Development and Application of Endothelial Cells Derived From Pluripotent Stem Cells in Microphysiological Systems Models

Abstract

The vascular endothelium is present in all organs and blood vessels, facilitates the exchange of nutrients and waste throughout different organ systems in the body, and sets the tone for healthy vessel function. Mechanosensitive in nature, the endothelium responds to the magnitude and temporal waveform of shear stress in the vessels. Endothelial dysfunction can lead to atherosclerosis and other diseases. Modeling endothelial function and dysfunction in organ systems in vitro, such as the blood-brain barrier and tissue-engineered blood vessels, requires sourcing endothelial cells (ECs) for these biomedical engineering applications. It can be difficult to source primary, easily renewable ECs that possess the function or dysfunction in question. In contrast, human pluripotent stem cells (hPSCs) can be sourced from donors of interest and renewed almost indefinitely. In this review, we highlight how knowledge of vascular EC development in vivo is used to differentiate induced pluripotent stem cells (iPSC) into ECs. We then describe how iPSC-derived ECs are being used currently in in vitro models of organ function and disease and in vivo applications.

Keywords: cell differentiation; induced pluripotent stem cells; organoids; vascular endothelium; vascular tissue engineering.

Figure 1

Summary of some important factors and pathways in EC development. Wnt signaling is necessary for specification of mesoderm and proper function in arterial ECs. FGF2, BMP4, and ETV2 are crucial for mesoderm formation and EC specification. VEGF/VEGFR2 signaling further specifies EC fate, with high and low concentrations leading to arterial or venous EC specificity, respectively. VEGF signaling continues to mediates downstream pathways and receptors that further direct arterial or venous EC specificity.

Figure 2

Current methods of iPSC culture and differentiation. Somatic cells are reprogrammed to iPSCs using 4 factors (Oct3/4, Sox2, c-Myc, and Klf4). iPSCs can be cultured as a monolayer or as 3D embryoid bodies. Endothelial differentiation can be achieved through the addition of small molecules to promote mesoderm then endothelial specification, or through genetic transcriptional activation or exogenous addition of ETV2.

Figure 3

Monolayer method of EC differentiation from iPSCs using small molecules. iPSCs transition to lateral mesoderm through addition of CHIR99021, BMP4, and FGF2 for 3 days. Endothelial specification is induced for 3 to 5 days using VEGF-A, SB431542, and forskolin. Sorting for CD144⁺ and CD31⁺ cells generates a pure differentiated EC population.

Figure 4

Applications of iPSC-derived ECs. Patient somatic cells are reprogrammed to iPSCs. For genetic diseases, gene editing can be used to correct genetic mutations. ECs differentiated from iPSCs can be used for disease modeling, cell therapies, drug screening, and vascular grafts.