Using Del-1 to Tip the Angiogenic Balance in Endothelial Cells in Modular Constructs

Abstract

Modular tissue engineering is a method of building vascularized tissue-engineered constructs. Submillimeter-sized collagen pieces (modules) coated with a layer of endothelial cells (EC; vascular component), and with embedded functional cells, are self-assembled into a larger, three-dimensional tissue. In this study, we examined the use of developmental endothelial locus-1 (Del-1), an extracellular matrix protein with proangiogenic properties, as a means of tipping the angiogenic balance in human umbilical vein endothelial cells incorporated in modular tissue-engineered constructs. The motivation was to enhance the vascularization of these constructs upon transplantation in vivo, in this case, without the use of exogenous mesenchymal stromal cells. EC were transduced using a lentiviral construct to overexpress Del-1. The Del-1 EC formed more sprouts in a fibrin gel sprouting assay in vitro compared with eGFP (control) transduced EC, as expected. Del-1 EC had a distinct profile of gene expression (upregulation of matrix metalloproteinase-9 [MMP-9], urokinase-type plasminogen activator [uPA/PLAU], vascular endothelial growth factor [VEGF-A], and intercellular adhesion molecule-1 [ICAM-1]; downregulation of angiopoietin-2 [Ang2]), also supporting the notion of "tipping the angiogenic balance". On the other hand, contrary to our expectations, when Del-1 EC-coated modules were implanted subcutaneously in a severe combined immunodeficient/beige animal model, the proangiogenic effect of Del-1 was less remarkable. There was only a small increase in the number of blood vessels formed in Del-1 implants compared with the eGFP implants, and only few blood vessels formed at the implant site in both cases. This was presumed due to limited EC survival after transplantation. We speculate that if we could improve EC survival in our study (for example, by adding other prosurvival factors or supporting cells), we would see a greater Del-1-induced angiogenic benefit in vivo as a consequence of increased Del-1 secretion by a higher number of surviving cells.

Crosstalk between bone marrow-derived mesenchymal stem cells and regulatory T cells through a glucocorticoid-induced leucine zipper/developmental endothelial locus-1-dependent mechanism

“…5). Further, in their studies, Ciucurel et al (33,34) showed that Del-1 has a bimodal effect on inflammatory cell recruitment, depending on the biologic context. Consistent with their conclusion, our data suggest that Del-1 acts as an immunomodulator by launching the balance between inflammatory responses and immune-regulatory mechanisms to re-establish and maintain the homeostatic mode of the microenvironment of the tissues.…”

Vasculogenesis and angiogenesis in modular collagen–fibrin microtissues

“…In particular, the proteins collagen Type I and fibrin have been used widely in regenerative medicine because of their abundance, versatility, and biological relevance (recently reviewed in [44] and [45]. The modular approach has been adapted to create collagen-based modules [46, 47], including for promoting vascularization [48, 49]. However, fibrin has been shown to generally be a more permissive matrix for vessel formation, and is commonly used in studies of both vasculogenesis and angiogenesis [50].…”

Del-1 Overexpression in Endothelial Cells Increases Vascular Density in Tissue-Engineered Implants Containing Endothelial Cells and Adipose-Derived Mesenchymal Stromal Cells

“…O ne of the key issues in tissue engineering is the lack of an internal vascular network and the need for a rapid connection to the host vasculature upon transplantation of tissue-engineered constructs. Here, we approach this issue using a combination of strategies: (1) a modular strategy to build endothelialized tissue constructs 1,2 ; (2) Developmental endothelial locus-1 (Del-1), an angiogenic extracellular matrix (ECM) matricellular protein, as a means of tipping the angiogenic balance in the transplanted ECs from quiescent to proangiogenic 3 ; and (3) adipose-derived mesenchymal stromal cells (adMSCs) as vascular support cells to aid the survival of endothelial cells (ECs) upon transplantation and to stabilize the newly formed blood vessels perhaps by adopting a pericyte role. 4,5 The modular approach consists in fabricating small tissue constructs (''modules''), and packing the modules together to form a larger tissue.…”

“…In a previous study, we transduced ECs to overexpress Del-1 using a lentiviral system, and we showed that the ECs overexpressing Del-1 formed more sprouts in vitro, and differentially expressed a number of genes known to be involved in angiogenesis. 3 However, the number of blood vessels formed in vivo was still limited, in a severe combined immunodeficient/beige (SCID/Bg), subcutaneous implant model, presumably due to extensive loss of ECs through apoptosis after implantation. In a different study using the same animal model and the modular approach (without Del-1), adMSCs embedded inside the modules prevented apoptosis of ECs.…”