Submitted on July 26, 2007
Accepted on January 31, 2008
TGF-
signaling promotes survival and repair in rat alveolar epithelial type 2 cells during recovery after hyperoxic injury
S Buckley1, W. Shi1, L Barsky2, and D Warburton3*
1 Developmental Biology/Regenerative Medicine and Surgery Program, Childrens Hospital Los Angeles Saban Research Institute, Los Angeles, California, United States
2 Research Immunology/Bone Marrow Transplant Programs, Childrens Hospital Los Angeles Saban Research Institute, Los Angeles, California, United States
3 Developmental Biology/Regenerative Medicine and Surgery Program, Childrens Hospital Los Angeles Saban Research Institute,, Los Angeles, California, United States
* To whom correspondence should be addressed. E-mail: dwarburton{at}chla.usc.edu.
Hyperoxic rats treated with inosine during oxygen exposure have increased levels of active TGF-
in the BAL, yet alveolar epithelial type 2 cells (AEC2) isolated from these animals have less hyperoxia-induced DNA damage, while expressing increased levels of active Smad2. To see if TGF-1 signaling per se protected AEC2 against hyperoxic damage, freshly isolated AEC2 from hyperoxic rats were incubated with TGF-1 for 24h, and assayed for DNA damage by FACS analysis of TUNEL labeling. TGF-1 was protective over a range of concentrations similar to that seen in the BAL of inosine-treated hyperoxic animals (50 - 5000 pg/ml). TGF-1 also augmented hyperoxia-induced DNA repair activity and migration, stimulated autocrine secretion of fibronectin, accelerated the closure of a monolayer scratch wound and restored hyperoxia-depleted VEGF secretion by AEC2 to normoxic levels. The TGF-receptor 1 ALK4,5,7 (activin-like kinase receptor-4,5,7) inhibitor peptide SB 505124 abolished the protective effect of TGF- on hyperoxic DNA damage, and increased TUNEL in normoxic cells. These data suggest that endogenous TGF--Smad signaling is for required for AEC2 homeostasis in vitro, while exogenous TGF-1 treatment of hyperoxia-damaged AEC2 results in a cell which is equipped to survive, repair, migrate, secrete matrix and induce new blood vessel formation more efficiently than AEC2 primed by hyperoxia alone.
