Orthodontic mechanical tension effects on the myofibroblast expression of alpha-smooth muscle actin.
OBJECTIVE
To detect myofibroblast formation on the tension side during orthodontic tooth movement in vivo and myofibroblast expression of alpha-smooth muscle actin (alpha-SMA) induced by tension both in vivo and in vitro.


METHODS
Fifty 6-week male rats were used in this in vivo study, and the right maxillary first molar was moved mesially, which served as the experimental group, and the left maxillary first molar served as the control. Rats were sacrificed at days 0, 3, 5, 7, and 14 after force loading. Myofibroblasts, identified with alpha-SMA, were examined through immunohistochemistry. For the in vitro study, human periodontal ligament (PDL) fibroblasts were obtained. Cyclic mechanical tension was applied to the fibroblasts for 0, 1, 3, 6, and 12 hours. Transmission electron microscopy was used to detect the ultrastructure of myofibroblasts. alpha-SMA mRNA gene expression was quantified by real-time quantitative PCR. The expression of alpha-SMA was detected by immunofluorescence and quantified by Western blotting.


RESULTS
In vivo, the myofibroblasts expressing alpha-SMA were identified both in the experimental group and in the control group. The expressions of alpha-SMA were increased in the tension areas of the experimental group over time, and reached the maximum in day 14. In vitro, fibronexus junctions and actin microfilaments in the cells could be found with transmission electron microscopy. Cyclic mechanical tension could significantly induce alpha-SMA expression at 12 hours (P < .01) than the controls.


CONCLUSIONS
Myofibroblasts existed in the PDL. The expressions of alpha-SMA in the myofibroblasts were significantly up regulated under tension both in vivo and in vitro.
Meng
Yao
Y
State Key Laboratory of Oral Diseases, Department of Orthodontics, West China Stomatological Hospital, Sichuan University, Guangdong, China.
Han
Xianglong
X
Huang
Lan
L
Bai
Ding
D
Yu
Hongyou
H
He
Yan
Y
Jing
Yan
Y
D008841:Actin Cytoskeleton / Q000648:ultrastructure; D000199:Actins / Q000032:analysis*; D000293:Adolescent; D000818:Animals; D001696:Biomechanical Phenomena; D015153:Blotting, Western; D002478:Cells, Cultured; D002648:Child; D005347:Fibroblasts / Q000378:metabolism* / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D007365:Intercellular Junctions / Q000648:ultrastructure; D008297:Male; D046529:Microscopy, Electron, Transmission; D032389:Myocytes, Smooth Muscle / Q000378:metabolism* / Q000648:ultrastructure; D010513:Periodontal Ligament / Q000166:cytology / Q000378:metabolism; D016133:Polymerase Chain Reaction / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D022502:Stress Fibers / Q000648:ultrastructure; D013314:Stress, Mechanical; D013997:Time Factors; D014087:Tooth Movement Techniques; D015854:Up-Regulation
D000199:Actins; C498862:Acta2 protein, rat