GOUT AS AN AUTOINFLAMMATORY DISEASE: FROM CELLULAR TO GENETIC MECHANISMS.

Abstract

Gout has been classified as an autoinflammatory disease because of its self-remitting course and the involvement of the innate immune system and IL-1β in its pathogenesis. During the last years, the evidence of NLRP3 inflammasome activation by monosodium urate (MSU) crystals and the beneficial effect of IL-1 blockade for the treatment of patients with gout, have reaffirmed the concept of gout as an autoinflammatory disease. However, some questions regarding its pathogenesis remain still unanswered. The presence of MSU crystals in asymptomatic joints or why not all individuals with hyperuricemia develop clinical gout, are some examples. In this thesis we centred our attention in the mononuclear phagocyte system with the hypothesis that the state of activation or maturation of monocytes and macrophages modulates the inflammatory response to MSU crystals._x000D_ Regarding macrophages, our hypothesis is that resident macrophages, after contact with MSU crystals, acquire an inflammatory phenotype, being able to produce inflammatory cytokines in the presence of a second signal or trigger. Therefore, to test it, we used an in vitro model of human monocyte-derived macrophages polarized towards M1 or M2 phenotypes in the presence of GM-CSF and M-CSF respectively, considering M2 macrophages a model of resident synovial macrophages. M1 and M2 macrophages failed to produce IL-1β after stimulation with MSU crystals or LPS. However, in the presence of MSU, M2 macrophages produced IL-1β and decreased IL-10 secretion when LPS was added. Surprisingly, soluble uric acid had a suppressive effect for expression of both cytokines. The production of IL-1β was explained because MSU crystals increased the presence of active caspase-1, reflecting inflammasome activation, whereas LPS induced pro-IL-1β and inactive caspase-1 production. Analysis of inflammasome activation in M1 and M2 macrophages revealed differences in inflammasome proteins, that could account for their different IL-1β production._x000D_ To investigate if the capacity of monocytes to react to MSU crystals could explain why some individuals develop gout, we compared the inflammasome activation induced by MSU crystals in PBMCs from gouty patients with healthy controls. PBMCs of patients with gout exhibited enhanced inflammasome activation after culture with MSU. Therefore, our results suggest that patients with gout have an increased reactivity to MSU crystals. To provide further insight, we genotyped exon 3 of NLRP3 gene in gout patients, without finding any association of gout with polymorphisms in this gene. Finally, we analyzed the distribution of different monocyte phenotypes or blood subpopulations in patients with gout. We observed an expansion of the intermediate subpopulation (CD14++CD16+) during gout flares, but no differences were observed in any of the subpopulations between asymptomatic patients and healthy controls.

Date of Award	21 Oct 2014
Original language	English
Supervisor	Manuel Juan Otero (Director) & Mònica Gumà Uriel (Director)