Mechanisms of fracture healing in aged mice, which is dependent on COX-2 derived PGE_2

摘要：考克斯-2诱导的PGE 2可通过机械刺激提供，对老年小鼠骨折修复中的软骨内重塑阶段起关键作用。它不仅协调下游分子如VEGFa和基质金属蛋白酶，而且还控制FGF-2。简介：骨折愈合随着年龄的增长而减慢。为了表征考克斯-2在老年考克斯-2基因敲除小鼠延迟修复过程中的作用，我们应用了低强度脉冲超声（LIPUS），我们以前报道过，它诱导考克斯-2，并在临床上用于加速修复过程。研究方法：在一岁大的考克斯-2基因敲除小鼠和它们的野生型同窝小鼠中，进行微聚焦X射线计算机断层扫描、（免疫）组织化学和mRNA分析以表征闭合稳定股骨骨折愈合延迟。通过从骨折后第4天施用组合的EP 2和EP 4激动剂，证实了从对照和LIPUS处理的愈伤组织的缺陷中的拯救达到野生型对应物的水平。结果：到第10天，软骨形成相对正常。此后，修复过程减慢，LIPUS没有加速。然而，该处理有效地增加了野生型同窝仔中的内软骨重塑的速率，这是衰老中延长的过程。在敲除的愈伤组织中，无论是否暴露于LIPUS，在第7天，VEGFa和MMP-9等关键组分的转录物完全缺失。此外，基础FGF-2水平在敲除中显著升高，而没有通过LIPUS进一步升高。结论：考克斯-2是老年小鼠骨折愈合不可或缺的;如果缺乏，软骨重塑停止，骨折间隙填充间充质组织持续存在。除了下游VEGFa和基质金属蛋白酶的损失外，FGF-2的增加可能进一步延迟重塑过程。

Abstract : COX-2-induced PGE2, which can be provided by mechanical stimulation, crucially affects endochondral remodeling phase in fracture repair of aged mice. It not only orchestrates downstream molecules such as VEGFa and matrix metalloproteinases, but also controls FGF-2. Introduction : Fracture healing slows with age. In order to characterize the role of COX-2 in the delayed repair process in aged COX-2 knockout mice, we applied low-intensity pulsed ultrasound (LIPUS), which, we previously reported, induces COX-2 and is clinically used to accelerate repair processes. Methods : In one-yr-old COX-2 KO mice and their wild type littermates, micro focused X-ray computed tomography, (immuno) histochemical and mRNA analyses were conducted to characterize delay in healing of closed stabilized femur fracture. By administering combined EP2 and EP4 agonists from day 4 post fracture, rescue from the defect of both control and the LIPUS treated callus was confirmed to the level of wild type counterparts. Results : Cartilage formed relatively normally up to day 10. Thereafter, the repair process slowed down and was not accelerated by LIPUS. The treatment, however, effectively increased the rate of endochondral remodeling in the wild type littermates, a process prolonged in senescence. In the knockout callus, transcripts of such critical components as VEGFa and MMP-9 were entirely missing at day 7, regardless of exposure to LIPUS. In addition, the basal FGF-2 level was significantly elevated in the knockouts without further elevation by LIPUS. Conclusion : COX-2 is indispensable for fracture healing in aged mice ; if absent, endochondral remodeling is halted and the fracture gap filled with mesenchymal tissue persists. In addition to the loss of downstream VEGFa and matrix metalloproteinases, increased FGF-2 is likely to further delay the remodeling process.