Another important aspect within the angiogenic cascade is

Another important aspect within the angiogenic cascade is endothelial migration. Since the PD 0332991 analysis demonstrated that DSCs and HGF-1 express multiple factors which are known to affect migration, such as ANGPT1, EDN1, IGFBP3, uPA and VEGF, a transwell migration assay was carried out to assess their chemotactic potential. Following 24h of incubation, DPSCs, SCAPs and HGF-1 significantly increased endothelial transmigration, while FSCs had no substantial impact. Given the high secretion of IGFBP3 by FSCs, the lack of a pronounced migration-stimulating effect was rather unexpected. However, the aforementioned dual role of IGFBP3 taken together with the lower secretion of VEGF and ANGPT1 probably established suboptimal conditions for endothelial migration. HGF-1 on the other hand, display a secretion profile similar to FSCs in terms of VEGF, IGFBP3 and ANGPT1 and do significantly enhance endothelial migration. This discrepancy can be explained by the potential contribution of other (yet to be identified) angiogenic factors which influence endothelial migration. With regard to the chemotactic properties of BMSCs, similar observations were made by Potapova et al. and others, who mentioned a significant increase in HUVEC transmigration caused by stromal cell-conditioned medium (Gruber et al., 2005; Potapova et al., 2007). In terms of tubulogenesis, functional assays showed a pronounced effect of DPSCs on endothelial tube formation, an outcome which also differed significantly from SCAPs and HGF-1. Earlier studies of Tran-Hung et al. and others, reported a similar increase and stabilization of endothelial tubular structures following direct co-culture of HUVECs and DPSCs, indicating a more pericyte-like behavior of DPSCs (Dissanayaka et al., 2012; Janebodin et al., 2013; Tran-Hung et al., 2006). Human and murine BMSCs on the other hand, are also capable of promoting endothelial tube formation, as was shown by a number of studies (Estrada et al., 2009; Lin et al., 2012; Sorrell et al., 2009; Wu et al., 2007). Since ANGPT1 and VEGF play an important role in the induction of tubulogenesis, the aforementioned increase can probably be explained by the angiogenic secretion profile of the different cell populations as DPSCs displayed a notably higher VEGF secretion compared to SCAPs, FSCs and HGF-1. In the last part of this study, a CAM assay was conducted in order to determine the angiogenic properties of DSCs in an in vivo setting. According to earlier reports of Laschke et al., the CAM assay is an ideal model to study vascular development due to its capability to support the ingrowth of blood vessels and its lack of a complete immune system which allows for the assessment of xenografts without rejection (Laschke et al., 2006). Following incubation with DSCs as well as HGF-1, a characteristic spoke wheel pattern could be distinguished caused by the radial ingrowth of blood vessels (Baiguera et al., 2012). In particular DPSCs and SCAPs significantly enhanced neoangiogenesis. In comparison, BMSCs were also found to promote blood vessel ingrowth in a CAM assay, notwithstanding the altered model the authors applied (Gruber et al., 2005; Oskowitz et al., 2011). Despite the expression of several angiogenesis-inhibiting factors such as TIMP, PAI-1, THBS1 and PTX3, these data collectively suggest a predominant pro-angiogenic impact of DSCs, and in particular DPSCs and SCAPs, in vitro and in vivo.
Conclusion This study was the first to describe the angiogenic properties of SCAPs and FSCs in an in vitro and in vivo setting. Furthermore, it compares three different dental stem cell populations, namely DPSCs, SCAPs and FSCs, together with a HGF-1 cell line with regard to their angiogenic expression profile and impact on endothelial cell behavior in vitro and in vivo. DSCs seemed to have a predominant pro-angiogenic impact on endothelial migration and tube formation, in vitro as well as in an in vivo set-up. Our results suggest a stronger angiogenic profile and function of DPSCs and SCAPs in comparison to FSCs and HGF-1, encouraging further investigation of both of these stem cell populations as potential therapeutic tools. The dental field can significantly benefit from the angiogenic properties of DSCs, in particular in pulp regeneration and whole tooth engineering, as vascular supply is an important burden to overcome in these applications.