Background: Resistance exercise has beneficial effects for patients with peripheral arterial diseases. The hypothesis that muscle growth promotes angiogenesis by interacting with neighboring cells in ischemic lesions was assessed.
Methods and results: Skeletal muscle-specific inducible Akt1 transgenic (Akt1-TG) mice that induce growth of functional skeletal muscles as a model of resistance training were used. Proteomics analysis identified significant upregulation of heme oxigenase-1 (HO-1) in muscle tissue in Akt1-TG mice compared with control mice. Blood flow recovery after hindlimb ischemia was significantly increased in Akt1-TG mice compared with control mice. Enhanced blood flow and capillary density in Akt1-TG mice were completely abolished by the HO-1 inhibitor, Tin-mesoporphyrin. Immunohistochemistry showed that HO-1 expression was not increased in muscle cells, but it was increased in macrophages and endothelial cells. Consistent with these findings, blood flow recovery after hindlimb ischemia was similar between control mice and skeletal muscle-specific HO-1-knockout mice. Adenoviral-mediated overexpression of Akt1 did not increase HO-1 protein expression in C2C12 myotubes; however, the conditioned medium from Akt1-overexpressing C2C12 myotubes increased HO-1 expression in endothelial cells. Cytokine array demonstrated that a panel of cytokine secretion was upregulated in Akt1-overexpressing C2C12 cells, suggesting paracrine interaction between muscle cells and endothelial cells and macrophages.
Conclusions: Akt1-mediated muscle growth improves blood flow recovery after hindlimb ischemia by enhancing HO-1 expression in neighboring cells.
Keywords: Angiogenesis; Heme oxygenase-1; Muscle growth.