Alveolar epithelial trans-differentiation, lung development and disease - Role of TGF B1 and microRNAs

Abstract

Scope and Method of Study:

The present study was undertaken to understand the role of TGF B1 and its down-stream signaling components in alveolar epithelial trans-differentiation, a phenomenon seen in acute lung injuries. The second aim was to elucidate the expression profile and possible roles of microRNAs in fetal lung development and in a chronic lung disease of development called Bronchopulmonary dysplasia (BPD). An in vitro model for transdifferentiation of alveolar epithelial cells was used and expression of TGF B1 and multiple components of its pathway and the effect of blocking the pathway on the process were looked into. The microRNA expression profile during different time points in fetal lung development was characterized and confirmed. Effect of miR-127 over expression on lung branching and morphology in an in vitro organ culture system was visualized and quantified using morphometric analysis. The BPD model in neonatal rat was established and microRNAs that significantly changed during disease and their expression pattern was confirmed. We have used a number of techniques like immunohisto/cytochemistry, western blotting, ELISA, real time PCR, adeno virus-mediated RNA interference and over expression, microarray and lung morphometry to address these biological questions.

Findings and Conclusions:

1. The trans-differentiation of alveolar epithelial type 2 cells to type 1 was modulated by autocrine signaling through TGF B1 pathway and was Smad mediated.

2. TGF B1 elicited its effect by altering the expression levels of cell cycle proteins, CDKs2, 4 and 6 and p15Ink4b and p21kip1.

3. Blocking the signaling through TGF B1 blocked the trans-differentiation process.

4. 21 microRNAs were identified that showed significant changes during fetal lung development and grouped into 4 distinct clusters based on their expression pattern.

5. miR-127 over expression significantly affected lung branching and morphogenesis implicating its role in fetal lung development.

6. A neonatal rat model for BPD was established.

7. 5 down-regulated and 4 up-regulated microRNAs were identified in BPD, providing an insight into the pathogenesis of BPD.