# Tie2‐Dependent Mechanisms Influence Leptomeningeal Collateral Dynamics and Reperfusion Following Stroke

## TL;DR

This study shows that activating Tie2 or removing EphA4 in blood vessels can improve recovery after stroke by enlarging collateral blood vessels.

## Contribution

The study identifies a novel molecular program involving Tie2 and EphA4 that can be targeted to enhance collateral vessel growth after stroke.

## Key findings

- Pharmacological activation of Tie2 or genetic loss of EphA4 increases collateral vessel size and improves recovery after stroke.
- Transcriptomic analysis reveals keratin-related genes are upregulated in meningeal tissue following treatment.
- Endothelial EphA4 limits Tie2 activation and collateral expansion, suggesting a therapeutic target for stroke.

## Abstract

Leptomeningeal collateral vessels help redistribute cerebral blood flow following arterial obstruction, reducing tissue damage. This study investigates the Tie2 receptor peptide agonist Vasculotide in a permanent middle cerebral artery occlusion (pMCAO) model. Vasculotide enhanced early diameter enlargement of pre‐existing pial collaterals, which may be mediated by structural remodeling, as evidenced by endothelial proliferation. These changes correlated with reduced infarct volume, blood‐brain barrier disruption, enhanced blood flow, and functional recovery at 3–28 days post‐pMCAO. Conditional endothelial cell (EC)‐specific EphA4 knockout (KO) mice exhibited increased Tie2 and Ang‐1 expression, mimicking the effects of Vasculotide on collateral size. Simultaneous genetic loss of EC‐specific EphA4 and Tie2 attenuated these outcomes. Nitric oxide inhibition partially blocked collateral enlargement in EC‐KO mice, suggesting the presence of additional contributors. Bulk RNAseq of meningeal tissue revealed upregulation of Krt5, Krt14, and Col17a1 in the ipsilateral meninges of Vasculotide‐treated and EC‐specific EphA4 KO mice. Notably, the number of Krt5‐expressing cells is increased on the leptomeningeal arterial vasculature of KO mice, suggesting a novel contribution to collateral enlargement. The opposing roles of EphA4 and Tie2 in collateral dynamics are demonstrated, and a novel molecular program is identified that can be targeted to enhance their diameter enlargement in ischemic stroke.

This work demonstrates that endothelial EphA4 limits Tie2 activation and curbs leptomeningeal collateral expansion after ischemic stroke. Pharmacological activation of Tie2 by an Ang‐1 mimetic or genetic loss of EphA4 stimulates collateral vessel growth, improves cerebral perfusion, and enhances neurological recovery. Transcriptomic profiling further reveals keratin‐associated remodeling pathways that support vascular adaptation.