Profiling of T helper cell-derived small RNAs reveals unique antisense transcripts and differential association of miRNAs with argonaute proteins 1 and 2

RNA interference mediated through antisense transcripts is a fundamentally important mechanism regulating gene expression that remains incompletely understood. Here, we have used next-generation sequencing to determine from mouse CD4+ T cells the functional implications of antisense transcripts binding to argonaute (AGO) proteins that mediate RNA interference and post-transcriptional gene silencing. This effort identified 90 new microRNAs (miRNAs) and six endogenous hairpin RNA-derived small interfering RNAs (siRNAs) mapping to distinct introns. Unexpectedly, 69 miRNAs were expressed as non-canonical isomiRs as the dominant AGO-binding transcript, with extensive 3' terminal nucleotide modifications. Furthermore, differential expression analysis between AGO1- and AGO2-bound miRNAs suggested preferential binding of isomiRs ending with 3' adenine residues to AGO1 and 3' uridine residues to AGO2. Analysis of the putative targets of all miRNAs suggested a striking preference for regulating transcription and transcription factors with additional evidence of a functional division of labor between AGO proteins in this regard. We further provide evidence that multiple mitochondrial genomic loci serve as the source of endogenous cis-natural antisense transcripts. These findings imply diversity in AGO protein function based on differential miRNA binding and indicate that RNA interference-based gene regulation is more complex than previously recognized.

Respiratory tract allergic disease and atopy: experimental evidence for a fungal infectious etiology

Allergic asthma is an obstructive lung disease linked to environmental exposures that elicit allergic airway inflammation and characteristic antigen-specific immunoglobulin reactions termed atopy. Analyses of asthma pathogenesis using experimental models have shown that T helper cells, especially T helper type 2 (Th2) cells and Th2 cytokines such as interleukin 4 (IL-4) and IL-13, are critical mediators of airway obstruction following allergen challenge, but the environmental initiators of lung Th2 responses are less defined. Our studies demonstrate that fungal-derived proteinases that are commonly found in home environments are requisite immune adjuvants capable of eliciting robust Th2 responses and allergic lung disease in mice. We have further shown that common household fungi readily infect the mouse respiratory tract and induce both asthma-like disease and atopy to otherwise innocuous bystander antigens through the secretion of proteinases. These findings support the possibility that asthma and atopy represent a reaction to respiratory tract fungal infection, suggesting novel means for diagnosis and therapy of diverse allergic disorders.

Proinflammatory role for let-7 microRNAS in experimental asthma

MicroRNAs (miRNAs) are short, non-coding RNAs that target and silence protein coding genes through 3'-UTR elements. Evidence increasingly assigns an immunosuppressive role for miRNAs in immunity, but relatively few miRNAs have been studied, and an overall understanding of the importance of these regulatory transcripts in complex in vivo systems is lacking. Here we have applied multiple technologies to globally analyze miRNA expression and function in allergic lung disease, an experimental model of asthma. Deep sequencing and microarray analyses of the mouse lung short RNAome revealed numerous extant and novel miRNAs and other transcript classes. Similar to mRNAs, lung miRNA expression changed dynamically during the transition from the naive to the allergic state, suggesting numerous functional relationships. A possible role for miRNA editing in altering the lung mRNA target repertoire was also identified. Multiple members of the highly conserved let-7 miRNA family were the most abundant lung miRNAs, and we confirmed in vitro that interleukin 13 (IL-13), a cytokine essential for expression for allergic lung disease, is regulated by mmu-let-7a. However, inhibition of let-7 miRNAs in vivo using a locked nucleic acid profoundly inhibited production of allergic cytokines and the disease phenotype. Our findings thus reveal unexpected complexity in the miRNAome underlying allergic lung disease and demonstrate a proinflammatory role for let-7 miRNAs.

A reversible, non-invasive method for airway resistance measurements and bronchoalveolar lavage fluid sampling in mice

Airway hyperreactivity (AHR) measurements and bronchoalveolar lavage (BAL) fluid sampling are essential to experimental asthma models, but repeated procedures to obtain such measurements in the same animal are generally not feasible. Here, we demonstrate protocols for obtaining from mice repeated measurements of AHR and bronchoalveolar lavage fluid samples. Mice were challenged intranasally seven times over 14 days with a potent allergen or sham treated. Prior to the initial challenge, and within 24 hours following each intranasal challenge, the same animals were anesthetized, orally intubated and mechanically ventilated. AHR, assessed by comparing dose response curves of respiratory system resistance (RRS) induced by increasing intravenous doses of acetylcholine (Ach) chloride between sham and allergen-challenged animals, were determined. Afterwards, and via the same intubation, the left lung was lavaged so that differential enumeration of airway cells could be performed. These studies reveal that repeated measurements of AHR and BAL fluid collection are possible from the same animals and that maximal airway hyperresponsiveness and airway eosinophilia are achieved within 7-10 days of initiating allergen challenge. This novel technique significantly reduces the number of mice required for longitudinal experimentation and is applicable to diverse rodent species, disease models and airway physiology instruments.

Divergent Roles for Airway Epithelial MMP7 and Retinoic Acid in Experimental Asthma (140.5)

The innate immune response of airway epithelial cells to aeroallergen likely initiates the development of T cell responses that are central to allergic inflammation. Although proteolytically active allergens induce the expression of interleukin (IL)-25/IL-17E, we show that epithelial matrix metalloproteinase 7 (MMP7) is expressed in human asthma, and is required for maximal activity of this cytokine in promoting T helper type 2 cell differentiation. Allergen-challenged MMP7-/- mice showed reduced airway hyperreactivity, allergic inflammatory cytokine, and increased expression of retinal dehydrogenase (RALDH)-1. Inhibition of RALDH-1 restored the asthma phenotype in MMP7-/- mice and inhibited lung T regulatory cell responses while exogenous administration of retinoic acid attenuated the asthma phenotype. Thus, MMP7 coordinates allergic lung inflammation by activating IL-25 while simultaneously inhibiting retinoid-dependent T regulatory cell development.

Divergent functions for airway epithelial matrix metalloproteinase 7 and retinoic acid in experimental asthma

The innate immune response of airway epithelial cells to aeroallergen initiates the development of T cell responses that are central to allergic inflammation. Although proteinase allergens induce the expression of interleukin 25 we show that epithelial matrix metalloproteinase 7 (MMP7) was expressed in asthma and was required for maximal activity of IL-25 in promoting T helper type 2 cell differentiation. Allergen-challenged Mmp7^−/− mice showed reduced airway hyperreactivity, allergic inflammatory cytokine production and increased expression of retinal dehydrogenase (RALDH)-1. Inhibition of RALDH-1 restored the asthma phenotype in Mmp7^−/− mice and inhibited lung T regulatory cell responses while exogenous administration of retinoic acid attenuated the asthma phenotype. Thus, MMP7 coordinates allergic lung inflammation by activating IL-25 while simultaneously inhibiting retinoid-dependent T regulatory cell development.

Neurokinin receptors in recurrent airway obstruction: a comparative study of affected and unaffected horses

The purpose of the study was to compare in vitro airway responses to neurokinin A & B (NKA and NKB) and expression of NK-2 receptors in airways of horses affected and unaffected with recurrent airway obstruction (RAO). Neurokinin-A, an inflammatory mediator belonging to the tachykinin family of neuropeptides, causes bronchoconstriction by binding to NK-2 receptors. Neurokinin-B is a lesser-known neuropeptide that acts on NK-3 receptors. Horses were placed into RAO-affected and RAO-unaffected groups based on their history, clinical scoring, and pulmonary function testing. Lung tissue from each lobe was collected for immunohistochemical staining for NK-2 receptors. Cumulative concentration-response relationships were determined on bronchial rings (4-mm wide) collected and prepared from the right diaphragmatic lung lobe to graded concentrations (half log molar concentrations 10(-7)M to 10(-4)M) of NKA and NKB. The results showed that NKA caused significantly greater contraction than NKB in both groups. In RAO-affected horses, both agents produced significantly greater bronchial contractions than those in the RAO-unaffected horses. Immunohistochemical staining showed that the overall NK-2 receptor distribution was significantly increased in bronchial epithelium and smooth muscles of bronchi and pulmonary vessels of RAO-affected than RAO-unaffected horses. The findings indicate that NK-2 receptors are up-regulated in RAO, suggesting that NK-2 receptor antagonists may have some therapeutic value in controlling the progression of airway hyperreactivity in horses affected with RAO.

Characterization of endothelin receptors in the peripheral lung tissues of horses unaffected and affected with recurrent airway obstruction

The purpose of the study was to determine and compare the expression of endothelin (ET) receptors in the peripheral lungs of healthy horses and those affected with recurrent airway obstruction (RAO) using reverse transcriptase polymerase chain reaction (RT-PCR), real-time PCR, Western blot analysis, and immunohistochemical techniques. Two groups of horses (7 healthy and 7 RAO-affected) were selected from a pool of horses destined for euthanasia. The grouping of horses was based on the history, clinical scoring, and pulmonary function testing. After euthanasia, gross postmortem evaluation of the lungs was conducted, and lung samples were collected and either stored at -80 degrees C or fixed in zinc-formalin for 12 h. The RT-PCR was performed by using specific primers for ETA and ETB receptors, and beta-actin. To determine the relative gene expression real-time PCR was performed. To detect ET receptor protein expression, Western blotting and immunohistochemical studies were performed using polyclonal antibodies against ETA and ETB receptors and beta-actin. The ET receptor expression was determined by performing either densitometric analyses or scoring of immunostaining. Statistical analyses were performed to detect differences in receptor expression within and between the 2 groups. The results indicated that ET receptor expression, particularly ETB receptors, was significantly greater in the peripheral lungs of RAO-affected horses than in those of healthy horses. Clinical trials using ET receptor antagonists, particularly ETB antagonists might help in developing a therapeutic strategy to treat this career-ending disease.

Immunohistochemical determination of the expression of endothelin receptors in bronchial smooth muscle and epithelium of healthy horses and horses affected by summer pasture-associated obstructive pulmonary disease

OBJECTIVE

To immunohistochemically determine the expression of endothelin (ET) receptors in bronchial smooth muscle and epithelium of healthy horses and horses affected by summer pasture-associated obstructive pulmonary disease (SPAOPD).

SAMPLE POPULATION

Tissue specimens obtained from 8 healthy and 8 SPAOPD-affected horses.

PROCEDURE

Horses were examined and assigned to healthy and SPAOPD groups. Horses were then euthanatized, and tissue specimens containing bronchi of approximately 4 to 8 mm in diameter were immediately collected from all lung lobes, fixed in zinc-formalin solution for 12 hours, and embedded in paraffin. Polyclonal primary antibodies against ET-A or ET-B receptors at a dilution of 1:200 and biotinylated IgG secondary antibodies were applied to tissue sections, followed by the addition of an avidin-biotin immunoperoxidase complex. Photographs of the stained slides were digitally recorded and analyzed by use of image analysis software to determine the intensity of staining. Two-way ANOVA was used for statistical analysis.

RESULTS

The left diaphragmatic lung lobe of SPAOPD-affected horses had a significantly greater area of bronchial smooth muscle that immunostained for ET-A, compared with that for healthy horses. All lung lobes of SPAOPD-affected horses, except for the right diaphragmatic lobe, had significantly greater staining for ET-B receptors in bronchial smooth muscle, compared with results for healthy horses.

CONCLUSIONS AND CLINICAL RELEVANCE

This study revealed overexpression of ET-A and, in particular, ETB receptors in the bronchial smooth muscle of SPAOPD-affected horses, which suggested upregulation of these receptors. These findings improve our understanding of the role of ET-1 in the pathogenesis of SPAOPD.

Endothelin receptor alterations in equine airway hyperreactivity

The purpose of this study was to evaluate the role of endothelin-1 (ET-1) and its receptors in the airway hyperreactivity of horses with obstructive pulmonary disease associated with summer pasture (SPAOPD). The right diaphragmatic lobe of the lung of 8 clinically healthy (unaffected) and 8 SPAOPD-affected horses was collected immediately after euthanasia. Bronchial rings (4 mm wide) were prepared and mounted in organ baths and attached to force transducers interfaced with a polygraph. Four rings were used to study each ET-1 receptor; 1 ring served as the control, and the other 3 were incubated with 10(-9), 10(-7), or 10(-5) M of either BQ-123, an ET(A)-receptor antagonist, or IRL-1038, an ET(B)-receptor antagonist. Cumulative concentrations (10(-8.5) to 10(-6) M) of ET-1 were applied to all rings. Using pooled pulmonary tissue from different regions of the lung, we performed a reverse-transcription polymerase chain reaction (RT-PCR) to determine ET(B)-receptor gene expression. Although ET-1 caused concentration-dependent bronchial ring contraction in both groups of horses, the rings of SPAOPD-affected horses had significantly greater contraction than the rings of unaffected horses. Whereas ET(A)-receptor blockade significantly increased the response to ET-1 in unaffected horses, ET(B)-receptor blockade significantly decreased the response in affected horses. The pA2 values showed a nonsignificant decrease in ET(A)-receptor affinity and a significant increase in ET(B)-receptor affinity in affected horses compared with unaffected horses. The ET(B)-receptor mRNA expression of the pooled pulmonary tissue showed a nonsignificant increase in affected horses compared with unaffected horses. The airway hyperreactivity to ET-1 observed in the bronchial rings from the affected horses appears to be due in part to activation of pulmonary ET(B) receptors, which appear to be inactive in unaffected horses.

Endothelins and airways--a short review

Endothelins (ETs) are a multifunctional large family of polypeptides. There are three well recognized members in this family (ET-1, ET-2, and ET-3) of which ET-1 appears to be the most important. They have been shown to play an important role in the pathogenesis of many life threatening diseases of humans and animals. They also perform a wide variety of physiological roles. The most important property of ETs is smooth muscle contraction, which allows them to play an important role in the pathogenesis of many vascular, gastrointestinal, urogenital and airway diseases. Another important feature of ETs is their influence on the immune system. Many animal and human studies have shown that antagonists of ET receptors can remarkably alleviate many disease symptoms. ETs produce their effect by acting via two established types of receptors namely ET-A and ET-B, which are present in various type of cells in the body. These receptors have varied and sometimes opposite functions. Pulmonary vascular endothelium is the richest source of ET in the body. Lung is the primary organ of ET metabolism and clearance. It has been reported that ETs play a pivotal role in the pathogenesis of asthma, chronic obstructive pulmonary disease, bronchiolitis obliterans and other important airway diseases. Many of these obstructive airway diseases are characterized by bronchoconstriction, mucous hyperplasia, airway remodeling and inflammation. ET is involved in all of these symptoms. In spite of its involvement in many diseases, the exact role of ET in the pathogenesis of these diseases remains unclear. The purpose of this review is to give the reader an insight regarding the importance of multitude and diverse roles played by ETs in various airway diseases.

Pharmacologic evaluation of neurokinin-2 receptor antagonists in the guinea pig respiratory tract

OBJECTIVE

To evaluate 3 neurokinin-2 (NK2) receptor antagonists on the basis of their ability to block neurokinin A (NKA)-induced contractile responses in various regions of the guinea pig respiratory tract.

ANIMALS

48 clinically normal guinea pigs.

PROCEDURE

After euthanasia, the trachea and lungs were removed en bloc. The spirally cut trachea was divided into lower, middle, and upper portions. The main bronchus was spirally cut. A lung strip was cut from the edge of the lung. Tissue strips were mounted in organ baths containing Tyrode solution at 37 degrees C and attached to force transducers interfaced with a polygraph. Lung strips were set at a tension of 1 g; other tissue strips were set at 2 g. After 45 minutes of equilibration, cumulative concentration-response (CR) relationships to graded concentrations of NKA were determined. In the treatment groups, tissues were incubated (30 minutes) with antagonists (MEN 10376, SR 48968, and SR 144190) at 3 concentrations (10(-9), 10(-7), and 10(-5)M) before CR relationships were determined. Effectiveness of SR 48968 against NKA was also tested in vivo.

RESULTS

Lung strips failed to contract, but all others responded in a concentration-dependent manner. Bronchial spirals were most sensitive. SR 48968 had the highest pA2 value and effectively blocked NKA.

CONCLUSIONS AND CLINICAL RELEVANCE

The bronchial region where airflow resistance is high was the most sensitive to NKA, suggesting the importance of NKA in bronchoconstriction. Nonpeptide antagonists (SR 48968 and SR 144190) were more potent than the peptide antagonist (MEN 10376), indicating their greater therapeutic potential as antiasthmatic agents.