Retinoic acid-induced proliferation of lung alveolar epithelial cells: relation with the IGF system

Author:

Nabeyrat Elodie1,Besnard Valérie1,Corroyer Sophie1,Cazals Véronique1,Clement Annick1

Affiliation:

1. Department of Pediatric Pulmonology, Institut National de la Santé et de la Recherche Médicale U142, Trousseau Hospital, St. Antoine Medical School, University of Paris, 75012 Paris, France

Abstract

Retinoids, including retinol and retinoic acid (RA) derivatives, are important molecules for lung growth and homeostasis. The presence of RA receptors and of RA-binding proteins in the alveolar epithelium led to suggest a role for RA on alveolar epithelial cell replication. In the present study, we examined the effects of RA on proliferation of the stem cells of the alveolar epithelium, the type 2 cells. We showed that treatment of serum-deprived type 2 cells with RA led to a stimulation of cell proliferation, with an increase in cell number in a dose-dependent manner. To gain some insights into the mechanisms involved, we studied the effects of RA on the expression of several components of the insulin-like growth factor (IGF) system that have been shown to be associated with the growth arrest of type 2 cells, mainly the IGF-binding protein-2 (IGFBP-2), IGF-II, and the type 2 IGF receptor. We documented a marked decrease in the expression of these components upon RA treatment. Using conditioned media from RA-treated cells, we provided evidence that the proliferative response of type 2 cells to RA was mediated through production of growth factor(s) distinct from IGF-I. We also showed that RA was able to reduce the decrease in cell number observed when type 2 cells were treated with transforming growth factor (TGF)-β1. These results together with the known stimulatory effect of TGF-β1 on IGFBP-2 expression led to suggest that RA may be associated with type 2 cell proliferation through mechanisms interfering with the TGF-β1 pathway.

Publisher

American Physiological Society

Subject

Cell Biology,Physiology (medical),Pulmonary and Respiratory Medicine,Physiology

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