Proliferation of vascular smooth muscle cells occurs during blood vessel development and neointimal formation. This is regulated by activation of proliferative signalling pathways involving transcription factors, such as nuclear factor-κB (NF-κB) and cAMP response element-binding protein (CREB), as well as the mitogen-activated protein kinases, extracellular signal-regulated kinase1/2 (ERK1/2). The activation of these pathways by growth factors, such as PDGF, in developing compared with fully developed vascular smooth muscle has not been investigated. The aim of this study was to examine the PDGF-induced activation of NF-κB, CREB and ERK1/2 in neonatal rat portal vein (PV), previously characterised as a developing smooth muscle phenotype (Tasker et al. 1999). Freshly isolated PVs from 2- to 4-day-old and 6-week-old Sprague-Dawley rats killed by cervical dislocation were stimulated with PDGF-BB for 0, 15, 30 and 60 min. Tissues were immediately homogenised, proteins separated using SDS polyacryalamide gel electrophoresis and subjected to immunoblotting with specific antibodies. Freshly isolated PV strips were also used for contraction studies using a force transducer.

CREB activation (as measured by phosphorylation of CREB) peaked at 30 min after stimulation with PDGF-BB (50 ng ml^-1) (increased 280 % compared with unstimulated control, n = 4) in the neonatal PV and decreased to control levels by 60 min. PV from adult rats was activated by PDGF-BB to a lesser extent and peaked much earlier (increased 170 % by 15 min, n = 4). In contrast, PDGF-induced NF-κB activation (as measured by degradation of inhibitory factor-κBα (I-κBα)) revealed a different time course in developing, compared with fully developed, PV. NF-κB was maximally activated at 30 min (30 % decrease in I-κBα, n = 3), whereas neonatal PV did not induce NF-κB activation at any time points examined (n = 3). ERK1/2 were maximally activated by PDGF-BB after 15 min in both the neonate and adult PV; however, activation was sustained at 60 min in the adult, whereas it returned to control levels in the neonate. PDGF-BB-induced contractility was significantly greater in adult PV strips compared with neonate (32.3 ± 9.1 % compared with 1.3 ± 0.3 %, respectively, of maximal K⁺ response, n = 5, mean ± S.E.M., P < 0.05, Student’s unpaired t test).

In conclusion, these findings suggest a diverse role for activation of transcription factors and ERK1/2 in developing vascular smooth muscle compared with fully developed smooth muscle. This may have an important role in the regulation of proliferation.

This study was supported by the British Heart Foundation.

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