MSX1 regulates flow-induced outward collateral remodeling. (A) Upon tamoxifen treatment, Cdh5-CreERT2;Msx1^fl/fl:Msx2^fl/fl mice were subjected to unilateral femoral artery ligation. Relative flow values were determined by high-resolution PET imaging. Blood flow was quantified as a ratio in the ligated versus the unligated leg, represented as a percentage for n = 4 Cdh5-Cre−;Msx1^fl/fl:Msx2^fl/fl and n = 3 Cdh5-Cre+;Msx1^fl/fl:Msx2^fl/fl littermates. *, P < 0.05. (B) Representative PET images of perfusion recovery upon femoral artery ligation in Cdh5-Cre− and Cdh5-Cre+ Msx1^fl/fl:Msx2^fl/fl littermates. (C) Representative micro-CT angiograms of the adductors for both the ligated and unligated hind limbs of Cdh5-Cre−;Msx1^fl/fl:Msx2^fl/fl (top) and Cdh5-Cre+;Msx1^fl/fl:Msx2^fl/fl mice (bottom) 7 d after unilateral femoral artery ligation. The arrowheads indicate collateral arteries. (D) Quantification of the amount of blood vessels per size in the micro-CT acquisition of the adductor region 7 d after ligation, represented as the ratio in the ligated versus the unligated adductor. n = 4 Cdh5-Cre−;Msx1^fl/fl:Msx2^fl/fl and n = 4 Cdh5-Cre+;Msx1^fl/fl:Msx2^fl/fl mice. #, P = 0.076; *, P < 0.05 versus Cdh5-Cre−;Msx1^fl/fl:Msx2^fl/fl mice. The solid line indicates the 1 ratio, which correlates with no remodeling. Error bars represent the SEM. Bars: (B) 3 mm; (C) 800 µm.