The anti-proliferative and anti-inflammatory response of COPD airway smooth muscle cells to hydrogen sulfide.

BACKBROUND: COPD is a common, highly debilitating disease of the airways, primarily caused by smoking. Chronic inflammation and structural remodelling are key pathological features of this disease caused, in part, by the aberrant function of airway smooth muscle (ASM). We have previously demonstrated that hydrogen sulfide (H2S) can inhibit ASM cell proliferation and CXCL8 release, from cells isolated from non-smokers. METHODS: We examined the effect of H2S upon ASM cells from COPD patients. ASM cells were isolated from non-smokers, smokers and patients with COPD (n = 9). Proliferation and cytokine release (IL-6 and CXCL8) of ASM was induced by FCS, and measured by bromodeoxyuridine incorporation and ELISA, respectively. RESULTS: Exposure of ASM to H2S donors inhibited FCS-induced proliferation and cytokine release, but was less effective upon COPD ASM cells compared to the non-smokers and smokers. The mRNA and protein expression of the enzymes responsible for endogenous H2S production (cystathionine-ß-synthase [CBS] and 3-mercaptopyruvate sulphur transferase [MPST]) were inhibited by H2S donors. Finally, we report that exogenous H2S inhibited FCS-stimulated phosphorylation of ERK-1/2 and p38 mitogen activated protein kinases (MAPKs), in the non-smoker and smoker ASM cells, with little effect in COPD cells. CONCLUSIONS: H2S production provides a novel mechanism for the repression of ASM proliferation and cytokine release. The ability of COPD ASM cells to respond to H2S is attenuated in COPD ASM cells despite the presence of the enzymes responsible for H2S production.

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.

BET bromodomains regulate transforming growth factor-ß-induced proliferation and cytokine release in asthmatic airway smooth muscle.

Airway smooth muscle (ASM) mass is increased in asthma, and ASM cells from patients with asthma are hyperproliferative and release more IL-6 and CXCL8. The BET (bromo- and extra-terminal) family of proteins (Brd2, Brd3, and Brd4) govern the assembly of histone acetylation-dependent chromatin complexes. We have examined whether they modulate proliferation and cytokine expression in asthmatic ASM cells by studying the effect of BET bromodomain mimics JQ1/SGCBD01 and I-BET762. ASM cells from healthy individuals and nonsevere and severe asthmatics were pretreated with JQ1/SGCBD01 and I-BET762 prior to stimulation with FCS and TGF-ß. Proliferation was measured by BrdU incorporation. IL-6 and CXCL8 release was measured by ELISA, and mRNA expression was measured by quantitative RT-PCR. ChIP using a specific anti-Brd4 antibody and PCR primers directed against the transcriptional start site of IL-6 and CXCL8 gene promoters was performed. Neither JQ1/SGCBD01 nor I-BET762 had any effect on ASM cell viability. JQ1/SGCBD01 and I-BET762 inhibited FCS+TGF-ß-induced ASM cell proliferation and IL-6 and CXCL8 release in healthy individuals (≥ 30 nM) and in nonsevere and severe asthma patients (≥100 nM), with the latter requiring higher concentrations of these mimics. JQ1/SGCBD01 reduced Brd4 binding to IL8 and IL6 promoters induced by FCS+TGF-ß. Mimics of BET bromodomains inhibit aberrant ASM cell proliferation and inflammation with lesser efficiency in those from asthmatic patients. They may be effective in reducing airway remodeling in asthma.

Airway smooth muscle hyperproliferation is regulated by microRNA-221 in severe asthma.

Increased airway smooth muscle (ASM) mass is a feature of asthmatic airways, and could result from augmented proliferation. We determined whether proliferation and IL-6 release are abnormal in ASM cells (ASMCs) from patients with severe asthma, and whether these features could be mediated by microRNA-221 and microRNA-222, through modulation of the cyclin-dependent kinase inhibitors, p21(WAF1) and p27(kip1). ASMCs cultured from bronchial biopsies of healthy subjects and patients with nonsevere or severe asthma were studied. Proliferation was measured by the incorporation of bromodeoxyuridine and IL-6 by ELISA. FCS and transforming growth factor (TGF)-ß caused greater proliferation and IL-6 release in patients with severe compared with nonsevere asthma and normal subjects. FCS + TGF-ß inhibited p21(WAF1) and p27(kip1) expression, and increased microRNA-221 (miR-221) expression in ASMCs from individuals with severe asthma. miR-221, and not miR-222, mimics the increased proliferation and IL-6 release induced by FCS + TGF in healthy ASM, whereas in patients with severe asthma, the inhibition of miR-221, but not miR-222, inhibited proliferation and IL-6 release. miR-221 inhibition led to the increased expression of FCS + TGF-ß-induced p21(WAF1) and p27(kip1). Dexamethasone suppressed proliferation in healthy subjects, but not in subjects with asthma. IL-6 was less suppressible by dexamethasone in patients with nonsevere and severe asthma, compared with healthy subjects. miR-221 did not influence the effects of dexamethasone. ASM from patients with severe asthma shows greater proliferation and IL-6 release than in patients with nonsevere asthma, but both groups show corticosteroid insensitivity. miR-221 regulates p21(WAF1) and p27(kip1) expression levels. Furthermore, miR-221 regulates the hyperproliferation and IL-6 release of ASMCs from patients with severe asthma, but does not regulate corticosteroid insensitivity.

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).

Hydrogen sulfide inhibits proliferation and release of IL-8 from human airway smooth muscle cells.

Hydrogen sulfide (H(2)S) is synthesized intracellularly by the enzymes cystathionine-γ-lyase and cystathionine-ß-synthase (CBS), and is proposed to be a gasotransmitter with effects in modulating inflammation and cellular proliferation. We determined a role of H(2)S in airway smooth muscle (ASM) function. ASM were removed from resection or transplant donor lungs and were placed in culture. Proliferation of ASM was induced by FCS and the proinflammatory cytokine, IL-1ß. Proliferation of ASM and IL-8 release were measured by bromodeoxyuridine incorporation and ELISA, respectively. Exposure of ASM to H(2)S "donors" inhibited this proliferation and IL-8 release. Methemoglobin, a scavenger of endogenous H(2)S, increased DNA synthesis induced by FCS and IL-1ß. In addition, methemoglobin increased IL-8 release induced by FCS, but not by IL-1ß, indicating a role for endogenous H(2)S in these systems. Inhibition of CBS, but not cystathionine-γ-lyase, reversed the inhibitory effect of H(2)S on proliferation and IL-8 release, indicating that this is dependent on CBS. CBS mRNA and protein expression were inhibited by H(2)S donors, and were increased by methemoglobin, indicating that CBS is the main enzyme responsible for endogenous H(2)S production. Finally, we found that exogenous H(2)S inhibited the phosphorylation of extracellular signal-regulated kinase-1/2 and p38, which could represent a mechanism by which H(2)S inhibited cellular proliferation and IL-8 release. In summary, H(2)S production provides a novel mechanism for regulation of ASM proliferation and IL-8 release. Therefore, regulation of H(2)S may represent a novel approach to controlling ASM proliferation and cytokine release that is found in patients with asthma.

Pharmacological studies of the mechanism and function of interleukin-1beta-induced miRNA-146a expression in primary human airway smooth muscle.

BACKGROUND: Despite the widespread induction of miR-146a during the innate immune response little is known regarding its biogenesis, function and mechanism. We have therefore examined the role of miR-146a during the interleukin (IL)-1beta-stimulated IL-6 and IL-8 release and proliferation in primary human airway smooth muscle (HASM) cells. METHODS: HASM cells were isolated from human lung re-section, cultured to a maximum of 3 - 6 passages and then exposed to IL-1beta. miR-146a expression were determined by qRT-PCR, IL-6 and IL-8 release by ELISA and proliferation using bromodeoxyuridine incorporation. The role of NF-kappaB and the MAP kinase pathways was assessed using pharmacological inhibitors of IKK2 (TPCA-1), JNK (SP600125), p38 MAP kinase (SB203580) and MEK-1/2 (PD98059). miR-146a function was determined following transfection of HASM with inhibitors and mimics using Amaxa electroporation. RESULTS: IL-1beta induced a time-dependent and prolonged 100-fold induction in miR-146a expression, which correlated with release of IL-6 and IL-8. Exposure to IL-1beta had no effect upon HASM proliferation. Pharmacological studies showed that expression of primary miR-146a was regulated at the transcriptional levels by NF-kappaB whilst post-transcriptional processing to mature miR-146a was regulated by MEK-1/2 and JNK-1/2. Functional studies indicated that IL-1beta-induced miR-146a expression does not negatively regulate IL-6 and IL-8 release or basal proliferation. However, inhibition of IL-1beta-induced IL-6 and IL-8 release was observed at the super-maximal intracellular miR-146a levels obtained by transfection with miR-146a mimics and indicates that studies using miRNA mimics can produce false positive results. Mechanistic studies showed that in the presence of super-maximal levels, the action of miR-146a mimics was mediated at a step following IL-6 and IL-8 mRNA transcription and not through down-regulation of IL-1 receptor associated kinase 1 (IRAK-1) and TNF receptor-associated factor 6 (TRAF6) protein expression, two predicted miR-146a targets involved in IL-1beta signalling. CONCLUSIONS: We have shown that IL-1beta-induced miR-146a expression in HASM and that this was regulated at the transcriptional level by NF-kappaB and at the post-transcriptional level by the MEK-1/2 and JNK-1/2. Unlike previous reports, studies using miRNA inhibitors showed that miR-146a expression did not regulate IL-6 and IL-8 release or proliferation and suggest miR-146a function and mechanism is cell-type dependent.

Role of miRNA-146a in the regulation of the innate immune response and cancer.

In mammalian cells, miRNAs (microRNAs) are the most abundant family of small non-coding RNAs that regulate mRNA translation through the RNA interference pathway. In general, it appears that the major function of miRNAs is in development, differentiation and homoeostasis, which is indicated by studies showing aberrant miRNA expression during the development of cancer. Interestingly, changes in the expression of miR-146a have been implicated in both the development of multiple cancers and in the negative regulation of inflammation induced via the innate immune response. Furthermore, miR-146a expression is driven by the transcription factor NF-kappaB (nuclear factor kappaB), which has been implicated as an important causal link between inflammation and carcinogenesis. In the present article, we review the evidence for a role of miR-146a in innate immunity and cancer and assess whether changes in miR-146a might link these two biological responses.

microRNA expression in the aging mouse lung.

BACKGROUND: MicroRNAs (miRNAs) are a novel class of short double stranded RNA that mediate the post-transcriptional regulation of gene expression. Previous studies have implicated changes in miRNA expression in the regulation of development and the induction of diseases such as cancer. However, although miRNAs have been implicated in the process of aging in C. elegans, nothing is known of their role in mammalian tissues. RESULTS: To address this question, we have used a highly-sensitive, semi-quantitative RT-PCR based approach to measure the expression profile of 256 of the 493 currently identified miRNAs in the lungs from 6 month (adult) and 18 month (aged) old female BALB/c mice. We show that, despite the characteristic changes in anatomy and gene expression associated with lung aging, there were no significant changes in the expression of 256 miRNAs. CONCLUSION: Overall, these results show that miRNA transcription is unchanged during lung aging and suggests that stable expression of miRNAs might instead buffer age related changes in the expression of protein-encoding genes.

Expression profiling in vivo demonstrates rapid changes in lung microRNA levels following lipopolysaccharide-induced inflammation but not in the anti-inflammatory action of glucocorticoids.

BACKGROUND: At present, nothing is known of the role of miRNAs in the immune response in vivo despite the fact that inflammation is thought to underlie multiple acute and chronic diseases. In these circumstances, patients are commonly treated with corticosteroids such as dexamethasone. RESULTS: To address this question, we have examined the differential expression of 104 miRNAs using real-time PCR during the innate immune response in mouse lung following exposure to aerosilised lipopolysaccharide (LPS). Following challenge, we observed rapid and transient increase in both the mean (4.3-fold) and individual levels of miRNA expression (46 miRNAs) which peaked at 3 hrs. Crucially, this increase was correlated with a reduction in the expression of tumour necrosis factor (TNF)-alpha, keratinocyte-derived chemokine (KC) and macrophage inflammatory protein (MIP)-2, suggesting a potential role for miRNAs in the regulation of inflammatory cytokine production. Examination of the individual miRNA expression profiles showed time dependent increases in miR-21, -25, -27b, -100, 140, -142-3p, -181c, 187, -194, -214, -223 and -224. Corticosteroid studies showed that pre-treatment with dexamethasone at concentrations that inhibited TNF-alpha production, had no effect either alone or upon the LPS-induced miRNA expression profile. CONCLUSION: We have shown that the LPS-induced innate immune response is associated with widespread, rapid and transient increases in miRNA expression in the mouse lung and we speculate that these changes might be involved in the regulation of the inflammatory response. In contrast, the lack of effect of dexamethasone in either control or challenged animals implies that the actions of glucocorticoids per se are not mediated through changes in miRNAs expression and that LPS-induced increases in miRNA expression are not mediated via classical inflammatory transcription factors.

Noncoding RNAs and Duchenne muscular dystrophy.

Noncoding RNAs (ncRNAs) such as miRNAs and long noncoding RNAs modulate gene transcription in response to environmental stressors and other stimuli. A role for ncRNAs in muscle pathologies has been demonstrated and further evidence suggests that ncRNAs also play a role in Duchenne muscular dystrophy (DMD). Studies investigating the differential expression of miRNAs in biological fluids between DMD patients and models of dystrophin deficiency (the MDX mouse model, canine models of DMD) and controls have been published, as these have a role in fibrosis. Long noncoding RNAs are differentially expressed in DMD patients and may, in part, have a mechanism of action via targeting of miRNAs. Although many of these recent findings need to be confirmed, ncRNAs may prove to be useful as potential biomarkers of disease. However, their use as therapeutic targets in DMD remains unclear.

Airway smooth muscle inflammation is regulated by microRNA-145 in COPD.

Chronic obstructive pulmonary disease (COPD) is a common, highly debilitating disease of the airways, primarily caused by smoking. Chronic inflammation and structural remodelling are key pathological features of this disease, in part caused by the aberrant function of airway smooth muscle (ASM) cells under the regulation of transforming growth factor (TGF)-ß. miRNA are short, noncoding gene transcripts involved in the negative regulation of specific target genes, through their interactions with mRNA. Previous studies have proposed that mRNA-145 (miR-145) may interact with SMAD3, an important downstream signalling molecule of the TGF-ß pathway. TGF-ß was used to stimulate primary human ASM cells isolated from healthy nonsmokers, healthy smokers and COPD patients. This resulted in a TGF-ß-dependent increase in CXCL8 and IL-6 release, most notably in the cells from COPD patients. TGF-ß stimulation increased SMAD3 expression, only in cells from COPD patients, with a concurrent increased miR-145 expression. Regulation of miR-145 was found to be negatively controlled by pathways involving the MAP kinases, MEK-1/2 and p38 MAPK. Subsequent, overexpression of miR-145 (using synthetic mimics) in ASM cells from patients with COPD suppressed IL-6 and CXCL8 release, to levels comparable to the nonsmoker controls. Therefore, this study suggests that miR-145 negatively regulates pro-inflammatory cytokine release from ASM cells in COPD by targeting SMAD3.

Role of microRNAs in allergic asthma: present and future.

PURPOSE OF REVIEW: MicroRNAs (miRNAs) modulate gene transcription in response to environmental stressors and other stimuli. A role for miRNAs in inflammation and immunity has been demonstrated and further evidence suggests that miRNAs also play a role in allergic asthma. RECENT FINDINGS: Studies investigating the differential expression of miRNAs in biological fluids between asthma patients and controls have been published, as have their role in immune cell subsets. Further development of miRNAs in therapy has been addressed. miRNA-146a has been implicated in autoimmunity and allergic inflammation and miRNA-155 in the development of atopy. Targeting of miRNA-1 and miRNA-145 has been used to inhibit lung inflammation in mouse models of asthma. Although these recent findings need to be confirmed, miRNAs may prove to be useful as potential biomarkers of disease. However, their use as therapeutic targets in the lung remains unclear. SUMMARY: There may be a potential role for using circulating miRNAs as biomarkers of disease status or response to therapy. The use of miRNAs as asthma therapy remains to be determined.

Epigenome-modifying tools in asthma.

Asthma is a chronic disease which causes recurrent breathlessness affecting 300 million people worldwide of whom 250,000 die annually. The epigenome is a set of heritable modifications and tags that affect the genome without changing the intrinsic DNA sequence. These marks include DNA methylation, modifications to histone proteins around which DNA is wrapped and expression of noncoding RNA. Alterations in all of these processes have been reported in patients with asthma. In some cases these differences are linked to disease severity and susceptibility and may account for the limited value of genetic studies in asthma. Animal models of asthma suggest that epigenetic modifications and processes are linked to asthma and may be tractable targets for therapeutic intervention.

Divergent intracellular pathways regulate interleukin-1beta-induced miR-146a and miR-146b expression and chemokine release in human alveolar epithelial cells.

We have previously reported that IL-beta-induced miR-146a and miR-146b expression negatively regulates IL-8 and RANTES release in human alveolar A549 epithelial cells. To determine the intracellular pathways that regulate this response, we demonstrate IL-1beta-induced activation of the nuclear factor (NF)-kappaB, extracellular regulated kinase (ERK)-1/2, c-jun N-terminal kinase (JNK)-1/2 and p38 mitogen activated kinase (MAP) kinase pathways. Subsequent pharmacological studies show that IL-1beta-induced miR-146a, IL-8 and RANTES production was regulated via NF-kappaB and JNK-1/2 whilst miR-146b expression was mediated via MEK-1/2 and JNK-1/2. These divergent intracellular pathways likely explain the differential expression and biological action of the miR-146 isoforms.

MicroRNA expression profiling in mild asthmatic human airways and effect of corticosteroid therapy.

BACKGROUND: Asthma is a common disease characterised by reversible airflow obstruction, bronchial hyperresponsiveness and chronic inflammation, which is commonly treated using corticosteroids such as budesonide. MicroRNAs (miRNAs) are a recently identified family of non-protein encoding genes that regulate protein translation by a mechanism entitled RNA interference. Previous studies have shown lung-specific miRNA expression profiles, although their importance in regulating gene expression is unresolved. We determined whether miRNA expression was differentially expressed in mild asthma and the effect of corticosteroid treatment. METHODOLOGY/PRINCIPAL FINDINGS: We have examined changes in miRNA using a highly sensitive RT-PCR based approach to measure the expression of 227 miRNAs in airway biopsies obtained from normal and mild asthmatic patients. We have also determined whether the anti-inflammatory action of corticosteroids are mediated through miRNAs by determining the profile of miRNA expression in mild asthmatics, before and following 1 month twice daily treatment with inhaled budesonide. Furthermore, we have analysed the expression of miRNAs from individual cell populations from the airway and lung. We found no significant difference in the expression of 227 miRNAs in the airway biopsies obtained from normal and mild asthmatic patients. In addition, despite improved lung function, we found no significant difference in the miRNA expression following one month treatment with the corticosteroid, budesonide. However, analysis of bronchial and alveolar epithelial cells, airway smooth muscle cells, alveolar macrophages and lung fibroblasts demonstrate a miRNA expression profile that is specific to individual cell types and demonstrates the complex cellular heterogeneity within whole tissue samples. CONCLUSIONS: Changes in miRNA expression do not appear to be involved in the development of a mild asthmatic phenotype or in the anti-inflammatory action of the corticosteroid budesonide.

Rapid changes in microRNA-146a expression negatively regulate the IL-1beta-induced inflammatory response in human lung alveolar epithelial cells.

Posttranscriptional regulation of gene expression by microRNAs (miRNAs) has been implicated in the regulation of chronic physiological and pathological responses. In this report, we demonstrate that changes in the expression of miRNAs can also regulate acute inflammatory responses in human lung alveolar epithelial cells. Thus, stimulation with IL-1beta results in a rapid time- and concentration-dependent increase in miRNA-146a and, to a lesser extent, miRNA-146b expression, although these increases were only observed at high IL-1beta concentration. Examination of miRNA function by overexpression and inhibition showed that increased miRNA-146a expression negatively regulated the release of the proinflammatory chemokines IL-8 and RANTES. Subsequent examination of the mechanism demonstrated that the action of miRNA-146a was mediated at the translational level and not through the down-regulation of proteins involved in the IL-1beta signaling pathway or chemokine transcription or secretion. Overall, these studies indicate that rapid increase in miRNA-146a expression provides a novel mechanism for the negative regulation of severe inflammation during the innate immune response.

Maternally imprinted microRNAs are differentially expressed during mouse and human lung development.

MicroRNAs (miRNAs) are a recently discovered class of noncoding genes that regulate the translation of target mRNA. More than 300 miRNAs have now been discovered in humans, although the function of most is still unknown. A highly sensitive, semiquantitative real-time polymerase chain reaction method was used to reveal the differential expression of several miRNAs during the development of both mouse and human lung. Of note was the up-regulation in neonatal mouse and fetal human lung of a maternally imprinted miRNA cluster located at human chromosome 14q32.31 (mouse chromosome 12F2), which includes the miR-154 and miR-335 families and is situated within the Gtl2-Dio3 domain. Conversely, several miRNAs were up-regulated in adult compared with neonatal/fetal lung, including miR-29a and miR-29b. Differences in the spatial expression patterns of miR-154, miR-29a, and miR-26a was demonstrated using in situ hybridization of mouse neonatal and adult tissue using miRNA-specific locked nucleic acid (LNA) probes. Of interest, miR-154 appeared to be localized to the stroma of fetal but not adult lungs. The overall expression profile was similar for mouse and human tissue, suggesting evolutionary conservation of miRNA expression during lung development and demonstrating the importance of maternally imprinted miRNAs in the developmental process.