Inflammasome gene profile is modulated in septic patients, with a greater magnitude in non-survivors

Abstract

Inflammasome signalling induces the processing and secretion of interleukin (IL)-1β and IL-18 which, coupled with pyroptosis, activate further the inflammatory response. In the present study we evaluated the expression of genes involved in inflammasome signalling pathways in septic patients, their interaction networks and the predicted functions modulated in survivors and non-survivors. Twenty-seven patients with sepsis secondary to community-acquired pneumonia admitted to intensive care units from three general hospitals in São Paulo were included into the study. We performed a polymerase chain reaction (PCR) array encompassing 35 genes related to the nucleotide-binding oligomerization domain and leucine-rich repeat-containing (NLR)-inflammasome in peripheral blood mononuclear cells obtained at admission and after 7 days of follow-up. Eleven healthy volunteers were used as the reference group. Increased NLRC4 and NLRP3 and decreased nucleotide-binding oligomerization domain (NOD1), and NLRP1 expression was observed in septic patients compared to healthy individuals; the IL-1β and IL-18 expression levels were also high in the patients. The gene expression changes followed the same patterns in surviving and non-surviving patients, with higher magnitudes observed in non-survivors. Functional analyses revealed, however, that activation and inhibition intensity for representing functions were different in survivors and non-survivors, as for production of reactive oxygen species, synthesis of nitric oxide and for the control of bacterial infections. Our results showed that the genes involved in the activation of the NLR-inflammasome cascades were altered substantially in septic patients, with a higher number of altered genes and a higher intensity in the disturbance of gene expression found among patients dying of sepsis.

Keywords: NLRP3; Toll-like receptor; interleukin-18; interleukin-1beta; pyroptosis.

Figure 1

Hierarchical clustering of differentially expressed genes when compared with healthy volunteers. D0S represents survival day 0, D0NS represents non‐survival day 0, D7S represents survival after day 7 and D7NS represents the day 7 non‐survival group. The red colour indicates up‐regulation and green indicates down‐regulation. The colour intensity depends upon the change ratio; the higher the ratio, the higher the intensity.

Figure 2

Identification of altered functions in septic patients (a), survival (b) and non‐survival (c) septic patients by ingenuity pathway analysis (IPA). Samples were obtained at D0. The node colour intensity represents activation (orange with positive Z‐score) and inhibition (blue with negative Z‐score) of functions, while genes up‐regulation is shown in red and down‐regulation in green.

Figure 3

Detection of interleukin (IL)‐18 in septic patients. Plasma levels were measured by enzyme‐linked immunosorbent assay (ELISA) and values are expressed in pg/ml. The data are represented as box‐plot, where D0 and D7 represent the days of sample collection. *P ≤ 0·05 compared to healthy volunteers.