Aging Fibroblasts Resist Phenotypic Maturation Because of Impaired Hyaluronan-Dependent CD44/Epidermal Growth Factor Receptor Signaling

• Published in: The American journal of pathology Vol. 176; no. 3; pp. 1215 - 1228
• Main Authors: Simpson, Russell M.L, Wells, Alan, Thomas, David, Stephens, Philip, Steadman, Robert, Phillips, Aled
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 01.03.2010; ASIP; American Society for Investigative Pathology
• Subjects: Adult; Animals; Biological and medical sciences; Cattle; Cell Differentiation - drug effects; Cell Separation; Cellular Senescence - drug effects; Dermis - cytology; Enzyme Activation - drug effects; Epidermal Growth Factor - pharmacology; Extracellular Signal-Regulated MAP Kinases - metabolism; Fibroblasts - cytology; Fibroblasts - drug effects; Fibroblasts - enzymology; Glucuronosyltransferase - metabolism; Humans; Hyaluronan Receptors - metabolism; Hyaluronan Synthases; Hyaluronic Acid - metabolism; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Pathology; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Phenotype; Protein-Serine-Threonine Kinases - metabolism; Receptor, Epidermal Growth Factor - metabolism; Receptors, Transforming Growth Factor beta - metabolism; Regular; Signal Transduction - drug effects; Smad2 Protein - metabolism; Transforming Growth Factor beta1 - pharmacology; Transmembrane protein; Ageing; Cell adhesion molecule; Epidermal growth factor receptor; Signal transduction; Anatomic pathology; Phenotype; Growth factor receptor; Glycosaminoglycan; Hyaluronic acid; Dependent receptor; Fibroblast; Age
• ISSN: 0002-9440; 1525-2191
• DOI: 10.2353/ajpath.2010.090802

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)-β1-dependent phenotypic activation uses two distinct but cooperating pathways that involve TGF-β 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-β receptor, Smad2, EGF, EGF-R, and ERK1/2) attenuated TGF-β1 induction of α-smooth muscle actin. We present evidence that the HA receptor CD44 co-immunoprecipitates with EGF-R after activation by TGF-β1. 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-β1-mediated HA-CD44/EGF-R association and α-smooth muscle actin induction. Taken together, these results demonstrate that HA can serve as a signal integrator by facilitating TGF-β1-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.