Downregulation Of Sox8 Mediates Monosodium Urate Crystal-induced Autophagic Impairment Of Cartilage

Background.Gout arthritis,characterized by hyperuricemia which leads to the formation of monosodium urate(MSU)crystals,is the most common inflammatory joint disease among young men.A large scaled study showed that acute gout attack in local joints was associated with subsequent clinical osteoarthritis in this joint.Imaging and histopathological studies also found the presence of MSU deposits on the surface of articular cartilage and in the tendons at the initial stage of gout attack.During the attack of gouty arthritis,many cytokines may have direct damage to articular cartilage.These cytokines may directly lead to apoptosis of cartilage cells and eventually lead to osteoarthritis.Except for inflammation in the joint,the mechanism by which external chemical signals such as MSU crystals,cause damage to chondrocytes remains unclear.Hyun Sook Hwang et al.found that MSU crystals lead to chondrocyte death by inhibiting phosphorylation of AKT/mTOR signaling pathway and activating autophagy.Autophagy is an intracellular degradation system mediated by the PI3K signaling pathway.However,the key molecule during chondrocyte autophagic death in acute gouty arthritis have not been identified.In this study,we found that downregulation of Sox8 inhibited PI3K/AKT/mTOR pathway,resulting in MSU-induced autophagic death of chondrocytes,and the overexpression of Sox8 significantly reduced cartilage damage in MSU-induced gouty arthritis.Objective.The purpose of this study was to investigate whether MSU crystal induced cartilage injury is related to autophagic signal and the key molecule mediating the injury.Methods.Firstly,mRNA sequencing was performed on the cartilage of rats with gouty arthritis induced by MSU and control rats,and then MSU crystals were used to treat human chondrocytes to evaluate the role of Sox8 in autophagic cartilage injury.Secondly,the expression of Sox8 was up-regulated or down-regulated by recombinant Sox8 lentivirus vector or si-Sox8 respectively.After that,confocal microscopy was used to observe the transfection of mRFP-GFP-LC3 plasmid.Autophagy vacuole was stained with monodansylcadaverine(MDC)and flow cytometry was used to detect autophagosomes stained by MDC.The morphology of autophagosomes were observed by transmission electron microscopy.The ratio of LC3-Ⅱ/Ⅰ in the presence or absence of bafilomycin A1 and the expression levels of Sox8,Beclinl,and the protein in the PI3K signaling pathway were detected by Western blot.In vivo,the effect of Sox8 on cartilage of acute gouty model rats was evaluated by safranin O/fast green staining and Western blot.Results.In both acute gouty arthritis model rats and MSU treated chondrocytes,the expression of Sox8 was remarkably down-regulated.In chondrocytes,MSU crystals reduced the expression of Sox8,inhibited PI3K/AKT/mTOR signaling pathway,and increased autophagy level according to the results from mRFP-GFP-LC3 plasmid,MDC staining and western blot.Overexpression of Sox8 significantly inhibited MSU crystal induced autophagy by increasing phosphorylation levels in PI3K signaling pathway.In gouty arthritis model rats,overexpression of Sox8 can significantly reduce cartilage damage.Conclusion.Downregulation of Sox8 plays an important role in MSU induced autophagy of chondrocytes by regulating PI3K signaling pathway.Overexpression of Sox8 may serve as a novel therapy to prevent the impairment of cartilage in gout arthritis.