Comparative study assessing effects of sonic hedgehog and VEGF in a human co-culture model for bone vascularisation strategies.

The morphogen sonic hedgehog (Shh) seems to mediate adult repair processes in bone regeneration and vascularisation. In this study we investigated the effects of Shh on co-cultures consisting of human primary osteoblasts and outgrowth endothelial cells in terms of angiogenic activation and vessel maturation in comparison to the treatment with the commonly used proangiogenic factor, VEGF. Both, stimulation with VEGF or Shh, leads to an increase in the formation of microvessel-like structures compared to untreated controls. In contrast to VEGF, proangiogenic effects by Shh could already be observed after 24 h of treatment. Nevertheless, after 14 days the angiogenic activity of OEC was comparable in VEGF- or Shh-treated co-cultures. Furthermore, Shh and VEGF resulted in different growth factor expression or release profiles. Compared to VEGF, Shh stimulates also the expression and secretion of angiopoietins which was detected as early as 24 h of treatment. Moreover, smooth muscle cell-related markers, such as alpha-smooth muscle actin, desmin and myocardin, as well as basement membrane components were clearly upregulated in response to Shh treatment compared to VEGF- or untreated controls. In terms of growth factors relevant for vessel stabilisation and maturation increased levels of PDGF-BB, angiopoietin-1 and TGF-beta were observed in cell culture supernatants when treated with Shh. This was in accordance with higher levels of smooth muscle actin in Shh-treated samples indicating the potential of Shh to improve the angiogenic activity and vessel stabilisation of human tissue engineered constructs. Experiments using cyclopamine, a Shh pathway inhibitor, blocked the effects of Shh.