PDGF-Ralpha gene expression predicts proliferation, but PDGF-A suppresses transdifferentiation of neonatal mouse lung myofibroblasts

Respir Res. 2009 Nov 25;10(1):119. doi: 10.1186/1465-9921-10-119.


Background: Platelet-derived growth factor A (PDGF-A) signals solely through PDGF-Ralpha, and is required for fibroblast proliferation and transdifferentiation (fibroblast to myofibroblast conversion) during alveolar development, because pdgfa-null mice lack both myofibroblasts and alveoli. However, these PDGF-A-mediated mechanisms remain incompletely defined. At postnatal days 4 and 12 (P4 and P12), using mouse lung fibroblasts, we examined (a) how PDGF-Ralpha correlates with ki67 (proliferation marker) or alpha-smooth muscle actin (alphaSMA, myofibroblast marker) expression, and (b) whether PDGF-A directly affects alphaSMA or modifies stimulation by transforming growth factor beta (TGFbeta).

Methods: Using flow cytometry we examined PDGF-Ralpha, alphaSMA and Ki67 in mice which express green fluorescent protein (GFP) as a marker for PDGF-Ralpha expression. Using real-time RT-PCR we quantified alphaSMA mRNA in cultured Mlg neonatal mouse lung fibroblasts after treatment with PDGF-A, and/or TGFbeta.

Results: The intensity of GFP-fluorescence enabled us to distinguish three groups of fibroblasts which exhibited absent, lower, or higher levels of PDGF-Ralpha. At P4, more of the higher than lower PDGF-Ralpha + fibroblasts contained Ki67 (Ki67+), and Ki67+ fibroblasts predominated in the alphaSMA + but not the alphaSMA- population. By P12, Ki67+ fibroblasts comprised a minority in both the PDGF-Ralpha + and alphaSMA+ populations. At P4, most Ki67+ fibroblasts were PDGF-Ralpha + and alphaSMA- whereas at P12, most Ki67+ fibroblasts were PDGF-Ralpha- and alphaSMA-. More of the PDGF-Ralpha + than - fibroblasts contained alphaSMA at both P4 and P12. In the lung, proximate alphaSMA was more abundant around nuclei in cells expressing high than low levels of PDGF-Ralpha at both P4 and P12. Nuclear SMAD 2/3 declined from P4 to P12 in PDGF-Ralpha-, but not in PDGF-Ralpha + cells. In Mlg fibroblasts, alphaSMA mRNA increased after exposure to TGFbeta, but declined after treatment with PDGF-A.

Conclusion: During both septal eruption (P4) and elongation (P12), alveolar PDGF-Ralpha may enhance the propensity of fibroblasts to transdifferentiate rather than directly stimulate alphaSMA, which preferentially localizes to non-proliferating fibroblasts. In accordance, PDGF-Ralpha more dominantly influences fibroblast proliferation at P4 than at P12. In the lung, TGFbeta may overshadow the antagonistic effects of PDGF-A/PDGF-Ralpha signaling, enhancing alphaSMA-abundance in PDGF-Ralpha-expressing fibroblasts.

Publication types

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

MeSH terms

  • Actins / metabolism
  • Animals
  • Animals, Newborn
  • Cell Differentiation / drug effects*
  • Cell Line
  • Cell Proliferation*
  • Cell Transdifferentiation
  • Cells, Cultured
  • Fibroblasts / cytology*
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism*
  • Gene Expression Regulation
  • Lung / cytology*
  • Lung / drug effects
  • Lung / growth & development
  • Mice
  • Mice, Transgenic
  • Platelet-Derived Growth Factor / pharmacology*
  • Receptor, Platelet-Derived Growth Factor alpha / genetics
  • Receptor, Platelet-Derived Growth Factor alpha / metabolism*
  • Signal Transduction / physiology
  • Smad2 Protein / metabolism
  • Smad3 Protein / metabolism
  • Transforming Growth Factor beta / pharmacology


  • Actins
  • Platelet-Derived Growth Factor
  • Smad2 Protein
  • Smad2 protein, mouse
  • Smad3 Protein
  • Smad3 protein, mouse
  • Transforming Growth Factor beta
  • alpha-smooth muscle actin, mouse
  • platelet-derived growth factor A
  • Receptor, Platelet-Derived Growth Factor alpha