Abstract 131: Mitogen-Activated Protein Kinase Kinase Activation is Necessary for Macrophage Accumulation, Compensatory Growth of Blood Vessels and Muscle Regeneration Following Femoral Artery Ligation

Lower limb peripheral vascular disease (PVD) results from the occlusion of arteries leading to reduced blood flow and limb ischemia. Compensatory growth of blood vessels may be sufficient to overcome limb ischemia but for some patients therapeutic intervention, even limb amputation, is required. To gain insight into the mechanisms regulating compensatory growth of blood vessels we used a mouse model of hindlimb ischemia. The ischemic lesions were confirmed and compensatory arteriogenesis was evaluated by high frequency power Doppler ultrasound. In this model, compensatory growth occurs mainly through arteriogenesis. While signaling by mitogen activated protein kinase kinases 1 and 2 (MEK 1 and 2) is required for developmental and tumor angiogenesis, it is unknown whether MEK1/2 activity drives other physiologic vascular growth such as arteriogenesis. We hypothesized that MEK 1/2 activity is necessary for hindlimb re-vascularization following femoral artery ligation. To test this we ligated the femoral artery in mice and then treated them with PD0325901, an allosteric MEK1/2 inhibitor. Following femoral artery ligation active MEK signaling was detected in spindle-shaped cells located within regions of intense angiogenesis and myocyte proliferation. MEK inhibition with PD0325901 reversibly blocked neovascularization, muscle regeneration, and caused extensive coagulative necropathy. MEK inhibition not only prevented arteriogenesis in ischemic limbs but also caused a reduction in arterial diameter. Finally, MEK inhibition prevented accumulation of CD68+ cells in ischemic tissues and skewed systemic cytokine expression towards a persistent, pro-inflammatory phenotype. Our investigation provides pharmacologic evidence demonstrating an essential role for MEK signaling in angiogenesis and arteriogenesis in response to hind limb ischemia. Further, we observed activation of MEK signaling is required for accumulation of macrophages in ischemic tissues and prevents down-regulation of systemic pro-inflammatory cytokines. Lastly, since the effects of MEK inhibition on reperfusion are reversible, we can use MEK inhibitors to create a mouse model of chronic limb ischemia that mimics aspects of PVD.