The role of the angiogenesis in the endochondral occification A use of osteopetradic as mouse experimental model

软骨内成骨发生在血管侵入肥大软骨细胞腔隙之前。虽然已经有报道称，破骨细胞或破软骨细胞主要负责面向血管侵入前沿的横隔膜的降解或吸收，但仍有一些问题需要澄清。在本研究中，我们使用单核/巨噬细胞谱系遗传缺陷的op小鼠进行形态学研究。尽管缺乏trap阳性破骨细胞或破软骨细胞和F4/80阳性巨噬细胞，但op小鼠的股骨或胫骨骨骺厚度和形态均正常。电镜下，血管侵袭前沿细胞仅为血管内皮细胞和血管周围细胞，未见破骨细胞和巨噬细胞。这也被层粘连蛋白免疫组织化学作为内皮细胞鉴定的标记物所证实。免疫组织化学和电子免疫组织化学显示MMP-9蛋白在血管侵袭前的细胞成分和细胞外基质中均有表达。MMP-9基因在位于同一区域的细胞中也有表达，其中至少有一部分是血管内皮细胞。VEGF蛋白在骺生长板的骺骺软骨细胞中表达强烈，在增生性软骨细胞中表达弱。从目前的研究来看，我们认为由MMP-9和VEGF主导的血管入侵是造成软骨细胞间隙横隔破裂的主要原因，而破骨细胞和巨噬细胞都没有参与这一现象。

Enchondral ossification is preceded the vascular invasion into hypertrophic chondrocyte lacunae. Although it has been described that the osteoclasts or chondroclasts are primarily responsible for the degradation or resorption of the transverse septa facing to the vascular invasion front, there are some questions to be clarified. In this study, we conducted morphological aprorch using the op mouse that has an inheritent deficiency of monocyte/macrophage lineage.In the femoral or tibial epiphysis of the op mice appeared to be normal thickness and morphology despite the lack of both TRAP-positive osteoclasts or chondroclasts and F4/80 positive macrophages. Electron microscopically, the cells found in the vascular invasion front are only vascular endothelial cells and perivascular cells and neither osteoclasts nor macrophages were observed at all. This was also confirmed by the laminin immunohistochemistry as a marker for endothelial cell identification.Immunohistochemistry and electron immunohistochemistry demonstrated the expression of MMP-9 protein in both cellular component and extraoellular matric at the front of the vascular invasion. The expression of MMP-9 geen also recognized in the cells located in the same region, at least some of which were vascular endothelial cells. The expression of VEGF protein, was found intensely in the metaphysic and weakly in the hypertrophic chondrocytes in the epiphyseal growth plate.From the present study, we suggest that the vascular invasion leaded by MMP-9 and VEGF is primarily responsible for the break down of the transverse septa of hypetrophic chondrocytes lacunae and neither osteoclastic cells nor macrophages involve in this phenomenon.