Background Familial Mediterranean fever (FMF) and Pyogenic Arthritis, Pyoderma gangrenosum and Acne (PAPA) syndrome are autoinflammatory disorders that are thought to share similar pathoetiology. While FMF is due to mutations of MEFV gene encoding for Pyrin, PAPA syndrome is caused by genetic variants of CD2 binding protein 1 (CD2BP1). Since Pyrin is able to bind CD2BP1 in a newly identified inflammasome called Pyroptosome, FMF and PAPA have been recently recognized as disorders of the same pathway, probably involving caspase-1 mediated interleukin (IL)-1β secretion, as suggested by the response to anti IL-1 treatment. However, a clear involvement of IL-1β is still controversial, especially because most of the data derive from studies applying not homogeneous experimental approaches.
Objectives To investigate in our cohorts of FMF and PAPA patients whether 1) MEFV/CD2BP1 mutated monocytes displayed enhancedredox-stress and IL1β secretion, 2) IL1β pathway activationcorrelated with type of mutation and 3) pyroptosome-related IL1β secretion was mediated by NLRP3 inflammasome.
Methods Thirteen genetically confirmed FMF pediatric patients (7 with 2 high penetrance and 6 with 1 high penetrance and 1 low penetrance or 2 low penetrance mutation) and 10 asymptomatic parents (healthy carriers, HC) were evaluated. Four PAPA (2 children and 2 adults) patients carrying different CD2BP1 mutations (E250Q, E250K and E256G) were also analyzed and compared to 25 healthy donors (HD). Peripheral blood primary human monocytes were freshly isolated and studied at baseline and after 3-6-18 hours (h) of TLRs in vitro activation. Intracellular reactive oxygen species (ROS) were examined by biochemical assay. Monocyte pattern of secretion of IL-1β, IL-18 and IL-1Ra was assessed by ELISA. The involvement of NLRP3 inflammasome was investigated by in vitro silencing.
Results FMF patients carrying high penetrance MEFV mutations displayed higher ROS levels than HD at baseline. The same pattern was observed for PAPA patients carrying the E250Q and E256G mutations. Overall FMF and PAPA monocytes displayed enhanced but not anticipated IL1β and IL18 secretion, in the presence of IL1Ra levels comparable to HD. Increased IL-1β pathway activation was greater in the presence of more severe MEFV mutations and in pediatric E250Q(+) and E256G(+) PAPA patients. Silencing of NLRP3 in representative cases inhibited IL-1β secretion in both FMF (N=1), FMF HC (N=3), PAPA (N=2) and HD (N=6).
Conclusions MEFV and CD2BP1 mutated monocytes are under sustained oxidative stress. This parallels an enhanced pattern of secretion of the pro-inflammatory IL1β, with greater effect in the presence of high-penetrance mutations in FMF and E249Q or E256G mutation in PAPA patients. Results from in vitro silencing experiments in freshly isolated monocytes suggest that NLRP3 inflammasome may be involved.
Disclosure of Interest None Declared
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