Fibrotic healing of adult and late gestation fetal wounds correlates with increased hyaluronidase activity and removal of hyaluronan.

The lack of scarring and fibrosis in healing fetal skin wounds may relate to a prolonged presence of hyaluronan (HA). It has been suggested that fetal wounds may lack hyaluronidase, but the hyaluronidase levels in fetal wounds remain unknown. The size of HA influences its biological action, especially in relation to angiogenesis, which is also reduced in fetal wound healing. The present study determined the levels and size of HA, as well as hyaluronidase levels, in fetal and adult lamb wounds. Wire mesh cylinders, or polyvinyl acetate sponges, were placed subcutaneously in fetal lambs at 75, 100 or 120 days gestation. Wound fluid and wound tissue were harvested 3, 7 or 14 days later. Samples were digested with papain and both HA and hyaluronidase activity were determined in a competitive ELISA assay. Size distribution of HA was estimated using a Sephacryl S1000 column and fractions were collected for HA determination. Adult wound fluid HA remained low (4-5 micrograms/ml) over the 14 days. Fetal fluids were similar on day 3, but increased to 15-25 micrograms/ml by day 7. In 75/100-day wounds, HA remained elevated at 14 days, but in 120-day fluids decreased to levels similar to adult fluid. The HA in all fluids was polydisperse with a main peak at 200 kDa. Hyaluronidase levels were detected in all samples, reaching a peak 7 days post-wounding. In adult wound fluids hyaluronidase was much higher than the fetal wound fluids. These data suggest that lower hyaluronidase levels in fetal wounds may underlie the different pattern of HA deposition seen in fetal wounds.