John W. Holloway

Association of the ADAM33 gene with asthma and bronchial hyperresponsiveness

Asthma is a common respiratory disorder characterized by recurrent episodes of coughing, wheezing and breathlessness. Although environmental factors such as allergen exposure are risk factors in the development of asthma, both twin and family studies point to a strong genetic component. To date, linkage studies have identified more than a dozen genomic regions linked to asthma. In this study, we performed a genome-wide scan on 460 Caucasian families and identified a locus on chromosome 20p13 that was linked to asthma (log10 of the likelihood ratio (LOD), 2.94) and bronchial hyperresponsiveness (LOD, 3.93). A survey of 135 polymorphisms in 23 genes identified the ADAM33 gene as being significantly associated with asthma using case-control, transmission disequilibrium and haplotype analyses (P = 0.04–0.000003). ADAM proteins are membrane-anchored metalloproteases with diverse functions, which include the shedding of cell-surface proteins such as cytokines and cytokine receptors. The identification and characterization of ADAM33, a putative asthma susceptibility gene identified by positional cloning in an outbred population, should provide insights into the pathogenesis and natural history of this common disease.

Incidence of schizophrenia and other psychoses in ethnic minority groups: results from the MRC AESOP study

BACKGROUND The incidence of schizophrenia in the African-Caribbean population in England is reported to be raised. We sought to clarify whether (a) the rates of other psychotic disorders are increased, (b) whether psychosis is increased in other ethnic minority groups, and (c) whether particular age or gender groups are especially at risk. METHOD We identified all people (n=568) aged 16-64 years presenting to secondary services with their first psychotic symptoms in three well-defined English areas (over a 2-year period in Southeast London and Nottingham and a 9-month period in Bristol). Standardized incidence rates and incidence rate ratios (IRR) for all major psychosis syndromes for all main ethnic groups were calculated. RESULTS We found remarkably high IRRs for both schizophrenia and manic psychosis in both African-Caribbeans (schizophrenia 9.1, manic psychosis 8.0) and Black Africans (schizophrenia 5.8, manic psychosis 6.2) in men and women. IRRs in other ethnic minority groups were modestly increased as were rates for depressive psychosis and other psychoses in all minority groups. These raised rates were evident in all age groups in our study. CONCLUSIONS Ethnic minority groups are at increased risk for all psychotic illnesses but African-Caribbeans and Black Africans appear to be at especially high risk for both schizophrenia and mania. These findings suggest that (a) either additional risk factors are operating in African-Caribbeans and Black Africans or that these factors are particularly prevalent in these groups, and that (b) such factors increase risk for schizophrenia and mania in these groups.

Variant LTC 4 synthase allele modifies cysteinyl leukotriene synthesis in eosinophils and predicts clinical response to zafirlukast

Clinical trials with leukotriene synthesis inhibitors and cysteinyl leukotriene (cys-LT) receptor antagonists have shown that cys-LTs (LTC4, LTD4, and LTE4) are the predominant mediators of bronchoconstriction in response to diverse asthma triggers including allergen, PAF, sulphur dioxide, and non-steroidal anti-inflammatory drugs (NSAIDs).1 In addition, inhalation of a single dose of a cys-LT causes persistent eosinophilia in the bronchial mucosa and sputum of asthmatic patients,2 3 and LT modifier drugs significantly reduce airway and blood eosinophilia in clinical asthma.4 We have shown that, in the asthmatic airway, eosinophils represent the majority of cells that express the terminal enzyme in the cys-LT pathway, LTC4 synthase, and hence have the capacity to generate cys-LT upon stimulation.5 6 Inflammation and bronchoconstriction in the asthmatic airway may be sustained by a vicious cycle of cys-LT synthesis and eosinophil recruitment (fig 1). Anomalies in the genetic and cytokine factors that regulate cys-LT pathway enzymes in eosinophils may thus be central to the pathophysiology of asthma. Figure 1 Schematic diagram illustrating that genetic and cytokine factors modulate the vicious cycle of cysteinyl leukotriene synthesis and eosinophil recruitment in the asthmatic airway. Cys-LTs are synthesised from membrane derived arachidonic acid. During stimulus-specific cell activation, arachidonic acid released by phospholipases including cytosolic phospholipase A2(PLA2)is translocated to the 5-lipoxygenase activating protein (FLAP) and converted in two steps to leukotriene (LT)A4 by 5-lipoxygenase (5- LO). LTA4 is converted to LTB4 by cells expressing LTA4hydrolase, and/or to LTC4 by cells expressing LTC4 synthase, which conjugates LTA4 to reduced glutathione. After carrier mediated cellular export of LTC4, the sequential cleavage of glutamate and glycine residues provides the extracellular receptor active metabolites LTD4 and LTE4, respectively. Cys-LTs act at specific …

A genome-wide association study identifies CDHR3 as a susceptibility locus for early childhood asthma with severe exacerbations

Asthma exacerbations are among the most frequent causes of hospitalization during childhood, but the underlying mechanisms are poorly understood. We performed a genome-wide association study of a specific asthma phenotype characterized by recurrent, severe exacerbations occurring between 2 and 6 years of age in a total of 1,173 cases and 2,522 controls. Cases were identified from national health registries of hospitalization, and DNA was obtained from the Danish Neonatal Screening Biobank. We identified five loci with genome-wide significant association. Four of these, GSDMB, IL33, RAD50 and IL1RL1, were previously reported as asthma susceptibility loci, but the effect sizes for these loci in our cohort were considerably larger than in the previous genome-wide association studies of asthma. We also obtained strong evidence for a new susceptibility gene, CDHR3 (encoding cadherin-related family member 3), which is highly expressed in airway epithelium. These results demonstrate the strength of applying specific phenotyping in the search for asthma susceptibility genes.

Genetics of allergic disease

Allergic diseases are complex genetic diseases resulting from the effect of multiple genetic and interacting environmental factors on their pathophysiology. Recent years have seen considerable progress in unraveling the contribution of these factors to an individual subjects susceptibility to, subsequent development of, and severity of disease. This has resulted in increasing insight into novel areas of allergic disease pathophysiology, for example the significant role played by locally acting tissue susceptibility factors like epithelial/epidermal barrier function and remodeling, such as filaggrin, ADAM33, and GSDML/ORMDL3, in patients with atopic dermatitis and asthma. Furthermore, studies of gene-environment interactions and Mendelian randomization approaches have led to increased insight into the importance of environmental triggers for allergic disease. Studies of the timing of action of genetic variants in determining disease susceptibility have highlighted the importance of in utero development and early life in determining susceptibility to allergic disease. In the future, genetic discoveries in allergic disease will potentially lead to better endophenotyping, prognostication, prediction of treatment response, and insights into molecular pathways to develop more targeted therapy for these conditions.

Cooperative Effects of Th2 Cytokines and Allergen on Normal and Asthmatic Bronchial Epithelial Cells

In sensitized individuals, exposure to allergens such as Dermatophagoides pteronyssinus (Der p) causes Th2 polarization and release of cytokines, including IL-4 and IL-13. Because Der p extracts also have direct effects on epithelial cells, we hypothesized that allergen augments the effects of Th2 cytokines by promoting mediator release from the bronchial epithelium in allergic asthma. To test our hypothesis, primary bronchial epithelial cultures were grown from bronchial brushings of normal and atopic asthmatic subjects. RT-PCR showed that each culture expressed IL-4Rα, common γ-chain, and IL-13Rα1, as well as IL-13Rα2, which negatively regulates IL-13 signaling; FACS analysis confirmed IL-13Rα2 protein expression. Exposure of epithelial cultures to either Der p extracts, TNF-α, IL-4, or IL-13 enhanced GM-CSF and IL-8 release, and this was partially suppressible by corticosteroids. Simultaneous exposure of the epithelial cultures to IL-4 or IL-13 together with Der p resulted in a further increase in cytokine release, which was at least additive. Release of TGF-α was also increased by TNF-α and combinations of IL-4, IL-13, and Der p; however, this stimulation was only significant in the asthma-derived cultures. These data suggest that, in an allergic environment, Th2 cytokines and allergen have the potential to sustain airway inflammation through a cooperative effect on cytokine release by the bronchial epithelium. Our novel finding that IL-4, IL-13, and allergen enhance release of TGF-α, a ligand for the epidermal growth factor receptor that stimulates fibroblast proliferation and goblet cell differentiation, provides a potential link between allergen exposure, Th2 cytokines, and airway remodelling in asthma.

TOLL-LIKE RECEPTOR 4 POLYMORPHISM AND SEVERITY OF ATOPY IN ASTHMATICS

Endotoxin exposure may have a protective effect against asthma and atopy. An Asp299Gly polymorphism in the Toll-like receptor 4 (TLR4) gene reduces responsiveness to endotoxin. This study determined the effect of TLR4 polymorphism on the risk and severity of asthma and atopy. In all, 336 UK Caucasian families with ≥2 affected sibs (physicians diagnosis of asthma and current medication use) and 179 Caucasians without asthma or a family history of asthma were genotyped using ARMS-PCR. No association of the TLR4 polymorphism was found with the risk of developing asthma, either in parent-affected sibling trios, or in case–control analyses (P>0.05). In the first affected asthmatic siblings, the atopy severity score (based on size and number of positive skin-prick tests and specific IgE) was higher in those with the Asp/Gly or Gly/Gly genotypes (mean 1.8, s.d. 1.1, n=39) compared to those with the Asp/Asp genotype (mean 1.2, s.d. 1.0, n=279) (P=0.003, t-test). No associations were found with total IgE, FEV1 % predicted, slope of FEV1 response to methacholine or asthma severity score (P>0.05). This study confirms the previously observed lack of association of TLR4 polymorphisms with asthma. In contrast, the findings suggest that genetically determined hyporesponsiveness to endotoxin may increase atopy severity.

Polymorphisms in the interleukin-4 and interleukin-4 receptor alpha chain genes confer susceptibility to asthma and atopy in a Caucasian population

Background  IL‐4 by binding to its receptor (IL‐4R) is essential for the development of airway inflammation present in asthma, through the induction of IgE synthesis in B cells and differentiation of T cells to a Th2 phenotype.

Genetic susceptibility to the respiratory effects of air pollution

There is large variation between individuals in their response to air pollutants. This review summarises the existing evidence that genetic factors influence the mechanisms of lung injury caused by air pollutants. Genetic association studies have compared the adverse effects of air pollutants between subjects with specific genotypes in biologically relevant genes. In human studies of ozone exposure, polymorphisms in oxidative stress genes (NQO1, GSTM1, GSTP1) modify respiratory symptoms, lung function, biomarkers and risk of asthma. Inflammatory gene polymorphisms (TNF) influence the lung function response to ozone, and the effect of different levels of ozone on the development of asthma. Polymorphisms in oxidative stress genes (GSTM1, GSTP1) alter the response to combined exposure to ragweed pollen and diesel exhaust particles. Importantly, polymorphisms in an oxidative stress gene (GSTM1) have predicted patients with asthma who benefit from antioxidant supplementation in Mexico City, which has chronically high ozone exposure. Genetic linkage studies of families have not been feasible for studying the effects of air pollution in humans, but some progress has been made with pedigrees of specially bred mice, in identifying chromosomal regions linked to effects of ozone or particles. A high priority now, in addition to avoiding exposure in the most susceptible people, is to clearly identify the most effective and safe chemopreventive agents for individuals who are genetically susceptible to the adverse effects of air pollution (eg, antioxidants to be taken during high ozone levels).There is large variation between individuals in their response to air pollutants. This review summarises the existing evidence that genetic factors influence the mechanisms of lung injury caused by air pollutants. Genetic association studies have compared the adverse effects of air pollutants between subjects with specific genotypes in biologically relevant genes. In human studies of ozone exposure, polymorphisms in oxidative stress genes (NQO1, GSTM1, GSTP1) modify respiratory symptoms, lung function, biomarkers and risk of asthma. Inflammatory gene polymorphisms (TNF) influence the lung function response to ozone, and the effect of different levels of ozone on the development of asthma. Polymorphisms in oxidative stress genes (GSTM1, GSTP1) alter the response to combined exposure to ragweed pollen and diesel exhaust particles. Importantly, polymorphisms in an oxidative stress gene (GSTM1) have predicted patients with asthma who benefit from antioxidant supplementation in Mexico City, which has chronically high ozone exposure. Genetic linkage studies of families have not been feasible for studying the effects of air pollution in humans, but some progress has been made with pedigrees of specially bred mice, in identifying chromosomal regions linked to effects of ozone or particles. A high priority now, in addition to avoiding exposure in the most susceptible people, is to clearly identify the most effective and safe chemopreventive agents for individuals who are genetically susceptible to the adverse effects of air pollution (eg, antioxidants to be taken during high ozone levels).

IL-4 Receptor α Is an Important Modulator of IL-4 and IL-13 Receptor Binding: Implications for the Development of Therapeutic Targets

IL-4 is a key cytokine associated with allergy and asthma. Induction of cell signaling by IL-4 involves interaction with its cognate receptors, a complex of IL-4Rα with either the common γ-chain or the IL-13R chain α1 (IL-13Rα1). We found that IL-4 bound to the extracellular domain of IL-4Rα (soluble human (sh)IL-4Rα) with high affinity and specificity. In contrast with the sequential mechanism of binding and stabilization afforded by IL-4Rα to the binding of IL-13 to IL-13Rα1, neither common γ-chain nor IL-13Rα1 contributed significantly to the stabilization of the IL-4:IL-4Rα complex. Based on the different mechanisms of binding and stabilization of the IL-4R and IL-13R complexes, we compared the effects of shIL-4Rα and an IL-4 double mutein (R121D/Y124D, IL-4R antagonist) on IL-4- and IL-13-mediated responses. Whereas IL-4R antagonist blocked responses to both cytokines, shIL-4Rα only blocked IL-4. However, shIL-4Rα stabilized and augmented IL-13-mediated STAT6 activation and eotaxin production by primary human bronchial fibroblasts at suboptimal doses of IL-13. These data demonstrate that IL-4Rα plays a key role in the binding affinity of both IL-13R and IL-4R complexes. Under certain conditions, shIL-4Rα has the potential to stabilize binding IL-13 to its receptor to augment IL-13-mediated responses. Thus, complete understanding of the binding interactions between IL-4 and IL-13 and their cognate receptors may facilitate development of novel treatments for asthma that selectively target these cytokines without unpredicted or detrimental side effects.