Bone Cell Biology and Imaging Laboratory, Hospital for Special Surgery, 535 East 70th St., New York, NY 10021, USA.
J Appl Physiol (1985). 2010 Dec;109(6):1930-8. doi: 10.1152/japplphysiol.00839.2010. Epub 2010 Oct 14.
Physiological disturbances, including temporary hypoxia, are expected to drive angiogenesis during bone repair. Evidence suggests that the angiogenic ligand vascular endothelial growth factor (VEGF)-A plays an important role in this process. We characterized the expression of two receptors that are essential for mediating VEGF signaling, VEGFR1/Flt-1 and VEGFR2/Flk-1/KDR, in a mouse rib fracture model. Their mRNA and protein levels were assessed in four healing phases, which were characterized histologically as hemorrhage formation on postfracture day (PFD) 1, inflammatory response on PFD 3, initiation of callus development on PFD 7, and the presence of a mature callus on PFD 14. Transcript was detected for VEGFR1 and VEGFR2, as well as VEGF. While mRNA expression of VEGFR1 was monophasic throughout all healing phases, VEGFR2 showed a biphasic profile with significantly increased mRNA expression during callus formation and maturation. Expression of VEGF mRNA was characterized by a more gradual increase during callus formation. The protein level for VEGFR1 was below detection sensitivity during the initial healing phase. It was then restored to a stable level, detectable through the subsequent healing phases. Hence, the VEGFR1 protein levels partially mirrored the transcript expression profile. In comparison, the protein level of VEGFR2 increased gradually during the healing phases and peaked at callus maturation. This correlated well with the transcriptional expression of VEGFR2. Intact bone from age-matched male mice had considerable protein levels of VEGFR1 and VEGF, but no detectable VEGFR2. Together, these findings uncovered expression signatures of the VEGF-VEGFR axis in endochondral bone repair.
生理紊乱，包括暂时缺氧，预计会在骨修复过程中促进血管生成。有证据表明，血管生成配体血管内皮生长因子 (VEGF)-A 在这个过程中起着重要作用。我们在小鼠肋骨骨折模型中对介导 VEGF 信号的两个受体，VEGFR1/Flt-1 和 VEGFR2/Flk-1/KDR 的表达进行了描述。在四个愈合阶段评估了它们的 mRNA 和蛋白水平，这四个阶段在组织学上分别表现为骨折后第 1 天的出血形成、第 3 天的炎症反应、第 7 天的骨痂形成开始和第 14 天的成熟骨痂存在。检测到了 VEGFR1 和 VEGFR2 以及 VEGF 的转录物。虽然 VEGFR1 的 mRNA 表达在整个愈合阶段都是单峰的，但 VEGFR2 的表达呈现双峰模式，在骨痂形成和成熟过程中显著增加。VEGF mRNA 的表达特征是在骨痂形成过程中逐渐增加。VEGFR1 的蛋白水平在初始愈合阶段低于检测灵敏度。然后，它恢复到稳定水平，在随后的愈合阶段可以检测到。因此，VEGFR1 蛋白水平部分反映了转录表达谱。相比之下，VEGFR2 的蛋白水平在愈合阶段逐渐增加，并在骨痂成熟时达到峰值。这与 VEGFR2 的转录表达很好地相关。与年龄匹配的雄性小鼠的完整骨组织具有相当水平的 VEGFR1 和 VEGF 蛋白，但没有检测到 VEGFR2。总的来说，这些发现揭示了 VEGF-VEGFR 轴在软骨内骨修复中的表达特征。
