesia, rigidity, and postural instability, related to the loss of dopaminergic neurons in the substantia nigra; and (b) non-motor symptoms including anxiety, depression, apathy, hallucinations, constipation, orthostatic hypotension, sleep disorders, hyposmia/anosmia, and cognitive impairment.  

Superoxide Dismutase 1 (SOD1): an enzyme that is encoded by the SOD1 gene located on chromosome 21 and is associated with apoptosis and familial ALS.  

Tau: a protein that plays a crucial role in maintaining the stability and function of neurons in the brain. It is predominantly found in neurons, where it stabilizes microtubules, which are part of the cell's cytoskeleton. Microtubules are essential for maintaining cell shape, enabling intracellular transport, and facilitating cellular division. Hyperphosphorylation of tau is evident in various neurodegenerative diseases, where the abnormally phosphorylated molecules lead to the detachment of tau from the microtubules. These detached tau proteins can aggregate to form insoluble fibrils, known as neurofibrillary tangles. Diseases impacted by tau aggregation are called tauopathies, and include Alzheimer's disease, progressive supranuclear palsy, frontotemporal dementia (FTD), and corticobasal degeneration.  

Transactive Response DNA Binding Protein of 43 kDa (TDP-43): a highly conserved nuclear RNA/DNA-binding protein encoded by the TARDBP gene involved in the regulation of RNA processing.