Figure 3.

Homologous serum and inflammatory cytokines promote circular smooth muscle cells (CSMC) growth in vitro via platelet-derived growth factor (PDGF). (A) Proliferation of CSMC in cohort cultures exposed to either 2% FCS or 2% adult rat serum (RS) for 48 hrs. The effect of RS was reduced to control levels by the PDGF-Rβ inhibitor imatinib (*P < 0.05 versus RS; **P > 0.05 versus serum-free control; n = 4). Inset, representative image of immunoblot showing the presence of PDGF-BB in both FCS and RS as a 31 KD dimer, with detectable monomer (15 KD) in RS. Left lane, recombinant PDGF-BB. (B) Pro-inflammatory cytokines did not affect growth of CSMC directly, but strongly promoted the effect of PDGF-BB. Replicate cultures of CSMC were synchronized and exposed to PDGF-BB (10 ng/ml), cytokine (50 ng/ml) or cytokine + PDGF-BB, and cell proliferation was evaluated 2 days later. In triplicate cultures from three independent experiments, there was no direct effect of any cytokine (black bars), while the pro-inflammatory interleukin (IL)-1β, tumour necrosis factor (TNF)-α and IL17A significantly increased the response of cells to PDGF-BB (grey bars; *P < 0.05 compared with PDGF-BB alone).