Follistatin-like 1, a Secreted Muscle Protein, Promotes Endothelial Cell Function and Revascularization in Ischemic Tissue through a Nitric-oxide Synthase-dependent Mechanism

Myogenic Akt signaling coordinates blood vessel recruitment with normal tissue growth. Here, we investigated the role of Follistatin-like 1 (Fstl1) in the regulation of endothelial cell function and blood vessel growth in muscle. Transgenic Akt1 overexpression in skeletal muscle led to myofiber growth that was coupled to an increase in muscle capillary density. Myogenic Akt signaling or ischemic hind limb surgery led to the induction of Fstl1 in muscle and increased circulating levels of Fstl1. Intramuscular administration of an adenoviral vector expressing Fstl1 (Ad-Fstl1) accelerated flow recovery and increased capillary density in the ischemic hind limbs of wild-type mice, and this was associated with an increase in endothelial nitric oxide synthase (eNOS) phosphorylation at residue Ser-1179. In cultured endothelial cells, Ad-Fstl1 stimulated migration and differentiation into network structures and inhibited apoptosis under conditions of serum deprivation. These cell responses were associated with the activating phosphorylation of Akt and eNOS. Conversely, transduction with dominant-negative Akt or LY294002 blocked Fstl1-stimulated eNOS phosphorylation and inhibited Fstl1-stimulated cellular responses. Treatment with the eNOS inhibitor N-G-nitro-L-arginine methyl ester also reduced endothelial cell migration and differentiation induced by Ad-Fstl1. The stimulatory effect of Ad-Fstl1 on ischemic limb reperfusion was abolished in mice lacking eNOS. These data indicate that Fstl1 is a secreted muscle protein or myokine that can function to promote endothelial cell function and stimulates revascularization in response to ischemic insult through its ability to activate Akt-eNOS signaling.