Vimentin Regulates Activation of the NLRC4 Inflammasome

NLRC4 inflammasome activation and subsequent maturation of IL‐1β has been implicated in inflammation and acute lung injury (ALI). Cellular inflammation involves two signals. The first signal is either a pathogen‐associated molecular pattern (PAMP) or damage‐associated molecular pattern (DAMP) which activates toll‐like‐receptors (TLR) which causes the NF‐κB induction of pro‐IL‐1β. The second signal, mediated by bacterial flagellin, involves formation of a NLRC4 inflammasome which activates caspase‐1 and maturation of IL‐1β. We have used a flagellin (fliC) strain of Pseudomonas aeruginosa (PAO1) to activate the NLRC4 inflammasome. Previously it was shown that vimentin expression was involved in NLRP3 inflammasome activation. We hypothesized that vimentin is important in the NLRC4 inflammatory response and that the absence of vimentin would reduce hallmarks of lung inflammation. To determine the role of vimentin in the NLRC4 inflammatory pathway, wild‐type (WT) and vimentin‐knockout ( Vim −/− ) mice were subjected to a lethal dose of PAO1, which induces both pro‐inflammatory cytokine expression and induces a systemic inflammatory response that is associated with significant mortality. Wild‐type mice displayed about a 2‐fold increase in mortality compared with Vim −/− mice. Vim −/− mice had a median survival of more than 40 h, whereas WT animals had a median survival of 20 h. Histopathological examination showed that the lungs of PAO1‐treated WT mice had severe alveolar damage, characterized by interstitial edema, and more fluid and debris in the airspace than the PAO1‐treated Vim −/− mice. WT mice exposed to PAO1 exhibited an increase in wet‐to‐dry lung weight ratio and total protein concentration in the bronchoalveolar lavage fluid (BALF), whereas Vim −/− mice failed to exhibit such an increase. PAO1 induces rapid production and release of pro‐inflammatory cytokines and chemokines, which are sufficient to induce lung inflammation and ALI in mice and humans. When WT and Vim −/− mice were exposed to PAO1 for 6 h, significantly more caspase‐1 and IL‐1β were found in BALF from WT mice than in Vim −/− mice. PAO1 mediated markers that are NLRC4‐independent, such as tumor necrosis factor α (TNF‐α), were not affected by the loss of vimentin. Additionally, whole lung homogenates prepared from WT and Vim −/− mice exposed to PAO1 had increased levels of pro‐IL‐1β protein. These data suggest that vimentin is not involved in the TLR‐mediated NF‐κB activation and upregulation of pro‐IL‐1β. Rather, vimentin is required for the second step in for PAO1‐induced activation of caspase‐1 and maturation of IL‐1β via the NLRC4 inflammasome. Support or Funding Information This work was supported by National Heart, Lung, and Blood Institute (HL128194; HL071643)