Vascular Morphogenesis of Adipose-Derived Stem Cells is Mediated by Heterotypic Cell-Cell Interactions

Abstract

Adipose-derived stromal/stem cells (ASCs) are a promising cell source for vascular-based approaches to clinical therapeutics, as they have been shown to give rise to both endothelial and perivascular cells. While it is well known that ASCs can present a heterogeneous phenotypic profile, spontaneous interactions among these subpopulations that result in the formation of complex tissue structures have not been rigorously demonstrated. Our study reports the novel finding that ASCs grown in monolayers in the presence of angiogenic cues are capable of self-assembling into complex, three-dimensional vascular structures. This phenomenon is only apparent when the ASCs are seeded at a high density (20,000 cells/cm(2)) and occur through orchestrated interactions among three distinct subpopulations: CD31-positive cells (CD31+), α-smooth muscle actin-positive cells (αSMA+), and cells that are unstained for both these markers (CD31-/αSMA-). Investigations into the kinetics of the process revealed that endothelial vessel-like structures initially arose from individual CD31+ cells through proliferation and their interactions with CD31-/αSMA- cells. During this period, αSMA+ cells proliferated and appeared to migrate toward the vessel structures, eventually engaging in cell-cell contact with them after 1 week. By 2 weeks, the lumen-containing CD31+ vessels grew greater than a millimeter in length, were lined with vascular basement membrane proteins, and were encased within a dense, three-dimensional cluster of αSMA+ and CD31-/αSMA- cells. The recruitment of αSMA+ cells was largely due to platelet-derived growth factor (PDGF) signaling, as the inhibition of PDGF receptors substantially reduced αSMA+ cell growth and vessel coverage. Additionally, we found that while hypoxia increased endothelial gene expression and vessel width, it also inhibited the growth of the αSMA+ population. Together, these findings underscore the potential use of ASCs in forming mature vessels in vitro as well as the need for a further understanding of the heterotypic interactions among ASC subpopulations.

Adipose Stromal Cells Differentiate Along a Smooth Muscle Lineage Pathway Upon Endothelial Cell Contact via Induction of Activin A

“…Similarly, it has been shown that PDGF-BB, secreted by EC, was responsible for 10T1/2 cell directional migration in a semisolid underagarose coculture model, 32 whereas blocking PDGF-BB signaling prevents accumulation of αSMA+ASC around EC cords 26 in a model similar to ours. It is not clear how a physiologically meaningful gradient of chemoattractants might be established in 2-dimensional culture models.…”

“…Recently, these observations were supported by several other studies using similar models. 26,27 To extend our understanding of the mechanisms governing the interactions between EC and ASC further, specifically the ones that prompt ASC transition from a progenitor phenotype toward smooth muscle lineage, we conducted the present study using an in vitro model of EC-ASC cocultivation. 25 …”

Platelet-Derived Growth Factor and Spatiotemporal Cues Induce Development of Vascularized Bone Tissue by Adipose-Derived Stem Cells

“…The lipoaspirate tissue was processed to isolate the adherent population from the stromal vascular cell fraction, as previously described. 16 The adherent population (passage 0) was trypsinized and cryopreserved 40 for shipment to the Johns Hopkins University.…”

“…In addition to their well-studied osteogenic capacity, 12,13 ASC cultures have also been shown to give rise to endothelial cells 14,15 and lumen-containing vessels. [16][17][18] However, the ability of ASCs to undergo direct differentiation to endothelial cells remains contentious. 19 Recent findings suggest that these vessels may arise due to a minute subpopulation of residual committed endothelial cell progenitors that undergoes extensive proliferation and selfassembly to form vascular networks.…”

“…19 Recent findings suggest that these vessels may arise due to a minute subpopulation of residual committed endothelial cell progenitors that undergoes extensive proliferation and selfassembly to form vascular networks. 16,20 Recently, a few groups have shown promise in the potential of using ASCs 4,21 or fresh adipose stromal vascular fraction (SVF) 22,23 to form vascularized bone. However, robust vascular network development coupled with dense mineral deposition has yet to be demonstrated, which may limit the extent of integration and functional outcome of the tissue.…”