Chondrocytes Promote Vascularization in Fracture Healing Through a FOXO1-Dependent Mechanism

Abstract

Chondrocytes play an essential role in fracture healing by producing cartilage, which forms an anlage for endochondral ossification that stabilizes the healing fracture callus. More recently it has been appreciated that chondrocytes have the capacity to produce factors that may affect the healing process. We examined the role of chondrocytes in angiogenesis during fracture healing and the role of the transcription factor forkhead box‐O 1 (FOXO1), which upregulates wound healing in soft tissue. Closed fractures were induced in experimental mice with lineage‐specific FOXO1 deletion by Cre recombinase under the control of a collagen‐2α1 promoter element (Col2α1Cre+FOXO1L/L) and Cre recombinase negative control littermates containing flanking loxP sites (Col2α1Cre–FOXO1L/L). Experimental mice had significantly reduced CD31+ new vessel formation. Deletion of FOXO1 in chondrocytes in vivo suppressed the expression of vascular endothelial growth factor‐A (VEGFA) at both the protein and mRNA levels. Overexpression of FOXO1 in chondrocytes in vitro increased VEGFA mRNA levels and VEGFA transcriptional activity whereas silencing FOXO1 reduced it. Moreover, FOXO1 interacted directly with the VEGFA promoter and a deacetylated FOXO1 mutant enhanced VEGFA expression whereas an acetylated FOXO1 mutant did not. Lastly, FOXO1 knockdown by siRNA significantly reduced the capacity of chondrocytes to stimulate microvascular endothelial cell tube formation in vitro. The results indicate that chondrocytes play a key role in angiogenesis which is FOXO1 dependent and that FOXO1 in chondrocytes regulates a potent angiogenic factor, VEGFA. These studies provide new insight into fracture healing given the important role of vessel formation in the fracture repair process. © 2018 American Society for Bone and Mineral Research.

IFT80 Is Required for Fracture Healing Through Controlling the Regulation of TGF-β Signaling in Chondrocyte Differentiation and Function

“…Both osteoblasts and hypertrophic chondrocytes express high levels of VEGF, which promotes both the aggregation and proliferation of endothelial MSCs into a vascular plexus, and growth of new vessels from already existing ones . It has recently been shown that the transcription factor FOXO1 mediates expression of VEGF by chondrocytes, which plays a significant role in angiogenesis during the transition from cartilage to bone in postnatal fracture healing . In the current study, we found that IFT80 in chondrocytes was necessary for blood vessel formation in fracture callus and was needed for expression of VEGF, PDGF, and angiopoietin 1.…”

“…(50) It has recently been shown that the transcription factor FOXO1 mediates expression of VEGF by chondrocytes, which plays a significant role in angiogenesis during the transition from cartilage to bone in postnatal fracture healing. (4) In the current study, we found that IFT80 in chondrocytes was necessary for blood vessel formation in fracture callus and was needed for expression of VEGF, PDGF, and angiopoietin 1. These data point to the important function of IFT80 in chondrocytes by contributing to the cellular events that occur in the formation of a hard fracture callus and provide mechanistic insight into the regulation of IFT80 in chondrocytes to promote angiogenesis.…”

“…The soft callus is replaced by hard callus through revascularization and calcification, and finally remodeled by resorption of cartilage and replacement by bone to restore the osseous structure and function. Recent studies have demonstrated that chondrocytes play a critical role in this process …”

“…Recent studies have demonstrated that chondrocytes play a critical role in this process. (3,4) Primary cilia are essential cellular organelles that are anchored at the cell surface membrane to sense environmental cues and transduce extracellular signals. They have complicated structures containing a microtubule-based cytoskeleton called the axoneme and a mother centriole-formed basal body.…”

Sleep, brain vascular health and ageing

“…Ginkgo biloba extract has shown a preservative effect on mesenteric arterioles of old rats through vascular elasticity and AKt/FOXO3a signalling pathway (Chen et al 2019). Angiogenesis in the fracture repair process is regulated by chondrocytes through FOXO 1-dependent upregulation of VEGFA mRNA, while silencing FOXO 1 reduces angiogenesis (Zhang et al 2019). Thus, a close relation between FOXO and ageing process is a key factor in maintaining vascular properties.…”