Aging fibroblasts resist phenotypic maturation because of impaired hyaluronan-dependent CD44/epidermal growth factor receptor signaling

Am J Pathol. 2010 Mar;176(3):1215-28. doi: 10.2353/ajpath.2010.090802. Epub 2010 Jan 21.


Fibroblast differentiation into myofibroblasts is a key event during normal wound repair. We have previously demonstrated an age-related defect in this process associated with impaired synthesis of hyaluronan (HA) synthase (HAS) 2 but failed to prescribe its role in a mechanistic sense. Here we demonstrate that in addition to HAS2, there is loss of EGF receptor (EGF-R) in aged cells, and both are required for normal fibroblast functionality. Analysis of molecular events revealed that in young cells, transforming growth factor (TGF)-beta1-dependent phenotypic activation uses two distinct but cooperating pathways that involve TGF-beta receptor/Smad2 activation and EGF-mediated EGF-R/extracellular signal-regulated kinase (ERK) 1/2 signaling, and the latter is compromised with in vitro aging. Pharmacological inhibition of any of the five intermediates (TGF-beta receptor, Smad2, EGF, EGF-R, and ERK1/2) attenuated TGF-beta1 induction of alpha-smooth muscle actin. We present evidence that the HA receptor CD44 co-immunoprecipitates with EGF-R after activation by TGF-beta1. This interaction is HA-dependent because disruption of HA synthesis abrogates this association and inhibits subsequent ERK1/2 signaling. In aged fibroblasts, this association is lost with resultant suppression of ERK1/2 activation. Forced overexpression of EGF-R and HAS2 in aged cells restored TGF-beta1-mediated HA-CD44/EGF-R association and alpha-smooth muscle actin induction. Taken together, these results demonstrate that HA can serve as a signal integrator by facilitating TGF-beta1-mediated CD44-EGF-R-ERK interactions and ultimately fibroblast phenotype. We propose a model to explain this novel mechanism and the functional consequence of age-dependent dysregulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Animals
  • Cattle
  • Cell Differentiation* / drug effects
  • Cell Separation
  • Cellular Senescence* / drug effects
  • Dermis / cytology
  • Enzyme Activation / drug effects
  • Epidermal Growth Factor / pharmacology
  • ErbB Receptors / metabolism*
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Fibroblasts / cytology*
  • Fibroblasts / drug effects
  • Fibroblasts / enzymology
  • Glucuronosyltransferase / metabolism
  • Humans
  • Hyaluronan Receptors / metabolism*
  • Hyaluronan Synthases
  • Hyaluronic Acid / metabolism*
  • Phenotype
  • Protein Serine-Threonine Kinases / metabolism
  • Receptor, Transforming Growth Factor-beta Type I
  • Receptors, Transforming Growth Factor beta / metabolism
  • Signal Transduction* / drug effects
  • Smad2 Protein / metabolism
  • Transforming Growth Factor beta1 / pharmacology


  • Hyaluronan Receptors
  • Receptors, Transforming Growth Factor beta
  • SMAD2 protein, human
  • Smad2 Protein
  • Transforming Growth Factor beta1
  • Epidermal Growth Factor
  • Hyaluronic Acid
  • Glucuronosyltransferase
  • HAS2 protein, human
  • Hyaluronan Synthases
  • ErbB Receptors
  • Protein Serine-Threonine Kinases
  • Extracellular Signal-Regulated MAP Kinases
  • Receptor, Transforming Growth Factor-beta Type I