ASC oligomer favor caspase-1^CARDdomain recruitment after intracellular potassium efflux

Abstract

Signaling through the inflammasome is important for the inflammatory response. Low concentrations of intracellular K + are associated with the specific oligomerization and activation of the NLRP3 inflammasome, a type of inflammasome involved in sterile inflammation. Subsequent to NLRP3 oligomerization, ASC protein binds and form oligomeric filaments culminating in large protein complexes named ASC specks. ASC specks are also initiated from different inflammasome scaffolds, as AIM2, NLRC4 or Pyrin. ASC oligomers induce the recruitment of caspase-1 through interactions between their respective caspase activation and recruitment domains (CARD), and favoring its activation. So far ASC oligomerization and caspase-1 activation are considered as a K +independent process. Here we found that ASC oligomers change their structure upon low intracellular K + independently of NLRP3 and allow the ASC CARD domain to be more accessible for the recruitment of pro-caspase-1 CARD domain. Therefore, conditions that decrease intracellular K + not only drive NLRP3 responses, but also enhance the recruitment of pro-caspase-1 by ASC specks formed by different inflammasomes, indicating that intracellular K + homeostasis is a key regulatory step for inflammasome regulation.the SPF-animal house from IMIB-Arrixaca for mice colony maintenance. We thank the members of the Pelegrin's laboratory for comments and suggestions.

The two pore potassium channel THIK‐1 regulates NLRP3 inflammasome activation

“…Although Cl − efflux was required to form an ASC speck, K + efflux was required to permit activation of caspase‐1 (Green et al, 2018). These previous findings are supported by recent research which demonstrated low intracellular K + levels trigger a conformational change in ASC oligomer structure resulting in enhanced caspase‐1 recruitment and activation (Martín‐Sánchez et al, 2020). In the present study, we show that inhibition of K2P channels, non‐selective K + channel inhibition, and K + efflux blockage, all inhibited caspase‐1 activation without blocking the formation of NLRP3‐dependent ASC specks in response to ATP.…”

Inflammasome activation in response to aberrations of cellular homeostasis in epithelial cells from human cornea and retina

“…A low extracellular K + concentration has been shown to stimulate conformational changes in the NLRP3 receptor protein and NLRP3 inflammasome activation whereas a high extracellular K + concentration (over 50 mM) prevents the activation, suggesting that K + efflux plays a crucial role in the assembly of the NLRP3 inflammasome complex (Mariathasan et al, 2006;Muñoz-Planillo et al, 2013;Pétrilli et al, 2007;Tapia-Abellan et al, 2021). Recently, a low level of intracellular K + was reported to affect also the structure of ASC specks and further facilitate the CARD domain of ASC to recruit the CARD domain of caspase-1 during the assembly of the inflammasome complex (Martín-Sánchez et al, 2023).…”

Nanoscale organization of the endogenous ASC speck

“…In cells, ASC specks were visualized by microscopy using immunofluorescence or expression of ASC tagged with a fluorescent protein. Upon overexpression, the resulting speck was typically much larger than 1 µm and occasionally showed filaments protruding from the edge of the structure 20,[22][23][24][25] . In contrast, diffractionlimited immunofluorescence imaging of the endogenous ASC speck revealed a spot of about 1 µm in diameter.…”