Role of microRNAs in lung development and pulmonary diseases.

2013·0.94 MB·English

by  Sessa, Roberto

Review Article
Role of microRNAs in lung development
and pulmonary diseases
Roberto Sessa, and Akiko Hata
Cardiovascular research institute, University of California San Francisco, CA 94158, USA
ABSTRACT
MicroRNAs (miRNAs) are a class of small noncoding RNA which exert post-transcriptional gene regulation activity by targeting
messenger RNAs. miRNAs have been found to be involved in various fundamental biological processes and deregulation of
miRNAs is known to result in pathological conditions. In this review, we provide an overview of recent discoveries on the role played
by this class of molecules in lung development and in pulmonary diseases, such as asthma, cystic fibrosis, chronic obstructive
pulmonary disease, and pulmonary artery hypertension. Considering the relevant role of these miRNAs under physiological and
pathological conditions, they represent new clinical targets as well as diagnostic and prognostic tools. Therefore, this review pays
special attention to recent advances and possible future directions for the use of miRNAs for clinical applications.
Key Words: asthma, COPD, cystic fibrosis, microRNA, pulmonary arterial hypertension, pulmonary development, pulmonary
disease
lin-4 let-7
Significant development has been made towards understanding target gene exCpareensosriao[7hn,8a] pbdoisttis-t erlaengascnrsipCt.i eolnegaallny.s The first
the contribution of microRNAs (miRNAs) in d[e1,2v]elopment of miRNAs and were discovered in 1993 and 2000
lung and pathogenesis of pulmonary diseases. This review respectively in ( ) as genes
will provides an overview on the role of miRNAs in lung disease involved in developmental timing by mediating sequence
reassuming recent findings that extent our perspective on the speCc. iefliecg paonsst-transcriptional regulation of gene expression.
importance of these molecules in guiding the cellular response Initially this new class of RNA was thought to be present only
upon different stress conditions. Interestingly, it appears that in , however, it was quickly revealed that it ex[i9s,1t0s]
this class of non-coding regulatory RNA play a key role in in many different animal species, including mammals.
several aspects of inflam[3m] ation which is a determinant feature Spatially and chronologically restricted expression patterns,
in many lung diseases such as cystic fibrosis, emphysem[a4,] and evolutionary conservation of miRNAs suggested that
asthma and Chronic Obstructive Pulmonary Disease (CODP). they have a broad regulatory function in plants and animals.
It is believed that miRNAs are involved in various aspects It has been shown that the whole miRNA system regulat[e11s]
of innate and acquired immunity, and therefore,[ 5i,6n]directly greater than 60% of protein-coding genes in a human cell.
involved in these inflammatory lung diseases. In this Close to 2000 human miRNAs have been described to date
review, we will discuss the involvement of miRNAs in lung (Sanger miRBase version 19, http://www.mirbase.org/
development as well as the pathogenesis of various pulmonary blog/2012/08/mirbase-19-released/), which play critical
diseases (Table 1). roles in development and physiological and pathological
MICRORNA BIOGENESIS AND
processes.
FUNCTION
MiRNAs are mainly encoded in either inter-genic regions
or within protein coding genes, usually introns. The
molecular origins ofA mccieRssN tAhiss aanrtidc lme oRnNlinAe targets are not well
Quick Response Code: Website: www.pulmonarycirculation.org
miRNAs are small noncoding RNAs that function by regulating
Address correspondence to: DOI: 10.4103/2045-8932.114758
Dr. Akiko Hata
Cardiovascular Research Institute
University of California San Francisco How to cite this article: Sessa R, Hata A.
Role of microRNAs in lung development
555 Mission Bay Blvd. South, Room 252T
and pulmonary diseases. Pulm Circ 2013;3:
San Francisco, CA 94158
315-28.
Fax: [phone]
Email: [email protected]
Pulmonary Circulation | April-June 2013 | Vol 3 | No 2 315
Sessa and Hata: miRNAs pulmonary development and disease
Table 1: miRNAs in lung disease
COPD
to few thousand nucleotides in length (Fig. 1). RNA
miR-223; miR-1274[58] Up
miR-923; miR-937; miR-125b-1 Down polymerase II is involved in the production of this capped
miR-101 and miR-144[61] Up and polyadenylated stem-loop-structured pri-miRNA,
miR-146a[65] Up even though it has been found that some pri-miRNAs, in
miR-452[63] Down
suggested paper on miRNA screening related to particular those that lie within the[1 4A]lu repeats, can be
COPD[58,67] and CS[63,191] produced by RNA polymerase III. Subsequently the
Asthma pri-miRNA undergoes processing by RNA endonucleases
miR-126[80] Up
(RNase) in two sequential cleavage steps. The first
miR-145a[79] Up
miR-146a; miR-146b; miR-181[192] Up cleavage takes place in the nucleus by the type III RNase
let-7[78] Down Drosha that liberates a shorter oligonucleotide of about
miR-21[76] Up
miR-221; miR-222[83] Up ~70-90 nucle[o17t]ide (nt) in length called precursor-miRNA
miR-106a[81] Up (pre-miRNA). Drosha cleaves pri-miRNAs together with
miR-20b[94] Down a cofactor known as DiGeorge syndrome critical region
miR-155[193] Up gene 8 (DGCR8) which represents an important hub for
miR-133a[194] Down
Cystic fibrosis many regulatory proteins in[1v8o,1l9v]ed in the regulation of the
miR-155[107,195] Up miRNA maturation process (Fig. 1). The pre-miRNA is
miR-101; miR-494[103] Up then exported to the cytoplasm by the Exportin 5 protein
miR-126[100] Down
where it is further processed by the RNase III enzyme Dicer.
miR-138[196] Down
Idiopathic Pulmonary Fibrosis Dicer generates a ~22 nt double-strand ribonucleotides
miR-29[124] Down with 5’ [p20h]osphate and two nucleotides 3’ overhangs
miR-2[177] Up
(Fig. 1). In the subsequent step, the two strands are
miR-154[123] Up
let-7d[120] Down separated and [o21n]e of them is recruited by the Argonaute
miR-17[122] Down (Ago) proteins to form a multi-protein comp[2l2e]x known
miR-155; miR-125b[122] Up as the RNA-induced silencing complex (RISC) (Fig. 1).
suggested paper on miRNA screening in bleomycin-induce
This loaded RISC machinery is able to guide the miRNA to
lung fibrosis[172]
PAH target partially complementary sequences, usually present
miR-17-92[131,146,149] Up in the 3’-untranslated region (UTR), on mRNA transcripts.
miR-206[197] Down
Generally, just one strand of miRNA is accumulated inside
miR-143-145[157] Down
miR-21[139,140,144] Up the cell and loaded in the RISC complex by association
miR-27a[144] Down with Ago1 and Ago2 which are the two most [h23i]ghly
miR-204[141,149] Down
expressed Ago proteins present in mammalian cells. The
miR-210[147,148] Up
miR-424[198] Down other strand, often referred as “miRNA*”, was originally
miR-503[198] Down considered as a byproduct of the miRNA biogenesis,
miR-150[135] Down however recent fin[24d-2i8n]gs demonstrated that it retains
Acute lung Injury
biological activities. The 6-8 nucleotide sequence at the
miR-127[173] Down
mi21-; miR-155; miR-146[170] Up 5’-end of miRNA which contributes to base paring with the
miR-32*; miR-466-5p; miR-466-3p[171] Up target mRNAs is referred as the “seed sequence”. In recent
years contrasting results have been published regarding the
List of miRNAs that are differentially expressed in lung pathologies, as
reported in the literature. Up and Down indicate if the miRNA is elevated mechanism of miRNA binding to Ago proteins. Ago2 is the
or reduced in diseased tissues, respectively; COPD: chronic obstructive
pulmonary disease; PAH: pulmonary artery hypertension is the only isoform with RNase activity and mainly acts to
promote mRNA degradation while Ago1[ 2s9e]ems optimized
for cleavage-independent repression. Furthermore,
Ago2 appears to have selectivity[ 2f9o,3r0 ]siRNA-like duplexes
established, however, it is su[g12g,1e3s]ted that miRNAs originate with more extensive base pairing It is noted that miR*
from transposome elements. Indeed, several miRNA loci strands represe[n31t] an abundant fraction of RNA species
have been described at a repetitive element transposition bound to Ago2. Therefore, miR:miR* duplex could be
and subsequent t[1r4a]nscription across two tandems, inverted bifunctional with one strand associated with Ago1 which
repeat elements. Alternatively, miRNAs in plants seems to functions as a cleavage-independent repression of the
be originated from inverted duplication event of the target mRNA, and the miR* associated with Ago2 whi[c32h] triggers
gene that can form a self-complementary hairpin with the
a cleavage-dependent repression of the mRNA.
potential to spawn in new miRN[1A5,1 g6]enes if it can confer an miRNAs IN LUNG DEVELOPMENT
advantage of positive selection.
The biogenesis of miRNAs begins with the transcription of
th3e1 p6rimary transcript (pri-miRNA) of about few hundreds miRNAs haPvuelm ornaapryi dCliryc uelamtioenr |g Aepdr il-nJounte o2n01ly3 |a Vs ocl r3i |t iNcoa l2ly
Sessa and Hata: miRNAs pulmonary development and disease
Figure 1: miRNA Biogenesis. miRNAs are transcribed in the nucleus by the RNA polymerase type II as long primary transcripts (pri-miRNA) of a few hundred
up to few thousand nucleotides (nt). The pri-miRNA is cleaved by the microprocessor containing Drosha, which is the type III RNase designated for the cleavage
of pri-miRNAs, in complex with several cofactors including DiGeorge syndrome Critical Region 8 (DGCR8). The processing of the pri-miRNA by the Drosha
complex gives rise to RNA with a short hairpin structure of 70−90 nt called precursor miRNA (pre-miRNA). The pre-miRNA is then exported from the nucleus
to the cytoplasm by Exportin 5 and then cleaved by the RNase type III enzyme Dicer. Dicer cleaves the pre-miRNA within a multi-protein complex that among
several components contain two double-stranded RNA binding proteins, the human immunodeficiency virus transactivating response RNA-binding protein
(TRBP) and PACT. As a result of cleavage by Dicer, pre-miRNA becomes the ~ 22 nt sequence, which is known as the mature form of the miRNA. One of
two strands of the mature miRNA is loaded into the RNA-Induced Silencing Complex (RISC) which contains Argonaute (Ago), and is guided to the 3’-UTR
of target messenger RNA (mRNA) where it then promotes translational inhibition or degradation of mRNA.
contributing to various pulmonary diseases but also to Ago2 are enriched in distal epithelium and mesenchyme
normal development of the lung and maintenance of its respectively, further underscoring the important role of
homeostasis. Lung development can be arbitrarily divided miRNAs in the dynamic chang[4e0s] occurring during lung
into 6 stages that are found in all mammalian species: remodeling and maturation. Evaluation of miRNA
embryonic, glandular, canalicular, saccular, alveolar and expression patterns during the different phases of lung
vascular maturation. After the initial differentiation of developme[n41t] revealed 27 miRNAs which are differentially
lung epithelial cells from the endoderm, the epithelial expressed. For instance miR-29a plays a role in limiti[n41g]
tube is formed with little to no lumen in the glandular proliferation in the late stage of lung development.
phase. In the canalicular phase, bronchioles are produced It is also highly expressed in the adult lung and from
and undergo thinning of the interstitium and a flattening over-expression[ 4i2n] lung cancer cells appears to inhibit
of the epithelium in order to form alveolar ducts and air tumorigenicity. The expression of the miR-17~92
sacs during the sec[u33la]r phase. At the final stage, alveoli are cluster, which includes 6 m[43iR] NA genes (miR-17, -18a, -19a,
formed after birth. -20a, -19b-1[,4 1a]nd -92-1), is decreased as development
progresses. An gene ontology (GO) analysis of the
Fetal lung development is a complex process temporally an[3d4] predicted targets of this cluster show that these miRNAs
spatially orchestrated by a complex set of many genes. control genes which are critical for proper developmental
The signalling molecules involved in lun[3g5] development progress, such as transcriptional factors and regulators
include fibroblast growth f[a36c]tors (F[3G7]Fs), transformi[n38g] of nucleic acid metabolism. The overexpr[4e4s]sion of this
growth factor- β (TGF-β), Wnts and hedgehogs. cluster is observed in lung cancer cells. Studies on
The evidence that miRNAs play a role in lung development the role of miR-17-92 locus in lung development have
derive from mice with conditional knockout of Dicer in lung found that miRNAs in this locus are highly expressed in
epithelial cells that exhibit a failure of epithelial branching, undifferentiated lung progenitor epithelial cells and, by
underscoring the essential reg[u39l]atory role of miRNAs in regulating the cell cycle regulator gene Reti[4n5o,46b]lastoma-like
lung epithelial morphogenesis. At embryonic stage 11.5 2 (Rbl2), it promotes their proliferation. In contrast,
(EPu1lm1o.5n)a riyn C tihrceu lalutionng | e Appirtihl-Jeulniael 2 b0r1a3n |c hVoinl 3g |r eNgoi o2n, Ago1 and miR-127 and miR-351 are expressed transiently du3r1i7ng
Sessa and Hata: miRNAs pulmonary development and disease
the sacculo-alveolar phase initially in the mesenchymal miR-223, which has been demonstrated [t5o9] be upregulated
compartment and later in the lung epithelial cells, upon lipopolysaccharide (LPS) e[5x8]posure, and miR-1274a
suggesting their roles lie in the cellular reorganization and being the most highly induced. In this study, the authors
differentiation pr[o41c]ess during mesenchymal to epithelial identified transforming growth factor (TGF)-β, Wnt and
transition (EMT). focal adhesion pathways as the most relevant pathways
in whi[c58h] miRNAs may be involved in the pathogenesis of
Additional studies on the miRNA expression pattern in COPD. In the same study, members of the miR10/107
lungs revealed two miRNAs, miR-200c and miR-195, family; miR-15b, 424, 107, were all upregulated with
which are specifically expressed in lung and nine miRN[A47s] miR-15b more abundantly localized in areas of emphysema
co-expressed in other organs, especially in the heart. as well as fibrosis preventing th[6e0] expression of SMAD7, an
miR-29a and miR-29b are upregulated in adult lun[4g8]s, while inhibitor of the TGF-β signaling. A recent study addressed
miR-154 is more abundant in neonatal lungs. These the role of two up regulated miRNAs, miR-101 and miR-144,
data indicate a similarity in the overall expression profile upon cigarette smoke exposure of human airway epithelial
between mouse and human lungs throughout the lung cells and in vivo[6 1i]n lungs of mice exposed to smoke and in
developmental process and highlight the evolutionarily COPD patients. It found that both these miRNAs target
conserved roles of miRNAs in this process. Finally, the cystic fibrosis transmembrane conductance regulator
evaluation of the miRNA signature in aged lungs has been (CFTR) which is a chloride channel found to be suppres[s62e]d
carried in order to figure out any characteristic changes by exposure to airway pollutants and cigarette smoke.
in miRNAs regulation, however no substantial difference
in miR[4N9]A expression have been observed in aged mouse MiRNA/mRNA microarray expression analyses carried
lungs. out on human alveolar macrophages from smoker and
miRNAs IN LUNG DISEASE non-smokers, found a general down modulation of miRNA
expression in smokers. In particular, low expression
of miR-452 has been linked to increa[s63e]d expression of
matrix metalloproteinase 12 (MMP12), which is know[6n4]
In this section, we will discuss the link between deregulation to be associated with the development of emphysema.
of miRNAs and the pathogenesis of different pulmonary Interestingly, this study delineate an association between
diseases (Table 1) as well as the potential therapeutic deregulation of miRNAs and macrophage polarization
approaches based on restoration of the physiological from an M2 immunosuppression-activate[6d3] phenotype to
mChiRrNoAn sicig onabtsutrreu.ctive pulmonary disease an M1 microbicidal-activated phenotype.
A regulatory role of miRNAs has also been observed in
Chronic obstructive pulmonary disease (COPD) presents the fibrobrasts of tissue specimens derived from s[6m5]okers
as the reduction of airflow due to abnormalities in the affected by COPD who underwent surgery. This
small airways compartment and associated infiltration experiments focused on the role of prostaglandin (PG) E2
of inflammatory cells, thickening of the alveolar wall since it is an important mediator of tissue inflammation
and ultimat[e50ly] damage of the lung parenchymal and that in[c66r]eases in expression in the lungs of patients with
epithelium. It encompasses both emphysema and COPD. Its production is induced by pro-inflammatory
chronic asthmatic bronchitis. Emphysema results from cytokines such as IL-1β and TNF-α and depends on the
progressive alveolar septal destruction with concomita[n51t] expression of COX-2 together with [t65h]e expression of
reduction of the surface area available for gas exchange, miR-146a which targets COX-2 mRNA. The induction of
while bronchitis constricts the airways clogging them wi[t5h2] miR-146a takes place both in COPD and control fibroblast,
the accumulation of inflammatory mucous exsudate. but to a lesser extend in COPD fibroblast. In this context
Although cigarette smoke is a main risk fac[t5o3]r for COPD, only miR-146a is thought to be a feedback control mechanism
20% of smokers develop this pathology, thus there are that limits the intensity and duration of inflammation
additional factors that are implicated in the pathogenesis by reduc[6i5n]g the level of COX2 and hence the production
of COPD, whi[c54h] is infl[5u5e] nced by a combination [o56f] of PGE2.
environmental, genetic and epigenetic components.
Study of miRNAs differentially expressed between non- Recently the search for biomarkers for early detection of
smokers and smokers found that cigarette smoke results, COPD has drawn attention on the role of circulating miRNAs.
generally, [5i7n] the downregulation of miRNA expression A study found five deregulated circulating miRNAs in serum
(Table 1). Seventy miRNAs were found differentially of COPD patients, four of them downregulated (miR-20,
expressed in lung whole tissue between s[5m8]oking patients miR-28-3p, miR-34c-5p and miR-100) and one up[6r7e]gulated
affected by COPD and healthy smokers. Among these (miR-7) in comparison with healthy individuals. Finally,
di3ff1e8rentially expressed miRNAs 57 were up regulated with similar attePmulpmtosn taory aCpirpculyla tmioniR |N AApr iel-xJpunree s2s0i1o3n | s Vigonl 3a t|u Nroe 2as
Sessa and Hata: miRNAs pulmonary development and disease
[79]
a diagnostic tool, suggest the possibility of distinguishing steroid treatment. T lymphocyte polarization is also
COPD patients from lung can[6c8e,6r9 ]patients by measuring their regulated by miR-126, which is a potent and specific inducer
mAsiRthNmA eaxpression pattern. of the Th2[ 8a0]llergic response and TLR4 signalling present
in asthma. Exposing the airways to a miR-126 inhibitor
abolished HDM induced airway hyper responsiveness and
Asthma is a lung condition that is increasingly prevalent attenuated m[80u]cus hyper-secretion and accumulation of
in the western world, which is triggered by a sustained eosinophils. Beneficial effects have also been obtained
inflammatory response in the airway that is caused by a by knocking down miR-106a in the ovoalbumin sensitized
combination of air pollutants and genetic predisposition. murine model of asthma; in this experiment knock-down
Asthma is characterized by reversible airway obstruction, of miR-106a increased the level of the anti-inflammatory
peribronchial inflammation and airway hyper cytok[i8n1e] IL-10 and reduced the Th2 response alleviating
responsiveness (AHR). A relevant feature of asthma is AHR. The anti-inflammatory role of IL-10 is also
the occurrence of acute exacerbation events that involve dependent on its role in counteracting the LPS mediated
enhanced contraction of the airway smooth muscle layer induction of miR-155, which increases PIP3 levels
in response to inhaled stimuli and are the consequence of and ac[t8i2v]ates the downstream signalling of NF-KB and
AHR. In the late stages of the disease, airway remodelling MAPK. Studies have also been performed that address
occurs which consists of epithelial desquamation, globet the role of mast cells in asthma. The miR-221, -222 family
cells hyperplasia, smooth muscle cell hypertrophy and was demonstrated to be transcriptionally induced upon
hyperplasia, an increase in matrix protein deposition, mast cell activation. In particular miR-221favors mast
basement membrane thickenin[g70 ]and growth, and cell activation upon IgE-antigen complex stimulation
proliferation of new blood vessels. The inflammatory by promoting [8c3e]ll adherence, cytokine production and
response plays a pivotal role in the progression and degranulation.
pathology of asthma featuring a production of IgE and
involving a consistent recruitment of leukocytes, in A comprehensive study of miRNAs differentially expressed
particular eosinophi[7ls1] together with type 2 T-helper (Th2) in lung tissue of mice challenged with ovoalbumin – a model
cells and mast cells. TGF-β signalling has been found to recapitulating the main phases of asthma progression –
play a key role in the r[e7m2]odelling that occurs during the found 58, 66 and 75 miRNAs significantly modulated b[84y]
progression of asthma. Indeed TGF-β, in addition to its short, intermediate and long-term challenge respectively.
pro-fibro[7t3i]c action, charact[e74r]ized by increased synthesis of Bioinformatics analysis of the data coming from this study
collagen and fibronectin, also promotes airway[7 s5m] ooth found out miRNA-regulators of several pathways ranging
muscle cell proliferation and epithelial apoptosis. from cell cycle, TGF-β, protein synthesis and inflammation.
Interestingly, cell proliferation is more pronounced in the
Several aspects of asthma have been linked to the early stages of asthma than in the late ones. MiR-574-5p is
deregulation of miRNAs (Table 1). Of particular interest involved in cell proliferation and inversely correlated with
is the involvement of miRNAs in the regulation of the NuSAP, a microtubule-a[s85s]ociate protein involved in mitotic
immune response and inflammation by targeting several spindle organization. MiR-29b and miR-29c, which
immune receptors and cytokines. In this context, miR-21 are correlated with matrix deposition and target MMPs,
has been described to target IL-12 w[h76i]ch is a major cytokine are downregulated in the late stages. Notably miR-146a,
involved in Th1 cell polarization. MiR-21 ablation in which is regulated by Toll Like Receptors (TLRs) was t[h84e]
mice challenged with ovalbumin has been described to only miRNA found to be regulated in all three phases.
mitigate the progression of the pathology by alleviating the Forced expression of miR-146a decreases the productio[8n6 ,8o7f]
allergic immune response and skewin[7g7 ]the balance between various pro-inflammatory cytokines and chemokines.
Th1 and Th2 responses toward Th1. In a opposite way, a Moreover, T cell receptor driven NF-kB activation of
cell polarization toward a Th2 response has been observed miR-146a is important in down-regulating NF-kB activity in
to be concomitant with [t7h8]e down modulation of let-7 family a negative feed back loop, at least partly through repressing
in inflamed airways. Exogenous administration of the NF-kB signalling transducers TRAF6[ 8a8]nd IRAK1, thus
let-7 in asthmatic mice was shown to reduce the level of modulating the T-cell immune response.
IL-13, an impor[t7a8n] t mediator of the Th2 response during
allergic events. An additional miRNA involved in t[h79e] It is worth mentioning that increasing evidence suggests
Th2 response and eosinophil recruitment is miR-145. that angiogen[8e9,s9i0s] plays an important role in the progression
Mice challenged with House Dust Mite (HDM) allergen of asthma. Vascular endothelial growth factor
and then treated with miR-145 inhibitor displayed a (VEGF) levels are increased in tissues obtained from
reduction of pro-inflammation cytokines, IL-13 and IL-5, asthmatic subjects and[9 1i]t has been[ 9d2]emonstrated th[9a3t]
and alleviation of asthma symptoms. The anti-inflammatory alveolar epithelial cells, fibroblast and leukocytes
ePffuelmctosn aoryf mCiricRu-la1t4io5n |in Ahpirbil-iJtuonre w20e1r3e |c oVmol p3 a|r Naob l2e to those of produce VEFG during the inflammatory process. Alve3o1l9ar
Sessa and Hata: miRNAs pulmonary development and disease
macrophages (AM) are an important source of VEGF during transcriptional regulatory protein SIN3A. MiR-138 relieves
lung injury. Increased miR-20b expression in[94 ]AM from the transcriptional repression of SIN3A and allows the
asthmatic mice decreases VEGF protein levels. Analysis ex-pression of wild type and m[91u]tant form of CFTR restoring
of the contribution of the vasculature to the establishment Cl transport in CF epithelia.
of the aberrant inflammation response may lead to
new insights in the treatment of asthma. For instance, In vitro comparison of differentially expressed miRNAs
overexpression of miR-181b in endothelial cell inhibits between CF epithelial cells and control epithelia[1l0 c7]ells found
NF-kB nuclear localization and signalling which dow[n95-] miR-155 to be highly elevated in diseased tissues (Table 1).
modulates leukocyte influx hence decreasing lung injury. The same trend is mirrore[d10 7i]n CF lung epithelial cells and
This discovery suggests that miR-181b may be a new target circulating CF neutrophils. MiR-155 specifically inhibits
fCoyr satnitci -fiinbflraomsmisatory therapy. Phosphatidylinositol 3,4,5-trisphosphate 5-phosphatase 1
(SHIP1) expression, thereby promoting activation of the
[96] PI3K/Akt signalling pathway and promo[t1i0n7]g expression
Cystic Fibrosis (CF) is a monogenic lung disease of the pro-inflammatory IL-8 cytokine – the well-
characterized by mucus airway obstruction, neutrophil- characterized chemotactic agent for neutrophils.
dominated airway inflammation and bacterial infection th[9a7t]
leads to progressive pulmonary damage and emphysema. Advances in the care of patient with CF have lead to a
The gene involved in the insurgence of CF is the CFTR dramatic increase in patient survival and a concomitant
encoding for an ATP-dependent anion channel-protein observation of additional complications, such as
present in the apical part of the epithelium. CTFR tumorigenesis in other organs ascribable to mutation
coordinates the secretion and absorption [o98f] NaCl, fluid and loss of expression of CFTR. Interestingly, the tumor
and airway surface liquid homeostasis. The most suppression activity of CFTR is at [l1e08a]st in part mediated
common CFTR mutation causes erroneous protein folding by the up modulation of miR-193b that in turn targets
and degrad-a tion, which u+ltimately leads to an imbalance urokinase-type plasminogen activator (uPA) k[1n09o]wn to be
between Cl secretion/Na absorption and airway surface iIndvioolpveadt hini cv apruiolums omnaaligrnya fnitb trroaistiss of cancer.
liquid depletion. As a consequence of the epithelial layer
dehydration, mucociliary clearaPnsecued iosm iomnpaas iareerdu gwinhoicsha
affecSttas pihnynloactoec cimusm auurneeu sdefences favoring infection by Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive
opportunistic pathogens s[u99c]h as fibrotic interstitial pneumonia of unknown caus[1e10s]
and . Neutrophil-dominated airway characterized by a rapid progression over a few years.
inflammation has been implicated as a driving force in the However, several IPF risk factors are known; these include
airway remodelling and bronchiectasis. These processes, viral infection, occupational activities assoc[i1a1t1e]d with a
characterized by bronchial wall thickening and tissues high pr[1o1b2]ability of dust or [v11a1p] our inhalation, cigarette
fibrosis, are mediated by the production of reactive oxygen smoke and pollutants. IPF appears to be initially
species and metallo-proteases. triggered by persist[e11n3]t and repetitive microinjuries to the
alveolar epithelium. Continuous damage of the epithelial
The first work describing mi[R6,1N00A]s involvement in CF was cells leads to the destruction of the basal membrane and
published by Oglesby et. al. (Table 1). In this work, hence the activation of coagulation and metalloproteinases.
miR-126 was shown to target TOM1 protein, a known Later steps of IPF include the massive deposition of
regulato[r10 1o]f endosomal trafficking of ubiquitinated extracellular matrix by activated myofibroblasts derived
proteins, which is also a negati[v10e2 ]regulator of IL-1β, from different sources, such as fibroblast, pericytes,
TNF-α and LPS signalling pathway. miR-126, which is alveolar epithelial cells and mesothelial cells. IPF is
highly expressed in the lung, is down modulated in the characterized by aberrant activation of de[1v1e4]lopmen[1t1a5l]
epithelium of CF patients; this leads to increased expression signalling pathways,[ 1s16u]ch WNT/β-catenin, TGF-β
of TO[1M001] and decreased NF-kB-induced cytokines, such as and Sonic hedgehog. TGF-β is considered the driv[i1n17g]
IL-8. This mechanism may be an attempt of the lung force of epithelial-to-mesenchymal transition (EMT).
epithelium to [c6]ompensate for the high pro-inflammatory Cells expressing both epithelial and mesenchymal mark[e11r8s]
burden of CF. miRNA Responsive elements (MRE) for have been found in mice treated with TGF-β inhalation.
miR-101 and miR-494 have been identified in the 3’UTR In vitro stimulati[o11n9] of alveolar epithelial cells with TGF-β
of the CFTR transcripts th[1e03s]e miRNAs have be shown to can induce EMT. The first miRNA demonstr[a12t0e]d to be
inhibit CFTR translation. Notably, these two miRNAs involved in the pathogenesis of IPF was let-7d. Let-7d
are elevated in CF patients and their alteration has been is downregulated in samples from IPF patients, wh[i1c2h0]
linked to other changes in pro-inflammato[1r04y-1 0c6y]tokines, was sufficient to cause EMT in lung epithelial cells
cells cycle progression and carcinogenesis. CFTR is (Table 1). Decreased let-7d is m[12e0d]iated by TGF-β via a
als3o2 0indirectly regulated by miR-138, which targets the SMAD-depePunlmdeonnatr ym Cierccuhlaatinonis |m A.pril-J uInneh 2i0b1i3t i|o Vno lo 3f |l eNto- 72d
Sessa and Hata: miRNAs pulmonary development and disease
triggers a global decrease in lung epithelial markers[1 2a0n] d suggested that this mutation may cause susceptibility to
a concomitant increase in alveolar septal thickening. other factors. Indeed, genetic and en[v12ir7]onmental[ 1s2t8i]muli
such as dysregu[l1a29t]ed inflamm[1a3t0i]on, hypoxia and
Levels of miRNAs have been evaluated in different RNA aberrant Notch3 and TGF-β signalling can promote
samples from biopsies of IPF pat[i1e2n1]ts with varying speeds the insurgence of PAH.
of disease progression (Table 1). Generally, both slowly
and rapidly progressive IPF biopsies revealed a down A first clue that suggested that miRNAs play a role in the
modulation of several miRNAs compared to normal tissue pathogenesis of PAH derived from the observation that
and specific miRNAs signature can provide[1 p22r]edictive clues BMPR2 protein, but not its messenger, is reduced in PAH
about the progression rate of the disease . Interestingly, animal models. From this initial observation it has been
many upregulated mRNA found in IPF are implicated in EMT found that IL-6 induces the expression of the miR-17-92
and correlate wit[h12 t2h] e downmodulation of the respective cluster through STAT3 activatio[n13 a1]nd that several miRNAs
targeting miRNA. Furthermore, a decrease in key RISC from this cluster target BMPR2 (Table 1). Caruso et al.
components such as AGO1 and AGO2 has been observed. reported a screening of differentially expressed miRNAs
Another study found that 43 miRNAs are significantly in th[e1 3m2]onocrotaline and hypoxia induced rat models of
upregulated in lung tissues from IPF patients and that the PAH. In this study the authors found miRNAs similarly
majority of them belong to th[1e2 3m] iR-155 family present as deregulated between the two PAH models, in addition
a cluster on chromosome 14. Up regulation of miR-155 they also discovered specific miRNA signature in each
was triggered in vitro upon stimulation with TGF-β. Finally, group. The discovery of differentially regulated miRNAs
biochemical studies confirmed a mitogenic effect of TGF[1-2β3] between hypoxia and monocrotaline treated rats is in
on fibroblast mediated by miR-155 and WNT/β-catenin. agreement with the differential pathobiology found in
Two additionally studies connecting TGF-β signalling to the two models. Indeed, monocrotaline challenge mainly
miRNA regulation in IPF have been performed on miR-21 targets the pulmonary vascular endothelium triggering
and miR-29. Mice with bleomycin-induced fibrosis present strong inflammation while hypoxia stimulates cha[1n33g,1e34s]
increased level of miR-21 in [7t7h]e lungs that is primarily also in medial and adventitial with less inflammation.
localized in myofibroblasts. MiR-21 upregulation is Moreover, researchers have identified specific ch[1a32n]ges
induced by TGF-β and promotes the activation of pulmonary in miRNAs signature during PAH progression. An
fibroblast by targeting SMAD7, thus fun[7c7t]ioning in an additional screening on deregulated miRNAs in circulating
amplifying circuit to promote lung fibrosis. Reciprocally, microvesicles of PAH patients and rat models found that the
miR-29 is suppressed by TGF-β in human fetal lung downregulation of miR-150 c[1o35r]relates with the severity and
fibroblast. Knockdown of miR-29 derepressed extracellular prognosis of PAH (Table 1).
matrix-associated genes and several fibrosis[1-2r4e]lated genes,
including collagens, laminins and integrins. Restoration MiR-21 is consistently downregulated in mon[o13c2r]otaline-
of miRNA expression by targeting miRNAs up regulated injected rats but not during hypoxia exposure. MiR-21
during IPF may represent a valuable novel therapeutics expression [i1s3 6i]nduced by pro-inflammatory cytokines
tPruealmtmoennta froyr tahritse prayt hhoylopgey.rtension such as IL-6 and [T13G7]F-β/BMP and it is known to drive
SMC differentiation. A recent work from Parikh et al.
demonstrated on pulmonary artery endothelial cells that
Pulmonary Artery Hypertension (PAH) is a disease BMP-dependent signalling activation of miR-21 represses
characterized by hyperproliferation and neointima Rho-kinase activation, thus counteracting the R[1h3o8]
formation leading to vasoconstriction of the pulmonary signalling in promoting pulmonary vascular pathology.
artery and ultimately right ventricular heart failure Moreover, miR-21-null mice presented overexpression
and death. Both pulmonary artery smooth muscle cells of RhoB and hyperactivation of Rho-kinase activ[i1t39y]
(PASMCs) and pulmonary artery endothelial cells (PAECs) accompanied by exaggerated manifestation of PAH.
are involved in this disease and extensive studies have been in vitro administration of a miR-21inhibitor in hypoxia-
performed on these cells looking for the aberrant molecular exposed mice reduces pulmonary vascular remo[1d40e]lling and
mechanisms responsible for the establishment of PAH. PAH-associated right ventricular hypertrophy.
Regarding heritable PAH, which is the most frequent form
of the disease, in almost 70% of cases the genetic alteration One of the first studies providing evidences for the
is represented by an autosomal dominant mutation in involvement of a specific miRNA in the etiology of
the bon[1e2 5m] orphogenic protein receptor 2 (BMPR2) in human PA[H14 1f]ocused on the downregulation of miR-204
PASMC. More rarely, mutations of Endoglin and acti[v12in6] (Table 1), which had been previously show[n14 2t]o be
receptor-like kinase 1 (ALK1) have been identified. associated with cell proliferation i[n14 3c]ancer cells and
However, since mutation of BMPR2 occur in just slightly epithelial retinal depolarization. In PASMC STAT3
mPoulrmeo ntahray nC ihrcaullaft ioonf t|h Aep rcila-Jsuen eo 2f0 h1e3 r|i tVaobl l3e |P NAoH 2 it has been mediates downregulation of miR-204 which enha3n2c1es
Sessa and Hata: miRNAs pulmonary development and disease
the activity of Src ther[e14b1]y increasing proliferation and phenotype in PAH, several studies tried to decipher the
resistance to apoptosis. role played by miRNAs in this conte[x15t4. ]MiR-206, previously
described as tumor suppressor, is downregulated
A connection between PAH insurgenceS, MthAeD T9G F-β signalling in hypertensive mouse with excessive right ventricular
pathway and miRNAs has been described in a form of systolic pressure. Its anti proliferative action is mediated by
heritable[1 P44A,1H45 ]that presents a mutated gene (protein directly targetin[g12 N9]otch3, whose signalling is known to be
Smad8). This work demonstrated the role of Samd8 elevated in PAH. Two miRNAs highly expressed in SMC;
in promoting miRNA expression by the non-canonical BMP miR-145 and miR-143, have been shown to play a pivotal
pathway. Specifically, two miRNAs have been described to role in the modulation of SMC phenotype. In particular,
be regulated by the non-canonical BMP pathway, miR-21 their expression is transcriptionally activated by both
and miR-27a, whose exp[1r4e4]ssion are reduced in PAEC and TGF-β and BMP4 and promotes a contractile phenoty[1p55e]
PASMC in PAH patients. Moreover, miR-21 expression in SMC by targeting the Kruppel-like factor-4 (KLF4).
levels are correlated[1 4w4]ith cell proliferation in PAEC derived Knock-out of both miRNAs in mice leads to[ 1a5 6d]evelopment
from PAH patients. of thinner medial layer and hypotension. One recent
work investigated the effect of miR-145 modulation in the
In a monocrotaline-induced rat model, miR-17 suppression
pathogenesis of PAH and demonstrated that its expression
with anti-miR-17 treatment has been shown to significan[1t4l6y] is induced by [h15y7p]oxia and that its expression is elevated in
counteract the pathological severity of the disease.
PAH patients. Genetic ablation or inhibition of miR-145
In both in vitro and in vitro treatment with anti-miR-17
by antisense oligonucleotides in hypoxia-challenged anim[15a7l]
a significant increasing of the miRNA’s target p21 has
exhibits a protective effect against PAH development.
been shown to be a central mechanism in [t1h46e] repression Additional studies reported a downregulation of miR-145
of the SMC proliferative feature of PAH. A hypoxia
during neointimal formation upon rat carotid balloon
induced miRNA found to be relevant in the pathology of
vascular injury and adenoviral overexpression o[1f5 8m] iR-145
PAH is miR-210, indeed it has been demonstrated that
confers a protective role against vessel wall. On the
miR-210 expression increased in microarray analysis on
contrary, a different study reported that mice deleted in
hum[a14n7 ]in hypoxic PASMC and in whole lungs of hypoxic
miR-143 and/or miR-145, develop reduced neointima
mic. The induction of miR-210 is HIF-1α-dependent
formation upon carotid artery ligatio[n15,9 ]thus pointing to
and triggers anti-apoptotic[1 e47f]fects via directly targeting the
a protective role of miR-145 ablation. This phenotype
transcription factor E2F3. Previously work carried out
is probably due to a depletion of SMC in the media due
on PAECs showed an additional mechanism of adaptation
to hypoxic conditions in which miR-210, by targeting Iron- to the absence[1 6o0]f these important miRNAs during the
development. The effects of miR-145 null mice in
Sulfur Cluster Assembly Proteins 1/2 (ISCU) repres[1s4e8]s
hypoxia-induced PAH and neointimal formation is likely
mitochondrial metabolism, thus facilitating glycolysis.
dependant on regulatory networks influenced by a plethora
Additional clues about the involvement of miRNAs in the of miR-145 direct and indirect targets a[1f5f9e]cting cytoskeleton
dynamics and thus cell migration. It is interesting
hypoxia-induced PAH focused on the cytoprotective action
to speculate that the effect of miR-145 on cytoskeleton
of secreted membrane microvesicles, called [e14x9o] somes,
organization and cell migration is context-dependent and
delivered from mesenchymal stem cells (MSC). Several
that the effect of its deregulation can be different depending
reports showed that treatment with these microvesicles
on the state of smooth muscle cell differentiation and
ameliorates sym[1p50t-1o5m2]s and prevents progression in PAH and
on the microenvironment. Detailed analysis of miRNA
vascular injury. In one recent report, it was shown that
intravenous delivery of mesenchymal stromal cell-derived expression has been performed in PAH patients by [i1s6o1]lating
exosomes (MEX) interferes with early hy[1p49o]xic signals in plexiform (PLs) and concentric lesions (CLs). This
the lung by counteracting inflammation. In particular analysis f[1o6c2]used on expression of the endothelial-specific
MEX inhibits MCP-1 release and monocyte recruitment miR-126 and the SMC-specific miR-145 and miR-143.
together with decreasing STAT3 phosphorylation, Expression of miR-143 and miR-145 was significantly
which is an important mediator in the inflammato[1r53y] lower in PLs compared with CLs and healthy tissue.
and pro-proliferative response triggered by hypoxia. Decreased expression of miR-143/145 may reflect the
Inhibition of STAT3 activation also affects in[d13u1]ction of the more proliferative and undifferentiated phenotype of SMCs
miR-17/92 cluster which targets BMPR2. Moreover, present in PLs. On the other hand, the expression level
treatment with exosomes from MSC also interferes with of miR-126 was higher in PLs when compared to CLs, in
the STAT3 downregulation by miR-20[414,1 w] hich inhibits pro- acco[1r6d3]ance with the higher abundance of EC in PLs than in
proliferative action of STAT3 in SMC. PLs. Thus this study provided a specific miRNA signature
for different hypertensive pulmonary lesions potentially
Du3e22 to the key role of the PASMC hyperproliferative providing nPeuwlm doinaagryn Coisrctuicla ttiooon l|s .April-June 2013 | Vol 3 | No 2
Sessa and Hata: miRNAs pulmonary development and disease
Acute lung injury and acute respiratory distress
syndrome [173]
Fc receptor for IgG (IgG FcγRI - CD64) that activate
the cells in the clearance of the immunocomplexes and in
Acute lung injury (ALI) is a phenotypically variable acute promoting inflammation by secreting cytokines. The same
respiratory failure clinically characterized by progressive study demonstrated that overexpression of this miRNA can
hypoxemia, reduced lung compliance and intense prevent exaggerated inflammation during injurious[1 s73t]imuli
inflammation that results from either direct injury to the and the set of ALI in mice treated with bleomycin.
lung (pneumonia, thoracic trauma, smoke-related lung
injury) or an indirect insult (pancreatitis). ALI together A study on the role of miRNAs in the pathogenesis of ALI
with its most severe manifestation namely the acute also identified the invo[l1v7e4]ment of miR-16 in the resolution
respiratory distress[ 1s6y4n] drome (ARDS) has a high incidence of pulmonary edema. In this work, mice exposed to
and high mortality. Cellular characteristics of ALI and hyperoxia exhibited a decrease in miR-16 together with
ARDS are the loss of alveolar-capillary membrane integrity decreased expression of the epithelial sodium chan[n17e5l]
consisting of a leakage of the endothelium and degradation which is critical for driving fluids out of alveolar space.
of the alveolar basement membrane with the consequent MiR-16 [h17a6s] been found to target the serotonin transporter
extravasation of fl[u16i5d]s from the circulation to the inside (SERT). In vitro experiments using human alveolar
the small airways. epithelial cells demonstrates that overexpression of
miR-16 reduces SERT and increases the epithelial sodium
It is well recognized that only a small proportion of exposed transporter proposing miR-16 as a candidate for [t1h74e]
individuals will ultimately develop these syndromes and treatment of pulmonary edema and prevention of ALI.
miRNAs AS THERAPEUTIC TARGETS
has been proposed that there is a geneti[c16 p6-r16e8d]isposition
to the development of ALI pathology. Recently,
efforts in determining the genetic component of ALI/ARDS
pathogenesis have been extended to the involvement of
The recent achievements in manipulating miRNA expression
miRNAs in this process (Table 1). Several genes involved
in animal models of related human diseases, together with
in the immune response and inflammation, already
the increasing rate of discoveries about the role played
described to be targeted by miRNAs, have b[e16e9n] suggested
by miRNAs in several human disorders have raised the
as candidates in the establishment of ALI. A detailed
study investigating changes in miRNA expression upon possibility of using these molecules as a new class of
lung injury has been performed using the mode[l1 7o0f] injury therapeutic tools. Along with this concept, from the gain-
trigged by high volume tidal ventilation (HVTV). In this and loss-of function studies it appears that dysregulation
study HVTV applied to mice induced an[17 0u]pregulation of of miRNAs is well-tolerated in normal tissues but that it
several miRNAs, with a few exceptions. Inflammatory can influence the behavio[1u77r] of the tissues experiencing
and TGF-β-signalling miRNA-gene networks have been pathological conditions. The first clinical trial of a
identified by in-silico pathwa[1y70 ]analysis as significant miR-122 mimicry as a therapy for suppression of hepatitis C
modulated in the onset of ALI. MiR-21 was one of the virus (HCV) is currently under going.
most upregulated and treatment of mice with antisense
oligonucleotides against miR-21 before HVTV ameliorated Several molecular strategies have been employed in
induction of pulm[1o7n0]ary edema associated with the order to down modulate or overexpress miRNAs in vitro.
ventilation injury. Other miRNAs associated with Anti-microRNA oligonucleotides (anti-miR) have been
inflammation, such as miR-155, let-7 and miR[17-01]46, are generated and extensively chemically modified in order to
similarly deregulated upon HVTV treatment (Table increase the effectiveness and stability. Modification of the
1). Another expression analysis on the effects of stress pahnotsapghoomdiire sotleigr obsackbone with a phosphorothioate linkage
ventilation was performed by stretching rat alv[1e71o]lar between nucleot[i1d78e]s or including a 2’O-methyl group
epithelial cells to mimic mechanical ventilation. In ( ) are two common modifications for
this study, the m[17a1j]ority of miRNAs were again found to increasing stability and decreasing the in vitro clearance.
be upregulated. Interestingly the highest fold-change Additionally, antagomirs containing[1 7a9 ]cholesterol moiety
occurred in the detection of miR-32*, sugge[s17t1i]ng a are thought to favour cellular uptake. Special interest has
functional role for this miRNA passenger strand. The been focused on the use of the Locked Nucleic Acid (LNA)
authors of this work have also demonstrated a functional that present a modification in the ribose ring improving
link between the levels of miR-466d-5p and miR-46[167f1-]3p, nuclease resistant and conferring an high affinity for
and the inhibition of stretch-induced permeability. complementary sequence. LNA antagomirs against miR-33
showed beneficial effects in non-human primates for the
An analysis of the miRNAs expre[1s7s2]ion profile of mice with treatment of atherosclerosis by increasing the level of high-
bleomycin-induced lung injury showed that miR-127 density lipo[p18r0o]tein and lowering the level of low-density
isP udlmowonnar ym Coirdcuulalatitoend | iAnp rmil-Jaucnreo 2p0h1a3g |e sV. oMl 3i R| -N1o2 27 targets the lipoprotein. Systemic delivery of antagomir has b3e23en
Sessa and Hata: miRNAs pulmonary development and disease
ACKNOWLEDGMENT
proven effective in the treatment of cardiac[ 1h81y]pertrophy
and[1 8f2i]brosis by down modulating miR-133 and miR-
We apologize to those colleagues whose references we have omitted from
21 respectively. The anti-miR-21 therapeutic [7e7]ffect this discussion; due to space restrictions and our focus we were unable to
against fibrosis has also proven effective in the lungs and
include all articles on this interesting and diverse subject matter. We wish
for the treatment of diabe[1t8i3c] nephropathy using a mouse to express our thanks to the members of the Hata lab for critical reading
model of type 2 diabetes. Currently, the most effective of the manuscript and discussion, in particular we are especially grateful
means of delivering anti-[ 1o84r] mimic miRNA is through adeno- to Matthew Blahna for his critical contribution in critical reading of the
manuscript. This work was supported by grants from the National Institute
associated virus (AAV). This system benefits from the
of Health (HL093154 and HL108317), the American Heart Association
advantage of potential tissue enrichment as a result of the
(0940095N) and the LeDucq foundation Transatlantic network grant
natural tropism of the different AAV serotypes. Moreover, to A.H.
the exogenous sequence can be continually expressed, REFERENCES
resulting in a robust replacement or inhibition of miRNA
expression. 1. Garofalo M, Romano G, Di Leva G, et al. EGFR and MET receptor tyrosine
kinase-altered microRNA expression induces tumorigenesis and gefitinib
resistance in lung cancers. Nat Med 2012;18:74-82.
It has been demonstrated that the introduction of miR-29
2. Calin GA, Croce CM. MicroRNA signatures in human cancers. Nat Rev
in the lung protects animals from th[e18 5i]nsurgence of the Cancer 2006;6:857-66.
pathology in bleomycin-treated rats. The therapeutic 3. Hassan T, McKiernan PJ, McElvaney NG, Cryan SA, Greene CM.
Therapeutic modulation of miRNA for the treatment of proinflammatory
potential of miR-29 in pulmonary fibrosis was examined
lung diseases. Expert Rev Anti Infect Ther 2012;10:359-68.
in both the induction phase and during established lung 4. Pagdin T, Lavender P. MicroRNAs in lung diseases. Thorax 2012;67:183-4.
disease induced by bleomycin using the Sleeping Beauty 5. O’Neill LA, Sheedy FJ, McCoy CE. MicroRNAs: the fine-tuners of Toll-like
receptor signalling. Nat Rev Immunol 2011;11:163-75.
(SB) transposon-mediated gene transfer system. Progresses
6. Oglesby IK, McElvaney NG, Greene CM. MicroRNAs in inflammatory lung
in delivery of SB transposons have been achieved in t[1h86e] disease--master regulators or target practice? Respir Res 2010;11:148.
treatment of [P18A7]H, in inhibiting lung allograft fibrosis, 7. Reinhart BJ, Slack FJ, Basson M, et al. The 21-nucleotide let-7 RNA regulates
developmental timing in Caenorhabditis elegans. Nature 2000;403:901-6.
in lymphoma[188] and in various systemic disease, such as
8. Lee RC, Feinbaum RL, Ambros V. The C. elegans heterochronic gene
haemophilia.
lin-4 encodes small RNAs with antisense complementarity to lin-14. Cell
1993;75:843-54.
There are a few potential challenges for the clinical 9. Lagos-Quintana M, Rauhut R, Lendeckel W, Tuschl T. Identification of novel
genes coding for small expressed RNAs. Science 2001;294:853-8.
application of miRNA modulation methods, which
10. Pasquinelli AE, Reinhart BJ, Slack F, et al. Conservation of the sequence
include off-target effects of antagomirs, and the pot[e18n9t,1i9a0l] and temporal expression of let-7 heterochronic regulatory RNA. Nature
toxicity of phosphorothionate oligonucleotides. 2000;408:86-9.
11. Friedman RC, Farh KK, Burge CB, Bartel DP. Most mammalian mRNAs
For the treatment of pulmonary diseases, there is the
are conserved targets of microRNAs. Genome Res 2009;19:92-105.
great advantage that miRNA-related therapeutics can be 12. Smalheiser NR, Torvik VI. Alu elements within human mRNAs are probable
delivered via inhalation. Inhalation will decrease systemic microRNA targets. Trends Genet 2006;22:532-6.
13. Borchert GM, Holton NW, Williams JD, et al. Comprehensive analysis of
exposure of miRNA-related therapeutics and, therefore,
microRNA genomic loci identifies pervasive repetitive-element origins.
limit potential off-target effects and toxicity to other organs. Mob Genet Elements 2011;1:8-17.
CONCLUDING REMARKS 14. Borchert GM, Lanier W, Davidson BL. RNA polymerase III transcribes
human microRNAs. Nat Struct Mol Biol 2006;13:1097-101.
15. Cuperus JT, Fahlgren N, Carrington JC. Evolution and functional
diversification of MIRNA genes. Plant Cell 2011;23:431-42.
16. Wang Y, Hindemitt T, Mayer KF. Significant sequence similarities
miRNA biology is a key mechanism for mediating cellular in promoters and precursors of Arabidopsis thaliana non-conserved
microRNAs. Bioinformatics 2006;22:2585-9.
responses under various stress conditions. Lung tissues are
17. Pillai RS. MicroRNA function: multiple mechanisms for a tiny RNA? RNA
constantly under threat of various stresses, such as chemical 2005;11:1753-61.
irritants and air pollutants. Indeed, growing evidence 18. Wada T, Kikuchi J, Furukawa Y. Histone deacetylase 1 enhances microRNA
processing via deacetylation of DGCR8. EMBO Rep 2012;13:142-9.
supports the idea that deregulation of protein coding gene
19. Macias S, Plass M, Stajuda A, Michlewski G, Eyras E, Cáceres JF. DGCR8
expression as a result of aberrant expression of miRNAs HITS-CLIP reveals novel functions for the Microprocessor. Nat Struct Mol
is contributing to various stages of the pathogenesis of Biol 2012;19:760-6.
20. Kok KH, Ng MH, Ching YP, Jin DY. Human TRBP and PACT directly
pulmonary diseases. Therefore, better understanding of
interact with each other and associate with dicer to facilitate the production
the relationship between miRNAs and their target genes of small interfering RNA. J Biol Chem 2007;282:17649-57.
will lead to a development of more effective therapies. It is 21. Peters L, Meister G. Argonaute proteins: mediators of RNA silencing. Mol
Cell 2007;26:611-23.
plausible to apply miRNA mimicry or antagonist as novel
22. Hammond SM, Boettcher S, Caudy AA, Kobayashi R, Hannon GJ.
therapeutic tools. Finally, it is clear that a characteristic Argonaute2, a link between genetic and biochemical analyses of RNAi.
miRNA expression profile (or signature) is linked to a Science 2001;293:1146-50.
23. Wang D, Zhang Z, O’Loughlin E, et al. Quantitative functions of Argonaute
specific pathological condition (Table 1). Thus, miRNA
proteins in mammalian development. Genes Dev 2012;26:693-704.
signature can be used as a diagnostic tool or for the
de3v2e4lopment of more personalized therapeutic strategy. Pulmonary Circulation | April-June 2013 | Vol 3 | No 2