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

Formation of a perfusable microvascular network (mu VN) is critical for tissue engineering of solid organs. Stromal cells can support endothelial cell (EC) self-assembly into a mu VN, but distinct stromal cell populations may play different roles in this process. Here we describe the differential effects that two widely used stromal cell populations, fibroblasts (FBs) and pericytes (PCs), have on mu VN formation. 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 mu VNs in fibrin gels cast within a microfluidic chamber. ECs alone failed to fully assemble a perfusable mu VN. Human lung FBs stimulated the formation of EC-lined mu VNs within microfluidic devices. RNA-seq analysis suggested that FBs produce high levels of hepatocyte growth factor (HGF). Addition of recombinant HGF improved while the c-MET inhibitor, Capmatinib (INCB28060), reduced mu VN 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. Different stromal cell types provide different functions in microvessel assembly by ECs. FBs support mu VN formation by providing paracrine growth factors whereas PCs directly interact with ECs to modify microvascular morphology.