NALP3 Inflammasome Activation by Fibrillar Abeta Peptides and the Role for Alzheimer’s Disease

Lay Summary

Molecular Imaging May Reveal Inflammatory Processes Involved in Alzheimer’s Disease

Investigators will use molecular FRET imaging in a mouse model of dementia to gain a better understanding of inflammatory and toxic processes involved in Alzheimer’s disease.

Alzheimer’s disease is characterized by senile plaques that consist of amyloid beta peptide. The plaques are surrounded by immune microglial cells, which are the only immune cells that reside in the brain.  Research has demonstrated that the amyloid beta peptide can induce microglial cells to produce inflammatory substances, including cytokines, chemokines and neurotoxic factors.  These substances are thought to contribute to neurodegeneration that can lead to progressive cognitive and motor impairment.  The processes by which this occurs, however, are not well understood.

The investigators found that immune microglial cells contain a receptor complex (called NALP3 inflammasome).  NALP3 evolved to recognize aggregated proteins and the peptides that compose them.  Its activation leads to generation of inflammatory cytokines, such as interleukin-1, and neurotoxic factors.  They have found that cells from genetically modified mice that lack components of this NALP3 receptor complex fail to recognize these protein aggregates and do not mount an inflammatory response.

The investigators will use cellular FRET imaging, which shows how molecules affect one another, in mice that lack components of the NALP3 receptor complex. They will determine whether the mice are protected from developing dementia, and from damaging inflammation.  They also will characterize the components that the modified NALP3 receptor lacks, for further development into potential therapeutic agents.

Abstract

NALP3 Inflammasome Activation by Fibrillar Abeta Peptides and the Role for Alzheimer's Disease

Alzheimer’s (AD) disease is characterized by the appearance of neuritic (senile) plaques consisting of extracellular amyloid beta peptide (A), which are surrounded by activated microglial cells. It is well established that A can induce microglia to produce pro-inflammatory cytokines, chemokines and neurotoxic factors. These factors are believed to contribute to the neurodegeneration that can lead to progressive cognitive and motor impairment.

We found that the proteinaceous aggregates formed by A but not by the revA control peptide could lead to the activation of a cytosolic receptor complex that controls the activity of the inflammatory caspase-1. Active caspase-1 is known to catalytically process the precursor cytokine pro-IL-1 leading to release of active IL-1. Caspase-1 itself is controlled by cytosolic multi-receptor complexes termed inflammasomes. A activates the NACHT-, LRR-, and PYD domain-containing protein 3 (NALP3) inflammasome leading to recruitment of the adaptor molecule apoptosis-associated speck-like protein (ASC) and subsequent cleavage of caspase-1. Notably, we also found that the activity of the NALP3 inflammasome was critical for the secretion of neurotoxic factors, including NO and TNF, as well as for chemokines. In vivo, ablation of the caspase-1 activating pathway or ablation of IL-1 signaling components led to greatly diminished microglial recruitment to injected A in the brain suggesting that the NALP3 inflammasome pathway plays a critical role in the development of inflammation and neurotoxicity in vivo.

We propose to study the role of A-induced NALP3 inflammasome activation and IL-1 family cytokines for the production of inflammatory mediators and neurotoxic factors in vitro. We also propose to test the in vivo relevance of our findings by crossing double transgenic mice expressing a chimeric mouse/human amyloid precursor protein (Mo/HuAPP695swe) and a mutant human presenilin 1 (PS1-dE9) with NALP3-KO and ASC-KO mice. These mice will be analyzed for signs of AD and amount of A plaque formation will be assessed using brain section confocal imaging. Finally, we will generate and characterize NALP3 inflammasome reporter cell lines that can be harnessed for drug discovery.