Stimulation of cell proliferation by hyaluronidase during in vitro aging of human skin fibroblasts.

The effect of the degradation of extracellular hyaluronan on the proliferation of human skin fibroblasts in serial cultures during in vitro aging was investigated. Human skin fibroblasts at different time intervals from 3rd to 36th passages were exposed after plating to bovine testicular hyaluronidase. The enzyme treatment resulted in an increase in cell proliferation (cell number vs. time) as compared to the untreated control fibroblasts. The effect was dose dependent, reversible, and was independent of the type of the glycosidic linkage cleaved in hyaluronan. The increased proliferation was observed at all passages when untreated cells underwent mitosis. The degradation of hyaluronan induced cell proliferation up to the presenescent phase. Depletion of hyaluronan did not induce proliferation of postmitotic fibroblasts. The incorporation of 3H-glucosamine into hyaluronan decreased with increasing cell passages (increase of the number of population doublings). Twenty-fourth passage fibroblasts accumulated about two time less hyaluronan in the medium than ninth passage cultures. Following hyaluronidase treatment, the amount of newly synthesized, labeled hyaluronan increased in the medium. Accordingly, the fibroblasts restored the degraded hyaluronan even in the declining phase of proliferation (phase III according to Hayflick).