Transient Support from Fibroblasts is Sufficient to Drive Functional Vascularization in Engineered Tissues

Abstract

Formation of capillary blood vasculature is a critical requirement for native as well as engineered organs and can be induced in vitro by coculturing endothelial cells with fibroblasts. However, whether these fibroblasts are required only in the initial morphogenesis of endothelial cells or needed throughout is unknown, and the ability to remove these stromal cells after assembly can be useful for clinical translation. In this study, a technique termed CAMEO (Controlled Apoptosis in Multicellular Tissues for Engineered Organogenesis) is introduced, whereby fibroblasts are selectively ablated on demand, and it is utilized to probe the dispensability of fibroblasts in vascular morphogenesis. The presence of fibroblasts is shown to be necessary only during the first few days of endothelial cell morphogenesis, after which they can be ablated without significantly affecting the structural and functional features of the developed vasculature. Furthermore, the use of CAMEO to vascularize a construct containing primary human hepatocytes that improved tissue function is demonstrated. In conclusion, this study suggests that transient, initial support from fibroblasts is sufficient to drive vascular morphogenesis in engineered tissues, and this strategy of engineering-via-elimination may provide a new general approach for achieving desired functions and cell compositions in engineered organs.

Reconstituting the dynamics of endothelial cells and fibroblasts in wound closure

“…1 in the supplementary material ). Previous work has shown that similar vasculogenic tissues do get stiffer over time, 8,12 with this increasing stiffness dependent largely on the presence of fibroblasts within the tissue. 8 …”

“…1(a) ] with an approximate tissue thickness of 0.5 mm. The PDMS mold used in this study was adapted from a previously published platform 8 to enable the formation of vascular networks without fluid flow and to allow for tissue injury by uncovering the central gel region. We utilized a composite gel of 0.4 mg/ml collagen I and 2.5 mg/ml fibrinogen because these composite gels have been shown to retain the robust vasculogenesis, which is observed in pure fibrin gels, 10 while also incorporating collagen I, a fibrous matrix molecule that imparts strength to mature tissue.…”

“…The mold, modified from a previously published study, 8 was formed using soft lithography. Polydimethylsiloxane [PDMS, Sylgard 184, Dow-Corning)] was mixed at a standard ratio of 1:10 (PDMS base to cross-linking reagent) and then was added to a mold (Protolabs) and cured in a 60 °C oven overnight.…”

“… 5–9 This body of work has shown that fibroblasts are essential to the process of vascular network formation and stability 6 due to their secretion of soluble factors 7,9 and matrix components. 8 Given the ability of fibroblasts to support vascular network formation in 3D gels in vitro , we sought to investigate whether fibroblasts contribute to the process of endothelial cell ingrowth and repopulation of the newly formed granulation tissue.…”

Bone‐on‐a‐Chip: Microfluidic Technologies and Microphysiologic Models of Bone Tissue

“…[ 98 ] In contrast to the EC cell lining technique, vasculogenesis and angiogenesis‐based methods can be combined with advanced microfluidic‐based techniques to recreate 3D microvascular networks that can be adapted into organ‐on‐a‐chip platforms. [ 99–105 ] A tri‐culture of human bone marrow mesenchymal stem cells (hBM‐MSCs), osteogenically differentiated (OD) hBM‐MSCs, and human umbilical vein endothelial cells (HUVECs) embedded in 2.5 mg mL −1 fibrin gel were used to recreate the bone microvasculature. [ 106 ] Experimental results showed the formation of functional microvascular networks after 4 days.…”