Unraveling the Role of EphA4 in Immune-Mediated Arteriogenesis After Ischemic Stroke

Stroke, a life-threatening condition, primarily resulting from ischemic events often caused by occlusion of the middle cerebral artery (MCA). Pre-existing leptomeningeal collateral (LMC) vessels connect MCA branches to anterior or posterior arteries, situated along the brain's cortical surface or meninges, under healthy conditions these vessels remain dormant due to their small diameters and relatively low flow velocity. LMCs serve as vascular redundancies that retrogradely re-supply blood to help salvage the penumbra following cerebral vascular occlusion. Their outward growth or remodeling (arteriogenesis) is essential for promoting cerebral reperfusion and preventing tissue damage after ischemic stroke. Increased fluid shear stress on collateral vessel wall activates arteriogenesis result in the activation of the endothelium and subsequent recruitment of peripheral-derived immune cells (PDICs), which have been shown to aid this unique adaptive process in other organ systems, however their role and mechanism(s) involved in LMC remodeling in stroke has not previously been evaluated. Initial findings suggest the EphA4, a well-established axonal growth and guidance receptors, plays a novel role in LMC arteriogenesis. This dissertation examined PDIC-specific functions of EphA4 using GFP labeled bone marrow chimeric mice subjected to permanent middle cerebral artery occlusion (pMCAO). We assessed immune cell population changes, infarct volume, functional recovery, characterized subtypes of infiltrated immune cell, and measured collateral vessel diameters. Additionally, we explored the Tie2-mediated PI3K signaling pathway in peripheral-derived monocyte/macrophages (PDM) treated with soluble Tie2-Fc and a PI3K p110α inhibitor. The results from this dissertation show that loss of PDIC-specific EphA4 led to increased collateral remodeling, associated with decreased infarct volume, improved cerebral blood flow, and functional recovery within 24 hours post-pMCAO. The crosstalk between EphA4-Tie2 signaling in PDMs, regulated through PI3K/Akt axis, inhibited pial collateral remodeling. In conclusion, our findings highlight the negative regulatory role of PDM-specific EphA4 in collateral growth and remodeling by inhibiting Tie2 function via the PI3K regulated pathway. Peripheral myeloid-derived EphA4 emerges as a new regulator of cerebral vascular injury and neuroinflammation following acute ischemic stroke.