INHIBITION OF SERUM AND TRANSFORMING-GROWTH-FACTOR-BETA (TGF-BETA-1)-INDUCED DNA-SYNTHESIS IN CONFLUENT AIRWAY SMOOTH-MUSCLE BY HEPARIN

1 Airway remodelling occurs in asthma and involves an increase in airw ay smooth muscle mass through cell proliferation and hypertrophy. Incr eased eosinophil density in the airways is a feature of asthma. Eosino phils exhibiting activation in the airways of asthmatics also exhibit increased expression of transforming growth factor beta (TGF-beta 1). We have examined the capacity of TGF-beta 1 and epidermal growth facto r (EGF) to influence airway smooth muscle division and the effect of h eparin on TGF-beta 1, EGF and serum-induced smooth muscle DNA synthesi s in confluent airway smooth muscle cells (ASMC) as an indication of e ntry into S phase preceding mitogenesis. 2 ASMC were obtained from cel l populations growing out from explanted bovine trachealis muscle sect ions. Cell division was monitored in sparse plated cells by direct cel l counting following nuclear staining. Cell DNA synthesis in confluent cells was monitored by uptake of [H-3]-thymidine. 3 TGF-beta 1 (100 p M) inhibited FBS (10%)-induced smooth muscle division in sparsely plat ed cells (40%). TGF-beta 1 (100 pM) increased cell DNA synthesis (200% ) in confluent cells in the presence of bovine serum albumin (BSA, 0.2 5%). EGF (0.7 nM) also increased airway smooth muscle DNA synthesis (6 9%) in the presence of BSA (0.25%). The facilitatory effect of TGF-bet a 1 was observed between 1-100 pM, while that of EGF was observed betw een 20-200 pM. 4 Heparin inhibited serum and TGF-beta 1-induced DNA sy nthesis in confluent ASMC (55%), consistent with our previous observat ion of inhibition of division in sparsely populated ASMC (Kilfeather e t al., 1995a). This action of heparin was observed between concentrati ons of 1-100 mu g ml(-1). Heparin did not inhibit DNA synthesis in res ponse to EGF. An anti-mitogenic effect of heparin was also observed ag ainst responses to combined exposure to TGF-beta 1 and EGF. 5 There wa s a clear inhibitory effect of heparin in absolute terms against serum -induced division in cells plated at 10, 20 and 45 x 10(3) cells cm(-2 ). The inhibitory effect of heparin was also observed at a plating den sity of 45,000 cells cm(-2) when responses to serum were expressed as fold-stimulation of basal DNA synthesis. 6 These findings demonstrate a potential role of TGF-beta 1, EGF and heparin-related molecules in r egulation of airway smooth muscle division.