Objective-Capillary network formation represents a specialized endothelial cell function and is a prerequisite to establish a continuous vessel lumen. Formation of endothelial cell connections that form the vascular structure is regulated, at least in part, at the transcriptional level. We report here that related transcription enhancer factor-1 (RTEF-1) plays an important role in vascular structure formation. Methods and Results-Knockdown of RTEF-1 by small interfering RNA or blockage of RTEF-1 function by the transcription enhancer activators domain decreased endothelial connections in a Matrigel assay, whereas overexpression of RTEF-1 in endothelial cells resulted in a significant increase in cell connections and aggregation. In a model of oxygen-induced retinopathy, endothelial-specific RTEF-1 overexpressing mice had enhanced angiogenic sprouting and vascular structure remodeling, resulting in the formation of a denser and more highly interconnected superficial capillary plexus. Mechanistic studies revealed that RTEF-1 induced the expression of functional gap junction proteins including connexin 43, connexin 40, and connexin 37. Blocking connexin 43 function inhibited RTEF-1-induced endothelial cell connections and aggregation. We further found that gap junction proteins, specifically connexin (Cx) 37, Cx40, and Cx43, were significantly regulated by RTEF-1 and acted as adhesion sites that enhanced endothelial cellular connections and aggregation, as well as promoted the timely formation of competent vascular networks. We selected a mouse retina model for our in vivo studies because of the retinal vasculature developing shortly after birth in a highly stereotypic manner, 9 and RTEF-1 appeared as an essential gene for retinal vascular development by enhancing angiogenic sprouting and promoting the formation of a denser primary capillary network in an oxygen-induced retinopathy (OIR) model. These observations indicate that RTEF-1 coordinated endothelial cell-to-cell connections and is essential for the assembly of vascular networks in vitro and in vivo.
Materials and Methods
Cell CultureHuman umbilical vein endothelial cells (Lonza, Allendale, NJ) were cultured in endothelial basal medium-2 (Lonza). Human microvascular endothelial cells-1 (HMEC-1, Center for Disease Control and Prevention, Atlanta, GA) were cultured in MCDB-131 (Invitrogen, Carlsbad, CA). HMEC-1 is an immortalized HMEC line that retains the morphological, phenotypic, and functional characteristics of normal HMEC.10 Human embryonic kidney 293 and 293T were cultured in DMEM (Invitrogen).
Retroviral Transduction and Small Interfering RNA TransfectionThe coding sequence of RTEF-1 (NM_003213) was subcloned from a PXJ40/RTEF-1 construct (a gift from Dr Alexandre Stewart, University of Ottawa) into the pBMN-GFP vector (Orbigen, San Diego, CA) to produce pBMN-GFP-RTEF-1. 293T cells were transfected with pBMN-GFP (or pBMN-GFP-RTEF-1), pMD-VSVG, pJK3, and pCMV-tat using Polyethylenimine (Polysciences, Warrington, PA) as previously reported 11 to a packag...