Prevascularization promotes endogenous cell-mediated angiogenesis by upregulating the expression of fibrinogen and connective tissue growth factor in tissue-engineered bone grafts

Abstract

BackgroundVascularization is one of the most important processes in tissue-engineered bone graft (TEBG)-mediated regeneration of large segmental bone defects. We previously showed that prevascularization of TEBGs promoted capillary vessel formation within the defected site and accelerated new bone formation. However, the precise mechanisms and contribution of endogenous cells were not explored.MethodsWe established a large defect (5 mm) model in the femur of EGFP+ transgenic rats and implanted a β-tricalcium phosphate (β-TCP) scaffold seeded with exogenous EGFP− cells; the femoral vascular bundle was inserted into the scaffold before implantation in the prevascularized TEBG group. Histopathology and scanning electron microscopy were performed and connective tissue growth factor (CTGF) and fibrin expression, exogenous cell survival, endogenous cell migration and behavior, and collagen type I and III deposition were assessed at 1 and 4 weeks post implantation.ResultsWe found that the fibrinogen content can be increased at the early stage of vascular bundle transplantation, forming a fibrin reticulate structure and tubular connections between pores of β-TCP material, which provides a support for cell attachment and migration. Meanwhile, CTGF expression is increased, and more endogenous cells can be recruited and promote collagen synthesis and angiogenesis. By 4 weeks post implantation, the tubular connections transformed into von Willebrand factor-positive capillary-like structures with deposition of type III collagen, and accelerated angiogenesis of endogenous cells.ConclusionsThese findings demonstrate that prevascularization promotes the recruitment of endogenous cells and collagen deposition by upregulating fibrinogen and CTGF, directly resulting in new blood vessel formation. In addition, this molecular mechanism can be used to establish fast-acting angiogenesis materials in future clinical applications.Electronic supplementary materialThe online version of this article (10.1186/s13287-018-0925-y) contains supplementary material, which is available to authorized users.

Prevascularized hydrogels with mature vascular networks promote the regeneration of critical‐size calvarial bone defects in vivo

“…Finally, the precise mechanism with which prevascularization enhances bone formation is not clearly understood. However, a study with prevascularized tissue‐engineered bone grafts in a large segmental bone defect model (Cheng et al., 2018) found that prevascularization promoted the formation of fibrin‐like reticular structure and increased cell infiltration, increased expression of fibrinogen and connective tissue growth factor, enhanced deposition of collagen type I/III, promoted vWF+ (von Willebrand factor) capillary‐like tubular connections and angiogenesis. In this study, one or more of the above mechanisms might be critical for the enhanced bone generation in the mature prevascularized hydrogel grafts.…”

Schwann cells promote prevascularization and osteogenesis of tissue-engineered bone via bone marrow mesenchymal stem cell-derived endothelial cells

“…Prevascularization involves vascularization of the scaffold in vitro or in vivo and is a promising method for enhancing the vascularization of tissue constructs upon implantation [ 49 ]. We previously performed prevascularization with the insertion of the vascular bundle into scaffolds, which can promote the recruitment of endogenous cells and collagen deposition to establish fast-acting angiogenesis and osteogenesis [ 50 , 51 ]. Prevascularization also induced by endothelial cells in vitro, which can form original vessel structures in vitro to achieve better vascularization and osteogenic efficacy, has been used in TEB construction before implantation [ 52 , 53 ].…”

Vascularization converts the lineage fate of bone mesenchymal stem cells to endothelial cells in tissue-engineered bone grafts by modulating FGF2-RhoA/ROCK signaling

“…Images of the center field of view in ten independent samples were captured using a laser scanning confocal microscope (A1R, Nikon, Tokyo, Japan). Cell counts were quantified using ImageJ software 48 .…”