Abstract 648: Reduced Expression of Phosphoprotein Enriched in Astrocytes-15 (PEA-15) Increases Neointimal Hyperplasia

Neointimal hyperplasia from increased vascular smooth muscle cell (VSMC) proliferation remains a significant clinical problem. Phosphoprotein enriched in astrocytes-15 (PEA-15) is an extracellular signal-regulated kinases 1/2 (ERK1/2) binding protein. We have previously demonstrated in vitro that PEA-15 acts as a cytoplasmic “anchor” in VSMCs and prevents ERK1/2 translocation to the nucleus, decreasing proliferation. We now assess the hypothesis that expression of PEA-15 regulates the development of neointimal hyperplasia. Arterial injury was induced by wire denudation with ligation of the carotid artery in C57BL/6 mice and examined 3, 7 and 14 days after surgery. Neointima formation was significantly increased in injured arteries from day 7 compared to control arteries. PEA-15 protein expression was significantly decreased in injured arteries in comparison to control vessels 3 days after arterial injury (ratio to GAPDH - 0.29±0.10 vs. 0.91±0.1, n=3), preceding significant neointima formation at day 7. A similar decrease in PEA-15 protein and mRNA levels was observed in human saphenous vein rings incubated ex vivo in 30% serum for 14 days to induce neointimal hyperplasia (protein ratio to GAPDH - 0.36±0.05 vs. freshly isolated veins 1.34±0.20, n=5). This coincided with increases in proliferative markers. To determine a causal relationship between decreased PEA-15 expression and neointimal formation, we induced arterial injury in mice deficient in PEA-15 (PEA-15-/-). There was a significantly exaggerated neointima formation in PEA-15-/- mice 7 days after surgery compared to C57BL/6 mice at the same time point (intima-to-media ratio - 0.95±0.26 vs. 0.35±0.09, n=3-5). The mechanisms involved were investigated. Immunolocalization of ERK1/2 was assessed in primary cultured VSMCs isolated from aortae of C57BL/6 and PEA-15-/- mice. In unstimulated VSMCs from PEA-15-/- mice, there was a significant increase in nuclear staining of ERK1/2 compared with cells from C57BL/6 mice. In conclusion, decreased PEA-15 expression occurs in VSMCs during the development of neointima hyperplasia which may increase proliferation. Targeting this pathway could be beneficial in the treatment of restenosis.