The Influence Of RhPDGF-BB On The Expression Of FAK In The Osteoclast During Orthodontic Tooth Movement In Rats

The rate of bone resorption is one of critical factors in orthodontic tooth movement. Platelet derived growth factor-BB(PDGF-BB) is an important cytokine on skeletal metabolism which participates in the bone formation and resorption. Our former studies have showed that the number of osteoclasts and the expression of integrin alphavbeta3 were obviously increased in the compression sides of the orthodontic tooth movement model rats after local injection the low does of recombinant human platelet derived growth factor-BB (rhPDGF-BB), meanwhile, it accelerated the rate of orthodontic tooth movement. Focal adhesion kinase(FAK) is a significant tyrosine kinases in integrin alphavbeta3-mediated cell singnaling,it plays a predominan role in the reconstruction of cytoskeletal organization, osteoclast adhesion, osteoclast aggregation and bone resorption. The experiment was designed to observe the influence of rhPDGF-BB on FAK in the osteoclasts during orthodontic tooth movement and to explore the mechanism of rhPDGF-BB in improving the orthodontic tooth movement.[Objective] To observe the effect of rhPDGF-BB on the expression of FAK in osteoclastsduring orthodontic tooth movement in Sprague-Dawley (SD) rats. To explore the role of rhPDGF-BB on osteoclasts of periodontal tissues remodeling process and the downstream pathways of osteoclasts in the orthodontic tooth movement.[Methods] The first upper left maxillary molar was moved mesially by a closed-coilspring delivered a force of 50g for establishing orthodontic movement model in male SD rats. 80 model rats were randomly divided into two groups: Control group (group A) and Experimental group(group B),40 animals each group. According to the force time (1day,4days, 7days,10days and 14days), each group was subdivided equally into five subgroups(A1/B1,A4/B4,A7/B7,A10/B10 and A14/B14) of eight. The Experimental groups were respectively injected rhPDGF-BB in dosages of 10ng in buccal submucosal area of the molar every other day, while the Control group injected equivalent volumes of PBS. Eight rats in each subgroup were sacrificed at different time points (1,4,7,10 and 14days) after appliance placement. The distance of the tooth movement was measured by the stereomicroscope. Tissue sections around the first maxillary left molar were stained with tartrate-resistant acid phosphatase(TRAP) histochemistry to analyze the quantity changes of osteoclasts on the compression side of tooth. The expression of FAK in osteoclasts was detected by immunohistochemical techniques on the same side.[Results] 1. Tooth movement:â‘ With the force time passing, the distance of orthodonticstooth movement in group A and group B increased. Group B which injected rhPDGF-BB moved more rapidly than group A at each time point.â‘¡There was no significant difference between subgroup A1 and subgroup B1 (P>0.05) ,other groups showed significant differences(P<0.01). 2. Osteoclast counting:â‘ The number of osteoclasts in group B began to increase in the first day and reached at peak at day 4 ,then gradually decreased after day4. The total tendency of group A is the same as group B, but the peak was occurred at day7. All of the trend is gently than group B .â‘¡At every point, the number of osteoclasts in group B is more than group A(P<0.01).â‘¢There were significant differences within group A(P<0.01)at every point . In group B,beside the the day1 and day14, all of the subgroup in group B have significant differences( P<0.01). 3. The expression of FAK:â‘ The expression of FAK in osteoclasts increased with time and arrived at peak at day4 , and then gradually decreased after day4. At every point the expression of FAK in group B is higher than group A(P<0.05) and reached at peak at day4.â‘¡Within group B, besides the day10 and day14, all of the subgroup of group B have significant differences( P<0.01). Within group A, besides day1 and day14, all of the subgroup of group A have significant differences( P<0.01).[Conclusions] 1.rhPDGF-BB is a local regulation factor which promote the skeletal metabolism of orthodontic tooth movement. 2.FAK participates in the downstream signaling in osteoclast of orthodontic tooth movement via local regulation of exogenous rhPDGF-BB.