MicroRNA 29 Family Serves a Key Role in Lung Development and the Prevention of Lung Pathology

Abstract Even with remarkable advances in the care of preterm infants, chronic lung disease in the form of bronchopulmonary dysplasia (BPD) continues to be a significant pathologic consequence of prematurity. BPD is caused by the interruption of physiologic lung development and exposure of the immature newborn lung to high O2 tensions. BPD is characterized by a simplified alveolar structure, arrested lung growth, impaired vascular development and lung fibrosis (1). To identify effective treatment strategies for BPD, it is important to understand the molecular mechanisms underlying this disorder. MicroRNAs (miRNA, miR) are known to regulate growth, development and repair of the developing lung; whereas, dysregulation of miRNA expression has been associated with pulmonary disease. Specifically, members of the miR-29 family have been linked to pulmonary cancers, fibrosis, and BPD. Previous studies from our laboratory indicate that developmental induction of miR-29 expression in the fetal lung near term serves a key role in promoting surfactant-producing type II cell differentiation and function through repression of TGF-β2 signaling (2). To understand the role of miR-29 in protection against BPD, in the present study, we created mice in which the entire miR-29 family (miR-29a/b1 and miR-29b2/c) (miR-29 dKO) was disrupted. Upon exposure of miR-29 dKO and WT neonatal mice to hyperoxia (95% O2) for 5 days immediately after birth, expression levels of the proinflammatory cytokines and chemokines, IL-1 β, TGF-β1, CXCL2 and IL-6, were significantly increased in the lungs of miR-29 dKO mice, compared to WT. Furthermore, lungs of miR-29 dKO adult mice manifested increased expression of their direct targets, TGF-β2 and TGF-β3. This was associated with increased collagen deposition, as evidenced by enhanced trichrome staining, suggesting the development of lung fibrosis. HDAC4 (a direct target of miR-29) and proinflammatory TNF-α, which have been implicated in pulmonary fibrosis, also were upregulated in the lungs of miR-29 dKO mice. Overall, our studies suggest a key role of the miR-29 family and its targets in prevention of inflammatory and profibrotic signaling in the neonatal lung leading to lung pathology. Supported by: NIH R01-HL050022 (C.R.M.) References: (1)Michael, Zoe, et al. “Bronchopulmonary dysplasia: an update of current pharmacologic therapies and new approaches.” Clinical Medicine Insights: Pediatrics 12 (2018): 1179556518817322.(2)Guo, Wei, Houda Benlhabib, and Carole R. Mendelson. “The microRNA 29 family promotes type II cell differentiation in developing lung.” Molecular and cellular biology 36.16 (2016): 2141-2141.

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Strain-induced fetal type II epithelial cell differentiation is mediated via cAMP-PKA-dependent signaling pathway

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00068.2006 ◽

2006 ◽

Vol 291 (4) ◽

pp. L820-L827 ◽

Cited By ~ 32

Author(s):

Yulian Wang ◽

Benjamin S. Maciejewski ◽

Nicole Lee ◽

Ophira Silbert ◽

Nathan L. McKnight ◽

...

Keyword(s):

Cell Differentiation ◽

Signaling Pathway ◽

Lung Development ◽

Protein C ◽

Mechanical Strain ◽

Surfactant Protein ◽

Type Ii ◽

Surfactant Protein C ◽

Type Ii Cell ◽

Dependent Signaling Pathway

The signaling pathways by which mechanical forces modulate fetal lung development remain largely unknown. In the present study, we tested the hypothesis that strain-induced fetal type II cell differentiation is mediated via the cAMP signaling pathway. Freshly isolated E19 fetal type II epithelial cells were cultured on collagen-coated silastic membranes and exposed to mechanical strain for varying intervals, to simulate mechanical forces during lung development. Unstretched samples were used as controls. Mechanical strain activated heterotrimeric G-protein αs subunit, cAMP, and the transcription factor cAMP response element binding protein (CREB). Incubation of E19 cells with the PKA inhibitor H-89 significantly decreased strain-induced CREB phosphorylation. Moreover, adenylate cyclase 5 and CREB genes were also mechanically induced. In contrast, components of the PKA-independent (Epac) pathway, including Rap-1 or B-Raf, were not phosphorylated by strain. The addition of forskolin or dibutyryl cAMP to unstretched E19 monolayers markedly upregulated expression of the type II cell differentiation marker surfactant protein C, whereas the Epac agonist 8-pCPT-2′- O-Me-cAMP had no effect. Furthermore, incubation of E19 cells with the PKA inhibitor Rp-2′- O-monobutyryladenosine 3′,5′-cyclic monophosphorothioate or transient transfection with plasmid DNA containing a PKA inhibitor expression vector significantly decreased strain-induced surfactant protein C mRNA expression. In conclusion, these studies indicate that the cAMP-PKA-dependent signaling pathway is activated by force in fetal type II cells and participates in strain-induced fetal type II cell differentiation.

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Role of endogenous TGF-β in glucocorticoid-induced lung type II cell differentiation

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00088.2006 ◽

2007 ◽

Vol 292 (1) ◽

pp. L249-L257 ◽

Cited By ~ 28

Author(s):

Theresa M. McDevitt ◽

Linda W. Gonzales ◽

Rashmin C. Savani ◽

Philip L. Ballard

Keyword(s):

Cell Differentiation ◽

Transforming Growth Factor ◽

Fetal Lung ◽

Hormone Treatment ◽

Type Ii ◽

Gene Suppression ◽

Surfactant Production ◽

Type Ii Cell ◽

Human Fetal Lung

In the fetal lung, endogenous transforming growth factor (TGF)-β inhibits early morphogenesis and blocks hormone-induced type II cell differentiation. We hypothesized that endogenous TGF-β inhibits type II cell differentiation and that the stimulatory effects of glucocorticoids result in part from suppression of TGF-β. Epithelial cells were isolated from human fetal lung and cultured under defined conditions with and without dexamethasone plus cAMP to promote type II cell differentiation. Control cells produced TGF-β, which was activated in part by αVβ6-integrin. Treatment with dexamethasone, but not cAMP, reduced TGF-β1 and -β2 transcripts and TGF-β bioactivity in culture medium. To examine the effects of decreased TGF-β in the absence of glucocorticoid, cells were treated with antibodies to TGF-β and its receptors. By real-time RT-PCR, antibody blockade of TGF-β reduced serpine1, a TGF-β-inducible gene, and increased gene expression for sftpa, sftpb, sftpc, and titf1, mimicking the response to hormone treatment. By microarray analysis, 29 additional genes were induced by both TGF-β antibody and hormone treatment, and 20 other genes were repressed by both treatments. For some genes, the fold response was comparable for antibody and hormone treatment. We conclude that endogenous TGF-β suppresses expression of surfactant proteins and selected other type II cell genes in fetal lung, in part secondary to increased expression of titf1, and we propose that the mechanism of glucocorticoid-induced type II cell differentiation includes antagonism of TGF-β gene suppression. Surfactant production during fetal development is likely influenced by relative levels of TGF-β and glucocorticoids.

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