Pharmacological inhibition of IKKß dampens NLRP3 inflammasome activation after priming in the human myeloid cell line THP-1.

The NLRP3 inflammasome is a critical component of the innate immune response to sterile inflammation. Its regulation involves a priming step, required for up-regulation of inflammasome protagonists and an activation step leading to NLRP3 inflammasome complex assembly, which triggers caspase-1 activity. The IκKß kinase regulates canonical NF-κB, a key pathway involved in transcriptional priming. We found that IκKß also regulates the activation and function of the NLRP3 inflammasome beyond the priming step. Two unrelated IκKß inhibitors, AFN700 and TPCA-1, when applied after priming, fully blocked IL-1ß secretion triggered by nigericin in THP-1 cells. Both inhibitors prevented neither inflammasome assembly, as monitored by measuring the formation of ASC specks, nor the generation of caspase-1 p20, a hallmark of caspase-1 activity, but they impaired the initial cleavage and activation of procaspase-1. These data thus indicate that IκKß activity is required for efficient activation of NLRP3, suggesting that IκKß may fulfill a dual role in coupling priming and activation of the NLRP3 inflammasome.

Fragments of HdhQ150 mutant huntingtin form a soluble oligomer pool that declines with aggregate deposition upon aging.

Cleavage of the full-length mutant huntingtin (mhtt) protein into smaller, soluble aggregation-prone mhtt fragments appears to be a key process in the neuropathophysiology of Huntington's Disease (HD). Recent quantification studies using TR-FRET-based immunoassays showed decreasing levels of soluble mhtt correlating with an increased load of aggregated mhtt in the aging HdhQ150 mouse brain. To better characterize the nature of these changes at the level of native mhtt species, we developed a detection method that combines size exclusion chromatography (SEC) and time-resolved fluorescence resonance energy transfer (TR-FRET) that allowed us to resolve and define the formation, aggregation and temporal dynamics of native soluble mhtt species and insoluble aggregates in the brain of the HdhQ150 knock-in mouse. We found that mhtt fragments and not full-length mhtt form oligomers in the brains of one month-old mice long before disease phenotypes and mhtt aggregate histopathology occur. As the HdhQ150 mice age, brain levels of soluble full-length mhtt protein remain similar. In contrast, the soluble oligomeric pool of mhtt fragments slightly increases during the first two months before it declines between 3 and 8 months of age. This decline inversely correlates with the formation of insoluble mhtt aggregates. We also found that the pool-size of soluble mhtt oligomers is similar in age-matched heterozygous and homozygous HdhQ150 mouse brains whereas insoluble aggregate formation is greatly accelerated in the homozygous mutant brain. The capacity of the soluble mhtt oligomer pool therefore seems exhausted already in the heterozygous state and likely kept constant by changes in flux and, as a consequence, increased rate of insoluble aggregate formation. We demonstrate that our novel findings in mice translate to human HD brain but not HD patient fibroblasts.