New insight into the genes susceptible to asthma

Functional analysis of the impact of ORMDL3 expression on inflammation and activation of the unfolded protein response in human airway epithelial cells

Background

The gene ORMDL3 was shown to be associated with early-onset asthma susceptibility in multiple independent genome-wide and candidate-gene association studies. Asthmatic patients have elevated expression levels of this gene. ORMDL3 encodes a transmembrane protein localized in the endoplasmic reticulum (ER) that may be involved in ER stress and inflammation. It is essential to validate the genetic associations linking ORMDL3 with asthma through functional studies that confirm the biological relevance of this gene in disease. We investigated the effects of manipulating ORMDL3 expression levels in vitro in airway cells on innate immune inflammatory responses, ER stress and activation of the unfolded protein response (UPR).

Methods

ORMDL3 expression levels were manipulated in airway cells using an overexpression plasmid and siRNA technologies. Successful modulation of ORMDL3 was confirmed at both the gene and protein level. The functional impact of modulation of ORMDL3 expression levels on inflammatory responses and activation of the UPR were quantified using complementary cellular and molecular immunology techniques.

Results

Cells with altered ORMDL3 levels responded equally well to innate immune stimuli and produced similar levels of pro-inflammatory cytokines compared to wild-type cells. Treatment with ER stress inducers, thapsigargin and tunicamycin, resulted in activation of the unfolded protein response (UPR). However, we observed no difference in UPR activation in cells with ORMDL3 knockdown compared to cells with normal ORMDL3 levels.

Conclusions

Our results suggest that ORMDL3 variation in the airway epithelium is unlikely to play a significant role in modulating innate immune responses and the UPR in the lung.

Genome-wide association study identifies PERLD1 as asthma candidate gene

Background

Recent genome-wide association studies (GWAS) for asthma have been successful in identifying novel associations which have been well replicated. The aim of this study is to identify the genetic variants that influence predisposition towards asthma in an ethnic Chinese population in Singapore using a GWAS approach.

Methods

A two-stage GWAS was performed in case samples with allergic asthma, and in control samples without asthma and atopy. In the discovery stage, 490 case and 490 control samples were analysed by pooled genotyping. Significant associations from the first stage were evaluated in a replication cohort of 521 case and 524 control samples in the second stage. The same 980 samples used in the discovery phase were also individually genotyped for purposes of a combined analysis. An additional 1445 non-asthmatic atopic control samples were also genotyped.

Results

19 promising SNPs which passed our genome-wide P value threshold of 5.52 × 10^-8 were individually genotyped. In the combined analysis of 1011 case and 1014 control samples, SNP rs2941504 in PERLD1 on chromosome 17q12 was found to be significantly associated with asthma at the genotypic level (P = 1.48 × 10^-6, OR_AG = 0.526 (0.369-0.700), OR_AA = 0.480 (0.361-0.639)) and at the allelic level (P = 9.56 × 10^-6, OR = 0.745 (0.654-0.848)). These findings were found to be replicated in 3 other asthma GWAS studies, thus validating our own results. Analysis against the atopy control samples suggested that the SNP was associated with allergic asthma and not to either the asthma or allergy components. Genotyping of additional SNPs in 100 kb flanking rs2941504 further confirmed that the association was indeed to PERLD1. PERLD1 is involved in the modification of the glycosylphosphatidylinositol anchors for cell surface markers such as CD48 and CD59 which are known to play multiple roles in T-cell activation and proliferation.

Conclusions

These findings reveal the association of a PERLD1 as a novel asthma candidate gene and reinforce the involvement of genes on the 17q12-21 chromosomal region in the etiology of asthma.

Harnessing opportunities in non-animal asthma research for a 21st-century science

The incidence of asthma is on the increase and calls for research are growing, yet asthma is a disease that scientists are still trying to come to grips with. Asthma research has relied heavily on animal use; however, in light of increasingly robust in vitro and computational models and the need to more fully incorporate the 'Three Rs' principles of Replacement, Reduction and Refinement, is it time to reassess the asthma research paradigm? Progress in non-animal research techniques is reaching a level where commitment and integration are necessary. Many scientists believe that progress in this field rests on linking disciplines to make research directly translatable from the bench to the clinic; a '21st-century' scientific approach to address age-old questions.

The increasing challenge of discovering asthma drugs

The prevalence of asthma continues to rise. Current drugs provide symptomatic relief to some, but not all, patients. Despite the need for new therapeutics, and a huge research effort, only four novel agents from two classes of drugs - the antileukotrienes and an anti-IgE antibody - have been approved in the last 30 years. This review highlights three particular issues that contribute to the challenge of identifying new therapeutics. First is an over-reliance on animal models of allergy to define targets and expectations of efficacy that has met with poor translation to the clinical setting. While sensitivity to particular aeroallergens is one key risk factor for asthma, atopy and asthma are not synonymous, and while about half of adult asthmatics are atopic the incidence of allergic asthma is probably <50%. The second issue is a fundamental disconnect between the directions of basic research and clinical research. Basic research has developed a detailed, reductive, unifying mechanism of antigen-induced, T helper type 2 cell-mediated airway inflammation as the root cause of asthma. In contrast, clinical research has started to identify multiple asthma phenotypes with differing cellular components, mediators and sensitivities to asthma drugs, and probably varying underlying factors including susceptibility genes. Finally, different features of asthma - bronchoconstriction, symptoms, and exacerbations - respond diversely to treatment; effects that are not captured in animal models which do not develop asthma per se, but utilize unvalidated surrogate markers. Basic research needs to better integrate and utilize the clinical research findings to improve its relevance to drug discovery efforts.