There are two alveolar epithelial cell types in lung. Type II and Type 1. Upon lung injury, Type II cells serve as progenitors and differentiate into type 1 cells to heal the tissue. Our lab had had recently identified a novel transitional cell state assumed by type 2 cells as they differentiate into type 1 cells during normal regeneration after lung injury. We want to understand whether the transitional cells are related with ineffectual type 1 cell differentiation which may cause critical regenerative defect in pulmonary fibrosis. We set out with the goal of investigating the molecular mechanism of physiological and pathological alveolar repair in mouse model.