OBJECTIVETo investigate characteristics of pulmonary stem cells labeled with bromodeoxyuridine (Brdu) and telomerase reverse transcriptase (TERT) in lung tissue, as well as the effects of proliferation and differentiation of the stem cells on lung development and repair of pulmonary injury.

METHODSA model of hyperoxia in neonatal rats was made by exposing the rats to 95% O2 for 7 d. Before sacrificing the rats, Brdu was injected through peritoneum, and immune staining positive cells were analyzed after the rats were sacrificed. TERT positive cells were stained by an immunohistochemical method. At the same time, the double staining for surfactant protein C (SPC) and Brdu or SPC and TERT were performed. Lung histologic study was done on HE stained tissue slices.

RESULTS(1) The lung with hyperoxic injury had thinner walls of alveoli, simple alveolar structure, fewer and larger alveoli, expanded and shrunken alveoli, and there were many fell-off alveolar epithelial cells in the alveolar cavities as well. (2) The cells positively stained with Brdu located in septa, mucosa and submucosa of various bronchi, scattering in epithelium of bronchi, and the number of positive cells was low, having a large nucleus. The TERT-positive cells were apparent in the septa and alveolar walls of peripheral lung tissue, characterized by uneven distribution in the lung lobes, the number of positive cells was less than that of Brdu-positive cells [integral of expression (1.61 +/- 0.83) vs. (0.62 +/- 0.55), P < 0.05]. The number of Brdu- and TERT-positive cells had no significant difference in hyperoxic rats compared to that in controls [integral of expression (1.43 +/- 0.85) vs. (1.61 +/- 0.83); (0.62 +/- 0.55) vs. (0.83 +/- 0.84), P > 0.05]. (3) After double staining, a few positive cells were found in double-stained tissues with SPC and Brdu or TERT. (4) The cells positively stained with SPC antibody had different size. The percentage of positive cells was not significantly different between the hyperoxia group (80.3%) and control group (78.6%). The Brdu positive staining located in nucleus of cells that had larger size than the cells not stained, round nucleus with intense staining (seldom, pole-shaped) and the number of such cells was less than that of the SPC positive cells. The percentage of positive cells was not significantly different between the hyperoxia group (28.5%) and control group (21.4%). (5) The TERT staining located in nucleus of cell that had smaller size than the cells not stained, various nuclear shape, including round intensively stained, round slightly stained, pole-shaped and divided shape. The percentage of positive cells was not significantly different between the hyperoxia group (2.3%) and control group (1.5%).

CONCLUSIONS(1) Brdu and TERT, as markers of stem cells having different capability of differentiation, possess special characteristics, respectively. The cells with Brdu could be transit amplifying cell (TAC) which retains characteristics of stem cells originated from differentiated stem cells, while, the cells stained with TERT especially reflects the characteristics of stem cells. (2) The proliferation and differentiation of pulmonary stem cells during hypoxic lung injury are limited and may be related with arrest of alveolization.