Differential functional roles of fibroblasts and pericytes in the formation of tissue-engineered microvascular networks in vitro

Aims Formation of a perfusable microvascular network (μVN) is critical for tissue engineering of solid organs. Stromal cells can support endothelial cell (EC) self-assembly into a μVN, but distinct stromal cell populations may play different roles in this process. Here we investigated the effects that two widely used stromal cells populations, fibroblasts (FBs) and pericytes (PCs), have on μVN formation. Methods and results We examined the effects of adding defined stromal cell populations on the self-assembly of ECs derived from human endothelial colony forming cells (ECFCs) into perfusable μVNs in fibrin gels cast within a microfluidics chamber. ECs alone fail to fully assemble a perfusable μVN. Human lung FBs stimulate the formation of EC lined μVNs within microfluidic devices. RNA-seq analysis suggested that FBs produce high levels of hepatocyte growth factor (HGF), and addition of recombinant HGF improved μVN formation within devices. Human placental PCs could not substitute for FBs, but in the presence of FBs, PCs closely associated with ECs, formed a common basement membrane, extended microfilaments intercellularly, and reduced microvessel diameters. Conclusions Different stromal cell types provide different functions in microvessel assembly by ECs. FBs support μVN formation by providing paracrine growth factors whereas PCs directly interact with ECs to modify microvascular morphology. Statement of Contribution Natalia Kosyakova, Derek Kao, William G. Chang were primarily responsible for the conception, design, interpretation of experiments, and drafting of the manuscript. Francesc López-Giráldez carried out analysis of RNA-seq data. Susann Spindler and Gregory Tietjen assisted with microvessel analysis software. Morven Graham and Xinran Liu assisted with the electron microscopy. Kevin J. James and Jee Won Shin assisted with data collection. Jordan Pober assisted with a critical review of manuscript and experimental design.