Altered Cellular Kinetics in the Growth Plate according to Alterations in the Weight Bearing

Kang, Ho Jung; Kong, Sun Young; Park, Kun Bo; Joo, Sun Young; Yang, Ick Hwan; Park, Hui Wan; Kim, Hyun Woo

Abstract

PURPOSE
To examine the effects of change in the weight bearing on the growth plate metabolism, a simulated animal model of weightlessness was introduced and the chondrocytes' cellular kinetics were evaluated.
MATERIALS AND METHODS
Unloading condition on the hind-limb of Sprague-Dawley rats was created by fixing a tail and lifting the hind-limb. Six rats aged 6 weeks old were assigned to each group of unloading, reloading, and control groups of unloading or reloading. Unloading was maintained for three weeks, and then reloading was applied for another one week thereafter. 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 control groups. 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 increase of the ratio of positive BrdU stained cells. However, apoptotic changes in the growth plate were not affected by the alterations of weight bearing.
CONCLUSION
Alterations in the weight bearing induced changes in the chondrocytic proliferative potential of the growth plate and have no effects on the apoptosis occurred. This may suggest that deprived weight bearing due to various clinical situations hamper normal longitudinal bone growth, and further studies regarding the factors for reversibility of chontrocytic proliferation upon variable mechanical stresses are needed.