| Stress is the adaptive and non-specific response of the organisms to theenvironments whether they are external, internal or psychological-social. Thebody is always in a stress state to produce adaptation and antagonistic reactionto the complex enviroment they live. In modern society, the physiological andpsychological functions of human beings are affected by various kinds ofstresses, such as fierce competition, speedy work pace, increase of life stress, etal. Now it has been getting more and more attention on the role of psychologicalstress in the development and treatment of disease, with changing frombiomedical model to the medical model of social-psychological andaccompanying improvement in the biaxial theory of disease. It has become a hottopic on the role of psychological stress in the development and treatment ofdisease.It has been confirmed that psychological stress can cause structural abnormality and dysfunction of stomatognathic system. However, thestomatognathic system is consisted of muscles, jaw and temporomandibularjoint, which could influence each other. It was still not clear on the influence ofpsychological stress on the morphological changes, the expression ofextracellular matrix and remodeling of subchondral bone in condylar cartilage.For these reasons, we studied the effect and mechanism of psychological stresson the structure of condylar cartilage by establishing a chronic unpredictablemild psychological stress model, which could make rats in the state ofpsychological stress. The results could provide experimental evidence andtheoretical basis on the pathogenesis and prevention measures in stomatognathicsystem diseases induced by psychological stress.This research was divided into two parts and the main results were as follow:The first part was the establishment and evaluation of chronicunpredictable mild stress (CUMS) model. The rats were randomly divided intocontrol group, psychological stress group and drug group. Each group wascomprised of three subgroups according to three different experiment timepoints,4weeks,8weeks and12weeks. Open field test was used in order to testthe behavior of rats. The rats’ weights and the levels of CORT and ACTH inserum were also measured meanwhile. Compared to control group and druggroup, the weight gain in psychological stress group were significantly reduced(p＜0.05). The results of open field test demonstrated that the distance moved inopen field of rats in psychological stress group were smaller than that in controlgroup and drug group (p＜0.05), and the time of animals in psychological stressgroup spent in the central part of open field were longer than that in controlgroup and drug group (p＜0.05). Compared to control group and drug group, theserum contents of CORT and ACTH in psychological stress group significantlyincreased in each time point (p <0.05). These results confirmed that CUMS model used in this study could provide a long-term psychological stress to rats,which can guarantee the progress of the follow-up studies.The second part was the research on the effect and mechanism ofpsychological stress on the structure of rat condylar cartilage. Firstly, HEstaining, scanning electron microscopy and Micro CT method were used tostudy the histological changes in condylar cartilage induced by psychologicalstress. Then we tested whether the pathological change was accompanied by therelease of inflammatory cytokines. Secondly, we tested whether abnormalrelease of inflammatory cytokines would change the expression of matrixmetallo proteinases (MMPs) and tissue inhibitor of metal protease (TIMP).Thirdly, we tested whether the changed expression of MMPs could cause theimbalance of synthesis and degradation in extracellular matrix and how itchanged. Lastly, we tested whether inflammatory cytokines could activateOPG/RANK/RANKL system, which led the destruction of the subchondral bone.The results were as follow:1. There were progressive destructions occurred on the surface of condylarcartilage after8weeks and12weeks of psychological stress, such as theformation of cracks, fiber breakage and other pathological changes of collagenfibers, et al. HE staining and Micro CT results confirmed that typical degenerationwas occurred on condylar cartilage and subchondral bone happened progressiveabsorption, which got more seriously with time-dependent.2. Compared to the control group and drug group in the same time point,the expression levels of IL-beta, IL-6and TNF-alpha were significantlyincreased in4weeks,8weeks and12weeks psychological stress groups (p＜0.05). The expression in12weeks psychological stress group was significantlyhigher than that in8weeks group (p＜0.05). Expression levels of IL-beta, IL-6and TNF-alpha in4weeks,8weeks and12weeks drug groups were significantly higher than that of control group in the same point (p＜0.05).3. The mRNA and protein expression of MMP-3and MMP-9in ratcondylar cartilage cells were significantly increased in all psychological stressgroups than that of control groups and drug groups in the same time point (p＜0.05), which were increasing with time-dependent (p＜0.05). The secretion ofMMP-3in12weeks drug group was significantly higher than that in12weekscontrol group (p＜0.05). Compared to the control group and drug group in thesame time point, the secretion of TIMP-1increased significantly in12weekspsychological stress group (p＜0.05).4. The mRNA and protein expression of aggrecan and collagen II in8weeks and12weeks psychological stress groups were significantly lower thanthat of control groups and dug groups in the same time point (p＜0.05). Theexpression in12weeks psychological stress group was significantly lower than8weeks group (p＜0.05).5. The mRNA and protein expression of OPG gradually decreased in8weeks and12weeks psychological stress groups were significantly lower thanthat of control groups and dug groups in the same time point (p＜0.05). ThemRNA and protein expression of RANKL and RANKL/OPG ratio in8weeksand12weeks psychological stress group were significantly higher than that ofcontrol groups and dug groups in the same time point (p＜0.05). The mRNA andprotein expression of RANKL and RANKL/OPG ratio in12weekspsychological stress group were significant higher than that in4weeks and8weeks psychological stress groups(p＜0.05).Conclusion1. CUMS model is an ideal animal model which could make rats inlong-term psychological stress and reduce the effect of physical factors on studyresults. 2. Psychological stress could cause structural changes of TMJ, which maybe one of the pathological basis occurred in temporomandibular joint diseases.3. Psychological stress led increased secretion of inflammatory cytokines inthe condylar cartilage, such as IL-beta, IL-6and TNF-alpha, which could be oneof the reasons for up-regulating expression of MMPs and TIMP-1induced bypsychological stress. Increased secretion of MMP-3, MMP-9and TIMP-1in ratcondylar cartilage cells may be one of the reasons for faster degradation ofextracellular matrix after the psychological stress. Psychological stressaccelerated the degradation of aggrecan and collagen II in rat condylar cartilage,which got more seriously with time-dependent. It could be one of mechanism inthe destruction of extracellular matrix after psychological stress.4. Long-term psychological stress could activate OPG/RANK/RANKLsystem in the condylar cartilage. After psychological stress, the expression ofOPG gradually decreased, meanwhile, the expression of RANKL andRANKL/OPG ratio gradually increased, which indicated that psychological stresscaused the destruction of condylar subchondral bone. It may be one of mechanismin the destruction of condylar subchondral bone after psychological stress.5. Drugs can significantly reduce the effect of psychological stress, but itcould not completely fight against the role of psychological stress. |
