The Mechanism Of PDCD4 In Temporomandibular Joint Osteoarthritis

Objective: The attenuation in chondrocyte function or numbers leads to cartilage degradation,a vital character of temporomandibular joint osteoarthritis(TMJOA).Studies have found that autophagy and apoptosis are closely related to the function and number of chondrocytes.Programmed cell death 4(PDCD4)has been found to inhibit autophagy and at the same time induce apoptosis in many tumor cells.However,the role of PDCD4 in TMJOA is uncertain.In this study,we examined whether the abnormal autophagy and apoptosis as well as expression of PDCD4 occurred in chondrocytes of TMJOA and the underlying mechanisms.Methods: In vivo,the TMJOA model was established by injection of sodium iodoacetate(MIA)into the superior cavity of the TMJ of SD rats.Hematoxylin and eosin(HE)was used to detect the histological change of the condyle.The cartilage matrix glycoprotein changes were detected with safranin green(safranin O)and microCT was used to detect changes in subchondral bone.Immunohistochemistry was used to detect the expression of PDCD4,autophagy-related proteins LC3 II,Beclin1and antiapoptotic protein Bcl2.In vitro,the condylar chondrocytes of rats were treated with10ng/ml and 100ng/ml IL1β for 6h,12 h,24h and 48 h respectively,to establish the inflammatory damage model of chondrocytes.Western blot was used to detect the expression of PDCD4,autophagy-and apoptosis-related proteins and phosphorylated Akt(p-Akt)and JNK(p-JNK).The level of LC3 II were detected by cell immunofluorescence,and the changes of apoptosis level in chondrocytes were detected by flow cytometry.PDCD4 was inhibited by transfection of the specific small interference RNA,and western blot was used to detect the level of autophagy related proteins,apoptosis-related proteins,p-Akt and p-JNK after inhibiting PDCD4.Finally,the chondrocytes which inhibited PDCD4 were treated with SC79,an Akt activator,and Anisomycin,an JNK activator.After Akt and JNK activation,the expression of autophagy-related proteins and apoptosis-related proteins were detected by western blot.Results: HE and micro-CT showed significant degeneration of cartilage in the experimental group,and the reduction of chondrogenic matrix glycoprotein in the experimental group was confirmed by safranin O staining.Compared with the control group,the up-regulation of PDCD4 and down-regulation of Beclin1,LC3 II,Bcl2 in the cartilage of MIA-induced TMJOA was detected by immunohistochemistry.In vitro,PDCD4,PARP,p-Akt and p-JNK were significantly increased,LC3 II,Beclin1,ATG5 and Bcl2 were significantly decreased by Western blot after 10ng/ml IL1β treatment.LC3 II decreased detected by cell immunofluorescence and cell apoptosis level was increased detected by flow cytometry.Transfection of the specific small interference RNA against PDCD4 in chondrocytes markedly restored the autophagy inhibition and apoptosis promotion induced by IL1β,meanwhile,the level of phosphorylated Akt and JNK was decreased in these cells.The expression of LC3II/LC3 I,Beclin1,ATG5 and Bcl2 were decreased,while PARP increased after Akt activation.However,,the expression of PARP was decreased,while Bcl2,LC3II/LC3 I,Beclin1 and ATG5 protein levels still increased after JNK activation.Conclusion: PDCD4 is highly expressed in the rat cartilage of MIA-induced TMJOA and IL1β-treated chondrocytes.PDCD4 inhibits autophagy and promotes apoptosis via Akt in these cells.