Cell-based functional studies
Several studies investigated miRNA-based molecular mechanisms ex
vivo /in vitro in different cell types involved in asthma
pathogenesis138-143.
miR-155 is one of the most frequently investigated miRNAs in regards to
asthma and AD. miR-155 was shown to be induced by hyper-stretch in human
bronchial epithelial
cells144 and targets
Src homology 2 domain–containing inositol 5-phosphatase 1 (SHIP1)
production and activates Janus Kinase (JNK) signaling leading to KC (the
functional IL-8 paralog) secretion in mouse models. miR-181b was
observed to be decreased in bronchial brushings and plasma from patients
with asthma and inversely correlated with eosinophil counts in
sputum145.
Overexpressing this miRNA in a bronchial epithelial cell line (BEAS-2B)
confirmed the regulation of the target Secreted Phospho Protein 1 (SPP1)
and reduced IL-13 induced secretion of IL-1β and CC-Motif Chemokine
Ligand 11 (CCL11). In this line, miR-181b was induced following addition
of dexamethasone. Further, miR-27b has been described to be decreased in
HDM induced experimental asthma, with a proposed function in the
regulation of the PI3K-AKT pathway via targeting Spleen Associated
Tyrosine Kinase (SYK) and Epidermal Growth Factor Receptor (EGFR) in a
bronchial epithelial cell line
(16-HBE)55.The let-7
miRNA family is also very abundant in the lung and their inhibitionin vivo ameliorated murine experimental
asthma69; in
particular, let-7a was shown to regulate IL-13
expression135 in
vitro . In concordance to its effect in skin
keratinocytes,35,36miR-146a was shown to have anti-inflammatory function in human lung
alveolar epithelial cell line
A549146,147and in HBECs.148
Besides epithelial cells, several studies have investigated
miRNA-regulated mechanisms in airway smooth muscle cells. In
vitro stimulation of hASMCs with a cytokine cocktail (IL-1β, TNF-α,
IFN-γ) caused an increase in miR-146a with the observed effect being
stronger in cells from asthmatic donors compared to healthy
controls149. As
inhibition of miR-146a increases cyclooxygenase-2 (COX-2) levels and
IL-1β secretion by hASMCs, the authors suggested that miR-146a may be an
interesting anti-inflammatory factor in asthma. In line with this study,
upregulation of miR-145 in hASMCs was demonstrated upon cytokine
stimulation and was associated with enhanced migration and proliferationin vitro 150.
Inhibition of miR-145 reversed this effect through the reduced
expression of collagen type I and contractile protein MHC via targeting
of Krüppel-like factor 4 (KLF-4). Finally, miR-21 was shown to modulate
hASMCs proliferation in vitro , via targeting PTEN, as identified
by lentiviral overexpression
experiments151. miR-21
has been previously associated with asthma development, mainly due its
targeting of i.e.
IL-12p35125,152,
highlighting the multi-functional roles of miRNAs in several cell types
contributing synergistically to asthma pathology.