Inflammasome activation in Ankylosing Spondylitis is associated to gut dysbiosis.

BACKGROUND This study evaluated the activation and functional relevance of inflammasome pathways in AS patients and rodent models and their relationship to dysbiosis. METHODS Inflammasome pathway was evaluated in the gut and peripheral blood of 40 AS patients by RT-qPCR, IHC, flow cytometry and confocal microscopy and compared to 20 healthy controls (20) and 10 Crohn's disease patients. Silver stain visualized bacteria in human samples and antibiotics were administered to HLA-B27 transgenic rats. The NLRP3 inhibitor MCC950 was administered to SKG mice and ileal and joint tissues assessed by IHC and qRT-PCR. The role of inflammasome in modulating IL-23/IL-17 axis was studied ex-vivo. RESULTS NLRP3, NLRC4 and AIM2 expression were increased in the gut of HLA-B27 TG rats and reduced by antibiotics (p<0.05). In curdlan-treated SKG mice, NLRP3 blockade prevented ileitis and delayed arthritis onset (p<0.05). Compared to HC,in the ileum of AS patients, NLRP3 (2.33 vs 22.2, p<0.001), NLRC4 (1.90 vs 6.47, p<0.001), AIM2 (2.40 vs 20.8, p<0.001), Caspase-1 (2.53 vs 24.8, p<0.001), IL-1β (1.07 vs 10.93, p<0.001) and IL-18 (2.56 vs 15.67, p<0.001) were over-expressed and Caspase-1 activity was increased (p<0.01). The score of adherent and invasive mucosa-associated bacteria was higher in AS (p<0.01) and correlated with the expression of inflammasome components in PBMC (p<0.001). NLRP3 expression associated with disease activity (ASDAS-CRP) (r2 =0.28, p<0.01) and IL23A (r2 =0.34, p<0.001). In vitro, inflammasome activation in AS monocytes was paralleled by increased serum levels of IL-1β and IL18. The induction of IL-23p19, IL-17A, and IL-22 was IL-1β-dependent. CONCLUSIONS Inflammasome activation occurs in rodent models and AS patients, is associated with dysbiosis, and is involved in triggering ileitis in SKG mice. Inflammasome drives type 3 cytokine production with an IL-1β-dependent mechanism in AS patients.