Controlling physiological angiogenesis by hypoxia-induced signaling.

The full sequence of signals leading to new blood vessel formation is a physiological response to tissue hypoxia through upregulation of angiogenic factor cascades. Controlled initiation of this mechanism for therapeutic/engineered angiogenesis must rely on precisely localized hypoxia. Here we have designed a 3D in vitro model able to test the effect and predictability of spatially positioned local hypoxic stimuli using defined cell depots within a 3D collagen matrix. Cell-mediated hypoxia was engineered using human dermal fibroblasts (HDFs), to generate a local population of Hypoxia-Induced Signaling (HIS) cells. HIS cell depots released angiogenic factors which induced directional endothelial cell (EC) migration and tubule formation in a spatially defined assay system. Non-hypoxic baseline control cultures induced minimal EC migration with little tubule formation. Furthermore, depots of HIS cells, positioned in the core of 3D collagen constructs directed host vessel in-growth deep into the implant by 1 week, which was at least 7 days earlier than in non-hypoxia pre-conditioned constructs. The functionality of in vivo vascularisation was verified by real-time monitoring of O2 levels in the core of implanted constructs. These findings establish the angiogenic potential of HIS cells applicable to in vitro tissue modeling, implant vascularization and engineering predictable angiogenic therapies.