A Preliminary Study On The Involvement Of SGK-1 In Cartilage Destruction And Inflammatory Pain In Temporomandibular Joint Osteoarthritis

Objective: This study aimed to explore the role of serum and glucocorticoid-induced protein kinase 1（SGK-1）in the occurrence of temporomandibular joint osteoarthritis（TMJ-OA）in vivo and vitro,and to explore whether SGK-1 can be used as a potential therapeutic target to prevent or treat TMJ-OA articular cartilage degeneration and effectively relieve joint pain.Methods : Experimental rat TMJ-OA model was constructed by intra-articular injection of monosodium iodoacetate（MIA）for 28 days.At day1,day 7,day 14,day 21 and day28 after injection of MIA,von-frey apparatus was used to stimulate the bilateral joint area of rats,and pain behavior was assessed by measuring the head withdrawal threshold（HWT）.The histological structure changes of left intact TMJ were observed by hematoxylin eosin（HE）staining,and the differences of proteoglycan deposition in TMJ cartilage extracellular matrix were compared by Safranin O-fast green staining.Real-time PCR was performed to examine the expression levels of m RNA of SGK-1,interleukin-1 β（IL-1β）,cyclooxygenase-2（COX-2）and matrix metalloproteinase-13（MMP-13）in the right mandibular condylar cartilage（MCC）.HE stain was used to observe the histological structure changes of the trigeminal ganglion（TG）of TMJ-OA rats.Real-time PCR was performed to examine the expression levels of m RNA of SGK-1,COX-2 in the right TG.The primary chondrocytes of rat MCC were isolated and cultured,and identified by toluidine blue staining.MCC cells of P2 generation were stimulated with inflammatory factor IL-1β in order to induce MCC cell injury.Western blot was used to detect the differential expression of SGK-1 protein in MCC cells.Results:MIA injection successfully induced typical OA-like lesions in the TMJ within28 days.The results of behavioral test indicated that administration of MIA led to the significant decreases in head withdrawal threshold（HWT）and induce hyperalgesia in rats.The results of HE staining of the left intact TMJ showed that the mandibular condyle cartilage and subchondral bone structure were disordered in TMJ-OA group.The results of Safranin O-fast green staining showed that the cartilage proteoglycan was abnormal deposition and the cartilage matrix was destroyed in TMJ-OA group.Compared with rats in control groups,the expression levels of SGK-1,MMP-13,IL-1β and COX-2 in MCC of TMJ-OA group were upregulated（p <0.05）.HE staining of the left TG showed demyelinating changes of nerve fibers and increased schwann cells in TMJ-OA group.Compared with rats in control groups,the expression levels of SGK-1,COX-2 in TG of TMJ-OA group were upregulated（p <0.05）.The primary MCC cells of rat were isolated and cultured.,toluidine blue staining showed that the cells were blue stained,so the cells can be identified as chondrocytes.Western blot results showed that compared with the control group,the expression of SGK-1 protein in injured MCC cells was increased under the stimulation of IL-1β（p <0.05）.Conclusions: In the pathological process of TMJ-OA,SGK-1 may plays an important role not only in cartilage structural damage but also in pain transmission.Inhibition of upregulated SGK-1 expression in MCC and TG of TMJ-OA patients may be a new approach to treat TMJ-OA,but its specific molecular mechanism still needs further study.