Session Title: Pediatric Rheumatology - Pathogenesis and Genetics
Session Type: Abstract Submissions (ACR)
Background/Purpose: Familial Mediterranean Fever (FMF) is an autoinflammatory disease due to mutations of MEFV gene which encodes for Pyrin. FMF does not behave as a pure recessive disorder but clinical manifestations may parallel the actual amount of mutant pyrin. In agreement with this concept, correlation between genotype and FMF symptoms has been described. Growing evidence suggests that aberrant interleukin (IL) 1β signaling occurs in FMF. However, whether genetic variants of the MEFV gene result in differences in IL1β levels has never been explored. Moreover, the role of NLR family pyrin domain containing 3 (NLRP3) inflammasome in this contest is still largely unclear. Thus, we evaluated if IL1β pathway activation (1) is enhanced in FMF; (2) correlates with the type of MEFV mutation; and (3) is mediated by NLRP3.
Methods: Twenty FMF patients (FMFp) were evaluated and compared with 14 MEFV healthy carriers (HC) and 30 healthy donors (HD). Among patients, 12 were genetically confirmed (i.e. carrying 2 mutations) while 8 had clinical manifestations even if carrying 1 single mutation in heterozygosity. Ten out of 20 FMFp were under colchicine treatment and all of them were in controlled disease activity. Monocytes were freshly isolated and studied at baseline and after LPS in vitro activation. Monocyte nucleofection with NLRP3 siRNA or appropriate Mock controls was performed in 23 subjects (i.e. 7 FMFp, 9 HC, 3 HD) using Nucleofector™ Technology (Amaxa). IL1β and IL1 receptor antagonist (ILRa) pattern of secretion (3-6-18h) was analyzed by ELISA assay. Differences in oxydative state were evaluated by assessing levels of reactive oxygen species (ROS) and the cysteine release, as markers of pro- and antioxidant responses, respectively.
Results: Monocytes purified from FMFp displayed enhanced IL1β release. Interestingly, lL1β secretion correlated with number and penetrance of MEFV mutations, with higher levels in the presence of 2 high penetrance mutations in FMFp, and 1 high penetrance mutation in HC, respectively. Silencing of NLRP3 activity in monocytes freshly isolated from patients and controls consistently inhibited lL1β secretion. Contrary to what previously described in diseases caused by mutations that primarily affect the NLRP3 (i.e. Cryopyrinopaties) L1β release in pyrin mutated monocytes was featured by a more physiological kinetics. Consistent with this finding, FMFp monocytes basally produced more ROS but had a conserved, although impaired, cysteine release. Finally, IL1Ra levels were comparable to HD.
Conclusion: MEFV mutated monocytes display enhanced IL1β secretion, which correlates with the number of high-penetrance mutations. In contrast to what found in the animal model, IL1β secretion in FMFp monocytes is NLRP3-dependent. Interestingly, contrary to what previously reported in NLRP3 mutated cells, monocytes carrying MEFV mutation (1) have conserved antioxidant machinery capable of restraining the oxidative stress, (2) do not show stress-related defect in protein synthesis, (including IL1Ra production) and (3) display a more physiological pattern of secretion of lL1β.
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ACR Meeting Abstracts - http://acrabstracts.org/abstract/correlation-between-mefv-genotype-and-interleukin-il1%ce%b2-secretion-and-role-of-the-nlr-family-pyrin-domain-containing-3-nlrp3-inflammasome-in-patients-with-familial-mediterranean-fever-fmf/