title: Aging fibroblasts resist phenotypic maturation because of impaired hyaluronan-dependent CD44/epidermal growth factor receptor signaling.
abstract: 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.
authors.affiliation: Institute of Nephrology, Department of Oral Surgery, Cardiff University School of Medicine, Heath Park, Cardiff CF14 4XN, UK.
authors.forename: Russell M L
authors.initials: RM
authors.lastname: Simpson
authors.forename: Alan
authors.initials: A
authors.lastname: Wells
authors.forename: David
authors.initials: D
authors.lastname: Thomas
authors.forename: Philip
authors.initials: P
authors.lastname: Stephens
authors.forename: Robert
authors.initials: R
authors.lastname: Steadman
authors.forename: Aled
authors.initials: A
authors.lastname: Phillips
mesh_terms: D000328:Adult; D000818:Animals; D002417:Cattle; D002454:Cell Differentiation / Q000187:drug effects; D002469:Cell Separation; D016922:Cellular Senescence / Q000187:drug effects; D020405:Dermis / Q000166:cytology; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D014453:Glucuronosyltransferase / Q000378:metabolism; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D000076002:Hyaluronan Synthases; D006820:Hyaluronic Acid / Q000378:metabolism*; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051899:Smad2 Protein / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology
chemical_list: D018960:Hyaluronan Receptors; D018125:Receptors, Transforming Growth Factor beta; C497782:SMAD2 protein, human; D051899:Smad2 Protein; D053773:Transforming Growth Factor beta1; D004815:Epidermal Growth Factor; D006820:Hyaluronic Acid; D014453:Glucuronosyltransferase; C101754:HAS2 protein, human; D000076002:Hyaluronan Synthases; D066246:ErbB Receptors; D017346:Protein Serine-Threonine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I