Abstract 242: p21-Activated Kinase Regulates Vascular Smooth Muscle Migration Leading to Arterial Stenosis
Introduction p21-activated kinases are effectors of Rac and Cdc42 GTPase signaling for a diverse array of cellular functions as both kinases and as non-enzymatic ligands. The role of PAK1 in regulatory vascular smooth muscle cell (VSMC) function is unclear despite involvement in cytoskeletal dynamics critical to vascular homeostasis. We tested the hypothesis that Pak1 controls vascular smooth muscle migration and in vivo response to vascular injury using a murine model of Pak1 ablation (Pak1−/−).
Methods and Results Descending aortas of wild-type or Pak1−/− mice, and VSMCs from cultures of aorta, were isolated for biochemical and migration assays. Pak1 and Pak2 were highly expressed in VSMCs (n=6), the predominant isoform being Pak2. Pak1−/− cells migrated at a rate 40% +/−5% less than WT cells in response to PDGF-beta (n=6). Additionally, we observed a 35% +/− 9% reduction in neointimal hyperplasia in Pak1−/− animals (n=8) following femoral artery ligation compared to WT controls (n=7). To investigate the possible intracellular mechanisms contributing to the protection from injury seen in Pak1−/− animals, we analyzed arterial segments and VSMCs for altered phosphorylation events, and determined that Erk1/2, Mek1/2, MLC20, cofilin, and filamin-A phosphorylation following PDGF stimulation reflected attenuated migratory signaling in Pak1−/− versus WT controls. While we could not verify that Pak1−/− cells had an altered proliferation response to PDGF, we did observe that Pak1−/− smooth muscle cells had altered F-actin bundles.
Conclusions This study sought to determine the role of Pak1 in vessel repair following vascular injury. We found that in a murine Pak1−/− model, neointimal hyperplasia was reduced, which might be partially explained by a commensurate reduction in smooth muscle migration rate in response to PDGF. Likewise, altered intracellular signaling within known migratory pathways might explain the reduced migration rate and commensurate inhibition of legion progression. Considering that specific inhibitors have been recently described that target Pak1 and Pak2, these studies indicate that the Pak signaling axis may prove to be a clinically efficacious therapeutic target.