Thymosin ß4 promotes endothelial progenitor cell angiogenesis via a vascular endothelial growth factor-dependent mechanism

Abstract

Endothelial progenitor cells (EPCs) are a promising cell source for tissue repair and regeneration, predominantly through angiogenesis promotion. Paracrine functions serve a pivotal role in EPC-mediated angiogenesis, which may be impaired by various cardiovascular risk factors. Therefore, it is important to identify a solution that optimizes the paracrine function of EPCs. Thymosin ß4 (Tß4) is a peptide with the potential to promote tissue regeneration and wound healing. A previous study demonstrated that Tß4 enhances the EPC-mediated angiogenesis of the ischemic myocardium. In the present study, whether Tß4 improved angiogenesis by enhancingtheparacrineeffectsofEPCswasinvestigated.Atube formation assay was used to assess the effect of angiogenesis, and the paracrine effects were measured using an ELISA kit. The results indicated that Tß4 improved the paracrine effects of EPCs, evidenced by an increase in the expression of vascular endothelial growth factor (VEGF). EPC-conditioned medium (EPC-CM) significantly promoted human umbilical vein endothelial cell angiogenesis in vitro, which was further enhanced by pretreatment with Tß4. The effect of Tß4 pretreated EPC-CM on angiogenesis was abolished by VEGF neutralizing antibody in vitro, indicating that increased VEGF secretion had a pivotal role in Tß4-mediated EPC angiogenesis. Furthermore, transplantation of EPCs pretreated with Tß4 into infarcted rat hearts resulted in significantly higher VEGF expression in the border zone, compared with EPC transplantation alone. To further investigate whether the Akt/eNOS pathway was involved in Tß4-induced VEGF secretion in EPCs, the expression levels of VEGF in EPC-CM were significantly decreased following knockdown of Akt or eNOS by small interfering RNA transfection. In conclusion, Tß4 significantly increased angiogenesis by enhancing the paracrine effects of EPCs, evidenced by the increased expression of VEGF. The RAC-a serine/threonine-protein kinase/endothelial nitric oxide synthase signal transduction pathway was involved in the regulation of Tß4-induced VEGF secretion in EPCs. Further studies are required to investigate the long-term prognosis of patients with coronary heart disease following Tß4-pretreated EPC transplantation.