Prevascularization of self-organizing engineered heart tissue by human umbilical vein endothelial cells abrogates contractile performance.

Establishing vascularization is a critical obstacle to the generation of engineered heart tissue (EHT) of substantial thickness. Addition of endothelial cells to the formative stages of EHT has been demonstrated to result in prevascularization, or the formation of capillary-like structures. The detailed study of the effects of prevascularization on EHT contractile function is lacking. Here, we evaluated the functional impact of prevascularization by human umbilical vein endothelial cells (HUVECs) in self-organizing EHT. EHT fibers were generated by the self-organization of neonatal rat cardiac cells on a fibrin hydrogel scaffold with or without HUVECs. Contractile function was measured and force-length relationship and rate of force production were assessed. Immunofluorescent studies were used to evaluate arrangement and distribution of HUVECs within the EHT fibers. RT-PCR was used to assess the transcript levels of hypoxia inducible factor-1a (Hif-1α). EHT with HUVECs manifested tubule-like structures at the periphery during fiber formation. After fiber formation, HUVECs were heterogeneously located throughout the EHT fiber and human CD31+ tubule-like structures were identified. The expression level of Hif-1α did not change with the addition of HUVECs. However, maximal force and rate of force generation were not improved in HUVECs containing EHT as compared to control EHT fibers. The addition of HUVECs may result in sparse microvascularization of EHT. However, this perceived benefit is overshadowed by a significant decrease in contractile function and highlights the need for perfused vascularization strategies in order to generate EHT that approaches clinically relevant dimensions.