Latent Upregulation of Nlrp3, Nlrc4 and Aim2 Differentiates between Asymptomatic and Symptomatic Trichomonas vaginalis Infection

Trichomonas vaginalis is a parasitic protozoan that causes trichomoniasis. The involvement of NLRP3 inflammasome in trichomoniasis has been discussed in recent studies. The present study aimed to find out the involvement of Nlrp3, Nlrc4, and Aim2 in the BALB/c mouse model infected with symptomatic and asymptomatic isolates of T. vaginalis by quantitative real-time PCR and immunohistochemistry. Our results showed a significantly increased expression of Nlrp3 in the vaginal tissue of the symptomatic group on the 2^nd dpi and 14^th dpi in the asymptomatic group, respectively. The cervical tissue of asymptomatic groups expressed higher Nlrp3 on 14^th dpi than the symptomatic group. The Nlrc4 was expressed on 14^th dpi in the vaginal and cervical tissues of mice infected with asymptomatic group as compared to the symptomatic group. Aim2 expression in vaginal tissue was highest at early time points in both the infected groups as compared to controls. However, in cervical tissues, a significant increase of Aim2 expression was observed on 14^th dpi in asymptomatic as compared to the symptomatic group. The significantly higher expression of caspase-1 and caspase-4 was observed in cervical tissues of the asymptomatic group on 14^th dpi as compared to the symptomatic group, respectively. All NLRs together resulted in higher IL-1β expression in the vaginal tissues of the symptomatic and asymptomatic groups. We conclude from this study that early expression of Nlrp3, Nlrc4, and Aim2 was seen in the symptomatic group as compared to the late-onset asymptomatic in the vaginal and cervical tissues.

WDR90 is a new component of the NLRC4 inflammasome involved in Salmonella Typhimurium resistance

Inflammasomes are pivotal cytosolic molecular platforms involved in infection resistance. As multiprotein complexes, they consist of NOD-like receptors (NLRs), the adaptor proteins apoptosis-associated speck-like protein containing a CARD (ASC) and the effector molecules caspase-1 and caspase-11, whose assembly and activation depends on homotypic interactions. Here we describe WD repeat containing protein 90 (WDR90) as a new inflammasome component. We found that zebrafish wdr90 is highly induced by guanylate binding protein 4 (Gbp4) independently of inflammasome activation and caspase-1 activity. This gene encodes an evolutionarily conserved protein with unknown functions that contains several WD40 domains, which are involved in coordinating multiprotein complex assembly. Functional studies in zebrafish larvae showed that forced expression of wdr90 increased caspase-1 activity and inflammasome-dependent resistance to Salmonella enterica serovar Typhimurium infection. Wdr90 acted upstream of zebrafish caspase a (Caspa), the functional homolog of mammalian caspase-1, and Asc. Reconstitution experiments of the human inflammasome in HEK293 cells demonstrated that WDR90 was able to physically interact with and to alter the cellular distribution of NLRC4, but not of NLRP3 and AIM2. These results highlight the complexity of the inflammasome and the interest of studying fish immunity to understand not only the evolution of the immune system but also human immunity.

NLRP3 lacking the leucine-rich repeat domain can be fully activated via the canonical inflammasome pathway

NLRP3 is a cytosolic sensor triggered by different pathogen- and self-derived signals that plays a central role in a variety of pathological conditions, including sterile inflammation. The leucine-rich repeat domain is present in several innate immune receptors, where it is frequently responsible for sensing danger signals and regulation of activation. Here we show by reconstitution of truncated and chimeric variants into Nlrp3^−/− macrophages that the leucine-rich repeat domain is dispensable for activation and self-regulation of NLRP3 by several different triggers. The pyrin domain on the other hand is required to maintain NLRP3 in the inactive conformation. A fully responsive minimal NLRP3 truncation variant reconstitutes peritonitis in Nlrp3^−/− mice. We demonstrate that in contrast to pathogen-activated NLRC4, the constitutively active NLRP3 molecule cannot engage wild-type NLRP3 molecules in a self-catalytic oligomerization. This lack of signal amplification is likely a protective mechanism to decrease sensitivity to endogenous triggers to impede autoinflammation.

Activation of the NLRP3 inflammasome is associated with various diseases but its activation mechanism is not fully understood. Here, the authors determine the impact of different NLRP3 domains on sensing NLRP3 triggers, inflammasome assembly and regulation of NLRP3 inflammasome activation.