Influence Of Sleep Deprivation On Expression Of MKK4and C-fos In Mandibular Condylar Cartilage Of Rats

Objective:The aim of this study was to observe the pathological changes and to investigate the expression changes of mitogen-activated protein kinase kinase4(MKK4) and c-fos in mandibular condylar cartilage of rats subjected to sleep deprivation (SD). We expected to find out the influence that SD exert on temporomandibular joints (TMJs) of rats and to explore the pathological mechanisms by which SD causes temporomandibular disorders (TMDs), thereby revealing the relation between sleep and the pathogenesis of TMD.Methods:One hundred and twenty female Wistar rats were randomly divided into6groups with20in each:2-day SD (SD2d),4-day SD (SD4d),6-day SD (SD6d),8-day SD (SD8d), large-platform control (LC) and cage control (CC).After sleep-deprived by using the modified multiple platform method (MMPM) for respective time, SD rats were sacrificed. LC and CC rats were sacrificed at the same time as SD8d group rats. Open field test (OFT) was performed before sacrifice to assess the mental status of rats. Blood samples were extracted to detect the changes of the concentration of serum corticosterone (CROT) and serum adrenocorticotrophic hormone (ACTH), thus to evaluate the predictive validity of this animal models. After making pathological sections of TMJs, Hematoxylin-eosin (HE) staining was used to observe the morphological changes in cartilage, and immunohistochemistry and real-time quantitative PCR were performed to detect the expression changes of MKK4and c-fos.Results:As illustrated in the OFT, the crossing scores and rearing scores of SD group rats in the open field were larger than thoes of CC and LC groups (p<0.01). Compared with CC group and LC group, the serum concentrations of CORT and ACTH of SD group rats were significantly increased (p<0.01).Pathological alterations were examined in TMJs of rats. As shown in HE stained sections, the fibrous articular superficial surfaces became tough, or even cracked and exfoliated in SD6d and SD8d groups. The histopathological changing regions are relevant to functions of TMJs.RT-qPCR showed no significant difference in levels of MKK4and c-fos mRNA between CC group and LC group (P>0.05). The expression of MKK4mRNA impaired significantly in all SD groups (all P<0.01) compared with CC group. Furthermore, the mRNA levels of MKK4were significantly lower in SD4d, SD6d and SD8d groups (both P<0.01) than SD2d group. The expression of c-fos mRNA increased significantly in all SD groups (all P<0.01) compared with CC group. Specifically, we only found significant difference between SD2d and SD8d groups (P<0.01) in mRNA levels of c-fos among all SD groups.Conclusion:1、SD model of MMPM, through depriving rapid eye movement (REM) sleep, could produce the psychological states such as anxiety and irritation, and turned out to be a relatively ideal SD model2、SD could induce structural changes of TMJs, which may serve as the pathological basis of TMD. 3、SD could cause the expression variations of MKK4and c-fos in mandibular condylar cartilages of rats. The impact grew even more substantial with the elongation of SD time. These may be correlated with pathological changes in mandibular condylar cartilage in rats induced by SD.