Introduction: 

Upon cellular injury, intracellular material that locally controls homeostasis and initiates repair processes will be released from damaged cells. Released nucleic acids and RNAs have been shown to be involved in different biochemical pathways.

Objectives: 

The present study was performed to investigate the impact of extracellular ribonucleic acids, especially tRNA, on vasculogenesis of mouse embryonic stem (ES) cells.

Methods and Results: 

tRNA and also whole cell RNA but not DNA dose-dependently stimulated vasculogenesis of ES cells as assessed by PECAM-1 immunohistochemistry and stimulated cell growth as determined by an in vitro wound healing assay. This observation was confirmed by pre-incubation of ES cells with RNase. The phosphorylation level of VEGF-R2 and PI3K proteins was enhanced upon treatment of ES cells with tRNA. Consequently, tRNA-induced vasculogenesis and wound healing was abolished in presence of the VEGF-R2 inhibitor (SU5614) or the PI3K inhibitor (LY294002). Furthermore, tRNA treatment increased protein expression of hypoxia-induced factor-1a (HIF-1a), vascular endothelial growth factor (VEGF) and neuropilin-1 (NRP-1), and elevated reactive oxygen species (ROS) generation as well as mRNA expression of Nox-2and-4isoforms of NADPH oxidase. The tRNA-induced ROS production was inhibited in the presence of free radical scavengers (trolox and N-(2-mercapto-propionyl)-glycine) as well as the NADPH oxidase inhibitors apocynin and VAS2870. Moreover, the stimulation of vasculogenesis as well as enhancement of HIF-1a expression upon tRNA treatment was abolished in the presence of free radical scavengers and NADPH oxidase inhibitors.

Conclusions: 

Our findings indicate that extracellular tRNA treatment enhances vasculogenesis in ES cells via ROS elevation and activation of VEGF-R2 and PI3K.