The Role of Microtubule in the Regulation of Endochondral Bone Formation in the Developing Mouse Cranial Base / 체질인류학회지

Endochondral bone formation of the developing cranial base is a complex process. This mechanism requires precise orchestration of many cellular events and cartilage matrix metabolism, such as proliferation, becoming round in shape, termination of proliferation, hypertrophic size-increase, and finally programmed cell death. Active formation and degradation of cartilage matrix take place, in which microtubules are involved for intracellular events; bone apposition follows these events. However, the involvement of microtubules during these changes in the developing cranial base has not been identified yet. Thus, we investigated the involvement of microtubules in the regulation of endochondral bone formation during cranial base development. Using tubulin-binding drug nocodazole, we examined the effects of altering the structure and function of microtubules during in vivo organ culture of the mouse cranial base. Cultured specimens were analyzed with HE staining, immunohistochemistry, and cell counting in order to study the morphological and molecular changes that occurred in the tissues. Disruption of the microtubular array by nocodazole reduced cells expressing proliferation marker Ki67, osteogenic marker BSP, and BMP4 within the sphenooccipital synchondrosis region; chondrocyte hypertrophy was ceased in the hypertrophic zone; degeneration of cartilage matrix and bone matrix apposition was inhibited in the ossification center of the basooccipital cranial base. Our data demonstrated that disruption of microtubules by nocodazole have multiple inhibitory effects on the sequential changes that occur during endochondral bone formation, suggesting the importance of normal microtubule-polymerization in cranial base development.

Effects of Changes in Mechanical Loading on Endochondral Bone Formation in Hindlimb-suspended Rats / 항공우주의학회지

BACKGROUND: To examine the effects of changes in mechanical loading on endochondral bone formation, a simulated rat model of weightlessness was introduced and the changes in the growth plate were evaluated. METHODS: Unloading condition on the hindlimb of Sprague-Dawley rats was created by fixing a tail and lifting the hindlimb. Six rats aged 6 weeks old were assigned to each group of unloading and reloading with their control group. Unloading was maintained for three weeks, and then reloading was applied for another one week afterwards. Histomorphometry for the assessment of vertical length of the growth plate, 5-bromo-2'-deoxyuridin (BrdU) immunohistochemistry for cellular kinetics, and biotin nick end labeling TUNEL assay for chondrocytes in the growth plate were performed. RESULTS: The vertical length of the growth plate and the proliferative potential of chondrocytes were decreased in the unloading group than those of the control group. Inter-group differences were more significant in the proliferative and hypertrophic zones. Reloading increased the length of growth plate and proliferative potential of chondrocytes as evidenced by the increase of the ratio of positive BrdU stained cells. However, the apoptotic changes in the growth plate were not affected by the alterations of the weight bearing. CONCLUSION: Alterations in the weight bearing induced changes in the chondrocytic proliferative potential of the growth plates and had no effect on the apoptosis occurrence. This may suggest that deprived weight bearing due to various clinical situations hamper normal longitudinal bone growth. Further studies regarding the factors for reversibility of chondrocytic proliferation upon variable mechanical stresses are needed.