Abstract 166: Loss Of Endothelial Cell Specific EphA4 Improves Acute Leptomeningeal Collateral Growth Following Ischemic Stroke

Leptomeningeal anastomoses, or pial collateral vessels, are a major determinant of patient outcome following ischemic stroke. These vessels form in the pia mater of the brain during development and connect distal arterioles of cerebral arteries. Following vascular obstruction, pial collaterals expand through arteriogenesis, an adaptive process that allows for retrograde perfusion into the obstructed artery and its affected tissue. However, acute arteriogenesis following ischemic stroke has been poorly investigated, therefore our research aims to fill this knowledge gap. Our novel pre-clinical murine findings suggest EphA4, a receptor tyrosine kinase, plays a role in restricting arteriogenesis following permanent middle cerebral artery occlusion (pMCAO). To investigate the role of endothelial cell-specific EphA4 in acute arteriogenesis, we employed 3-month old conditional endothelial cell (EC)-specific EphA4 knockout ( EphA4 fl/fl /Cdh5::Cre ERT2 ; KO) and wild type ( EphA4 fl/fl ; WT) mice. Compared to WT controls, we find KO mice displayed a significant reduction in infarct volume (24.0±1.8mm 3 vs 14.3±2.5mm 3 ; n=9) which correlated with larger ipsilateral pial collateral vessels as early as 4.5-hours (27.31±0.6um vs 32.41±0.8um; n=15) and up to 24-hours post-pMCAO (31.14±0.8um vs 36.7±0.9um; n=15). Additionally, our previous work has indicated that EphA4 may exert its inhibitory function on arteriogenesis by hindering Tie2 signaling. To identify gene expression changes in the collateral vessels and connecting cerebral arteries, the pial surface was carefully isolated from four mice per sample and pooled. Analysis of mRNA expression in the pial surface 24-hours post-pMCAO revealed that WT mice had significantly higher fold change of angiopoietin-2 (1.4±0.2 vs 0.8± 0.09; n=5) and Tie1 (5.3±1.8 vs 0.9±0.2; n=5) compared to KO mice, indicating potential inhibition of Tie2 signaling. These findings demonstrate that EC-specific EphA4 negatively regulates collateral growth and inhibition of this receptor could serve as a novel therapeutic strategy for improving collateral response following ischemic stroke.