Bahney Chelsea S, Hu Diane P, Taylor Aaron J, Ferro Federico, Britz Hayley M, Hallgrimsson Benedikt, Johnstone Brian, Miclau Theodore, Marcucio Ralph S
University of California, San Francisco (UCSF) and San Francisco General Hospital (SFGH), Orthopaedic Trauma Institute, San Francisco, CA, USA; Department of Bioengineering and Material Science, University of California, Berkeley, CA, USA.
J Bone Miner Res. 2014;29(5):1269-82. doi: 10.1002/jbmr.2148.
Although bone has great capacity for repair, there are a number of clinical situations (fracture non-unions, spinal fusions, revision arthroplasty, segmental defects) in which auto- or allografts attempt to augment bone regeneration by promoting osteogenesis. Critical failures associated with current grafting therapies include osteonecrosis and limited integration between graft and host tissue. We speculated that the underlying problem with current bone grafting techniques is that they promote bone regeneration through direct osteogenesis. Here we hypothesized that using cartilage to promote endochondral bone regeneration would leverage normal developmental and repair sequences to produce a well-vascularized regenerate that integrates with the host tissue. In this study, we use a translational murine model of a segmental tibia defect to test the clinical utility of bone regeneration from a cartilage graft. We further test the mechanism by which cartilage promotes bone regeneration using in vivo lineage tracing and in vitro culture experiments. Our data show that cartilage grafts support regeneration of a vascularized and integrated bone tissue in vivo, and subsequently propose a translational tissue engineering platform using chondrogenesis of mesenchymal stem cells (MSCs). Interestingly, lineage tracing experiments show the regenerate was graft derived, suggesting transformation of the chondrocytes into bone. In vitro culture data show that cartilage explants mineralize with the addition of bone morphogenetic protein (BMP) or by exposure to human vascular endothelial cell (HUVEC)-conditioned medium, indicating that endothelial cells directly promote ossification. This study provides preclinical data for endochondral bone repair that has potential to significantly improve patient outcomes in a variety of musculoskeletal diseases and injuries. Further, in contrast to the dogmatic view that hypertrophic chondrocytes undergo apoptosis before bone formation, our data suggest cartilage can transform into bone by activating the pluripotent transcription factor Oct4A. Together these data represent a paradigm shift describing the mechanism of endochondral bone repair and open the door for novel regenerative strategies based on improved biology.
尽管骨骼具有很强的修复能力,但在一些临床情况(骨折不愈合、脊柱融合、翻修关节成形术、节段性骨缺损)中,自体或异体移植试图通过促进骨生成来增强骨再生。当前移植治疗相关的关键失败因素包括骨坏死以及移植组织与宿主组织之间的整合有限。我们推测当前骨移植技术的根本问题在于它们通过直接成骨来促进骨再生。在此,我们假设利用软骨促进软骨内骨再生将借助正常的发育和修复序列来产生一个血管化良好且能与宿主组织整合的再生组织。在本研究中,我们使用小鼠节段性胫骨缺损的转化模型来测试软骨移植促进骨再生的临床效用。我们还利用体内谱系追踪和体外培养实验进一步测试软骨促进骨再生的机制。我们的数据表明,软骨移植在体内支持血管化且整合良好的骨组织再生,随后提出了一个利用间充质干细胞(MSC)软骨生成的转化组织工程平台。有趣的是,谱系追踪实验表明再生组织源自移植组织,提示软骨细胞转化为骨。体外培养数据表明,软骨外植体在添加骨形态发生蛋白(BMP)或暴露于人类血管内皮细胞(HUVEC)条件培养基后会矿化,表明内皮细胞直接促进骨化。这项研究为软骨内骨修复提供了临床前数据,有可能显著改善各种肌肉骨骼疾病和损伤患者的预后。此外,与肥大软骨细胞在骨形成前发生凋亡的传统观点相反,我们的数据表明软骨可通过激活多能转录因子Oct4A转化为骨。这些数据共同代表了软骨内骨修复机制描述的范式转变,并为基于改进生物学的新型再生策略打开了大门。