Abstract
Hyaluronic acid (HA), a glycosaminoglycan located between keratinocytes in the epidermis, accumulates dramatically following skin wounding. To study inductive mechanisms, a rat keratinocyte organotypic culture model that faithfully mimics HA metabolism was used. Organotypic cultures were needle-punctured 100 times, incubated for up to 24 hours, and HA analyzed by histochemical and biochemical methods. Within 15 minutes post-injury, HA levels had elevated two-fold, increasing to four-fold by 24 hours. HA elevations far from the site of injury suggested the possible involvement of a soluble HA-inductive factor. Media transfer experiments (from wounded cultures to unwounded cultures) confirmed the existence of a soluble factor. From earlier evidence, we hypothesized that an EGF-like growth factor might be responsible. This was confirmed as follows: (1) EGFR kinase inhibitor (AG1478) completely prevented wounding-induced HA accumulation. (2) Rapid tyrosine-phosphorylation of EGFR correlated well with the onset of increased HA synthesis. (3) A neutralizing antibody that recognizes heparin binding EGF-like growth factor (HB-EGF) blocked wounding-induced HA synthesis by > or =50%. (4) Western analyses showed that release of activated HB-EGF (but neither amphiregulin nor EGF) occured after wounding. In summary, rapid HA accumulation after epidermal wounding occurs through a mechanism requiring cleavage of HB-EGF and activation of EGFR signaling.