Umasundari Sivaprasad

Th2 Cytokines and Atopic Dermatitis

Atopic dermatitis (AD), a chronic relapsing inflammatory skin disease, is increasing in prevalence around the world. Intensive research is ongoing to understand the mechanisms involved in the development of AD and offer new treatment options for patients suffering from AD. In this review, we highlight the importance of allergic Th2 responses in the development of the disease and summarize relevant literature, including genetic studies, studies of human skin and mechanistic studies on keratinocytes and mouse models of AD. We discuss the importance of the skin barrier and review recent findings on the pro-Th2 cytokines TSLP, IL-25, and IL-33, notably their ability to polarize dendritic cells and promote Th2 responses. After a brief update on the contribution of different T-cell subsets to AD, we focus on Th2 cells and the respective contributions of each of the Th2 cytokines (IL-4, IL-13, IL-5, IL-31, and IL-10) to AD. We conclude with a brief discussion of the current gaps in our knowledge and technical limitations.

Trefoil factor 2 rapidly induces interleukin 33 to promote type 2 immunity during allergic asthma and hookworm infection

The repair protein trefoil factor 2 promotes Th2 responses to helminth infection and allergens in part by inducing IL-33.

Epithelial EGF receptor signaling mediates airway hyperreactivity and remodeling in a mouse model of chronic asthma.

Increases in the epidermal growth factor receptor (EGFR) have been associated with the severity of airway thickening in chronic asthmatic subjects, and EGFR signaling is induced by asthma-related cytokines and inflammation. The goal of this study was to determine the role of EGFR signaling in a chronic allergic model of asthma and specifically in epithelial cells, which are increasingly recognized as playing an important role in asthma. EGFR activation was assessed in mice treated with intranasal house dust mite (HDM) for 3 wk. EGFR signaling was inhibited in mice treated with HDM for 6 wk, by using either the drug erlotinib or a genetic approach that utilizes transgenic mice expressing a mutant dominant negative epidermal growth factor receptor in the lung epithelium (EGFR-M mice). Airway hyperreactivity (AHR) was assessed by use of a flexiVent system after increasing doses of nebulized methacholine. Airway smooth muscle (ASM) thickening was measured by morphometric analysis. Sensitization to HDM (IgG and IgE), inflammatory cells, and goblet cell changes were also assessed. Increased EGFR activation was detected in HDM-treated mice, including in bronchiolar epithelial cells. In mice exposed to HDM for 6 wk, AHR and ASM thickening were reduced after erlotinib treatment and in EGFR-M mice. Sensitization to HDM and inflammatory cell counts were similar in all groups, except neutrophil counts, which were lower in the EGFR-M mice. Goblet cell metaplasia with HDM treatment was reduced by erlotinib, but not in EGFR-M transgenic mice. This study demonstrates that EGFR signaling, especially in the airway epithelium, plays an important role in mediating AHR and remodeling in a chronic allergic asthma model.

Exposure to allergen and diesel exhaust particles potentiates secondary allergen-specific memory responses promoting asthma susceptibility

BACKGROUND Exposure to traffic pollution particulate matter, predominantly diesel exhaust particles (DEPs), increases the risk of asthma and asthma exacerbation; however, the underlying mechanisms remain poorly understood. OBJECTIVE We sought to examine the effect of DEP exposure on the generation and persistence of allergen-specific memory T cells in asthmatic patients and translate these findings by determining the effect of early DEP exposure on the prevalence of allergic asthma in children. METHODS The effect of DEPs on house dust mite (HDM)-specific memory responses was determined by using an asthma model. Data from children enrolled in the Cincinnati Childhood Allergy and Air Pollution Study birth cohort were analyzed to determine the effect of DEP exposure on asthma outcomes. RESULTS DEP coexposure with HDM resulted in persistent TH2/TH17 CD127(+) effector/memory cells in the lungs, spleen, and lymph nodes of adult and neonatal mice. After 7 weeks of rest, a single exposure to HDM resulted in airway hyperresponsiveness and increased TH2 cytokine levels in mice that had been previously exposed to both HDM and DEPs versus those exposed to HDM alone. On the basis of these data, we examined whether DEP exposure was similarly associated with increased asthma prevalence in children in the presence or absence of allergen exposure/sensitization in the Cincinnati Childhood Allergy and Air Pollution Study birth cohort. Early-life exposure to high DEP levels was associated with significantly increased asthma prevalence among allergic children but not among nonallergic children. CONCLUSION These findings suggest that DEP exposure results in accumulation of allergen-specific TH2/TH17 cells in the lungs, potentiating secondary allergen recall responses and promoting the development of allergic asthma.

IL-13Rα2 Membrane and Soluble Isoforms Differ in Humans and Mice

Although mice have nanogram per milliliter serum levels of soluble (s) IL-13Rα2, humans lack sIL-13Rα2 in serum. Our data provide a mechanism for this biological divergence. In mice, discrete transcripts encoding soluble and membrane forms of IL-13Rα2 are generated by alternative splicing. We used small interfering RNA to specifically deplete the transcript encoding membrane (mem) IL-13Rα2 (full-length) or sIL-13Rα2 (ΔEx10) in murine cells. Depletion of the full-length transcript decreased memIL-13Rα2 but had no effect on the level of sIL-13Rα2 in cell supernatants at baseline or following cytokine stimulation. Depletion of the ΔEx10 transcript decreased sIL-13Rα2 in supernatants at baseline and following stimulation. In contrast to mice, we were unable to find a transcript encoding sIL-13Rα2 in humans and siRNA-mediated depletion of full-length IL-13Rα2 decreased both sIL-13Rα2 and memIL-13Rα2 in human cells. Inhibition of matrix metalloproteinases (MMP)/MMP-8 abolished production of sIL-13Rα2 from human cells. Thus, sIL-13Rα2 is derived exclusively from the memIL-13Rα2 transcript in humans through MMPs/MMP-8 cleavage of memIL-13Rα2, supporting a limited role for sIL-13Rα2 in humans and highlighting the potential importance of memIL-13Rα2 in human immunity. These observations require consideration when results of murine IL-13 studies are applied to humans.

Identification of KIF3A as a Novel Candidate Gene for Childhood Asthma Using RNA Expression and Population Allelic Frequencies Differences

Background Asthma is a chronic inflammatory disease with a strong genetic predisposition. A major challenge for candidate gene association studies in asthma is the selection of biologically relevant genes. Methodology/Principal Findings Using epithelial RNA expression arrays, HapMap allele frequency variation, and the literature, we identified six possible candidate susceptibility genes for childhood asthma including ADCY2, DNAH5, KIF3A, PDE4B, PLAU, SPRR2B. To evaluate these genes, we compared the genotypes of 194 predominantly tagging SNPs in 790 asthmatic, allergic and non-allergic children. We found that SNPs in all six genes were nominally associated with asthma (p<0.05) in our discovery cohort and in three independent cohorts at either the SNP or gene level (p<0.05). Further, we determined that our selection approach was superior to random selection of genes either differentially expressed in asthmatics compared to controls (p = 0.0049) or selected based on the literature alone (p = 0.0049), substantiating the validity of our gene selection approach. Importantly, we observed that 7 of 9 SNPs in the KIF3A gene more than doubled the odds of asthma (OR = 2.3, p<0.0001) and increased the odds of allergic disease (OR = 1.8, p<0.008). Our data indicate that KIF3A rs7737031 (T-allele) has an asthma population attributable risk of 18.5%. The association between KIF3A rs7737031 and asthma was validated in 3 independent populations, further substantiating the validity of our gene selection approach. Conclusions/Significance Our study demonstrates that KIF3A, a member of the kinesin superfamily of microtubule associated motors that are important in the transport of protein complexes within cilia, is a novel candidate gene for childhood asthma. Polymorphisms in KIF3A may in part be responsible for poor mucus and/or allergen clearance from the airways. Furthermore, our study provides a promising framework for the identification and evaluation of novel candidate susceptibility genes.

Downregulation of glutathione S-transferase pi in asthma contributes to enhanced oxidative stress

BACKGROUND Glutathione S-transferase pi (GSTPi) is the predominant redox regulator in the lung. Although evidence implicates an important role for GSTPi in asthma, the mechanism for this has remained elusive. OBJECTIVES We sought to determine how GSTPi is regulated in asthma and to elucidate its role in maintaining redox homeostasis. METHODS We elucidated the regulation of GSTPi in children with asthma and used murine models of asthma to determine the role of GSTPi in redox homeostasis. RESULTS Our findings demonstrate that GSTPi transcript levels are markedly downregulated in allergen- and IL-13-treated murine models of asthma through signal transducer and activator of transcription 6-dependent and independent pathways. Nuclear factor erythroid 2-related factor 2 was also downregulated in these models. The decrease in GSTPi expression was associated with decreased total glutathione S-transferase activity in the lungs of mice. Examination of cystine intermediates uncovered a functional role for GSTPi in regulating cysteine oxidation, whereby GSTPi-deficient mice exhibited increased oxidative stress (increase in percentage cystine) compared with wild-type mice after allergen challenge. GSTPi expression was similarly downregulated in children with asthma. CONCLUSIONS These data collectively suggest that downregulation of GSTPi after allergen challenge might contribute to the asthma phenotype because of disruption of redox homeostasis and increased oxidative stress. Furthermore, GSTPi might be an important therapeutic target for asthma, and evaluation of GSTPi expression might prove beneficial in identifying patients who would benefit from therapy targeting this pathway.

IL-13Rα2 Has a Protective Role in a Mouse Model of Cutaneous Inflammation

IL-13 is expressed in lesions of atopic dermatitis (AD) and has been associated with increased disease severity. IL-13 has two cognate receptors: IL-13Rα1 and IL-13Rα2. Although IL-13Rα2 expression is known to be induced in response to IL-13 in keratinocytes, its function in AD has never been evaluated. We characterized the loss of skin barrier function and the development of cutaneous inflammation in IL-13Rα2–null versus wild-type BALB/c mice following an epicutaneous allergen-sensitization/challenge model that shares similarities with human AD. Mice lacking IL-13Rα2 had significantly increased transepidermal water loss, cutaneous inflammation, peripheral eosinophilia, and IgG1 and IgE levels compared with wild-type mice. The rate of resolution of the cutaneous inflammation was not significantly altered in the IL-13Rα2–null mice. IL-13 induced expression of IL-13Rα2 in keratinocyte cell lines and primary human keratinocytes. Depletion of IL-13Rα2 in a keratinocyte cell line resulted in increased STAT6 signaling in response to IL-13. In conclusion, IL-13Rα2 serves a protective role in the pathogenesis of allergic inflammation and loss of skin barrier function in a mouse model of AD, suggesting that it may be an important endogenous regulator of IL-13–induced cutaneous inflammation in humans.

A nonredundant role for mouse Serpinb3a in the induction of mucus production in asthma

BACKGROUND Asthma is a major public health burden worldwide. Studies from our group and others have demonstrated that SERPINB3 and SERPINB4 are induced in patients with asthma; however, their mechanistic role in asthma has yet to be determined. OBJECTIVE To evaluate the role of Serpin3a, the murine homolog of SERPINB3 and SERPINB4, in asthma. METHODS We studied wild-type Balb/c and Serpinb3a-null mice in house dust mite or IL-13-induced asthma models and evaluated airway hyperresponsiveness, inflammation, and goblet cell hyperplasia. RESULTS Airway hyperresponsiveness and goblet cell hyperplasia were markedly attenuated in the Serpinb3a-null mice compared with the wild-type mice after allergen challenge, with minimal effects on inflammation. Expression of sterile alpha motif pointed domain containing v-ets avian erythroblastosis virus E26 oncogene homolog transcription factor (SPDEF), a transcription factor that mediates goblet cell hyperplasia, was decreased in the absence of Serpinb3a. IL-13-treated Serpinb3a-null mice showed attenuated airway hyperresponsiveness, inflammation, and mucus production. CONCLUSION Excessive mucus production and mucus plugging are key pathologic features of asthma, yet the mechanisms responsible for mucus production are not well understood. Our data reveal a novel nonredundant role for Serpinb3a in mediating mucus production through regulation of SPDEF expression. This pathway may be used to target mucus hypersecretion effectively.

SERPINB3/B4 Contributes to Early Inflammation and Barrier Dysfunction in an Experimental Murine Model of Atopic Dermatitis

Serine proteases are critical for epidermal barrier homeostasis and their aberrant expression and/or activity is associated with chronic skin diseases. Elevated levels of the serine protease inhibitors SERPINB3 and SERPINB4 are seen in patients with atopic dermatitis and psoriasis. However their mechanistic role in the skin is unknown. To evaluate the contribution of Serpinb3a (mouse homolog of SERPINB3 and SERPINB4) in atopic dermatitis, we examined the effect of topical Aspergillus fumigatus extract exposure in wild-type and Serpinb3a null mice on transepidermal water loss (TEWL), sensitization and inflammation. Allergen exposure induced Serpinb3a expression in the skin, along with increased TEWL, epidermal thickness, and skin inflammation, all of which were attenuated in the absence of Serpinb3a. Attenuated TEWL correlated with decreased expression of the pro-inflammatory marker S100A8. Silencing of SERPINB3/B4 in human keratinocytes decreased S100A8 expression supporting a role for SERPINB3/B4 in initiation of the acute inflammatory response. RNA-Seq analysis following allergen exposure identified a network of pro-inflammatory genes induced in the wild type mice that was absent in the Serpinb3a null mice. In conclusion, Serpinb3a deficiency attenuates barrier dysfunction and the early inflammatory response following cutaneous allergen exposure, supporting a role for Serpinb3a (mice) and SERPINB3/B4 (humans) early in atopic dermatitis.