BACKGROUND/PURPOSE - The midgestation fetus heals incisional skin wounds scarlessly, whereas large excisional wounds scar. High concentrations of hyaluronan (HA) are associated with scarless fetal as opposed to scar-forming adult wound repair. Because expression of the HA receptors, CD44 and RHAMM (Receptor for HA-Mediated Motility), has been associated with adult wound fibroplasia, the authors postulated that fetal excisional wounds would show increased expression of CD44 and RHAMM as compared with incisional wounds.
METHODS - Two models of fetal wound healing were examined. Fetal skin from human abortuses was heterotransplanted subcutaneously into severe combined immunodeficient (SCID) mice. Fourteen days after grafting, incisional or 2-mm excisional wounds were created (n = 6 per time-point). In addition, incisional and excisional (6 to 10 mm) wounds (n = 5 per time-point) were created on the backs of 70- to 75-day fetal lambs (term, 145 days). Tissue from both models was harvested at sequential time-points after injury. Wounds were studied histologically for fibroplasia and assayed for their HA content. CD44 and RHAMM expression were analyzed by immunohistochemistry and immunoblotting.
RESULTS - As expected, in both models, incisional wounds healed scarlessly, whereas excisional wounds showed fibroplasia. Incisional wounds of fetal lambs maintained a significantly higher HA content than excisional wounds 3 days after injury. Between 1 and 7 days in either human or sheep fetal wounds, immunostaining for CD44 and RHAMM markedly increased along the margins of excisional wounds as compared with incisional wounds and unwounded skin. Immunoblot analysis confirmed this increased HA receptor expression in both models.
CONCLUSIONS - HA receptor expression increased in both human and sheep fetal excisional wounds and correlated with fibroplasia and a reduced HA content. The authors speculate that strategies to limit the expression or function of HA receptors during postnatal wound repair may modify the development of scar.