Figure 6.

Inflammatory factors cause growth of freshly isolated control adult circular smooth muscle cells (CSMC) via accelerated expression of platelet-derived growth factor (PDGF)-Rβ. (A) Typical outcome of RT-PCR of CSMC at 6 days after isolation from the control colon, showing accelerated appearance of mRNA for PDGF-Rβ in CSMC exposed to conditioned medium (CM) from the inflamed intestine (inflamed CM) versus control CM (C-CM). (A–C) Separate experiments testing inflamed CM from each of three animals; Co, untreated control CSMC. (B) Quantification of appearance of mRNA for PDGF-Rβ among CSMC from each of four animals at 6 days in vitro, exposed to CM from Day 2 of TNBS-colitis. Each data point shows average response ±SE Horizontal bar, mean response (P < 0.05 compared to control). (C) qPCR outcome showing that serum-free DMEM containing the pro-inflammatory cytokines interleukin (IL)-1β or tumour necrosis factor (TNF)-α but not transforming growth factor (TGF)-β promoted appearance of mRNA for PDGF-Rβ in freshly isolated CSMC by Day 3 in vitro (*P < 0.05 versus DMEM alone; n = 3). (D) Adult rat serum causes proliferation of freshly isolated adult CSMC via PDGF-Rβ. Cohort cultures were grown in either 2.5% FCS, 2.5% RS or RS with the PDGF-Rβ inhibitor imatinib. Cell proliferation stimulated by RS (≥Day 8; P < 0.05) was completely blocked by imatinib without toxicity.