To further characterize A549 cells in ALI cultures, immunofluorescent staining assay was used to determine the expression of cell-specific markers of AECI and AECII cells.
AECII cells were reported to lose phenotype markers over time when they were cultured in monolayer (17), but they might be able to express cell type-specific markers in an ALI interface culture (4).
Subpopulations of ALI cultured A549 cells exhibited abilities to partially express cell type-specific markers of AECI and AECII cells.
AECII cells have a potency to give rise to new AECII cells and differentiate into AECI cells during alveolar injury repair and regeneration, therefore they have been considered progenitor cells in the alveoli (3,4,18).
A previous study has suggested that dipalmitoyl phosphatidyl choline-containing multilamellar bodies (MLB) are ultrastructural hallmark of AECII cells (28).
Two- week-old membranes of A549 air-liquid interface (ALI) cultures were used for determination of the expression of AECI cell specific marker aquaporin-5 (AQP-5) and AECII cell marker surfactant protein C (SP-C) by immunofluorescent staining assay.
Furthermore, a recent study demonstrated that TGF-[beta] could induce expression of extracellular matrix metalloproteinase inducer (EMMPRIN) in AECII cells, which in turn activated the Wnt/[beta]-catenin signaling pathway.
For example, the expression of WNT1-inducible signaling protein-1 (WISP1), a Wnt target gene, was elevated in AECII cells of both a mouse model of pulmonary fibrosis and in IPF patients .