The miRNA-29 Family Serves a Key Role in Type II Cell Differentiation in Developing Fetal Lung

Presentation Number: OR44-5
Date of Presentation: June 24th, 2014

Wei Guo*1, Houda Benlhabib1 and Carole R Mendelson2
1University of Texas Southwestern Med Ctr, Dallas, TX, 2Univ Texas Southwestern Med Ctr, Dallas, TX

Abstract

Type II cells are highly specialized epithelial cells of the lung alveoli that uniquely synthesize pulmonary surfactant, a developmentally-regulated, surface-active lipoprotein that is essential for breathing. Inadequate surfactant production by the lungs of prematurely born infants can result in respiratory distress syndrome, a major cause of neonatal morbidity and mortality. Surfactant protein A (SP-A), the major surfactant protein, is a well-established marker of type II cell differentiation. To define the mechanisms controlling type II cell differentiation, we investigated the role of microRNAs (miRNA, miR), ~22 nt non-coding RNAs that are potent posttranscriptional inhibitors of gene expression. We conducted miRNA microarray of epithelial cells isolated from mid-gestation human fetal lung (HFL) explants before and after 48 and 96 h of culture ± cAMP, which enhances type II cell differentiation and SP-A expression. Interestingly, we found that expression of all members of the miR-29 family increased during type II cell differentiation and was induced by cAMP. In parallel studies in mice, we also observed developmental upregulation of miR-29 family members in epithelial cells isolated from mouse fetal lung between E15.5 and E18.5 gestation, in concert with type II cell differentiation and induction of SP-A expression. To determine the functional role of miR-29 family members during type II cell differentiation, we transfected LNA miR-29 family inhibitor (anti-miR-29) into cultured HFL type II cells. Upon highly efficient knockdown of all miR-29 family members, we observed a dramatic loss of SP-A expression and decrease in lamellar body accumulation, indicating that miR-29 is required for type II cell differentiation and function. Known targets of miR-29 include DNMT3a/b, KLF4, HDAC4 and TGF-β, a recognized inhibitor of type II cell differentiation and SP-A expression. Notably, knockdown of miR-29 resulted in increased expression of TGF-β2 and downstream mediators, including phospho-Smad2 and the transcriptional silencer, ZEB1. Co-treatment of the cells with TGF-β inhibitor restored the induction of SP-A and lamellar body accumulation. Altogether, our findings suggest that upregulation of miR-29 expression in developing fetal lung serves a crucial role in type II cell differentiation and function by targeting the inhibitory TGF-β signaling pathway and its downstream mediators.

 

Nothing to Disclose: WG, HB, CRM