Targeting angiogenesis for fracture nonunion treatment under inflammatory diseases

摘要 骨折不愈合是一个重要的临床问题。在美国，大约有160万块骨头 骨折每年都要经历长时间的愈合或骨不连。骨折不愈合的治疗通常包括 在实践中，复杂而庞大的程序，有时需要多次手术，因此增加 医疗保健的费用，并导致明显的病人残疾。患有这些临床疾病的主要人群 并发症是有炎症情况的患者，例如，老年患者、吸烟、糖尿病或类风湿 关节炎(RA)患者，强调慢性全身炎症在骨折中的潜在有害作用 再来一次。 这一建议的首要假设是慢性炎症导致骨折不愈合。 通过Dnmt3b下调介导的血管生成缺陷，并局部传递OPN和CXCL12修复 炎症条件下的血管生成和骨折修复。这一假设得到了我们初步的支持 数据表明，在骨折修复过程中，Dnmt3b在骨折骨痂中高表达，而Dnmt3b在骨折修复过程中 巨噬细胞对细胞因子反应的主要DNA甲基转移酶(DNMT)。与我们的建议相关，我们提供 有证据表明，炎症信号以一种依赖于NF-κB的方式抑制DNMT3B。一如既往地，小鼠 软骨细胞功能丧失(LOF)表现为血管生成和骨折修复受损； 软骨细胞的功能获得(GOF)在体外表现出抗炎保护作用并加速 小鼠的骨折修复。炎症和Dnmt3b LOF介导的血管生成缺陷 与骨桥蛋白(OPN)和CXCL12(C-X-C基序趋化因子配体12)和 外源性OPN和CXCL12可恢复体外血管生成能力。为了进一步检查局部治疗的疗效 OPN和CXCL12在体内的传递，我们开发了一种优化的OPN和CXCL12生物材料片 CXCL12，并显示出强健的血管生成过程和RA小鼠骨折愈合的恢复。 提出了三个主要的具体目标。具体目标1将描述以下机制： 在骨折修复过程中，炎症通过下调DNMT3b的表达来减少血管生成。特定目标2将 确定OPN和CXCL12在血管生成中的最佳释放动力学。具体目标3将决定 OPN和CXCL12缓释对小鼠血管生成和骨折不愈合的治疗作用这个 拟议的研究将加强我们对全身炎症(通过核因子-2)的机制的理解 κB途径)通过DNMT3b影响血管生成过程。这项工作将建立一种重要的治疗方法 促进血管生成和骨折愈合的选项。

ABSTRACT Fracture nonunion poses a significant clinical problem. In the United States, approximately 1.6 million bone fractures encounter prolonged healing or nonunion each year. Fracture nonunion treatment usually involves complicated and massive procedures in practice, and sometimes needs multiple surgeries, therefore increases the cost of health care and results in marked patient disability. The major population bearing with these clinical complications are patients with inflammatory conditions, e.g, elder patients, smoking, diabetic or rheumatoid arthritis (RA) patients, highlighting the potential deleterious role of chronic systemic inflammation in fracture r epair. The overarching hypothesis of this proposal is that chronic inflammation results in fracture nonunion through Dnmt3b downregulation mediated angiogenesis defect, and local delivery of OPN and CXCL12 restores angiogenesis and fracture repair under inflammatory conditions. This hypothesis is supported by our preliminary data wherein we show that Dnmt3b is highly expressed in fracture callus during fracture repair and Dnmt3b is the major DNA methyltransferase (Dnmt) responsive to cytokines in MPCs. Relevant to our proposal, we provide evidence that inflammatory signals inhibit Dnmt3b in an NF-κB-dependent manner. Consistently, mice with Dnmt3b loss-of-function (LOF) in chondrocytes display impaired angiogenesis and fracture repair; and Dnmt3b gain-of-function (GOF) in chondrocytes shows protective effect from inflammation in vitro and accelerates fracture repair in mice. Mechanistically, angiogenesis defect mediated by inflammation and Dnmt3b LOF coincide with downregulation of OPN (Osteopontin) and CXCL12 (C-X-C Motif Chemokine Ligand 12) and exogenous OPN and CXCL12 can restore angiogenesis capacity in vitro. To further examine the efficacy of local delivery of OPN and CXCL12 in vivo, we have developed an optimized biomaterial sheet loaded with OPN and CXCL12 and showed a robust angiogenesis process and a restoration of fracture union in RA mice. Three main Specific Aims are proposed. Specific Aim 1 will delineate the mechanism by which inflammation reduces angiogenesis via downregulating Dnmt3b during fracture repair. Specific Aim 2 will determine the optimal release kinetics of OPN and CXCL12 on angiogenesis. Specific Aim 3 will determine the therapeutic effect of sustained OPN and CXCL12 release on angiogenesis and fracture nonunion in mice. The proposed studies will enhance our understanding of mechanisms by which systemic inflammation (via the NF- κB pathway) affects the angiogenic process through Dnmt3b. This work will establish an important therapeutic option to improve the angiogenesis and fracture healing.