Effect of tensile force on expression of PTHrP and thickness of hypertrophic zone in organ-cultured mouse spheno-occipital synchondroses.
OBJECTIVE
Responses of spheno-occipital synchondroses to direct tensile stress have not been identified before. This study was, therefore designed to evaluate expression of PTHrP, and thickness of hypertrophic zone in spheno-occipital synchondroses in response to such stress, using mouse in vitro model.


METHODS
Spheno-occipital synchondroses together with adjacent structures were excised from fifty-five 2-day-old mice that were randomly assigned to 6 control and 5 experimental groups for 5 experimental periods (n=5). In the experimental groups, tensile force of 0.2g was applied across the synchondroses, using helical springs. In 5 control groups, the springs were made inactive. Both groups were then cultured for 6, 24, 48, 72 h and 7 days. Another control group was cultured without any springs for 7 days to compare with natural growth of the synchondroses from a group of five 9-day-old mice. Alcian blue-PAS staining was used to study growth of the synchondroses; immunohistochemical staining to identify PTHrP and type X collagen expression. The area of PTHrP expression and thickness of hypertrophic zone, demarcated by type X collagen expression, were measured.


RESULTS
Quantitative analysis showed that PTHrP expression increased significantly at hour 24 of the force application in the experimental group (p<0.05), then reduced from hour 24 to 72 with a significant drop from hour 24 to 48 (p<0.01); and the thickness of hypertrophic zone significantly increased at hour 48 (p<0.01).


CONCLUSIONS
Our findings suggested that the growth of spheno-occipital synchondroses could be modified by tensile stress; and a light continuous force could enhance its growth, as evidenced by an increase in PTHrP expression and thickness of hypertrophic zone.
Rukkulchon
Bell K
BK
Orthodontics, Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, Hong Kong, SAR, China.
Wong
Ricky W K
RW
D000818:Animals; D049109:Cell Proliferation; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism*; D020219:Chondrogenesis / Q000502:physiology*; D015870:Gene Expression; D006984:Hypertrophy / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009777:Occipital Bone / Q000033:anatomy & histology / Q000254:growth & development*; D009924:Organ Culture Techniques; D010012:Osteogenesis / Q000502:physiology*; D044162:Parathyroid Hormone-Related Protein / Q000235:genetics / Q000378:metabolism*; D019291:Skull Base / Q000033:anatomy & histology / Q000254:growth & development; D013100:Sphenoid Bone / Q000033:anatomy & histology / Q000254:growth & development*; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology; D015854:Up-Regulation / Q000502:physiology
D044162:Parathyroid Hormone-Related Protein