Robust Functional Vascular Network Formation In Vivo by Cooperation of Adipose Progenitor and Endothelial Cells

Abstract

Abstract-Rapid induction and maintenance of blood flow through new vascular networks is essential for successfully treating ischemic tissues and maintaining function of engineered neo-organs. We have previously shown that human endothelial progenitor cells (EPCs) form functioning vessels in mice, but these are limited in number and persistence; and also that human adipose stromal cells (ASCs) are multipotent cells with pericytic properties which can stabilize vascular assembly in vitro.In this study, we tested whether ASCs would cooperate with EPCs to coassemble vessels in in vivo implants. Collagen implants containing EPCs, ASCs, or a 4:1 mixture of both were placed subcutaneously into NOD/SCID mice. After a range of time periods, constructs were explanted and evaluated with regard to vascular network assembly and cell fate; and heterotypic cell interactions were explored by targeted molecular perturbations. The density and complexity of vascular networks formed by the synergistic dual-cell system was many-fold higher than found in implants containing either ASCs or EPCs alone. Coimplantation of ASCs and EPCs with either pancreatic islets or adipocytes produced neoorgans populated by these parenchymal cells, as well as by chimeric human vessels conducting flow. This study is the first to demonstrate prompt and consistent assembly of a vascular network by human ASCs and endothelial cells and vascularization by these cells of parenchymal cells in implants. Mixture of these 2 readily available, nontransformed human cell types provides a practical approach to tissue engineering, therapeutic revascularization, and in vivo studies of human vasculogenesis. A ssembly of new vascular networks for therapeutic purposes has been critical but elusive for tissue engineering and angiogenesis. A general requirement for preserving viability within a regenerating region is that a vascular bed is assembled or expanded sufficiently to ensure adequate tissue perfusion. Also important to success of such applications is the ability of any network to anastomose or inosculate promptly with the vessels of immediately adjacent tissues. Cell-based revascularization therapies were tested in patients with various ischemic diseases. These studies used progenitor cells from bone marrow 1,2 and skeletal muscle 3,4 to treat patients with myocardial infarction, 1,2 heart failure, 3-6 and peripheral vascular disease. 7,8 Despite accumulating data and recent metaanalyses 9,10 that support the hypothesis that progenitor cells have high potential for promoting tissue revascularization and functional recovery, invasive methods of cells harvest and their low abundance may limit adoption some of progenitor cells for therapies. Recent approaches were focused on evaluating cells derived from more available tissues including adipose tissue 11,12 and umbilical cord blood. 13,14 Endothelial progenitor cells (EPCs) isolated from adult peripheral blood, 15 bone marrow, umbilical cord blood, 13 and vessel wall 16 were intensively studied over the past decade. ...

Hydrogel-based microfluidics for vascular tissue engineering

“…This phenomenon was associated with an increased expression of ECM proteins such as laminin, collagen IV, as well as cellular αSMA [2,4]. In our study, we applied a 1:4 co-culture ratio of hASCs to HUVECs for encapsulation into PEGylated fibrin hydrogel constructs and confirmed that the considerable expression of collagen IV, laminin and αSMA is dependent on co-culture of hASCs and HUVECs within the PEGylated fibrin gel (Figure 2).…”

“…There are two explicit mechanisms of blood vessel growth: vasculogenesis, the de novo formation of blood vessels by endothelial progenitor cells, and angiogenesis, the sprouting of new vessels from preexisting ones. For engineering of microvasculature within a 3-D cell laden biomaterial construct, many biological extracellular matrix (ECM) materials and cell co-cultures have been studied with respect to their vasculogenic potential [1][2][3][4]. Mimicking the embryonic environment for vasculogenesis is a popular strategy; for example, experiments on encapsulation of vascular progenitor cells within 3-D biological ECM have been undertaken, in which angioblasts and mesenchymal stem cells self-organize into a microvascular network and form a capillary bed [5].…”

“…Human umbilical vein endothelial cells (HUVECs) were used as vascular precursor cells and human adipose derived stem cells (hASCs) were used as stromal cells to support HUVEC morphogenesis via secretion of pro-angiogenic growth factors [2,4]. It is hypothesized (a) that a cell friendly environment will support in vitro vasculogenesis that is induced by the interaction of HUVECs and hASCs, and (b) that PEGylated fibrin gel can be a strong candidate material for cell encapsulation and hydrogel based microfluidic device fabrication.…”

Placental Mesenchymal Stromal Cells Derived from Blood Vessels or Avascular Tissues: What Is the Better Choice to Support Endothelial Cell Function?

“…In the Matrigel assay, both cell types were able to adhere to and support endothelial network formation without differentiation into ECs as documented by absent expression of the endothelial marker vWf. Thus, even though MSCs do not seem to be able to take over the functional role of ECs, several studies have shown that the coapplication of MSCs with endothelial or endothelial progenitor cells is required for the formation of stable, functional vessels in vivo [48,[62][63][64]. MeleroMartin et al and Au et al demonstrated a perivascular location of MSCs in the newly formed vessels, suggesting that MSCs act as pericytes [48,62].…”

Human endothelial colony-forming cells serve as trophic mediators for mesenchymal stem cell engraftment via paracrine signaling

“…Studies have also demonstrated that human blood-derived ECFCs have inherent and robust vasculogenic properties. Following transplantation into immunodeficient mice, ECFCs can self-assemble into long-lasting microvascular networks that anastomose with the host vasculature (5,6). The function of ECFC-lined microvessels has been shown to be similar to that of normal microvessels in several respects, including nonthrombogenicity, blood flow, regulation of macromolecule permeability, and capacity to induce leukocyte-endothelial interactions in response to cytokine activation (5,7).…”