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

Heavy Metal Exposure-Mediated Dysregulation of Sphingolipid Metabolism

Exposure to heavy metals (HMs) is often associated with inflammation and cell death, exacerbating respiratory diseases including asthma. Most inhaled particulate HM exposures result in the deposition of HM-bound fine particulate matter, PM2.5, in pulmonary cell populations. While localized high concentrations of HMs may be a causative factor, existing studies have mostly evaluated the effects of systemic or low-dose chronic HM exposures. This report investigates the impact of local high concentrations of specific HMs (NaAsO2, MnCl2, and CdCl2) on sphingolipid homeostasis and oxidative stress, as both play a role in mediating responses to HM exposure and have been implicated in asthma. Utilizing an in vitro model system and three-dimensional ex vivo human tissue models, we evaluated the expression of enzymatic regulators of the salvage, recycling, and de novo synthesis pathways of sphingolipid metabolism, and observed differential modulation in these enzymes between HM exposures. Sphingolipidomic analyses of specific HM-exposed cells showed increased levels of anti-apoptotic sphingolipids and reduced pro-apoptotic sphingolipids, suggesting activation of the salvage and de novo synthesis pathways. Differential sphingolipid regulation was observed within HM-exposed lung tissues, with CdCl2 exposure and NaAsO2 exposure activating the salvage and de novo synthesis pathway, respectively. Additionally, using spatial transcriptomics and quantitative real-time PCR, we identified HM exposure-induced transcriptomic signatures of oxidative stress in epithelial cells and human lung tissues.

ORMDL3 regulates NLRP3 inflammasome activation by maintaining ER-mitochondria contacts in human macrophages and dictates ulcerative colitis patient outcome

Genome-wide association studies in inflammatory bowel disease have identified risk loci in the orosomucoid-like protein 3/ORMDL sphingolipid biosynthesis regulator 3 (ORMDL3) gene to confer susceptibility to ulcerative colitis (UC), but the underlying functional relevance remains unexplored. Here, we found that a subpopulation of the UC patients who had higher disease activity shows enhanced expression of ORMDL3 compared to the patients with lower disease activity and the non-UC controls. We also found that the patients showing high ORMDL3 mRNA expression have elevated interleukin-1β cytokine levels indicating positive correlation. Further, knockdown of ORMDL3 in the human monocyte-derived macrophages resulted in significantly reduced interleukin-1β release. Mechanistically, we report for the first time that ORMDL3 contributes to a mounting inflammatory response via modulating mitochondrial morphology and activation of the NLRP3 inflammasome. Specifically, we observed an increased fragmentation of mitochondria and enhanced contacts with the endoplasmic reticulum (ER) during ORMDL3 over-expression, enabling efficient NLRP3 inflammasome activation. We show that ORMDL3 that was previously known to be localized in the ER also becomes localized to mitochondria-associated membranes and mitochondria during inflammatory conditions. Additionally, ORMDL3 interacts with mitochondrial dynamic regulating protein Fis-1 present in the mitochondria-associated membrane. Accordingly, knockdown of ORMDL3 in a dextran sodium sulfate -induced colitis mouse model showed reduced colitis severity. Taken together, we have uncovered a functional role for ORMDL3 in mounting inflammation during UC pathogenesis by modulating ER-mitochondrial contact and dynamics.

Overexpression of ORMDL3 confers sexual dimorphism in diet-induced non-alcoholic steatohepatitis

OBJECTIVE

The bioactive sphingolipid metabolites ceramide and sphingosine-1-phosphate (S1P) accumulate with overnutrition and have been implicated in non-alcoholic steatohepatitis (NASH) development. ORMDL3, a negative regulator of the rate-limiting step in ceramide biosynthesis, has been identified as an obesity-related gene. Therefore, we assessed the role of ORMDL3 in diet-induced obesity and development of NASH.

METHODS

Globally overexpressing Ormdl3-Flag transgenic mice (ORMDL3TG) were fed a western high-fat, carbohydrate and cholesterol enriched diet, with high fructose-glucose drinking water. Physiological, biochemical and sphingolipidomic analyses were employed to measure the effect of ORMDL3 overexpression on NASH development.

RESULTS

ORMDL3TG male but not female mice fed a western high-fat diet and sugar water had exacerbated adipocyte hypertrophy together with increased severity of white adipose inflammation and fibrosis. Hepatic steatosis, dyslipidemia, impaired glucose homeostasis, hyperinsulinemia, and insulin resistance were significantly more severe only in obese ORMDL3TG male mice that accompanied dramatic liver fibrosis, inflammation, and formation of hepatic crown-like structures, which are unique features of human and murine NASH. Obesogenic diet induces ORMDL expression in male mice but reduces it in females. Mechanistically, overexpression of Ormdl3 lowered the levels of S1P and ceramides only in obese female mice and antithetically increased them in tissues of obese males. ORMDL3TG male mice exhibited a much greater induction of the UPR, propagating ER stress that contributed to their early development of NASH.

CONCLUSIONS

This study uncovered a previously unrecognized role for ORMDL3 in sexual dimorphism important for the development and progression of NASH.

TNF-α and Poly(I:C) induction of A20 and activation of NF-κB signaling are independent of ABCF1 in human airway epithelial cells

ABCF1 is the most characterized member of the ABCF family in eukaryotes with proposed functions related to innate immunity in fibroblasts, macrophages, and epithelial cells. Currently, a mechanistic link between ABCF1 and immune responses in human airway epithelial cells (HAECs) remains to be clearly defined. The present study aimed at characterizing the function of ABCF1 in the context of nuclear factor nuclear factor κB (NF-κB) mediated pro-inflammatory responses in an immortalized human airway epithelial cell line, HBEC-6KT. We demonstrated that with ABCF1 silencing under basal conditions, TNF Alpha Induced Protein 3 (TNFAIP3/A20) protein expression and downstream expression and activation of transcription factors, NF-κB and Interferon regulatory factor 3 (IRF-3), were not disrupted. We followed with investigations of ABCF1 function under a pro-inflammatory stimuli that are known to be regulated by A20. We demonstrated that under Polyinosinic:polycytidylic acid (Poly(I:C)) and tumor Necrosis Factor-α (TNF-α) challenge with ABCF1 silencing, there was a significant reduction in secreted levels of interleukin-8 (IL-8) and a trend for reduced IL-6. However, we observed no changes to the expression levels of A20 and the activation status of the transcription factors, NF-κB and IRF-3. Collectively, these studies demonstrate that Poly(I:C) and TNF-α induced IL-8 is regulated by ABCF1 via pathways independent of NF-κB and IRF-3 activation.

Translational Analysis of Moderate to Severe Asthma GWAS Signals Into Candidate Causal Genes and Their Functional, Tissue-Dependent and Disease-Related Associations

Asthma affects more than 300 million people globally and is both under diagnosed and under treated. The most recent and largest genome-wide association study investigating moderate to severe asthma to date was carried out in 2019 and identified 25 independent signals. However, as new and in-depth downstream databases become available, the translational analysis of these signals into target genes and pathways is timely. In this study, unique (U-BIOPRED) and publicly available datasets (HaploReg, Open Target Genetics and GTEx) were investigated for the 25 GWAS signals to identify 37 candidate causal genes. Additional traits associated with these signals were identified through PheWAS using the UK Biobank resource, with asthma and eosinophilic traits amongst the strongest associated. Gene expression omnibus dataset examination identified 13 candidate genes with altered expression profiles in the airways and blood of asthmatic subjects, including MUC5AC and STAT6. Gene expression analysis through publicly available datasets highlighted lung tissue cell specific expression, with both MUC5AC and SLC22A4 genes showing enriched expression in ciliated cells. Gene enrichment pathway and interaction analysis highlighted the dominance of the HLA-DQA1/A2/B1/B2 gene cluster across many immunological diseases including asthma, type I diabetes, and rheumatoid arthritis. Interaction and prediction analyses found IL33 and IL18R1 to be key co-localization partners for other genes, predicted that CD274 forms co-expression relationships with 13 other genes, including the HLA-DQA1/A2/B1/B2 gene cluster and that MUC5AC and IL37 are co-expressed. Drug interaction analysis revealed that 11 of the candidate genes have an interaction with available therapeutics. This study provides significant insight into these GWAS signals in the context of cell expression, function, and disease relationship with the view of informing future research and drug development efforts for moderate-severe asthma.

ORMDL3 regulates cigarette smoke-induced endoplasmic reticulum stress in airway smooth muscle cells

BACKGROUND

Orosomucoid 1-like protein 3 (ORMDL3), a transmembrane protein localized in the endoplasmic reticulum (ER), has been genetically associated with chronic obstructive pulmonary disease (COPD), in addition to childhood-onset asthma. However, the functional role of ORMDL3 in the pathogenesis of COPD is still unknown.

OBJECTIVE

Because cigarette smoke is the major risk factor for COPD, we aimed to investigate the role of ORMDL3 in cigarette smoke-induced human airway smooth muscle cell (HASMC) injury.

METHODS

The mRNA and protein expression of ORMDL3 was examined in HASMCs from nonsmokers and smokers without or with COPD. Knockdown of ORMDL3 in primary healthy HASMCs was performed using small interfering RNA before exposure to cigarette smoke medium (CSM) for 24 hours. Inflammatory, proliferative/apoptotic, ER stress, and mitochondrial markers were evaluated.

RESULTS

Elevation of ORMDL3 mRNA and protein expression was observed in HASMCs of smokers without or with COPD. CSM caused significant upregulation of ORMDL3 expression in healthy nonsmokers. ORMDL3 knockdown regulated CSM-induced inflammation, cell proliferation, and apoptosis. Silencing ORMDL3 led to reduction of CSM-induced ER stress via inhibition of unfolded protein response pathways such as activating transcription factor 6 and protein kinase RNA-like ER kinase. ORMDL3 was also involved in CSM-induced mitochondrial dysfunction via the mitochondrial fission process.

CONCLUSIONS

We report the induction of ORMDL3 in HASMCs after cigarette smoke exposure. ORMDL3 may mediate cigarette smoke-induced activation of unfolded protein response pathways during airway smooth muscle cell injury.

Ablation of ORMDL3 impairs adipose tissue thermogenesis and insulin sensitivity by increasing ceramide generation

Objective

Genome-wide association studies identified ORMDL3 as an obesity-related gene, and its expression was negatively correlated with body mass index. However, the precise biological roles of ORMDL3 in obesity and lipid metabolism remain uncharacterized. Here, we investigate the function of ORMDL3 in adipose tissue thermogenesis and high fat diet (HFD)-induced insulin resistance.

Methods

Ormdl3-deficient (Ormdl3^−/−) mice were employed to delineate the function of ORMDL3 in brown adipose tissue (BAT) thermogenesis and white adipose tissue (WAT) browning. Glucose and lipid homeostasis in Ormdl3^−/− mice fed a HFD were assessed. The lipid composition in adipose tissue was evaluated by mass spectrometry. Primary adipocytes in culture were used to determine the mechanism by which ORMDL3 regulates white adipose browning.

Results

BAT thermogenesis and WAT browning were significantly impaired in Ormdl3^−/− mice upon cold exposure or administration with the β3 adrenergic agonist. In addition, compared to WT mice, Ormdl3^−/− mice displayed increased weight gain and insulin resistance in response to HFD. The induction of uncoupling protein 1 (UCP1), a marker of thermogenesis, was attenuated in primary adipocytes derived from Ormdl3^−/− mice. Importantly, ceramide levels were elevated in the adipose tissue of Ormdl3^−/− mice. In addition, the reduction in thermogenesis and increase in body weight caused by Ormdl3 deficiency could be rescued by inhibiting the production of ceramides.

Conclusion

Our findings suggest that ORMDL3 contributes to the regulation of BAT thermogenesis, WAT browning, and insulin resistance.

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ORMDL3 is downregulated in WAT of obese mice and humans and upregulated in response to cold exposure.

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Loss of Ormdl3 in mice exacerbates the overall metabolic phenotypes caused by HFD-induced obesity.

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Ormdl3 ablation impairs BAT thermogenesis and WAT browning.

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Ormdl3 deficiency is sufficient for negatively regulating ceramide levels.

ORMDL3 Functions as a Negative Regulator of Antigen-Mediated Mast Cell Activation via an ATF6-UPR-Autophagy-Dependent Pathway

Antigen (Ag)-mediated mast cell activation plays a critical role in the immunopathology of IgE-dependent allergic diseases. Restraining the signaling cascade that regulates the release of mast cell-derived inflammatory mediators is an attractive therapeutic strategy to treat allergic diseases. Orosomucoid-like-3 (ORMDL3) regulates the endoplasmic reticulum stress (ERS)-induced unfolded protein response (UPR) and autophagy. Although ERS/UPR/autophagy pathway is crucial in Ag-induced mast cell activation, it is unknown whether ORMDL3 regulates the ERS/UPR/autophagy pathway during mast cell activation. In this study, we found that ORMDL3 expression was downregulated in Ag-activated MC/9 cells. Overexpression of ORMDL3 significantly inhibited degranulation, and cytokine/chemokine production, while the opposite effect was observed with ORMDL3 knockdown in MC/9 cells. Importantly, ORMDL3 overexpression upregulated mediators of ERS-UPR (SERCA2b, ATF6) and autophagy (Beclin 1 and LC3BII). Knockdown of ATF6 and/or inhibition of autophagy reversed the decreased degranulation and cytokine/chemokine expression caused by ORMDL3 overexpression. Moreover, in vivo knockdown of ORMDL3 and/or ATF6 enhanced passive cutaneous anaphylaxis (PCA) reactions in mouse ears. These data indicate that ORMDL3 suppresses Ag-mediated mast cell activation via an ATF6 UPR-autophagy dependent pathway and thus, attenuates anaphylactic reaction. This highlights a potential mechanism to intervene in mast cell mediated diseases.

Role of unfolded proteins in lung disease

The lungs are exposed to a range of environmental toxins (including cigarette smoke, air pollution, asbestos) and pathogens (bacterial, viral and fungal), and most respiratory diseases are associated with local or systemic hypoxia. All of these adverse factors can trigger endoplasmic reticulum (ER) stress. The ER is a key intracellular site for synthesis of secretory and membrane proteins, regulating their folding, assembly into complexes, transport and degradation. Accumulation of misfolded proteins within the lumen results in ER stress, which activates the unfolded protein response (UPR). Effectors of the UPR temporarily reduce protein synthesis, while enhancing degradation of misfolded proteins and increasing the folding capacity of the ER. If successful, homeostasis is restored and protein synthesis resumes, but if ER stress persists, cell death pathways are activated. ER stress and the resulting UPR occur in a range of pulmonary insults and the outcome plays an important role in many respiratory diseases. The UPR is triggered in the airway of patients with several respiratory diseases and in corresponding experimental models. ER stress has been implicated in the initiation and progression of pulmonary fibrosis, and evidence is accumulating suggesting that ER stress occurs in obstructive lung diseases (particularly in asthma), in pulmonary infections (some viral infections and in the setting of the cystic fibrosis airway) and in lung cancer. While a number of small molecule inhibitors have been used to interrogate the role of the UPR in disease models, many of these tools have complex and off-target effects, hence additional evidence (eg, from genetic manipulation) may be required to support conclusions based on the impact of such pharmacological agents. Aberrant activation of the UPR may be linked to disease pathogenesis and progression, but at present, our understanding of the context-specific and disease-specific mechanisms linking these processes is incomplete. Despite this, the ability of the UPR to defend against ER stress and influence a range of respiratory diseases is becoming increasingly evident, and the UPR is therefore attracting attention as a prospective target for therapeutic intervention strategies.

ORMDL3 and Asthma: Linking Sphingolipid Regulation to Altered T Cell Function

Orosomucoid like 3 (ORMDL3) encodes an ER-resident transmembrane protein that regulates the activity of serine palmitoyltransferase (SPT), the first and rate-limiting enzyme for sphingolipid biosynthesis in cells. A decade ago, several genome wide association studies revealed single nucleotide polymorphisms associated with increased ORMDL3 protein expression and susceptibility to allergic asthma. Since that time, numerous studies have investigated how altered ORMDL3 expression might predispose to asthma and other autoimmune/inflammatory diseases. In this brief review, we focus on growing evidence suggesting that heightened ORMDL3 expression specifically in CD4⁺ T lymphocytes, the central orchestrators of adaptive immunity, constitutes a major underlying mechanism of asthma pathogenesis by skewing their differentiation and function. Furthermore, we explore how sphingolipid modulation in T cells might be responsible for these effects, and how further studies may interrogate this intriguing hypothesis.

Increased expression of serine palmitoyl transferase and ORMDL3 polymorphism are associated with eosinophilic inflammation and airflow limitation in aspirin-exacerbated respiratory disease

BACKGROUND

Patients with aspirin-exacerbated respiratory disease (AERD) are known to have poor clinical outcomes. The pathogenic mechanisms have not yet been completely understood.

OBJECTIVE

We aimed to assess the involvement of the de-novo synthetic pathway of sphingolipid metabolism in patients with AERD compared to those with aspirin tolerant asthma (ATA).

METHODS

A total of 63 patients with AERD and 79 patients with ATA were enrolled in this study. Analysis of mRNA expression of serine palmitoyl transferase, long-chain base subunit 2 (SPTLC2) and genotyping of ORMDL3 SNP (rs7216389) was performed.

RESULTS

Significantly higher levels of SPTLC2 mRNA expression were noted in patients with AERD, which showed significant positive correlations with peripheral/sputum eosinophil counts and urine LTE4 (all P<0.05). The levels of SPTLC2 mRNA expression showed significant negative correlations with the level of FEV1 and FEV1/FVC (P = 0.033, r = -0.274; P = 0.019, r = -0.299, respectively). Genotype frequencies of ORMDL3 SNP (rs7216389) showed no significant differences between the AERD and ATA groups. Patients with AERD carrying the TT genotype of ORMDL3 had significantly lower levels of FVC (%) and PC20 methacholine than those carrying the CT or CC genotype (P = 0.026 and P = 0.030).

CONCLUSION & CLINICAL RELEVANCE

This is the first study that shows the dysregulated de novo synthetic pathway of sphingolipids may be involved in the eosinophilic inflammation and airflow limitation in AERD.

Differential Expression of Ormdl Genes in the Islets of Mice and Humans with Obesity

The orosomucoid-like (Ormdl) proteins play a critical role in sphingolipid homeostasis, inflammation, and ER stress, all of which are associated with obesity and βcell dysfunction. However, their roles in β cells and obesity remain unknown. Here, we show that islets from overweight/obese human donors displayed marginally reduced ORMDL1-2 expression, whereas ORMDL3 expression was significantly downregulated compared with islets from lean donors. In contrast, Ormdl3 was substantially upregulated in the islets of leptin-deficient obese (ob/ob) mice compared with lean mice. Treatment of ob/ob mice and their islets with leptin markedly reduced islet Ormld3 expression. Ormdl3 knockdown in a β cell line induced expression of pro-apoptotic markers, which was rescued by ceramide synthase inhibitor fumonisin B1. Our results reveal differential expression of Ormdl3 in the islets of a mouse model and humans with obesity, highlight the potential effect of leptin in this differential regulation, and suggest a role for Ormdl3 in β cell apoptosis.

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Islets of overweight/obese human donors display markedly reduced ORMDL3 expression

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Ormdl3 expression was significantly upregulated in the islets of ob/ob mice

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Leptin treatment markedly reduced Ormld3 expression in the islets of ob/ob mice

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Fumonisin B1 restores increased apoptotic marker levels induced by Ormdl3 silencing

Update on the role of endoplasmic reticulum stress in asthma

Asthma has long attracted extensive attention because of its recurring symptoms of reversible airflow obstruction, airway hyperresponsiveness (AHR) and airway inflammation. Although accumulating evidence has enabled gradual increases in understanding of the pathogenesis of asthma, many questions regarding the mechanisms underlying asthma onset and progression remain unanswered. Recent advances delineating the potential functions of endoplasmic reticulum (ER) stress in meeting the need for an airway hypersensitivity response have revealed critical roles of unfolded protein response (UPR) pathways in asthma. In this review, we highlight the roles of ER stress and UPR activation in the etiology, pathogenesis and treatment of asthma and discuss whether the related mechanisms could be targets for therapeutic strategies.

The ORMDL3 asthma susceptibility gene regulates systemic ceramide levels without altering key asthma features in mice

BACKGROUND

Genome-wide association studies in asthma have repeatedly identified single nucleotide polymorphisms in the ORM (yeast)-like protein isoform 3 (ORMDL3) gene across different populations. Although the ORM homologues in yeast are well-known inhibitors of sphingolipid synthesis, it is still unclear whether and how mammalian ORMDL3 regulates sphingolipid metabolism and whether altered sphingolipid synthesis would be causally related to asthma risk.

OBJECTIVE

We sought to examine the in vivo role of ORMDL3 in sphingolipid metabolism and allergic asthma.

METHODS

Ormdl3-LacZ reporter mice, gene-deficient Ormdl3^-/- mice, and overexpressing Ormdl3^Tg/wt mice were exposed to physiologically relevant aeroallergens, such as house dust mite (HDM) or Alternaria alternata, to induce experimental asthma. Mass spectrometry-based sphingolipidomics were performed, and airway eosinophilia, T_H2 cytokine production, immunoglobulin synthesis, airway remodeling, and bronchial hyperreactivity were measured.

RESULTS

HDM challenge significantly increased levels of total sphingolipids in the lungs of HDM-sensitized mice compared with those in control mice. In Ormdl3^Tg/wt mice the allergen-induced increase in lung ceramide levels was significantly reduced, whereas total sphingolipid levels were not affected. Conversely, in liver and serum, levels of total sphingolipids, including ceramides, were increased in Ormdl3^-/- mice, whereas they were decreased in Ormdl3^Tg/wt mice. This difference was independent of allergen exposure. Despite these changes, all features of asthma were identical between wild-type, Ormdl3^Tg/wt, and Ormdl3^-/- mice across several models of experimental asthma.

CONCLUSION

ORMDL3 regulates systemic ceramide levels, but genetically interfering with Ormdl3 expression does not result in altered experimental asthma.

Investigating the regulatory role of ORMDL3 in airway barrier dysfunction using in vivo and in vitro models

The airway epithelium (AE) is the main protective barrier between the host and external environmental factors causing asthma. Allergens or pathogens induce AE dysfunction, including epithelial permeability alteration, trans‑epithelial electrical resistance (TEER) reduction, upregulation of inflammatory mediators and downregulation of junctional complex molecules. Orosomucoid‑like protein isoform 3 (ORMDL3), a gene closely associated with childhood onset asthma, is involved in airway inflammation and remodeling. It was hypothesized that ORMDL3 plays an important role in regulating AE barrier function. In vivo [chronic asthma induced by ovalbumin‑respiratory syncytial virus (OVA‑RSV)] in mice) and in vitro (human bronchial epithelial cells and 16HBE cells) models were used to assess ORMDL3's role in AE function regulation, evaluating paracellular permeability, TEER and the expression levels of junctional complex molecules. The effects of ORMDL3 on the extracellular signal‑regulated protein kinase (ERK) pathway were determined. In mice with OVA‑RSV induced chronic asthma, ORMDL3 and sphingosine kinase 1 (SPHK1) were upregulated whereas the junction related proteins Claudin‑18 and E‑cadherin were downregulated. Overexpression of ORMDL3 resulted in decreased TEER, downregulation of junctional complex molecules and induced epithelial permeability. In contrast, ORMDL3 inhibition showed the opposite effects. In 16HBE cells, ORMDL3 overexpression induced SPHK1 distribution and activity, while SPHK1 inhibition resulted in increased TEER upon administration of an ORMDL3 agonist or ORMDL3 overexpression. In addition, ERK activation occurred downstream of SPHK1 activation in 16HBE cells. High levels of ORMDL3 result in damaged AE barrier function by inducing the SPHK1/ERK pathway.

Conjugated bile acids attenuate allergen-induced airway inflammation and hyperresponsiveness by inhibiting UPR transducers

Conjugated bile acids (CBAs), such as tauroursodeoxycholic acid (TUDCA), are known to resolve the inflammatory and unfolded protein response (UPR) in inflammatory diseases, such as asthma. Whether CBAs exert their beneficial effects on allergic airway responses via 1 arm or several arms of the UPR, or alternatively through the signaling pathways for conserved bile acid receptor, remains largely unknown. We used a house dust mite-induced (HDM-induced) murine model of asthma to evaluate and compare the effects of 5 CBAs and 1 unconjugated bile acid in attenuating allergen-induced UPR and airway responses. Expression of UPR-associated transcripts was assessed in airway brushings from human patients with asthma and healthy subjects. Here we show that CBAs, such as alanyl β-muricholic acid (AβM) and TUDCA, significantly decreased inflammatory, immune, and cytokine responses; mucus metaplasia; and airway hyperresponsiveness, as compared with other CBAs in a model of allergic airway disease. CBAs predominantly bind to activating transcription factor 6α (ATF6α) compared with the other canonical transducers of the UPR, subsequently decreasing allergen-induced UPR activation and resolving allergic airway disease, without significant activation of the bile acid receptors. TUDCA and AβM also attenuated other HDM-induced ER stress markers in the lungs of allergic mice. Quantitative mRNA analysis of airway epithelial brushings from human subjects demonstrated that several ATF6α-related transcripts were significantly upregulated in patients with asthma compared with healthy subjects. Collectively, these results demonstrate that CBA-based therapy potently inhibits the allergen-induced UPR and allergic airway disease in mice via preferential binding of the canonical transducer of the UPR, ATF6α. These results potentially suggest a novel avenue to treat allergic asthma using select CBAs.

Nitric oxide alters hyaluronan deposition by airway smooth muscle cells

Asthma is a chronic inflammatory disease that is known to cause changes in the extracellular matrix, including changes in hyaluronan (HA) deposition. However, little is known about the factors that modulate its deposition or the potential consequences. Asthmatics with high levels of exhaled nitric oxide (NO) are characterized by greater airway reactivity and greater evidence of airway inflammation. Based on these data and our previous work we hypothesized that excessive NO promotes the pathologic production of HA by airway smooth muscle cells (SMCs). Exposure of cultured SMCs to various NO donors results in the accumulation of HA in the form of unique, cable-like structures. HA accumulates rapidly after exposure to NO and can be seen as early as one hour after NO treatment. The cable-like HA in NO-treated SMC cultures supports the binding of leukocytes. In addition, NO produced by murine macrophages (RAW cells) and airway epithelial cells also induces SMCs to produce HA cables when grown in co-culture. The modulation of HA by NO appears to be independent of soluble guanylate cyclase. Taken together, NO-induced production of leukocyte-binding HA by SMCs provides a new potential mechanism for the non-resolving airway inflammation in asthma and suggests a key role of non-immune cells in driving the chronic inflammation of the submucosa. Modulation of NO, HA and the consequent immune cell interactions may serve as potential therapeutic targets in asthma.

Oxidative and endoplasmic reticulum stress in respiratory disease

Oxidative stress and endoplasmic reticulum (ER) stress are related states that can occur in cells as part of normal physiology but occur frequently in diseases involving inflammation. In this article, we review recent findings relating to the role of oxidative and ER stress in the pathophysiology of acute and chronic nonmalignant diseases of the lung, including infections, cystic fibrosis, idiopathic pulmonary fibrosis and asthma. We also explore the potential of drugs targeting oxidative and ER stress pathways to alleviate disease.

The Role of Autophagy and Related MicroRNAs in Inflammatory Bowel Disease

Accumulating evidence demonstrates that microRNA- (miR-) mediated posttranscriptional regulation plays an important role in autophagy in inflammatory bowel disease (IBD), a disease that is difficult to manage clinically because of the associated chronic recurrent nonspecific inflammation. Research indicates that microRNAs regulate autophagy via different pathways, playing an important role in the IBD process and providing a new perspective for IBD research. Related studies have shown that miR-142-3p, miR-320, miR-192, and miR-122 target NOD2, an IBD-relevant autophagy gene, to modulate autophagy in IBD. miR-142-3p, miR-93, miR-106B, miR-30C, miR-130a, miR-346, and miR-20a regulate autophagy by targeting ATG16L1 through several different pathways. miR-196 can downregulate IRGM and suppress autophagy by inhibiting the accumulation of LC3II. During the endoplasmic reticulum stress response, miR-665, miR-375, and miR-150 modulate autophagy by regulating the unfolded protein response, which may play an important role in IBD intestinal fibrosis. Regarding autophagy-related pathways, miR-146b, miR-221-5p, miR-132, miR-223, miR-155, and miR-21 regulate NF-κB or mTOR signaling to induce or inhibit autophagy in intestinal cells by releasing anti- or proinflammatory factors, respectively.

Phenotypic and genetic aspects of epithelial barrier function in asthmatic patients

The bronchial epithelium is continuously exposed to a multitude of noxious challenges in inhaled air. Cellular contact with most damaging agents is reduced by the action of the mucociliary apparatus and by formation of a physical barrier that controls passage of ions and macromolecules. In conjunction with these defensive barrier functions, immunomodulatory cross-talk between the bronchial epithelium and tissue-resident immune cells controls the tissue microenvironment and barrier homeostasis. This is achieved by expression of an array of sensors that detect a wide variety of viral, bacterial, and nonmicrobial (toxins and irritants) agents, resulting in production of many different soluble and cell-surface molecules that signal to cells of the immune system. The ability of the bronchial epithelium to control the balance of inhibitory and activating signals is essential for orchestrating appropriate inflammatory and immune responses and for temporally modulating these responses to limit tissue injury and control the resolution of inflammation during tissue repair. In asthmatic patients abnormalities in many aspects of epithelial barrier function have been identified. We postulate that such abnormalities play a causal role in immune dysregulation in the airways by translating gene-environment interactions that underpin disease pathogenesis and exacerbation.

ORMDL3 Facilitates the Survival of Splenic B Cells via an ATF6α-Endoplasmic Reticulum Stress-Beclin1 Autophagy Regulatory Pathway

The genetic association of orosomucoid-like 3 (ORMDL3) with an array of immunoinflammatory disorders has been recently unraveled in multiple ethnic groups, and functional exploration has received attention of the particular relevance of this gene in endoplasmic reticulum stress, lipid metabolism, and inflammatory response. In this study, we demonstrated the upregulation of ORMDL3 in both patients with systemic lupus erythematosus and lupus mice compared with controls. By establishing ORMDL3 knockout mice (Ormdl3^-/-), we showed that silencing Ormdl3 in vivo significantly decreased the proportions of mature B lymphocytes and transitional 2B cells in spleen and B1a cells from abdominal cavity perfusion fluid, the secretion of IgG and IgM, and the expression of Baff. Additionally, knockdown of Ormdl3 augmented the apoptosis of total splenic cells and splenic CD19⁺ B cells but did not affect B cell proliferation and cell cycle. Subsequently, we in vitro and in vivo demonstrated that ORMDL3 potentially mediates the autophagy via the ATF 6-Beclin1 autophagy pathway, and it facilitates the survival of splenic B cells via promoting autophagy and suppressing apoptosis. Taken together, we uncovered a role of ORMDL3 in fine-tuning B cell development and survival, besides highlighting a potential mechanism by which ORMDL3 regulates autophagy via ATF6 pathway.

Environment Changes Genetic Effects on Respiratory Conditions and Allergic Phenotypes

The prevalence of asthma and allergic diseases is disproportionately distributed among different populations, with an increasing trend observed in Western countries. Here we investigated how the environment affected genotype-phenotype association in a genetically homogeneous, but geographically separated population. We evaluated 18 single nucleotide polymorphisms (SNPs) corresponding to 8 genes (ADAM33, ALOX5, LT-α, LTC4S, NOS1, ORMDL3, TBXA2R and TNF-α), the lung function and five respiratory/allergic conditions (ever asthma, bronchitis, rhinitis, dermatitis and atopy) in two populations of Inuit residing either in the westernized environment of Denmark or in the rural area of Greenland. Our results showed that lung function was associated with genetic variants in ORMDL3, with polymorphisms having a significant interaction with place of residence. LT-α SNP rs909253 and rs1041981 were significantly associated with bronchitis risk. LT-α SNP rs2844484 was related to dermatitis susceptibility and was significantly influenced by the place of residence. The observed gene-phenotype relationships were exclusively present in one population and absent in the other population. We conclude that the genotype-phenotype associations relating to bronchitis and allergy susceptibility are dependent on the environment and that environmental factors/lifestyles modify genetic predisposition and change the genetic effects on diseases.

Endoplasmic reticulum stress in lung disease

Exposure to inhaled pollutants, including fine particulates and cigarette smoke is a major cause of lung disease in Europe. While it is established that inhaled pollutants have devastating effects on the genome, it is now recognised that additional effects on protein folding also drive the development of lung disease. Protein misfolding in the endoplasmic reticulum affects the pathogenesis of many diseases, ranging from pulmonary fibrosis to cancer. It is therefore important to understand how cells respond to endoplasmic reticulum stress and how this affects pulmonary tissues in disease. These insights may offer opportunities to manipulate such endoplasmic reticulum stress pathways and thereby cure lung disease.

Upregulation of miR-665 promotes apoptosis and colitis in inflammatory bowel disease by repressing the endoplasmic reticulum stress components XBP1 and ORMDL3

MicroRNAs are critical post-transcriptional regulators of gene expression and key mediators of pathophysiology of inflammatory bowel disease (IBD). This study is aimed to study the role of miR-665 in the progression of IBD. Real-time PCR analysis was used to determine miR-665 expression in 89 freshly isolated IBD samples and dextran sulfate sodium (DSS)-induced colonic mucosal tissues. The role of miR-665 in inducing apoptosis and colitis were examined by Annexin V, TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) staining, colony formation in vitro and DSS-induced colitis mice model in vivo. Moreover, luciferase reporter assay, western blot analysis and microribonucleoprotein immunoprecipitation were performed to determine that miR-665 directly repressed XBP1 (X-box-binding protein-1) and ORMDL3 expression. Herein, our results revealed that miR-665 was markedly upregulated in active colitis. Gain-of-function and loss-of-function studies showed that ectopic expression of miR-665 promoted apoptosis under different inflammatory stimuli. Importantly, delivery of miR-665 mimic promoted, while injection of antagomiR-665 markedly impaired DSS-induced colitis in vivo. Mechanistically, we demonstrated that miR-665 induced apoptosis by inhibiting XBP1 and ORMDL3. Taken together, our findings reveal a new regulatory mechanism for ER stress signaling and suggest that miR-665 might be a potential target in IBD therapy.

Benomyl-induced effects of ORMDL3 overexpression via oxidative stress in human bronchial epithelial cells

The respiratory system is a major site of exposure route during pesticide use. Although pesticide exposure is associated with chronic respiratory diseases including asthma, the underlying pathophysiological mechanism remains to be elucidated. In this study, we investigated the in vitro effects of benomyl-induced ORMDL3 overexpression on the toxicological mechanism using the human bronchial epithelial cell line 16HBE14o-. Benomyl increased reactive oxygen species and Ca²⁺ levels, and asthma-related ADAM33 and ORMDL3 expression in 16HBE14o- cells. Considering the change in Ca²⁺ level and protein expression, we focused on ORMDL3 to elucidate the mechanism of benomyl-induced asthma. Antioxidant treatment showed that benomyl-induced ORMDL3 and endoplasmic reticulum stress could be triggered by oxidative stress. Furthermore, ORMDL3 knockdown alleviated the effects of benomyl on intracellular Ca²⁺, and the expression of metalloproteinases, and proinflammatory cytokines involved in the pathogenesis of asthma. In conclusion, our results suggest that benomyl-induced ORMDL3 overexpression via oxidative stress might be a mechanism involved in asthma. Moreover, antioxidants and alleviating mechanisms that reduce ORMDL3 levels could serve as promising therapeutic targets for pesticide-induced asthma.

Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Airway structure and function are key aspects of normal lung development, growth, and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, chronic obstructive pulmonary disease, and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and, finally, interactions with other airway cell types such as epithelium, fibroblasts, and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This review emphasizes established and recent discoveries that underline the central role of ASM and sets the stage for future research toward understanding how ASM plays a central role by being both upstream and downstream in the many interactive processes that determine airway structure and function in health and disease.

Effect of a chemical chaperone, tauroursodeoxycholic acid, on HDM-induced allergic airway disease

Endoplasmic reticulum (ER) stress-induced unfolded protein response plays a critical role in inflammatory diseases, including allergic airway disease. However, the benefits of inhibiting ER stress in the treatment of allergic airway disease are not well known. Herein, we tested the therapeutic potential of a chemical chaperone, tauroursodeoxycholic acid (TUDCA), in combating allergic asthma, using a mouse model of house dust mite (HDM)-induced allergic airway disease. TUDCA was administered during the HDM-challenge phase (preventive regimen), after the HDM-challenge phase (therapeutic regimen), or therapeutically during a subsequent HDM rechallenge (rechallenge regimen). In the preventive regimen, TUDCA significantly decreased HDM-induced inflammation, markers of ER stress, airway hyperresponsiveness (AHR), and fibrosis. Similarly, in the therapeutic regimen, TUDCA administration efficiently decreased HDM-induced airway inflammation, mucus metaplasia, ER stress markers, and AHR, but not airway remodeling. Interestingly, TUDCA administered therapeutically in the HDM rechallenge regimen markedly attenuated HDM-induced airway inflammation, mucus metaplasia, ER stress markers, methacholine-induced AHR, and airway fibrotic remodeling. These results indicate that the inhibition of ER stress in the lungs through the administration of chemical chaperones could be a valuable strategy in the treatment of allergic airway diseases.

Polymorphisms and haplotypes of the chromosome locus 17q12-17q21.1 contribute to adult asthma susceptibility in Slovenian patients

One of the major asthma susceptibility loci is 17q12-17q21.1, but the relationship between this locus and adult asthma is unclear. Association analysis of 13 single nucleotide polymorphisms (SNPs) and haplotypes from 17q12-17q21.1 was performed in 418 adult patients with asthma and 288 controls from Slovenia. Single SNP analysis revealed only marginal associations with adult asthma for SNPs located in GSDMA, GSDMB, ORMDL3 and ZPBP2 genes, and rs7219080 was the most highly associated. Analyses of asthma phenotypes found no association with atopy or lung function, but rs2305480 and rs8066582 were associated with childhood asthma and rs9916279 was associated with asthma in smokers. Notably, haplotypes consisting of rs9916279, rs8066582, rs1042658, and rs2302777 harbouring PSMD3, CSF3 and MED24 genes were highly associated with asthma. The four most common haplotypes, TCCG, TTTA, CCCA and TTCA, were more frequent in patients with asthma, whereas TTCG, TCCA, TCTA and TTTG were more frequent in controls. Only 3% of asthma patients belonged to haplotypes TTCG, TCCA, TCTA and TTTG compared with nearly one-third (31%) of controls. Associations confirmed that the 17q12-17q21.1 locus harbours a genetic determinant for asthma risk in adults and suggest that in addition to the previously known ORMDL3-GSDM locus, CSF3-PSMD3-MED24 also plays a role in asthma pathogenesis.

Icariin inhibits foam cell formation by down-regulating the expression of CD36 and up-regulating the expression of SR-BI

Icariin is an important pharmacologically active flavonol diglycoside that can inhibit inflammation in lipopolysaccharide (LPS)-stimulated macrophages. However, little is known about the molecular mechanisms underlying the inhibitory effect of Icariin in the formation of foam cells. In this study, macrophages were cultured with LPS and oxidized low-density lipoprotein (oxLDL) in the presence or absence of Icariin. RT-PCR and western blot were used to detect the levels of mRNA and protein expression of CD36, scavenger receptor class B type I (SR-BI) and the phosphorylation of p38MAPK. It was demonstrated that 4 µM or 20 µM Icariin treatment significantly inhibited the cholesterol ester (CE)/total cholesterol (TC) and oxLDL-mediated foam cell formation (P < 0.05). The binding of oxLDL to LPS-activated macrophages was also significantly hindered by Icariin (P < 0.05). Furthermore, Icariin down-regulated the expression of CD36 in LPS-activated macrophages in a dose-dependent manner and CD36 over-expression restored the inhibitory effect of Icariin on foam cell formation. The phosphorylation of p38MAPK was reduced by Icariin, indicating that Icariin reduced the expression of CD36 through the p38MAPK pathway. In addition, Icariin up-regulated SR-BI protein expression in a dose-dependent manner, and SR-BI gene silencing restored the inhibitory effect of Icariin on foam cell formation. These data demonstrate that Icariin inhibited foam cell formation by down-regulating the expression of CD36 and up-regulating the expression of SR-BI. Therefore, our findings provide a new explanation as to why Icariin could inhibit atherosclerosis.

Airway reactivity and sphingolipids-implications for childhood asthma

Asthma is a clinically heterogeneous disorder, whose onset and progression results from a complex interplay between genetic susceptibility, allergens, and viral triggers. Sphingolipids and altered sphingolipid metabolism have emerged as potential key contributors to the pathogenesis of asthma. Orosomucoid-like 3 gene (ORMDL3) and the asthma susceptibility locus 17q21 have been strongly and reproducibly linked to childhood asthma, but how this gene is functionally linked to asthma is incompletely understood. ORMDL proteins play an integral role in sphingolipid homeostasis and synthesis, and asthma-associated ORMDL3 polymorphisms have been associated with early viral respiratory infections and increased risk of asthma. ORMDL proteins act as inhibitors of serine palmitoyl-CoA transferase (SPT), the rate-limiting enzyme for de novo sphingolipid synthesis, and decreased sphingolipid synthesis through SPT increases airway hyperreactivity, which is independent of allergy or inflammation. In allergic models of asthma, the sphingolipid mediators sphingosine-1-phosphate (S1P) and ceramide have been shown to be important signaling molecules for airway hyperreactivity, mast cell activation, and inflammation. This review will highlight how sphingolipids and altered sphingolipid metabolism may contribute towards the underlying mechanisms of childhood asthma.

Aberrant ORM (yeast)-like protein isoform 3 (ORMDL3) expression dysregulates ceramide homeostasis in cells and ceramide exacerbates allergic asthma in mice

BACKGROUND

Asthma, a chronic inflammatory condition defined by episodic shortness of breath with expiratory wheezing and cough, is a serious health concern affecting more than 250 million persons. Genome-wide association studies have identified ORM (yeast)-like protein isoform 3 (ORMDL3) as a gene associated with susceptibility to asthma. Although its yeast ortholog is a negative regulator of de novo ceramide biosynthesis, how ORMDL3 contributes to asthma pathogenesis is not known.

OBJECTIVES

We sought to decipher the molecular mechanism for the pathologic functions of ORMDL3 in asthma and the relationship to its evolutionarily conserved role in regulation of ceramide homeostasis.

METHODS

We determined the relationship between expression of ORMDL3 and ceramide in epithelial and inflammatory cells and in asthma pathogenesis in mice.

RESULTS

Although small increases in ORMDL3 expression decrease ceramide levels, remarkably, higher expression in lung epithelial cells and macrophages in vitro and in vivo increased ceramide production, which promoted chronic inflammation, airway hyperresponsiveness, and mucus production during house dust mite-induced allergic asthma. Moreover, nasal administration of the immunosuppressant drug FTY720/fingolimod reduced ORMDL3 expression and ceramide levels and mitigated airway inflammation and hyperreactivity and mucus hypersecretion in house dust mite-challenged mice.

CONCLUSIONS

Our findings demonstrate that overexpression of ORMDL3 regulates ceramide homeostasis in cells in a complex manner and suggest that local FTY720 administration might be a useful therapeutic intervention for the control of allergic asthma.

Polymorphisms related to ORMDL3 are associated with asthma susceptibility, alterations in transcriptional regulation of ORMDL3, and changes in TH2 cytokine levels

BACKGROUND

Chromosome 17q21, harboring the orosomucoid 1-like 3 (ORMDL3) gene, has been consistently associated with childhood asthma in genome-wide association studies.

OBJECTIVE

We investigated genetic variants in and around ORMDL3 that can change the function of ORMDL3 and thus contribute to asthma susceptibility.

METHODS

We performed haplotype analyses and fine mapping of the ORMDL3 locus in a cross-sectional (International Study of Asthma and Allergies in Childhood Phase II, n = 3557 total subjects, n = 281 asthmatic patients) and case-control (Multicenter Asthma Genetics in Childhood Study/International Study of Asthma and Allergies in Childhood Phase II, n = 1446 total subjects, n = 763 asthmatic patients) data set to identify putative causal single nucleotide polymorphisms (SNPs) in the locus. Top asthma-associated polymorphisms were analyzed for allele-specific effects on transcription factor binding and promoter activity in vitro and gene expression in PBMCs after stimulation ex vivo.

RESULTS

Two haplotypes (H1 and H2) were significantly associated with asthma in the cross-sectional (P = 9.9 × 10(-5) and P = .0035, respectively) and case-control (P = 3.15 × 10(-8) and P = .0021, respectively) populations. Polymorphisms rs8076131 and rs4065275 were identified to drive these effects. For rs4065275, a quantitative difference in transcription factor binding was found, whereas for rs8076131, changes in upstream stimulatory factor 1 and 2 transcription factor binding were observed in vitro by using different cell lines and PBMCs. This might contribute to detected alterations in luciferase activity paralleled with changes in ORMDL3 gene expression and IL-4 and IL-13 cytokine levels ex vivo in response to innate and adaptive stimuli in an allele-specific manner. Both SNPs were in strong linkage disequilibrium with asthma-associated 17q21 SNPs previously related to altered ORMDL3 gene expression.

CONCLUSION

Polymorphisms in a putative promoter region of ORMDL3, which are associated with childhood asthma, alter transcriptional regulation of ORMDL3, correlate with changes in TH2 cytokines levels, and therefore might contribute to the childhood asthma susceptibility signal from 17q21.

Risk of childhood asthma is associated with CpG-site polymorphisms, regional DNA methylation and mRNA levels at the GSDMB/ORMDL3 locus

Single-nucleotide polymorphisms (SNPs) in GSDMB (Gasdermin B) and ORMDL3 (ORMDL sphingolipid biosynthesis regulator 3) are strongly associated with childhood asthma, but the molecular alterations contributing to disease remain unknown. We investigated the effects of asthma-associated SNPs on DNA methylation and mRNA levels of GSDMB and ORMDL3. Genetic association between GSDMB/ORMDL3 and physician-diagnosed childhood asthma was confirmed in the Swedish birth-cohort BAMSE. CpG-site SNPs (rs7216389 and rs4065275) showed differences in DNA methylation depending on carrier status of the risk alleles, and were significantly associated with methylation levels in two CpG sites in the 5′ UTR (untranslated region) of ORMDL3. In the Swedish Search study, we found significant differences in DNA methylation between asthmatics and controls in five CpG sites; after adjusting for lymphocyte and neutrophil cell counts, three remained significant: one in IKZF3 [IKAROS family zinc finger 3 (Aiolos); cg16293631] and two in the CpG island (CGI) of ORMDL3 (cg02305874 and cg16638648). Also, cg16293631 and cg02305874 correlated with mRNA levels of ORMDL3. The association between methylation and asthma was independent of the genotype in rs7216389, rs4065275 and rs12603332. Both SNPs and CpG sites showed significant associations with ORMDL3 mRNA levels. SNPs influenced expression independently of methylation, and the residual association between methylation and expression was not mediated by these SNPs. We found a differentially methylated region in the CGI shore of ORMDL3 with six CpG sites less methylated in CD8⁺ T-cells. In summary, this study supports that there are differences in DNA methylation at this locus between asthmatics and controls; and both SNPs and CpG sites are independently associated with ORMDL3 expression.

Chemical chaperones mitigate experimental asthma by attenuating endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress and consequent unfolded protein response (UPR) are important in inflammation but have been poorly explored in asthma. We used a mouse model of allergic airway inflammation (AAI) with features of asthma to understand the role of ER stress and to explore potential therapeutic effects of inhaled chemical chaperones, which are small molecules that can promote protein folding and diminish UPR. UPR markers were initially measured on alternate days during a 7-day daily allergen challenge model. UPR markers increased within 24 hours after the first allergen challenge and peaked by the third challenge, before AAI was fully established (from the fifth challenge onward). Three chemical chaperones-glycerol, trehalose, and trimethylamine-N-oxide (TMAO)-were initially administered during allergen challenge (preventive regimen). TMAO, the most effective of these chemical chaperones and 4-phenylbutyric acid, a chemical chaperone currently in clinical trials, were further tested for potential therapeutic activities after AAI was established (therapeutic regimen). Chemical chaperones showed a dose-dependent reduction in UPR markers, airway inflammation, and remodeling in both regimens. Our results indicate an early and important role of the ER stress pathway in asthma pathogenesis and show therapeutic potential for chemical chaperones.

Genome-wide association studies to advance our understanding of critical cell types and pathways in rheumatoid arthritis: recent findings and challenges

PURPOSE OF REVIEW

A significant number of loci implicated in rheumatoid arthritis (RA) susceptibility have been highlighted by genome-wide association studies (GWAS). Here, we review the recent advances of GWAS in understanding the genetic architecture of RA, and place these findings in the context of RA pathogenesis.

RECENT FINDINGS

Although the interpretation of GWAS findings in the context of the disease biology remains challenging, interesting observations can be highlighted. Integration of GWAS results with cell-type specific gene expression or epigenetic marks have highlighted regulatory T cells and CD4 memory T cells as critical cell types in RA. In addition, many genes in RA loci are involved in the nuclear factor-kappaB signaling pathway or the Janus kinase (JAK)-signal transducers and activators of transcription (STAT) signaling pathway. The observation that these pathways are targeted by several approved drugs used to treat the symptoms of RA highlights the promises of human genetics to provide insights in the disease biology, and help identify new therapeutic targets.

SUMMARY

These findings highlight the promises and need of future studies investigating causal genes and underlined mechanisms in GWAS loci to advance our understanding of RA.

Impaired sphingolipid synthesis in the respiratory tract induces airway hyperreactivity

Asthma is a clinically heterogeneous genetic disease, and its pathogenesis is incompletely understood. Genome-wide association studies link ORM (yeast)-Like protein isoform 3 [corrected] (ORMDL3), a member of the ORM gene family, to nonallergic childhood-onset asthma. Orm proteins negatively regulate sphingolipid (SL) synthesis by acting as homeostatic regulators of serine palmitoyl-CoA transferase (SPT), the rate-limiting enzyme of de novo SL synthesis, but it is not known how SPT activity or SL synthesis is related to asthma. The present study analyzes the effect of decreased de novo SL synthesis in the lung on airway reactivity after administration of myriocin, an inhibitor of SPT, and in SPT heterozygous knockout mice. We show that, in both models, decreased de novo SL synthesis increases bronchial reactivity in the absence of inflammation. Decreased SPT activity affected intracellular magnesium homeostasis and altered the bronchial sensitivity to magnesium. This functionally links decreased de novo SL synthesis to asthma and so identifies this metabolic pathway as a potential target for therapeutic interventions.

17q21 locus and ORMDL3: an increased risk for childhood asthma

Genetic variations in the 17q21 locus are strongly associated with childhood nonallergic asthma. Expression of the 17q21 genes, orosomucoid like 3 (ORMDL3) and gasdermin B (GSMDB), is affected by these disease-associated variants. However, until recently, no functional connection of the protein products coded by these genes with asthma was known. Lately, it has been identified that ORMDL3 function has been related to various cellular processes that could be relevant for the pathogenesis of asthma. This includes dysregulation of the unfolded protein response (UPR) associated with airway remodeling and also an effect of ORMDL3-dysregulated sphingolipid synthesis on bronchial hyperreactivity. These findings are crucial for a better understanding of the mechanism of childhood asthma and may lead to asthma therapeutics that target pathways previously not thought to be related to this common pediatric respiratory disease. Furthermore, this may validate the unbiased genome-wide association study (GWAS) approach for complex diseases such as asthma, to better define pathomechanisms and drug targets.