HEPARIN STIMULATES FIBROBLAST GROWTH INDUCED BY PDGF

Heparin binds to smooth muscle cells and endothelial cells. It inhibits the proliferation of the smooth muscle cells and modulates the growth of endothelial cells. Fibroblasts which represent an other cell type belonging to the vascular wall could also have their growth modified by heparin. We have at first, demonstrated that 125I unfractionated heparin bigds to cultured human skin fibroblasts with a Kd of 1.16 10 M.A low molecular weight heparin fraction (PK 10169) competed (50 %)with I unfractionated heparin, but at aless extent than cold unfractionated heparin(90%).As it has been reported with endothelial and smooth muscle cells, about 30% of the bound unfractionated heparin was internalized bythe fibroblasts. Heparin alone at the concentration ranges from 0 to 10-5M has no effect on fibroblast proliferation measured by the H thymidine uptake. When the cellproliferation was induced by pure PDGF, heparin potentiated markedly the fibroblast growth.The effgct started at 10-8 M heparinand reached a plateau from 10-6 M to 10-5 M. Similar stimulationwas observed when the growth was induced by FGF or EGF. Low molecular weight heparin enhanced the fibroblast proliferation induced by PDGF but at a less extent than unfractionated heparin, chondroltin sulfate has no effect. When added during the cell culture growth withhuman serum (5%), unfractionated heparin increased by 48 the cell proliferation as measured bycell counting at the 6th day of the culture. PDGF did not modify the heparin binding on fibroblast cultures either at 4°C or 37°C and did not alter the process of heparin internalization. JDGF binding to the cultured fibroblast (Kd 10.1 ± 3.4 10-10 M)was not modified by the presence of heparin when studied at 4°C.In conclusion : i) cultured human fibroblasts bind and internalize heparin, ii) heparinand heparin fraction stimulate the fibroblastgrowth induced by PDGF, iii) since the binding of PDGF is not modified by bound heparin, the mechanism of stimulation remains unknown.