Activation of p38MAPK signaling cascade in a VSMC injury model: role of p38MAPK inhibitors in limiting VSMC proliferation.

INTRODUCTION: P38 mitogen-activated protein kinase (MAPK) has a crucial role in regulating signaling pathways implicated in the cellular events leading to restenosis. We examine p38MAPK activation in response to vascular cell injury, its biological effects and determine whether selective p38MAPK inhibitors, SB220025/SB203580, decrease vascular smooth muscle cell (VSMC) proliferation.
METHODS: Human aortic VSMCs were cultured and wounds made on the monolayers to elicit mitogenic responses and induce p38MAPK activation. P38MAPK inhibitor pretreatment, at varying doses (1-100 microM) and treatment duration was used to block p38MAPK phosphorylation. Cytotoxicity, viability, proliferation and apoptosis were determined and expression of p38MAPK/phospho-p38MAPK was obtained by chemiluminiscent immunoblot analysis.
RESULTS: Phosphorylation of p38MAPK depended on injury severity and was inhibited by both p38MAPK inhibitors, but not by SB202474, a specific antagonist of p38MAPK inhibitors. VSMCs treated with p38MAPK inhibitors showed a dose-dependent decrease in viable cell number, apoptosis and proliferation, reversing the deleterious effects of p38MAPK activation comparable to controls (p < 0.05).
CONCLUSIONS: This wound injury model activates the p38MAPK-signaling cascade in VSMC and causes cell proliferation that can be abrogated by pre-incubation with p38MAPK selective synthetic inhibitors in a time and dose-dependent manner. SB220025 used here for the first time in VSMC reveals itself to be a stronger p38MAPK inhibitor than SB203580 and being a second generation inhibitor may be the preferred drug for novel therapeutic maneuvers.