The proliferative effects of retinoic acid on primary cultures of adult rat type II pneumocytes depend upon cell density

In Vitro Cell Dev Biol Anim. 2010 Jan;46(1):20-7. doi: 10.1007/s11626-009-9236-z. Epub 2009 Sep 29.


Retinoic acid (RA) is important for maintaining integrity of alveolar epithelial cells, but the mechanism has not been defined. We cultured type II pneumocytes at confluent, high cell density (10(4) cells/mm(2)) and found that RA (10(-6) M) inhibited thymidine incorporation to 60% of control, despite a dose-dependent increase in epidermal growth factor receptor (EGFR) levels. However, at lower, subconfluent density (10(2) cells/mm(2)), RA stimulated thymidine incorporation to 280% of control. EGF increased thymidine incorporation at concentrations as low as 0.1 ng/mL, but no further increase was observed at higher concentrations up to 100 ng/mL. In subconfluent cells co-treated with EGF (100 ng/mL) and increasing concentrations of RA (10(-8) M-10(-5) M RA), thymidine incorporation was significantly greater at all concentrations than RA alone, with greatest increases observed at 10(-7) (422% of control) and 10(-6) (470% of control) M RA. In summary, the effects of RA on thymidine incorporation are sensitive to changes in cell density. RA inhibits thymidine incorporation at high cell density and stimulates thymidine incorporation at low density. RA increases EGFRs in cultured type II pneumocytes, and EGF stimulates thymidine incorporation independent of the cultured cell density. These data may help to explain how RA mediates lung repair in vivo.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Aging / physiology*
  • Alveolar Epithelial Cells / cytology*
  • Alveolar Epithelial Cells / drug effects*
  • Alveolar Epithelial Cells / metabolism
  • Animals
  • Cell Count
  • Cell Proliferation / drug effects
  • Cells, Cultured
  • DNA / biosynthesis
  • Electrophoresis, Polyacrylamide Gel
  • Epidermal Growth Factor / pharmacology
  • ErbB Receptors / metabolism
  • Fluorescence
  • Male
  • Rats
  • Rats, Sprague-Dawley
  • Tretinoin / pharmacology*


  • Tretinoin
  • Epidermal Growth Factor
  • DNA
  • ErbB Receptors