Am. J. Respir. Cell Mol. Biol., Vol 11, No. 4, 10 1994, 416-425.
Regulation of alveolar type II cell differentiation and proliferation in adult rat lung explants
WV Kinnard, R Tuder, P Papst and JH Fisher
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262.
Alveolar type II cells produce pulmonary surfactant and serve as the stem
cell of the alveolar epithelium by proliferating and transforming into type
I cells. The study of the differentiated function and proliferative
capacity of type II cells in response to injury in vivo has been hindered
by the complexity of the systemic response to injury. In vitro studies have
in turn been limited by the impaired proliferative potential and loss of
markers of differentiation in isolated type II cells maintained in culture.
We describe an in vitro system in which type II cells proliferate
spontaneously and simultaneously maintain differentiated characteristics.
Other investigators have maintained slices of adult lung in culture after
agarose infusion for up to 9 wk. To further develop this model for the
study of epithelial cell differentiation and proliferation, we assessed
epithelial differentiation, proliferative capacity, and regulation of
cell-specific gene expression in slice explants of agarose-infused rat
lungs. We prepared 1-mm-thick explants and maintained them in culture for
up to 2 wk. Maintenance of differentiation was confirmed morphologically by
light and electron microscopy, by the accumulation of epithelial
cell-specific surfactant proteins, and by phospholipid analysis.
Proliferative capacity was assessed by measuring [3H]thymidine
incorporation in alveolar and small airway cells at baseline and in
response to growth stimuli. Type II cell proliferation was inhibited in a
dose-dependent manner by glucocorticoids. Glucocorticoids regulated RNA
levels in explants in a manner similar to that seen in vivo and in fetal
lung explants. The alveolar epithelium in adult lung slice explants
maintains differentiated function and the ability to proliferate, thereby
providing a useful system for the study of distal airway and alveolar cell
homeostasis and response to injury.
