Department of Periodontics, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA.
Department of Implantology, School of Stomatology, Jilin University, Changchun, China.
J Bone Miner Res. 2019 Mar;34(3):547-556. doi: 10.1002/jbmr.3610. Epub 2018 Nov 20.
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 FOXO1 ) and Cre recombinase negative control littermates containing flanking loxP sites (Col2α1Cre FOXO1 ). 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.
软骨细胞在骨折愈合中起着至关重要的作用，它们产生软骨，为软骨内骨化形成一个胚胎，稳定愈合的骨折痂。最近人们认识到，软骨细胞具有产生可能影响愈合过程的因子的能力。我们研究了软骨细胞在骨折愈合过程中的血管生成作用，以及转录因子叉头框 O1（FOXO1）的作用，FOXO1 上调软组织的伤口愈合。通过胶原 2α1 启动子元件（Col2α1Cre FOXO1）下的 Cre 重组酶，在实验小鼠中诱导具有谱系特异性 FOXO1 缺失的闭合性骨折，Cre 重组酶阴性对照同窝仔鼠含有侧翼 loxP 位点（Col2α1Cre FOXO1）。实验小鼠的 CD31 新生血管形成明显减少。体内软骨细胞中 FOXO1 的缺失抑制了血管内皮生长因子-A（VEGFA）的蛋白和 mRNA 水平的表达。体外软骨细胞中 FOXO1 的过表达增加了 VEGFA mRNA 水平和 VEGFA 转录活性，而沉默 FOXO1 则降低了它。此外，FOXO1 与 VEGFA 启动子直接相互作用，去乙酰化的 FOXO1 突变体增强了 VEGFA 的表达，而乙酰化的 FOXO1 突变体则没有。最后，siRNA 敲低 FOXO1 显著降低了软骨细胞在体外刺激微血管内皮细胞管形成的能力。结果表明，软骨细胞在血管生成中起着关键作用，这种作用依赖于 FOXO1，软骨细胞中的 FOXO1 调节一种有效的血管生成因子，VEGFA。这些研究为骨折愈合提供了新的见解，因为血管形成在骨折修复过程中起着重要作用。2018 年美国骨骼与矿物质研究协会。
