Surfactant protein A influences reepithelialization in an alveolocapillary model system.
OBJECTIVE
Restoring the barrier integrity of the alveolar epithelium after injury is pivotal. In the current study, we evaluated the effects of surfactant, surfactant protein A (SP-A), transforming growth factor β (TGF-β), and analogues of SP-A on alveolar epithelial repair. Additionally, we assessed the influence of microvascular endothelial cells on reepithelialization.


METHODS
Repair was studied in an in vitro model system consisting of a bilayer coculture of A549 and human pulmonary microvascular endothelial cells (HPMECs), which stably expressing fluorescent proteins. The epithelial repair was assessed in a scratch assay using vital fluorescence microscopy and compared with a monolayer of A549 cells.


RESULTS
HMPEC cells differentially modulated the response of the A549 cells. Surfactant and SP-A augmented the reepithelialization in the presence of HPMECs, whereas in the absence of HPMECs, surfactant inhibited wound healing and SP-A failed to alter the response. Like SP-A, a structural analogue of its collagenous tail domain augmented the reepithelialization in the model system, whereas an analogue of its head domain did not alter the response. Additionally, we demonstrated that TGF-β associated with SP-A was able to initiate the Smad-dependent TGF-β pathway and that both TGF-β and TGF-β free SP-A were able to stimulate wound healing in the bilayer model.


CONCLUSIONS
These data show that surfactant, SP-A and TGF-β, influence epithelial repair in vitro and that the microvascular endothelial cells can modulate the response. This indicates that surfactant and SP-A could play a role in alveolar epithelial repair and that the microvascular endothelium may be involved in these processes.
Department of Paediatrics, School for Oncology and Developmental Biology (GROW), Maastricht University Medical Centre, P.O. Box 5800, 6202, AZ Maastricht, The Netherlands. C.Willems@maastrichtuniversity.nl
Coen H M P
CH
Willems
Luc J I
LJ
Zimmermann
Renate M R
RM
Langen
Maria J A
MJ
van den Bosch
Nico
N
Kloosterboer
Boris W
BW
Kramer
J Freek
JF
van Iwaarden
D002460:Cell Line; D045744:Cell Line, Tumor; D018920:Coculture Techniques; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology*; D006801:Humans; D011650:Pulmonary Alveoli / Q000166:cytology / Q000502:physiology*; D037662:Pulmonary Surfactant-Associated Protein A / Q000737:chemistry / Q000494:pharmacology*; D011663:Pulmonary Surfactants / Q000494:pharmacology; D012038:Regeneration; D016212:Transforming Growth Factor beta / Q000494:pharmacology
D037662:Pulmonary Surfactant-Associated Protein A; D011663:Pulmonary Surfactants; D016212:Transforming Growth Factor beta