New variants in NLRP3 inflammasome genes increase risk for asthma and Blomia tropicalis-induced allergy in a Brazilian population

Abstract

Atopic asthma is a chronic lung disease of lower airways caused mainly due to action of T-helper (Th) 2 type cytokines, eosinophilic inflammation, mucus hypersecretion and airway remodelling. Interleukin (IL)-33 increases type 2 immunity polarization in airway playing critical role in eosinophilic asthma. On the other hand, NLRP3 inflammasome activation results in the release of caspase-1 (Casp-1) which, in its turn, promotes IL-33 inactivation. Recent studies have shown associations between NLRP3 variants and inflammatory diseases. However, no study with genes in NLRP3 inflammassome route has been conducted so far with asthma and atopy in any population to date. Blood samples were collected from 1246 asthmatic and non-asthmatic children. Associations were tested for single nucleotide polymorphism (SNP)s in NLRP3 and CASP1 with asthma and markers of atopy and in cultures stimulated with Blomia tropicalis (Bt) mite crude extract. The T allele of rs4925648 (NLRP3) was associated with increased asthma risk (OR 1.50, P = 0.005). In addition, the T allele of rs12130711 polymorphism, whithin the same gene, acted as a protector factor for asthma (OR 0.78, P = 0.038). On the other hand, the C allele of rs4378247 NLRP3 variant was associated with lower levels of IL-13 production when peripheral blood cells were stimulated with Bt (OR 0.39, P = 4E-04). In addition, the greater the number of risk alleles in IL33/NLRP3/CASP1 route the greater was the risk for asthma. The T allele of rs7925706 CASP1 variant was also associated with increased risk for asthma (OR 1.47, P = 0.008). In addition, this same allele increased the eosinophil counts in blood (mm3) in asthmatic individuals compared with non-asthmatic (P = 0.0004). These results suggest that NLRP3 and CASP1 polymorphisms may be associated with susceptibility for asthma and markers of atopy in our population.

Keywords: Allergy; Asthma; CASP1; Inflammasome; NLRP3; Variants.

Fig. 1

Immunopathogenesis of Bt-induced atopic asthma in the IL-33/NLRP3/CASP1 route. The contact of Bt with cells of the aerial epithelium results in damage and consequent release of IL-33. This, in turn, favors the Th2 response profile by activating several innate and adaptive immune cells, with high production of proinflammatory cytokines, also increasing degranulation and specific IgE production. On the other hand, activation of the intracellular NLRP3 receptor, present in the cytoplasm of the cells involved in this response, results in NLRP3 inflammasome formation and Casp-1 release. Casp-1 acts by inhibiting the IL-33 action and, consequently, attenuates the inflammation caused by this cytokine in airway.

Fig. 2

LD plot of significance analysis of 17 SNPs on NLRP3, analyzed in our population. Top bar indicates the physical location of each variant. The colors of each square vary according to the degree of LD, being the total equilibrium in color white with value of r² equal to 0 and total unbalance in color black with value of r² equal to one. The different shades of gray show an intermediate imbalance with a value of r² > 0 and < 0.8. This analysis was perfomed with Haploview software.

Fig. 3

Eosinophil number per mm³ in blood of asthmatic subjects according to genotype of CASP1 SNP rs7925706. Bars represent the median of eosinophils number according with each group genotyp, represented by its holders. CC: median = 5.800 and CT/TT: median = 9.850. The analyis of the data was by Manny-Whitney test. ***P < 0.001.