Collateral remodeling is critical for blood flow restoration in peripheral arterial disease and is triggered by increasing fluid shear stress in preexisting collateral arteries. So far, no arterial-specific mediators of this mechanotransduction response have been identified. We show that muscle segment homeobox 1 (MSX1) acts exclusively in collateral arterial endothelium to transduce the extrinsic shear stimulus into an arteriogenic remodeling response. MSX1 was specifically up-regulated in remodeling collateral arteries. MSX1 induction in collateral endothelial cells (ECs) was shear stress driven and downstream of canonical bone morphogenetic protein-SMAD signaling. Flow recovery and collateral remodeling were significantly blunted in EC-specific Msx1/2 knockout mice. Mechanistically, MSX1 linked the arterial shear stimulus to arteriogenic remodeling by activating the endothelial but not medial layer to a proinflammatory state because EC but not smooth muscle cellMsx1/2 knockout mice had reduced leukocyte recruitment to remodeling collateral arteries. This reduced leukocyte infiltration in EC Msx1/2 knockout mice originated from decreased levels of intercellular adhesion molecule 1 (ICAM1)/vascular cell adhesion molecule 1 (VCAM1), whose expression was also in vitro driven by promoter binding of MSX1.