| Objective: Condylar cartilage maintains a remodeling state throughoutthe life process. Except for being subject to the control of such factors as thebody’s own inheritance, body fluids and nerves, various stress stimuli acted onlocal parts also play an important role. Condylar cartilage cells are able toexperience all kinds of stress stimuli. With the action of biomechanical stress,condylar cartilage will produce the conversion of machinery-chemistry-biological signals, showing a series of reactions like cell proliferation,differentiation and programmed cell death. However, we still fail to realizehow internal chondrocytes respond to mechanical stress stimulation andmediate the transduction of stimulation signals into cells after condylarcartilages are subject to mechanical stress, thereby regulating cellularmechanisms of the remodeling of condylar cartilages. Recently, a c-fos gene isfound to have involved in the signal transduction and regulation of condylarcartilage remodeling. Mainly concentrating in the cell nucleus, c-fos is anucleoprotein in cell-oncogene. It does not express when cells are in aquiescent stage; generally, its expression synchronously occurs with cellgrowth and proliferation. The main functions of a proto-oncogene are toregulate cell growth, proliferation and differentiation. Studies have found thatthis gene is closely related to proliferation of cartilage cell and formation ofcartilage. In this experiment, immunohistochemical staining was used to detectthe expression and varying patterns of c-fos in condyle during mandibularfunctional protrusion in growing rats. The mechanism of c-fos mandibularforward positioning on the condylar cartiage remodeling in the cell wasexplored to provide experimental evidence for the clinical orthopedictreatment of bone. Methods: seventy4-week-old healthy male Sprague-Dawley (SD) ratswere selected, weighing about90g. They were randomly and equally dividedinto an experimental group and a control group. According to the experimentalperiod (1,3,7,14,21,28and35days), the groups were respectively classifiedinto7subgroups (5in each), so there were a total of14subgroups. The studywas performed after the rats were allowed to acclimate for1week. In theexperimental group, self-made mandibular advancement inclined bite plateappliance was cemented on rat incisors by3M glass ionomer. Through a chainrubber ring, it was connected with face bow on both sides via nasomaxillarycomplex, thereby making the inclined bite plate get a stable retention. The rats’limbs were wrapped tightly with a medical adhesive plaster, which effectivelyprevented any damage caused by the rats’ forepaws to the appliance and facialtissue. The appliance was used for24h. In the control group, no experimentaloperation was done. All animals were allowed to soft food and free water.They were reared under the same environment till the end of the experiment.Drawing materials, conventional fixation, demineralization, dehydration andencapsulation were conducted1,3,7,14,21,28,35days after the experiment.Condylar histological change was observed by HE staining after paraffinsection. Expression of c-fos protein was detected by the immunohistochemicalmethod. ZKPACS-G Zoneking software cell image analysis system was usedto grade immunohistochemical staining, with IHS value representing stainingintensity. All of the results were processed with SPSS13.0statistical software.T-test was used for the comparisons between the experimental group and thecontrol group when making statistical analysis, while the one-way ANOVAmethod was employed for comparisons among subgroups. If the p-value wassmaller than0.05, they were statistically significant. The test level α=0.05.Results:1General observationIn the experimental group, rats’mandibles were in a moderatelyforwarding condition. Their upper and lower front teeth were corresponding. After removing the appliance, the jaw could not retreat. In the control group,the rats’ front teeth covered about3mm.2Condylar morphological changesIn the control group, with the time extension, the condylar cartilageshowed age-related changes, demonstrating thinner cartilage and moresignificant middle and rear of the changes in the cartilage. In the experimentalgroup, since Day3rd, different tissue layers of condylar cartilage were thicker;the number of cartilage cells increased; there were significant changes incondylar middle and rear parts while the former part did not changesignificantly. On Day21th, different layers of condylar cartilage graduallystabilized; the transitional layer was still significantly thicker than the controlgroup; and the late chondrocytes, osteoblasts, and a large number of originalbone trabeculas and undergrown marrow cavity were seen.3FOS protein expression level and distributionNo positive colored particles were seen in the blank control group (PBSreplaced primary antibodies). In the control group, only a small number ofc-fos proteins were positive in the hypertrophic cartilage layer, and they havebeen maintaining a low expression level until Day21th; later their expressiongradually decreased to a very low level. The difference between groups wasnot statistically significance (P>0.05). On Day3rd, c-fos proteins in theexperimental group were enhanced significantly in the condylar cartilage.IHS=2.2±1.10, which had significant difference compared to the control groupIHS=IHS=1.0±0.70(P>0.05). On Day7th, the experimental groupIHS=6.0±1.22possitive expression continued to improve, which hadsignificant difference compared to the control group IHS=1.0±0.70(P <0.05).On Day14th, the experimental group IHS=6.0±1.58, basically remaining atthe same expression level as Day7th. On Day21th, the experimental groupIHS=3.6±1.67. Positive cells in most samples began to decrease, which stillhad significant difference compared with the control group (P <0.05). On Day28th, the experimental group IHS=2.4±1.14, which still had statisticallysignificant difference with the control group IHS=0.8±0.45. On Day35th, c-fos protein dropped to an extremely low level; the experimental groupIHS=0.4±0.54, and the control group IHS=0.4±0.54, showing no statisticaldifference.Conclusions:c-fos adjusted the remodeling process of the condylar cartilages in ratsafter mandibular protrusion.c-fos played an important role in the condylar cartilage cell proliferationand differentiation.c-fos mediated the transduction from mechanical forces to biochemicalsignals in the remodeling process of rats’ condylar cartilages, which played animportant role for biological signals to transfer from outside to inside thenucleus. |
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