Cardiac-specific activation of signal transducer and activator of transcription 3 promotes vascular formation in the heart.

Signal transducer and activator of transcription 3 (STAT3) functions in cell proliferation, differentiation, and cell survival. Previously, we have demonstrated that the activation of STAT3 is required for glycoprotein 130-mediated induction of VEGF in cardiac myocytes, but the functional importance of STAT3 as an angiogenic mediator remains to be determined. To address this issue, we first generated the adenoviral vector expressing constitutively active STAT3 (caSTAT3). Adenoviral gene transfer of caSTAT3 induced an increase in the expression of VEGF in cultured cardiomyocytes. The conditioned medium from caSTAT3-transfected cardiomyocyte culture promoted endothelial tubule formation, which was inhibited by anti-VEGF antibody. Next, we generated the transgenic (TG) mice with cardiac-specific overexpression of caSTAT3 and demonstrated that caSTAT3 TG mice showed evidence of VEGF induction in the hearts. The caSTAT3 TG hearts also demonstrated increased capillary density accompanied by an increase in the expression of VE-cadherin, an endothelial-specific component. These data indicate that caSTAT3 TG hearts exhibit an enriched vascular structure compared with non-transgenic hearts. The study presented here provides the first evidence that activation of STAT3 controls vessel growth in vivo and suggests that STAT3 contributes to cardiac adaptation by regulating vascular function under the conditions of stress.