Presently, the poor understanding in the pathogenesis of IPF has resulted in a lack of effective therapies. In the current study, we showed that the lncRNA H19 was up-regulated in the fibrotic lungs of IPF patients and bleomycin-treated mice. Functionally, H19 deficiency reduced pulmonary inflammation and inhibiting Il6/Stat3 signaling. H19 knockout ameliorated bleomycin-induced pulmonary fibrosis through attenuating the TGF-β/Smad and S1pr2/Sphk2 pathways. Moreover, we also indicated that H19 expressed in the type 2 epithelial cells (AEC2s) and contributed to the proliferation of AEC2s.
H19 is an imprinted and maternally expressed transcript, which is one of the few well-characterized lncRNA [
32,
33]. Aberrant expression of
H19 has been related to a variety of human diseases [
34‐
38]. Using a public datasets, it showed that IPF patients had higher levels of
H19 mRNA in lungs when compared to the control subjects. Similarly,
H19 mRNA also increased in a model of bleomycin-induced pulmonary fibrosis. In current study, we also showed that
H19 expression increased in lungs of bleomycin-treated mice and located at alveolar epithelium and capillaries. From the above findings, we hypothesize that
H19 may play an important role in the pathogenesis of IPF. To realize our aim of this study, we firstly generated a
H19 deficiency mouse (
H19−/−).
Pulmonary inflammation and fibrosis caused by repetitive lung injury underlies the IPF. In vivo studies, we showed that
H19−/− mice could attenuate bleomycin-induced pulmonary inflammation. During the bleomycin-induced mice, the CD11b and Ccr2 mRNA expression increased the lung of wild type mice, but not in that of
H19−/− mice. Recently, Li et al., reported that
H19 significantly induced the expression and secretion of chemokine (C–C motif) ligand 2 (CCL-2) that could accumulate the monocytes from circulation into livers [
39]. It thus suggests that
H19 contributes to the pulmonary inflammation may via attracting the CD11b monocytes into the lung after injures. The signaling studies presented here revealed that Il6/Stat3 was reduced in the bleomycin damaged lungs of
H19−/− mice. In the injured lung, STAT3 rapidly activated and increased the production of the proinflammatory molecules
IL1β,
IL6,
TNF-α,
iNOS and
CCL2 [
40‐
43]. It thus propose that
H19−/− mice reduced bleomycin-induced pulmonary inflammation may through attenuating the Il6/Stat3 signaling. In vivo studies further revealed
H19 deficiency significantly reduced bleomycin-induced pulmonary fibrosis. TGF-β/smad signaling is one of the key pathways responsible for pulmonary fibrosis [
31,
44‐
46]. The current study indicated that
H19−/− mice attenuated the TGF-β/smad signaling in bleomycin damaged lungs by reducing the expression of
Tgfb1 mRNA and activated the Smad2/3 protein. Consistently, in vitro study revealed that
H19 can target miR-140 and regulate the TGF-β/Smad3 pathway [
24]. Moreover,
H19 could enhance TGF-β signaling in both hepatic stellate cells and hepatocytes and facilitate liver fibrosis [
47].
H19 has been reported to accelerate TGF-β1-induced tenogenic differentiation in vitro and promoted tendon healing in a mouse tendon defect model [
48]. Sphingosine-1-phosphate and its receptor S1pr2 have been shown to promote lung fibrosis [
49‐
53]. Our previous study also showed that
H19 could activate the S1pr2/SphK2 signalling pathway in the cholestatic livers. The current study indicated that S1pr2/SphK2 signalling was activated in the bleomycin-treated lungs, but these effects were attenuated by
H19 knockout. We thus propose that
H19 contribute to lung fibrosis of IPF may via regulating both TGF-β/smad and S1pr2/SphK2 signalling. Epidermal growth factor receptor (EGFR) is a major driver of lung adenocarcinoma, which is essential to lung cancer cell proliferation [
54]. The present study also showed
H19 deficiency repressed EGFR activating and suppressed the ACE2s proliferation.