Decoding asthma:Translating genetic variation in IL33 and IL1RL1 into disease pathophysiology

<p>Asthma is a complex disease that results from the interaction between genetic predisposition and environmental factors. Recently, genome-wide association studies have identified a number of genes that significantly contribute to asthma. Two of these genes, IL33 and IL-1 receptor-like 1 (IL1RL1), act in one signal transduction pathway. IL33 encodes a cytokine released on damage of cells, whereas IL1RL1 encodes part of the IL-33 receptor complex. Recent progress made in functional studies in human subjects and mouse models of allergic airway disease indicate a central role of IL-33 signaling in driving T(H)2 inflammation, which is central to eosinophilic allergic asthma. Here, IL-33 acts on cells of both the adaptive and innate immune systems. Very recently, a novel population of IL-33-responsive innate immune cells, the type 2 innate lymphoid cells, was found to produce hallmark TH2 cytokines, such as IL-5 and IL-13. The relevance of these cells for asthma is underscored by the identification of retinoic acid-related orphan receptor a (RORA), the gene encoding the transcription factor critical for their differentiation, as another asthma gene in genome-wide association studies. This review describes the mechanisms through which genetic variation at the IL33 and IL1RL1 loci translates into increased susceptibility for asthma. We propose that genetic variation associated with asthma at the IL33 and IL1RL1 loci can be dissected into independent signals with distinct functional consequences for this pathway that is central to asthma pathogenesis. (J Allergy Clin Immunol 2013; 131:856-65.)</p>

The role of the IL-33/IL-1RL1 axis in mast cell and basophil activation in allergic disorders

Interleukin-33 (IL-33) is a recently discovered cytokine that belongs to the IL-1 superfamily and acts as an important regulator in several allergic disorders. It is considered to function as an alarmin, or danger cytokine, that is released upon structural cell damage. IL-33 activates several immune cells, including Th2 cells, mast cells and basophils, following its interaction with a cell surface heterodimer consisting of an IL-1 receptor-related protein ST2 (IL-1RL1) and IL-1 receptor accessory protein (IL-1RAcP). This activation leads to the production of a variety of Th2-like cytokines that mediate allergic-type immune responses. Thus, IL-33 appears to be a double-edged sword because, in addition to its important contribution to host defence, it exacerbates allergic responses, such as allergic rhinitis and asthma. A major purported mechanism of IL-33 in allergy is the activation of mast cells to produce a variety of pro-inflammatory cytokines and chemokines. In this review, we summarize the current knowledge regarding the genetics and physiology of IL-33 and IL-1RL1 and its association with different allergic diseases by focusing on its effects on mast cells and basophils

Predictive value of serum sST2 in preschool wheezers for development of asthma with high FeNO

Wheezing is common in childhood. However, current prediction models of pediatric asthma have only modest accuracy. Novel biomarkers and definition of subphenotypes may improve asthma prediction. Interleukin-1-receptor-like-1 (IL1RL1 or ST2) is a well-replicated asthma gene and associates with eosinophilia. We investigated whether serum sST2 predicts asthma and asthma with elevated exhaled NO (FeNO), compared to the commonly used Asthma Prediction Index (API). Using logistic regression modeling, we found that serum sST2 levels in 2-3 years-old wheezers do not predict doctors' diagnosed asthma at age 6 years. Instead, sST2 predicts a subphenotype of asthma characterized by increased levels of FeNO, a marker for eosinophilic airway inflammation. Herein, sST2 improved the predictive value of the API (AUC=0.70, 95% CI 0.56-0.84), but had also significant predictive value on its own (AUC=0.65, 95% CI 0.52-0.79). Our study indicates that sST2 in preschool wheezers has predictive value for the development of eosinophilic airway inflammation in asthmatic children at school age

Huntington disease in the South African population occurs on diverse and ethnically distinct genetic haplotypes

<p>Huntington disease (HD) is a neurodegenerative disorder resulting from the expansion of a CAG trinucleotide repeat in the huntingtin (HTT) gene. Worldwide prevalence varies geographically with the highest figures reported in populations of European ancestry. HD in South Africa has been reported in Caucasian, black and mixed subpopulations, with similar estimated prevalence in the Caucasian and mixed groups and a lower estimate in the black subpopulation. Recent studies have associated specific HTT haplotypes with HD in distinct populations. Expanded HD alleles in Europe occur predominantly on haplogroup A (specifically high-risk variants A1/A2), whereas in East Asian populations, HD alleles are associated with haplogroup C. Whether specific HTT haplotypes associate with HD in black Africans and how these compare with haplotypes found in European and East Asian populations remains unknown. The current study genotyped the HTT region in unaffected individuals and HD patients from each of the South African subpopulations, and haplotypes were constructed. CAG repeat sizes were determined and phased to haplotype. Results indicate that HD alleles from Caucasian and mixed patients are predominantly associated with haplogroup A, signifying a similar European origin for HD. However, in black patients, HD occurs predominantly on haplogroup B, suggesting several distinct origins of the mutation in South Africa. The absence of high-risk variants (A1/A2) in the black subpopulation may also explain the reported low prevalence of HD. Identification of haplotypes associated with HD-expanded alleles is particularly relevant to the development of population-specific therapeutic targets for selective suppression of the expanded HTT transcript.</p>

Phenotypic and functional translation of IL1RL1 locus polymorphisms in lung tissue and asthmatic airway epithelium.

The IL1RL1 (ST2) gene locus is robustly associated with asthma; however, the contribution of single nucleotide polymorphisms (SNPs) in this locus to specific asthma subtypes and the functional mechanisms underlying these associations remain to be defined. We tested for association between IL1RL1 region SNPs and characteristics of asthma as defined by clinical and immunological measures and addressed functional effects of these genetic variants in lung tissue and airway epithelium. Utilizing 4 independent cohorts (Lifelines, Dutch Asthma GWAS [DAG], Genetics of Asthma Severity and Phenotypes [GASP], and Manchester Asthma and Allergy Study [MAAS]) and resequencing data, we identified 3 key signals associated with asthma features. Investigations in lung tissue and primary bronchial epithelial cells identified context-dependent relationships between the signals and IL1RL1 mRNA and soluble protein expression. This was also observed for asthma-associated IL1RL1 nonsynonymous coding TIR domain SNPs. Bronchial epithelial cell cultures from asthma patients, exposed to exacerbation-relevant stimulations, revealed modulatory effects for all 4 signals on IL1RL1 mRNA and/or protein expression, suggesting SNP-environment interactions. The IL1RL1 TIR signaling domain haplotype affected IL-33-driven NF-κB signaling, while not interfering with TLR signaling. In summary, we identify that IL1RL1 genetic signals potentially contribute to severe and eosinophilic phenotypes in asthma, as well as provide initial mechanistic insight, including genetic regulation of IL1RL1 isoform expression and receptor signaling

Phenotypic and functional translation of IL33 genetics in asthma.

BACKGROUND:Asthma is a complex disease with multiple phenotypes that may differ in disease pathobiology and treatment response. Interleukin 33 (IL33) single nucleotide polymorphisms (SNPs) have been reproducibly associated with asthma. IL33 levels are elevated in sputum, and bronchial biopsies of asthma patients. The functional consequences of IL33 asthma SNPs remain unknown. OBJECTIVE:We studied whether IL33 SNPs associate with asthma-related phenotypes and with IL33 expression in lung or bronchial epithelium. We investigated the effect of increased IL33 expression on human bronchial epithelial cell (HBEC) function. METHODS:Association between IL33 SNPs (Chr9: 5,815,786-6,657,983) and asthma phenotypes (Lifelines/DAG/GASP cohorts) and between SNPs and expression (lung tissue, bronchial brushes, HBECs) was done using regression modelling. Lentiviral overexpression was used to study IL33 effects on HBECs. RESULTS:161 SNPs spanning the IL33 region associated with one or more asthma phenotypes after correction for multiple testing. We report one main independent signal tagged by rs992969 associating with blood eosinophil levels, asthma and eosinophilic asthma. A second, independent signal tagged by rs4008366 presented modest association with eosinophilic asthma. Neither signal associated with FEV1, FEV1/FVC, atopy, and age of asthma onset. The two IL33 signals are expression quantitative loci (eQTLs) in bronchial brushes and cultured HBECs, but not in lung tissue. IL33 overexpression in vitro resulted in reduced viability and ROS-capturing of HBECs, without influencing epithelial cell count, metabolic activity or barrier function. CONCLUSION:We identify IL33 as an epithelial susceptibility gene for eosinophilia and asthma, provide mechanistic insight, and implicate targeting of the IL33 pathway specifically in eosinophilic asthma

Mental health and life satisfaction of individuals with spinal cord injury and their partners 5 years after discharge from first inpatient rehabilitation

STUDY DESIGN: Cross-sectional study. OBJECTIVES: To describe and compare mental health and life satisfaction between individuals with spinal cord injury (SCI) and their partners 5 years after discharge from first inpatient rehabilitation; and to examine if injury severity moderates the association between individuals' with SCI and their partners' mental health and life satisfaction. SETTING: Dutch community. METHODS: Sixty-five individuals with SCI and their partners completed a self-report questionnaire. Main outcome measures were the mental health subscale of the Short-Form Health Survey and the Life Satisfaction Questionnaire. RESULTS: Levels of mental health and life satisfaction of individuals with SCI and partners were similar, with median scores of 76 and 4.8 versus 76 and 4.6, respectively. Moderate to strong correlations between individuals with SCI and their partners were found for the mental health (rS = 0.35) and life satisfaction scores (rS = 0.51). These associations were generally stronger in the subgroup of individuals with less severe SCI. Associations between scores on separate life domains ranged from negligible (0.05) to moderate (0.53). Individuals with SCI and their partners were least satisfied with their 'sexual life'. Compared with their partners, individuals with SCI were significantly more satisfied in the domains 'leisure situation', 'partnership relation' and 'family life', and less satisfied in 'self-care ability'. CONCLUSIONS: This study showed similarities but also differences in mental health and life satisfaction between individuals with SCI and their partners. In clinical practice, attention on mental health and life satisfaction should, therefore, focus on different domains for individuals with SCI and partners