Epigenetics and miRNA emerge as key regulators of smooth muscle cell phenotype and function

New Insight into Muscle-Type Cofilin (CFL2) as an Essential Mediator in Promoting Myogenic Differentiation in Cattle

Meat quality and meat composition are not separated from the influences of animal genetic improvement systems; the growth and development of skeletal muscle are the primary factors in agricultural meat production and meat quality. Though the muscle-type cofilin (CFL2) gene has a crucial influence on skeletal muscle fibers and other related functions, the epigenetic modification mechanism of the CFL2 gene regulating meat quality remains elusive. After exploring the spatiotemporal expression data of CFL2 gene in a group of samples from fetal bovine, calf, and adult cattle, we found that the level of CFL2 gene in muscle tissues increased obviously with cattle age, whereas DNA methylation levels of CFL2 gene in muscle tissues decreased significantly along with cattle age by BSP and COBRA, although DNA methylation levels and mRNA expression levels basically showed an opposite trend. In cell experiments, we found that bta-miR-183 could suppress primary bovine myoblast differentiation by negatively regulated CFL2. In addition, we packaged recombinant adenovirus vectors for CFL2 gene knockout and overexpression and found that the CFL2 gene could promote the differentiation of primary bovine myoblasts by regulating marker genes MYOD, MYOG and MYH3. Therefore, CFL2 is an essential mediator for promoting myogenic differentiation by regulating myogenic marker genes in cattle myoblasts.

Epigenetic Regulation Mechanisms of the Cofilin-1 Gene in the Development and Differentiation of Bovine Primary Myoblasts

As the quality of beef products has received increasing attention, it is essential to explore the underlying transcriptional and epigenetic mechanisms of meat traits. Our project uses Qinchuan cattle as the research subject. First, we examined the spatiotemporal expression pattern of the CFL1 gene in a panel of fetal bovine, calf, and adult cattle samples. Then, we performed DNA methylation experiments of CFL1 on myogenesis and muscle maturation using the BSP amplification and COBRA sequencing techniques and found that high DNA methylation levels showed low expression levels. Next, we performed an assay between bta-miR-182 and the CFL1 gene and demonstrated that miR-182 could promote bovine primary myoblast differentiation by negatively regulated the expression of CFL1. Finally, we constructed an adenovirus overexpression and interference vector and found that CFL1 could suppress the differentiation of bovine primary myoblasts. In summary, our experiment comprehensively analyzes the epigenetic regulation mechanisms of the CFL1 gene in the development and differentiation of bovine primary myoblasts. This has far-reaching significance for improving the meat production and meat quality of Qinchuan cattle. This can provide reliable data support and a theoretical research basis for the rapid and efficient breeding selection of local yellow cattle and the genetic improvement of meat quality.

lncRNA-NEAT1 Sponges miR-128 to Promote Inflammatory Reaction and Phenotypic Transformation of Airway Smooth Muscle Cells

OBJECTIVE

Pediatric asthma is still a health threat to the children. Long noncoding RNA-NEAT1 (lncRNA-NEAT1) was reported to be positively correlated with the severity of asthma. We aimed to study the effects and mechanism of lncRNA-NEAT1on inflammatory reaction and phenotypic transformation of airway smooth muscle cells (ASMCs) in the bronchial asthma.

METHOD

The degree of lncRNA-NEAT1 and miR-128 mRNA in children with bronchial asthma and healthy individuals was tested by qRT-PCR. After the inflammatory reaction and phenotypic transformation of PDGF-BB-induced ASMCs, the expression of lncRNA-NEAT1 or miR-128 in the AMSC was disturbed in the AMSC. Subsequently, the expression of lncRNA-NEAT1 and miR-128 was detected by the way of qRT-PCR, and western blot was applied to measure the expression of MMP-2, MMP-9, α-SMA, calponin, NF-κB, and so on in the cells. The content of TNF-α, IL-1β, IL-6, and IL-8 in the cell culture supernatant was checked by ELISA. MTT, Transwell, and flow cytometry were used to detect cell proliferation, migration, and apoptosis. Further, the targeting relations between lncRNA-NEAT1 and miR-128 were evaluated by the dual-luciferase reporter assay.

RESULT

In the sputum of children with bronchial asthma, lncRNA-NEAT1 was significantly upregulated while miR-128 was rapidly downregulated. Besides, lncRNA-NEAT1 and miR-128 were competitively combined and, for their expression, negatively correlated.

CONCLUSION

lncRNA-NEAT1 sponges miR-128 to boost PDGF-BB-induced inflammatory reaction and phenotypic transformation of ASMCs to aggravate the occurrence and development of childhood bronchial asthma.

circRNA-Mediated Inhibin-Activin Balance Regulation in Ovarian Granulosa Cell Apoptosis and Follicular Atresia

Ovarian granulosa cells (GC) play an essential role in the development and atresia of follicles. Emerging studies suggest that non-coding RNAs are involved in the regulation of GC apoptosis. Here, we aimed to analyze the function of ssc-circINHA-001, coded by the first exon of the inhibin subunit α gene (INHA), in resisting GC apoptosis and follicular atresia by enhancing the expression of the inhibin subunit β A (INHBA) through a cluster of miRNAs. A higher expression of ssc-circINHA-001 in healthy follicles compared to early atretic follicles was detected by qRT-PCR. Its circular structure was confirmed by RNase R treatment and reversed PCR. The function of ssc-circINHA-001 in GC resistance to apoptosis was detected by in vitro transfection of its si-RNA. Furthermore, the dual-luciferase reporter assay suggested that ssc-circINHA-001 adsorbed three miRNAs, termed miR-214-5p, miR-7144-3p, and miR-9830-5p, which share the common target INHBA. A low expression of ssc-circINHA-001 increased the levels of the free miRNAs, inhibited INHBA expression, and thus raised GCs apoptosis through a shift from the secretion of activin to that of inhibin. Our study demonstrated the existence of a circRNA–microRNAs–INHBA regulatory axis in follicular GC apoptosis and provides insight into the relationship between circRNA function and its coding gene in inhibin/activin balance and ovarian physiological functions.

Downregulation of miR-140-3p Contributes to Upregulation of CD38 Protein in Bronchial Smooth Muscle Cells

In allergic bronchial asthma, an increased smooth muscle contractility of the airways is one of the causes of the airway hyperresponsiveness (AHR). Increasing evidence also suggests a possible involvement of microRNAs (miRNAs) in airway diseases, including asthma, although their roles in function and pathology largely unknown. The current study aimed to determine the role of a miRNA, miR-140-3p, in the control of protein expression of CD38, which is believed to regulate the contraction of smooth muscles, including the airways. In bronchial smooth muscles (BSMs) of the mice that were actively sensitized and repeatedly challenged with ovalbumin antigen, an upregulation of CD38 protein concurrently with a significant reduction of miR-140-3p was observed. In cultured human BSM cells (hBSMCs), transfection with a synthetic miR-140-3p inhibitor caused an increase in CD38 protein, indicating that its basal protein expression is regulated by endogenous miR-140-3p. Treatment of the hBSMCs with interleukin-13 (IL-13), an asthma-related cytokine, caused both an upregulation of CD38 protein and a downregulation of miR-140-3p. Transfection of the hBSMCs with miR-140-3p mimic inhibited the CD38 protein upregulation induced by IL-13. On the other hand, neither a CD38 product cyclic ADP-ribose (cADPR) nor its antagonist 8-bromo-cADPR had an effect on the BSM contraction even in the antigen-challenged mice. Taken together, the current findings suggest that the downregulation of miR-140-3p induced by IL-13 might cause an upregulation of CD38 protein in BSM cells of the disease, although functional and pathological roles of the upregulated CD38 are still unclear.

Emerging role of non-coding RNAs in allergic disorders

RNA transcripts that not undergo translation into polypeptides recently came into focus of research. Long non-coding RNAs (lncRNAs), microRNAs (miRNAs) and circular RNAs (circRNAs) comprise the most important groups of these transcripts. LncRNAs have a length over 200 nucleotides and like mRNAs, have regulated transcription in a tissue specific manner. Biogenesis and function of lncRNAs is related to cell differentiation, response to stimuli and regulation of immune responses. LncRNAs can interact with both miRNAs and mRNAs. MiRNAs are characterized by a length of 22-24 nucleotides. MiRNAs regulate expression of genes at the post-transcriptional level. LncRNAs together with miRNAs are considered as regulators of the immune system. Alterations in their biogenesis is an important mechanism in the development immune related disorders. CircRNAs are products of aberrant maturation of protein-coding transcripts in a process of back-splicing, in which a single strand RNA molecule attains a closed circle shape. Despite a low expression, some circRNA were found to titrate miRNAs and interfere with maturation of legitimate protein-coding transcripts. We summarize the current knowledge on the role of non-coding transcripts in allergic disorders: asthma, atopic dermatitis, allergic rhinitis and urticaria. The reviewed data suggest lncRNA and miRNAs as therapeutic targets and biomarkers of allergic disorders.

MicroRNA-221 is overexpressed in the equine asthmatic airway smooth muscle and modulates smooth muscle cell proliferation

Airway wall remodeling, including hyperplasia and hypertrophy of smooth muscle (ASM) cells leading to an increased smooth muscle mass, is considered central to asthma. However, molecular pathways responsible for ASM remodeling remain poorly understood. MicroRNAs (miRNAs) have emerged as key regulators of inflammatory and repair processes affecting the lungs and can downregulate protein expression by inhibiting target mRNA translation. We therefore hypothesized that miRNAs are involved in ASM remodeling in asthma by modulating ASM proliferation. We have analyzed the expression of miRNAs in bronchial smooth muscle from asthmatic horses during disease exacerbation and remission and from controls. Their involvement in ASM cell proliferation was then studied. Our results shown that miR-26a, miR-133, and miR-221 were upregulated in ASM from horses with asthma exacerbation compared with asthma remission and controls. MiR-221 induced cell hyperproliferation and reduced the expression of contractile gene markers in ASM cells. These changes were associated with the decreased mRNA expression of cell cycle regulatory genes (p53, p21, and p27). In conclusion, we demonstrated for the first time an upregulation of miR-221 in asthmatic airway smooth muscle and confirm the involvement of miR-221 in ASM cell proliferation by regulation of the cell cycle arrest genes. Targeting miR-221 network genes may represent a novel approach for the treatment of ASM remodeling in asthma.

Smooth muscle cell-driven vascular diseases and molecular mechanisms of VSMC plasticity

Vascular smooth muscle cells (VSMCs) are the major cell type in blood vessels. Unlike many other mature cell types in the adult body, VSMC do not terminally differentiate but retain a remarkable plasticity. Fully differentiated medial VSMCs of mature vessels maintain quiescence and express a range of genes and proteins important for contraction/dilation, which allows them to control systemic and local pressure through the regulation of vascular tone. In response to vascular injury or alterations in local environmental cues, differentiated/contractile VSMCs are capable of switching to a dedifferentiated phenotype characterized by increased proliferation, migration and extracellular matrix synthesis in concert with decreased expression of contractile markers. Imbalanced VSMC plasticity results in maladaptive phenotype alterations that ultimately lead to progression of a variety of VSMC-driven vascular diseases. The nature, extent and consequences of dysregulated VSMC phenotype alterations are diverse, reflecting the numerous environmental cues (e.g. biochemical factors, extracellular matrix components, physical) that prompt VSMC phenotype switching. In spite of decades of efforts to understand cues and processes that normally control VSMC differentiation and their disruption in VSMC-driven disease states, the crucial molecular mechanisms and signalling pathways that shape the VSMC phenotype programme have still not yet been precisely elucidated. In this article we introduce the physiological functions of vascular smooth muscle/VSMCs, outline VSMC-driven cardiovascular diseases and the concept of VSMC phenotype switching, and review molecular mechanisms that play crucial roles in the regulation of VSMC phenotypic plasticity.

Circulating microRNAs and prediction of asthma exacerbation in childhood asthma

BACKGROUND

Circulating microRNAs have shown promise as non-invasive biomarkers and predictors of disease activity. Prior asthma studies using clinical, biochemical and genomic data have not shown excellent prediction of exacerbation. We hypothesized that a panel of circulating microRNAs in a pediatric asthma cohort combined with an exacerbation clinical score might predict exacerbation better than the latter alone.

METHODS

Serum samples from 153 children at randomization in the Childhood Asthma Management Program were profiled for 754 microRNAs. Data dichotomized for asthma exacerbation one year after randomization to inhaled corticosteroid treatment were used for binary logistic regression with miRNA expressions and exacerbation clinical score.

RESULTS

12 of 125 well-detected circulating microRNAs had significant odd ratios for exacerbation with miR-206 being most significant. Each doubling of expression of the 12 microRNA corresponded to a 25-67% increase in exacerbation risk. Stepwise logistic regression yielded a 3-microRNA model (miR-146b, miR-206 and miR-720) that, combined with the exacerbation clinical score, had excellent predictive power with a 0.81 AUROC. These 3 microRNAs were involved in NF-kβ and GSK3/AKT pathways.

CONCLUSIONS

This combined circulating microRNA-clinical score model predicted exacerbation in asthmatic subjects on inhaled corticosteroids better than each constituent feature alone.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00000575 .

Schisandrin B down-regulated lncRNA BCYRN1 expression of airway smooth muscle cells by improving miR-150 expression to inhibit the proliferation and migration of ASMC in asthmatic rats

OBJECTIVE

The mechanism of Schisandrin B on the proliferation and migration of airway smooth muscle cells (ASMCs) in asthmatic rats was explored.

METHODS

SD rats were divided into three groups: control (group 1), model (group 2) and model + Schisandrin B (group 3). miR-150 and lncRNA BCYRN1 levels were measured by qRT-PCR. The combination of BCYRN1 and miR-150 was detected by RNA pull down. ASMCs' viability/proliferation/migration were examined by WST-1 assay and 24-well Transwell system.

RESULTS

Schisandrin B up-regulated miR-150 expression and down-regulated BCYRN1 expression in sensitized rats. Schisandrin B reversed the expression of miR-150 and BCYRN1 in MV-treated ASMCs. In addition, Schisandrin B inhibited the viability, proliferation and migration of MV-induced ASMCs. We also found miR-150 inhibited BCYRN1 expression which was proved by experiments using ASMCs transfected with miR-150 inhibitor.

CONCLUSION

Schisandrin B increased miR-150 expression and decreased BCYRN1, and BCYRN1 expression was inhibited by miR-150, which indicated that Schisandrin B could regulate BCYRN1 through miR-150.

Transcriptional profiling identifies the long noncoding RNA plasmacytoma variant translocation (PVT1) as a novel regulator of the asthmatic phenotype in human airway smooth muscle

BACKGROUND

The mechanism underlying nonsevere and severe asthma remains unclear, although it is commonly associated with increased airway smooth muscle (ASM) mass. Long noncoding RNAs (lncRNAs) are known to be important in regulating healthy primary airway smooth muscle cells (ASMCs), whereas changed expression has been observed in CD8 T cells from patients with severe asthma.

METHODS

Primary ASMCs were isolated from healthy subjects (n = 9) and patients classified as having nonsevere (n = 9) or severe (n = 9) asthma. ASMCs were exposed to dexamethasone and FCS. mRNA and lncRNA expression was measured by using a microarray and quantitative real-time PCR. Bioinformatic analysis was used to examine relevant biological pathways. Finally, the lncRNA plasmacytoma variant translocation 1 (PVT1) was inhibited by transfection of primary ASMCs with small interfering RNAs, and the effect on ASMC phenotype was examined.

RESULTS

The mRNA expression profile was significantly different between patient groups after exposure to dexamethasone and FCS, and these were associated with biological pathways that might be relevant to the pathogenesis of asthma, including cellular proliferation and pathways associated with glucocorticoid activity. We also observed a significant change in lncRNA expression, yet the expression of only one lncRNA (PVT1) is decreased in patients with corticosteroid-sensitive nonsevere asthma and increased in patients with corticosteroid-insensitive severe asthma. Subsequent targeting studies demonstrated the importance of this lncRNA in controlling both proliferation and IL-6 release in ASMCs from patients with severe asthma.

CONCLUSIONS

lncRNAs are associated with the aberrant phenotype observed in ASMCs from asthmatic patients. Targeting PVT1 might be effective in reducing airway remodeling in asthmatic patients.

Aberrant DNA Methylation of Phosphodiesterase [corrected] 4D Alters Airway Smooth Muscle Cell Phenotypes

Airway hyperresponsiveness (AHR) is a hallmark feature in asthma characterized by exaggerated airway contractile response to stimuli due to increased airway sensitivity and chronic airway remodeling. We have previously shown that allergen-induced AHR in mice is associated with aberrant DNA methylation in the lung genome, suggesting that AHR could be epigenetically regulated, and these changes might predispose the animals to asthma. Previous studies demonstrated that overexpression of phosphodiesterase 4D (PDE4D) is associated with increased AHR. However, epigenetic regulation of this gene in asthmatic airway smooth muscle cells (ASMCs) has not been examined. In this study, we aimed to examine the relationship between epigenetic regulation of PDE4D and ASMC phenotypes. We identified CpG site-specific hypomethylation at PDE4D promoter in human asthmatic ASMCs. We next used methylated oligonucleotides to introduce CpG site-specific methylation at PDE4D promoter and examined its effect on ASMCs. We showed that PDE4D methylation decreased cell proliferation and migration of asthmatic ASMCs. We further elucidated that methylated PDE4D decreased PDE4D expression in asthmatic ASMCs, increased cAMP level, and inhibited the aberrant increase in Ca(2+) level. Moreover, PDE4D methylation reduced the phosphorylation level of downstream effectors of Ca(2+) signaling, including myosin light chain kinase and p38. Taken together, our findings demonstrate that gene-specific epigenetic changes may predispose ASMCs to asthma through alterations in cell phenotypes. Modulation of ASMC phenotypes by methylated PDE4D oligonucleotides can reverse the aberrant ASMC functions to normal phenotypes. This has provided new insight to the development of novel therapeutic options for this debilitative disease.

Effects of miRNA-145 on airway smooth muscle cells function

The pathological changes of airway smooth muscle (ASM) contribute to airway remodeling during asthma. Here, we investigated the effect of miR-145 on ASM function. We found that miR-145 was aberrantly more highly expressed in ASM cells exposed to cytokine stimulation that mimic the airway conditions of patients with asthma. Repression of miR-145 resulted in decreased ASM cell proliferation and migration in a dose-dependent manner and down-regulation of type I collagen and contractile protein MHC in ASM cells. qRT-PCR and Western blot analysis demonstrated that miR-145 negatively regulated the expression of downstream target Krüppel-like factor 4 (KLF4) protein, and overexpression of KLF4 attenuated the effects of miR-145 on ASM cells. Further studies showed that KLF4 significantly up-regulated the expression of p21 and down-regulated matrix metalloproteinase (MMP-2 and MMP-9). In conclusion, miR-145 overexpression in ASM cells significantly inhibited KLF4, and subsequently affected downstream p21, MMP-2, and MMP-9 expressions, eventually leading to enhanced proliferation and migration of ASM cells in vitro.

Hypertensive epigenetics: from DNA methylation to microRNAs

The major epigenetic features of mammalian cells include DNA methylation, posttranslational histone modifications and RNA-based mechanisms including those controlled by small non-coding RNAs (microRNAs (miRNAs)). An important aspect of epigenetic mechanisms is that they are potentially reversible and may be influenced by nutritional-environmental factors and through gene-environment interactions. Studies on epigenetic modulations could help us understand the mechanisms involved in essential hypertension and further prevent it's progress. This review is focused on new knowledge on the role of epigenetics, from DNA methylation to miRNAs, in essential hypertension.

Homodimerization of RBPMS2 through a new RRM-interaction motif is necessary to control smooth muscle plasticity

In vertebrates, smooth muscle cells (SMCs) can reversibly switch between contractile and proliferative phenotypes. This involves various molecular mechanisms to reactivate developmental signaling pathways and induce cell dedifferentiation. The protein RBPMS2 regulates early development and plasticity of digestive SMCs by inhibiting the bone morphogenetic protein pathway through its interaction with NOGGIN mRNA. RBPMS2 contains only one RNA recognition motif (RRM) while this motif is often repeated in tandem or associated with other functional domains in RRM-containing proteins. Herein, we show using an extensive combination of structure/function analyses that RBPMS2 homodimerizes through a particular sequence motif (D-x-K-x-R-E-L-Y-L-L-F: residues 39–51) located in its RRM domain. We also show that this specific motif is conserved among its homologs and paralogs in vertebrates and in its insect and worm orthologs (CPO and MEC-8, respectively) suggesting a conserved molecular mechanism of action. Inhibition of the dimerization process through targeting a conserved leucine inside of this motif abolishes the capacity of RBPMS2 to interact with the translational elongation eEF2 protein, to upregulate NOGGIN mRNA in vivo and to drive SMC dedifferentiation. Our study demonstrates that RBPMS2 possesses an RRM domain harboring both RNA-binding and protein-binding properties and that the newly identified RRM-homodimerization motif is crucial for the function of RBPMS2 at the cell and tissue levels.

Role of non-coding RNAs in maintaining primary airway smooth muscle cells

Background

The airway smooth muscle (ASM) cell maintains its own proliferative rate and contributes to the inflammatory response in the airways, effects that are inhibited by corticosteroids, used in the treatment of airways diseases.

Objective

We determined the differential expression of mRNAs, microRNAs (miRNAs) and long noncoding RNA species (lncRNAs) in primary ASM cells following treatment with a corticosteroid, dexamethasone, and fetal calf serum (FCS).

Methods

mRNA, miRNA and lncRNA expression was measured by microarray and quantitative real-time PCR.

Results

A small number of miRNAs (including miR-150, −371-5p, −718, −940, −1181, −1207-5p, −1915, and −3663-3p) were decreased following exposure to dexamethasone and FCS. The mRNA targets of these miRNAs were increased in expression. The changes in mRNA expression were associated with regulation of ASM actin cytoskeleton. We also observed changes in expression of lncRNAs, including natural antisense, pseudogenes, intronic lncRNAs, and intergenic lncRNAs following dexamethasone and FCS. We confirmed the change in expression of three of these, LINC00882, LINC00883, PVT1, and its transcriptional activator, c-MYC. We propose that four of these lincRNAs (RP11-46A10.4, LINC00883, BCYRN1, and LINC00882) act as miRNA ‘sponges’ for 4 miRNAs (miR-150, −371-5p, −940, −1207-5p).

Conclusion

This in-vitro model of primary ASM cell phenotype was associated with the regulation of several ncRNAs. Their identification allows for in-vitro functional experimentation to establish causality with the primary ASM phenotype, and in airway diseases such as asthma and chronic obstructive pulmonary disease (COPD).

Alterations of the lung methylome in allergic airway hyper-responsiveness

Asthma is a chronic airway disorder characterized by recurrent attacks of breathlessness and wheezing, affecting 300 million people around the world (available at: www.who.int). To date, genetic factors associated with asthma susceptibility have been unable to explain the full etiology of asthma. Recent studies have demonstrated that the epigenetic disruption of gene expression plays an equally important role in the development of asthma through interaction with our environment. We sensitized 6-week-old C57BL/6J mice with house-dust-mite (HDM) extracts intraperitoneally followed by 5 weeks of exposure to HDM challenges (three times a week) intratracheally. HDM-exposed mice showed an increase in airway hyper-responsiveness (AHR) and inflammation together with structural remodeling of the airways. We applied methylated DNA immunoprecipitation-next generation sequencing (MeDIP-seq) for profiling of DNA methylation changes in the lungs in response to HDM. We observed about 20 million reads by a single-run of massive parallel sequencing. We performed bioinformatics and pathway analysis on the raw sequencing data to identify differentially methylated candidate genes in HDM-exposed mice. Specifically, we have revealed that the transforming growth factor beta signaling pathway is epigenetically modulated by chronic exposure to HDM. Here, we demonstrated that a specific allergen may play a role in AHR through an epigenetic mechanism by disrupting the expression of genes in lungs that might be involved in airway inflammation and remodeling. Our findings provide new insights into the potential mechanisms by which environmental allergens induce allergic asthma and such insights may assist in the development of novel preventive and therapeutic options for this debilitative disease.

Brain-derived neurotrophic factor in the airways

In addition to their well-known roles in the nervous system, there is increasing recognition that neurotrophins such as brain derived neurotrophic factor (BDNF) as well as their receptors are expressed in peripheral tissues including the lung, and can thus potentially contribute to both normal physiology and pathophysiology of several diseases. The relevance of this family of growth factors lies in emerging clinical data indicating altered neurotrophin levels and function in a range of diseases including neonatal and adult asthma, sinusitis, influenza, and lung cancer. The current review focuses on 1) the importance of BDNF expression and signaling mechanisms in early airway and lung development, critical to both normal neonatal lung function and also its disruption in prematurity and insults such as inflammation and infection; 2) how BDNF, potentially derived from airway nerves modulate neurogenic control of airway tone, a key aspect of airway reflexes as well as dysfunctional responses to allergic inflammation; 3) the emerging idea that local BDNF production by resident airway cells such as epithelium and airway smooth muscle can contribute to normal airway structure and function, and to airway hyperreactivity and remodeling in diseases such as asthma. Furthermore, given its pleiotropic effects in the airway, BDNF may be a novel and appealing therapeutic target.

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

It is now established that airway smooth muscle (ASM) has roles in determining airway structure and function, well beyond that as the major contractile element. Indeed, changes in ASM function are central to the manifestation of allergic, inflammatory, and fibrotic airway diseases in both children and adults, as well as to airway responses to local and environmental exposures. Emerging evidence points to novel signaling mechanisms within ASM cells of different species that serve to control diverse features, including 1) [Ca(2+)]i contractility and relaxation, 2) cell proliferation and apoptosis, 3) production and modulation of extracellular components, and 4) release of pro- vs. anti-inflammatory mediators and factors that regulate immunity as well as the function of other airway cell types, such as epithelium, fibroblasts, and nerves. These diverse effects of ASM "activity" result in modulation of bronchoconstriction vs. bronchodilation relevant to airway hyperresponsiveness, airway thickening, and fibrosis that influence compliance. This perspective highlights recent discoveries that reveal the central role of ASM in this regard and helps set the stage for future research toward understanding the pathways regulating ASM and, in turn, the influence of ASM on airway structure and function. Such exploration is key to development of novel therapeutic strategies that influence the pathophysiology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis.