Vascular Invasion And The Differentiation Of The Cartilage Cells In The Process Of Endochondral Ossification

Objective:Angiogenesis in bone growth and fracture healing and bone formation are coupled. Although people have had to understand, but there is no in-depth study of the specific relationship. In this study, we detecting the expression of CD31, collagen Ⅱ and Fas,in the process of endochondral ossification. to investigate the relationship between the vascular invasion and cartilage ossification, and the biological mechanisms of the degeneration of cartilage cells. Methods: we select health rats of 1 to 19 days in each group. The rats were killed by surgery decapitated. And their femoral bones were removed. After conventional fixed, embedded, slices. using HE staining method to observe vascular intrusion. Using immunohistochemistry to observe the expression of CD31、collagen and Fas protein. And using RTⅡ-PCR to detect the expression of CD31 m RNA、collagenⅡm RNA. Results: Morphological observation found that: there is only a small amount of blood vessel invasion in the first five days of rat femur, there is a large number of vascular invasion in the 7 to 13 days of rat femur.The cartilage matrix begins to calcify, blood vessels reduce in the 15 to 19 days of rat femur. From the immunohistochemical results we found that CD31 is expressed in cartilage cells and osteogenesis area; Collagen Ⅱmainly is expressed in cartilage hyperplasia and hypertrophy of cartilage cells, Fas mainly in hypertrophy and osteogenesis area. From RT-PAR detecting,we found that CD31 m RNA, collagenⅡ m RNA is expressed in each day. With the speeding up of the bone development, vascular invasion increased, the expression of CD31 m RNA increased with the increase of day age, and then bone development slow, CD31 m RNA expression begin to decline. The peak value of expression of CD31 m RNA at 13 th day. The peak value of expression of collagen Ⅱm RNA appeared in 17 th days. Conclusion:1)Epiphyseal plate growth zone and the secondary ossification center have different ways of osteogenesis, cartilage cells in the secondary ossification center have no proliferative stage. Within the femoral ossification process, vascular invasion and bone development are coordinated with each other to promote the process of endochondral ossification.2) There is another ossification plate between Epiphyseal plate and the second ossification center.3) The hypertrophic chondrocyte is not the end cell, the hypertrophic chondrocyte has the endothelial phenotype, and it could differentiate into the vascular endothelial cells, participate in the build of vascular, and promote vascular invasion.