Extracellular matrix deposition by fibroblasts is necessary to promote capillary‐like tube formation in vitro

Abstract

The contribution of the cellular and fibrillar microenvironment to angiogenesis still remains unclear. Our purpose was to evaluate the effect of the extracellular matrix deposited by fibroblasts on the capacity of human endothelial cells to form capillaries in vitro. We have drastically decreased the amount of extracellular matrix surrounding fibroblasts in our model of endothelialized-reconstructed connective tissue (ERCT) by culturing it without ascorbate. Under these conditions, the number of capillary-like tubes (CLT) formed by endothelial cells was reduced by up to 10-fold after 31 days of culture compared to controls. This decrease was due neither to a variation of MMP-2 and MMP-9 secretion, nor to a reduction in the number of fibroblasts and/or endothelial cells, or a diminution of fibroblast growth factor 2 (FGF2) synthesis. The secretion of vascular endothelial growth factor (VEGF) by fibroblasts accounted for 25-70% of the capillary-like tube formation when tissues were cultured in the presence or absence of ascorbate, as demonstrated by VEGF-blocking studies. The culture of endothelial cells on a similar extracellular matrix but in the absence of living fibroblasts did not promote the formation of CLT, even when tissues were fed with fibroblast-conditioned medium. Thus, the deposition of a rich extracellular matrix by living fibroblasts appeared necessary, but not sufficient to promote capillary-like formation. Fibroblasts seem to induce endothelial cells to spontaneously form CLT by secreting and organizing an abundant extracellular matrix, which creates a microenvironment around cells that could in turn trap growth factors produced by fibroblasts and promote three-dimensional cell organization.

Engineered vascularized bone grafts

“…Coculturing with an additional cell type to serve as mural cells and inclusion of ECM are necessary to maintain and mature the networks (5-11). The ability to precisely control in vitro experimental conditions directly led to identifying the mechanisms of many fundamental aspects of this process over the past several decades (5)(6)(7)(10)(11)(12)(13)(14). Several groups have recently shown that microvascular structures that are preformed in vitro by using endothelial and smooth muscle progenitor cells can anastomose with the host vasculature when implanted in a nude mouse model (15)(16)(17)(18)(19)(20).…”

Aerobically Derived Lactate Stimulates Revascularization and Tissue Repair via Redox Mechanisms

“…5, right panel). The vascular conduits in the implants of hypoxic mice were also immature, poor in collagen, thin-walled, and apparently friable, often ruptured, and resembled cells seen in ascorbic acid depletion when collagen deposition is impaired (6).…”

Fibroblast-Endothelial Partners for Vascularization Strategies in Tissue Engineering

“…24 Understanding this process remains a challenge, since fibroblasts have the capacity to alter the mechanical extracellular microenvironment, thereby regulating vascularization processes. 25 Fibroblast-derived proteins, including growth factors and matrix proteins, have been shown to modulate EC sprouting and the expansion of capillary-like networks in vitro, [26][27][28] contributing to the role of fibroblasts as periendothelial cells in vivo. 29 Thus, the hypothesis underlying herein is that, when cocultured with OECs or mature ECs, different types of fibroblasts will exert distinct influences in the assembly of capillary-like structures.…”