[Decreased stimulation of hyaluronic acid synthesis by PDGF, IGF-I or serum in the aging process of skin fibroblasts in vitro].

Human skin fibroblasts of phase II ("young" cells derived from populations with a low population doubling level) and of phase III ("old" cells from populations, which were approx. 2 population doublings before the last possible subculture) were kept under subconfluent conditions in a defined serum-free medium. Thereby the cells are in a non-proliferative "quiescent" state. Glycosaminoglycan (GAG)- and especially hyaluronan (HA)-synthesis and release into the medium were investigated by the incorporation rate of 14C-glucosamine. About 95% of the synthesized (48 h) GAGs and HA were medium-released and 5% cell-bound. HA synthesis rate of phase III-cultures was significantly reduced, as compared with phase II-cultures. Stimulation of HA-synthesis of phase III-cells--in comparison with phase II-cells--by serum, PDGF or IGF-I was strongly reduced. While HA-synthesis of phase II-cells was maximally stimulated by 5% FCS or 20 ng/ml PDGF, phase III-cells dit not exhibit a saturation kinetics up to 20% FCS or 60 ng/ml PDGF. The strongly reduced HA-synthesis rate of phase III-cells--compared with phase II-cells--in the non-stimulated quiescent state as well as after stimulation by PDGF, IGF-I or serum might be considered as a biomarker of in vitro (and in vivo?) ageing.